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Graco Inc. Liquid Finishing Rotary Bell Atomizer Turbine

Volume I

May 7, 2013

Course Advisors: Design Team: Industry Advisors:

Prof. Brad Bohlman Nicholas Johnsen Joe Daniski

Prof. Will Durfee Scott Kelly John Ingebrand

Ian Nesser

Patrick Quinn

Ethan Stout

Kevin Van Batavia

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Table of Contents

Title ............................................................................................................... 1

Executive Summay....................................................................................... 4

Team Contributions……………………………………………………….. 5

1 Problem Definition............................................................................. 7

1.1 Problem Scope........................................................................... 7

1.2 Technical Review........................................................................................... 7

1.2.1 Rotary Bell Atomizer...................................................................... 7

1.2.2 Turbine Components...................................................................... 8

1.3 Design Requirements................................................................. 11

1.3.1 Maintaining Continuous Speeds between 30k and 40k RPM……. 12

1.3.2 Working Air Pressure: Under 90 psi ………………………….... 12

1.3.3 Air Consumption: Under 24 SCFM …………………………….. 12

1.3.4 Production Cost < 250 U.S. dollars ……………………………… 12

1.3.5 Life Expectancy > 2,500 hours…………………………………… 12

2 Design Description............................................................................. 13

2.1 Summary of Design…………………………………………. 13

2.2 Detailed Description………………………………………… 14

2.2.1 Functional Block Diagram………………………………………. 14

2.2.2 Functional Description………………………………………….. 15

2.2.3 Overview Drawing………………………………………………. 15

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2.3 Additional Uses……………………………………………… 17

3 Evaluation…………………………………………………………. 18

3.1 Evaluation Plan……………………………………………… 18

3.2 Evaluation Results………………………………………….. 18

3.2.1 Speed: 30,000-40,000 RPM …………………………………… 18

3.2.2 Working Air Pressure: Under 90 psi…………………………… 19

3.2.3 Air Consumption: Under 24 SCFM……………………………. 19

3.2.4 Cost: Under $250………………………………………………. 20

3.2.5 Operating Life: 2500 hours…………………………………….. 20

3.3 Discussion…………………………………………………... 20

3.3.1 Strengths and Weaknesses……………….…………..………… 20

3.3.2 Next Steps……………………………………………………… 21

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Executive Summary

The goal of the turbine project was to design and prototype a turbine component for use in an

automated paint sprayer. This turbine will be placed within a robotic arm assembly, and is

responsible for rotating a bell cup which atomizes the incoming paint stream. Potential

customers of this product include John Deere, Caterpillar, and other companies that require

superior paint coverage on their products. The basic design specifications for this project are as

follows; the unloaded turbine must spin at speeds greater than 30,000 rpm, the air pressure to

achieve this speed must not exceed 90 psi, the air consumption must not exceed 24 cubic feet per

minute, the cost of the turbine and labor must not exceed 250 dollars, and the turbine must have

an operating life of at fewest 2,500 hours.

The design is composed of four key components – the housing, shaft, bearings, and rotor. The

rotor is press-fit onto the shaft, which is bonded to the inside of the bearings. The outside

diameters of the bearings are then bonded to the inside of the housing. This construction allows

the shaft to spin freely inside the housing component. The turbine assembly is operated when a

pressurized air source is fed into the rear end of the housing. This pressurizes a pathway inside

the housing which directs the airflow into four radial jets aimed at the rotor blades. The air

pressure exerts a torque on the rotor, causing it and the shaft to spin. Paint is fed through the

hollow shaft to a bell cup which is screwed onto the end of the shaft. The cup flings the paint

droplets into the air, atomizing them shortly after departure.

The design was evaluated using the specifications listed above. Using an incremental increase in

pressure, a series of different designs were tested for compliance with the design specifications.

The best design was found to be a rotor with a curved blade style, and four 0.136” inlet air-

holes, with ABEC 5 ceramic ball bearings. This design resulted in an operating speed of 35,500

rpm at 20 psi while consuming 8 SCFM. The total cost of this design was $143.32, which was

well under the $250 target. The calculated life for this design was 9000 hours which also

exceeded the required specification. The final proposed design is shown below.

