Group 5 - Kawasaki Compressor 2 Gate 3
Project Management: Coordination Review
Cause for Corrective Action
So far the project plan is serving us well. It is, however, still a plan and, therefore, an idealized outline for the flow of events. As the semester nears the end, schedules become more demanding and personal obligations more numerous. A shortcoming of many long term plans is the limited ability to adapt to unforeseen complications. This is when one must rely on the versatility of his team.
In the most recent gate, communication was good, people were eager to complete the required tasks, and it seemed as though there were plenty of time. However, when it came to organizing an initial meeting, personal obligations hindered some from being present. Due to the limitation of lab hours, some team members had to assume roles that were not their originally outlined roles, such as an editor becoming a dissector. To some this would seem like an obstacle, but it allowed our team to become more versatile by stepping out of our respective comfort zones and turning weaknesses into strengths.
Still, time is an issue. With all tasks itemized, distributed, and completed, there is still not enough time to confidently review the final draft as a single entity. As to the question of handling future challenges, there will undoubtedly be future challenges, but the team will make the necessary compromises to get the job done. The solution that would solve any shortcomings of our now and future plans is an infeasible one, having more hours in a day.
Product Archaeology: Product Evaluation
|Picture Containing Component||Copies of Component Used||Detailed Decription|
|1||1||Air filter cover: coated black metal cap that allows air to flow through the filter while keeping it in place; part is likely die cast|
|1||1||Air filter: replaceable porous filter with semi-rigid black plastic frame|
|1||1||Air filter cup: coated black metal cup mated to a threaded metal inlet tube that connects to the intake manifold|
|2||1||Intake Manifold: cast metal manifold with integrated heat sink and synthetic seal, mated with discharge hose connection|
|3||2||Screw: small metal screw to hold discharge valve and restrictor in place|
|3||2||Washer: metal washer provides buffer between screw and parts|
|3||2||Metal spacer: provides extra clearance to screw|
|3||1||Separator plate: metal plate with three bored discharge hole and one intake hole to facilitate proper air flow about the valves|
|3||1||Discharge valve: thin curved flexible metal valve(likely rolled and stamped); it works in reaction to pressure change|
|3||1||Valve restrictor: thick metal piece in shape of the valve acts to limit valve movement|
|4||1||Intake valve: thin flexible metal valve(likely rolled and stamped) that functions in reaction to pressure change|
|4||1||Gasket: thin gasket(likely stamped) acts as a seal the piston cylinder and valve plate|
|5||1||Piston cylinder: cast and finished metal cylinder with four bored holes and integrated heat sink houses piston|
|6||4||Bolts: metal bolts to hold piston cylinder assembly to crankcase (threads likely formed by turning)|
|7||1||Piston head: metal piston head(likely finished by grinding)|
|7||3||Metal O-rings: eliminate the possibility of gaps between the piton head and interior cylinder wall|
|7||1||Pin: metal pin secure connection between piston head and connecting rod|
|7||1||Connecting rod: metal connecting rod(likely forged) transforms crankshaft's rotational motion into vertical motion|
|7||2||Pressure clips: metal clips keep pin from sliding out of place|
|8||1||Crankcase: cast metal crankcase house crankshaft, piston assembly, and lubricant|
|8||1||Gasket: acts as seal between the piston cylinder and the crankcase|
|9||1||Crankshaft: cast metal crankshaft is counter-weighted and provides rotational motion to the connecting rod|
|9||1||Allen bolt: metal Allen bolt connects crankshaft to the rest of the rotating shaft that is acted upon by the motor|
|10||1||Crankcase back plate: cast metal plate completes crankcase and has a view port for checking lubrication levels|
|10||1||Seal: synthetic seal prevents lubricant leakage|
|11||1||Lubricant inlet plug: plastic plug stops inlet for lubricant when not in use|
|11||2||O-rings: synthetic o-rings guarantee integrity of the seal between lubricant inlet plug and inlet|
|8, 12||1||Rotating shaft: metal shaft(partially formed by turning) manifests energy from the motor as rotation motion to the fan and crankshaft|
|12||2||Bearings: ball bearing type rolling element bearings diminish hindrance to the rotational capabilities of the shaft|
|13||1||Motor: the motor comprises the cylindrical metal core and drawn conductive wire that is bundled and coated, electricity is imported and exported through the fiberglass sheathed cords that are visible, the system is ground by the green wire|
|14||1||Motor cover: cast metal motor cover acts to contain and secure motor to crankcase|
|15||4||Bolt: metal bolt fastens motor cover to crankcase|
|15||4||Metal spacer: increases clearance between the bolt and motor cover|
|16||1||Cooling fan: cast metal fan provides cooling to the motor|
|16||1||Allen screw: metal screw puts pressure on the rotating shaft to hold the fan in place|
|16||1||Pressure clip: metal clip prevents the fan from sliding along the shaft|
|17, 18||1||Circuit Breaker: the circuit breaker resets the electrical connection; it is composed of a plastic push switch, a metal nut which secures it in place, a plastic case, and two conductive terminals|
|19||1||Metal nut: used to fasten the capacitor|
|19||1||Metal washer: provides a buffer between the nut and the compressor|
