TATA MOTORS_BREAKDOWN ANALYSIS OF SHOT BLASTING SYSTEM
1. FAILURE ANALYSIS OF SHOT
BLAST SYSTEM
(FRAME FACTORY,TML JAMSHEDPUR)
AVISHEK GHOSH
JADAVPUR UNIVERSITY
KOLKATA
2. ACKNOWLEDGEMENT
We would like to deeply thank our project supervisor Mr Ashok Kumar for his
unconditional support, guidance and understanding, continuous support throughout
our work which will be infinitely profitable for the rest of our life.
We would like to thank Tata Motors Jamshedpur workers especially Mr Rajeev Ranjan
(Manager) for his support in the case study while pursuing my project.
We are indebted to our fellow students, staffs and friends for their continuous support
and the brainstorming discussions and I strongly believe that what we have leaned
from them during the study period is worthy to articulate for problem solving.
Our thanks also goes to MTC Department of Tata Motors especially to Mr Johnson
Mathews for providing every possible help during the course of our training period.
2
3. CONTENTS
3
SL. No. TOPIC Pg. No.
1 ACKNOWLEDGEMENT 1
2 INTRODUCTION TO TATA MOTORS 5
i)Major milestones in Tata Motors 6
3 INTRODUCTION TO FRAME FACTORY 8
4 PROCESSES INVOLVED IN PTCED 9
5 PAINT PRE TREATMENT 10
6 WHAT IS SHOT BLASTING 11
7 MAJOR COMPONENTS OF SBM 12
i) Cabin 13
ii) Bucket elevator 14
iii) Air separator 15
iv) Abrasive Hopper 16
v) Abrasive Gates 17
vi) Blast units 18
vii) Screw conveyer 19
viii) Roller conveyer 20
ix) Abrasive removal device 21
x) Specifications of abrasives 22
8 REPRESENTATIVE BREAKDOWN DATA ANALYSIS OF SBM FOR ONE MONTH 23
9 REPRESENTATIVE CUMULATIVE SBM BREAKDOWN DATA FOR ONE MONTH 24
10 BREAKDOWN DATA ANALYSIS OF PTCED (APR'15-MAR'16) 25
11 SBM BREAKDOWN DATA ANALYSIS (APR'15-MAR'16) 26
12 ANALYSIS OF SBM BREAKDOWN DATA (APR'15-MAR'16) 27
13 FISHBONE DIAGRAM OF SHOTS ON LM 28
14 ANALYSIS OF FISHBONE DIAGRAM OF SHOTS ON LM 29
4. 4
SL. No. TOPIC Pg. No.
15 SUGGESTIONS AND RECOMMENDATIONS 34
16 AIR AMPLIFIER 37
i)Working Principle 38
ii)Coanda Effect 39
iii)Amplifier to increase efficiency and intensity 40
iv)Maintaining the integrity of amplifier air 41
v)Performance parameters of Air amplifiers 42
vi)Determination of total output and air consumption of air amplifiers 44
17 IMPROVEMENT OVER AIR AMPLIFIER 45
i)Air jets 46
ii)Star profile air nozzles 47
18 FORCE DELIVERY COMPARISION FOR DIFFERENT AIR NOZZLES 48
19 APPLICABILITY IN PRESENT SCENARIO 49
20 REPRESENTATIVE CALCULATIONS 50
21 IMPLEMENTATION OF THE IDEA 53
22 FISHBONE DIAGRAM OF BLAST WHEEL BLADE WEAR 55
23 ANALYSIS OF FISHBONE DIAGRAM OF BLAST WHEEL BLADE WEAR 56
24 SUGGESTIONS AND RECOMMENDATIONS 61
25 WEAR REDUCTION 64
26 COMPONENT DESIGN 66
27 REPRESENTATIVE CALCULATIONS 68
28 POSSIBLE MODIFICATION 69
29 ADVANTAGES 71
30 MECHANICS OF CONTROL CAGE SHOT TRANSFER 72
31 DISCUSSIONS 74
32 REFERENCES 75
5. INTRODUCTION TO TATA MOTORS
Tata Engineering & Locomotives Company (TELCO) now TATA MOTORS is the automobile front-
runner of India. The company’s Head office is in Mumbai while its works operates at Jamshedpur,
Pantnagar, Lucknow, Ahmedabad, Sanand, Dharwad and Pune in India, as well as in Argentina,
South Africa and Thailand. Since first rolled out in 1954, Tata Motors has produced and sold over
4 million vehicles in India.
Tata Motors' principal subsidiaries purchased the British premium car maker Jaguar Land
Rover (the maker of Jaguar, Land Rover, and Range Rover cars) and the South Korean commercial
vehicle manufacturer Tata Daewoo. Tata Motors has a bus-manufacturing joint venture
with Marcopolo (Tata Marcopolo), a construction-equipment manufacturing joint venture
with Hitachi (Tata Hitachi Construction Machinery), and a joint venture with FiatChrysler which
manufactures automotive components and Fiat Chrysler and Tata branded vehicles.
The company is the world's fourth largest truck manufacturer, the world's second largest bus
manufacturer, Tata Motors in 2005 was ranked among the top 10 corporations in India with an
annual revenue exceeding INR 320 billion. In 2010, Tata Motors surpassed Reliance to win the
coveted title of 'India's most valuable brand' in an annual survey conducted by Brand Finance
and The Economic Times.
5
6. 6
The major milestones in TATA MOTORS
YEAR MILESTONES ACHIEVED
2000 • Axle division of Jamshedpur plant becomes HV Axle Ltd., a 100% subsidiary of Telco. Gear
Box division of Jamshedpur plant becomes HVTL, 100% subsidiary of Telco.
• Growth Division of Pune plant becomes Telco Automation Ltd., a100% subsidiary of Telco.
• 50,000 Tata Indica sold out in 12 months since commencement of deliveries.
