DESIGN OF BUCKET ELEVATOR WITH AUTO BELT TENSIONER UNIT

A
Project Report
ON
“IMPROVED DESIGN OF AUTO BELT TENSIONER UNIT FOR
BUCKET ELEVATOR”
(Submitted to fulfill the partial requirements of the AMIE section B
Examination in Mechanical Engineering Branch)
Under The Guidance Of
Dr. S. Haranath, FIE
Principal B M S College Of Engg(Retd), Bengaluru
F-010043-5
Prepared By
SOMASHEKHAR MUDALAGI
ST556135-9
(An ISO 9001: 2008 Certified Organization)
December 2016

CERTIFICATE OF ORIGINALITY
This is to certify that the project work “Improved Design of Auto Belt
Tensioner Unit for Bucket Elevator” submitted by Somashekhar Mudalagi
ST556135-9 for AMIE degree of The Institution of Engineers(India), Kolkata.
embodies the work done by him under my supervision.
Approved by
Project guide
F-010043-5
The institution of Engineers(India)
Kolkata

CERTIFICATE
This is to certify that the project work titled “Improved Design of Auto
Belt Tensioner Unit for Bucket Elevator” is a bonafide work carried out by
Somashekhar Mudalagi, a student for examination of The Institution of
Engineers(India), Kolkata. Under my technical guidance.
Approved by
Project guide
F-010043-5
Kolkata

ACKNOWLEDGEMENTS
I express my sincere gratitude to my project guide of Dr. S Haranath,
who helped me to bring out this project in good manner with his
precious suggestion and rich experience.
I am grateful to many people who have been instrumental in making my
dreams come true.
Somashekhar Mudalagi
ST556135-9

DECLARATION
I Somashekhar Mudalagi, declare that the work entitled “Improved
Design of Auto Belt Tensioner Unit for Bucket Elevator” has been
successfully completed under the guidance of Dr. S. Haranath, This dissertation
work is submitted to The Institution of Engineers (India), Kolkata. for partial
fulfillment of the requirements for the award of AMIE in Mechanical
Engineering during the year December 2016. Further, the work carried by me
has not been submitted previously by anyone to any university.
ST556135-9
Approved by
Project guide
F-010043-5
Kolkata

APPROVAL OF SYNOPSIS
This is to certify that the synopsis for the project work titled “Improved
Design of Auto Belt Tensioner Unit for Bucket Elevator” is approved by me
and project work is an original one.
ST556135-9
Approved by
Project guide
F-010043-5
Kolkata

AMIE(I) Project Report
The Institution of Engineers (India)
SYNOPSIS
TITLE OF THE PROJECT:
“IMPROVED DESIGN OF AUTO BELT TENSIONER UNIT FOR BUCKET
ELEVATOR”
OBJECTIVE:
To provide auto belt tensioner unit to existing bucket elevator for
handling of grains in rice mill, which should be reliable, safe and of less
maintenance cost.
RATIONALE FOR THE STUDY:
1. To operate the equipment safely for the given requirements
2. Efficient discharge of rice grain
3. Approach with new development idea
4. Providing supplementary calculations as required.
METHODOLOGY USED:
Following methodology are used for design the new equipment
1. Requirement understanding
2. Problem identification

3. Data collection
4. Development of solution
5. Review of task
6. Delivery of task
THE EXPECTED CONTRIBUTION FROM THE STUDY:
Improved design of auto belt tensioner unit for bucket elevator of
advanced bulk material handling equipment in food processing industry, which
allows less human intervention in functioning of equipment and ensure constant
rate of output from the equipment.
LIST OF ACTIVITIES TO BE CARRIED OUT TO COMPLETE THE
PROJECT:
ACTIVITY CHART
Activities
Vs Week number
1 2 3 4 5 6 7
Remarks
Project Selection
Start date
19-12-2016
Data collection
Data study
Suggestions and
improvement
Checking of results
Preparation of Final
report
Completed date
03-02-2016

SOFTWARE APPLICATIONS USED
i. Auto CAD Mechanical
ii. Auto desk Inventor and Solid works
iii. PTC Windchill

