Pt guide 4 16

April 2016designworldonline.com motioncontroltips.com
Transmission
REFERENCE GUIDE
POWER
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Haydon Kerk 4-16.indd 3 4/29/16 9:59 AM

4 DESIGN WORLD 4 • 2016 www.designworldonline.com
PowerTransmission
REFERENCEGUIDE
MOTION
designs continually
evolve, but will always
rely on mechanical devices, particularly
where the drive of an electric motor
engages a load to execute machine
tasks. In fact, as the technical reviews
in this 2016 Power Transmission
Reference Guide explain, applications
for mechanical motion components only
proliferate as technical innovations make
them increasingly effective.
Consider this Reference Guide’s
section on bearings by Associate Editor
Mike Santora. The most common bearing
applications are in heavy machinery and
industrial setups as always, but renewable-
energy use is spurring innovations to get
higher capacities as turbines push the
limits of bearing designs.
There’s also increased demand
for complete system solutions over
components, which is changing the
POWER-TRANSMISSION
COMPONENTS ARE MAINSTAYS
POWER-TRANSMISSION
COMPONENTS ARE MAINSTAYS
design of linear systems, actuators and gearmotors, as well as subsystems
such as conveyors and robotics. Consider the section on gearmotors in
this Reference Guide by Senior Editor Miles Budimir. Here, manufacturers
are predesigning and assembling more motors than ever with gearboxes
upfront, for an ever-expanding array of ac gearmotors and servo
gearmotors. Such gearmotors are increasingly accurate as well, particularly
those sporting planetary gearsets.
That’s thanks in part to how manufacturers are making gearing with
the latest approaches in design, machining and assembly. Check out
the sections in this Reference Guide covering gear-design consultation,
custom gear designs and analysis, as well as general speed reducers, worm
gearing, and shaft-mount sets. These articles detail common and custom
offerings that optimize inertia matching and speed output. In fact, today’s
software now lets designers get design-specific gearing—and other power-
transmission components—at lower cost than that of general-purpose
offerings from just a decade ago.
In fact, today’s moving designs rely on an increasingly diverse array
of mechanical components to protect expensive subsystems and change
motion-system dynamics to simplify programming. These actuators,
ballscrews, bearings, brakes, chains, collars, couplings, gearing, rails and
rack-and-pinion sets transmit power in ways that get higher performance
than ever.
LISA EITEL
SENIOR EDITOR
@DW_LISAEITEL
DW half p
Editorial_PTGuide_V3.LE.MD.indd 4 4/29/16 10:20 AM

