volume ii - university of minnesota · graco inc. liquid finishing rotary bell atomizer turbine...
TRANSCRIPT
Graco Inc. Liquid Finishing Rotary Bell Atomizer Turbine
Volume II
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
2
Table of Contents
1 Problem Definition Supporting Documents………………………. 4
1.1 Annotated Bibliography…………………………………… 4
1.1.1 Summary…………………………………………………… 4
1.1.2 References…………………………………………………… 4
1.2 Patent Search……………………………………………… 6
1.2.1 Objectives................................................................................ 6
1.2.2 Search Criteria………………………………………………… 6
1.2.3 Findings…………………………………………………..... 6
1.3 User Need Research…………………………………….. 9
1.4 Concept Alternatives…………………………………. 11
1.4.1 Turbine Design………………………………………………… 11
1.4.2 Bearing Placement…………………………………………… 13
1.4.3 Housing Design……………………………………………… 14
1.5 Concept Selection………………………………………… 16
1.5.1 Rotor Design…………………………………………………… 16
1.5.2 Bearing Design………………………………………………… 17
1.5.3 Housing Design……………………………………................. 17
1.5.4 Concept Chosen……………………………………………… 18
2 Design Description Supporting Documents…………………… 18
2.1 Manufacturing Plan……………………………………… 18
2.1.1 Manufacturing Overview …………………………………… 18
2.1.2 Part Drawings………………………………………………… 20
3
2.1.3 Bill of Materials…………………………………………….. 24
2.1.4 Manufacturing Procedure……………………………………… 24
3.0 Evaluation Supporting Documents…………………………… 26
3.1 Evaluation Reports……………………………………… 26
3.1.1 Speed: 30,000-40,000 RPM……………………………..… 26
3.2.2 Working Air Pressure: Under 90 psi…………………………… 29
3.2.3 Air Consumption: Under 24 SCFM……………………………. 30
3.2.4 Cost: Under $250………………………………………………. 31
3.2.5 Operating Life: 2500 hours…………………………………….. 31
3.2 Cost Analysis……………………………………………… 33
3.3 Environmental Impact Statement………………………… 34
3.4 Regulatory and Safety Considerations……………………. 35
4
1 Problem Definition Supporting Documents
1.1 Annotated Bibliography
1.1.1 Summary
The research that was executed for this project included: air motors, balance calculations,
bearing fatigue life and ratings, impulse and reaction turbines, pneumatic air turbines, adhesives,
and accelerated life testing. The research that was performed aided in the project by:
mathematically solving for bearing life, understanding how and why air turbines work, how to
conduct accelerated life testing, and understanding the different specifications required for
adhering metal parts together.
1.1.2 References
[1] Air Bearing Technology. 2nd ed. Dorset: GSI Group, 2007. Print. Westwind Air
Bearings.
This document describes the basic principles of an air bearing. It explains in detail the two types
of air bearings and their advantages over ball bearings.
[2] Xie, Xiaofan. Comparison of Bearings --- For the Bearing Choosing of High-speed
Spindle Design. Salt Lake City: Dept. of Mechanical Engineering, University of Utah, 04 June
2012. PDF
When selecting a bearing for a high speed spindle it is important to choose the right one for the
design. This research paper is a detailed overview highlighting the difference in most types of
bearings which are used in industry today.
[3] Beardmore, Roy. "RoyMech." RoyMech. N.p., 31 Jan. 2013. Web. 1 Mar. 2013.
<http://www.roymech.co.uk/index3.htm>.
This site provides useful information, tables and formulas related to mechanical engineering and
engineering materials. It provides access to data for design engineers and lists valuable
engineering standards.
[4] Kuznsov, Yuriy. "DEVELOPMENT OF SMALL SIZE PNEUMATIC MACHINES
WITH TURBINE DRIVE GEARS." DEVELOPMENT OF SMALL SIZE PNEUMATIC
MACHINES WITH TURBINE DRIVE GEARS. State Technical University of Nizhniy Novgorod,
2003. Web. 04 Mar. 2013. <http://e-
noosphere.com/Noosphere/En/Magazine/Default.asp?file=20060501_Kuznecov_Chuvakov_Him
ich.htm>.
Research on turbine blade crowns and unique aerodynamic configurations of turbine stages are
described in this document.
[5] "Ransburg :: Aerobell 33 Rotary Atomizer." Ransburg :: Aerobell 33 Rotary
Atomizer. N.p., n.d. Web. 04 Mar. 2013. <http://site.ransburg.com/general-products/item/56/>.
