Design for Manufacturing Screw Conveyor Assembly

1. 1
DESIGN FOR MANUFACTURING SCREW
CONVEYOR ASSEMBLY
By
AKHILESH KULKARNI - 1001535677
IMTIYAZ MIRZA - 1001420170
PRATIK BANSODE - 1001398104
ANKIT SUTARIA - 1001505011
VISHWAJEET DHAMDERE - 1001552530
A project report submitted in partial fulfillment of
The requirements for the course of
DESIGN FOR MANUFACTURING
SUBMITTED TO
Dr. Robert Taylor

2. 2
LIST OF CONTENTS
Introduction 5
Conceptual Design 6
2.1) House of Quality
2.2) Product Design Specification 7
2.3) Morphological Analysis 8
2.4) Concept Chart 10
2.5) Weighted Decision Matrix 14
Preliminary Design
Review
15
3.1) Material Selection 14
3.2) Manufacturing Process
Selection
16
3.3) Design for Manufacturing 19
3.4) DFA Evaluation 21
3.5) Tolerance Analysis 22
Final Design Review
4.1) Failure Mode and Effective
Analysis (FMEA).
22
4.2) Reliability Analysis 23
4.3) Mean Time Between Failure
4.4) Fault Tree Analysis
25
26
4.5) Cost Analysis 27
4.6) Ergonomics and Safety
Analysis
27
4.7) Horse Power and Screw
Diameter Calculation
28
Part Model and Assembly
Drawings
31

3. 3
LIST OF FIGURES
FIG [1] PHYSICAL
DECOMPOSITION
9
FIG [2] PRODUCT
ARCHITECTURE
10
FIG [3] BLOCK DIAGRAM OF
THE SCREW CONVEYOR
ASSEMBLY
10
FIG [4] REPRESENTATION OF
CONCEPTS
12
FIG [5] ASHBY CHARTS 14
FIG [6] STRENGTH – MAX.
SERVICE TEMPERATURE
CHART
15
FIG [7] FAULT TREE ANALYSIS 16

4. 4
LIST OF TABLES
TAB [1] House of Quality 6
TAB [2] Engineering characteristics
with appropriate direction
6
TAB [3] Morphological Chart 9
TAB [4] Concept Chart 10
TAB [5] Weighted Decision Matrix 13
TAB [6] Pairwise Comparison of
Properties
15
TAB [7] Weighted Property Index
Chart
16
TAB [8] Material Selection Chart 16
TAB [9] Process selection Chart 18
TAB [10] Manufacturing Process
Shortlisting
19
TAB [11] Selected Manufacturing
Process
19
TAB [12] DFM Worksheet 21
TAB [13] DFA Evaluation Table 21
TAB [14] F.M.E.A 23
TAB [15] Safety Factor Reliability
Analysis
24
TAB [16] Total costs Incurred 26
TAB [17] Properties 27

5. 5
1) Introduction
A screw conveyor assembly is generally depicted as a mechanism used to move liquid or granular materials
from one part of a manufacturing plant to another [1]. The applications of the assembly are following, but not
limited to transfer of semi solid materials, industrial minerals, chemicals, cement, plastics, wood chips, cereal
grains, animal feed and various bulk material handling industries [2]. A typical screw conveyor system consists
of Transmission, gearbox, motor, outlet, bearing support, covers, trough and Inlet.
For this project, we are aiding Martin sprocket, a power transmission and material handling company, by
investigating a design change by replacing two of the mobile belt conveyors into a single screw conveyor
assembly. Targets are set towards the conveyor system being cost effective while maintaining better quality and
performance.
Some of the requirements and conditions of this design that must be met are the following: The screw
conveyor must be able to transfer 25 tons of material per hour or more. It must be at least 4 inches wide to
accommodate the ease for transfer. The length of the whole conveyor must amount to 50 feet and should be able
to work efficiently in an arid climate ranging up to 250 F. The material used for manufacturing the conveyor must
be corrosive resistant.
The design for manufacturing of any component or assembly involves a strategic planning and process usually
described in the Design for manufacturing textbook we have as a reference. It divides the whole process into three
categories i.e., Conceptual design, Preliminary or Embodiment design and Detail design. Each category contains
a set of rules that must be followed in order to obtain the desired result.
2) Conceptual Design
In the conceptual design, the main processes that need to be considered are quality function deployment,
product design specification, Morphological chart, concept chart and weighted decision matrix, all of which are
a part of problem definition and need identification, gathering information, concept generation, decision making
and concept selection.
First, we proceed with the quality function deployment which is a process of achieving quality-oriented
performance by keeping the requirements of customer as a reference. The product planning phase of quality
function deployment is called the house of quality [3].
2.1) The house of quality is a conglomeration of various groups that generally show the inter-relation between
the customer requirements and engineering characteristics. Room 1 has the customer requirements which are
gathered by various methods including focus groups, surveys, customer complaints, etc., All these are jotted down
and ranked to produce a column describing the rating of which requirement takes the highest to lowest priority.
Room 2 of the chart depicts the Engineering characteristics that we as engineers decide to accommodate with
respect to the customer requirements. Room 3 contains the correlation matrix showing how the inter-relation
between each engineering characteristic occurs. The relationship matrix in room 4 accurately depicts the relation
between customer requirements to the engineering characteristics. It also shows up to what degree is each relation
prominent by taking strength codes into consideration. The other functions of this chart include the Ranking of
the relationship matrix, the comparison of values with other competitors in the market, Technical assessment of
the values and achieving the targets. The House of quality prepared for this project is shown below

