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NCDA Design Final Report

Team 7: Silo PackerTASA Engineering

Design Engineers:

Adel Abumohor215 Beau Tree Dr.

Wilmington, DE 19810(302) 369-5883(302) 475-7707

[email protected]

Jeff Acheson213 Sussex Hall

Newark, DE 19717(302) 837-8824

[email protected]

Pete Sullivan351 Paper Mill Rd.Newark, DE 19711

(302) [email protected]

J. Michael Tate209 Gilbert Hall ANewark, DE 19717

(302) [email protected]

mailto:[email protected]




Table of Contents

Table of Contents: 2Summary 4Introduction: 5

Background: 5Customers: 5Wants: 6Constraints: 7

Concept Generation 7System Benchmarks 7Functional Benchmarks 9Metrics 10Target Values 10Concept Generation 11

Concept Selection 14Evaluation 14

Experiments 15Constraints 17Metrics 18

Selection 19Construction 21

Fabrication 21Assembly 22

Concept Testing 23Testing Plan 23Results 24

Concept Refinement 24Redesign 24Suggested Modifications 25

Conclusion 26Drawings 28Budget 41Sketches 42

Executive Summary:

TASA was commissioned to design and build a prototype test silo loader for Dr. Limin

Kung of the University of Delaware Department of Animal and Food Science. Agricultural

researchers use apparatus like these to fill small test silos in order to test how different bacterial

and chemical agents inhibit the spoilage of silage materials. Dr. Kung is one of a list of seven

customers, all related to agriculture, that come from both academic and commercial fields and

are involved in research similar to that done at UD. These customers desire an apparatus which

can allow them to pack a test silo quickly and easily, but with high accuracy and precision. This

apparatus must improve upon their current method of packing and meet storage requirements

and a very small budget.

We began addressing the problem by benchmarking various systems. We broke our

design into different functions like compacting devices and pressure sensors and determined

which items were the best in their particular area. In order to evaluate our benchmarks and also

our own concepts we distilled the customers wants into a list of ten metrics. We proposed

targets from our benchmarking and determined which metrics were critical to our design and

which were only peripheral to it.

We created concepts using our benchmarking as a foundation for ideas, but also reaching

beyond it for new and interesting concepts that may give us an edge on the competition. Our

concepts were grouped into four families of related ideas; extruders, horizontal pistons, vertical

pistons, and the “other” group.

We performed a series of experiments in order to test basic concepts used in all our

designs and to also determine some basic silage properties. We eliminated some designs because

their costs exceeded our budget limit. We ranked the concepts that were left against our critical

metrics in order to get a rough comparison and then did a complete ranking of the front-runners

in order to determine which concept was truly the best analytically. We took our best concept, a

vertical pneumatic piston, and designed its various components.

We fabricated a prototype from these parts designs and then created a testing procedure

for this prototype. Using the results from the testing procedure, we charted its performance

within our metrics. We evaluated the prototype’s performance against the target values set by

the metrics and made minor redesigns to specific areas. We also showed the original prototype

to Dr. Kung, who had some of his own comments.

We then slightly redesigned and rebuilt the prototype into order to increase the design’s

performance in several metrics and in order to create a safer final product. The end result is the

final prototype which was presented on Friday, April 23.

Introduction:

Background:

Silos are widespread in agricultural use to store livestock feed due to their low cost and

simple design. The basic concept behind the silage process is that bacteria use up all the oxygen

in the silo and so the silage material (the material which is packed inside the silo) doesn’t spoil

for extended periods as long as no oxygen is allowed to enter the storage system.

Due to its widespread use in agriculture, there is a substantial amount of research

currently being done by various commercial and academic groups into how to improve the silage

process. These groups perform numerous experiments on small test silos ranging in side from

eight inch PVC pipes to 5-gallon paint buckets. These silos model the larger systems found in

agricultural use, but do not naturally pack under the weight of their silage as farm silos do. For

this reason they are packed by personnel in these research groups, usually by some method

which utilized their own body weight.

Current packing methods are based around multiplying the users body weights by means

of a simple lever (for the small silos), and compressing the material in the large silos with the

packers’ feet. Due to the large number of these silos which must be filled, these methods often

fail to relieve the tedium and physical rigor of packing up to fifty silos at a sitting. An entire

work crew usually undertakes this task, but it is still not a pleasant duty for the individuals

involved. Also, since the packing methods are dependent upon body weight, different packers

give different packing results which is bad for research precision. These reasons demand a

design to automate the packing process.

TASA was commissioned to design and build a prototype experimental silo packer for

Dr. Limin Kung of the University of Delaware Department of Food and Animal Science. This

prototype should be able to quickly and reproducibly load a test silo without requiring extensive

manpower.

Customers:

Dr. Kung formed the basis for our customer group. We also consulted with Navin

Ranjit, one of Dr. Kung’s research assistants, in order to get the future user’s perspective. We

interviewed Richard Morris, the UD agricultural farmer whose farm will be where the proposed

apparatus will be stored and used. After this our customers branch out to other academic

researchers like Dr. Martin Stokes of the University of Maine and Dr. Joseph Harrison of

Washington State University, both of whom are doing research similar to Dr. Kung. We also

contacted commercial customers such as Chris Roden of Chr.Hansen Biosystems and Carol

Meyers of Kemin Industries. Both of these people are with agricultural chemical and bacteria

suppliers who also perform experiments similar to Dr. Kung’s. We prioritized these customers

in Table 1 in order to enable us to create a quantitative ranking of their wants.

Table 1 – List of CustomersRank Customer Organization Rate of Importance

1 Dr. Limin Kung UD Ag Department 0.502 Navin Ranjit UD Ag Department 0.253 Richard Morris UD Ag Farmer 0.054 Dr. Martin Stokes University of Maine 0.055 Dr. Joseph Harrison Washington State University 0.056 Chris Roden Chr.Hansen Biosystems 0.057 Carol Meyers Kemin Industries 0.05

These customers expressed various different desires. We took each of our customers and

listed each of their wants, prioritized them numerically by using the weighting shown in Table

2.