This is the current model Rotatory Atomizer used in the Ransburg atomizer.
5
[6] "Impulse and Reaction Turbines." - Turbines. CODECOGS, 25 Nov. 2009. Web. 04
Mar.
2013.<http://www.codecogs.com/reference/engineering/fluid_mechanics/machines/turbines/imp
ulse_and_reaction_turbines.php>.
Explains the difference between an impulse turbine and a reaction turbine, while going into
detail how each type of turbine works. The velocity triangles and calculations are explained for
both turbines
[7] “Selection of Bearing Type.” –Principles of bearing selection and application. SKF.
Web. 04 Mar. 2013.<http://www.skf.com/us/products/bearings-units-housings/ball-
bearings/principles/selection-of-bearing-type>.
Explains the different bearing characteristics to consider when selecting a specific style of
bearing for a given application.
[8] “Basic Rating Life.” –Principles of bearing selection and application. SKF. Web. 04
Mar. 2013.<http://www.skf.com/us/products/bearings-units-housings/ball-
bearings/principles/selection-of-bearing-size/selecting-bearing-size-using-the-life-
equations/basic-rating-life/index.html>.
Details the basic formula used to calculate the bearing life rating.
[9] “Air Bearing Basics.” –About Air Bearings. Nelson Air Corp. Web. 04 Mar.
2013.<http://www.nelsonair.com/NA_primer.htm>.
Describes basic background information regarding air bearings.
[10]”Atomization.” - Concept and Theory Training. Graco Technical Communications
Department, T. Brajdich, M. Hagman, B. Lind, G. Muir and A. Orr, 1995. Web. 04 Mar.
2013.<http://wwwd.graco.com/Distributors/DLibrary.nsf/Files/CT_Atomization_321027/$file/C
T_Atomization_321027.pdf>.
Explains general information regarding rotary bell atomizer concepts and theory.
[11]”Steam Turbine Electricity Generation Plants.” – Battery and Energy Technologies.
Electropaedia. Web. 04 Mar. 2013.<http://www.mpoweruk.com/steam_turbines.htm>.
General illustration of an impulse turbine.
6
1.2 Patent Search
1.2.1 Objectives
The main objective of the patent search was to find current designs relating to bell atomizer
turbine systems to gain relevant knowledge pertaining to our design. The patent research was
more specially aimed towards the turbine style and design ideas.
1.2.2 Search Criteria
The patents were found using Google’s Patent Search, using the keywords “Bell Atomizer
Turbine”
1.2.3 Findings
From our search there were a few interesting designs for a bell atomizer turbine that aided in the
final design of our product. From the gathered data, we were able to make our design using
some of the similar features but modifying them to fit our exact design specifications. First, US
patent #7721976 is a high speed rotating atomizer that is powered by air to drive an atomizing
bell to apply paint onto a part. A key part to this design is the air bearing which allows for
higher rotational speeds, and the impulse turbine which spins the shaft and converts the kinetic
energy from the moving air flow. In our design an impulse turbine was chosen but the profile of
the blades is much different from the one used in this case. Also, since our design is on a budget,
ball bearings were chosen since they are far less expensive. The second patent design found was
US patent #20130017068, which is an axial turbine for a rotary atomizer. This design is unique
in the fact that it uses an axial turbine and two ball bearings side by side. The axial turbine is
beneficial in the fact that the flow continues along the shaft at the point of entry which allows for
a component to cool the bearings. For our design so far we have chosen a radial turbine, which
places two bearings side by side towards the front of our shaft to allow for rotation.
7
Figure 1.2.3.1: Cover page of Patent #7721972
8
Figure 1.2.3.2: Cover page of Patent #0017068
9
1.3 User Need Research
The long term goal of this design project is to be part of a larger development program to
manufacture a pneumatic air powered turbine to be compatible with the Ransburg RMA-303 at a
lower cost. The primary user needs were produced by Graco Inc. by consulting with their
costumers to determine their needs. Listed below are potential customers that will use the
product.
Caterpillar
Auto shops
Bobcat
John Deere
Other industrial companies
The user needs were determined by conferring with Graco Inc representatives and the results
were complied with their respective importance in Table 1.3.1.