|19||1||Capacitor mounting bracket: made of injection molded plastic, it serves to give clearance around the capacitor|
|20||1||Start Capacitor: a capacitor that aids the motor in attaining and minimum sustainable speed|
|21||1||Electrical cord: supplies power to the compressor, consists of an insulating sheath, electrical wire, and a male terminal|
|22||1||Internal Electrics of Pressure Regulator: a pair of - connections, + connections, and a connection to ground deliver electricity from the power source to the rest of the system|
|23||1||Metal plate: it serves as part of the internal structure of the regulator|
|24||1||Metal plate: it serves as part of the internal structure of the regulator|
|24||1||Stiff metal spring: it serves as part of the internal structure of the regulator|
|25||1||Regulator switch: turns the device on and off, made of metal with a protective soft tip|
|27||1||Plastic adjustment screw|
|29||1||Plastic pin: internal component of the regulator|
|31||1||Stiff metal spring: internal component of the regulator|
|32||1||Stiff metal spring: internal component of the regulator|
|33||1||Plastic spacer: holds mechanical parts of the regulator in place while also anchoring a spring|
|34,35||1||Plastic regulator cover: serves to protect the inner workings of the regulator|
|36||1||Air transport line: copper pipe that transports the air that gets checked by the regulator|
|37||1||Air transport line: metal pipe transports compressed air from the piston chamber to the storage tank, has a spiral protective collar|
|38||1||Air transport line: coiled synthetic tube delivers compressed air for use with attachments|
|39||1||Gauges and regulation system: air flows and pressure is checked by the metal encased gauges, desired pressure can be finely adjusted by the black plastic knob|
|40||1||Air storage tank: eight gallon green welded cylindrical metal storage tank with handle and base attachments for ease of transport|
|41||1||Pressure release valve: metal screw-in valve that evacuates pressurized air|
|42||1||Handle bars: green tubular handle bars for utilizing the tank's wheel barrow design; made of extruded metal|
|43||1||Plastic cover: cover made from injection molded plastic serves to protect the exterior mechanical components and give clearance to the fan|
|44||2ea||Plastic restrictor: restrictor and screw act to limit the motion of the plastic cover|
|45||2ea||Rubber support and fastener: a support, two washers, and a nut act to support the tank when not in transport|
|46||2||Tire: plastic wheel with integrated rubber tire|
|47||2ea||Bolts for tire: a bolt, nut, washer, and spacer to fasten each tire|
|48||2||A pair of metal screws, washers, and bolts|
|49||4ea||Assorted metal screw: the first secures the handle bars, the last secures the crankcase to the tank|
This component filters the incoming air before it is compressed into the tank. There are three holes placed 120 degrees away from each other that allows the atmospheric air to enter the filter before being purified. This indirectly allows the machine to function properly by providing clean air for the rest of the system. Based on this, there is no build up of grime so this allows other components to work over a longer period of time. The flows, based on our flow sheet located at the end of this section, are: atmospheric air comes into the filter, cleaned atmospheric air and vertical kinetic energy(from piston) leave from the same step. The environment of the air filter is the outside atmospheric air which then links this environment to the rest of the system.
The general shape of the air filter is a cylinder. The position on the compressor makes the air filter symmetrical with respect to the x-axis; with respect to the y-axis, it is asymmetric. The cylindrical shape allows for a larger quantity of air to be pulled through the filter’s area by improving air flow around the cylinder. The air can pass through the filter at any point in the cylinder. The pleats and ridges of the air filter allow for maximum capture of dust, dirt, and particles to provide the best quality of air to the system. The filter weighs about two pounds. The dimensions of the top cover are: 2.5 inches outside diameter, 2.2 inches inside diameter, .3 inches outside height, .8 inches inside height; the bottom cover: 2.4 inches outside diameter, 2.0 inches inside diameter, .2 inches outside height, .8 inches inside height; the screw dimension: .8 inches length, .75 inches width; and the filter dimensions: .8 inches height, 1.8 inches width smaller plastic circle, 2.375 inches longer width.
The casing material is made out of aluminum because of its light weight. The connecting screw, that places the filter on the compressor, is made out of galvanized steel. The filter itself is made out of fibrous materials and is compressed between two plastic circles.
The manufacturing decisions impacted this part's material because to make it out of aluminum minimizes cost. The part needed to be light weight so it can be attached to the compressor by one horizontal screw. The global influence of material is that aluminum is an abundant metal in the Earth’s crust. The economic influence of material aluminum is a widely available material which correlates with its inexpensive price. The societal influence of the low cost of materials used for the air filter, in combination of other manufacturing processes for other parts, enables manufactures to sell the air compressor at a lower price. This makes it more available to a wide range of incomes of consumers. The environmental influence of the materials is that during the design process environmental factors did not play a role.