2008 • Tata Motors unveils Tata Nano, the People’s Car, at the 9th Auto Expo in Delhi on January
10, 2008.
• Tata Motors acquires the Jaguar and Land Rover brands from the Ford Motor Company.
2009 • Tata Motors announces commercial launch of the Tata Nano; Tata Nano draws over 2.03
lakh bookings; first 100,000 owners of the Tata Nano chosen; delivers first Tata Nano in the
country in Mumbai.
• Tata Motors ushers new era in Indian auto industry with its new, world-standard truck
range.
• Jaguar Land Rover introduces its premium range of vehicles in India.
• Tata Motors acquires remaining 79 per cent shares in Hispano Carrocera, one of the largest
manufacturers of bus and coach cabins in Europe.
2010 • New plant for Tata Nano at Sanand inaugurated.
7. 7
The company has following Joint
Venture to improve the range and the
quality of products.
TATA CUMMINS LTD (TCL)
MERCEDES BENZ INDIA LTD. (MBIL)
TATA HOLSET LTD (THL) Among the
venture abroad are the Tata Precision
Industries (TPI), Singapore and Nita
Company Ltd., Bangladesh.
PRODUCTS AND SERVICES
The product range of TATA MOTOR is quite large to
account for all in this report. Just a small list of
vehicles is given here:
1. Medium and heavy vehicles:
a. Rigid truck: LPTA 713, LPT1109&1112, SE1613, etc
b. Tractor trailer: LPS3516, LPS4018, LPS4923
c. TIPPERS: SK1613, LPK1615, LPK2516&1618 etc.
d. World Trucks - PRIMA
2. Light trucks:
a. Rigid truck: SFC407, LPT407, LPT709 etc.
b. Tippers: SFC407, LPK407&709 etc.
3. Small vehicles: Super Ace, Ace EX, 207DI EX etc.
4. Buses:
a. Public transport: LP1109, LPO918, etc
b. Intercity transport: LPO1316&1318
c. Charter buses: SFC407,LP407
5. Tata Motors Defence Solutions
8. 8
INTRODUCTION TO FRAME FACTORY
Steel Rolls supplied by TATA Steel & SAIL
Coils are decoiled and cut by decoiler and then straightened
Sheets are piled by magnetic stacker
5000T press is used for punching , cutting & bending using separate dies and
stacked
C section frames are sent to Vehicle Factory I & II for manual inspection of defects
(Burrs in holes, Taper and height of flanges) which are rectified using hand and
spot grinding
9. PROCESSES INVOLVED IN PTCED
9
Long Member (LM) prewashed using Ridoline at 40ºc to remove grease,oil and dirt
LM sent to Shot Blasting Machine(SBM) using roller conveyers for removal of mill
scale
LM are subjected to Paint pre treatment
LM loaded on hangars using Robotic Arms
LM are finally sent to baking oven (Temp 170-220ºC, Time cycle – 36 min) and
sent to Assembly Line
10. PAINT PRE TREATMENT
DIP DEGREASING: The LM are dipped in a tank of Ridoline to further wash away the dirt which may have
accumulated on it’s surface during shot blasting.
RAW WATER RINSE
DEMINARALISED WATER (DM) RINSE (Conductivity < 50µs/cm)
NANO COATING: The LM are dipped in a tank of TEC TALIS for pre paint coating to increase corrosion life of
LM (Conductivity < 2500µs/cm, pH: 3.8-4.5)
DM WATER RINSE 2 (Conductivity < 100µs/cm)
DM WATER RINSE 3 (Conductivity < 50µs/cm)
Cathodic Electrode Deposition(CED) BATH: Painting of LM is done in this chamber and a conductivity of
1000-1700 µs/cm and a pH of 5.3-5.8 is maintained (NVM < 15%)
ULTRA FILTRATION 1 RINSE (Conductivity < 800-1500µs/cm, pH: 5.0-5.7, NVM < 1%)
ULTRA FILTRATION 1 RINSE (Conductivity < 800-1500µs/cm, pH: 5.0-5.7, NVM < 0.7%)
RECIRCULATED DM WATER RINSE (Conductivity < 100µs/cm, pH: 6.0-7.0)
10
11. WHAT IS SHOT BLASTING?
Shotblasting is a method used to clean, strengthen (peen) or polish metal. Shot
blasting is used in almost every industry that uses metal,
including aerospace, automotive, construction , foundry, shipbuilding rail, and
many others. There are two technologies used: wheelblasting or airblasting.
Wheelblasting
Wheelblasting directly converts electric motor energy into kinetic abrasive energy by
rotating a turbine wheel. The capacity of each wheel goes from approximately 60 kg per
minute up to 1200kg/min. With these large amounts of accelerated abrasive, wheelblast
machines are used where big parts or large areas of parts have to be derusted, descaled,
deburred, desanded or cleaned in some form.
Airblasting
Airblast machines can take the form of a blastroom or a blast cabinet, the blast media is
pneumatically accelerated by compressed air and projected by nozzles onto the component.
For special applications a media-water mix can be used, this is called wet blasting.
In both air and wet blasting the blast nozzles can be installed in fixed positions or can be
operated manually or by automatic nozzle manipulators or robots.
The blasting task determines the choice of the abrasive media, in most cases any type of
dry or free running abrasive media can be used.
11
13. CABIN
The machine’s blast cabin is made of manganese steel to prevent
wear. The interior wall opposite to blast units is also provided
with replaceable manganese covering plates.
Inside the cabin there is a V- shaped metal sheet with holes(to
catch rough impurities).through the holes and the space between
the sheet and the cabin wall the abrasive passes together with
small impurities, to the hopper under the cabin. The mixture is
transported from the cabin hopper to the longitudinal screw
conveyer and then the transverse screw conveyer, at last the
mixture will be transported to the bucket elevator.