WWW.MOTIONCONTROLTIPS.COM
WEBINAR ALERT
DOWNLOAD ON DEMAND:
TRENDS TO WATCH
IN MOTION CONTROL
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So use this Reference Guide as a review of basic component
functions or as an update on what’s new in power-transmission
designs—and to get instructions on how to make the most of
proliferating features to meet evolving motion-system requirements.
As mechanical designs change, count on us Design World
editors to bring you technology updates to help you specify and
integrate the right components. We invite your feedback and
requests for technical information. There are innumerable ways
to reach us: Email me at leitel@wtwhmedia.com or tweet to
@DW_LisaEitel, @Linear_Motion and @Motion_Control.
Connect with our Design World Network Facebook page at
facebook.com/DesignWorldNetwork, and let us know what
designs you’re using or are looking to apply.
Also look out for the 2016 Motion Systems Handbook and
2016 Motion Casebook coming to you in August and November for
complete coverage of electronic and programming technologies
for motion designs, as well as real-world application examples
and illustrations to inform your next build. In the mean time, also
find all our motion-technology news announcements (as well as
technical archives) on our motion tips sites—motioncontroltips.
com, linearmotiontips.com, sensortips.com, bearingtips.com and
couplingtips.com.
Get a Free Power Basics Poster
teledynelecroy.com/motor-drive-analyzer | teledynelecroy.com/contactus
© 2015 Teledyne LeCroy, Inc. All rights reserved.
Line Voltage, Current, and Power – The Basics
THREE-PHASE
LINE VOLTAGE
Single-phase line voltage consists of one voltage
vector with:
• Magnitude (voltage)
• Angle (phase)
Typically, the single-phase is referred to as “Line” voltage, and
is referenced to neutral.
Neutral Line
The single-phase voltage vector rotates at a given frequency
• Typically, 50 or 60 Hz for utility-supplied voltage
At any given moment in time, the voltage magnitude is V * sin(α)
• V = magnitude of voltage vector
• α = angle of rotation, in radians
The resulting time-varying “rotating” voltage vector appears as
a sinusoidal waveform with a fixed frequency
• 50 Hz in Europe
• 60 Hz in US
• Either 50 or 60 Hz in Asia
• Other frequencies are sometimes used in non-utility
supplied power, e.g.
• 400 Hz
• 25 Hz
SINGLE-PHASE
Three-phase line voltage consists of three voltage vectors.
• By definition, the system is “balanced”
• Vectors are separated by 120°
• Vectors are of equal magnitude
• Sum of all three voltages = 0 V at Neutral
Typically, the three phases are referred to as A, B, and C,
but other conventions are also used:
• 1, 2, and 3
• L1, L2, and L3
• R, S, and T
The three voltage vectors rotate at a given frequency
The resulting time-varying “rotating” voltage vectors appear
as three sinusoidal waveforms
• Separated by 120°
• Of equal peak amplitude
Voltage value = VX*sin(α)
• VX = magnitude of phase voltage vector
VA-B
VA-N
120° VA
VB
VC
Neutral
A
B
C
ω (rad/s) or
freq (Hz)
120°
120°
120°
Neutral
Neutral Line
ω (rad/s) or
freq (Hz)
200
Time
AC Single-Phase “Utility” Voltage
120VAC
Volts(Peak),Line-Neutral
150
100
50
0
-50
-100
-150
-200
120 VAC Example
800
Time
AC Three-Phase “Utility” Voltage
480VAC
, Measured Line-Line
Volts(Peak),Line-Line
600
400
200
A-B Voltage
B-C Voltage
C-A Voltage
0
-200
-400
-600
-800
480 VAC Example
800
Time
AC Three-Phase “Utility” Voltage
480VAC
, Measured Line-Neutral
Volts(Peak),Line-Neutral
600
400
200
A-N Voltage
B-N Voltage
C-N Voltage
Three-phase Rectified DC
0
-200
-400
-600
-800
480 VAC Example
Line-Line Voltage Measurements
Line-Neutral Voltage Measurements
Important to Know
• Voltage is stated as “VAC”, but this is really VRMS
• Rated Voltage is Line-Neutral
• VPEAK = 2 * VAC (or 2 * VRMS )
• 169.7 V in the example below
• VPK-PK = 2 * VPEAK
• If rectified and filtered
• VDC = 2 * VAC = VPEAK
Voltages can be measured two ways:
• Line-Line (L-L)
• Also referred to as Phase-Phase
• e.g. from VA to VB, or VA-B
• Line-Neutral (L-N)
• Neutral must be present and accessible
• e.g. from VA to Neutral, or VA-N
• VL-L conversion to VL-N
• Magnitude: VL-N * 3 = VL-L
• Phase: VL-N - 30° = VL-L
Important to Know
• Voltage is stated as “VAC”, but this is really VRMS
• Rated Three-phase voltage is always Line-Line (VL-L)
• Line-Line is A-B (VA-B), B-C (VB-C), and C-A (VC-A)
• Line-Line is sometimes referred to as Phase-Phase
• VPEAK(L-L) = 2 * VL-L
• 679 V in the example to the right
• VPK-PK(L-L) = 2 * VPEAK(L-L)
If a neutral wire is present, three-phase voltages
may also be measured Line-Neutral
• VL-N = VL-L/ 3
• 277 VAC (VRMS) in this example
• VPEAK = 2 * VL-N
• 392 V in the example to the right
• VPK-PK = 2 * VPEAK
If all three phases are rectified and filtered
• VDC = 2 * VL-N * 3 = VPEAK * 3 = 679 V
in the example to the right
LINE CURRENT
Like voltage, the single-phase current vector rotates
at a given frequency
• Typically, 50 or 60 Hz
At any given moment in time, the current magnitude
is I*sin(α)
• I = magnitude of current vector
The resulting time-varying “rotating”
current vector appears as a sinusoidal
waveform
Like voltage, the resulting time-varying “rotating”
current vectors appear as three sinusoidal waveforms
• Separated by 120°
• Of equal peak amplitude for a balanced load
Current value = IX*sin(α)
• IX = magnitude of line current vector
Neutral Line
freq (Hz)
By definition, the system is “balanced”
• Vectors are separated by 120˚
• Vectors are of equal magnitude
• Sum of all three currents = O A at neutral (provided
there is no leakage of current to ground)
Like voltage, three-phase current has three different line
current vectors that rotate at a given frequency
SINGLE-PHASE
THREE-PHASE
A
B
C
ω (rad/s) or
freq (Hz)
120°
120°
120°
Neutral
Line Current Measurements
10 ARMS Example
Important to Know
• Current is stated as “lAC”, but this is really IRMS
• Line currents can represent either current
through a coil, or current into a terminal
(see image below) depending on the three-phase
winding connection
• IPEAK = 2 * IRMS
• 14.14A for a 10 ARMS current in the example
to the right
• IPK-PK = 2 * IPEAK
-15
-12
-9
-6
-3
0
3
6
9
12
15
LineCurrent(Peak)
Time
AC Three-Phase "Line" Currents
A Current
B Current
C Current
IC
IA
IB
A
B
C
N
A
B
C
IC IA
IB
LINE POWER
SINGLE-PHASE
Electric Power
• “The rate at which energy is transferred to a circuit”
• Units = Watts (one Joule/second)
For purely resistive loads
• P = I2R = V2/R = V * I
• The current vector and voltage vector are in perfect phase
I
Inductive load
V
P ≠ V * I
φ
N
I
Capacitive load
P ≠ V * I
V
φ
N
Real Power
ImaginaryPower
S
P
Q
φ
φ
φ
φ
QB
QC
QA
SB
SA
SC
PB
PA
PC
Phase Angle (φ)
• Indicates the angular difference between the
current and voltage vectors
• Degrees: - 90° to +90°
• Or radians: -π/2 to + π/2
For capacitive and inductive loads
• P ≠ V * I since voltage and current are
not in phase
• For inductive loads
• The current vector “lags” the voltage
vector angle φ
• Purely inductive load has angle φ = 90°
• Capacitive Loads
• The current vector “leads” the voltage
vector by angle φ
• Purely capacitive load has angle φ = 90°
THREE-PHASE
For purely resistive loads
• PA = VA-N * IA
• PB = VB-N * IB
• PC = VC-N * IC
• PTOTAL = PA + PB + PC
As with the single-phase case, Power is not the simple
multiplication of voltage and current magnitudes, and
subsequent summation for all three phases.
Apparent Power for each Phase
• |S|, in Volt-Amperes, or VA
• = VRMS * IRMS for a given power cycle
Real Power for each Phase
• P, in Watts
• = instantaneous V * I for a given
power cycle
Voltage is measured L-L
• Neutral point may not be accessible, or
• L-L voltage sensing may be preferred
Current is measured L-N
L-L voltages must be transformed to L-N reference:
Calculations are straightforward, as described above:
• PTOTAL= PA + PB + PC
• STOTAL = SA + SB + SC
• QTOTAL = QA + QB + QC
Voltage is measured L-L on two phases
• Note that the both voltages are measured with
reference to C phase
Current is measured on two phases
• The two that flow into the C phase
Mathematical assumptions:
• Σ(IA + IB + IC) = 0
• Σ(VA-B + VB-C + VC-A) = 0
This is a widely used and valid method
for a balanced three-phase system
VB-C
VA-C
IA
IB
A
B
C
N
A
B
C
VB-C
VA-C
IA
IB
Single-phase, Non-resistive Loads
Phase Angle
Single-phase Real, Apparent and Reactive Power
Three-phase, Resistive Loads Three-phase, Non-resistive Loads
Two Wattmeter Method – 2 Voltages, 2 Currents with Wye (Y or Star) or Delta (∆) Winding
VB-N
VA-N
VC-N
IC
IA
IB
A
B
C
N
VA-B
VB-C
VC-A
IC
IA
IB
A
B
C
N
Power Factor (PF, or λ)
• cos(φ) for purely sinusoidal waveforms
• Unitless, 0 to 1,
• 1 = V and I in phase, purely resistive load
• 0 = 90° out of phase, purely capacitive
or purely inductive load
• Not typically “signed” – current either
leads (capacitive load) or lags
(inductive load) the voltage
Voltage
Current
Note: Any distortion present on the Line voltage
and current waveforms will result in power
measurement errors if real power (P) is
calculated as |S|*cos(φ). To avoid measurement
errors, a digital sampling technique for power
calculations should be used, and this technique is
also valid for pure sinusoidal waveforms.
Resistive load
V
P=V * I
N
I
Power Factor
Line-Line Voltage Sensing Case
VB-N
VA-N
PTOTAL = VA-N * IA + VB-N * IB + VC-N * IC
VC-N
IB
IA
IC
N
φ
VB-N
VA-N
PTOTAL ≠ VA-N *IA + VB-N * IB + VC-N * IC
VC-N
IB
IAIC
N
Three-phase, Any Load
Apparent Power
• |S|, in Volt-Amperes, or VA
• = VRMS * IRMS for a given power cycle
Real Power
• P, in Watts
• = instantaneous V * I for a given power cycle
Reactive Power
• Q, in Volt-Amperes reactive, or VAr
• Q = S2 - P2
• Does not “transfer” to load during a power cycle,
just “moves around” in the circuit
Reactive Power for each Phase
• Q, in Volt-Amperes reactive, or VAr
• Q = S2 - P2
• PTOTAL = PA + PB + PC
• STOTAL = SA + SB + SC
• QTOTAL = QA + QB + QC
PTOTAL = VA-C * IA + VB-C * IB
STOTAL= VRMSA-C * IRMSA + VRMSB-C * IRMSB
QTOTAL = STOTAL
2 - PTOTAL
2
“Not True” RMS
Wye (Y) 3-phase Connection
• Neutral is present in the winding
• But often is not accessible
• Most common configuration
Delta (∆) 3-phase Connection
• Neutral is not present in the
winding (in most cases)A
B
C
N
A
B
C
For one power cycle
• The digital samples are grouped
into measurement cycles (periods)
• For a given cycle index i….
• The digitally sampled voltage
waveform is represented as having a
set of sample points j in cycle index i
• For a given cycle index i, there are
Mi sample points beginning at mi
and continuing through mi + Mi -1.
• Voltage, current, power, etc.
values are calculated on each
cycle index i from 1 to N cycles.
Digital Sampling Technique for Power Calculations�
Period 1
Mi = 18 points
Period 2
Mi = 18 points
mi = point 7 mi = point 25
VPK-PK
“True” RMS
For one power cycle
Three-Phase Winding Connections
VRMS
IRMS
Real Power
(P, in Watts)
Apparent Power
(S, in VA)
Reactive Power
(Q, in VAR)
Power Factor (λ)
Phase Angle (φ)
VRMSi = Vj
2
Mi
1
mi + Mi - 1
Σj=mi
IRMSi = Ij
2
Mi
1
mi + Mi - 1
Σj=mi
Pi = Vj * Ij
Mi
1
mi + Mi - 1
Σj=mi
Si = VRMSi * IRMSi
magnitude Qi = Si
2 - Pi
2
Sign of Qi is positive if the fundamental voltage
vector leads the fundamental current vector
λi =
Pi
Si
magnitude Φi = cos-1λi
Sign of Φi is positive if the fundamental voltage
vector leads the fundamental current vector
Formulas Used for Per-cycle Digitally Sampled Calculations
VRMS = VPK-PK
2 2
1 VRMS = VAC
2
MDA800 Series
Motor Drive Analyzers
8 channels, 12-bits, 1 GHz
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Learn more about the MDA800 and sign up to
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tlec-mda-poster-designworld.indd 1 2/5/16 2:04 PM
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PowerTransmission
REFERENCEGUIDE
6 DESIGN WORLD — MOTION 4 • 2016 motioncontroltips.com | designworldonline.com
VIDEO
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The PITTMAN Difference
When evaluating DC motor choices, it’s what’s inside that matters.
What’s Inside
Matters®
On the outside, this looks like an ordinary DC motor. In fact, this particular motor
is not a standard off-the-shelf part, but designed exactly to a customer’s specific
technical requirements. PITTMAN has an experienced team of engineers focused
on providing the perfect motor assembly to our customers demanding motion
applications.
• Special brush formulation for use in a very low humidity environment
• Bearing system to handle higher than normal axial loads
• Very tight balancing spec to minimize audible noise and vibration at high speeds
• Unique magnet charge pattern to minimize cogging at low speeds
• Specially chosen surface-mount components inside the motor to meet
an aggressive EMC requirement
• Numerous integrated spur and planetary gearboxes, encoders, brakes and drives
www.Pittman–Motors.com
343 Godshall Drive, Harleysville, PA 19438
USA: +1 267 933 2105
Europe: +33 2 40 92 87 51
Asia: +86 21 5763 1258
Pittman (AMETEK) 3-16.indd 7 4/29/16 10:00 AM

PTDA Updates ..............................................10
Actuators
Electrical ..................................................14
Rigid Chain ..............................................18
Ballscrews .....................................................20
Bearings ......................................................24
Belts, Pulleys ...........................................28
Brakes, Clutches ...................................31
Cabling ................................................32
Chain, Roller, Sprocket .......................34
Compression Springs ........................38
Couplings ..........................................41
Drives ................................................50
Gearing .............................................54
Gearmotors ........................................66
Leadscrews...........................................68
Linear Motion ........................................70
Locking Devices, Shaft Collars .................75
Lubrication ..................................................78
Motors ..........................................................80
Positioning Stages ........................................84
Seals .............................................................86
Shock, Vibration Damping ............................88
MOTIONCONTROLTIPS.COM
INSIDE
P04Power-transmission
components are
mainstays
VOL2
NO2
18 Cover photography by
Miles Budimir
Contents_PTGuide_V1.indd 8 5/3/16 10:42 AM

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Research, price, buy at: www.automationdirect.com/power-transmission
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If it is precision you need, our SureGear
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Worm Gearboxes
IronHorse® worm gearboxes are built to
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• Double Loop Couplings start at $34.00
• Oldham Couplings start at $14.25
• Beam-Style Servo Couplings start at $42.00
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Synchronous Drives
Our SureMotion line of synchronous drive
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• Drive pulleys start at $5.25
• Drive belts start at $2.00
SureMotion® Drive Couplings
Reduce the unwanted stress caused by shaft misalignment with our new
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variety of styles, torque ranges and coupling capabilities each designed
to enhance system performance and prevent costly failures.
AutomationDirect_PTGuide4-16.indd 9 4/29/16 10:32 AM