6. 6
TAB [1]: House of Quality
A reference is also shown regarding the engineering characteristics and they need to be addressed i.e., increased
or decreased by taking the customer’s needs into consideration.
TAB [2]: Engineering characteristics with appropriate direction

7. 7
2.2) Product Design Specifications are a set of conditions set in order to ensure quality oriented performance by
reducing cost for manufacturing [4]. The basic functions are all of the ones which were discussed as conditions
in the introduction. The special features include the length to be 50 feet and there is an inclination of 10 degree
which noticeably reduces the efficiency of the conveyor. Key performance targets include a tonnage capacity of
551 cubic feet per hour. The arid climatic conditions and the temperature is already known. The time limit that
we have set for the entire design process to be accomplished is a total of 13 months for both design and assembly.
We have taken a U trough formed channel that has corrosive resistance. Its manufacturing cost is set at an
approximate of 25000 US dollars while the retail price is set for 45000 US dollars. There is a warranty of 7years
for the whole assembly. A reference table is given below depicting the Product design specification including the
social and legal requirements along with the manufacturing specifications.
• PRODUCT DESIGN SPECIFICATION
Product Identification:
Product Name: Screw Conveyor Assembly System
Basic Function:
• Used to move feldspar lumps from a truck bed into a crushing plant
• Single permanent fixed screw used for this movement.
• The largest lumps are about 2-3/4 inches wide and comprise about 20% of the load
Special Features:
• The distance from the center of the inlet to discharge is 50 feet and the conveyor is at an inclination of 10
°.
• Variable speed motor
Key Performance Targets:
• Uses a motor with a power output of
• Tonnage capacity of 551.15 cubic feet /hr.
• Distance from the center of the inlet to discharge is 50 feet
• The conveyor is at an incline of 10°
Service Environment:
• Tough abrasive environment
• The system should be able to withstand the highest temperature of 300 Fahrenheit
• Loading and unloading vibrations on the system
• The system should be able to withstand corrosion
User Training Required
Proper knowledge and training required for the workers operating the system
Key Project Deadlines
• 9 Months to finalize the design
• 4 months for Assembly
Physical Description
• Distance from center of the Inlet to discharge is 50 feet
• Diameter of screw is 12 inches
• Corrosion Resistance
• U Trough formed channel
Financial Requirements
Pricing policy over life cycle
• Target manufacturing cost is $25,000.
• Estimated Retail price is $45,000.
Warranty Policy:
• 7-year warranty

8. 8
Expected Financial Performance
• To be Revealed
Level of Capital Investment required
• To Be Revealed
Life Cycle Targets
Useful Life
• 10 years
Cost of Installation and Operation
• Total cost of 100,000 dollar
Maintenance schedule and location
• Skilled personnel for repair and maintenance
• Maintenance has to take place where the plant is located
Repairability
• Fasteners, Flanges, Trough and cover mean time for failure is 2 years
• Conveyer screws for 3 years
• Bearings and thrust units for 2 years
• Shaft and coupling for 8 years
Social, Political and Legal Requirements
• Patents will be thoroughly checked in order to protect Intellectual property
• In terms of safety, Care shall be taken at each stage of the operation
• Environment and safety regulations are being followed
• Ethical and Federal standards are being maintained
Manufacturing Specifications
• Manufacturing and Assemble of all main components are to be done in House
• Bearing and Motors are to be ordered from third party manufacturers to reduce tooling costs using cost
analysis
• Assembly to be done in the same location as Manufacturing
We proceed on to concept generation and creation involving morphological methods.
2.3) Morphological analysis is a way where we can create new forms of concepts in order to have better
manufacturing methods that are cost efficient. Morphological analysis involves three basic steps. First is to divide
the overall problem into sub-problems, next we must generate solutions for each subproblem separately and
finally combining all the concepts in a meaningful way to produce different combinations of concepts [5].
We have taken 5 sub-systems that we can generate different concepts for and those are the type of screw, hangar,
the type of drive arrangement, the trough and the trough end. The following table shows the different variations
in the subsystems producing a typical morphological chart.