Cabin has a interface connected to the dust collector, the
adjusted air pipe throttle valve controls de-dusting extraction
amount and creates minus pressure in the cabin to prevent dust
overflowing.
13
Blast
unit
Abrasive
collecting
hopper
Interface
to filter
14. BUCKET ELEVATOR
The elevator transports the mixture of abrasive and impurities to the air separator.
Bucket elevator belt: The elevator belt equipped with buckets is made of fabric reinforces rubber.
The buckets are made of wear resistant tempered cast iron. The belt is connected by means of
clamp and screws.
Belt drum, control of belt movement, drive: The elevator belt moves between two drums. The
upper drum is provided with tensioning system and elevator drive.
In order to prevent backward start of the bucket belt due to weight of filled buckets ,the motor is
provided with brakes for backward running.
14
15. AIR SEPARATOR
The separator separates the mixture of abrasive, sand
and dust by transporting this mixture by a system of
cascades.
While the mixture blows over the cascades, the sucked
air separates in counter flow the abrasive from
impurities and dust.
Air separator Flap: The flap separator balances the
non-uniform feed of mixture. It ensures the uniform
layer thickness of abrasive, impurities and dust,
Expansion Chamber, Throttle Valve: After passing the
cascades, the sucked air enters the expansion chamber.
The rough impurities and dust and too fine abrasives
are separated.
15
1.Air separator flap
2.Screen
3.Abrasive outlet
4.Abrasive distributor
5.Door
6.Abrasive inlet
OUTLET
5
16. ABRASIVE HOPPER
Only clean abrasive after separated from mixture
of air separator can fall into storage hopper. It is
installed above the blast units with two lever
switches. At the bottom of hopper there are four
interfaces connected to the abrasive valves.
There are two lever switches equipped on the
hopper, if the high lever switch inspects there are
no abrasives , control panel will show warning
“MISSING ABRASIVE” to inform the operators to
add abrasive. If the low lever switch insects there
are no abrasives ,blast machine will stop
automatically
16
1
2
4
3
17. ABRASIVE GATES
The abrasives flows through a
pneumatically operated abrasive
feed valve to the corresponding
blast wheel. The abrasive flow is
regulated by an end stop, which
can be adjusted by means of a
stop bolt.
17
Inlet tube
insertion
Pneumatic
cylinder
Proximity
switch
Stop Bolt
Indicator
lever
18. BLAST UNITS
The blast machine has 4 blast units installed. The abrasive is fed
through the feed spout casing to the centre of the blast wheel, to the
impeller, where the abrasive gains the radial acceleration, from the
impeller, the abrasive is led through the rectangular opening in the
control cage to the blades of the blast wheel.
18
Blast wheel
BLAST UNIT WITH MOTOR Control Cage
Accelerator
Notch
19. SCREW CONVEYER
There are two screw conveyers (longitudinal and
transversal) under shot blast cabin. Transversal
screw conveyer transports abrasive from
longitudinal screw conveyer to bucket elevator and
then into separator. At the end of the screw shaft is
equipped with driving motor.
There is another screw conveyer used to transport
abrasive from abrasive replenisher to bucket
elevator.
19
SCREW CONVEYER
20. ROLLER CONVEYER
The roller conveyer consists of 10 pieces
of rollers. Three of them which direct
installed on blast hot pot are made of
special wear resist material. It is chain
driven. The driving parts outside the
cabin and speed of roller can be adjusted
by frequency changer. Roller conveyer
can also rotate clockwise and
anticlockwise. Distance ring is used to
prevent workpieces deviating, encoder is
equipped on the shaft end of transport
roller near the entrance of blast cabin to
inspect position of workpieces.
20
ROLLER CONVEYER
21. ABRASIVE REMOVAL DEVICE
Abrasive removal device is used to remove abrasive from
workpieces coming from blast cabin, it is composed of
three system:
High pressure blower- to remove most of abrasive
Low pressure blower- to remove residual abrasive
Compressed air removal device- to further and fully
remove abrasive, using of compressed air removal system
depends on the real situation, pressure air supply done by
customer.
Inside the abrasive removal cabin, there are nozzles which
are manually adjustable according to the height of the
workpieces by means of a threaded bar. The angle of
nozzle can be manually adjustable to the range 10º-50º.
There are some rubber curtains inside the removal cabin
and a silencer to reduce noise on high pressure blower.
21
1.High pressure removal system
2.Low pressure removal system
3.Compressed air removal system
4.Silencer
5.Rubber curtains
6.Nozzle
22. SPECIFICATIONS OF ABRASIVES
Abrasive: For ordinary usage, the resilient
abrasives made of cast steel or grains of
steel wire are suitable. The granules of hard
cast are not recommended. It has shorter life
times and it causes high wear.
Operating mixture: The operating mixture
consists of rounded grains of various size.
The rough grains must remove the covering
layers. The medium sized grains clean the
surface. The fine sized grains make the final
cleaning and smooth the surface.