Power Transmission
REFERENCE GUIDE
2016 LEADERSHIP DEVELOPMENT CONFERENCE
The Power Transmission Distributors Association (PTDA) held its 2016 Leadership Development Conference
in early March in the Historic District of Charleston, S.C.
PTDA members continuously seek ways to bring their future management team up-to-speed so they
can step into a supervisory role ready to excel. The 2016 Leadership Development Conference fulfilled
that need. Designed for emerging power transmission/motion control leaders who want to enhance their
management skills, network in small group settings, and learn best practices that support business results,
those that participated in this year’s conference benefited from two sessions:
• “Ready. Get Set. Lead”—a dinner program by Randy Disharoon, director global accounts, Rexnord
Industries, on how to quickly ramp up younger leaders for success to kick-off the conference
• “Businessopoly”—a full-day, interactive, team-oriented business simulation game, led by industry
veteran Michael Cinquemani, president and CEO, Master Power Transmission.
Cinquemani said, “We are going to really challenge people to give them a deeper understanding of their
decision-making: how it affects the profit and loss statement, the balance sheet, the statement of cash
flows, and then review their results compared to their initial plans.”
PTDAP O W E R T R A N S M I S S I O N
D I S T R I B U T O R S A S S O C I AT I O N
UPDATESMIKE SANTORA • ASSOCIATE EDITOR • @DW_MIKESANTORA
The PTDA Spring Governance Meetings attracted nearly 90 volunteer senior
leaders to Charleston, S.C., along with more than 45 Next-Gen members who
took part in the PTDA 2016 Leadership Development Conference. Attendees
played Businessopoly, the name PTDA gave to an interactive, hands-on board
game that teaches executive management skills.
PTDAUpdates_PTGuide_V3.indd 10 4/29/16 10:38 AM

11DESIGN WORLD — MOTIONmotioncontroltips.com | designworldonline.com 4 • 2016
PTDA WELCOMES
SIX NEW MEMBERS
PTDA has recently welcomed six
new member companies.
DISTRIBUTOR MEMBER
MJ May Material Specialists
(South Holland, Ill.) distributes
mechanical PT components,
bearings, motors, motor/motion
control, electrical/electronic
drives, material handling,
hydraulics/pneumatics, and PT
accessories. President Walter
Lopez said, “As a small business
looking to grow in the power
transmission market, it was a no-
brainer for us to join. The access
to manufacturers and opportunity
to strengthen established
relationships will greatly benefit us
in our quest to become a premier
distributor of power transmission
products.”
MANUFACTURER MEMBERS
Auburn Bearing & Manufacturing
(Macedon, N.Y.) manufacturers
bearings. “We chose to join PTDA
because a vast majority of our
sales are through an established
network of distributors across
the marketplace. PTDA will assist
us in expanding that network
even further,” said Peter Schroth,
president.
Helical Products Company,
a location of MW Industries,
(Rosemont, Ill.) manufactures
spring couplings and retaining
rings. Robert Jack, VP marketing
and strategic planning, said, “The
opportunity to network with both
manufacturers and distributors in
our industry is very valuable to us,
and we look forward to being an
active member and forging many
new relationships in the years to
come."
iwis Drive Systems (Indianapolis,
Ind.) manufactures chains and
sprockets. “iwis joined PTDA to
increase our network within the
industrial distribution arena. The
fact is, we have made significant
investments into new products
and value added services and
PTDA represents a powerful
tool for us to capitalize on these
initiatives,” said Kody Fedorcha,
VP, sales and marketing.

Rosta USA Corporation (South
Haven, Mich.) is a manufacturer of
motor bases.
Wittenstein (Bartlett, Ill.)
manufactures couplings, gearing,
motors, motor/motion control
products and linear motion
components. Tom Coyle,
director of sales NA, said, “We
are pleased to be a part of this
association. My goals as a member of PTDA are to leverage the wide
network of distributor organizations and contacts, gain access and new
perspectives to industry economics and trends, and finally to increase
exposure of Wittenstein,”
PTDA 2016 CANADIAN CONFERENCE
Registration is still open for the PTDA 2016 Canadian Conference, to
be held June 9-10, 2016, at The Westin Ottawa in Ottawa, Ontario. For
the 15th year, members of the Canadian power transmission/motion
control (PT/MC) industry gather for business networking, market-driven
education, a manufacturer industry showcase and more.
Networking opportunities abound at the PTDA 2016 Canadian
Conference. Participants have many opportunities to meet channel
partners—both new and established—in comfortable settings such as
the Industry Showcase Welcome Reception, featuring tabletop exhibits
from every registered PTDA manufacturer member company.
Along with networking, business market-driven education takes
center stage. Participants will hear information targeted to solve the
most vexing needs of the industry including information on corporate
culture, hiring, knowledge transfer and an update on the Canadian
mining industry. For more information about the Canadian Conference,
please visit www.ptda.org/CanadianConference.
Jim LaHaie, president, W.C. DuComb Co. and John Masek, SVP, Bearing Service Inc., took advantage
of PTDA’s complimentary Regional Networking Events and an optional Detroit Tigers game last year.
In 2016, complimentary PTDA Regional Networking Events are coming to Minneapolis, Chicago
and Cincinnati and are open to any employee of a PTDA member company or a prospective member
company.
PTDAUpdates_PTGuide_V3.indd 11 4/29/16 10:39 AM

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CGI-PTGuide4.16-Spread.indd 13 5/2/16 11:48 AM

PowerTransmission
REFERENCEGUIDE
MANY
applications call for converting rotary motion into motion that
moves in a straight line. For these applications, linear electric or
electromechanical actuators handle the task efficiently. In fact, today’s actuators are
so efficient that the variety available for different design needs has proliferated. That
means that actuators today are easier than ever to integrate into machinery; they’re
also less costly.
Electric actuators turn an electric motor’s power into linear motion in one of
three ways: through a linear motor, belt or screw drive. Linear motors are the most
technologically advanced and efficient method of directly transmitting the power of
the motor into the motion of the actuator. Instead of the rotor rotating in the stator,
the rotor travels in a linear, flat-array fashion along the stator.
Belt drive actuators are less costly, but can still move loads at fairly high linear
speeds. Because the motor is separate from the drive, the mechanical advantage
can increase thrust speed. The disadvantage of belt drives is that they wear over
time and require maintenance.
ELECTRIC ACTUATORS:
SMART DESIGNS EXCEL
LISA EITEL
SENIOR EDITOR
@DW_LISAEITEL
ElectricActuators_PT2016_V3.indd 14 4/29/16 10:40 AM

ELECTRIC ACTUATORS
Most screw drives take the form
of either rod-style actuators or rodless
cylinders. A motor transmits power
through a coupler or pulley arrangement
to rotate the screw and translate a nut
along the screw axis. Attached to this
nut is either the rod or saddle of the
actuator. Screw drives can use roller, ball
or leadscrews.
Electric actuators have several
benefits over hydraulic or pneumatic
actuators. For one, the operation
is cleaner because they operate
without the need for fluids or ancillary
equipment. They have the ability to
integrate power, control and actuation
mechanisms into one device. And they
combine force, velocity and positioning
in a single, compact motion control
device.
Another advantage is the ability
to constantly monitor feedback directly
from the motor and adjust performance
accordingly. Though not necessary for
every application, closed-loop operation
has the ability to adjust and correct
variances in the operation, resulting in
repeatable and accurate motion with
every move.
Today, the prices for drives for
electric actuators have come down,
which has opened new application
uses for the linear actuator. So, electric
actuators are more viable for applications
where hydraulic, pneumatic and manual
operations once ruled.
In many applications, servomotors
are replacing induction motors because
of their performance and energy efficiency. Direct drives are replacing
traditional motor-gearbox combinations because of their high dynamic
performance, high precision and long life. And electric actuators are replacing
pneumatic cylinders in many applications for similar reasons.
But the biggest improvements in the last five to ten years can be found
in the control systems integrated with electric actuators. Faster bus systems,
like industrial Ethernet and real-time communication, make the use of electric
actuators simpler.
Servo systems require fast communication and exchange of real-time
data between the drive and the overlaid machine control. The bus was always
the bottleneck in these systems. Now, with the much higher data rates and
real-time capacity of industrial Ethernet, the integration and the use of electric
actuators is easier. Stepper and servo drive options with Ethernet protocols
(Ethernet IP, Modbus, TCP) turn single-axis actuators into simple, low-cost
motion devices with infinite positioning, precise control and longer life.
Electric linear actuators are an alternative to pneumatic cylinders in several
applications because of the flexibility they deliver in the design of production
processes and production monitoring systems. In conveying applications,
for example, diverting and sorting functions are more
frequently controlled using electric actuators. Typically,
pneumatic actuators have been used, but the required
manual adjustments were often subject to human error.
Plus, the pneumatic actuators could only handle a small
amount of variability in product sizes. Electric actuators
are flexible by design.
For example, material handling
applications have experienced an
increase in the variety and variability
of package sizes. In packaging
machines, consumer
products manufacturers are
Linear positioning actuators of extremely long stroke
lengths — such as this LoPro linear actuator from Bishop-
Wisecarver — typically use belt drives. Polyurethane
belting is quiet and delivers long mechanical actuation
with good accuracy and high speeds. LoPro actuators are
three to 8 m long, but units to 15 m are possible.
Tolomatic ERD hygienic
all-stainless-steel
electric cylinders have
a roller-screw option that
boosts maximum thrust to
7,868 lbf (35.6 kN) for better life and
performance under high duty cycles than
ballscrew models.