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Team Contributions

Nic Johnsen

Work breakdown structure

Product design specifications

Statement of work

Background research

Turbine, housing and shaft design

Prototype building, modifications, and testing

Manufacturing plan write-up

Cost analysis write-up

Environmental impact statement

Ethan Stout

Concept generation

Background research (bearings, turbines, accelerated life testing)

Bearing selection and performance calculations

Design show poster creation

Design report writing and editing

Adhesive research for prototype construction

Prototype manufacturing and testing

Patent Research

Ian Neeser

Concept generation

Project management

Housing, shaft, and rotor design

Pro-E modeling and publishing

Project planning (WBS, Gantt chart, scope, etc.)

Manufacturing design

Prototype purchasing logistics

Pat Quinn

Conceptual design, PFMEA

Design specification analysis and evaluation

Technical review of existing products and technologies (bell atomizer, air bearings,

impulse turbines)

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Research regarding customer needs and applications, Competitor product analysis and

evaluation

Bearing selection, analysis, and performance calculations

Prototype manufacturing, assembly, and testing procedure

Data analysis and technical review of prototype performance tests

Scott Kelley

Concept generation

Pro-E modeling

Background Research

Design report writing and editing

Housing, shaft, and rotor design

Prototype manufacturing and testing

Kevin Van Batavia

Concept generation

Background research (impulse and reaction turbines, pneumatic air turbines, balance

calculation)

Design report assignments 1-5 final formatting and editing

Assembly tool design

Air consumption calculations

Curved rotor Pro-E modeling

Reverse Engineering (Die Grinder/Vane turbines)

Prototype building, modifications, and testing

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1 Problem Definition

Many products require finishes depending on their aesthetic standards and working

environments. For instance an automobile requires a paint application and finishing coat with

the durability to last the duration of the vehicle’s life in addition to having a finish that is

attractive to potential buyers. There are many ways to apply the finishes needed for products;

one of those ways is to use a robotic spray system such as a liquid finishing rotary bell atomizer.

This project focuses on a specific atomizer called the Ransburg RMA-303. This product is

powered by an air turbine which is situated inside the housing. The air turbine features an air

bearing, and retails for approximately $7,000. The focus of this project is to design a low cost

version of the air turbine and bearing assembly. A functional prototype will be designed to work

in the Ransburg RMA-303 model with the current bell cup.

1.1 Problem Scope

The problem is that current commercially available rotary atomization equipment is too

expensive for all potential customers. Due to this, our team’s scope is to design, prototype, and

test a pneumatic air powered turbine that costs a fraction of what is currently commercially

available for use on rotary atomization equipment. The new turbine assembly must be designed

such that it can be evaluated to meet certain performance requirements set forth by the advisor,

Graco Inc. The performance requirements that will be evaluated are maximum speed, air

pressure, air consumption, and life expectancy. In addition, the key parameter of interest is the

cost of the new assembly. In order to lower the cost of the new turbine assembly the values of

the performance requirements will be approximately half the values of the currently

commercially available products. By decreasing these values the new product will be designed

to target new customers who are interested in fine finish quality and low cost as opposed to the

ultra-fine finish and expensive cost of current products. The potential customers for the new

product are off-highway equipment manufacturers, such as Caterpillar, Bobcat, and John Deere.

Another key customer for this project is our advisor, Graco Inc., who hopes to someday make

this product commercially available.

1.2 Technical Review

1.2.1 Rotary Bell Atomizer

A rotary bell atomizer is used to achieve increased paint finish quality and higher paint transfer

efficiency. A better finish quality is achieved by atomizing the paint prior to being applied on the

product. Atomizing is when paint is turned into a directed mist of extremely small particles.

Paint is atomized by being sent through the middle of a spinning bell shaped cup where the

centrifugal force flings the paint off of the end. The faster the bell cup spins, the finer the paint

particles will be, thus giving a better finish quality.