22
SS 230 SHOTS
23. REPRESENTATIVE BREAKDOWN DATA ANALYSIS OF
SBM FOR ONE MONTH (OCTOBER-2015)
23
21%
16%
15%13%
13%
12%
10%
BREAKDOWN TREND FOR OCT-2015
BUCKET ELEVETOR
OUT FEED P/C
LONGITUDINAL
CONVEYOR
CLEANING ROLLER
LM SLIP
BLAST WHEEL
PROBLEM
TIME IN
MINUTES
BUCKET ELEVETOR 215
OUT FEED P/C 160
LONGITUDINAL
CONVEYOR 150
CLEANING ROLLER 130
LM SLIP 130
BLAST WHEEL 120
SHOTS LEAKGE 105
24. REASON FOR DOWNTIME
DOWNTIME IN
MINUTES
SBM LEAKAGE 105
MANUALLY SHOTS CLEANING 0
OUT FEED P/C 160
SHOTS ON LM 30
CLEANING ROLLER 130
PREWASH CONVEYOR 25
IN FEED P/C 85
LONGITUDINAL CONVEYOR
COVER 150
BLAST WHEEL 120
BUCKET ELEVETOR 215
UNLOADING HOIST 20
OUT FEED ROLLER CONVEYOR
FAULT 30
LOADING SLAT CONVEYOR 15
TOTAL 1035
24
REPRESENTATIVE CUMULATIVE SBM BREAKDOWN
DATA FOR ONE MONTH (OCTOBER-2015)
0
50
100
150
200
250
BREAKDOWNTIMEINMINUTES
REASON
BREAKDOWN OF SBM OCT-2015
25. BREAKDOWN DATA ANALYSIS OF PTCED (APR’15-MAR’16)
25
0
20
40
60
80
100
120
0
500
1000
1500
2000
2500
CUMULATIVEPERCENTAGEDOWNTIME
DOWNTIMEINMINUTES
REASON FOR BREAKDOWN
BREAKDOWN DATA ANALYSIS OF PTCED (APR’15-MAR’16)
27. ANALYSIS OF THE SBM BREAKDOWN DATA (APR’15-MAR’16)
On analysing the data of SBM breakdown data
over a period of 1 year (APR’15-MAR’16), the
following problems pertaining to the SBM
breakdown were found to be occurring
frequently and consumed a significant of the
total downtime which was 11987 minutes.
SHOTS ON LM (Total downtime-1540 minutes)
BLAST WHEEL FAILURE (Total downtime-2254
minutes)
27
13%
19%
68% SHOTS ON LM
BLAST WHEEL
FAILURE
OTHER PROBLEMS
28. FISHBONE DIAGRAM FOR SHOTS ON LM
28
SHOTS
ON LM
MANENVIRONMENT METHOD
MATERIAL MACHINE
Checking and
cleaning of LM not
done by operator
Improper
nozzle
orientation
LM having less number of
holes and improper
orientation
Improper size of shots
and incompatible
material
Conditions
inside SBM is too
dusty due to
malfunctioning
dust collector
Faulty rubber
curtain Nozzle choked
due to dust
particles
Air blowers not
working properly
29. 29
ANALYSIS OF THE FISHBONE DIAGRAM
On analysing the data and going through the findings
the following points were highlighted:
1.Low abrasive warning ignored by the operator leading
to uneven firing resulting in residual shots on LM.
2.At times when LM is stuck inside the machine of if
there is a problem with the centring of the LM SBM has
to be tuned to manual mode during which the automatic
nozzle is dysfunctional during which the LM is to be
thoroughly cleaned manually because after switching to
automatic mode the conveyer and the nozzle do not
start simultaneously which leads to some uncleaned
patches on LM.
MAN
Checking and cleaning of LM
not done by operator
Nozzle cleaned
by wire
30. 30
METHOD
Improper nozzle
orientation
For effective removal of the
shots on LM the nozzle angle
needs to be set at an angle of
50-55º failing to do so will lead
to residual shots on LM.
Nozzle not
inclined properly
31. 31
MACHINE
Nozzle choked due to dust
particles
Air blowers not
working properly
Despite having a dehumidifier installed in the compressor plant water droplets still come along with
the compressed air and due to the absence of any device to check the water content at the outlet of
the nozzle the dust particles adhere to the nozzle outlet during the period when the nozzle is idle i.e.,
air is not coming out of the nozzle because it is automatically controlled by a sensor which works
during the presence of LM.
Air Knife ioniser for dust removal
32. 32
MATERIAL
LM having less number of holes and
improper orientation
Improper size of shots and
incompatible material
Faulty rubber
curtain
Some LM like LPT 2518/62, LPT 1613/62,
LPT 3718/62 have comparatively lesser
number of holes due to which sometimes
the shots could not be completely
removed. Other problems include worn
out rubber curtains and problems in
centring of LM or due to bent LM due to
which the LM gets struck on the roller
conveyer leading to manual switching of
the machine which again leads to
manual cleaning.
Patches having less
holes
33. 33
ENVIRONMENT
Conditions inside SBM is too dusty
due to leakage of shots
A malfunctioning dust collector unit or a leaking blast unit may lead to a very dusty condition
inside the LM which may leading to blocking of the nozzle. The blast machine unit needs to be
cleaned failing, to do so may lead to dust accumulating on the nozzle.
34. SUGGESTIONS AND RECOMMENDATIONS
34
A Regulator, Filter (RF) Unit has been fitted to
limit the supply of compressed air to a pressure
of 5-5.2 bar from the main header pipe which
feeds to three pipes which are respectively 2 in.
, 1 in. and 1.5 in. in diameter. The innermost 2
in. pipe presently operates by bleeding out the
air at a pressure of around 4.8-5 bar by a series
of holes drilled on the pipe itself proceeding
further towards the exit of the machine comes
a deioniser air knife with a 1 in. pipe which only
removes minute dust particles using ionised air
and at last a 1.5 in. pipe does the final cleaning. RF UNIT 1.5 in. drilled pipe
The following accessories have already been added to the machine to eliminate the problem of
shots coming on LM :
Rubber curtains are provided which somewhat
remove the residual shots on the LM.
35. The innermost 2 in. pipe has nine holes (3 for each LM) drilled in it each having a diameter of
6mm providing a blast of air at a velocity of 35-40 m/sec.
35
Air Knife with ioniser to remove minute dust Inner 2 in. pipe for blowing off shots
36. 36
The table below compiles the losses due to the leakage of air from the open pipes with drilled
holes in it:
SIZE OF HOLE (mm) AIR LOSS (SCFM)
POWER REQUIRED
(kW)
ANNUAL COST
(INR)
0.75 1 0.2 6745
1.5 4 0.8 26890
3 17 3 101180
6 70 12 404750
10 150 25 843150
12 270 45 1517670
This shows that although the present systems in the machine cleans the shots but the
effectiveness is low primarily due to the
1)Air loss
2)Lack velocity and volume regulation of the air flow.