PowerTransmission
REFERENCEGUIDE
NSK’s MCM Series Monocarrier includes a ballscrew, linear
guide and supports in one compact structure. It boosts
accuracy and reduces installation time, and some versions are
available through a Quick Ship Program.
producing more package sizes with the
same manufacturing lines, which require
equipment to be adaptable enough to
handle different product sizes and types.
Electric actuators easily handle these
variability requirements and, over the life of
the motion system, can be less expensive.
SELECTING AN ELECTRIC ACTUATOR
The process for selecting an electric
actuator is similar to one for hydraulic
or pneumatic actuators, with a few
differences. Here are the essentials.
Start with the motion profile. This
establishes the demands for velocity and
time as well as force (or torque) and the
required travel distance. This is also the
place to determine the maximum stroke
needed as well as maximum and minimum
speed requirements.
Then calculate the load. This can have
many different components including
inertial load, friction load, the external
applied load, as well as the gravitational
load. Load calculations also depend on the
orientation of the actuator itself, whether
it’s horizontal or vertical.
Duty cycle is another important factor.
This is defined as the ratio of operating
time to resting time and is usually
expressed as a percentage. The cycling
rate may be in seconds, minutes, hours
or even days, and knowing the operating
hours per day may also be necessary.
Knowing the duty cycle helps the engineer
estimate the system life requirements
and can also eliminate problems such as
overheating, faster wear and premature
component failure due to an incorrectly
sized actuator.
Know the positional accuracy and
precision demanded by the application.
The actuator’s precision should meet or
exceed the application’s requirements
for accuracy, backlash, and straightness
and flatness of linear motion. This directly
impacts the cost of the system; if the
application doesn’t demand high
accuracy or precision, then there is no
need to buy a more expensive actuator
when a less expensive one will satisfy
the demands of the application.
Aside from the technical
specifications mentioned above, there
is also the need to select the proper
configuration for the actuator in the
final design. This includes mounting
considerations and the need for any
other external components, such as
holding brakes and communication and
power cables.
Lastly, consider the operating
environment for the actuator. What are
the temperature requirements? Are
there any contaminants such as water,
oil or abrasive chemicals? Contaminants
can affect seals and impact the working
life of the actuator. In such cases,
selecting the appropriate IP rating for
an application can guard against the
effects of contaminants.

1.800.255.4773 www.nskamericas.com
BALL BEARINGS | ROLLER BEARINGS | LINEAR MOTION PRODUCTS | TECHNICAL SERVICES
nsk k1TM
lubricaTion uniT
Experience long-term, maintenance-free operation with NSK K1™
Lubrication Units. These patented
units provide fresh, continuous oil flow onto the rail or shaft during operation, making them ideal for
environments where grease replenishment is undesirable or where grease is easily washed away.
Available on NSK linear guides, ball screws, Monocarrier™
actuators and Robot Modules, K1™
Lubrication
Units prolong life for up to 5 years or 10,000 km operational distance.
MAINTENANCE-
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NPA-SL-020 Design World ad_K1 Unit[250314]v1.indd 1 2014-03-25 3:14 PM
NSK 8-15.indd 17 4/29/16 10:04 AM

PowerTransmission
REFERENCEGUIDE
This is a custom loading-station scissor lift that
uses a SERAPID 40 chain actuator. Retractable
to table-top level, the platform can smoothly
lift a heavy load more than 10 ft. A space-
saving chain storage magazine fits compactly
at the bottom.
MECHANICAL COMPONENTS
AT THE HEART OF MOTION DESIGN
LISA EITEL • SENIOR EDITOR • @DW_LISAEITEL
RIGID-CHAIN
actuators work by pairing a drive
(usually an electric motor) with
a length of chain sporting shoulders on each link. The motor
output shaft—fitted with a specialty sprocket or pinion—applies
tangential force to the chain. Then the chain comes out and
straightens, and its links’ shoulders lock to form a rigid series.
When the motor runs in the opposite direction, the chain
shoulders disengage and allow for coiling.
Inside the actuator body, reaction plates and guides counter
thrust resistance and keep the chain on track. Links travel around
the pinion to exit the actuator body along the stroke path. Here,
the motor’s torque comes to act as forward thrust via the link
shoulder to the rest of the links’ shoulders. The last link in the
chain before the load has geometry that puts the thrust higher
than the articulation axis. This makes a moment that effectively
locks the link shoulders. In reverse, pulling force acts along the
links’ cross axes.
Rigid-chain actuators have the mechanical benefits of
conventional chain but can act in horizontal push setups or
vertically as jacks. Plus they’re compact. In contrast, traditional
chain drives can only pull, so need two drives for bidirectional
motion. Traditional screw jacks for vertical power transmission
need space for retraction that’s as long as the working stroke
itself.
Before specifying a rigid-chain actuator, determine
the application’s total load, including the transported load,
acceleration forces, external environmental forces, and that
due to friction—with a coefficient between 0.05 and 0.5 for
typical rigid-chain actuator setups. Next, determine what type
of actuator body and chain-storage magazine the application
can accommodate. Determine whether the chain will need to
change direction on its way from the magazine to actuator body.
Actuators usually feed chain around 90° or 180° turns.
Note that rigid-chain actuators can work alone or in tandem.
Twin-chain setups deliver high positioning accuracy and stability
where loads are large or bulky.
Common rigid
chain has two rows
of link plates and
shoulders; duplex
chain has three;
other options
abound.
Image courtesy
iwis Drive Systems
DW half page rv
RigidChainActuators_PTGuide_V3.LE.MD.indd 18 4/29/16 10:43 AM

Choose a rigid-chain actuator to satisfy the design geometry.
... but guided chain is most stable.
Unguided chain with shoulders up coils downwards ...
Common rigid-chain arrangements
Pinion
Actuator body
Input drive shaft
Chain link shoulders
RIGID CHAIN ACTUATORS
Unguided chain with shoulders up coils downward, which is useful but
not always stable enough for long strokes. That with shoulders down
(here, bottom) is slightly more stable. Use guided chain wherever space
permits.
Here, a pushing bar acts
as a yoke to keep loads steady,
with optional hooks for pulling
as well. Optimized geometry has
the force vector act on the load’s
center for balance. If twin-chain
setups are impossible, consider
adding framework to guide
awkward loads.
Guides on the chain also
help maintain stability—even
over very long strokes—because
they address side and buckling
forces. Such guides come in
different shapes with different
crampons and subcomponents
to engage the chain. Where use
of chain guides is impossible,
most designs run the chain
with link shoulders down for
moderate stability.
Some last design notes:
Standard chain is carbon steel
to withstand heat to 200° C,
but stainless, high-temperature,
and coated chain for long life
are other options. The required
length of chain is total design
stroke plus a few links to engage
the actuator pinions.
As with any power-
transmission setup, consult
the manufacturer for tips and
guidance on determining
necessary drive power and
other details.
SERAPID Inc. | 34100 Mound Rd. | Sterling Heights, MI | Tel +1 586-274-0774 | info-us@serapid.com | www.serapid.com
SOLUTIONS FOR PRECISION MOVEMENT OF VERY HEAVY LOADS
Press-mounted dual
push-pulls
QUICK DIE CHANGE STAGE AND ORCHESTRA LIFTS CUSTOM ENGINEERED SYSTEMS INDUSTRIAL LIFTS
LinearBeam
guided push-pull
LinkLi
li columns
RollBeam
Telescopic push-pull
DW half page rv.indd 1 4/12/2016 2:17:33 PM
RigidChainActuators_PTGuide_V3.LE.MD.indd 19 4/29/16 2:58 PM

PowerTransmission
REFERENCEGUIDE
This cutaway, courtesy of Nook
Industries, shows the inner workings
of a ballscrew, most notably the
recirculating balls and the deflector,
in relation to the screw assembly.
BALLSCREWS
B A S I C S O F
MILES BUDIMIR • SENIOR EDITOR • @DW_MOTION
BALLSCREWS
are a mainstay of motion actuation. Compared to
similar actuation methods such as leadscrews, they
typically cost a bit more but are generally more accurate. They also boast higher
efficiencies, even though they demand more lubrication because of the use of
recirculating balls.
The basic components of a ballscrew are a nut, a screw with helical grooves, and
balls (often made from steel, ceramic, or hard plastic material) that roll between the
nut, the screw and the grooves when either the screw or nut rotates. Balls are routed
into a ball return system of the nut and travel in a continuous path to the ball nut’s
opposite end. Seals are often used on either side of the nut to prevent debris from
compromising smooth motion.
Recent advances in manufacturing and materials have improved ballscrew
performance so machine designers today can get better linear motion with them
at lower cost. Some improvements include the fact that the latest generation of
ballscrews has more load density than ever, giving designers higher capacity from a
smaller package. There is also a trend toward more miniaturization, but also faster
ballscrews with rolled and ground screw manufacturing methods.
Ballscrews suit applications needing light, smooth motion, applications requiring
precise positioning, and when heavy loads must be moved. Examples include
machine tools, assembly devices, X-Y motion, Z motion, and robots.
Ballscrews are usually classified according to factors such as lead
accuracy, axial play and preload, and life/load relationship.
Lead accuracy refers to the degree to which the shaft’s
rotational movements are translated into linear
movement. With lead accuracy and axial
play determined by the manufacturing
method of the ballscrew shaft
and the assembly of the nut, high
lead accuracy and zero
axial play is generally
Ballscrews_PTGuide_V2-mb.indd 20 4/29/16 2:26 PM