Table 2 – Rate of Importance of Individual Customer WantsCustomer’s Want Rank Rate of Importance

1 0.252 0.203 0.154 0.155 0.106 0.107 0.05

The top ten of the wants mentioned are listed in Table 3 in a prioritized order. Some wants,

like reproducing desired results, stem from the design’s use as precision laboratory equipment. Other wants are

related to the desires to reduce the physical exertion and tedium of the packing process. Still other wants are

related to the desire to minimize the immediate and future expenditures on the group’s part and also ensure a long

operating life for the equipment. The Rate of Importance column, which was used to derive the final ranking of

the wants, is a normalized weighted average of each individual customer’s wants.

Table 3 – Net Customer Wants

Final Rank Want Rate of Importance1 Reproduce Desired Results 0.2492 Not Physically Demanding 0.2283 Fast Operation 0.1314 Simple User Operation 0.0915 Low Cost 0.0766 Easy To Clean 0.0677 Easy to Repair/Manufacture 0.0618 Easy to Transport 0.0589 Variable Silo Size 0.02410 Easy to Store 0.015

The customers also expressed certain constraints that had to be met by the final design.

Our design must be able to pass through a normal doorway, be movable by two people, be able

pack a silo as fast as current methods, be able to prevent the stopper from being recessed more

than a centimeter into the silo, and be built for under five hundred dollars. Most of these

constraints are derived from physical needs of storage and methods that will be used to extract

silage from the test silos themselves.

Concept Generation:

System Benchmarking:

Our team benchmarked a wide variety of systems that perform applications similar to the

job which will be accomplished by the silo packer, these systems are shown in Table 4 in ranked

order of importance.

Table 4 – System BenchmarksRank System

1 Stokes Pneumatic Loader2 Stokes Front End Loader3 Trash Compactors4 Shot-shell and Cartridge Loaders5 Pharmaceutical Capsule Filling Machines6 Soda Can Crushers

7 Current Apparatus

The Stokes Pneumatic Loader is a vertically mounted pneumatic piston driven by an air

compressor. Silage is put into the test silo and an attached filling tube mounted on top of the

silo. The piston then compresses the contents of the silo and the filling tube into the silo at high

pressure. A similar apparatus is also in service with Carol Myers of Kemin Industries.

The Stokes Front End Loader is used to compress the larger test silos. One five-gallon

bucket is filled with silage and another large bucket is put on top of it. A small front-end loader

then is used; its hydraulic scoop presses the top bucket into the lower one. The result is a large,

compressed silo. This works well, but the exact pressure exerted onto the silage is hard to

measure and sometimes damage can occur to the silos if the Bobcat operator is not well trained.

Trash compactors have the necessary ability to compact all types of materials. Trash

compactors do not usually put them in any sort of container however and they crush objects to

uniform volume but do not apply a uniform pressure. They do operate quickly and efficiently

however.

Shotshell and cartridge loaders have many of the characteristics we are looking for in a

design. The have a feed bin full of material, in this case gun powder, which can be precisely

loaded into a cylindrical container, in this case a bullet casing. The powder is then compressed

in the casing using a piston on a crank. The apparatus is very precise and accurate and is quite

fast as well, but is too small for our needs.

Pharmaceutical capsule filling machines precisely fill objects with a predetermined

amount of material. They do many small capsules at once with multiple pressing fingers and are

very precise because of this approach. The problem here is that these materials are not fibrous

like silage, they are powders or grains which have better packing and filling properties. This

apparatus is also very expensive.

Soda can crushers have the right components for a manually powered silo packer if it

were scaled up properly. A lever is used to apply a pressure to an object, in this case it would

have to be the silage not the silo itself. This apparatus is cheap, but cannot exert enough

pressure and would be labor intensive.

After comparing the system benchmarks, we determined that our strongest competitor is

the Stokes Pneumatic Loader. It is less expensive that some of the other systems and its

pneumatic piston provides excellent precision and accuracy while not sacrificing power.

Functional Benchmarking:

After we completed our system benchmarking we examined our various system

benchmarks for simple component functions which they held in common. From this, we

determined specific functons which individual parts of the design would have to accomplish.

These functions are compacting, material transport, container transport, pressure sensors, and

user controllers. This section is dedicated to an overview of the research we did with these as

well.

We examined compacting devices like power presses, pneumatic pistons, extrusion

screws, and pile drivers. After comparing these to each other and our wants, we determined that

the pneumatic piston is the best practice due to its low price and excellent mix of precision and

accuracy in pressure production.

Material transport was looked at with different mechanisms from the lawnmowers and

vacuum cleaners to hydraulic rams and extrusion screws. The best practice in this category is

the screw feeder because it reduces the number of necessary user actions and is highly

compatible with the test silo’s circular geometry.

The silo container itself can be moved through a variety of different methods from the

human hand to a conveyor. The conveyor belt is the best practice here. It is widely used,

inexpensive and is simple to use.

We looked at a multitude of products for measuring pressures ranging from piezoelectric

mats to load cells. The best practice here is the piezoelectric pressure sensor because it is the

most accurate and precise, but unfortunately it is priced much too high for our budget.

We looked at multiple ways to control our apparatus from push buttons to computer

keyboards, but we believe that the foot pedal is the best practice because it leaves the users hands

free for other activities.

Metrics:

From the list of wants we initially created upon talking to our customers, we created a list

of starting metrics that we felt would accurately measure their various desires. Table 5 consists of

a list of the top ten metrics cross-referenced with the want or wants they were derived from and their target values.

Table 5 - MetricsRank Metric Most Relevant

WantsTarget Value Target Derivation

1 Number of User Actions

Simple User Operation

3 Stokes Loader

2 Pressure Per Layer Reproducing Desired Results

100 psi Current Methods

3 Change in Pressure Reproducing Desired Results

30 psi Current Methods

4 Operating Force Not Physically Demanding

20 lbs OSHA Standards

5 Total Cost Low Cost $500 Budget6 Total Time to Fill Fast Operation 80 seconds Current Methods7 Number of Users Fast and Simple 2 Stokes Loader

Operation 8 Storage Volume Easy to Store and

Transport36 cubic ft. Current Apparatus

9 Number of Silo Sizes

Variable Silo Size 2 Stokes Loader

10 Weight Easily Transportable

88 lbs OSHA Standards

From this list of metrics in Table 5, we determined that the most critical metrics in our

design were the pressure metrics (total and per layer), the time to fill, and the operating force.