Table 1.3.1
# Need Importance
1 Turbine cost drastically reduced 5
2 Bearing cost drastically reduced 5
3 Functional in single direction 5
4 Turbine & bearing assembly easily accessible 2
5 Brake feature 3
6 Sufficient life requirement 5
7 Turbine is safe 4
8 Turbine can operate at working temperatures 5
9 Turbine can operate at working pressures 5
10 Turbine housing must be compact 3
11 Air consumption must meet standard 4
12 Bell cup must fit into housing 2
13 Turbine can operate at desired speed 5
14 Bearing can operate at desired speed 5
15 Housing can fit into Ransburg RMA-303 2
16 Acceleration time must be sufficient 3
17 Assembly is easy to load into sprayer 4
18 Housing cost must be cheap 5
19 Bearing can operate at working temperatures 5
20 Bearing can operate at working pressures 5
21 Bearing oil/grease compatibility 5
22 Aesthetically pleasing 1
23 Low noise level 1
10
24 Low vibration level 5
25 Explosive atmosphere safe 5
26 Hollow inner shaft diameter 5
27 Axial shaft loading 2
28 Max bearing temp during operation 4
29 Radial Shaft Loading 5
All of these user needs were then used to determine a product specification as shown in Table
1.3.2. Every user need was categorized to a design specification; however, it was acceptable to
use several needs for one specification. Each metric was then categorized by importance and
given both a marginal and ideal value. The marginal value is the lowest acceptable for the need
and the ideal value is the goal.
Table 1.3.2: Product Design Specifications
Need #'s Metric Importance Units Marginal Value Ideal Value
1 Turbine cost 5 US $ 10 to 50 15
2 Bearing cost 5 US $ 60 to 120 60
18 Housing cost 5 US $ 25 to 60 25
1,2 Total Cost 5 US $ < 250 100
3 Single functioning direction 5 Binary YES YES
4 Easily accessible 2 Binary YES YES
5 Brake feature 3 seconds <15 10
6 Life requirement 5 hours >2500 2500
8 Turbine can operate at working temps 5 deg F 120 max, 40 min 70
9 Trubine can operate at working pressures 5 psig 120 max 90
10 Housing must be compact 4 in^3 25 to 40 30
11 Air consumption rating 4 cfm 20 max 10 to 12
12 Bell cup must fit onto shaft 3 Binary YES YES
10 Housing length 4 in 2.5 to 3.75 3.65
10 Max housing diameter 5 in 2.5 to 3.5 3.25
13 Turbine speed 5 RPM 30k-40k 35k
14 Bearing speed 5 RPM 30k-40k 35k
16 Acceleration time 2 seconds 6 to 15 10
19 Bearing can operate at working temperature 5 deg F 120 max, 40 min 70
20 Bearing can operate at working pressure 5 psig 120 max 90
22 Aestheticly pleasing 1 Binary YES YES
23 Noise level 1 db low low
24 Vibration level 3 hz low low
25 Explosive safety 5 Binary YES YES
21 Bearing oil/grease cost 5 US $ 0 to 5 3
26 Hollow inner shaft diameter 5 in .6 to .7 0.63
27 Axial shaft loading 2 lbs 0 to 2 0
11
1.4 Concept Alternatives
There were many design alternatives generated in our group meetings to achieve our design
requirements. The three main components to consider when designing our rotary bell atomizer
turbine are the rotor, the bearing, and the housing. Using many iterations of different design
concepts, we were able to reach an optimal design.
1.4.1 Turbine Design
Concept #1 - Crescent Model:
This crescent design is an impulse turbine which is very similar to that of the Ransburg RMA-
303 which is currently being used in industry. The air hits one end of the crescent shape fin and
is directed out the other end causing the shaft to rotate. The benefits of the impulse turbine
design are that it is ideal for high speed applications and has more stable efficiency profiles.
Figure 1.4.1.1: Concept #1 PRO-E rendering
Concept #2 - Arc Model:
The arc model is currently being used in one of Graco’s smaller hand-held paint application
units. This design is a less complex than Concept #1 however, is still an impulse type turbine.
The air is directed at the blade pushing it forward, thus causing the shaft to move.
12
Figure 1.4.1.2: Concept #2 PRO-E rendering
Concept #3 - Paddle Model:
The paddle model is a very basic impulse turbine. The goal behind this design is a simple part to
manufacture while generating the desired performance.
Figure 1.4.1.3: Concept #3 PRO-E rendering
13
1.4.2 Bearing Placement
Concept #1 - Two bearings placed towards the front of the shaft:
In this design, two bearings are placed side by side towards the front of the shaft. By placing the
bearings together, we are able to create a more concentric alignment. Another effect of having
the bearings stacked, as opposed to using one bearing, is the stability provided.