9. 9
SCREW HANGER
DRIVE
ARRANGEMENT
TROUGH TROUGH ENDS
Full Pitch, Full
Flight
Style-220 Screw Drive Reducer
Angular Flange-
Rectangular
Standard Discharge
Half Pitch Style-226
Shaft mounted
Reducer
Angular flange Tubular Curved slide gate
Tapered pitch Style-326 Gear Motor Drive Angle flange U trough Inside Trough Ends
Variable Pitch Style-216
Base Type Reducer
Drive
U trough Formed
channel
Standard
Discharge spout
TAB [3]: Morphological Chart
After this, a decision is laid out to produce a few concepts by re-arranging the subsystems in order to
produce an efficient conveyor system. Although, an understanding of how the energy gets transformed when a
conveyor works is very important. For this, we can sketch a physical decomposition, the product architecture and
a block diagram to know how the screw conveyor assembly functions.
Physical Decomposition of Conveyor System and Product Architecture:
FIG [1]: Physical Decomposition

10. 10
FIG [2]: Product Architecture
FIG [3]: Block Diagram of the Screw Conveyor Assembly

11. 11
2.4) A Concept chart is generated by taking the morphological analysis into consideration.
CONCEPT SCREW TROUGH REDUCER HANGER
TROUGH
ENDS
1
Tapered
pitch
Tapered
pitch
Gear
Motor
Drive
Style-226
Curved slide
gate
2
Half
Pitch
Angle
Flange U-
trough
Screw
Drive
Reducer
Style-230
Flush and
Discharge spout
3
Full
Pitch,
Full
Flight
U trough
Formed
channel
Gear
Motor
Drive
Style-326
Standard
Discharge
4
Variable
Pitch
Angular
flange
Tubular
Screw
Drive
Reducer
Style-220
Standard
Discharge spout
TAB [4]: Concept Chart
A total of 4 concepts are chosen by arranging different subsystems together. The following charts show a
graphical representation of the concepts chosen

12. 12

13. 13
FIG [4]: Representation of Concepts
2.5) A Weighted decision matrix is an analysis done to select the best design concept out of the given options.
The various design criteria are considered which would significantly alter the performance rate of the entire
system. Motor characteristics, flow rate, surface hardness are some of the criteria that were taken, to name a few.
All of them are prioritized in terms of weight factors. This is a way to define which criteria has the largest or the
smallest impact on the conveyor. All the weight factors should sum up to 1 [6]. Now, for every concept that we
have, analysis is divided into three sub categories of Magnitude, score and rating. The behavior of magnitude may
range anywhere in the performance scale. Each behavior is assigned a similar score from 0- 10, 10 being the best.
These scores are multiplied with their respective weight factors to produce a Rating. The rating for a concept is
summed up in the end to produce a significant number which depicts the best of all the concepts considered.
The weighted decision matrix table given below shows an 8.04 concept rating for concept-3 which we
chose as the best of all. Although, this way of analyzing the concept has its own limitations because the magnitude,
the weight factor and the score that we assign is very subjective and can differ from one person to another very
rampantly. Therefore, the design team needs to have a certain experience in assigning the values.

14. 14
Weighted Decision Matrix
Design Criteria
WeightFactor
Units
Concept-1 Concept-2 Concept-3 Concept-4
Magnitude
Score
Rating
Magnitude
Score
Rating
Magnitude
Score
Rating
Magnitude
Score
Rating
Motor
Characteristics
0.0
3
HP Good 7
0.2
1
Good 7
0.2
1
Good 7
0.2
1
Good 7
0.2
1
Flow Rate 0.1 ft3
/hr Good 7 0.7 Good 7 0.7 Good 7 0.7 Good 7 0.7
Surface
Hardness
0.0
8
HB
V.
Good
8
0.6
4
V.
Good
8
0.6
4
Excell
ent
1
0
0.8 Good 7
0.5
6
Thermal
Expansion
0.0
8
ΔL/L
V.Go
od
8
0.6
4
Good 7
0.5
6
V.
Good
8
0.6
4
Satisfact
ory
5 0.4
Screw Pitch
0.1
1
Inches Good 7
0.7
7
Good 7
0.7
7
Good 7
0.7
7
Good 7
0.7
7
Conveyor
Loading
0.0
9
% Good 7
0.6
3
Good 7
0.6
3
Good 7
0.6
3
Good 7
0.6
3
Stiffness
0.0
9
lb/in Good 7
0.6
3
Good 6
0.5
4
Excell
ent
1
0
0.9 V. Good 8
0.7
2
Efficiency
0.1
5
% Good 7
1.0
5
Excell
ent
1
0
1.5
Excell
ent
1
0
1.5 Good 7
1.0
5
Trough Loading
0.0
9
% Good 7
0.6
3
Good 7
0.6
3
Good 7
0.6
3
Good 7
0.6
3
Corrosion Rate
0.1
8
mpy( mils per
year)
Excell
ent
10 1.8 Good 7
1.2
6
Good 7
1.2
6
Good 7
1.2
6
Total 1 7.7
7.4
4
8.0
4
6.9
3
TAB [5]: Weighted Decision Matrix