A basic representation of centrifugal atomization can be found in Figure 1.2.1.1. Paint transfer

efficiency is defined as the amount of paint that reaches the product divided by the amount of

paint used in the process. This transfer efficiency is increased by means of two different steps.

The first step is to negatively charge the atomized paint particles. This negative charge is applied

directly by an internal charge, known as electrostatic spray charging, where charge is picked up

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by the paint droplets as they travel to the bell cup. After the paint has been negatively charged it

is attracted to the grounded target as depicted in Figure 1.2.1.1. The second step for increasing

transfer efficiency is to use air flow to shape the direction of paint particles towards the product.

[10]

Figure 1.2.1.1: Centrifugal Atomization with Electrostatic Spray Charging [10]

1.2.2 Turbine Components

The most expensive component of high-end rotary bell optimizers is the turbine. The turbine

spins the bell cup to atomize the paint. Existing models use air impulse turbines equipped with

air bearings to achieve high rotational speeds and prolonged life expectancy. Our low cost

solution will focus on new bearing materials.

Air Bearings

Air bearings are capable of achieving very high rotational speeds with a longer life expectancy

than ball bearings. They are known as fluid bearings which use a pressurized film of air to

support the shaft inside the bore of the bearing. A basic depiction of an air bearing is shown

below figure 1.2.2.2. The pressurized air travels along the length of the shaft until it is exhausted

to atmosphere at either end. In the presence of radial loads, the air pressure surrounding the shaft

naturally adjusts to resist the force. With only pressurized air transferring forces between the

bore and shaft, internal friction is minimized. This allows the turbine to reach very high speeds

with little wear on the internal components of the turbine. [9]

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Figure 1.2.2.2: Hydrostatic Air Bearing: External Pressure Supply [9]

The majority of the turbine expenses can be attributed to the use of air bearings. They have a

high cost because they require precision manufacturing to maintain the proper functionality and

accuracy of the bell atomizer at high rotational speeds. Air bearings require a very small and

precise clearance between the bore and shaft. Variations in the geometry of these bearing

components will cause metal to metal contact and a break in the fluid cushion, ultimately

resulting in failure. [9]

Ball Bearings

Many factors must be accounted for when determining the appropriate ball bearing for a given

application. In the case of a rotary bell atomizer, our main concerns are life expectancy, speed,

radial loads, alignment precision, and integrated seals. Using the chart shown in Figure 1.2.2.2,

we determined that the deep groove ball bearing met the characteristic requirements the best. The

next step is to determine the size bearing needed for the application. The dimensions of our

turbine design required the inner diameter of our bearing to be 20mm. This bore size allows the

paint tube to pass through the middle of the shaft to the bell with the appropriate clearance. With

the bearing size and style determined, a desired rotational speed must be set. Material and

precision characteristics are then chosen such that both the speed and size requirements are met.

Lastly, proper lubricants, integrated seals, and maintenance requirements are determined to best

accommodate the bearing during operation. The life expectancy of the bearing can be calculated

using Equation 1.2.2.1.

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Figure 1.2.2.2: Relative bearing style selection chart [7]

Equation 1.2.2.1: Bearing life expressed in operating hours [8]

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Impulse Turbine

Turbines are rotary mechanisms that convert the kinetic energy from a fluid flow into rotational

work output. The current rotary bell atomizer model uses an air impulse turbine to exert a torque

on the bell cup and shaft. This style of turbine uses fixed nozzles that expel a jet stream of air

onto a fin that changes the direction of the fluid. The nozzles serve to accelerate the air

molecules by converting the fluid pressure into fluid velocity. Figure 1.2.2.3 illustrates the

general concept of an impulse turbine and Volume II, Section 1.4.1 discusses several possible

rotor designs that convert kinetic energy to torque in slightly different manners.

Figure 1.2.2.3: General Concept Impulse Turbine [11]

1.3 Design Requirements

There are five existing design requirements that our turbine must meet in order to meet the

design criteria. The design requirements of the turbine assembly are derived directly from

specific customer needs which uniquely define the problem at hand. The five design

requirements driving the project are listed below.