The air filter does have an aesthetic purpose because the accordion shape is used to capture maximum dirt, dust, and particles. The filter is an orange gold and the casing is black with a smooth surface finish. The casing’s color is black to just match the rest of the air compressor and its smooth surface finish is just for aesthetic appeal.
The casing was die casted because of the hollowed out middle section for the place of the air filter. The circles that keep the air filter in place were molded because they are made of a malleable plastic. The air filter itself is made out of paper which is folded and pleated into its shape and the casings.
The economic influences choose why die casting was used because it is a cost effective process for parts in high volume. The injection molding of the plastic circles was also cost effective. During the manufacturing process of design global, societal, and environmental influences were not taken into account.
Component Complexity Based on our scale complexity at the end of this section, this component is rated at a two. This is because the function of the air filter is simple and it does not need electrical power and is not pressurizing the air. The component form is also simple because of the geometry, materials, and assembly is not complicated. The interaction of the air filter is a number 1 on our complexity scale which is also located at the end of this section.
Piston and Connecting Rod
The function of the piston is to draw air into the system and compress it. First, the piston is moved by the crank shaft and upon being pulled downward there is a pressure difference between the air inside the cylinder and the outside atmospheric air. At the same time, there is a one way inlet valve that allows the atmospheric air to flow through to the cylinder. Once the piston is at the lowest point of its path, there pressure difference has become equal. Next the piston begins to move upwards and simultaneously the air is compressed and forced into a one way exit value. This valve allows the air to flow into the tank. As this cycle continues, the pressure will continue to build. Based on our flow sheet located below, we have rotational kinetic energy being converted to vertical kinetic energy which applies to the piston being displaced downward. The output of this function is vertical kinetic energy to displace the piston upwards. The flows out of this function are compressed air and kinetic energy of air.
The environment of the piston is air tight inside of the piston housing which allows for its function to occur.
The shape of the piston is a cylinder. The connecting rod is a trapezoid with to circles connected on the ends. The cylinder is symmetrically with respect to both axes. However, the connecting rod is symmetrical in its position in the air compressor with respect to the x and y axes, but not the z axis. The dimension of the connecting rod are: .4 inches width, 4.75 inches length, big circle inside diameter-.875 inches, big circle outside diameter-1.375 inches, small circle inside diameter-.625 inches, small circle outside diameter-.75 inches; the piston head dimensions: 1.875 inches diameter, 1.375 inches height. The piston and connecting rod together weigh about three pounds.
The piston’s shape is designed to reduce surface area while filling the cylinder which creates an air tight seal that allows the component to compress the air and move it through the piston’s cylinder. The connecting rod’s shape is designed to connect to the piston and the crankshaft, while keeping the piston head straight and allowing the movement of the crankshaft to keep the piston moving up and down.
The material the piston is made out of is aluminum because of its lightweight and rust resistance. The connecting rod is made of a steel alloy because it is able to bear heavy loads without becoming misshapen. The global influence of aluminum is it is an abundant metal in the Earth’s crust and the influence of steel alloys are they are created and not found in natural; it can be made globally with the correct manufacturing. The economic influences of using both aluminum and steel alloy are low priced materials. This allows the product to stay in a reasonable price range. The societal influences of materials are the low cost of aluminum and steel alloy for these components contribute to the air compressors lack of quality. This means this air compressor would most likely be used for recreational activities and not for professional use. During the design process of the piston and connecting rod environmental factors did not play a role.
The aesthetic purpose air tight to the cylinder, of the piston is so that it allows maximum pressure to pressurize the air. The smooth surface finish reduces friction to little or nothing. The color of the piston is just naturally metallic. The connecting rod’s aesthetic purpose is to have a tight fit to the piston and the crankshaft. It keeps the piston in an air tight position and while the crankshaft is moving in a circular motion. The surface finish of the connecting rod is as it was after manufacturing. However, the inside of the holes are smooth and allows for fluid motion. The outside part does not to have a specific surface finish because it is not in contact with any other part.
The manufacturing methods to make the piston, it is die casted and then forged. The piston shows parting lines on the inside to suggest that it was die casted. The connecting rod is made by forging because the seam lines are visible. Both the piston and connecting rod have holes drilled into them. The piston’s two holes are at 0 and 180 degrees when the center of the piston is at the origin. This is where the wrist pin is placed. The connecting rod’s center line places the origin of both of the drilled holes parallel to each other with varying diameters. The smaller diameter hole is slid onto the wrist pin, while the larger diameter hole is slid onto the crankshaft.
The economic benefit of using aluminum reduces the price of material so the manufacturing methods were more complicated in compensation. During the manufacturing method process global, societal, and environmental influences did not play a role.