These along with the low cost metric, which comes into play due to our low budget, form the

core that we used to roughly rank our concepts. We chose these as the chief metrics for

evaluation because they were simple, but spoke directly to many of our leading customers wants

like Reproduce Desired Results, Not Physically Demanding, and Fast Operation.

We had to discard the “Number of User Actions” want from the list of critical metrics

despite the fact is that it is our highest rated metric. It is simply not a good metric for critical

ranking because it is had to measure between concepts, and is potentially very similar for a wide

range of designs. It is also highly depended on the number of users operating the system

simultaneously.

Concept Generation:

Concept generation began by looking at the competitors and seeing what processes they

used to create their apparatuses. From there the focus was turned to the best practices in order

beat our competitors by integrating better technology or cheaper systems into our designs.

Concepts are located in several different families with branches that encompass

variations on the same idea. This tree structure logically occurs during any brainstorming

session when one idea leads to another and a good basic concept branches into many variations.

We attempted to use as many of the best practices in the creation of these concepts as possible,

but due to budget limits many of these we not able to integrate many of these systems into the

listed concepts.

Please note that if these written descriptions are not enough to understand the concept,

there are simple schematics of the concepts listed by concepts name and number in the Sketches

Appendix. Also be advised that these are not the only designs that were conceptualized, but, for

the sake of report brevity, we chose not to include all of the six or seven different concepts that

fit in most of the families. We also wanted to convey the breadth of different design concepts

rather that focus on a single area.

1 Extrusion

The Extruders come into play because their extrusion screw allows for continuous

feeding from a storage bin. They incorporate the best material transport benchmark, but

do not include many of the others due to their nature.

1.1 Straight Extruder: This is a classic extruder design. A screw is mounted to a

motor horizontally and draws the silage from a large feed bin and moves it down

into the test silo which is mounted horizontally at the end of the screw. A

constant pressure is kept at the silo end of the screw because the silo is mounted

into a carriage which allows it to move. The screw is always feeding new silage

in at the top of the previously compacted silage, until the silo moves so far back

that it trips a kill switch.

1.2 Tapering Extruder: This is similar to the design above, only instead of a standard

screw, this unit’s screw has a section of changing radius. As the silage moves

into the silo, it has already begun compacting because of the screw taper. It

enters the silo and is completely compacted from there. The pressure would be

regulated as above, but might not have to be as high as in the above case due to

the screw’s influence on compacting.

2 Horizontal Piston

These systems use the pistons which form the best compaction benchmark. They feature

a pneumatic piston and silo which are mounted horizontally.

2.1 Gravity Fed Piston: The compression chamber of the piston is filled with a mass

of silage falling from a bin above the chamber. This silage is then pressed into

the silo by the piston. The process of loading and pressing continues until the silo

is full.

2.2 Hand Fed Piston: The compression chamber of this system is filled by smaller

loads of silage than before. These loads are dropped into the compression

chamber by using a chute in the chamber’s top. This silage is then pressed into

the silo by the piston. As before, the process of loading and pressing continues

until the silo is full.

3 Vertical Piston

These systems use the pistons which form the best compaction benchmark. They feature

a pneumatic piston and silo which are mounted vertically.

3.1 Pneumatic Piston with a Vibrating Chute: The complete filling of the silo takes

several iterations of this process and between piston shots the silo is refilled by

sliding silage down into it through a chute which connects to an opening in the

feeding area’s wall. In order to keep the silage moving this ramp is being

vibrated.

3.2 Pneumatic Piston with a Screw Feeder: This design is very similar to the above,

but the feeding chamber and silo are filled with a screw feeder from a large bin

when the piston is not in operation instead of a chute. This is different because it

will allow a much larger feeding bin than the previous concept and utilized one of

our best function benchmarks.

3.3 Crank-Slider with a Hand Loader: This uses an electric motor to power a four-

bar slider mechanism which packs the silage found in the silo and feeding

chamber. The silage is fed into the feeding chamber from a horizontal chute. An

operator is pushing silage through this chute into the feeding chamber with a hand

held pushing tool, similar to what is found in food processors.

4 Other

These are not considered entirely practical, but may be considered innovative solutions to

the problem.

4.1 Centrifuge: Several silos are positioned in arms of centrifuge and spun at high

rates of speed. Silage is fed down a tube in the center of the centrifuge and is

dispersed into each of the arms through the centrifugal force. This design could

load many silos at once, but would have a hard time only filling one because of

possible loading imbalances.

4.2 Blower: Silage is blown from a feed bin into the silo at high velocity. This

sudden impact partially compacts the silage and the impact of the silage filling the

silo on top of it finishes the job. This design will most likely have problems due

to the cylindrical cross section of the silo as opposed to the rectangular cross-

section of many blowers.

4.3 Weight Press: Silage is fed into the silo through a chute and is then compacted

through the use of a piston on linear bearings. This piston is rigidly attached to a

step on the side of the apparatus. Operators apply force due to their body weight

to the step when the stand on it, the step is of course hooked to a scale so that the

force exerted by the people on the step can be kept relatively constant.

Concept Selection:

Evaluation:

Our first step in the evaluation process was to do testing on the applicability of several of

our design concepts. Using a clear plastic cylinder of roughly the same dimensions as a test silo,

we started to examine how well silage packed with the different orientations of the silo and

different sizes of the piston. After this we examined the properties of silage in relation to how it

slid and moved through channels.

Diameter Changes and Plungers Design:

The first step we took was qualitatively examine effect lips and sudden changes in

diameter had on the packing process.

1) Our initial experiment used a plunger of the same diameter as the silo’s interior and it

showed us immediate problems with such a design. As the plunger moved from the wider

diameter region into the smaller silo, it invariably jammed with silage and was unable to

enter the silo for more the a few millimeters. Even with several people pressing on the

plunger, the silage prevented any and all movement of the plunger past the lip.