1. The turbine must be capable of maintaining continuous speeds between 30k and 40k

RPM.

2. The turbine must be capable of maintaining operating speeds using an air pressure

of less than 90 psi.

3. The turbine air consumption must be no more than 24 SCFM of air.

4. The production cost must be no greater than 250 U.S. dollars

5. The operating life expectancy of the turbine must be at least 2,500 hours.

Stationary

Nozzles

Air Stream

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1.3.1 Maintaining Continuous Speeds between 30k and 40k rpm

For many applications, paints and coatings serve a primary purpose of preventing corrosion and

deterioration, with aesthetics being a secondary consideration. The desired rotational speed range

allows the turbine to maintain a high-grade finishing quality. The targeted customers, Caterpillar

and Bobcat, need their machinery to be adequately protected from a wide range of harsh

conditions encountered in the field while simultaneously maintaining a certain level of visual

quality. This level of quality and functionality is also desirable in many other industries such as

woodwork, plastics, industrial buildings, bridges, etc.

1.3.2 Working Air Pressure: Under 90 psi

The working air pressure of the turbine design is limited to 90 psi. This pressure is based on

common availability air sources across the industry. To be successful, the turbine design must

have a certain level of adaptability.

1.3.3 Air Consumption: Under 24 SCFM

The air consumption was limited to a volumetric flow rate under 24 SCFM as a requirement of

the customer. The turbine must operate efficiently in order to maintain or reduce the electricity

costs associated with compressors.

1.3.4 Production Cost < 250 U.S. dollars

Our sponsor specified that low turbine production cost is the driving factor and key desire within

the targeted industry. Companies like Caterpillar and Bobcat do not require the high-end paint

finishes like the automotive industry, but cheaper options with adequate performance capabilities

are not yet available. A low cost turbine with mid to high paint finishing capabilities has the

potential to reach a broad consumer base in this industry.

1.3.5 Life Expectancy > 2,500 hours

The turbine design must have a life expectancy long enough to remain cost effective to the

customer. Product replacement and maintenance costs must remain substantially lower over time

in comparison to the existing high-end turbines. This requires our turbine to last just under 6

months, operating 16 hours a day.

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2 Design Description

The following subsections provide an in-depth description of the low cost turbine design.

2.1 Summary of Design

Our design has four major components: housing (1), rotor (2), bearings (3), and shaft (4).

Figure 2.1: Picture depicting 4 major components:

Housing

The housing consists of two parts, a rear section and a front section, which directs the airflow

and secure the bearings. The rear section contains both the inlet hole, which provides a means

for the air to enter, and the exhaust holes, which provide a means for the air to exit once it has

finished turning the rotor. The front section provides the chamber for air to flow as well as the

space for the rotor to spin. It also provides the means of attaching the bearings.

Rotor

The second portion of the design is the rotor which utilizes the airflow to spin the shaft. It

provides the mechanism for converting the airflow into rotation of the shaft to facilitate usable

work. The airflow causes the rotor to spin, which in turn spins the shaft due to their physical

connection.

Bearings

The third portion of the design is the bearings, which secure and align the shaft. When selecting

a bearing, it is important to consider the application in which it will be used, the stresses that will

be applied and the lubrication between the sleeve and the balls. However, one of the most

important aspects to consider is the bearing life in its application. Bearing life is defined as the

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number of revolutions or operating time at a specific speed in which a bearing will perform until

failure occurs. The bearing life depends on various different factors; the loading, operating

speed, operating temperature, lubrication, contamination, maintenance, fitting, and many other

working factors. Due to all these factors, it is very hard to know the exact bearing life for an

individual bearing. However, the life of the bearing can be estimated by the basic life rating

(L10), which is a standard defined by ISO (International Organization for Standardization) and

ABMA (American Bearing Manufacturers Association). It is the life in which 90% of a large

group of similar bearings can be expected to obtain or exceed. This means only 10% of these

bearings fail due to material flaking which is the wearing of the ball and the sleeve.