CONTENTS
Charters Page No.
1. Introduction to Material handling equipment’s 1-7
2. Introduction to bucket elevator 8-17
3. Analysis of existing design 18-19
4. Modification of existing design 20-42
4.1 Explanation
4.2 Calculation
4.3 Modified design
5. Conclusion 43
References 44

1 The Institution of Engineers (India)
Chapter 1
INTRODUCTION TO MATERIAL HANDLING
EQUIPMENTS
Expressed in simple language, Material handling equipment relates
to the movement, storage, control and protection of materials, goods or
products throughout the process of manufacturing, distribution, consumption
and disposal. One of the definitions given by the American Material Handling
Society is: “Materials handling is the art and science of moving, packaging and
storing of substance in any form.” To do it safely and economically with
efficiency, different types of tackles, gadgets and equipment are used,
when the materials handling is referred to as mechanical handling of materials.
Material handling also should be considered within a system context.
Rarely, if ever, activities are performed in a one area or department of a facility
without having an impact on operations.
Examples:
i. Handling of materials for storage or warehousing from raw materials to
finished product stage will affect the efficiency with which the production
operations are performed out on the shop floor.

ii. The positioning of conveyor line in plant might improve material flow
through the facility or it could present a hindrance to plant traffic.
iii. A significant improvement in the efficiency of one operation,
without a corresponding improvement in a subsequent step in the work
sequence, may only result in a piling up of materials down the line.
These simple examples illustrate the points that maximize overall
productivity of the plant or warehouse. The material handling steps that
supports production and operations must be integrated into a system of
activities rather than being viewed as a number of isolated independent
procedure. In addition to considering time and place utility and system
approach, a thorough definition of material handling must also include the
human aspect. People are always a part of material handling whether the
operation is simple one, involving only a few items of equipment, or a
large, complex, automated system. Maintenance personnel keep the
equipment working properly and keep downtime to a minimum. Foremen
and supervisors oversee overall operations, making sure they meet the
objectives of the department or plant. Training in operating procedure, and in
safety practice, is usually required to make handling operation pay off as
expected.
Finally, the definition of the material handling must contain an
economic consideration. Certainly the delivery of parts and materials to a

specific time is not completely meaningful unless accomplished at an
acceptable cost so that an adequate return is realized. Material handling is
a system or combination of methods, facilities, labor, and equipment’s for
moving, packaging and storing of materials to meet specific objectives. A
materials handling operation can be simple and small, and involve only few
basic equipment’s. Or, it may be large, complex or automated. Material
handling equipment is generally separated into four main categories.
1. Storage and handling equipment
2. Engineered systems
3. Industrial trucks
4. Bulk material handling
BULK MATERIAL HANDLING:
Bulk material handling is an engineering field that is centered around the
design of equipment used for the handling of materials such as ores, coal,
cereals, wood chips, sand, gravel and stone in loose bulk form. It can also relate
to the handling of mixed wastes. Bulk materials handling plants and processes
quite often require the elevation (lifting) of bulk materials to other parts of the
plant or process. Numerous technologies and equipment are currently
available for this purpose to the designer and practitioner. Generally they are
classified in to three main categories.

 Pneumatic conveyor or air lifter
 Conventional screw conveyor
 Bucket elevator
PNEUMATIC CONVEYOR OR AIR LIFTER:
Conveyor is almost universal in application. It can travel for miles at
speeds up to 5.08 m/s and handle larger amount of weight in metric tons with
the help of belt. It can also operate over short distances at speeds slow enough
for manual picking, with a capacity of only a few kilograms per hour. Generally
they are use in inclined position and not preferable for vertical transport.
However, it is not normally applicable to processing operations, except
under unusual conditions. Belt conveyors inside the plant may have higher
initial cost than some other types of conveyors and, depending on idler
design, may or may not require more maintenance. However, a belt
conveyor given good routine maintenance can be expected to outlast almost any
other type of conveyor. Thus, in terms of cost per ton handled, outstanding
economy records have been established by belt conveyors. However, these
methods of elevation can experience a range of problems and limitations, such
as in case of pneumatic conveying or lifting:
 Relatively high operating costs e.g. blower and compressor
 Product velocities and wear rates especially for dilute-phase conveying.

Simple belt conveyor
CONVENTIONAL SCREW CONVEYOR:
 Relatively high operating speeds due to slippage between the screw flight
and particles and also due to the back-flow of material through the screw
flight and casing clearance,
 Undesirable casing or screw contact.