2) After this we attempted to compress the silage with a plunger that was noticeably smaller

than the interior diameter of the silo. It passed through the silage around the lip and was

successfully able to enter into the silo. Yet, as our clear test silo showed us, was able to

relatively uniformly compress the silage in the silo itself despite not covering the silos entire

cross-sectional area. This method is not perfect however, we experimented with looser and

denser packing and discovered that the more dense the packing the greater the likelihood of a

jam. We also experimented with the amount of silage that was to be packed and discovered

that the more silage that was used, the higher the chance of jamming.

3) We concluded that lips of any form should be avoided in our final design and the piston

should be smaller in radius than the silo to hopefully avoid jamming.

Orientation:

We examined silo orientation in relation to the uniformity of packing.

1) Our first trials were conducted with a vertical cylinder using small and large packing

volumes. The orientation performed well and uniformly packed the material through

repeated iterations. We noticed that once the silage was packed it tended to stay in the place,

the compacted silage moved very little when fresh silage was compacted on top of it.

2) We then switched to a horizontal packing scheme and had our fears about this orientation

confirmed, small silage loads do not pack uniformly. If a silage load is added which does

not completely fill the silo’s cross-section, the packed silage will contain air spaces that run

down the top of the silo. Repeated packing of small silage loads does not alleviate this

problem either as the new silage does not compact the old. This silo orientation also has an

inherent lip in its design where the silage feeds into the compression chamber. If it is

overfilled the piston is more likely to jam, if it is under-filled the packing will be highly non-

uniform.

3) A horizontal silo orientation will not produce reliable results, the silo must be oriented

vertically.

Silage Properties:

We then tested some simple silage properties to see what types of silo loading

mechanisms we could use for the apparatus.

1) First we looked at silage slipping down plates of two different materials. We used the slip

angle to approximate friction for the silage. For both materials the silage began to slip at

approximately 400, a relatively high angle to pitch any kind of chute. We also noticed that

all the silage did not slip, often some residual silage was left on the plate even when it was

tilted to 900. This occurred less when the silage was compressed before it was placed on the

plate.

2) Next we attempted to throw the silage down the plate with a small initial velocity to see if it

would continue to slide. This did not occur and the silage usually stopped within a few

inches from where it touched the plate.

3) Next we examined how silage moved down a two inch wide aluminum channel. Motion was

highly dependent upon the amount of silage used and the silage slipped down the channel

under its own weight at approximately 450 of incline. We also discovered that the more

silage, the greater the slope of the plate before the silage begins to move. This is most likely

due to contact between the silage and the walls of the channel.

4) Lastly, we examined what effect a narrowing channel has. We built a channel that narrowed

down to the two inch channel to see if such a feeding ramp would work. Results depended

on the amount of silage, as did the results for the channel, but some things were the same for

all tests. The area where the angled sides changed over to the two inch straight channel was

always trouble spot. The silage could use the angled sides for support even when the channel

was tilted to 900.

5) The conclusion we drew from these experiments is that the silage must be forcibly fed into

the compression chamber, it will not just slide there under its own weight.

Constraints:

Next we eliminated designs which did not fit our customer constraints. Our design must

be able to pass through a normal doorway, be moved by two people, pack a silo as fast as current

methods, prevent the stopper from being recessed more than a centimeter into the silo, and be

built for under five hundred dollars. After pricing the screws necessary to build the extrusion

designs, we realized that they were not possible without going over budget. The designs which

use electrical motors will require both a motor and a transmission to gear the motors down

enough to operate at the desired speed and force. This raises their price above the budget

constraints as well. The pneumatic piston designs also have problems working under the budget,

but the farm has both a portable compressor and airlines which are available to our primary

customer. This means that these items do not need to be purchased and that the pneumatic

designs fall below the budget cap.

Metrics:

After using our constraints and the data from the experiments that were conducted, we

were able to eliminate five of the original ten proposed designs as unfeasible. The remaining

five designs were compared using our critical metrics in order to narrow the field further. Table

6 shows how they compare.

Table 6 – Critical MetricsRank Name Pressure per

Layer (PPL)(psi)

Change in PPL

(psi)

Operating Force (lbs)

Total Cost ($)

Total Time to Fill (s)

1 Piston With a Hand Feeder

100/100 5/30 15/20 600/500 65/80

2 Piston with Vibrating Chute

100/100 5/30 15/20 500/500 80/80

3 Weight Press 100/100 20/30 100+/20 300/500 80/804 Centrifuge 75/100 30/30 5/20 500/500 120/805 Blower 50/100 30/30 5/20 500/500 40/80

It is relatively obvious that the weight last three design are not in contention with the first

two due to bad reproducibility or shear repeated physical exertion. After looking at these critical

metrics, we can weed these five possible designs into two leading contenders which we will now

examine further using all of our metrics. Table 7 shows the comparison between the two designs along

with the set target values for each metric and each metric’s relative rate of importance.

Table 7 – Final Competing DesignsMetric Rate of

ImportanceTarget Value Hand Fed

Crank SliderVibrating Chute

Number of User Actions

0.145 3 3 3

Pressure Per Layer 0.124 100 psi 100 psi 100Change in Pressure 0.124 30 psi 5 psi 5 psi

Operating Force 0.112 20 lbs 15 lbs 15 lbsTotal Cost 0.110 $500 $600 $500

Total Time to Fill 0.085 80 sec 65 sec 80 sec

Number of Users 0.067 2 2 2Storage Volume 0.061 36 cubic ft. 11.5 cubic ft. 11.5 cubic ft.

Number of Silo Sizes 0.058 2 1 1Weight 0.046 88 lbs 60 lbs 60 lbs.

As is plain to see from our metrics, the hand fed Crank-slider is better than its

competitor, the vibrating feeder in terms of the required time to fill a silo. The hand feeder

actually pushes the silage into the compression chamber, allowing for fast and reliable loading.