Figure 1.4.2.1: Drawing of Concept #1
Concept #2 - Two bearings placed at both ends of the shaft:
This design has two bearings, where one bearing is placed at the back of the shaft and one
bearing is placed at the front of the shaft. This variation offers a more balanced load on the
shaft.
Figure 1.4.2.2: Drawing of Concept #2
14
1.4.3 Housing Design
Concept #1 – One Bearing Location Design:
The stacked bearing house design holds both bearings in the front housing unit. The air comes in
the through the inlet located on the rear housing unit and is channeled through numerous outlets
in the front housing to drive the turbine. The air is then exhausted out the rear housing unit.
Figure 1.4.3.1: Front housing of Concept #1
Figure 1.4.3.2: Rear housing of Concept #1
15
Concept #2 - Two Bearing Location Design:
The two bearing location design has a bearing placed inside both the front and rear housings.
This design allows for the turbine to be placed in between the bearings, thus allowing for a more
evenly distributed load.
Figure 1.4.3.3: Front housing of Concept #2
Figure 1.4.3.4: Rear housing of Concept #2
16
1.5 Concept Selection
In order to select a final design concept for each of the components, numerous criteria were
chosen to see the performance of all the possible design concepts. Different weights were
assigned to each of the criteria and the performance of each design concept was scored on a scale
of one to five. A total weighted score was then calculated for all the design concepts to choose
which design would be best for our rotary bell atomizer turbine. The criteria chosen for the
matrix was based on the requirements set forth by Graco beforehand.
1.5.1 Rotor Design Concept Selection:
Table 1.5.1: Rotor Design Evaluation Matrix
Criteria Weight
(1-5)
Concept #1
Concept #2
Concept #3
Turbine Cost 5 + + +
Functioning Single Direction 3 + + -
Braking 2 + + +
Turbine can operate at working
temperatures 2 + + +
Turbine can operate a working
pressures 2 - + -
Can operate for required time 5 - + -
Air consumption 4 + + +
Turbine can operate at desired
speed 5 - + -
Acceleration time 3 - + -
Ease of loading 4 + + +
Low noise level 3 - - -
Low vibration level 3 + + -
Total score 23 38 17
17
1.5.2 Bearing Design Concept Selection:
Table 1.5.2: Bearing Design Evaluation Matrix
Criteria Weight
(1-5)
Concept #1
Concept #2
Bearing cost 5 + +
Turbine and bearing assembly easily
accessible 2 + -
Can operate for required time 5 + +
Bearings can operate at desired speed 5 + +
Acceleration time 3 + +
Ease of loading 4 + -
Bearings can operate at working temperatures 5 + +
Bearings can operate at working pressures 5 + +
Low noise level 4 + +
Low vibration level 4 - +
Explosive atmosphere safe 5 + +
Loading on shaft 4 - +
Manufacturability 5 + -
Total score 48 45
1.5.3 Housing Design Concept Selection:
Table 1.5.3 Housing Design Evaluation Matrix
Criteria Weight
(1-5)
Concept #1
Concept #2
Manufacturing cost 5 + -
Turbine and bearing assembly easily accessible 2 + -
Can operate for required time 5 + +
Bearings can operate at desired speed 5 + +
Ease of loading 4 + -
Low noise level 4 + +
Low vibration level 4 - +
18
Explosive atmosphere safe 5 + +
Loading on shaft 4 - +
Manufacturability 5 + -
Total score 35 27
1.5.4 Concept Chosen:
All rotor concepts were evaluated through prototype testing. The concept chosen based on this
testing was Concept #2, the curved rotor design. The results can be found in Volume II, Section
3.1.1.
The bearing placement design concept chosen was Concept #1, the stacked bearing design. This
design allows for more efficient manufacturability and simplicity. In addition, this design allows
for greater accuracy in the alignment of the bearings.
The housing concept chosen was Concept #1. This concept allowed for easier access to the
bearings as well as allowing the exhaust to be directed away from the direction of paint flow.
2 Design Description Supporting Documents
2.1 Manufacturing Plan (Product)
The following sections 2.1 through 2.1.4 will describe the manufacturing plan for the pneumatic
air turbine. The sections include: manufacturing overview, part drawings, bill of materials, the
manufacturing procedure. This manufacturing plan is for the two-bearing stacked design.