Simple screw conveyor
BUCKET ELEVATOR:
Bucket elevator is a type of vertical or inclined transport equipment that
efficiently moves goods between floors, vessel or other structure. Elevator is
generally powered by electrical motors that either drive traction cables or
counterweight system like a hoist or pump hydraulic fluid to raise a
cylindrical piston like jack. Generally it is preferred for short distances
compared to belt conveyor. It is more preferable to transport the materials
vertically. The detail explanation of bucket elevator is given in next chapter.

Simple bucket elevator

Chapter 2
INTRODUCTION TO BUCKET ELEVATOR
Bucket elevators are the simplest and most dependable units for making
vertical lifts. They are available in a wide range of capacities and may operate
entirely in the open or be totally enclosed. The trend is toward highly
standardized units, but for special materials and high capacities it is wise to use
specially engineered equipment. Main variations in quality are in casing
thickness, bucket thickness, belt or chain quality, and drive equipment.
The main purposes of bucket elevators are used to lift bulk materials from one
height to another. They are a reliable and well-proven piece of equipment
Method of Operation:
Bucket elevators operate by using an endless belt or chain on which
buckets with rectangular sections are mounted. The belt or chain revolves
between a top and bottom pulley and the buckets move with it. At the bottom
the buckets pick up product fed into the elevator boot and at the top the product
is discharged as the bucket turns downward over the head pulley.

CLASSIFICATION OF BUCKET ELEVATOR
Generally bucket elevators are classified in mainly two types.
 Belt type bucket elevator.
 Chain type bucket elevator.
Now a day there are many types of bucket elevators are available and
each one is different from other according to their feature, application, and
design. The major classifications of bucket elevators are as follows.
1. Centrifugal discharge elevators
2. Positive discharge elevators
3. Gravity or continuous discharge bucket elevator
4. Horizontal discharge bucket elevator
5. Twin leg bucket elevator
6. Single and double bucket elevator
7. High or super capacity bucket elevator
1. CENTRIFUGAL DISCHARGE ELEVATORS:
In a centrifugal discharge elevator, buckets are fixed on to belt or chain at
regular pitch to avoid interference in loading and discharge. This type of
elevators is mostly vertical in operation and can handle practically any free
flowing fine or small lumpy materials. The material is fed into the boot of the

elevator and scooped up by the buckets as they pass round the bottom pulley or
sprocket. The material is discharged by centrifugal force as the buckets pass
over the head or sprocket.
Centrifugal Discharge Elevators
2. POSITIVE DISCHARGE ELEVATORS
These types of bucket elevators are widely used for elevating light, fluffy,
fragile materials like free flowing powders and granular products in a range of
industries in vertical as well as inclined position. Buckets are mounted at a
well spaced interval, are loaded by digging material from the boot or by
feeding the material in to them. After passing over head wheels, the buckets
are inverted over the discharge spout, providing a positive discharge
material. Generally they have higher conveying capacity.

Positive Discharge Elevators
3. GRAVITY OR CONTINUOUS DISCHARGE BUCKET ELEVATOR
This elevator consists of a series of steel made buckets mounted on spigot
pins between two chains or on the belt with the help of special types of screw.
Also sometime the buckets are mounted continuously on the normally surface
belts. Continuous type steel buckets are used leaving minimum clearance
between the buckets. The buckets retain the material being carried and travelled
vertically, until they are mechanically tipped at discharge positions. Gravity
discharge elevators supplied as close bucket discharge type, central discharge
type, or Idler wheel discharge. Generally a slow speed design gravity bucket
elevator is primarily installed for elevating large lumpy, free-flowing
material, sluggish material and abrasive material. Our standard units are
usually chain driven, either friction drive or toothed sprocket. These elevators

offer reliability with minimum wear and positive discharge emptying of the
bucket.
Gravity or Continuous Discharge Bucket Elevator
4. HORIZONTAL DISCHARGE BUCKET ELEVATOR
These elevators are designed and engineered to conform to general
practice in the handling of grain. In particular they are found in flour mills and
animal feed mills, where whole grain is being transferred into intake silos. Also
these types of bucket elevators are widely used for elevating aggregate, hard
rock, coal from mine in vertical horizontal as well as inclined horizontal
position. Head and foot shafts are provided with roller bearings. Buckets are
made of steel and mounted on the belt with special types of screw. Casing of
steel are welded and dust tight. The curve hood is designed for proper