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Rotron regenerative blowers.
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REFERENCE GUIDE
POWER TRANSMISSION
www.cjmco.com
Phone: 860-643-1531
291 Boston Tpke, Bolton, CT 06043
Engineering Solutions for Clutches & Brakes
Clutches,Brakes & Power
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associated with relatively higher-cost
precision ground ballscrews, while
lower lead accuracy and some axial
play is associated with lower cost rolled
ballscrews. Fabricated by rolling or
other means, ballscrew shafts yield a
less precise but mechanically efficient
and less expensive ballscrew.
Axial play is the degree to which
a ball nut can be moved in the screw
axis direction without any rotation of
either nut or screw. Preload is applied
to eliminate axial play. The process
of preloading removes backlash and
increases stiffness.
Ball recirculation inside the ball nut
can affect precision and repeatability.
Thus, ball nuts are available with a range
of preload options to reduce or remove
the axial play as they rotate around the
screw. Minimal axial play allows better
accuracy, for example, because no
motion is lost from the clearance in the
balls as they reengage.
There are several techniques for
preloading. Some common methods
include oversizing the balls inside
the nut housing; using the so-called
“double-nut” or “tension nut” method;
or by using a manufactured offset in
the raceway spiral to change the angle
of ball engagement (the “lead shift”
method) and deliberately force the balls
into a preload condition. Each method
has its advantages and disadvantages,
but all serve to minimize or eliminate
backlash between the nut and screw.
Perhaps the biggest overall
benefit of a ballscrew is that it has high
efficiencies that can be well over 90%.
By contrast, Acme lead screws average
about 50% efficiency or less. There are
also minimum thermal effects. Backlash
can be eliminated through preloading.
Ballscrews also offer smooth movement
over the full travel range. The higher
cost of ballscrews can be offset by
decreased power requirements for
similar net performance.
One drawback to ballscrews is that
they require high levels of lubrication.
Ballscrews should always be properly
lubricated, with the correct type of
lubricant, to prevent corrosion, reduce
friction, extend operating life, and
ensure efficient operation.
Because ballscrews are a bearing
system, they’ll need some type of
lubrication to avoid metal-to-metal
contact of the balls in the raceway.
While the lubrication choice can be
either oil or grease, it’s advisable to
avoid solid additives (such as graphite)
as they will clog the recirculation
system. An NLGI no. 2 type grease
is recommended but it should also
depend on the application, whether
food-grade or another special type
of lubrication is required. Ballscrews,
especially those used in machine tools,
generally require lubricants with EP
additives to prevent excessive wear.
The lube amount will be fixed,
but the frequency of lubrication will
vary depending on factors such as
the move cycle characteristics, or
contamination in the environment.
Contaminated lubrication can increase
friction. In addition, ballscrews can fail
if the balls travel over metal chips or
dirt in the ball thread raceway. Using
lubricants recommended by machine
tool manufacturers can help prevent
this effect. Using telescopic covers or
bellows can help keep ballscrews clean
when used in environments with many
contaminants.
A sample ballscrew assembly, such as the Precision Metric Ball Screws (PMBS) series
from Nook Industries, features a single nut with flange, uses precision thread-rolling
technology and is available in a wide range of leads and diameters.
Ballscrews_PTGuide_V2-mb.indd 22 4/29/16 10:47 AM

Together a winning combination for today’s
servomotor applications.
Our ServoClass® couplings have been recently redesigned
to enable your actuator to go even faster and achieve
the positional accuracy that will take your designs
to the next level. Our couplings will do all this
with low bearing loads.
3 New sizes now available.
Now, size, select and see the right
ServoClass® coupling solution for your
application with Zero-Max 3D CAD files.
Check our FAST deliveries.
www.zero-max.com 800.533.1731
© 2010 ZERO-MAX
Your ball screw
Your servomotor
Our coupling
# Zero-Max_full_pgs_r10_Design World 2/12/10 4:02 PM Page 1
Zero Max ad 8-15.indd 23 4/29/16 10:05 AM

PowerTransmission
REFERENCEGUIDE
DESIGN WORLD — MOTION 4 • 201624
BEARINGS
REVIEW OF
IT’S EASY
for bearings to go unnoticed—an out of sight,
out of mind mentality. This attitude is common
among so many because bearings are simple, internal machine
elements. However, that doesn’t make them any less crucial for motion
applications. The purpose of a bearing is to reduce frictional forces
between two moving parts by giving a surface something to roll on,
rather than slide over. There are basic features that all bearings share,
but specific application needs demand many different variations of this
universal motion system component.
A bearing usually consists of smooth rollers or metal balls and
the smooth inner and outer surfaces, known as races, that the rollers
or balls roll against. These rollers or balls act as the load carrier for
the device, allowing it to spin freely. Bearings typically encounter two
kinds of load: radial and axial. Radial loads occur perpendicular to the
shaft, while axial loads occur parallel to the shaft. Depending on the
application the bearing is being used in, some bearings experience
both loads simultaneously. There are many different types of bearings,
each suitable for different purposes in varying applications.
BALL BEARINGS
One of the most common forms of bearings is the ball bearing. As
the name implies, ball bearings use balls to provide a low friction
means of motion between two bearing races. Since the contact area
between the balls and races is so small, ball bearings cannot support
as large a load as other bearing types and are best suited for light to
moderate loads. However, their small surface contact also limits the
heat generated by friction, meaning that ball bearings can be used in
high-speed applications.
ROLLER BEARINGS
Possibly the oldest form of bearing, roller bearings can be spherically
or cylindrically shaped and are commonly used in applications like
conveyor belt rollers. Because of their shape, roller bearings have
greater surface contact than ball bearings, and are thus able to handle
larger loads without deforming. Their shape also allows for a moderate
amount of thrust load since the weight is distributed across cylinders
instead of spheres.
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Bearings_PTGuide_V3.indd 24 4/29/16 10:53 AM

BEARINGS
25DESIGN WORLD — MOTIONmotioncontroltips.com | designworldonline.com
NEEDLE
ROLLER BEARINGS
When you need to reduce friction
between two moving parts but have
very limited space to do so, a needle
roller bearing may be just what you’re
looking for. A needle roller bearing is a
roller bearing with rollers whose length
is at least four times their diameter.
Despite their low cross section, the
large surface area of the needle
roller bearing allows them to support
extremely high radial loads.
They usually consist of a cage,
which orients and contains the needle
rollers and an outer race, which is
sometimes the housing itself. The
bearings can often be found in two
different arrangements. The first is a
radial arrangement, in which the rollers
run parallel to the shaft. The second
is a thrust arrangement, in which
the rollers are placed flat in a radial
pattern and run perpendicular to the
shaft.
These bearings are often
used in automotive applications,
such as rocker arm pivots, pumps,
compressors and transmissions. The
drive shaft of a rear-wheel drive vehicle
typically has at least eight needle
bearings (four in each U joint) and
often more if it is particularly long, or
operates on steep slopes.
Spherical roller bearings like
Koyo’s RZ Spherical Roller
Bearing have a greater surface
contact than ball bearings, and
are thus able to handle larger
loads without deforming.
THRUST BALL BEARINGS
Thrust ball bearings are designed for
use in applications with primarily axial
loads and are capable of handling shaft
misalignment. These bearings are also
useful in high-speed applications, such
as in the aerospace and automotive
industries.
THRUST ROLLER BEARINGS
Thrust roller bearings are designed so
that the load is transmitted from one
raceway to the other, meaning that
these bearings can accommodate radial
loads. Bearings like these also have a
self-aligning capability that makes them
immune to shaft deflection and alignment
errors.
TAPERED ROLLER BEARINGS
Tapered roller bearings feature tapered
inner and outer ring raceways with
tapered rollers arranged between them,
angled so the surface of the rollers
converge at the axis of the bearing. These
bearings are unique in that, unlike most
bearings that can handle either axial
or radial loads, they can handle large
amounts of load in both directions.
A single row taper bearing is limited
in that it can only take high axial loads
from one direction, but if adjusted against
a second tapered roller bearing, that
axial load is counteracted. This allows the
bearings to accept high radial and axial
loads from multiple directions.
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Bearings_PTGuide_V3.indd 25 4/29/16 2:33 PM

PowerTransmission
REFERENCEGUIDE
Depending on application requirements, some ball bearing are
made with magnetic, lubricant-free motion plastics like this igus
xiros M180 which uses a lightweight polymer ball bearing.
The ability of a tapered roller bearing to accommodate angular misalignment of the
inner ring in relation to the outer ring is limited to a few minutes of arc. As with other roller
bearings, tapered roller bearings must be given a minimum load, especially in high speed
applications where the inertial forces and friction can have a damaging effect between the
rollers and raceway.
LINEAR MOTION BEARINGS
Linear motion bearings are specifically designed to allow motion in one direction and are
typically used to carry a load on a slide or rail. They can be powered by a motor or by
hand and experience over turning moments of force instead of radial and axial loads.
PLAIN BEARINGS
Plain bearings are the simplest form of bearing available, as they have no moving parts.
They are often cylindrical, though the design of the bearing differs depending on the
intended motion. Plain bearings are available in three designs: journal, linear and thrust.
Journal style bearings are designed to support radial motion where a shaft rotates
within the bearing. Linear bearings are often used in applications requiring slide plates,
as these bearings are designed to permit motion in a linear motion. Finally, a plain thrust
bearing is designed to do the same job as its roller bearing counterpart, but instead of
using cone shaped rolling elements, the bearing uses pads arranged in a circle around
the cylinder. These pads create wedge-shaped regions of oil inside the bearing between
the pads and a rotating disk, which supports applied thrust and eliminates metal-on-metal
contact.
Out of all the bearing types available, plain bearings tend to be the least expensive.
They can be made from a variety of materials including bronze, graphite and plastics, such
Bearings_PTGuide_V3.indd 26 4/29/16 10:55 AM