The vibrating chute may work well, but it will be prone to clogging if it is overfilled and it lacks

an easy means to clear these blockages. While the hand-feeder is cheaper than any system for

vibrating our loading chute, the motor and transmission for the slider crank is much more

expensive than the pneumatic cylinder.

Final Selection:

The team conducted experiments to determine silage’s material properties and used them

to determine which designs would perform well and which would most likely suffer problems

that would reduce their effectiveness. Then the team made sure than the design could be built

within or very close to our budget. We took the remaining designs that lacked significant

problems and ranked them according to our critical metrics (for brevity). Finally we took the

best parts of these designs and combined them to form the final concept which will go to

prototype.

Let us now go into more depth with the final concept. Engineering drawings are located

in the next section of the report if these text descriptions are not clear enough.

There are a few basic sections to this design; the piston, the frame, the door, the silo

mount, the silo and extension, the electrical setup, and the pneumatic equipment.

The piston is a 16 in. stroke, 2.5 in. diameter pneumatic cylinder with a 1 in diameter

driving rod. Its large stroke length allows for a large compression chamber which can be filled

with silage and its bore size gives a high factor of safety in compression. The large driving rod

allows the piston to accept high shear loading which may be caused by silage binding around the

sides of the piston. Indepth analysis on the piston itself is in the analysis appendix.

The frame is made of two basic pieces: the beam and the plate. The tube is a vertical

piece of 0.25 in. wall, 2in by 2in steel square tubing 40 inches in length. It accepts the high

moment loads of the piston, is large and therefore easy to fasten other components to, and has a

high factor of safety to take into account any stress concentrations around bolt holes, etc. The

plate is 3/8 in steel plate. It is the surface upon which the silo sits and accepts the high bending

load of the piston. These two pieces are welded together at the base of the tube. The analysis of

the frame is in the solid mechanics analysis appendix.

The door is made of 1/16 steel sheet. Its main feature is a large opening which is cut in

the center of its length in order to allow the viewing of the piston’s position. It has 4, ¾ in.

aluminum ribs to give it bending strength along its curved surface. It also has 2 vertical side ribs

to give it strength in the axial direction and allow for easier hinge fixation. The door is attached

to the silo mounts by hinges and is held closer by an automobile trunk mechanism.

The silo mounts themselves are made of aluminum for easy machining. They have

curved surfaces which accept the silo and put it on the pistons axis. There are four mounts

placed along the 16 inch length of the silo and extension. These are bolted to the frame.

The silo and extension are made up of a standard 8 in. long by 2 in. diameter PVC test

silo. The extension is a clear plexiglass tube 8 in. long and 2 in. in internal diameter. These two

are connected using a rubber plumbing coupler. The internal diameters of both objects are the

same. This part of the system is removable so that several silos and their extension can be filled

while another is being packed.

The electrical equipment is made up of several components. A limit switch prevents the

apparatus from operating when the door is open. A fuse protects the system from surges and

other phenomenon. A red light tells the operator when the system is live. A rocker switch

completes the circuit and energizes the solenoids in the spool valve allowing the piston to move.

The switch is spring loaded so that the piston always stops if someone is not actively using the

switch. The electrical system runs off a standard household 110 line.

The pneumatic system also has many parts. A regulator is used to monitor and vary the

pressure in the system and the resulting piston force. A safety valve protects the other parts of

the system from damage due to excessive pressure. A needle valve allows the user to alter the

speed at which the piston operates. A spool valve is connected to the electrical system and

governs the direction in which the air flows through the pneumatic cylinder.

Construction

Fabrication

This took place in the machine shop at Spencer Lab and also at the machine shop in 124

Worrilow Hall. A complete section of drawings is found in the drawings appendix.

Because the most of the components of the system were designed to be machined at

relatively low tolerances, we were able to avoid using expensive machine tools like the

Bridgeport Mills in favor of cheaper, less precise tools like a simple drill press.

Most of the parts of the pneumatic and electric systems were bought, not built. Most of

the major electrical components can be bought from Radio Shack’s standard stock. Most of the

pneumatic components can be purchased from Granger and delivered in only a day. This makes

the system both easy to build and easy to repair if parts break due to extended use or even

misuse.

Most of the components are bolted or screwed into the final design. If they need to be

removed or replaced for any reason, this can be done quickly and easily. The steel frame itself

was welded into one piece to provide a solid piece on which all the other system components can

be attached.

Most components are made of mild steel in order to be inexpensive and strong enough to

take repeated use. A few parts, like the pistons themselves and the silo mounts, are made of

aluminum. Aluminum was used because of the relative ease of machining it for the silo mounts

and its resistance to corrosion in the case of the piston heads.

Assembly

Assembly took place at 124 Worrilow Hall. Final assembly uses a minimum number of

tools. Final assembly only required a flat head and philips head screwdriver, 7/16 in wrench, ½

in wrench, and a 9/16 in wrench.

System Testing

Testing Plan:

After the prototype was built, its performance had to be compared to the metric target

values. This required a period of testing using a specific testing plan.

1) The prototype was weighted and then a rough estimate of the storage space it will take up

was made using the exterior dimensions of the packer.

2) The operating force was estimated after taking the force that was required to operate various

different components. The highest operating force required to operate the packer is the force

required to close the door because of the strength of the door latch.

3) Total cost was calculated from the amount spent to date.

4) The number of silo sizes can be calculated by inspection.

5) The packing time for one person packing a single silo was taken. Different individuals were

used in order to ascertain the level of skill required to operate the packer and whether the

filling time was variant with the user.

6) The packing time for a group of users was taken in order to take into account the effect

multiple packers will have on the system. The old apparatus is designed to be used with

multiple individuals packing the silos in order to speed the packing time. Our apparatus is

packed similarly since the silo and extension can be changed easily between packs.

7) Using the old apparatus we found an average mass of packed silage in a silo. Trials were

then conducted calculating the effect of the change in pressure on the packed density of the

silage. It was found that, while the packer can operate at 100 psi, it packs best at 65 psi. The

amount of silage packed is the same as with previous equipment, but the lower packing

pressure prevents the silage from blowing the lower stopper off the silo as the silage

elastically expands after it is packed.