discharge of the grain. The boot can be loaded from the front or back side
or both. Generally they have higher conveying capacity.
Horizontal Discharge Bucket Elevator
5. TWIN LEG BUCKET ELEVATOR
The twin lagged or double trunk legging bucket elevator has been
designed and engineered to provide efficient high capacities for handling
various grains, feeds, mill stock and similar free flowing granular materials.

The elevator is self-supporting with extra large heads and boot pulleys. They
are fabricated from heavy gauge steel and are dust and waterproof and with
provision for easy clean out. It is manufactured in many different sizes
to suit individual requirements. It has double trunk legging construction with
vertical angle supports are included on taller units.
Twin Leg Bucket Elevator
6. SINGLE AND DOUBLE BUCKET ELEVATOR
The construction of these types bucket elevators are same as other
types accept that the number and types of buckets are use is different. The

capacity of double bucket elevators is more compare to single bucket elevator
and also high capacity motor is required in operation. The size of double
bucket elevator is large compare to single bucket elevator since two
buckets are use in one row. The double bucket elevators are used lift heavy
materials and also where the higher output is required. Generally these
types of bucket elevators are used in aggregate plant, hard rock plant, cement
plant where the lift of heavy material is possible.
7. HIGH OR SUPER CAPACITY BUCKET ELEVATOR
Super capacity bucket elevators are a continuous discharge type
with buckets mounted between two strands of chain or on the belt. This
type of elevator is used where higher capacities, severe service or higher
shaft centers are required. The high or super capacity bucket elevators are
designed to provide efficient high capacities for handling various grains, feeds,
mill stock and similar free flowing granular materials. It is manufactured
in many different size to suit individual requirements. It has double trunk
legging construction with connecting angles provided on regular interval
flange section. Vertical angle supports are included on taller units.

APPLICATION OF BUCKET ELEVATOR
For stable work and application widely bucket elevator are used. By using
this one should get high Productivity. This bucket elevator is normally
designed and made for metallurgy, chemical industry, building materials,
mine, pulp and paper industries, ports and terminal, grain and vegetable
oil, food, fodder, plastic and medicine related application. Bucket elevator
systems are used for the following industrial fields.
 Cement factories: For lime, clay gypsum, clinker and cement additives
like pyrite, silicate, oxide etc
 Environment and water treatment: Waste for combustion, biomass,
sludge, ashes etc.
 Power plant: For coal, lignite and desulphurization product like
gypsum, ashes, sludge.
 Fertilizers and Chemical: For raw materials and additives
handling, phosphate, nitrate.
 Steelworks and Aluminum smelter: For coke, ashes, blast furnace
slag, coke, alumina, crushed bath, covers material.
 Food industry: For sugar, flour, vegetables pulp, slaughterhouse waste
etc.
Bucket elevator is used for perpendicular transport of the grain, powder
and disperse materials, and suitable for the oil, animal feed and chemical

industry etc. This Bucket Elevator is a fixed elevator categorized as feeding
device of delivering powdery and granular materials upward vertically. It has
simple structure, smaller cover, short shipping route and low pollution. Wood
chips are received from belt conveyor by centrifugal discharge bucket elevator
and delivered to a distributed belt conveyor over silos.

Chapter 3
ANALYSIS OF EXISTING PROBLEM
DETAIL A
Existing design of manual belt tensioner unit-side view of machine

Table: Bill of material for existing belt tensioner unit for the above figure
Due to continuous operation of equipment and development of heat, belt
gradually increases its length, and after equipment is stopped the belt regains its
shape due to elastic nature of material. Due to increase in length of belt during
operation, slip occurs causing reduction of output discharge capacity of
equipment.
To overcome this difficulty the practice is to periodically set the lead
screw manually to increase the tension in the belt and maintain its discharge
capacity.
To avoid the manual interference and make it automatic, springs are
introduced along with the lead screw. These springs enable the belt to maintain
the tension without slipping.
ITEM NUMBER PART NAME QUANTITY
1 lead screw rod full threaded 1
2 Tension Nut 4
3 Fixed bracket 1
4 Movable bracket 1