BEARINGS
The greater surface contact of roller bearings enables them to
handle larger loads without deforming. Demonstrating just a few of
the many types of roller bearings, here we see a needle, spherical,
tapered and cylindrical roller bearing. Image courtesy of AST.
as Nylon, PTFE and polyacetal.
Improvements in material
characteristics have made plastic
plain bearings increasingly popular
in recent years. Plain bearings of
all types, however, are lightweight,
compact and can carry a substantial
load.
As far as lubrication is
concerned, some plain bearings
require outside lubrication while
others are self-lubricating. Plain
bearings made of bronze or
polyacetal, for example, contain
lubricant within the walls of
the bearing, but require some
outside lubrication to maximize
performance. For other plain
bearings, the material itself acts
as the lubricant. Such is the case
with bearings made from PTFE or
metalized graphite.
The growing popularity of plain
plastic bearings and increasingly
stringent industry standards
has resulted in more consumers
requiring the bearings to meet FDA
and RoHS standards. There has
even been a call for the bearings to
meet the standards of EU directive
10/2011/EC, which also takes the
material manufacturing process
into account.
Common applications for drawn cup needle
roller bearings like this from Koyo include:
precision gear boxes, machine tool, medical
equipment, precision assembly equipment,
robotics, after-market racing equipment and
aerospace.
APPLICATIONS
Bearings are all around us in everyday life and most of the time they go unnoticed. But
without them, many of the tasks we undertake would move along much less smoothly.
The ball bearings’ simple design, ability to operate at high speeds and relatively low-
maintenance requirements, makes them one of the most common roller bearings found
in a variety of industrial applications.
For example, deep groove ball bearings are often used in small- to medium-sized
electric motors because of their ability to accommodate both high speeds and radial
and axial loads. Self-aligning ball bearings, on the other hand, are ideal for use in fans.
These bearings have two rows of balls with a common raceway in the outer ring. This
design allows for angular misalignment while maintaining running accuracy. They are,
however, one of the most difficult bearings to install correctly.
Tapered roller bearings are another form of
bearing that just about every industry depends
on one way or another. They are usually found in
applications where support for axial and radial loads
is required, such as in a tire hub where the bearing
must deal with the radial load from the weight of
the vehicle and the axial load experienced while
cornering. These bearings are also commonly found
in gearboxes where they are generally mounted with
a second bearing of the same type in a face-to-face
or back-to-back orientation. They provide rigid shaft
support, keeping deflection to a minimum. This
reduced shaft deflection minimizes gear backlash.
Tapered bearings also have the advantage of
having less mass but high efficiency, however this
does limit their overall speed.
In applications where bearings are mounted
vertically, they are typically oriented in a face-to-
face setup, while horizontal applications use a
back-to-back setup. Some pumps use this design
because of shaft deflection concerns.
Bearings_PTGuide_V3.indd 27 4/29/16 2:36 PM

PowerTransmission
REFERENCEGUIDE
BELTS & PULLEYS
THE BASICS OF
Belts and pulleys lift loads, use mechanical advantage to apply forces, and transmit
power.They also form the basis of industrial conveyors big and small. Here are the
fundamentals of their operation and how to apply them.
Shown here is a Gates Carbon Drive CDN system—designed
to be lower in cost for new bike applications. It leverages
new materials and geometries, with nine carbon cords
embedded within engineered polymer belt and a patented
11-millimeter tooth pitch profile for lower tension. Like
many new belt applications, it replaces chain drives.
INDUSTRIAL
belt drives consist of rubber belts that wrap around drive
pulleys, in turn driven by electric motors. In a typical setup, the
belt also wraps around one or more idler pulleys that keep the belt taut and on track. The
main reasons that engineers pick belt drives over other options is that modern varieties
require little if no maintenance; they’re less expensive than chain drives; and they’re quiet
and efficient, even up to 95% or more. In addition, the tensile members of today’s belts—
cords embedded into the belt rubber that carry the majority of the belt load—are stronger
than ever. Made of polyester, aramid, fiberglass or carbon fiber, these tensile cords make
today’s belt drives thoroughly modern power-transmission devices.
Manufacturers generally describe belts and pulleys with five main geometries. Pitch
diameter is the drive pulley’s diameter. Center distance is the distance between the two
pulleys’ centers. Minimum wrap angle is a measure of how much the belt wraps around
the smallest pulley. Belt length is how long the belt would be if cut and laid flat. Finally, in
the case of toothed belts (also called synchronous belts) the pitch is the number of teeth
per some length—so a 3-mm pitch means that the belt has one tooth every 3 mm, for
example.
APPLYING SYNCHRONOUS BELTS
Some general guidelines are applicable to all timing belts, including miniature and
double-sided belts. First of all, engineers should always design these belt drives
with a sufficient safety factor—in other words, with ample reserve horsepower
capacity. Tip: Take note of overload service factors. Belt ratings are
generally only 1/15 of the belt’s ultimate strength. These ratings are set
so the belt will deliver at least 3,000 hours of useful life if the end user
properly installs and maintains it. The pulley diameter should never
be smaller than the width of the belt.
BeltsPulleys_PTGuide_V1.LE.indd 28 4/29/16 4:10 PM

29DESIGN WORLD — MOTION 4 • 2016
BELTS & PULLEYS
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As mentioned, belts are
quieter than other power-
transmission drive options
… but they’re not silent.
Noise frequency increases
proportionally with belt speed,
and noise amplitude increases
with belt tension. Most belt
noise arises from the way
in which belt teeth entering
the pulleys at high speed
repeatedly compresses the
trapped pockets of air. Other
noise arises from belt rubbing
against the flange; in some
cases, this happens when the
shafts aren’t parallel.
Pulleys are metal or
plastic, and the most suitable
depends on required
precision, price, inertia, color,
magnetic properties and the
engineer’s preference based
on experience. Plastic pulleys
with metal inserts or metal
hubs are a good compromise.
Tip: Make at least one pulley
in the belt drive adjustable to
allow for belt installation and
tensioning. Also note that in a
properly designed belt drive,
there should be a minimum of
six teeth in mesh and at least
60° of belt wrap around the
drive pulley.
Other tips:
• Pretension belts with the proper
recommended tension. This extends life
and prevents belt ratcheting or tooth
jumping.
• Align shafts and pulleys to prevent
belt-tracking forces and belt edge wear.
Don’t crimp belts beyond the smallest
recommended pulley radius for that
belt section.
• Select the appropriate belt for the
design torque.
• Select the appropriate belt material
for the environment (temperature,
chemical, cleaning agents, oils and
weather). Belt-and-pulley systems
are suitable for myriad environments,
but some applications need special
consideration. Topping this list are
environmental factors.
Dusty environments do not generally
present serious problems as long as the
particles are fine and dry. In contrast,
particulate matter can act as an abrasive
and accelerates belt and pulley wear. Debris
should be prevented from falling into belt
drives. Debris caught in the drive is generally
either forced through the belt or makes
the system stall. In either case, serious
damage occurs to the belt and related drive
hardware.
Light and occasional contact with
water—during occasional washdowns, for
example—has little serious effect. However,
These PowerGrip TruMotion timing belts from Stock
Drive Products have nylon tooth facing for longer and
quieter running and less dust. Fiberglass tensile cords
resist elongation and have a high flex life.
BeltsPulleys_PTGuide_V1.LE.indd 29 5/3/16 9:22 AM

PowerTransmission
REFERENCEGUIDE
prolonged contact with constant spray or
submersion can significantly reduce tensile
strength in fiberglass belts and make aramid
belts break down and stretch out. In the same
way, occasional contact with oils doesn’t
damage synchronous belts. But prolonged
contact with oil or lubricants, either directly
or airborne, significantly reduces belt service
life. Lubricants cause the rubber compound to
swell, break down internal adhesion systems
and reduce felt tensile strength. While alternate
rubber compounds may provide some marginal
improvement in durability, it’s best to prevent oil
from contacting synchronous belts.
The presence of ozone can be detrimental
to the compounds used in rubber synchronous
belts. Ozone degrades belt materials in much
the same way as excessive temperatures.
Although the bumper materials used in belts
are compounded to resist the effects of ozone,
eventually chemical breakdown occurs and
they become hard and brittle and begin
cracking. The amount of degradation depends
on the ozone concentration and generation of
exposure.
Rubber belts aren’t suitable for cleanrooms,
as they risk shedding particles. Instead, use
urethane timing belts here … keeping in mind
that while urethane belts make significantly less
debris, most can carry only light loads. Also,
none have static conductive construction to
dissipate electrical charges.
Shown here are Baldor-Maska
sheaves for V-belt drives,also
called friction drives for the way
they operate. Minimum allowable
sheave diameter depends on the
belt shape and material, whether
that’s synthetic, neoprene,
urethane, or rubber.
This setup has an electronic warning system from ContiTech
to alert operators when a conveyor is elongating or at risk of
ripping. Called CONTI PROTECT and most useful on industrial
and mining conveyors, the system uses magnetic markings
on the belts to track irregularities in the splice length and
detects longitudinal rips before they grow. Such monitoring
systems are just one example of how belt-drive technologies
have kept pace with 21st-centrury design concepts.
BeltsPulleys_PTGuide_V1.LE.indd 30 4/29/16 2:59 PM

www.designworldonline.com 4 • 2016 DESIGN WORLD 31
BRAKES & CLUTCHES
BRAKES
and clutches are a mainstay in motion designs
that need to stop, hold or index loads.
Especially over the last five years, a technology trend toward
application-specific designs has quickened as several industries
are pushing the performance envelope of stock components.
Brakes are used to stop a load, typically a rotating load,
while clutches are used to transfer torque. There are many
different types of brakes and clutches.
A brake would be used in applications where accurate
stopping of the load is needed and the motor will stop as well.
A clutch would be used in applications where it’s desirable
to engage or disengage a load and motor while leaving the
motor to run all the time. When a clutch is used, the load will be
allowed to coast to a stop.
A clutch and brake combination would be used where the
load will be started and stopped while the motor continues to
rotate. Both clutches and clutch brakes can mount to a motor
shaft or be base-mounted and have input through a belt drive,
chain drive or coupling.
The motor horsepower and motor frame size play a key
role in determining which specific brake or clutch to select. In
the case of base-mounted units, it may be necessary to define
the RPM at that location. Manufacturers provide quick selection
charts where unit size is determined by finding the intersection
of motor horsepower and speed at the clutch shaft. The charts
are commonly created using the dynamic torque capacity for the
product and the torque capacity for the motor plus an overload
factor of some value. Using this method presumes that you’ve
selected a motor that’s sized appropriately to the application. In
applications where cycle rates are considered aggressive for the
inertia of the load, it’s a good idea to consult with the application
support staff of the manufacturer regarding the heat dissipation
capacity.
Coil voltage is another consideration. The most common
options are 6, 24 and 90 Vdc with 90 V being widely preferred in
North American markets, while 24 V is more common in Europe.
In both cases, brake and clutch manufacturers can offer power
supplies to convert ac to dc if required.
BRAKES & CLUTCHES
MORE INDISPENSABLE THAN EVER
Shaft-mounted electric clutches
from New Torque have a static
torque rating from 15 to 202 Nm,
voltage of 24 to95 Vdc, and power
of 16 to 50 W.
Some clutches and brakes — as
the ones from Carlyle Johnson
Machine Company shown here
— can last 15 years on average,
with some products lasting 50
years or more.
Shown here is an ac solenoid
shoe Brake from Ametek. Gemco
industrial brakes stop industrial
machines in steel mills, gantries,
cranes, and commercial laundry
equipment. They are tough and
long-lasting.
This is a Force Control
Industries coupler brake. In
fact, the company’s Posistop and
MagnaShear coupler brakes mount
between motors and reducers, so
engineers can eliminate separate
brake motors.
BrakesClutches_PTGuide_V3.indd 31 4/29/16 11:14 AM