Shaft

The final portion of the design is the shaft which is connected to the bell cup which in turn is

responsible of atomizing the paint. The shaft also provides a means of connecting the turbine

and bearings. In addition, the shaft provides a pathway for the paint to flow to the bell cup.

2.2 Detailed Description

2.2.1 Functional Block Diagram

Figure 2.2.1: Functional Block Diagram of Automated Paint Spray

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2.2.2 Functional Description

1) Housing

The housing collects and directs the pressurized air to the backsides of the rotor blades.

When its brake port is pressurized, the air is directed at the front side of the rotor blades,

causing the shaft to decelerate more quickly. The housing also constrains the bearings,

which in turn, constrains the rest of the components.

2) Rotor:

The rotor is fixed to the shaft, and spins it using its rotational energy acquired from the

moving air molecules.

3) Bearings

The bearings constrain the shaft to the housing. Which in turn constrains the bell cup and

rotor to the housing also.

4) Shaft:

The bell cup is screwed onto the end of the shaft. The shaft transmits its rotational

energy (originally taken from the rotor) to the bell cup.

5) Bell Cup:

The bell cup receives paint from the feeder and flings it off at a very high velocity,

causing the paint droplets to atomize.

2.2.3 Overview Drawings

Figure 2.2.3: Assembly line drawing: (1) Housing; (2) Rotor; (3) Bearings; (4) Shaft; (5) Bell

Cup

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1) Housing

Figure 2.2.3.1: Rear Housing

Figure 2.2.3.2: Front Housing showing air distribution

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2) Rotor

Figure 2.2.3.3: Turbine

2.3 Additional Uses

There are a number of additional uses in which our design or a modified version of it could be

applied. It can be applied in any application where a relatively high rate of rotational speed is

required without the need for sustaining moderately heavy loads. One example in particular

could be for a hand held cutting wheel or light grinder. There are also a number of feasible

variations that could be applied to our design which include the number and placement of the

bearings as well as the shape or characteristic of the turbine.

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3 Evaluation

3.1 Evaluation Plan

The air powered turbine design was evaluated on the basis of five primary design requirements

that were set forth in the problem definition phase of the project. In Table 3.1 a summary of the

design requirements and each corresponding validation plan are shown.

Table 3.1 Summary of Design Requirements and Method of Evaluation

Design Requirements Method of Evaluation

Rotational Speed: The turbine must achieve an

operating rotational speed of 30k to 40k rpm.

A digital tachometer will be used to measure

the rotational speed while operating.

Working Air Pressure: The air pressure at the

operating rotational speed must be under 90

PSIG.

Air pressure gauges will be used to monitor the

pressure while the turbine is operating.

Working Air Consumption: The air

consumption under operating conditions must

be under 24 SCFM.

A flow meter will be used to measure air flow

while the turbine is operating.

Cost: The total manufacturing cost of the

turbine must be less than $250.

A cost analysis of each of the components for

the turbine assembly, as well as labor costs will

be done.

Operation Life: The turbine must have an

operating life of 2500 hours.

Due to the limitation of time calculations will

be made by hand and an accelerated life test

will be performed to best estimate the turbine

life.

3.2 Evaluation Results

3.2.1 Speed: 30,000 – 40,000 RPM (Supporting Documents: V.2, Section 3.1.1)

The turbine speed requirement lies at the foundation of the design. The operating speed is

directly reflected in the paint finish quality of the bell atomizer and stands as the reasoning

behind this specific range of operation. The goal of this evaluation is to determine an optimal

combination of design characteristics that will result in the highest rotational speed output.

Speed maximization was tested on the basis of two design characteristics consisting of rotor

design and inlet hole size. Three rotor designs were assembled into a set of the turbine’s first

iteration prototypes. The assemblies were evaluated by their speed output at a constant pressure

input of 90 psi. A second iteration of prototypes were manufactured with inlet hole diameters

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ranging from .089 to 0.1495 inches. Rotational speeds produced by each port size were

documented in relation to working air pressures ranging from 10 to 90 psi.

Of the first iteration of prototypes, the simple rotor design was unable to complete the speed test

due to operational failure. The second iteration of prototypes managed to produce data with clear

relationships between inlet diameter and speed output.