Chapter 4
MODIFICATION OF EXISTING DESIGN
4.1 EXPLANATION
In the earlier method it involves more frequent human intervention.
Hence to increase tension automatically a new development using two springs
introduced on either side of bucket elevator bottom shaft.
Before running the equipment the springs are compressed using the
tension nuts. Then the springs always tries to expand its length but it is
restricted by belt tension. When the belt tension reduces because of its increased
length due to continuous operation of equipment and development of heat. This
increase in belt length causes the springs to elongate, which tries to get back to
original position.
Hence the springs cause to maintain tightness of the pulley with belt
surface, thus achieving continuous constant discharge of bucket elevator, with
less human involvement.

4.2 CALCULATION
During design of bucket elevator a few factors are considered for design
and based on this input data whole design calculations were carried out. The
following factors are considered during design.
 Capacity = 30 Tonne/hour
 Lifting height (H) = 5.5 m
 Material for lifting: Rice
 Average bulk density: 850 Kg/m3
 Application: In rice mills to transfer large amount of rice from ground
floor to required destination (floor).
 Properties of material: Dry, Sharp edges, Lighter than metal
 Specific requirements: It should have excellent chemical resistance
and it should have higher transmission capacity.
 Service required – intermittent - up to 12 hours per day 6 days a week
 Boot design: Open boot bottom, elevator will placed on a concrete floor
SPACING BETWEEN THE BUCKETS
Bucket selected is of 375 mm wide x 220 mm projection with a volume of
6 liters. Empty mass of each bucket is 2.5 kg.

Assuming that 75% of the volume will be filled during working of equipment
Discharge capacity = 6 liters × 0.75 = 4.5 liters.
Hence, mass of grains per bucket = 0.0045 X 850 = 3.825 kg
Capacity of each bucket is 3.825kg
To prevent the bucket deformation while passing around the pulley and to avoid
over-stressing both buckets and belt have to be spaced 3 to 4 times the bucket
projection.
Considering the bucket spacing = 3.6 times the bucket projection
Bucket spacing = 3.6 × 220 =792 mm
Slightly increased bucket spacing to rounding off the value to 800 mm
BELT SPEED
Speed of buckets per sec = 2.17 Buckets/Sec

Bucket spacing = 800 mm = 0.8 m
Speed of the belt = 2.17 × 0.8 = 1.736 m/s
HEAD PULLEY DIAMETER
A simplifying assumption is made that the throw commences at the top of the
head pulley. According to centrifugal discharge at this point the centrifugal
force and gravity force are balanced.
Where,
m = mass in kg
v = belt speed in m/s
r = pulley radius in m
Gravity force = mg
Where,
g = gravity constant 9.8 m/sec
Putting both forces equal to each other
Pulley diameter, d = 2 x 0.307 = 0.614 m = 614 mm

THE DRIVE SPEED
With the head pulley size determined and the linear belt speed known, the N
(rev/min) of the head pulley can be calculated
LENGTH OF THE BELT
In an open belt drive, both the pulleys rotate in the same direction, of radius r1
and r2 and having center distance x. The length of the belt can be calculated by
using below formula.
Length of belt required for open belt drive,
( )
( )

Two pulleys (r1 and r2) are 307 mm radius, on parallel
shafts are spaced, x = 8500 mm apart.
(Centre distance arrived based on suitable modification
in the CAD design by iteration method to maintain
proper ground clearance and top chute length.)
Hence the length of belt required,
( )
( )
L = 18929 mm
NUMBER OF BUCKETS
Total length of belt = 18929 mm
Bucket spacing = 800 mm
FORCE APPLIED
To calculate the belt tension, total force applied will be equal to sum of all
rotating components weight. Hence, Now we will calculate weight of all
individual rotating components of equipment.
1. Weight of the pulley
Material: gray cast iron