8) We measured the variation in packing pressure by examining the dynamic fluctuation in

system pressure during the packing of several test silos.

Results:

The results from these various experiments are reported in Table 8. As you can see the

silo packer prototype beats the targeted values in every way except in the number of silo sizes.

We consulted our primary customer and he approved of this in order to keep the final costs of

the project down since we had deliberately solved the problem for the more difficult of the test

silo types.

Table 8 - Test DataMetric Target Value Prototype

Number of User Actions 3 3Max Pressure Per Layer 100 psi 100 psiChange in Pressure 30 psi 5 psiOperating Force 20 lbs 5 lbsTotal Cost $500 $450Total Time to Fill 80 sec 80 secNumber of Users 2 2Storage Volume 36 cubic ft. 4 cubic ft.Number of Silo Sizes 2 1Weight 88 lbs 42 lbs

The primary information learned from testing was that our machine produced results that

were comparable to the results from the old machine. This meant that the pressure per layer and

change in pressure per layer were correct because they were satisfactory in the old machine. We

also learned that our machine is significantly faster than the old machine when filling multiple

silos and at least as fast for filling a single silo while requiring less user effort to do either.

Weight and measurement tests showed that our machine fell well under the maximum values set

for both weight and volume. By filling multiple silos using a variety of user configurations, we

found that the optimum setup for minimum filling time is to have one user fill silo / sleeve units

while the other loads the pre filled units into the machine and compresses them. This test caused

us to make more filling sleeves to keep the second user busy while waiting for the first user to

finish his task.

Redesign:

Current Improvements:

The system underwent minor changes to make small improvements in its overall

performance:

1) We added handles and knobs to make it easier to close the door and easier to use the door

release.

2) We added steel safety shields around the sides of the silo mounts and between the silo

mounts and the bottom edge of the pneumatic piston. This removes some safety concerns

because fingers cannot be placed in a position where they could be crushed by the piston.

3) We extended the length of the door so that it reaches from the base plate to the bottom of the

pneumatic piston. This removes some safety concerns because fingers cannot be placed in a

position where they could be crushed by the piston.

4) We gave all the steel parts a coat of primer and a paint job in order to prevent corrosion from

the low pH silage juice and the environment in general.

Suggested Future Improvements:

The following areas could be improved in the future:

1) The door design is rigorous and complex, more rigorous and complex than it really needs to

be. A massed produced packer should remove many of the ribs to save weight.

2) The current design uses a donated spool valve. While this reduces cost, the current valve is

larger and more powerful than is really necessary for our design. A smaller more portable

valve would be preferable if another packer were to be built.

3) The system is rather loud. This sound comes from the exhaust of the pneumatic piston after

its direction is changed. We compensated for this by adding elbows which direct the sound

away from the users, but silencers would be a better solution to this problem because they

would baffle the sound entirely.

Conclusion

TASA was commissioned to design and build a prototype test silo loader for Dr. Limin

Kung of the University of Delaware Agricultural Department. We created a customer list and

benchmarked various systems. We broke our design into different functions like compacting

devices and pressure sensors and did further benchmarking to determine which items were the

best in their particular area. We distilled the customers wants into a list of ten metrics found.

We proposed targets from our benchmarking and determined which metrics were critical to our

design and which were only peripheral to it.

We created concepts using our benchmarking as a foundation for ideas, but also reached

beyond it for new and interesting concepts that may give us an edge on the competition. We

performed a series of experiments in order to test basic concepts used in all our designs and to

also determine some basic silage properties. We eliminated some designs and ranked the

concepts that remained. We took our best design, a vertical pneumatic piston, and designed its

various parts.

We fabricated a prototype from these parts designs and then created a testing procedure

for this prototype. Using the results from the testing procedure in order to chart its performance

within our metrics. We evaluated the prototype’s performance against the target values set by

the metrics and made minor redesigns to specific areas. We also showed the original prototype

to Dr. Kung, who had some of his own comments.

We then slightly redesigned and rebuilt the prototype into order to increase the design’s

performance in several metrics and in order to create a safer final product. The end result was

the final prototype which was presented on Friday, April 23. The system met and in mnost case

exceeded all our customer’s wants and constraints except one, the multiple silo want. After

consultation with the primary customer this is acceptable.

Our customer is more than satisfied with our work and is looking forward to being able

to use the completed apparatus when his testing begins again this summer.

Appendix I:

Concept Schematics:

1 Extrusion

1.1 Straight Extruder

1.2 Tapered Extruder

2 Horizontal Piston

2.1 Gravity Fed Piston

2.2 Hand Fed Piston

3 Vertical Piston

3.1 Pneumatic Piston with a Vibrating Chute

3.2 Pneumatic Piston with a Vibrating Chute

3.3 Crank Slider

4 Other

4.1 Centrifuge

4.2 Blower

4.3 Weight Press

Appendix II:

Design Analysis

Solid Mechanics Analysis

Bending Stress in the Main Beam

The main frame piece is a beam of 2in X 2in., 1/4in wall, steel square tubing. We need to make sure that this steel is strong enough to take any bending stresses we put on it.

M = F*l = (2.5in/2)2*125 psi*3 in.= 920 in*lbsc = 1 inI = 0.108 in4

Y of Steel = 30000 psiSafety Factor = 3.52 psi

This is a good safety factor for the beam, especially considering the stress concentrations around the bolts and other holes in the system.

Bending Stress at Weld:

The base plate joins the main beam at a weld. We need to make sure that the plate is strong enough to withstand the bending stress caused by the piston.

t = 3/8 inw = 3 in.M = F*l = (2.5in/2)2*125 psi*3 in.= 920 in*lbs

Y of Steel = 30000 psiSafety Factor = 2.3

This is a modest but acceptable safety factor on the steel plate.

Pneumatic System Analysis

The analysis of the pneumatics system consists of the following parts:

1) Determination of pneumatic cylinder size2) Determination of piping size

The objective of this analysis was to see if ¼” piping did not have pressure losses too high.