2.1.1 Manufacturing Overview
Housing: There are two parts to the housing; the front and back portions. The housing will be
manufactured out of 6061 Aluminum which will be anodized. The front portion consist of two
distinct diameters, the raw material will be turned on a lathe to reach those desired diameters and
required tolerances. After turning the diameters the center hole will be drilled out using a drill
press, the slots for housing the bearings and turbine rotor will also be drilled at this time. The
piece will then be placed in the CNC machine; the air channel and inlet air channels are
machined out along with refining of the bearing and rotor recesses. Finally the bolt holes are
drilled and tapped. The back portion of the housing consists of only one diameter and is turned
on a lathe to reach the required tolerances. After turning the diameter the piece is placed into the
CNC machine; the exhaust air holes along with the O-ring channel are milled out. Finally the
center hole is drilled on a drill press followed by the bolt holes and the inlet and brake air holes.
Shaft: The shaft will be manufactured out of 303 Stainless Steel. The shaft consists of two
different diameters and a center hole. The diameters are turned on a lathe to reach the required
19
dimensions and tolerances. The center hole is then drilled out. The inner portion of the front of
the shaft is then threaded and given a slight bevel to help stabilize the bell cup.
Turbine Rotor: The turbine rotor is made out of high density polyethylene. The turbine rotor is
cut out using the CNC machine. The piece is placed in the machine and the pattern is routed out.
Bearings: The bearings are outsourced to Boca Bearings.
Assembly: The first step in the assembly is to glue the bearing to the shaft. After letting the glue
cure the bearings are then glued into their slot in front portion of the housing. Once the glue is set
the turbine rotor is press fit onto the. The turbine rotor has a small extrusion which contacts the
inner diameter of the bearing aligning the rotor in place. After the rotor is set the back portion of
the housing is slid on to the shaft with the O-ring placed in its channel and gauge pins are
aligned. The bolts are then screwed into place and the NPT fittings for the inlet and brake air are
attached.
24
2.1.3 Bill of Materials
Table 2.1.3: Bill of Materials
Part
Number Quantity Description Material
Cost ($)
100-1 1 Shaft 303 SS 5.36
201-1 1 Turbine HDPE 10.36
302-1 1 Front Housing 6061 Aluminum 11.65
400-1 1 Back Housing 6061 Aluminum 10.77
700-1 2
Bearing - (20x32x7 mm) -
Boca Bearing
# SMR6804C-YUU/C3
SS over Ceramic Ball
Bearings
71.96
800-1 1
O-ring - McMaster #
9452K126 Buna-N
.11
801-1 2
NPT Fitting - McMaster #
5225K711
Black Nylon and Nickel-
Plated Brass
4.46
802-1 8
Housing Bolt - McMaster #
91251A110 Black-Oxide Alloy Steel
6.14
805-1 2
Gauge Pin - McMaster #
97395A439 316 SS
2.51
Labor 1 hour Assembly Labor 20.00
Total Cost $143.32
2.1.4 Manufacturing Procedure
Housing: 6061 Aluminum (Anodized)
Front Piece:
A. Place raw material onto lathe and turn diameters
a. 2” and 3.25”
B. Place piece onto drill press and drill center hole, bearing slot and turbine rotor slot
a. Center hole diameter = .926”
b. Bearing slot diameter = 1.261” .001”
c. Bearing slot depth from back = .824” .001”
d. Turbine rotor slot diameter = 1.800” .001”
e. Turbine rotor slot depth from back = .240” .001”
C. Place piece onto CNC machine and machine will cut out air channel and air inlet
channels also refine turbine rotor and bearing recesses
D. Drill and tap 8 bolt holes
a. 4-40 UNC-2A
Back Piece:
A. Place raw material onto lathe and turn diameter
a. 3.25”
25
B. Place piece onto CNC machine and cut out exhaust air holes and O-ring channel
C. Place piece onto drill press and drill out center hole
a. Center hole diameter = .85”
D. Drill and bore out intake and brake air holes
E. Tap NPT intake and brake air connection holes
Shaft: 303 Stainless Steel
A. Place raw material onto lathe and turn diameters
a. .866” with threaded inner diameter to allow for bell cup attachment
b. .780” bearing and rotor placement
c. .7860” .0005” step for rotor press
B. Place piece onto drill press and drill out center diameter
a. .640”
b. M18 X 10 .625” threaded and beveled for bell cup
Turbine Rotor: High Density Polyethylene
A. Place raw material onto CNC machine and start machine to cut out pattern
Bearings: Outsourced to Boca Bearings
Assembly:
A. Place a small amount of glue onto outer diameter of shaft near the front cliff of the shaft
and slip bearings over the shaft and down to step
a. Wipe excess glue off of shaft and clean area near bearings
b. Allow time for glue to set 5-10 minutes
B. Place a small amount of glue on the inner diameter of the bearing slot and slide front
portion of the shaft through the front hole of the housing and the bearings into their slot
a. Wipe excess glue off of shaft and clean area near bearings
b. Allow time for glue to set 5-10 minutes
C. Place turbine rotor onto the back of the shaft and press fit turbine rotor down to the
bearings
a. Rotor will have a slight extrusion on one side which should be the leading side of
the rotor when slid onto the shaft, that extrusion will butt up against the inner
diameter of the back bearing helping to align and place the rotor
D. Place O-ring into its channel on the back piece of the housing and place back piece of
housing onto shaft and align gauge pins
E. Screw in bolts and attach NPT air intake connection
26
3 Evaluation Supporting Documents
3.1 Evaluation Reports
3.1.1 Speed: 30000-40000 RPM
Introduction
The turbine design is required to have the capability of operating at speeds between 30,000 RPM
and 40,000 RPM. This speed parameter is the keystone of the turbine’s performance evaluation
as it defines the paint finish quality produced by the bell atomizer. The rotor design and inlet
port diameters were individually evaluated to maximize the rotational speed output.