ENGINEERS
can use a multitude of
cables (including data,
coaxial, and instrumentation cables) in industrial
settings for control networking, low and medium-
voltage power transmission and distribution,
and more. Most cables that distribute power to
motors are low-voltage designs rated for 2,000
V and below. That said, some facilities with
partial responsibility over the utility power they
consume use medium-voltage cables rated for
2,000 to 35,000 V.
Available as both single and multi-conductor
designs, these power cables must be able to
withstand high mechanical loads, speeds and
accelerations. Common applications include
machine tools, cranes, conveyors, portable
designs and stationary heavy-duty equipment.
Such cables can supply temporary ac or dc
power to motors and generators, and can
operate indoors and outdoors, depending on
their temperature rating.
The proper cable for an application depends
on its function and environment. For instance,
only use an unshielded cable when it will
operate in an enclosed space only accessible by
trained professionals. Such enclosures prevent
electromagnetic interference and keep plant
personnel safely away from potentially live
electrical charges.
Manufacturers usually construct low-voltage
cables with aluminum or copper conductors,
insulation and jacketing. Conductors can range
anywhere from finely stranded bare copper wires
to bunched strands of tinned annealed copper.
They come in both shielded and unshielded
versions and usually must be flame retardant and
oil resistant.
Power cables feature conductors that are
either stranded in layers inside or bundled
or braided. The stranded design is easier to
manufacture so costs less. It features long,
layered cores and firm strands wrapped with
an extruded jacket. In the bundled or braided
design, the conductors are braided around a
tension-proof center. By eliminating the layers, a
uniform bend radius is ensured.
To accommodate the complex and
sometimes cramped spaces where they operate,
industrial power cables must also have tight
bending radii, ranging anywhere from 5 to 15
times the overall cable diameter. Jacketing is also
crucial to meet these bending radii requirements.
Therefore, the use of flexible materials such as
PVC, TPE and CPE not only helps these cables
bend and flex but also protects them from
environmental damage.
Because their materials, shielding and
jacketing all vary, so do industrial power cables’
installation techniques. Installers can put cables
into fixed duct, shafts, and conduit; direct-bury or
even immerse the cables in water in water; or lay
cables into open-air applications.
Depending on where a cable is
manufactured and used, it must meet a variety of
approvals, including UL, CSA, TC, AWM, RoHS,
CE and more. In the U.S., the National Electrical
Code (NEC) sets the standards that designers
must usually follow. These codes ensure that the
cables have key performance features to satisfy
machine requirements—for example, to stop the
propagation of flames, satisfy the application’s
maximum voltage draw, withstand extreme
temperatures, and maintain integrity even when
exposed to oil.
THE BASICS OF
MARY GANNON • SENIOR EDITOR • @DW_MARYGANNON
INDUSTRIAL POWER
TRANSMISSION CABLES
REFERENCE GUIDE
POWER TRANSMISSION
Control cables, like this Chainflex continuous flex control design from igus, must be able to withstand high mechanical
loads, speeds and accelerations. These Chainflex cables are intended for use in Energy Chain cable carriers and conform to
key standards; are capable of torsion—depending on the cable; and can be used in high speeds and accelerations. They are
UV resistant, flame retardant, halogen free, and can withstand very high or extremely low temperatures. They are available
shielded or unshielded, with a choice of PVC, PUR and TPE outer jackets.
Cabling_PTGuide_V2 MG.indd 32 4/29/16 11:15 AM

• Flexible
Control Cables
• Continous Flex
Cables
• Torsion Cables
• Halogen-Free Cables
• European Cables
• Servo Motor Cables
Bus Cables •
Data Cables •
Tray Cables •
Silicone Cables •
Cable Accessories •
Specialty Cables •
Stock Available
for Immediate Delivery
SAB NORTH AMERICA344 Kaplan Drive, Fairfield NJ 07004
Phone: 866-722-2974 • Fax: 973-276-1515
info@sabcable.com • www.sabcable.com
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SAB_PTGuide4-16.indd 33 4/29/16 10:06 AM

PowerTransmission
REFERENCEGUIDE
THE BASICS OF
SPROCKETS &
CHAIN DRIVES
Shown here is an MPC sprocket from
Martin Sprocket and Gear Inc. for use
with a curvilinear timing belt. As a side
note, synchronous belt drives work as a
replacement for roller-chain drive systems
where lubrication is unacceptable.
ENGINEERS
have used chains in motion systems for
more than a century. They are versatile
and reliable components to drive machinery and convey products.
Now, advances in precision and technology let designers use
chains in more applications than ever. Remote installations benefit
from long-life chain that requires no lubrication, for example.
Chain-based machinery abounds, but the most common
industrial designs use roller chain. This type of chain consists of
five basic components: pin, bushing, roller, pin link plate and
roller link plate. Manufacturers make and assemble each of these
subcomponents to precise tolerances and heat treat them to
optimize performance. More specifically, modern roller chains
exhibit high wear resistance, fatigue strength and tensile strength.
Roller-chain applications generally fall into two categories: drives
and conveyors.
CHAIN-DRIVE APPLICATIONS
Most typical drive applications use an ASME/ANSI roller chain
wrapped around a driver sprocket (connected directly to the
motor or reducer) and the driven sprocket (often connected to a
machine’s conveyor head-shaft). This portion of the drive lets the
designer build a system that’s either faster or slower by simply
changing the ratio of teeth between the drive and driven sprocket.
The ratio of the teeth determines the reduction in rpm … so to
reduce rpm, the driven sprocket must be larger than the driver
sprocket. For example, if the driver sprocket has 15 teeth and the
driven sprocket has 30 teeth, the ratio is 2:1, so the rpm is halved
at the driven sprocket.
This Morse leaf chain from Power Transmission Solutions of
Regal-Beloit America is made of roller-chain-type links and riveted
pins for maximum strength for a given width. It works as tension
linkage or a lifting device at slow speeds.
ChainRollerSprockets_PTGuide_V3.indd 34 4/29/16 11:18 AM

CHAIN, ROLLER & SPROCKET
500
400
300
200
100
80
60
40
30
20
10
8
6
4
3
2
1
0.8
0.6
0.4
0.3
0.2
900
700
500
400
300
200
100
80
60
40
30
20
10
8
6
4
3
2
1
0.8
0.6
0.4
0.3
0.2
1,000
800
600
400
300
200
100
80
60
40
30
20
10
8
6
4
3
2
1
0.8
0.6
0.4
0.3
1,000
800
600
400
300
200
100
80
60
40
30
20
10
8
6
5
4
3
2
1
0.8
0.6
0.4
10
20
30
40
50
60
80
100
200
300
500
700
1,000
2,000
3,000
5,000
7,000
10,000
Roller-chaindrivecapacity(horsepower)
Chain strands
4 3 2 1
25T
22T
19T
25T25T
25T
25T
25T
25T
25T
25T22T
21T
21T
21T
21T
21T
21T
19T
19T17T
17T
17T
17T
17T
19T
19T
19T
15T
15T
23T
23T
23T
23T
240200
180160140120100
80
60
50
40
35
Speed of roller chain’s small sprocket (rpm)
Roller-chain selection chart
This is a Zone Touch case conveyor from Container Handling Systems
Corp. (CHSC), which uses chain drives that function as accumulating
sections. It has longer life than conventional machines with rollers
and fabric belts. It’s also quieter than roller
conveyors because its tabletop chain rides low-
friction UHMW wear strips and return ways.
The easiest way to select a roller chain is using
horsepower charts. First, obtain the motor horsepower and
rpm of the small driver sprocket. From this, determine the
chain size and number of teeth for the driver sprocket. Where
roller chain must drive applications that need long life without
contamination, pick chain with self-lubricating subcomponents.
Where roller chain must drive applications that need high
precision, pick chain with precision roller bearings at each link
connection.
CONVEYOR APPLICATIONS
Conveyor chains come in myriad versions to move product
horizontally, vertically or even around curved radii. The
most common conveyor chains are ASME-style (ANSI-style)
attachment chains. These chains include extended pins or
plates with tabs onto which parts or product-holding shoes
can bolt. Common versions are single-pitch attachment chain,
double-pitch attachment chain, hollow-pin chain, curved-
attachment chain and plastic-sleeve chain. The attachments let
engineers put special fixtures or blocks onto the chain to serve
specific conveyor functions.
One subtype of conveyor chain is the accumulating
conveyor. These stop discrete products even while the chain
is still moving, and they do so with minimal friction and wear.
Accumulating conveyors are suitable for
applications (such as assembly lines) that have products ride
through several stations. Tip: Select chain with top rollers or
side rollers to let discrete products idle while the conveyor
continues to run. Also pick custom attachments or work with
manufacturers that make custom fixtures to handle specific
parts. Many industries (including the automotive, food and
beverage, and consumer-products industries) use custom
attachments on their chain-based accumulator conveyors to
economically and consistently move.
CHAINS ENDURE SUBOPTIMAL
ENVIRONMENTS
The environments of many chain applications
are less than ideal. Some require clean
operation without the lubrication that can
contaminate products. Others expose
chain-driven machinery to weather, water
or chemicals. So, chain manufacturers offer
several products to meet these challenges.
Consider roller chain: One critical area
where roller chains need lubrication is the
pin-bushing contact zone. Self-lubricating
chains stay cleaner because the exterior of
the chain is free of excess lube. These chains
Morse inverted-tooth
chain drives from Power
Transmission Solutions
of Regal-Beloit America
come in HV versions for
high capacity at high
speed. Silent chain is
another option to make
smooth, silent drives at
slower speeds.