Therefore an adjustable device must be incorporated to deliver a high velocity, high volume flow
as per requirement consuming the least amount of compressed air.
37. 37
AIR AMPLIFIER
WHAT ARE AIR AMPLIFIERS?
A simple, low cost way to move air, smoke, fumes, and light materials. Air
Amplifiers utilize the Coanda effect, a basic principle of fluidics, to create air motion
in their surroundings. Using a small amount of compressed air as their power
source, Air Amplifiers pull in large volumes of surrounding air to produce high
volume, high velocity outlet flows. Quiet, efficient Air
Amplifiers will create output flows u p to 25 times their consumption rate.
Air Amplifiers have no moving parts, assuring maintenance free operation. No
electricity is required. Flow, vacuum and velocity are easy to control. Outlet flows
are easily increased by opening the air gap. Supply air pressure can be regulated to
decrease outlet flow. Both the vacuum and discharge ends of the Air Amplifier can
be ducted, making them ideal for drawing fresh air from another location, or
moving smoke and fumes away. Cycle time is dramatically reduced when aluminum
castings are cooled with the high volume airflow of two Air Amplifiers.
.
38. WORKING PRINCIPLE:
Compressed air flows through the inlet (1 ) into an
annular chamber (2). It is then throttled through a
small ring nozzle (3) at high velocity. This primary
airstream adheres to the Coanda profile (4), which
directs it toward the outlet. A low pressure area is
created at the center (5) inducing a high volume
flow of surrounding air into the primary airstream.
The combined flow of primary and surrounding air
exhausts from the Air Amplifier in a high volume,
high velocity flow.
38
39. THE COANDA EFFECT:
Coanda Effect: A moving stream of fluid in contact with a curved surface
will tend to follow the curvature of the surface rather than continue
traveling in a straight line.
DEMONSTRATION OF THE COANDA EFFECT:
To perform a simple demonstration of this effect, grab a spoon and find a
sink. You can easily demonstrate the Coanda effect for yourself. Conveniently,
these are often found together in the kitchen, no need for highly technical
lab. Get a small stream of water coming down from the sink, and then place
the bottom of the spoon next to the stream. Dangle the spoon next to the
stream coming from the tap.
What is unusual about the Coanda effect is the fact that the fluid or gas flow
is pulled so strongly by a curved surface. With a tap, the water will be
projected out at a remarkable distance. The degree to which the water and
the curved surface remain attached goes beyond the expected. A concave
curve will naturally push the flow, but the fact that a convex one would react
so strongly to fluid or gas is unusual.
39
40. AIR AMPLIFIERS TO INCREASE INTENSITY AND
EFFICIENCY
A variable air amplifier is another option when using compressed air. Air amplifiers produce a
constant, high velocity air stream for very targeted drying and blow-off applications. Efficiency is
maximized because additional free air is pulled through the unit along with the compressed air.
Variable air amplifiers typically provide coverage in the ¾ to 4” (19.1 to 101.6 mm) range at a
distance of 6” (152.4 mm). Commonly used for spot drying, blow-off and exhaust operations,
variable air amplifiers are ideally suited to robotic applications as well. Benefits of using variable
air amplifiers include:
Extremely efficient use of compressed air – up to 90% less than open pipes and 60% less than air
nozzles.
Delivers higher volumes of air and operates at higher pressures than air nozzles for fast drying and
blow-off.
Low noise.
40
41. MAINTAINING THE INTEGRITY OF THE AMPLIFIED AIR
Some air amplifiers feature a protruding leading edge design
that directs the airflow out of the knife in a straight stream,
producing an air stream that retains its integrity better than
other air amplifier. This design also takes advantage of the
Coanda effect and air entrainment to economically produce a
uniform and constant air stream. The Coanda effect induces the
supplied air to attach itself to the surface of the air amplifier and
helps maintain the integrity of the air stream further
downstream. This effect also creates a condition conducive to
entraining ambient air to increase the total volume of air.
Another advantage of the leading edge design is that it provides
a visual guide for positioning the air stream, pointing out the
direction of the flow. This allows easy positioning of the
amplifier to ensure maximum target coverage.
41
42. PERFORMANCE PARAMETERS OF AIR AMPLIFIERS
42
*Data provided by Spraying Systems Co. and is based on AA727 and AA707 WindJet® air nozzles. Assumes a 16 hour work day,
5 days a week
Open Pipe Equivalent impact Using
Air Amplifiers
Air Consumption
reduction %Size in.
(mm)
Air Consumption SCFM
(Nl/min)
5/32 (4) 19 (538) 1 25
¼ (6) 41 (1161) 2 28
5/16 (8) 94 (2662) 4 33
½ (12) 177 (5012) 7 35
5/8 (16) 309 (8750) 12 36
The following tables will represent the significant amount of saving of compressed air consumption as well as
show the amount of amplification that can be provided which will lead high velocity blast of air.
43. 43
Model Air Consumption Amplification Air Vol. at
Outlet
Air Vol. at 6”
(125mm)
Sound Level
SCFM SLPM Ratio SCFM SLPM SCFM SLPM dBA
120020 6.1 173 12 73 2066 219 6198 69
120021 8.1 229 18 146 4132 436 12339 72
120022 15.5 439 22 341 9650 1023 28951 72
120024 29.9 826 25 730 20659 2190 61977 73
120028 120 3396 25 3000 84900 9000 254700 88
Super Air Amplifier Performance at 80 PSIG (5.5 BAR)
44. DETERMINATION OF TOTAL OUTPUT FLOW AND AIR
CONSUMPTION OF AIR AMPLIFIERS
Total Airflow:
From the performance curves (above), determine total output flow for any Super Air Amplifier at
any pressure.