The piston and connecting rod are rated a four on our scale of complexity, refer below. The component function of the piston affects the complexity because the piston needs to maintain an air tight seal and minimal friction. This is why the piston needs to be made to a higher level of precision and quality. The component function of the connecting rod does not affect complexity, only the diameters of the holes need to be precise. The manufacturing methods affect the complexity because each part cannot exceed the respective variances.
The complexity of the interactions of these components with the system is a 2 on our interaction scale, view table below.
The hose’s function is to transport and release the buildup of the pressurized air stored in the tank. This component helps to control the pressurized air as it is about to be used. It also helps to extend the use of the tool. The flows associated with this component are kinetic energy of air and compressed air going into the hose and kinetic energy of air and compressed air leave the hose. Although these are the same flows, the efficiency of the component is not perfect and some of the flow is lost. Please refer to flow chart below
The environment surrounding the hose is atmospheric air and pressure, while the environment inside the hose is pressurized air.
The shape of the hose is a small, flexible tube that is coiled. The hose is symmetrical if the tube is cut in half. Another notable property is that it can be stretched to a longer length. This three dimensional component. On each end of the tube there is a connecting part: one to connect to the tank and the one to connect to the attachment. The diameter of the tube is .375 inches, the height of each coil is 4 inches, and the length of one coil is 12 inches and there are 29 coils so the entire coil length is 29 feet. Small connector diameter is .25 inches and big connector diameter is .50 inches. The component weighs about a pound and a half.
The component shape allows for the tube to reach further away from the air compressor without having to move the tank.
The material the component is made from a flexible, hard plastic. The flexibility allows the hose to extend its distance and the hard plastic protects the flow of air. The two connecting parts are made out of brass. Manufacturing decisions did not impact the material’s choice, but the function of the component did determine the material. The material choice for the hose was to ensure it would function properly under working circumstances was influenced through economic factors. Through the influence of environmental factors the material for the hose allows it to be used in all different locations and varying weather. Global and societal factors were not a concern in the materials process.
The tube has an aesthetic purpose because it is easy to store when it is coiled. The tube’s color is black and the surface is smooth because it is able to make contact with other surfaces and not get stuck and it is smooth for touch. The color of connecting parts is a light gold and the surface is smooth. The connecting part to the tank has threads to be able to be screwed in.
To make the tubing, the hose was molded. The evidence that supports this is that it is made out of a plastic, probably polyurethane, and majority of plastics are molded. The brass connectors were die casted. The connectors need to have tight tolerances to fit into the attachments and the tank and die casting achieves this task. The choice of molding for the manufacturing method of the plastic was impacted because of the limited ways to shape plastic. The manufacturing method of die casting the connectors was chosen because of the cost effectiveness in high volumes for this part. The shapes of these components were dictated by the materials chosen, not the manufacturing method. The economic factors that it is cheap and efficient to mold high volumes of plastics and die cast brass were the only concerns of manufacturing methods.
These components is rated a one on our complexity scale, check complexity table below. The component functions and forms are simple which contribute to the rating of a one. The manufacturing methods are of the components are more complex than the components themselves, but do not contribute to the components rating.
The interaction rating of these components is a 2 based on our scale, view details on scale table below.
The stator receives electrical power from the electrical cord from the outlet. It then brings the current into its copper coil, which creates a changing magnetic field, to spin the motor/crankshaft located in the middle of the magnetic field. This component absolutely helps other functions. The stator starts moving the current, to make the magnetic field, to move the motor/crankshaft, which moves the piston, which compresses the air. The flows going into the stator are current signal and electric energy for the stator to turn on and then current signal and electric energy come out of that to convert the electrical energy to rotational kinetic energy of motor/crankshaft through the magnetic field. These are all based on our flow figure.
The type of environment the stator works in is electrical but it also creates a magnetic environment as well.
The shape of stator is a hollow cylinder. It is symmetrical with respect to the x and y axes when the center is at the origin. This is a three dimensional component. The specific dimensions for the stator are: length of the stator is 5.75 inches, diameter is 5 inches. The stator weights about twenty pounds.
The stator is a hollow cylinder that contains the motor/crankshaft. It also is this shape because it creates a constant magnetic field across the cross section of the motor, when electric current runs through the copper wires, to move the motor/crankshaft.
The frame of the stator is made from iron, the inside walls of the frame are covered with coils of copper wire and fiberglass insulation. Manufacturing decisions did not impact the materials used because they are specific to creating an electromagnetic field. The wires coiled inside the stator frame need to have conductivity as a property, so copper wires satisfy this criterion. The global, societal, and environmental factors did not influence materials used on this part. Copper was chosen as the conductive material for the wire because of its price. Gold is a much better conductor, but far more expensive which is why is was not an economical benefit to use.
The aesthetic properties of the hollow cylinder are essential because it fits the motor and crankshaft appliance inside. This aesthetic property also enables the stator to create and even magnetic field for the motor/crankshaft. The color of the stator frame is a shiny black with no apparent purpose. The surface finish is smooth on both the entrance and exit ends. The outside of the frame surface finish is also smooth.