The curved rotor was chosen as the best design as it recorded an average speed 15,000 RPM

greater than that of the crescent design. The simple design was eliminated on the basis of

adequate functionality. Using the second iteration of prototypes, the inlet hole of 0.089 inches

was found to produce the highest speed output at a value 69,000 RPM. It was also noted that the

0.089 inch inlet produced greater output speeds at input pressures beyond 50 psig while the

0.136 inch inlet produced the greatest output speeds at pressures lower than 50 psig.

3.2.2 Working Air Pressure: Under 90 psi (Supporting Documents: V.2, Section 3.1.2)

The working air pressure design requirement was limited to 90 psi on the basis of standard

pressurized air supplies used throughout the industry. The goal of this experiment is to achieve

operational speeds at minimized working air pressures.

To evaluate speed efficiency in relation to air pressure, the data collected in the previous speed

experiments was analyzed with respect to inlet hole size. The data within the specified operating

speed range was the primary focus in order to determine which hole diameter and pressure were

capable of producing the highest speed output per unit of pressure.

The 0.136 inch inlet hole produced the largest turbine speed output at every pressure tested

within the operating speed range. Table 3.1.2 (Volume II) was made to specifically focus on the

0.136 inch inlet performance within this region. Each point was given a slope value with respect

to the adjacent data points to characterize trends within the plot.

We found the 0.136 inch inlet hole was the most efficient prototype within operating speeds.

This inlet diameter was found to operate more efficiently at lower working pressures. The most

efficient point was found to lie at a working pressure of 20 psi and produced an output speed of

34,000 RPM. It was noted that the Ransburg model operated at 40,000 RPM at a pressure of

20psi.

3.2.3 Air Consumption: Under 24 SCFM (Supporting Documents: V.2, Section 3.1.3)

Air consumption is a costly component of the turbine operation. Our goal is to minimize the air

consumed by the turbine design during operation in the required speed range.

The data relating air consumption with speed was recorded during the speed output experiment.

The relation of these two variables was evaluated on the basis of achieving adequate speeds at

efficient rates of air consumption. Figure 3.1.3 shows turbine speed versus air consumption was

created to evaluate the performance over the four inlet diameters.

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Table 3.1.3 was constructed to track the changing slope parameters of the 0.136 inch prototype.

From Figure 3.1.3, we determined the 0.136 inch inlet hole be the most efficient prototype within

the defined speed requirement range. Using the tabulated slope constants of this prototype plot,

we were able to determine that the most efficient air consumption rate was at 7.75 SCFM with an

output speed of 34,000 RPM.

3.2.4 Cost: Under $250 (Supporting Documents: V.2, Section 3.1.4)

Cost is a primary design requirement of the air turbine. The performance of the turbine design

remains irrelevant unless the production cost is less than $250. A cost analysis was performed

and determined the total project cost to be $143.

3.2.5 Operating Life: 2,500 hours (Supporting Documents: V.2, Section 3.1.5)

The low-cost turbine is only beneficial to the customer if the product life expectancy is of

adequate length to remain cost effective in the long term. To maintain value with the customer,

the life expectancy was determined through our project advisers to be 2,500 hours.

Normally products are tested continuously under operating conditions to determine life

expectancy. Due to time constraints, a physical analysis was not able to be conducted. Instead,

the bearings were labeled as the limiting component of the turbine. This allowed us to determine

the life expectancy of the turbine as it relates solely to the performance of the bearings. Possible

bearing loads were evaluated and used to mathematically determine the life expectancy of the

bearing, and subsequently, the turbine.

Using the basic rating life equation for bearings and supporting load calculations, the life

expectancy was plotted over the intended operational speed range of 30,000 RPM to 40,000

RPM. Figure 3.1.5 contains life expectancy curves over three different values of maximum radial

offset was included in the analysis.

From the plot we can conclude that our design will last well beyond the required 2,500 hours of

operation if the bearings are in fact the limiting components of our design.