3) Compressor engine/pump sizeThe compressor duty cycle was found to determine compressor pump size.

4) Accumulator sizeThe change in pressure in accumulator was found after an extension of pneumatic cylinder to see what accumulator size is necessary such that the pressure in the accumulator doesn’t drop too much.

Determination of Pneumatic Cylinder Size

Three choices needed to be made in choosing the pneumatic cylinder:Stroke length- A stroke length of 16 inches was chosen because the plunger needed to clear sum

of the lengths of the silo and silo sleave.Bore Size- The packing force produced by the pneumatic cylinder can be found by integrating

the cylinder pressure over the area of the bore. Also, sticking force needed to be accounted for which sometimes can be as high as 50% (Parker Fluid Power) of the total pushing force. We desired a pushing force of 300 pounds. Taking into account stickage, we found that a 3in bore cylinder was necessary. Dr. Kung adamantly refused to pay for a 3in bore cylinder. Therefore we went with the 2.5in bore cylinder.

Rod Diameter- The pneumatic cylinder manufacturer offered two rod diameter sizes for the 2.5 in bore cylinders. These were ½”, 5/8”. The ½” rod could withstand the buckling force(this analysis was done using the Parker Fluid Power charts for pneumatic cylinder buckling). However we went with the 5/8” rod based on possibly substantial side force loading during silo packing.

Side force

Determination of Piping Size:

The purpose of this analysis is to calculate the piping size such that the pneumatic cylinder can move from the retracted position to the fully extended position in one second. The dynamic pressure losses should not add up to more than half of the inlet pressure. That is: Given an inlet pressure of 115psi, dynamic pressure loss should not be more than 58psi. At half inlet pressure, the pressure should be strong enough to ensure no stickage (Parker FluidPower recommends that 50% of the pneumatic cylinder’s power may be lost due to stickage.)

Path of Compressed Air

1) Piggy Back Filter/regulator

2) Elbow: K=.9

11) Elbow: K=.9

3) Needle Valve

4) length 1

10) length 2

6) sudden expansion: K=.8

12) sudden expansion: K=.4

5) Elbow: K=.9

9) Elbow: K=.9

8) sudden contraction: K=.4

7) spool valve: K=4

Each component has a pressure drop. The analysis of each pressure drop varied. One of four methods were used to determine the pressure drops over each component:

1) Pressure given by manufacturer2) Equation for determining pressure drop was given by the manufacturer3) Moody Chart

4) Loss Coefficient, K

Results for ¼” piping:

Pressure into component (psi) Pressure loss (psi)1) Piggy Back 115.00 15.002) Elbow 100.00 0.863) Needle valve 99.14 9.934) Tube length1 89.21 1.095) Elbow 88.13 0.766) Sudden exp. 87.37 0.677) Spool Valve 86.70 3.318) Sudden Contraction 83.39 0.329) Elbow 83.07 0.7110) Tube length2 82.36 0.6811) Elbow 81.68 0.7012) Sudden expansion 80.97 0.70Pfinal 80.28

A final pressure of 80.28psi is adequate for our purposes. Therefore ¼” piping was used. Only the circuit, which controlled the extension of the pneumatic cylinder, was analyzed as the circuit, which controlled retraction, was virtually identical. The spreadsheet analysis can be found on the following page.

Pressure Losses Through System

P (psi) Pa (psi) G Q (SFCM) Q (m^3/s) loss: Cv Temp (R) K rho (kg/m^3) d (m) V (m/s) g (m/s^2)

L (m) mu (kg/ms)

Re f delta P (psi)

1 115 24.5 15

2 100 24.5 0.0012848 0.9 8 0.0064 40.57 0.8593267

3 99.14 15 1 24.5 0.78 530 7.9312539 9.9291097

4 89.21 7.1369251 0.0064 40.57 9.81 0.3 1.80E-05 1.02E+05 2.70E-02 1.0865463

5 88.13 24.5 0.0012848 0.9 7.0500014 0.0064 40.57 0.7572818

6 87.37 24.5 0.0012848 0.8 6.9894188 0.0064 40.57 0.6673549

7 86.7 24.5 0.0012848 4 6.9360304 0.0064 40.57 3.3112868

8 83.39 24.5 0.0012848 0.4 6.6711275 0.0064 40.57 0.3184821

9 83.07 24.5 0.0012848 0.9 6.6456489 0.0064 40.57 0.713848

10 82.36 6.5885411 0.0064 40.57 9.81 0.3 1.80E-05 9.43E+04 2.20E-02 0.6810893

11 81.68 24.5 0.0012848 0.9 6.534054 0.0064 40.57 0.7018609

12 80.97 24.5 0.0012848 0.9 6.4779051 0.0064 40.57 0.6958296

Pfinal 80.28

Compressor Engine and Pump Sizing

The duty cycle of the pneumatic cylinder consists of extension, pause, retraction, and finally a pause. Although the flow rate may be required to be as high as 24.5 SCFM for extension and retraction, the average flow rate over the entire duty cycle is only 3.27 SCFM.

Duty Cycle

Where SCFMavg is the average flow required to be produced by the air compressor engine. SCFtot is the total volume (not flow rate) of air used in the duty cycle in standard cubic feet. SCFext and SCFret are the volumes of compressed air displaced by the pneumatic cylinder.

Therefore since the required flow rate is 3.27 SCFM, an air compressor with an output of more than 8 SCFM will yield a safety factor of 2.45.

2 4 6 14128 10 16 18 seconds

24.5 SCFM

One cycle

Accumulator Sizing

If the accumulator is sized too small, there will be a large change in pressure between strokes and therefore causing the packing pressures will not be reproduced. An accumulator size of 20 gallons or greater will ensure a pressure change no greater than 2.2psi.

This analysis was carried out using the ideal gas law and conservation of mass:The initial mass of air in the accumulator (macc1) minus the mass of air moving into the pneumatic cylinder (mext) during extension is equal to the final mass of air in the accumulator (macc2).

Using the ideal gas law and assuming temperatures are constant:

Where Pacc2 is the pressure in the accumulator after one extension of the actuator, Vacc is the volume of the actuator, and Vext is the displacement for one extension of the actuator.