The stator was manufactured by die casting because of its need of close tolerances to fit the coils of wire in place. The function of the stator would be an example because it needs to be able to rotate the motor and crankshaft at high speeds and cannot afford to have error in dimensions. The material of steel did affect the decision to die cast or forge, but it eliminated the options to mold. The design of the stator frame and the stator slots is complex which affected the manufacturing decision to die cast. A global factor that influenced this part is the electrical power cord connected to the stator is a 120V power supply. This is only for locations that have outlets to support this amount of voltage. Die casting the stator is cheaper when made in high volumes, like for this product which is how it affected the economic aspect of this part. Environmental and societal factors did not influence the manufacturing methods.
On our complexity scale located below, this component is rated a 5. The component function affects the complexity because of the plethora of parts that rely on this one component working. The component form affects the complexity because of the intricate design. In more detail, the way the copper wires are weaved through stator slots and their fiberglass insulation all contribute to its complexity. The manufacturing method process requires more detail to properly align all the strands of copper.
Based on our interaction scale below, this component receives a 4.
The tank used for the storage of the pressurized air. This component does help multiple functions because it stores the air and also helps release when needed. The flows involved with this component are kinetic energy of air and compressed air go into the tank, the energy becomes potential while being stored, and kinetic energy of air and compressed air come out. This is based on our chart below. The environment the tank works in is a high pressure environment.
The shape of the tank resembles a silo tower, which is a cylinder with rounded sides. The tank utilizes the cylindrical shape to maximize the surface area to volume ratio. This means that the shape of the tank allows for more air to be stored inside of it as opposed to a cube or triangle of similar size. The tank is symmetric with respect to the x and y axes. This component also is a three dimensional object. The tank’s circumference is 31.5 inches, the length is 26 inches. This tank is also measured to have an eight gallon volume. The component weighs about 20 pounds without any pressurized air.
The tank has a large volume to store air, so it will also be able to release constant air for a longer period of time.
The tank’s material is steel. Manufacturing did not play a role in the decision to use steel for the tank. The tank definitely needed a sturdy, protective material instead of a malleable, flexible one. A societal factor is that since the tank is measured as eight gallons, and gallons is an English unit, this means that the compressor is suppose to be used in English unit countries. The environmental influential factors are that the tank is a rust resistant material, it is able to go into any location and perform its job.Global and economic factors did not influence the component form.
The look of the tank does not affect the main function of the tank. The bright green color of the tank serves no purpose other than recognition of the brand, Kawasaki. The surface finish is smooth with visible parting signs which do not serve as a function.
The tank was forged because of the strength it provides and the visible parting signs as mentioned above. Although steel did not dictate forging as the manufacturing method, it did eliminate molding. The method was unaffected by the shape design of the tank. A societal influence for the use of forging is to help prevent the tank from rupturing which protects the consumer’s health. The related economic factor is if the tanks were to break and cause injury to consumer’s, this would result in expensive settlements. Global and environmental did not play a role in the manufacturing methods.
Component Complexity The complexity of this component is rated a 1 based off the scale provided below. The component function of storing the pressurized air is a basic task. The component form is a simple shape and easy to make. The manufacturing methods themselves are complex and difficult but the part it is making is basic.
Based on the interaction scale shown below, this is gets a 1.
|1||Very simple parts that make up the component. The component is easily assembled, serves a simple purpose, and is easily manufactured.|
|2||Parts that make up this component are still fairly simple. The manufacturing process is not basic, but not difficult. Assembly may require tools or machinery.|
|3||Individual parts require more detail and complex manufacturing steps. The component may be difficult to assemble and requires some experience.|
|4||Involved steps and proper techniques are used to achieve a higher level of accuracy in the component; the function of component is based upon its performance so measurements and materials used should be of high quality.|
|5||Manufacturing techniques for parts must be perfected, there is no room for error; any error will result in failure in the part or system. Design is crucial to the efficiency of this part and its capabilities.|
|1||The interactions between this component and the rest of the system are insignificant to the overall goal. This means the task can be completed without this interaction.|
|2||The interactions between this component and the rest of the system are simple, but necessary for the overall goal. This means the task will not be completed, but majority of the system's flows will continue.|
|3||The interactions between this component and the rest of the system are necessary and complicated. This means the task will not be completed, but few of the system's flows will continue.|
|4||The interactions between this component and the rest of the system are essential and complex. This means the main task will not be completed and no flows will happen.|
Table 5: Flows Chart
Solid Modeled Assembly
We chose Solidworks as our CAD package because it was the software that our solid modeler had the most experience with. He also had the software already downloaded onto his laptop, making it a convenient choice.
We chose these parts specifically because they were the only ones that we were not able to disassemble. We thought that, by modeling these parts to the best of our ability, we would attain a better understanding of how the crankshaft subsystem and the air compressor itself functioned.