Example: A Model 120021 at 60 PSIG (4.1 BAR) supply air pressure has a total output flow of 120
SCFM (3398 SLPM).
Air Consumption:
Divide the total output flow by the amplification ratio (shown in the chart above) to determine air
consumption for any Super Air Amplifier
at any air pressure.
In the example above, the Model 120021 at 60 PSIG (4.1 BAR) supply air pressure has a total output
flow of 120 SCFM (3398 SLPM).
Dividing this total output flow by its amplification ratio of 18 gives an air consumption of 6.7 SCFM
(189 SLPM)
44
45. IMPROVEMENT OVER AIR AMPLIFIERS
One fundamental problem of air amplifiers is the drop in pressure while ensuring a high velocity,
high volume flow although not a problem but by maintaining the exact same performance
characteristics the pressure drop can be appreciably reduced by using accessories such as:
1) Air Jets
2) Star profile Air nozzles
These can provide a greater amount of force by using the amplified air and work on the principle
similar to that of air amplifiers.
45
46. AIR JETS
46
Air Jets are larger than nozzles and used when a wider area needs to
be hit with the amplified air. They are significantly more efficient than
nozzles although often use as much compressed air. Their best use is to
replace pairs of nozzles that are used for part ejection or for blow-off
applications that require greater force than that provided by air knives
or air movers. Nozzles are for point use while air jets can fan out
somewhat for better continuous blow-off when a row of them are
made. Air jets are all made adjustable with a lock ring to assure the
security of any gap setting.
Air Jets pull large volumes of surrounding "free" air through
the jet to create a directed airflow. The two styles include
the High Velocity Air Jet with high thrust for chip removal,
part ejection and drying; and the Adjustable Air Jet where
the airflow can be adjusted from a "blast" to a "breeze".
47. STAR PROFILE AIR NOZZLES
The air amplifying nozzle has the best force/air
consumption ratio known. Ideal when higher force
required in blow off applications.
It provides a high thrust, concentrated stream of
high velocity airflow for blow off, cooling, drying
and cleaning applications. The sound level is
extremely low and air consumption is minimal. The
compressed air is ejected through holes located in
recessed grooves that can not be blocked or dead
ended.
47
A) Incoming Air B) Amplified Air
C) Entrained ambient Air
48. FORCE DELIVERY COMPARISON FOR
DIFFERENT AIR NOZZLES
48
Force at 12" ( 305mm) from target
All sound levels measured at 3' ( 914mm)
All measurements taken at 80 PSIG ( 5. 5 BAR)
INLET (FNPT) AIR CONSUMPTION
AT 80 PSIG (5.5
BAR)
FORCE SOUND LEVEL (dBA)
SCFM SCLM Lbs GRAMS
1/8 17.5 495 1 462 82
1/4 32 906 1.8 792 87
3/8 35 991 1.9 850 82
1/2 60 1699 3.3 1497 87
3/4 91 2577 4.5 2041 96
1/2 98 2773 5.7 2585 85
1 168 4754 9.8 4445 89
49. APPLICABILITY IN THE PRESENT SCENARIO
After comparing performance, force delivery and air consumption data across a wide range of
manufacturers we can easily conclude that the above mentioned solution is one of the most efficient
and effective solution which can be easily incorporated into the present system with minimal cost.
But if there is any need for such modifications can be predicted by some calculations based on
assumptions listed below:
1. All of the supplied shots are completely spherical.
2. The material of the shots are homogenous and isotropic.
3. The shots occupy 50 % of the total volume of the long member after shot blasting is completed.
4. A C-Section of uniform section is considered.
49
50. 50
The shots supplied are of the following specifications SS 170 (Dia 0.4-0.7 mm) & SS 230 (Dia.
0.8-1 mm). Considering SS 230 shots of dia 1mm.
Density of stainless steel, ρ= 7.8g/cm3
Volume of shots =
4
3
Πr3 =
4
3
Π(0.5)3 =4.18x10-3 cm3
Mass of shots = ρ×
4
3
Πr3 = 7.8g/cm3×4.18x10-3 cm3 = 0.0326 gms.
REPRESENTATIVE CALCULATIONS
Representative C-Section
as per given dimensions
Considering a LM with uniform C-
Section having the following
dimensions
Length = 600cm
Breadth = 28.5 cm
Flange height = 6.5 cm
51. 51
Volume of the LM= 600×28.5×6.5 cm3 =111150 cm3
Considering half of the total volume effectively filled with shots,
Volume occupied = 0.5×111150 = 55575 cm3
Total no. of shots over the entire length of the LM =
55575 cm3
4.18x10−3 cm3 = 13.29x106
Total weight of the shots = 13.29x106×0.0326 =433430 gms =433.43 kgs.
Considering a length of 1 ft of the C- section,
Volume of LM= 30.48×28.5×6.5 cm3 =5646.42 cm3
Considering half of the total volume effectively filled with shots,
Volume occupied = 0.5×5646.42 = 2823.21 cm3
Total no. of shots over the entire length of the LM =
2823.21 cm3
4.18x10−3 cm3 = 679.41x103
Total weight of the shots = 679.41x103×0.0326 =22.15 kgs
52. In order to blow off the weight of shots according to the above calculations three air
nozzles (Star type or Air jet type) per LM of a force delivery capacity of 6804 gms can be
used which will give a combined capacity of 20412 gms which is enough to blow the
residual shots eliminating the need of any further pipes or manual cleaning.
DISCUSSION:
Since a C-Section without the presence of any holes is considered the weight of the shots
is overestimated .
A part of the shots falls off from the LM and the nozzle does not have to bear the whole
load as estimated.
There is gap between the packing of shots in real life but in the analysis we have
considered solid section leading to overestimation of the total load.
52
53. IMPLEMENTATION OF THE IDEA
Presently pipes approximately of total length 1.5 meters with 9 holes (3 for each LM) are being used.