15. 15
3) PRELIMINARY DESIGN REVIEW
• Manufacturing process and Material selection: Finding out the appropriate material and its respective
manufacturing process in comparison to the function and the mechanical properties of the conveyor
system.
• Design for Manufacturing Analysis: Ranking of appropriate mechanical characteristics in comparison
to the manufacturing processes chosen.
• Design for Assembly Analysis: Analyzing various assembly characteristics and giving them an
appropriate score.
• Tolerance Stack-up analysis: Tolerance analysis with respect to process capabilities.
3.1) Material Selection
• Materials are generally selected based on performance properties, manufacturing characteristics,
environmental profile and business considerations
• With respect to the design considerations, we need the following characteristics that accompany the
function and performance of the system
• Abrasive resistance
• Stiffness
• Thermal Expansion
• Fracture Toughness
• Cost
Selection of materials through Ashby Charts
• Ashby charts are based on large computerized material property database.
• Assist in selecting large number of materials for conceptual design.
• Polymers, Metals, Ceramics and Composites are available resources for material selection.
• The Elastic Modulus on Y-axis is Tabulated against Density on X-axis.
• Material selection is done through Material properties, Manufacturing issues, E/𝜌 ratio and maximum
service temperature.
FIG [5]: Ashby Charts

16. 16
FIG [6]: Strength-Max. Service Temperature chart
PROPERTY 1 2 3 4 5
RAW
TOTAL
WEIGHTING
FACTOR, wi
Abrasive
Resistance
- 1 1 1 1 4 0.4
Stiffness 0 - 1 0 1 2 0.2
Thermal
Expansion
0 0 - 1 1 2 0.2
Fracture
Toughness
0 0 0 - 1 1 0.1
Cost 0 0 0 1 - 1 0.1
TOTAL 10 1
TAB [6]: Pairwise Comparison of Properties

17. 17
Material
Abrasive
Resistance
(Rockwell
Hardness)
(w=0.4)
ß
Stiffness
(ksi)
(w=0.2)
ß
Thermal
Expansion
(µ-in/in-
°F)
(w=0.1)
ß
Fracture
Toughness
(Relative
Scale)
(w=0.2)
ß
Cost
(Relative
Scale)
(w=0.1)
ß
ϒ (Σ
wiβi)
304 SS 70 85 28000 90 9.89 91 3 60 2 100 83.1
316 SS 79 96 28000 90 9 100 4 80 3 67 89.1
AR 235 80 97 29000 93 9.34 96 4 80 4 50 88
AR 400 82 100 31000 100 9.5 95 5 100 5 40 93.5
TAB [7]: Weighted Property Index Chart
• AR400 has highest weighted property index
• Selecting AR400: Screw flight and shaft conveyor trough since highly abrasive material is being conveyed
• Selecting SS-316: For discharge because of corrosion and thermal expansion
3.2) Manufacturing Process Selection
The factors that influence the selection of process to make part are:
• Quality of parts required
• Complexity- shape, size, features
• Material
• Quality of part
• Cost to manufacture
• Availability, lead time, delivery schedule
Steps for manufacturing process selection
1. Identify the material and number of parts to be manufactured
2. Decide the objective of Manufacturing
3. Identify the constrain for selecting the manufacturing process
4. Rank the various options for Manufacturing processes and select the best one
• Step 1: Identify Material & number of parts
Based on the part specification, identify the material class, the required number of parts, and the size & shape.
Following are the components and its selected material
Component Material Justification
Trough SS316 Material Selection Process (Weighted Decision Matrix)
Shaft Standard Selection Standard Selection
Screws AR400 Material Selection Process (Weighted Decision Matrix)
End Plates SS316 Material Selection Process (Weighted Decision Matrix)
TAB [8]: Material Selection Chart
• Step 2: Decide the objective of Manufacturing