For any well-engineered product, safety is an important consideration behind the design process. This is especially true for a product like the Kawasaki Air Compressor. By essentially providing a reserve for highly pressurized air, there are a number of components which, if improperly designed, could fail, creating the potential for serious injury of the consumer. One such component is the air storage tank. In this section, the steps for the analysis of the maximum stress conditions of the air storage tank are presented. Treating the air storage tank as a thin-walled cylindrical pressure vessel from the study of the mechanics of solids, an engineer can determine an appropriate level of allowable stress for the air storage tank given a certain factor of safety, he or she could recommend the most economic material choice of the air storage tank, or if the allowable stress and material are already set from previous steps in the design process, he or she could determine whether normal operating conditions create stresses in the storage tank that are within this set value of allowable stress. In this analysis, it is assumed that the material and thus the ultimate stress are known, and that a factor of safety has been set earlier in the project. Therefore, the objective is to determine whether the air storage tank, under normal operating conditions, will exceed the desired level of allowable stress. The first four steps of this hypothetical analysis are outlined below.
In this problem, the ultimate strength and ultimate stress of the material used for the air storage tank are known, and are equal to σult and τult, respectively. The given factor of safety is equal to x. The maximum gage pressure inside the tank before the safety release valve is activated is equal to p. The inner radius of the tank is equal to r, and the wall thickness of the tank is equal to t. Determine the hoop stress σ1 in the tank, the longitudinal stress σ2, and then the maximum normal stress and maximum shearing stress experienced in the tank.
Diagrams of System
The first figure, Figure 1a, is a representation of the air compressor tank as a thin-walled cylindrical pressure vessel. This figure is in equilibrium. On the cylinder, a box is drawn representing the state of stress at that point on the tank's surface. Since the tank has been removed from its surroundings, all that is acting on it is the gage pressure of the compressed air inside the tank. This pressure causes two different types of stresses, hoop stress and longitudinal stress, represented by the terms σ1 and σ2 drawn on the box representing the state of stress at that point.
Figures 1b and 1c represent the derivations for the expressions for hoop stress and longitudinal stress, respectively. The shape in Figure 1b represents a section of the cylinder through the xy-plane. Based off of this section, a free-body diagram is drawn, illustrating the forces and stresses at work. Summing up forces in the z direction and setting them equal to zero (due to equilibrium), an expression for σ1, or hoop stress, is obtained.
Figure 1c represents the cylinder, sectioned across a plane parallel to the yz-plane. From the free-body diagram of this section, using a similar procedure from the last step, forces are summed in the x direction and set equal to zero, yielding an expression for σ2, which is longitudinal stress. Based on observation, one notices that the expression for hoop stress is twice that of longitudinal stress, leading to the conclusion that σ1=2*σ2.
Figure 1d is a summary of the generalized state of stress at the point originally shown in Figure 1a. From the expressions that were derived in Figures 1b and 1c, it is evident that this state of stress will apply at any point on the curved exterior of the cylinder as the formulas are independent of x, y, and z coordinates. It is necessary to draw this diagram, as it is needed to create Mohr's circle as shown in Figure 1e. Constructing Mohr's Circle will yield the result for maximum normal stress and shear stress experienced on the cylinder, or the wall of the air storage tank.
Figure 1e is a demonstration of Mohr's circle. Given the values for σ1 and σ2 from Figure 1d, one can plot corresponding points A and B on Mohr's circle. The maximum normal stress occurs at the greatest absolute value of σ on the graph, which happens to correspond to point A, or σ1 in this case. It is important to note that this would not be the case if there were values for shear in Figure 1d. The maximum shear stress occurs out-of-plane at the topmost point of the large dotted circle, at the point D', which happens to be equal to σ2, in this case. For an explanation of how to construct and interpret Mohr's circle in reference to these problems, please refer to Chapter 7 of the 5th edition of Mechanics of Materials by Beer, Johnston, DeWolf, and Mazurek.
Statement of Assumptions
Certain assumptions must be made in order to simplify this analysis so that it could potentially be conducted by an engineering undergrad. They are as follows:
1) The air storage tank is treated as a thin-walled cylindrical pressure vessel
2) The end caps of the air storage tank and the welds are disregarded: In this analysis, the primary concerns are the stresses in the cylindrical portion of the air storage tank.
3) The weights of the components resting on the tank are not considered: This assumption is made to simplify this analysis problem. In reality, the weight of the components on top of the tank along with the support reactions from beneath the tank introduce shear stresses, which must be taken into account on the generalized state of stress and Mohr’s Circle in Figure 1d and 1e, respectively. Since the shear term due to these forces is dependent on the location where one chooses to analyze (i.e. the exact location on the surface of the tank to find the generalized state of stress), it is impossible to demonstrate the procedure of how to consider these shear forces for all locations on the tank. It is assumed that an engineer who has passed a mechanics of solids course would have a working knowledge of this material, and therefore would be able to incorporate the shear terms introduced from these external forces accordingly. A corollary to this assumption is that the analysis considers the maximum stress and shear conditions for a free-standing air storage tank.