Method
The speed criteria will be tested over the course of two turbine prototype iterations. Each
prototype isolated an individual design component to evaluate the effects on the speed output.
The first iteration of prototypes evaluated rotor design performance and the second assessed the
performance over different inlet port sizes. Each of these variables was evaluated by comparing
the input air pressure with the resulting turbine speed. However, both air pressure and volumetric
flow rate were measured using gauges directly connected to the pressurized air source.
Rotational speeds were measured using a digital tachometer. The tachometer required a thin
piece of white tape be placed on the visible end of the turbine shaft so rpm measurements could
register on the device.
The first iteration of prototypes contained three identical turbine assemblies, each containing one
of three rotor designs (V.2, Section 1.5.1). The prototypes were operated at a constant air
pressure of 30 psi for 20 minutes to properly break in the bearings prior to testing. The turbines
were then operated at a constant air pressure of 90 psi over a ten minute period. Turbine speeds
were recorded at 30 second intervals over the duration of the test.
A second iteration of prototypes were manufactured to test the output speeds in relation to four
different inlet hole sizes. The four designs tested had diameters of 0.0595, 0.089, 0.136, and
0.1495 inches. Each turbine was assembled with the optimized rotor selected during the prior set
of tests. The input air pressure was varied between the pressures of 10 psi and 90 psi in steps of
5. The corresponding rotational speed was recorded at each step along with the volumetric flow
rate, which was required for subsequent performance analysis.
Results
The rotor performance evaluation over time is illustrated in Figure 3.1.1. It was noted in the data
acquisition that the simple rotor design was unable test at the prescribed input pressure of 90 psi.
The simple rotor became unstable beyond 40 psi so the test was conducted at the reduced
pressure of 37 psi. The performance data of the second prototype iteration is plotted in Figure
3.1.2. The Ransburg data is also included in Figure 3.1.2 for to compare performance. Figure
3.1.3 plots the turbine speed with respect to inlet port diameter to better illustrate the effect that
the hole size has on speed over a given pressure constant.
27
Figure 3.1.1.1: Rotor Design in Relation to Speed
Figure 3.1.1.2: Speed Evaluation vs. Pressure
28
Figure 3.1.1.3: Speed Evaluation vs. Inlet Hole Diameter at Constant pressure
Discussion
The experimental data used to evaluate rotor performance concluded that the curved design was
capable of producing the highest speed averaging to 40,000 RPM. The crescent rotor followed
with an average speed of 25,000 RPM. The simple rotor design failed to operate in a stable
manner so data was unable to be collected at the prescribed experimental pressure. Even after
decreasing the input pressure from 90 psi to 37 psi, the simple rotor design failed in under two
minutes time. This implies our data was constrained by turbine quality in the first iteration of
prototypes. The speed output of the curved and crescent rotor designs can be evaluated in
relation to one another but the speed output of the simple design is inadequate for the purpose of
comparison. However, rotor functionality can be evaluated across all three designs. This is
because three identical prototypes were used to test each rotor. Although we cannot
quantitatively compare the speed output between all three rotors, the simple design can be
eliminated based on its inability to function properly.