18. 18
• Manufacturing Cost Reduction
• Withstand Operating Conditions
• Manufacturing Cycle time
• Improve Overall Performance
• Maximum tool life
• Steps 3: Constraints for Selection of Manufacturing Process
• Stainless Steel Properties
• Cost of manufacturing
• Manufacturing feasibility
• Lead time
• Step 4: Rank various options and select the best one
Screening of Manufacturing Process based on PRIMA selection
As the material selected is SS316, AR400 and Quantity considered 1 to 100 following are feasible
manufacturing processes.
• For AR400
1. Centrifugal Casting
2. Ceramic Mold Casting
3. Manual Machining
4. Electrical Discharge Machining
5. Chemical Machining
6. Ultrasonic Machining
For SS316
1. Investment Casting
2. Ceramic Mold Casting
3. Manual Machining
4. Superplastic Forming
5. Spinning
6. Electrical Discharge Machining
7. Chemical Machining
8. Ultrasonic Machining
Factors influencing manufacturing process selection
Based on Quantity of parts 1. Sand Casting
Considering economic batch size of 100 2. Investment Casting
3. Forging
4. Electro Machining
5. Conventional Machining

19. 19
Based on Size
1. Screw (1 to 10kg) 1. Conventional Machining
2. Forming
3. Forging
2. Trough (10 to 100 kg) 1. Sand Casting
2. Forging
3. Conventional Machining
3. End Plates (1 to 10 kg) 1. Conventional Machining
2. Forming
3. Forging
Based on Shape and Feature Complexity
1. Screw (F7) Casting
1. Sand Casting
2. Investment Casting
Sheet Metal
1. Bending
2. Deep Drawing
Machining Process
1. Milling
2. Trough (Shape and Complexity- T4) Casting
1. Sand Casting
2. Investment Casting
Sheet Metal
1. deep Drawing
2. Spinning
3. End Plates (S5, S6, F6) Casting
1. Sand Casting
2. Investment Casting
Deformation Processes
1. Hot impression die forging
2. Cold forging
Machining Process
1. Milling
TAB [9]: Process Selection Chart

20. 20
Part Process
Cycle
time
Process
flexibility
Material
Utilization
Quali
ty
Equipment and
Tooling cost
Tot
al
Trough
Forming 3 1 3 4 1 12
Sand Casting 2 5 2 2 1 12
End
Plates
Sand Casting 2 5 2 3 1 13
Forming 3 1 3 4 1 12
Screw
Flight
Sheet Metal
Forming
3 1 3 4 1 12
TAB [10]: Manufacturing Process Shortlisting
• For Screw
1. Forming
• For End Plates
1. Sand Casting
2. Forming
• For Trough
1. Sand Casting
2. Forming
Manufacturing process selection:
We select the manufacturing process
Component Material Justification
Trough SS316 Forming
Shaft Standard Selection Standard Selection
Screws AR400 Forming
End Plates SS316 Casting
Tab [11]: Selected Manufacturing Process
3.3) Design for Manufacturing:
Screw flight – DFM worksheet – Forming
PART (ID or Description or features) Screws
Step-1(Part Details)
Quantity 38
Primary operation on the part Forming
Secondary operation on the part Welding
Instances of tolerances
Step-2(DFM analysis)
Bend angle (-1 if it is 90° else +1) 1
Ratio of channel width to leg height (if 2:1 then -1 else +1) 1
The width -1

21. 21
of the formed portion ( -1 if 3 times the stock thickness else +1)
Grain direction ( -1 if along the grain direction else +1) 1
The bend radius ( -1 if equal to sheet thickness and +1 if lesser than the sheet thickness)
Stiffening ribs provided if extra resistance required ( -1 if present)
2 Total
Trough – DFM Worksheet – Forming
PART (ID or Description or features)
c
channel
U
shape
Step-1(Part Details)
Quantity 10 5
Primary operation on the part
forming forming
Secondary operation on the part drilling drilling
Instances of tolerances
Step-2(DFM analysis)
Bend angle (-1 if it is 90° else +1) -1 1 0
Ratio of channel width to leg height (if 2:1 then -1 else +1) 1 1 2
The width
-1 -1
-
2of the formed portion ( -1 if 3 times the stock thickness else +1)
Grain direction ( -1 if along the grain direction else +1) 1 1 2
The bend radius ( -1 if equal to sheet thickness and +1 if lesser than the sheet
thickness) -1 -1
-
2
Stiffening ribs provided if extra resistance required ( -1 if present)
Total 0
End plates – DFM Worksheet – Casting
PART (ID or Description or features) End Plate
Step-1(Part Details)
Quantity 2
Primary operation on the part Casting
Secondary operation on the part Drlling
Instances of tolerances