Each holes are 6 mm in diameter and the area covered by the blast of air from each nozzle is not
presently determined. Using EXAIR SUPER AIR NOZZLE of 6 FNPT (Catalogue available from
manufacturer website on request) the width of the effective blast air is shown below as per various
models available:
53
Super Air Amplifier Airflow Pattern
MODEL # A B C D
120020 inch 1.25 2.2 4.4 6
mm 32 56 104 152
120021 inch 2 2.9 4.7 6.5
mm 51 74 119 165
120022 inch 2.75 3.55 5.15 6.75
Mm 70 90 131 171
54. 54
The figure shows the width of the blast at different distances of the nozzle from the workpiece is
shown presently the workpieces are placed at 6” from the opening and this nozzle provides a blast
of 152 mm. The maximum width of a LM is 285 mm so two super air nozzles placed at a distance of
160 mm can be used to clean out all of the shots.
55. FISHBONE DIAGRAM FOR BLAST WHEEL
BLADE WEAR
55
BLAST WHEEL
BLADE WEAR
MANENVIRONMENT METHOD
MATERIAL MACHINE
Throttle valve not set at
correct opening
The compressed air supply
valve to pneumatic cylinder
not opened
Blade wear
not checked
as specified
Improper material of shots
and blast wheel blade
Humid conditions
leading to
coalescing of
shots.
V belt broken
leading to
improper loading Puncturing of
compressed air
pipe to pneumatic
cylinder
Throttle valve
broken or worn
56. 56
ANALYSIS OF THE FISHBONE DIAGRAM
On analysing the data and going through the findings
the following points were highlighted:
MAN
Throttle valve not set at correct opening
The compressed air supply valve
to pneumatic cylinder not
opened
1. If the throttle valve opening is not at a correct opening
angle initially during starting the machine then improper
amount of blasting media will be fired leading to uneven
wearing.
2. The valve supplying compressed air to the pneumatic
cylinder might not be opened by the workers leading to
absence of blasting media on the wheels.
57. 1. The blades are to be inspected mainly by visual
inspection and this is to be done manually and
the thickness reduction is to be determined
manually and failure to abide by guidelines
may lead to excessive wear and breaking of
blast wheel.
2. The V-Belt driving the impeller must be checked
, failing to do so will lead to vibrations and
wear
57
METHOD
Blade wear not checked
as specified
Correctly operating
wheel
A Misbalanced worn-
out wheel
58. 1. If the throttle valve is worn
or broken then excessive
amount of shots will be
supplied to the wheels
leading to the excessive
wear of the blades.
2. A worn out control cage or
the accelerator can also
damage the wheels.
58
MACHINE
V belt broken leading to
improper loading Puncturing of compressed
air pipe to pneumatic
cylinder
Throttle valve
broken or worn
WORN OUT BLADE NEW BLADE
59. The material being used presently for the blast
wheel blade is steel strengthened and hardened
with Manganese and shots are made of Stainless
Steel. If the blades are not properly alloyed and
improper abrasives are used pre mature wearing
may occur.
59
MATERIAL
Improper material of shots
and blast wheel blade
Schematic representation of hot-spot
60. Presence of humidity on shots may lead
them to coalesce together to form rock hard
ball like structure which if permitted to enter
the blast wheel unit may severely damage
the blades. A wire mesh has been
incorporated at the entry of the air
separator to prevent any such particles
entering into the unit.
60
ENVIRONMENT
Humid conditions leading to
coalescing of shots.
Wire mesh to prevent entry of coalesced shots to blast unit
61. “A centrifugal blast machine is probably the most
self-destructive of all modern mechanical
machines.” Enormous numbers of hard particles
are pressed against unlubricated rotating surfaces,
hence generating fiendish wear problems.
These mechanisms are called “Adhesive wear” and
“Abrasive wear”. For both mechanisms we have
either “two body” or “three body” situations.
These alternatives are illustrated in fig.1.
61
SUGGESTIONS AND RECOMMENDATIONS
62. ADHESIVE WEAR: As the name implies, adhesive
wear occurs when two surfaces physically adhere
to one another. This type of wear is often called
“galling.” Adhesion takes the form of micro-welds
formed between the two surfaces. Two nascent
metal surfaces pressed together will micro-weld to
one another at points of contact. “Nascent”
means newborn and implies a surface completely
free from oxide protection. Relative movement of
the two surfaces breaks apart the tiny points of
adhesion, causing wear.
62
63. ABRASIVE WEAR: Abrasive wear mainly occurs when a
harder material rubs against a softer material. Emery
paper contains particles that are harder than metals—
hence its usefulness for rust removal. That is an example
of two-body wear. Metallurgists use diamond-
impregnated polishing wheels to produce ultrasmooth
surfaces. That is three-body wear. Both two- and three-
body wear occurs in shot blasting situations. Abrasive
wear characteristically occurs when an asperity on the
harder surface strikes an asperity of the softer surface.
This is illustrated in fig.4. As an asperity on the harder
surface strikes an asperity on the softer surface
something has to give! In this case it is the asperity on
the softer surface which is work-hardened until it
fractures.
63
64. WEAR REDUCTION
Material selection and component design are the two major factors in wear reduction.
Material Selection: Material selection has benefited from the enormous advances made in developing
wear-resistant materials. The choice is now so large that it is easy to over-simplify selection. Consider, for
example, using just hardness as a wear resistance criterion. The assumption then is that the higher the
hardness the greater will be the wear resistance. This assumption is only valid when comparing materials
that have similar microstructures. Fig.5 illustrates schematically two types of wear-resistant alloys
having the same measured hardness but with quite different microstructures. Each grain of the single-
phase material has a similar hardness.
64
65. Component Design: All components that are in a
wear environment must be designed to withstand
wear to a specified extent. Commercial
considerations are of paramount importance for both
supplier and user. A balance has to be obtained
between cost and useful life. If, for example, it was
possible to design a component that had an infinite
life then suppliers would soon go out of business. On
the other hand if a component had to be replaced
frequently then users would be prepared to pay a
premium. A universal example is that of light bulbs.