From the second iteration of speed tests, we were able to draw meaningful conclusions based on
the correlations of inlet hole size with the turbine output speed. The inlet hole diameter of 0.089
inches produced the largest output speed of the entire test. This maximum speed was recorded as
69,000 RPM with an input pressure of 85 psi. Between pressures 50 psi and 90 psi, the inlet
diameter of 0.089 inches has the largest speed output over each pressure interval. At pressures
below 50psi, the 0.136 inch inlet hole has the largest speed output over each pressure interval.
This crossing phenomenon is also witnessed between the 0.0595 inch and 0.1495 inch inlet
holes. Interestingly, the smaller 0.0595 inch inlet hole produces higher speed outputs between the
two at pressures approximately beyond 50 psi. The larger 0.1495 inch inlet produces higher
output speeds at pressures below 50 psi. This experimental data can be used to draw a decisive
conclusion with regards to inlet hole size as it correlates to speed output.
29
3.1.2 Working Air Pressure: Under 90 PSI
Introduction
The working air pressure is to remain within commonly available levels throughout the industry.
This requires the turbine reach operational speeds with an input air pressure less than 90 PSIG.
The input pressure was tested using each inlet hole diameter to optimize input pressure in
relation to output speed.
Method
This test required analysis relating input pressure to output speed. The data necessary to define
this relation was recorded in the previous rotational speed experiment. Pressure versus speed
with respect to inlet hole size can now be evaluated on the basis of output speed efficiency
within the intended operating range of 30,000 to 40,000 RPM.
Results
The plot relating input pressure to rotational speed can be referenced in Figure 3.1.1.2 of the
previous experiment for the purpose of this analysis. Table 3.1.2 tabulates the 0.136 inch hole
data set within the operating range of 30,000 RPM to 40,000 RPM. The other three hole sizes are
neglected due to the results of the speed analysis for pressures less than 40,000 RPM.
Table 3.1.2: 0.136 inch diameter prototype within operational speed range
Input Pressure
[psi]
Output
Rotational Speed
[krpm]
Local Slope
Constant
10 19.8 2.06
15 30.1 1.42
20 34 0.54
25 35.5 0.25
30 36.5 0.1
35 36.5 0.08
40 37.3 0.5
Discussion
As noted in the rotational speed analysis, the 0.089 inch inlet hole produced the largest output
speeds with input pressures beyond 50 psi. The 0.136 inch inlet hole produced the largest output
speeds for input pressures below 50 psi. The speed output corresponding to this crossing point is
42,500 RPM. This implies that the 0.136 inch hole produces larger output speeds per unit
pressure within the operational range of 30,000 RPM to 40,000 RPM as defined in the design
requirements. Furthermore, the output speed for this hole size only rises from 34,000 RPM to
37,300 RPM between the input pressure of 20 psi and 40 psi, respectively. The small slope
within this region requires a large increase in pressure to produce a small increase in rotational
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speed. From the selected data points tabulated in table 1, we can see how rotational speed per
unit pressure is greatly diminished beyond the input pressure 20 psi.
3.1.3 Air Consumption: Under 24 SCFM
Introduction
The turbine’s working air consumption directly relates to operating cost. For this reason, air
consumption was limited to a volumetric flow rate below 24 SCFM. Air consumption was tested
using each inlet hole diameter to optimize consumption in relation to output speed.
Method
The data required to analyze air consumption with respect to output speed was recorded during
the rotational speed performance experiment. With this data, the air consumption was evaluated
with respect to inlet hole size on the basis of output speed efficiency within the intended
operating range of 30,000 RPM to 40,000 RPM.
Results
Each inlet hole size is plotted in Figure 3.1.3 as turbine speed versus air consumption. Data
points were recorded at input pressures ranging from 10 psi to 90 psi. The Ransburg model was
also included in the plot for comparison. Table 3.1.3 tabulates the 0.136 inch hole dataset within
the operating range of 30,000 RPM to 40,000 RPM. Like the prior pressure experiment, the
remaining three hole sizes were neglected in the table because none produced larger rotational
speeds with respect to air consumption.