22. 22
Step-2(DFM analysis)
Sum
Number of secondary operations on the part (+1 for each operation) 1 1
Section thickness of the casting must be uniform ( -1 if yes and +1 if no) -1 -1
Straight parting lines ( -1 if yes); Stepped parting lines (+1 if yes) 0
Elimination of an undercut on the casting if present ( -1 if yes and +1 if no) 0
Presence of draft or taper (-1 if yes and +1 if no) 0
Presence of riser near heaviest section ( -1 if yes and +1 if no) 0
Presence of circular web to connect the ribs (-1 if present) 0
Presence of sharp corners (+1 if yes); Presence of rounded corners (-1 if yes) -1 -1
Presence of fillets or tapers (-1 if yes); Presence of sharp steps (+1 if yes) 1 1
Intersection of two walls at right angle is preferable ( -1 if yes) -1 -1
use of filter to reduce inclusions ( -1 if yes or +1 if no) 1 1
Small cored holes are avoided (+1 if any) 0
Total 1
TAB [12]: DFM Worksheet
3.4) DFA Evaluation Worksheet
TAB [13]: DFA Evaluation Table

23. 23
Explanation of measures of DFM and DFA
• DFM
1. For screw and trough forming is the ideal process.
2. For trough end plates sand casting is the ideal process.
• DFA
1. Room to decrease the number of screws manufactured by increasing the screw length.
2. Can reduce the number of saddles required.
3.5) Tolerance Analysis

24. 24
4) FINAL DESIGN REVIEW
In this phase detail design are finalize and proceed for the product manufacturing. Even FMEA evaluation are
done in this phase.
4.1) Failure Mode and Effective Analysis (FMEA)
FMEA is methodology for identifying potential problems for new or existing design. It identifies the mode of
failure of every component in a system and determines the effect on the system of each potential failure.
TAB [14]: F.M.E.A
• Highest Risk Priority Number- 270 and 175 for the screw section and coupling shaft respectively. Failure
of the screw section and coupling shaft will lead to complete shutdown of the plant.
• To prevent the failure of both the components, check the alignment of screw section while assembling the
system.
• Next highest RPN (96) is for shaft bearing. Failure of shaft bearing can be due to overloading,
contamination and misalignment. it can be prevented by using bearing material which can withstand high
wear and operating temperature.
4.2) Reliability Analysis
R Trough R Hanger R Bearing R Screw R Coupling

25. 25
• Safety Factor = 𝑆/𝜎 = strength / Stress = Capacity / Load
• Overall SF = 𝑆𝐹 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙 x 𝑆𝐹 𝑠𝑡𝑟𝑒𝑠𝑠 x 𝑆𝐹𝑡𝑜𝑙𝑒𝑟𝑎𝑛𝑐𝑒𝑠 x 𝑆𝐹 𝑓𝑎𝑖𝑙𝑢𝑟𝑒 𝑡ℎ𝑒𝑜𝑟𝑦 x 𝑆𝐹 𝑟𝑒𝑙𝑖𝑎𝑏𝑖𝑙𝑖𝑡y
SFvalues Explanation
SFmaterial 1.1 The material properties are known from a handbook or from manufacturer’s values.
SFstress 1.2 -
1.3
Average overloads of 20–50%. The stress analysis method may result in errors less than 50%.
SFtolerance 1 The manufacturing tolerances are average.
SFfailure
theroy
1.2 The failure analysis used is based on static uniaxial or multiaxial state of stress, or fully reversed
uniaxial fatigue stresses, multiaxial fully reversed fatigue stresses or uniaxial nonzero mean
fatigue stresses.
SFreliability 1.2 -
1.3
The reliability is on average 92–98%.
Safety Factor table for components
Part SFmaterial SFstress SFtolerance SFfailure theroy SFreliability SF
Trough 1.1 1.2 1 1.2 1.2 1.90
Screw 1 1 1 1 1.2 1.20
Coupling 1.1 1.2 1 1.2 1.2 1.90
Hanger 1.1 1.2 1 1.2 1.2 1.90
Hanger Bearing 1.1 1.25 1 1.2 1.3 2.15
End Bearing 1.1 1.25 1 1.2 1.3 2.15
TAB [15]: Safety Factor Reliability Analysis
For SS316 Material – Trough
Z = 0 −
𝑄 𝑏𝑎𝑟
𝜎 𝑄
Z = 0 −
35.52
10
= - 3.552
R = 1– 𝑃 𝑓