Change in accumulator pressure after one stroke versus various accumulator sizes.

Initial Accumulator Pneumatic Cylinder (Gage) Pressure Displacement (gal)

115 0.3398

Volume of Accumulator (Gage) Pressure Change in AccumulatorAccumulator (gal) after 1 Extension Pressure (psi)

5 106.7274055 8.27259447910 110.7277704 4.27222963715 112.1203014 2.87969856220 112.8281989 2.17180109925 113.2567345 1.74326553530 113.5440247 1.4559753235 113.7500212 1.24997877740 113.9049524 1.09504757145 114.0257125 0.97428749150 114.1224836 0.877516399

Appendix III:

Electrical and Pneumatic System Diagrams

Circuit Diagram

Circuit Description

The circuit includes a normally open limit switch ensuring that the pneumatic cylinder will not actuate unless the safety door is shut. When the momentary switch is put in the downward position, the pneumatic cylinder will actuate downward. When the momentary switch is put in the upward position, the pneumatic cylinder will actuate upward. The 5 Amp fuse will open if there is a short hence preventing fire or shock. The LED indicates to the user that the machine is plugged in.

LED

5 Amp Fuse

Normally Open Limit Switch

Momentary Switch

Solenoids 1 and 2

120 V AC

Schematic of the Air Flow through the Apparatus

Appendix IV:

Engineering Drawings

Appendix V:

Budget:

PART QTY PRICE $Pneumatic Piston 1 215.00Regulator 1 28.00Needle Valve 1 37.00Safety Valve 1 15.00Plexiglass Tubing, 6 ft. 1 60.00Rubber Couplers 9 45.003/8 in. Steel Plate 1 4.501/16 in Steel Sheet 1 3.00Hinges 2 5.00Safety Rubber 1 6.00Aluminum Silo Mounts 4 5.00Steel Square Tubing 1 30.00

TOTAL 453.50

Appendix VI:

Final Parts List

Part No Part Name Part Quantity1 Pneumatic Piston 12 ¼ in Air Hose, 4 ft. 13 ¼ in. Pneumatic Elbows 84 ¼ in Pneumatic T-Connectors 25 Electrical Wires 6 Electrical Box 17 Limit Switch 18 Main Beam 19 Locking Mechanism 110 Door11 Frame Base 112 Door Handle 113 Pressure Regulator 114 Needle Valve 115 Safety Valve 116 Spool Valve 117 Safety Shields 218 Mounting Brackets 419 Hinges 220 Ribs 421 Safety Rubber, 1 ft 122 Piston Plunger 323 Door Frame 224 Storage Sleeves 825 Rubber Couplers 926 1 qt. Red Paint 127 1 qt. Primer 128 5 Amp Fuse 129 LED Light 130 3-Way Toggle Switch 1

Appendix VII:

User Manual

Setup

1. Unfold and place the table in a flat, level location.

2. Mount the machine upright on the table by means of the mounting bracket at

its base.

3. Attach the air compressor hose to the nozzle shown here.

4. Plug the machine into an electrical socket. The red light will turn on to

indicate power.

5. Set the air pressure to the proper level by pulling up the knob shown here

and turning until gauge shows the correct pressure. Push the knob back

down after adjusting. A suggested starting pressure based upon previous

testing is 65 psi.

Usage

Preparing silo

1. Put a rubber stopper in one end of the empty silo. It is recommended that

the stopper be recessed approximately 0.25 in. into the silo. This should

reduce the likelihood of the piston loosening the bottom stopper.

2. Put the other end of the silo (the end without a stopper) into the rubber

connector of the storage sleeve.

Filling silo

1. Fill the silo and storage sleeve loosely with silage up to the top of storage

sleeve.

2. Place the silo and sleeve into the machine and close the safety door.

3. Hold the piston switch in the down position. This will cause the piston to

lower and compact the silage. Look through the observation window in the

door and release the switch once the piston stops moving. Hold the switch in

the up position until the piston has returned to its fully retracted position.

There should be an audible sound when the piston reached the fully retracted

position.

4. Open the door with the release knob, located behind the closing handle.

5. Remove the silo and sleeve and again fill loosely with silage to the top.

Repeat the above procedure until the silo is full. For maximum filling speed it

is recommended that two users work together. One user operates the piston

while the other fills a new storage sleeve and silo.

Finishing

1. Separate the silo from the storage sleeve.

2. Use a rubber mallet to force a second rubber stopper into the open end of the

silo.

Cleanup

1. Unplug the air hose. Make sure no pressure is left in the machine by flipping

the piston switch up and down at least twice with the door closed.

2. Unplug the electrical cord.

3. Brush away any bits of silage left on the machine and its table. Wipe away

any silage juice left on the machine and table.

4. Wash out the storage sleeves. Remove and clean the piston heads.

5. Unclamp the machine from the table and put in storage.

Troubleshooting

The piston will not move.

1. Plug in the electrical cord

2. Plug in the air hose

3. Close the safety door

4. Raise the air Pressure

5. Make sure the needle valve is open.

The bottom stopper comes off after compressing silage.

1. Send the piston back up before it stops completely.

2. Lower the air pressure.

3. Put less silage into the storage sleeve when loading for packing.

4. Recess the bottom stopper farther into the silo before packing.

I cannot remove the silo and storage sleeve.

1. Open the safety door.

2. Make sure the piston is not lowered inside of the silo and sleeve. If the piston

is lowered, retract the piston fully using the piston switch (the air lines and

power cord must be plugged in).

I cannot shut the safety door.

1. Make sure you handle the closure lever mounted to the door at the end

farthest from the door, this end with the black ball. This will drastically reduce

the amount of force required to close the door.

2. Reposition the silo / storage sleeve unit so that it rests in the center of the

aluminum silo mounts.

3. Reposition the rubber coupler on the storage sleeve so that only

approximately 1 in. of it is located on the plexiglass itself.

4. Remove the silo / storage sleeve unit, unplug the silo packer, and clean the

silage from the interior of the silo packer. Plug the silo packer back in.

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