The classic shot peening design problem is that of
blast wheels whose performance is adversely affected
by substantial wear.
65
66. COMPONENT DESIGN
With a blast-wheel we have both high
pressures and high speeds. Both accelerator
and throwing blades normally rotate at the
same angular velocity.
Two-body wear of a blast wheel will occur
when shot particles are moving along the
blades—shot as one body and the blade as
the second body. Another example is when
shot particles strike a component’s surface
to produce a dent. Three-body wear will
occur, for example, when shot particles are
trapped between the accelerator and the
control cage as infig.9.
66
67. Wear rate increases with both force and sliding speed. One way to reduce the wear rate would be to
reduce the diameter of the accelerator—hence reducing both sliding speed and centrifugal force.
That approach, however, induces several problems. One is that the throwing blade length must then
be a large fraction of the wheel radius. Long blades generate a relatively-large spread angle for the
thrown shot stream. Another problem is that exiting the shot through the control cage opening
becomes more difficult because the centrifugal force on the shot—pushing it out of the control
cage—is lower and also because the outlet slot has to occupy a greater angular proportion of the
control cage. The maximum number of throwing blades that can be accommodated without
interfering with the shot stream also decreases with increase in blade length. Wear reduction might,
however, be effected by component design modification. Such a modification would need to reduce
the sliding speed without reducing the accelerator diameter. A modification is presented here which
could offer substantial advantages in terms of wear reduction, increased shot stream concentration
and reduction of component number.
67
68. REPRESENTATIVE CALCULATIONS
If, for example, the blade tips sweep a
circumference of 1.0 m at 60 r.p.s. then the
thrown shot will have a velocity of at least
60ms-1. If, for the same example, the
accelerator has a circumference of ⅓m (radius
53mm) then shot is scouring the control cage
at a sliding speed of 20ms-1. This shot is also
being pressed into the accelerator/ control
cage interface with an acceleration of some
770 times that of gravity!
That figure comes from dividing the square of
the circumferential velocity by the radius of
rotation [(20ms-1)2/0.053m = 7540m.s-2 =
770g, where g = 9.8m.s-2].
68
69. POSSIBLE MODIFICATION
Wear reduction might, however, be effected by component design modification. Such a modification
would need to reduce the sliding speed without reducing the accelerator diameter. A modification is
presented here which could offer substantial advantages in terms of wear reduction, increased shot
stream concentration and reduction of component number.
This modification involves:
(a) Not having a separate, static, control cage. Instead every throwing blade has an outlet slot
(b) Having one fewer slot in the accelerator than there are blade outlet slots (and hence blades)
(c) Rotating the accelerator at a specified faster rate than the throwing wheel. This rate synchronizes
the accelerator and outlet slots - so that they always coincide at only one point on the circumference
69
70. The accelerator’s angular rotation rate has to be
faster than that of the throwing blade wheel by
the ratio of the number of throwing blades to the
number of accelerator slots. In fig.10 there are
eight throwing blades and seven accelerator
slots. Hence the accelerator rotation rate has to
be 8/7 times that of the throwing blade wheel.
The reason for the matched, but different,
rotation speeds is that an accelerator slot and a
blade slot must only coincide at the same, fixed,
angular position – such as P in fig.10.
Coincidence is achieved when the product of
angular rotation speed and number of slots is the
same for both accelerator and blade wheel.
70
71. ADVANTAGES
There are several advantages that can be attributed to the suggested system:
The most important advantage is that the relative surface speeds between the moving parts are
greatly reduced for given diameters of accelerator and blade wheel.
For example, a relative surface speed of 35 m.s-1 for an eight bladed wheel would be reduced to 5
m.s-1. This would lead to reduced shot breakage and wear, together with reduced accelerator cage
and blade wheel wear.
A second advantage is the number of basic components is reduced from three to two—from
accelerator, control cage and blade wheel to simply accelerator and blade wheel. That means that
there are now only two major sources of wear and breakage.
With the reduced overall wear it is possible to increase the wheel blade and accelerator diameters
so as to accommodate a greater number of blades on a given wheel. That, in turn, leads to a more
concentrated thrown shot stream.
71
72. MECHANICS OF CONTROL CAGE SHOT TRANSFER
Conventional blast wheels have two stages of shot transfer:
(i) Shot has to emerge from a slot and cross over the static slot
(ii) To be collected by a moving blade. With the suggested
system, shot transfers directly onto a moving blade.
The differences in the respective movements are illustrated. The
exit slot for a conventional wheel has to be several times the
width of the cage slot. That is to allow time for the surface
layers of the shot in the accelerator slot to be transferred to the
exit slot. Once in the exit slot the shot is travelling across a “no
man’s land” until it crosses into the path of the moving blade.
The forward face of the exit slot may be sharply angled to
bounce shot into the path of the blade. Once shot is collected by
the blade it is propelled outwards by centrifugal force until it
reaches the blade tip.
72
73. With the suggested modification, shot is
transferred directly to the root of a moving blade
as soon as the accelerator slot starts to coincide
with an exit slot. It is important to note that the
relative speed of the slots is much less than that
for a conventional wheel. For an “8/7” modified
wheel, the relative motion is seven times slower
than that for a conventional wheel. That means
that the exit slot does not need to be much wider
than the accelerator slot – there is seven times as
much time for exiting of shot per degree of wheel
rotation. Shot transfer, being direct to the blade,
is much more orderly than that with a
conventional wheel.
73
74. DISCUSSION
The suggested modification of blast wheel design is purely an academic exercise designed to
illustrate the types of thought processes and calculations that might be encountered in
product re-design.
Improvement of wear performance is a constant factor for equipment manufacturers. A
balance has to be struck between cost and longevity.
74