26. 26
R = 1 – 0.002 = 0.998
𝑅Trough = 0.998
System Reliability, R = 0.998 x 0.998 x 0.861 x 0.998 x 0.999 = 0.8549
Steps to improve Systems Reliability:
• Can use different bearing material which can increase the bearing reliability. By changing the material form
Hard iron to Bronze the bearing reliability can be increased from 0.861 to 0.9693.
4.3) Mean time between failure
𝑇̅ = 1 / 𝜆
=
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡𝑖𝑚𝑒 𝑢𝑛𝑖𝑡𝑠 𝑑𝑢𝑟𝑖𝑛𝑔 𝑤ℎ𝑖𝑐ℎ 𝑎𝑙𝑙 𝑖𝑡𝑒𝑚𝑠 𝑤𝑒𝑟𝑒 𝑒𝑥𝑝𝑜𝑠𝑒𝑑 𝑡𝑜 𝑓𝑎𝑖𝑙𝑢𝑟𝑒
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑓𝑎𝑖𝑙𝑢𝑟𝑒𝑠
𝜆 = 2 × 10−7
per 1000 h
𝜆 = 2 × 10−10
/ h
MTTF = 𝑇̅ = 1 / 2 ×10−10
ℎ𝑜𝑢𝑟𝑠 = 5 × 109
ℎ𝑜𝑢𝑟𝑠
4.4) Fault Tree Analysis
FIG [7]: Fault Tree Analysis
R Trough R Hanger
R Bearing+
end bearing
R Screw R Coupling
0.998 0.998 0.861 0.998 0.999

27. 27
4.5) Cost Analysis
Material Cost
• 316SS – $ 4 / lb
• AR400– $ 21 / lb
Labor Cost
$ 50 / hour (Machining) [2]
$ 25 / hour (Assembly) [2]
Tooling Cost
For forming
Tooling cost, ct ($/set) = 50,000
Total production run, n (units) = 200,000
Tooling life, nt (units) = 100,000
Sets of tooling required, k = 2 × 2
CT unit cost of tooling = $2
For casting
Tooling cost, ct ($/set) = 80,000
Total production run, n (units) =500,000
Tooling life, nt (units) 100,000
Sets of tooling required, k= 5 × 2
CT unit cost of tooling =$ 1.6
Equipment Cost
• CNC machine cost = $13000
• Recovery time = 5 years
• Cost per hour = 130005×365×8 = $ 0.89
• Parts/hour = 10
• Cost per part = 0.89/10
• E = $ 0.09
Tooling Cost
we can take typical overhead cost to be $ 5 per part
Unit Part Cost
Part Material
Max Dimensions of raw
material
Weight of raw
material
Rate
Total
Cost
Trough SS316 144*17*2.5 1710 $4/lb 3540
Screws AR400 Dia 16 inch N/A N/A 30
Shaft Standard Dial 3.5 inch * 600 442.61 $4/lb 360
Hanger
Bearing
Style 326 N/A N/A $40/unit 40
Coupling Shaft
From H
section
Dia 3 inch * 13 inch N/A
$110 /
unit
110
Motor N/A N/A N/A $1600 1600
Total 5680
TAB [16]: Total Costs Incurred

28. 28
Labor cost
• Number of parts per hour = 10 / hr
• Labor cost (machining) per hour = $ 50 / hr
• Labor cost (assembly) per hour = $ 25 / hr
• Total Labor cost = 75 / hr
• Labor cost / part = 75/10
• L = $ 7.5
Total Cost
Total Cost = M + L + O + T + E
= 5680 + 7.5 + 5 + 2+1.6 + 0.09
= $5696.19
4.6) Ergonomics and Safety Analysis:
Steps to Improve Ergonomic
• Avoid sharp corners and edges
• Using standard components and tools
Safety Concerns
• Material Leakage
• Overloading
• Material Failure
• Excessive misalignment of the shaft
Safety Mechanism
• Create a standard check-sheet to inspect misalignment of the shaft and bearings
• Replace bearings after their intended use
Periodic inspection of screws and shaft after their intended use
• Warnings and Labels to ensure safe use
Safety and Ergonomics Rules
• Labelling and locating all controls/adjustments
• All installation and operating instructions are clearly labelled
4.7) Horse Power and Screw Diameter Calculations
Step 1: Screw Diameter Calculations
Material to be conveyed: Silica Sand
Material Properties:
Material Weight
Lb/ft3
Material
code
Bearing Component
Series
Material
Factor (Fm)
Trough
Loading
Fledspar
Lumps
100 D7-36 H 2 2.0 15
TAB [17]: Properties