4) Gage pressure is constant: In order to use the equations provided, one must assume a constant value of p, which is set to the maximum gage pressure determined by the product envelope.
5) Wall thickness, t, is constant: Due to imprecise manufacturing methods, it is possible that the wall thickness of the tank is not exactly uniform throughout. Nevertheless, slight variations are unlikely to affect the end result by much, and so this is a reasonable assumption.
6) Radius, r, of the tank is constant.
There are only a few equations, so to speak, required for use in this analysis. After obtaining σ1 and σ2, along with the value for shear for the general state of stress (which happens to be zero here), one utilizes Mohr's circle to obtain the values of maximum normal stress and shearing stress.
After values for maximum normal stress and maximum shearing stress are obtained, they can be compared to the values of σall and τall. If the values obtained are within the limits of σall and τall, then previous design has been a success. If, however, results from the analysis yield values that are greater than σall and τall, then one may need to reconsider design to make the structure of the air storage tank safer. It is known that even if a material is not subjected to its ultimate normal or shearing strength, if it repeatedly stressed at values close to it, then due to effects of fatigue, the material may fail. This is part of the reason why real-world engineering applications are designed with specific factors of safety in mind.
The following section provides three suggestions for design revisions to the Kawasaki Air Compressor. It is important to keep in mind that this compressor is most likely meant for personal or light commercial use. Although access to documentation on this product is limited, the target audience can be deduced due to a few characteristics of the air compressor. For instance, compared to compressors used for industrial applications, this compressor has a relatively small capacity. Also, this compressor has a compression cycle that frequently switches on and off based on pressure inside the air storage tank, implying that it is intended for relatively sporadic use, unlike the constant use that is demanded from industrial or larger commercial applications (such air compressors, when powered, are on constantly on due to the high demand for pneumatic power and the design consideration that a heavy-use compressor that operates continuously would maintain better than on that frequently turns on and off).  Cognizant of the observations made above, although it is tempting to recommend design revisions such as creating a centrifugal air compression system (with very high pressurizing capabilities of up to around 1200 psi), this would be highly impractical for the intent of home or small business use, aside the fact that the revision would be far outside the original product envelope.  The following suggested revisions are attempts to ameliorate user interface and overall product performance while trying not to deviate too far from the original product envelope.
Improved Handle to Air Storage Tank
The first design revision addresses the flat metal handle located on the tank above the wheels. This handle is angled at roughly 40 degrees and is difficult to use under the weight of the compressor. The larger handle can be used in combination with the wheels to easily move the unit on the ground, but if one needs to pick the compressor up off the ground it is much more difficult. The larger handle is not sturdy enough to bear the weight of the compressor which forces the user to lift the unit using the rear handle. The handle in the rear of the tank is made of steel and welded on to the tank. The design of this handle did not take into account that a person’s hand will be wedged under the handle bearing a large portion of the weight. The handle’s angle causes the weight to be distributed over a small area causing greater pressure. This makes the compressor less mobile since it would be restricted to movement in the x and z axis. This revision would entail a more ergonomic handle, a small hallow cylinder made of steel. The steel cylinder would allow for better weight distribution on the users hand when lifting. In the process of lifting the forces acting on one’s hand change direction, when on the ground the handle the fingers bear the initial weight and as the unit is raised higher the palm begins to support more. The cylindrical handle would allow for comfortable movement throughout the act of lifting. The impact of this improvement would encompass a slightly higher cost because more steel would be necessary to form this design and the steel would have to be machined into the proper shape. In addition to the cylinder a foam surround could be added to the handle but this would be costly and ultimately unnecessary. The foam surround would not attract more customers because it plays a small role in the appeal of the unit. The handle would be equally effective without the foam as it will most likely not be lifted very often by homeowners. This revision would affect the economic factor raising the cost of the overall production, but it would also increase the ease of use which pertains to societal aspects of the compressor.
Changes to Fan Blades
For a second potential design revision, one could consider altering the design of the fan blades to a more efficient design. Consider Figure 3 to the left, which displays the placement of the fan relative to the rest of the assembly (for a closer look at the fan, refer to ‘Pic 16 Fan’ in Table 1 of this gate). It does not take long to spot the inefficiency of the current design of the fan. As described in Gate 2, the function of the fan, which is attached to one end of the crankshaft, is to provide cooling to the critical components placed behind it in Figure 3, such as the electric motor. The way it is designed now, the fan blades are perpendicular to the direction in which air is expected to flow. However, it should be intuitively apparent that this is not the most efficient design of blades. If one observes the arrangement of blades of different fans, such as ceiling fans and box fans, one feature is common among them: the blades are placed at some slight angle to the direction of airflow, rather than being placed perfectly orthogonal to the direction of air flow (as is the case here). Essentially, what the slight angling of the blades does is that it makes the blades more aerodynamically efficient, and thus more efficient at performing their task of moving air. Therefore, the design revision here is to simply design the blades so that they have a smaller angle of attack (certainly less than the current value of 90 degrees). This revision addresses performance, which can be generalized as addressing societal and economic concerns. With a fan that is more efficient at cooling the critical components of the compressor, this ensures that such critical components face less wear and will maintain for longer periods of time, addressing the societal concern (or expectation) that products be well-engineered and reliable. This lends itself to economic concerns, as an air compressor that is more reliable will require fewer maintenance costs, which is also a plus. It is also possible that with more efficient cooling, the compressor itself could operate at a slightly more efficient level, another economic concern (the compressor would use slightly less energy to adequately pressurize the same amount of air over a given time period).