• Available from stock from over 30
Martin locations throughout North
America
• MTOs in days not weeks:
» QD bushed
» MST®
bushed
» Finished bore
» Stainless steel
» Aluminum
» And more...
• Over 350 MPC®
SKUs on the shelf
• Stocked in TB and Minimum Plain Bore
• Compatible with all leading
Curvilinear Belts
Martin's MPC®
Sprockets are manufactured in various sizes, dimensions and capacities to
meet a variety of industrial requirements.These include a wide range of loads, speeds, and
demanding applications such as blowers, conveyors, pumps and mixers.
MPC
®
SYNCHRONOUS
SPROCKETS
Direct drop-in for the most popular tooth profile
martinsprocket.com • 817 258 3000
MartinSprockett_PTGuide4-16.indd 36 4/29/16 10:11 AM

CHAIN, ROLLER & SPROCKET
A1 chain (sometimes called B1 one-hole chain) has links
with one hole and a bent attachment. A2 is similar
but always double pitch with two attachment holes per link.
K1 (B2 one-hole) and K2 (B2 two-hole) chains
both have bent attachments on both sides.
D1 (E1) and D3 (E2) chains have extended pins.
Single-pitch WA1 (WCB1 one hole) chain and wide-contour
WA2 (WCB1 two holes) chain both have bent attachments
on one side and one or two holes per link.
WSK1 (WCS2 one-hole or WM1) and WSK2
(WCS2 two holes or WM2) is wide-contour chain
with straight attachments on both sides.
WK1 (WCB2 one-hole) and WK2
(WCB2 two holes) is wide-contour
chain with bent attachments.
SK1 chain (sometimes called S2 one-hole or M1 chain) has straight attachments
on both sides. SK2 (S2 two holes or M2) is the same but with two holes per link.
SA1 (S1 one-hole or M35) chain and SA2 (S1 two holes or M35-2) chain
both have straight attachments on one side, but the latter has two holes per link.
Power-transmission and conveyor chain attachment options
Roller-chain sprockets come in myriad versions,
but most are shaft-ready designs. The sprocket
here is from the Power Transmission Solutions
division of Regal-Beloit America.
also attract less dust and particulates than regular chains. Such
roller chains are useful where oil contamination is a concern,
including paper-product or wood-processing industries.
SPECIALTY COATINGS AND STAINLESS STEEL CAN DELAY
OR PREVENT CORROSION
Nickel-plated chains offer another alternative for chain coatings,
providing some protection for mildly corrosive environments.
Stainless-steel chains offer superior corrosion resistance; however,
designers must be aware that regular stainless steels cannot be
hardened in the same manner as carbon steel. Therefore, the load
carrying capacity of stainless steel is lower than carbon steel.
Proper chain maintenance requires periodic inspection. All
chains must be checked for damage, wear and chemical attack
on a regular basis.
Another issue is wear elongation. Eventually
roller chains wear so much that they necessitate
replacement—typically at 1.5 to 2% (12.180
in./ft to 12.240 in./ft) elongation.
Chains may work until they reach
3% elongation, but are at
increased risk for suboptimal
performance.

PowerTransmission
REFERENCEGUIDE
COMPRESSION SPRINGS
THE BASICS OF
When hit by an object, oil inside this Zimmer shock
absorber floods a spiraling channel from its fat opening
to its narrow end. Sold by Intercon Automation Parts, the
shock absorber relies on compression springs to return to
its extended position after each cycle.
ENGINEERS incorporate compression
springs in designs that need
linear compressive forces and mechanical energy storage—
designs such as pneumatic cylinders and push-button
controls, for example. The most conventional compression
spring is a round metallic wire coiled into a helical form.
The most common compression spring, the straight
metal coil spring, bends at the same diameter for its entire
length, so has a cylindrical shape. Cone-shaped metal
springs are distinct in that diameter changes gradually from
a large end to a small end; in other words, they bend at a
tighter radius at one end. Cone-shaped springs generally
go into applications that need low solid height (the total
height when compressed) and higher resistance to surging.
Whether cylindrical or cone shaped, helical compression
springs often go over a rod or fit inside a hole that controls
the spring’s movement. Other configuration types include
hourglass (concave), barrel (convex), and magazine (in
which the wire coils into a rectangular helix).
Most compression springs have squared and ground
ends. Ground ends provide flat planes and stability under
load travel. Squareness is a characteristic that influences
how the axis force produced by the spring can be
transferred to adjacent parts.
Although open ends may be suitable in some
applications, closed ends afford a greater degree of
squareness. Squared and ground end compression springs
are useful for applications that specify high-duty springs;
unusually close tolerances on load or rate; minimized solid
height; accurate seating and uniform bearing pressures;
and minimized buckling.
The key physical dimensions and operating
characteristics of these springs include their outside
diameter (OD), inside diameter, wire diameter, free length,
solid height, and spring rate or stiffness.
• Free length is the overall length of a spring in the
unloaded position.
• Solid height is the length of a compression spring
under sufficient load to bring all coils into contact with
adjacent coils. 
• Spring rate is the change in load per unit deflection in
pounds per inch (lb/in.) or Newtons per millimeter (N/
mm).
The dimensions, along with the load and deflection
requirements, determine the mechanical stresses in the
spring.
When the design loads a compression spring, the
coiled wire is stressed in torsion and the stress is greatest at
the wire surface. As the spring is deflected, the load varies,
causing a range of operating stress. Stress and stress range
affect the life of the spring. The higher the stress range, the
lower the maximum stress must be to obtain comparable
CompressionSprings_PTGuide_V2.indd 38 4/29/16 11:21 AM

RotorClip_PTGuide4-16.indd 39 4/29/16 10:12 AM

PowerTransmission
REFERENCEGUIDE
life. Relatively high stresses may be used when the stress range
is low or if the spring is subjected to static loads only. The stress
at solid height must be low enough to avoid permanent damage
because springs are often compressed solid during installation.
HOW TO SELECT COMPRESSION SPRINGS
Here are the most important factors to consider when selecting
helical compression springs.
The OD of a spring expands under compression. Be sure
to consider this if the spring goes into a tube or a bore during
assembly. Also remember that the OD of a spring is subject to
manufacturing tolerances, just as any mechanical part. If the
tolerance range is positive, the spring’s dimensions may be slighter
larger and can add to the overall assembly’s envelope size. Most
spring suppliers specify work-in-hole diameters for their springs
to factor in manufacturing tolerances and the OD’s expected
expansion. Look for this information to quickly select from stock
spring catalogs, or use this information to better communicate
product needs when ordering custom-made springs.
Consider loading or travel requirements on the compression
spring. The spring rate (also called the spring constant) is the
relationship of the force to compress a spring by a unit of length,
typically pounds per inch. So with a given load, the product designer
can calculate expected spring travel. The further the spring travels,
the more stress it endures. So at a critical point, stress can yield
the wire material … causing a phenomenon called spring set. After
spring set, the spring can’t expand back to its original unloaded
length. Even so, in some assemblies, such springs can still function.
Stress formulas and online calculators predict spring set.
Otherwise, a starting rule of thumb is to avoid solid height by at
least 20% (so that there’s always 20% of the spring’s total travel left
during the normal range of operation).
Compression spring-end types are standard or special. Standard
ends are either plain open or closed. Either can be ground or not
ground. The ends actually affect the spring rate. So, springs with
dissimilar ends that are otherwise identical (with the same total coils,
wire size, and OD) have different spring rates. Ground ends require
more manufacturing effort. However, combined with closed ends,
round ends improve the squareness of the loading force and reduce
spring-buckling tendencies.
Some manufacturers include closed and ground ends in
standard catalog stock design, while some don’t. Be sure to know
the difference. Special end examples include reduced coil for screw
mounting, offset legs to work as alignment pins, and enlarged coils
to snap into ring grooves.
Spring materials abound and include everything from carbon
steel to exotic alloys. Music wire is a high-carbon spring steel and is
the most widely used material. Stainless steel 302 has less strength
than music wire, but adds general corrosion resistance. Nickel alloys
make a lot of springs branded under various trademarks and are
chosen for extreme high or low operating temperatures, specific
corrosive environments, and non-magnetic qualities. Springs made
of phosphor bronze and beryllium copper are copper alloys for
good corrosion resistance and electrical conductivity.
This concave (hourglass-shaped)
compression spring can stay centered,
even in large-diameter bores.
Surging is when a spring builds compression-wave
motion when subject to vibrations close to its
natural frequency. This cone-shaped compression
spring resists surging. The larger outer coils
collapse before the smaller inner coils, so forces
on the spring also increase the spring rate for a
natural damping effect. Photo courtesy Lee Spring.
This compression spring has reduced ends.
This compression spring has
a barrel shape for lateral
stability.
CompressionSprings_PTGuide_V2.indd 40 4/29/16 11:21 AM

Pt guide 4 16

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