29. 29
• Material Code Interpretation
D-7: Granular 7” and under (3” to 7”)
3 : Average flowability
7 : Extremely Abrasive Material
Required Capacity (ft3
/hr) : 550 ft3
/hr
Selecting the diameter as per the CF from the Design Catalogue,
Diameter
(Inch)
Capacity ft3/hr Max RPM
1 RPM Max RPM
16 15.6 700 45
Step 2: HP required to drive the Screw Conveyor
𝑯𝑷 = 𝑯𝑷 𝒇 + 𝑯𝑷 𝒎 + 𝑯𝑷𝒊𝒏𝒄𝒍𝒊𝒏𝒂𝒕𝒊𝒐𝒏
Where HPf=Horse Power to run an Empty Conveyor
HPm=Horse Power to run the loaded Conveyor
HPinclination=Extra Horse Power Required due to inclination
𝐻𝑃𝑓 =
𝐿 𝑁 𝐹𝑑 𝑓𝑏
1000000
Where, L=Total length of the conveyor = 50
N=Operation Speed = 45 RPM
Fd=Conveyor diameter Factor = 106
fb= Hanger Bearing Factor=4.4
∴ 𝐻𝑃1 =
50 × 45 × 106 × 4.4
1000000
∴ 𝑯𝑷 𝒇 = 𝟏. 𝟎𝟓 𝑯𝑷
Now,
𝐻𝑃𝑚 =
𝐶 𝐿 𝑊 𝐹𝑚 𝐹𝑓 𝐹𝑝
1000000
Where C= Capacity (ft3
/hr) = 555.55 ft3
/hr
W= Weight of the material =90 lb/ft3
Ff = Flight Factor = 1.0
Fp= Paddle Factor = 1.0
Fm=Material Factor = 2.0

30. 30
∴ 𝐻𝑃2 =
555.55 × 50 × 90 × 2 × 1 × 1
1000000
∴ 𝑯𝑷 𝒎 = 𝟓 𝑯𝑷
Now
𝐻𝑃3 =
𝑙𝑏
𝑚𝑖𝑛
× 𝐻𝑒𝑖𝑔ℎ𝑡 (𝑓𝑡)
33000
Where
𝑙𝑏
𝑚𝑖𝑛
= 833.33
𝑙𝑏
𝑚𝑖𝑛
Height = 50 × tan 45 = 8.816 𝑓𝑡
𝐻𝑃𝑖𝑛𝑐𝑙𝑖𝑛𝑎𝑡𝑖𝑜𝑛 =
833.33 × 8.816
33000
= 𝟎. 𝟐𝟐𝟐𝟔 𝑯𝑷
∴ 𝐻𝑃 = 𝐻𝑃𝑓 + 𝐻𝑃𝑚 + 𝐻𝑃𝑖𝑛𝑐𝑙𝑖𝑛𝑎𝑡𝑖𝑜𝑛
∴ 𝐻𝑃 = 0.74 + 4.51 + 0.05 = 𝟔. 𝟐𝟕 𝑯𝑷
Now
𝑇𝑜𝑡𝑎𝑙 𝐻𝑃 =
𝐻𝑃×𝐹0
𝑒
Where F0 = Overload Factor = 1.0
E= Screw Drive = 0.88
∴ 𝑇𝑜𝑡𝑎𝑙 𝐻𝑃 =
5.4 × 1
0.88
= 𝟕. 𝟏𝟐𝟓 𝑯𝑷
Step 3: Calculating Torque
𝑇𝑜𝑟𝑞𝑢𝑒 =
63025 × 𝐻𝑃
𝑅𝑃𝑀
=
63025 × 7.125
45
= 𝟗𝟗𝟕𝟖. 𝟗𝟓 𝒍𝒃. 𝒊𝒏
Step 4: Expansion of Screw Conveyor Handling Hot Materials
∆𝐿 = 𝐿(𝑡1 − 𝑡2)𝐶
Where ∆𝐿= Increment of change in length (in)=50 ft
t1= Upper limit of temperature (o
F)=250o
F
t2= Ambient temperature (o
F) = 73.4o
F
C= Coefficient of Linear Expansion = 9.9 x 10-6
∆𝐿 = 50 × 12 × 10−6
× 9.9 × (250 − 73.4)
∴ ∆𝑳 = 𝟏. 𝟎𝟒𝟗 𝒊𝒏

31. 31
5) PART MODEL AND ASSEMBLY DRAWINGS
COUPLING
DISCHARGE FLANGE

32. 32
DRIVE SHAFT
END SHAFT
HANGAR

33. 33
SCREW
TROUGH

34. 34

35. 35
ASSEMBLY MODELS
BALL BEARING

36. 36
REFERENCES
[1] "Flexible Screw Conveyors | Mix Integrity | How It Works" [Online] Accessed [12/07/2018]
[2] https://www.powderprocess.net/Dosing.htm [Online] Accssed [12/07/2018]
[3] [4] [5] [6] George E. Dieter, Linda C. Schmidt “ Engineering Design, Fifth Edition” [Accessed:
12/07/2018]