Improvement to the Off-Auto/On Switch
Part of the regulator is considered for the final recommendation of design revisions. This recommendation is fairly simple: that is, to come up with a sturdier, more reliable way to turn the compressor on and off. Refer to Figure 4 to the right, which shows the regulator and the switch that is being referred to. For a better picture of the regulator switch itself, refer to ‘Pic 25 Regulator Switch’ under Table 1 of this Gate. Although one did not have the luxury of actually operating the compressor prior to dissection to see real live performance, upon the switch from the off to on position and back a few times, it was evident that this particular component could have been designed better. To operate the switch (turning the setting from ‘Off’ to ‘Auto/On’) there was significant resistance posed by the lever which was the switch. In Figure 4, the switch is shown in the ‘Off’ position, and to switch it to the ‘Auto/On’ position, one needed to rotate the lever counterclockwise 90 degrees from that position, so that the red tip would be pointing upwards relative to the picture displayed. Upon dissection, the reason for such resistance when switching from ‘Off’ to ‘Auto/On’ became apparent. Essentially, by turning the lever to ‘Auto/On,’ one would create a mechanical connection, allowing for the electric circuit which allows the electric motor, and thus the compressor as a whole, to operate. So that this mechanical connection could not be inherently toggled on and off, a spring was strategically placed so that there would be a decent amount of resistance when turning the regulator switch (so that one would not inadvertently turn on the compressor when not needed). For the design revision, it is suggested that a more conventional on-off switch be used, such as the one pictured to the left in Figure 5. The advantage of using the current design in the air compressor is that it is cheap, and it makes the process of cycling between active compression and stand-by while in the ‘Auto/On’ mode simpler. Using a more conventional switch such as the one in Figure 5 to the left would require more intricate circuitry and design within the regulator. Relative to the price of the entire air compressor, this revision would not have an appreciable impact on the final price of the compressor (perhaps a few dollars at most), and so one may wonder why the current design is implemented to deliver the same result. The only conclusion that can be reached is that, similar to the example of the fan, Kawasaki was looking for additional ways to save costs when producing this compressor (when looking at the fan, due to its relative lack of smooth finish and the impurities in the final piece, it appears to have been die cast, a cheaper process than one that would be used to make actual fan blades, such as investment casting).
This design revision addresses the societal concerns associated with user interface and ergonomics. North American consumers (whom this product is directed at, viz. Gate 1 product profiles) are exacting consumers, and they have the societal value that the products they buy be dependable, or at least give the impression that they are dependable. (Proof of such societal values can be found in domestic consumer protection laws, such as various states' 'lemon laws' regarding newly purchased automobiles). The current lever setup for the switch is annoying to operate, and moreover, based on its cheap structure, feels especially prone to failure. Understanding that this assessment may be subjective, whether or not this system is actually prone to failure, it is nevertheless inferior design, because it still gives the user the impression that it may fail. A good analogy is designing a structurally sound bridge which is allowed to flex regularly. Even if engineers are confident that the bridge will not collapse, if the consumer receives an impression otherwise, it is not good design. Furthermore, this has economic implications for the manufacturer, as too many impressions of inferiority from a product may mean a lost customer for life for that particular manufacturer. Essentially, even if Kawasaki does appreciate cost savings with the current setup, it cannot ignore these societal concerns of perceived reliability, as these ignored societal concerns may turn into economic concerns for the company in the long-run through lost potential sales.
- "Air Compressor Buyer's Guide: Everything You Need to Know ." 360MachineTools. N.p., 2010. Web. 17 Nov 2010. <http://www.360machinetools.com/air-compressor-buyers-guide.htm>.
- "Different Type Air Compressors." Davey Compressor Company. N.p., n.d. Web. 17 Nov 2010. <http://www.daveycompressor.com/differenttype.html>.
- Klenck, Thomas. "How it Works: Air Compressor." Popular Mechanics. Hearst Communication, 01 May 1997. Web. 17 Nov 2010. <http://www.popularmechanics.com/home/improvement/energy-efficient/1275131>.
Figures 1a, 1b, 1c, and 1e are from the lectures of Dr. Christine Human, University at Buffalo, Department of Civil, Structural, and Environmental Engineering.
Figure 5 can be retrieved from the following link: http://shop.razor.com/product.php?productid=16474&cat=287&page=1
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