3.3 Discussion

3.3.1 Strengths and Weaknesses

There are a few major strengths and weaknesses that we’ve identified in our design. A strength

we have identified is our design’s ability to reach the required RPM speeds. Through testing

different options for our design we have found a design that was able to exceed the requirement

for speed. This allows us some freedom in new design changes with bearings and exhaust ports.

Cost is another strength of our design; we had a cost requirement of less than $250 and our first

prototype had an estimated cost of about $200. By being below the required cost on our first

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iteration allowed we were able to explore higher quality bearings to improve product life.

Furthermore, we project our cost to be even lower when forecasted for mass production, which

adds to this strength.

One of the weaknesses is the life expectancy. We have a goal of 2500 hours for a life expectancy

but that goal cannot be validated in the amount of time we have. With the projects time

constraints, it will require engineering judgment to estimate how long our design will last. There

are options to perform accelerated life testing by means of heating the components to a higher

operating temperature or running the turbine at a higher speed than what it is rated at. There are

issues with both tests, the accelerated speed testing method would be running the bearings out of

their rated speeds and it would be difficult to tell how that would affect the bearings and the

effect that the heat test will have is tough to quantify. In our first design, we encountered issues

with the bearings coming unglued from the housing. We identified that the problem occurred

because the glue was not allowed to set long enough and an insufficient amount of glue was

used. For our second design we have decided to use press fits and not use the gluing technique.

We thought we could turn this weakness into a strength by press fitting the bearings onto the

shaft and into the housing. In the second design we tried the press fits and it was too tight of a fit

resulting in a high friction force on the bearings. We determined that pressing the bearings

would not be an option at this stage of the product’s life and gluing the bearings would have to

suffice.

3.3.2 Next Steps

The next step in the design process would be to start moving the proof of concept towards a test

worthy prototype. The current design has met the initial conditions of speed, air pressure, air

consumption, and potential cost. As the prototype stands right now, it is not ready for production

and requires additional characterization testing. Future needs that need to be addressed include;

the life, combustible environment testing, and spray pattern. Each of these needs require a set of

conditions that need to be laid out in advance to provide focus for testing. The life test has

already been set at an operating life of 2500 hours and was not completed during the initial tests

due to a lack of time. In order to accomplish this test, the current functional prototype needs to

be run at operating speed (40,000 rpm) for 2500 hours. If the prototype is still functioning after

this test, then it passes, otherwise the failure mode needs to be evaluated and a next iteration of

prototype designed to address the failure. The combustible environment test entails running the

proposed device in a combustible environment for a prolonged period of time to test for any

conflagrations. Any failures during this test results in a rework of the design to rework the

offending pieces. For the last test, spray pattern, the general mist quality and distribution pattern

are looked at. This test involves passing colored water through the device while it is running at

operating conditions. The water is intended to be evenly distributed along the testing surface

without having any large splashes or distortions. During testing, spray should not dribble off the

end of the device as this creates unnecessary waste.

Once these characterization tests have been completed a more intense analysis should be done in

order to optimize performance and make the device ready for manufacturing. Some things to

consider include the addition of an o-ring to replace the current NPT fittings, having the

assembly balanced to reduce off axis forces, and the creation of manufacturing fixtures. The

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removal of the NPT fittings creates a smaller profile and allows for less space to be taken up

within the robotic arm. Also, by putting an o-ring on the back of the turbine it allows for only

one hose to be used on the inside of the robotic arm, the single hose delivering paint. By having

the assembly balanced, the stresses as a result of unsteady loading become zero. Reducing the

amount of stress on the device will increase its life span and potentially help with its

performance. The last suggestion was to create manufacturing fixtures. These fixtures would be

used to assist in the assembly of the housing. One such fixture could be a simple profile cutout

of the front housing that allows for the shaft and bearing assembly to be inserted and glued into

the housing while maintaining proper alignment. Another convenient fixture would be to have

the shaft and bearings supported so that a precise alignment and positioning of the bearings could

be maintained on the shaft. Once these tasks have been accomplished, the turbine assembly will

be ready for manufacturing.