Density: 7200 kg/m3
(( )
( )
Mass of the pulley = 7200 × 0.032= 231 kg
Weight of the pulley = 231× 9.81 = 2266N
Added 10% of weight for pulley for construction elements like spokes,
fasteners and bushes etc.
Weight of the pulley = 2266× 1.1 = 2493 N
2. Weight of the belt
Belt material: JET FDA VLE
The reinforcement of the elevator belts consists of simple or double fabric
inserts (depending on the strength) with polyester threads in the warp,

polyamide threads in the weft and polyamide threads in the link of warp and
weft. This textile carcass is especially studied to have no plastic elongation. The
over plates consist of synthetic elastomers (material NBR). This elevator belt is
suitable for food contact.
Following are the belt details from supplier.
Supplier website: <http://www.stifnet.com/de/>
Weight of the belt = 18.929 × 4.3 × 9.81 = 799 N
3. Weight of all empty buckets
Number of buckets = 24
Mass of each bucket = 2.5 kg

Weight of all empty buckets = 2.5 x 24 × 9.81 = 589 N
4. Weightof the rice weighing in the bucket elevator
One side of bucket elevator is filled with rice another side will be empty
buckets, Hence only 12 buckets are carrying the rice product and mass of
rice per bucket = 3.825 kg
Weight of the rice weighing in the bucket elevator = 3.825×12×9.81= 450 N
SHAFT DESIGN
Force acting on shaft is the sum of all rotating components weights (excluding
its own weight)
= (2493 × 2) + 799 +589 + 450= 6824N
Shaft material: 45 C 8 steel
Density: 7850 kg/m3
Ultimate tensile stress= 700Mpa
Ultimate shear stress=500Mpa
Length of the shaft, L = 1 meter
Let factor of safety for the design=6
Torque to be transmitted by shaft
T = 6824 × 0.307 =2095 N-m

The maximum bending moment acts at point C (assuming shaft is centrally
loaded)
Let, d = Diameter of the shaft
According to maximum shear stress theory, equivalent twisting moment,
√ √
d = 54.8 mm
According to maximum normal stress theory, equivalent bending moment,
( √ ) ( )
( )

d = 51.26 mm
Taking the larger of the two values, we have, d = 54.8 55 mm
Therefore, total force/load to be transferred from geared motor
F = 6824 +366 = 7190N
THE TENSION IN THE BELT
The power transmitted by a belt, P = ( )v
Where,
T1 = Tension in the belt on the tight side

T2 = Tension in the belt on the slack side
θ = Angle of contact in radians
v = Velocity of the belt in m/s
µ = Coefficient of friction between belt and pulley
For belt drive, tension equations allows T1 to be determined
Power required to drive the arrangement,
( )
( )
With the available data now we can calculate the belt tension along with
suitable assumptions
( )
Where,
Coefficient of friction between belt and pulley, µ = 0.3
Angle of contact between belt surface and pulley, θ = 180° = π rad

DESIGN OF SPRING
Design of helical compression spring for a maximum load of 11615 N for a
deflection of 70 mm.
Consider the material for the spring: carbon steel
Compression spring nomenclature
Considered springs at both ends of the of the shaft of the bottom dead center.
Assuming load on each spring will be 0.5 x 11798= 5898 N, allowable shear
strength of material, τ = 420 MPa, modulus of rigidity of the material, G = 84
kN/mm2
,spring is designed as follows.
1. Mean diameter of the spring coil
Let, D = Mean diameter of the spring coil, and
d = Diameter of the spring wire
Wahl’s stress factor,

Where, spring index, C = 6.5
Maximum shear stress ( τ ),
Mean diameter of the spring coil,
D = C.d = 6.5 × 17 = 110.5 mm
and outer diameter of the spring coil,
Do = D + d = 110.5 + 17 = 127.5 mm
2. Number of turns of the coils
Let, n = Number of active turns of the coils.
Compression of the spring deflection ( δ ),
n = 7.71 ≈ 8 coils
The total number of turns, n’ = n+2 = 8 + 2 = 10

3. Free length of the spring
Free length of the spring
= n'.d+ δ + 0.15 δ = 10×17 + 70 + 0.15×70 = 250.5 mm
4. Pitch of the coil

4.3 MODIFIED DESIGN
DETAIL A
Modified design of auto tensioner unit-side view of machine

Table: Bill of material for new arrangement for the above Figurer
DETAILS OF NEW COMPONENTS
The modified assembly containing some of the newly created
components, those are necessary to form interference and sliding fits to produce
desired application with lead screw rod and bracket plate. Hence it is important
to understand about the types of fit before applying fits to components. Unless
otherwise specified in the drawings all dimension are in mm.
Engineering fits
There are three general categories of fits:
1. Clearance fits for when it may be desirable for the shaft to rotate or slide
freely within the hole.
2. Transition fits for when it is desirable that the shaft to be held precisely,
yet not so tightly that it cannot be disassembled, this is usually referred to
ITEM NUMBER PART NAME QUANTITY
1 Helical compression Spring 1
2 Tension Nut 2
3 Fixed bracket 1
4 Movable bracket 1
5 Guide bush-I 2
6 Guide bush-II 1
7 lead screw rod 1

as a Location or Transition fit.
3. Interference fits, for when it is desirable for the shaft to be securely held
within the hole and it is acceptable that some force be necessary for
assembly.
The ISO System of Limits and Fits is a coordinated system of hole and
shaft tolerances for engineering and manufacturing used for cutting tools,
material stock, gages, etc. If held to these tolerances, cutting tools, material
stock, and gages are generally available throughout the world.
The hole basis fits have four preferred hole tolerances (H11, H9, H8, and
H7); the shaft basis fits have four preferred shaft tolerances (h11, h9, h7, and
h6) as shown in below Table.
Prepared hole basis system

Description of preferred fits
lead screw rod:
Material: EN38

Guide bush-II:
Internal diameter tolerance should be achieved after bush is fitted into bracket
plate.
Material: Bronze copper
Guide bush-I
Material: Bronze copper

Helical compression Spring
Specifications:
Sl. No. Parameter Symbol Value Units
1 Wire diameter of spring d 17 mm
2 Material of spring carbon steel
3 Permissible shear stress τ 420 MPa
4 Max permissible
deflection
corresponding to max
load
δmax 70 mm
5 Load at max deflection W 5898 N
6 Spring rate (Stiffness of
spring)
K 84.25 N/mm
7 Free length of spring L 250.5 mm
8 Mean coil diameter Dm 110.5 mm
9 Guiding bush dia B 85 mm
10 Outside diameter Do 127.5 mm
11 Inside diameter Di 93.5 mm
12 Spring index C 6.5
13 Total no of turns (coils) n 10
14 Pitch of spring coil P 27.83 mm
Note: Spring to be Blackodized to prevent corrosion.

Fixed bracket plate for bush insert
Material: Stainless steel
The weldment to which this component is welding is made from stainless steel
material, hence it is also should be stainless steel. It is recommended from
FDA(Food and Drug Administration) that all the food grains contacting surfaces
are made from stainless steel material or other equivalent material.

ISOMETRIC VIEW OF MODIFIED BUCKET ELEVATOR
Modified auto belt tensioner unit design is implemented in the bucket elevator

Chapter 5
CONCLUSION
The current development of automatic belt tensioner unit is used to avoid
more human interference and maintain constant discharge of equipment which
in turn reduces the downtime of equipment, reduces manual work of operators,
improves efficiency and productivity of equipment and reduce the cost of
operation. This project will be base for future development on the tensioner unit
in the bucket elevator and other similar kind of equipment.
A more efficient discharge can be attained by implementation of electro-
mechanical devices like Tyco meter RPM sensor under closed loop connection
with servomotor to control the speed of the prime mover to ensure constant
discharge of equipment.

REFERENCES
Machine Design by R.S. Khurmi and J.K. GUPTA, 14th
edition, Eurasia
publishing house (pvt.) ltd.
Introduction of Material Handling by Siddharthy Ray, 1st
edition, New age
international publishers.
Belt Bucket Elevator Design by Mike Sondalini, 2nd
edition, Feed forward
publications.
<http://feeco.com/everything-need-know-bucket-elevator-design/>
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<http://www.wisetool.com/fit.htm>
<http://www.me.metu.edu.tr/courses/me114/Lectures/tolerancing.htm>
<http://www.mmto.org/dclark/Reports/Encoder%20Upgrade/fittolerences%20%
5BRead-Only%5D.pdf>
<http://www.mechanicalengineeringblog.com/3693-industrial-bucket-elevators-
vertical-bucket-conveyors-bucket-elevator-types/>

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