Figure 3.1.3: Speed output efficiency in relation to air consumption
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Table 3.1.3: 0.136 inch diameter prototype within operational speed range
Air Consumption
[SCFM]
Output
Rotational Speed
[krpm]
Local Slope
Constant
4.580302028 19.8 7.21
6.015412304 30.1 4.43
7.734101534 34 1.85
8.976822006 35.5 0.88
10.57560156 36.5 0.34
11.99236222 36.5 0.27
13.60233011 37.3 1.82
Discussion
From the plot in Figure 3.1.3, we are able to conclude that air consumption correlates to speed in
nearly the exact same manner that air pressure correlated to speed. In this case, the 0.136 inch
inlet hole produced the highest output speed per volumetric flow rate of the four prototypes for
air consumptions below 15.5 SCFM. We can see in the plot that the output levels off again in the
same regions as the pressure did. Using table 2 to quantify the characteristics of this region, we
can conclude that the output values begins to level off around the air consumption 7.75 SCFM
and speed 34,000 RPM. We must also note that the Ransburg performs similar to the 0.136 in
prototype in its range of peak efficiency.
3.1.4 Cost: Under $250
The turbine’s performance is only relevant if it is achieved through low cost means of
production. For this turbine to remain cost effective, the performance parameters must be
attained with an overall production cost less than $250. For details regarding the cost analysis
evaluation of the turbine design, reference Volume 2 Section 3.2.
3.1.5 Operating Life: 2500 Hours
Introduction Turbine longevity is the final design requirement and serves to unify the two driving design
classifications of performance and cost. The turbine must be designed to operate over a length of
time such that the rate of replacement remains cost effective in the long term. The critical life
expectancy to maintain a competitive price over time equates to a minimum of 2,500 operational
hours. This is slightly less than 6 months of running for 16 hours a day.
Method
Given the inexact nature of fatigue over extended periods of time, life expectancy can only be
defined to a probabilistic extent. Accurate analysis often requires several life tests be conducted
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under operational conditions before a life expectancy can be declared. Due to the time
constraints of the project, we were unable to run any prototypes long enough to draw meaningful
data. Instead, the assumption was made that the bearings are the limiting components of the
turbine assembly. By quantifying the possible loads present on the bearing, the life expectancy
could be mathematically determined using the basic rating life equation for bearings. The
maximum torque load on the turbine was determined be the tolerances of between the bearing ID
and the shaft OD.
Results
The bearing life expectancy is mathematically defined using the equation 1. The basic dynamic
load constant was provided by the manufacturer and has a value of 4032 N. The rotational speed
established as the variable ranging 30,000 RPM to 40,000 RPM. The equivalent dynamic bearing
load is calculated in Equation 1 along with the mass of the shaft and rotational speed unit
conversion.
Equation 1: Bearing life expressed in operating hours [8]
⁄
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Figure 3.1.5: Bearing Life as it relates to turbine speed and radial offset
Discussion
From the bearing life plot illustrated in Figure 3.1.5, we can see that the life expectancy drops
dramatically over the operational turbine speed range. In addition, the life expectancy drops
dramatically between the radial offset values separated only by 0.001 in. These dramatic drops
indicate that very slight differences operating differences can affect the life expectancy
exponentially. Although the tolerances are tight within the product design of our turbine, this
mathematical formula does not represent realistic expectations of the turbine life expectancy.
Even though we cannot rely on the accuracy of these results, the graphs do indicate that the
component tolerances in our design are held to a reasonable standard.
3.2 Cost Analysis
In the bill of materials our cost breakdown is shown in Table 2.1.3 this breakdown is only for the
physical materials needed to make our turbine. There are setup costs that go along with making
these components however; we had Graco give us an estimated setup cost for what it would take
to make all the components in house, a part from the bearings. This one time setup cost was is
estimated to be $112, this cost includes setting up the CNC machine for rotor production as well
as the lathe for machining the shaft and housing components.
We did estimate a labor cost for the entire part in the bill of materials, we estimated this cost to
be $20. This cost value comes from estimating the machining and build time for the product to
be about one hour. Depending on the cost of labor at the current time this cost could fluctuate
but it is a good starting point.
We used an annual forecast of 200 pieces to estimate our final cost of our product, so the cost
stated in the bill of materials is an accurate depiction of what a single unit of our product will
cost. Looking at the cost breakdown structure, the bearings are the component that stand out,
they are about half of the cost of the entire assembly. Being that the bearings are the only main
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component not to be made in house at Graco, this cost is unavoidable. The price of the bearings
does drop with quantity, so with larger orders and negotiations that bearing price could be
brought down even more. The majority of the cost for the other main components comes from
the material that they are machined out of as well as the total setup cost discussed earlier. The
housing is the component that requires the most material but it is machined out of aluminum to
keep cost down as well as other reasons.
There is only one operating cost associated with the cost turbine it is the cost of air consumption.
When operating a pneumatic air powered device the costly component is the air consumption not
the air pressure. Our air turbine does require more air consumption than the Ransburg model at
operating speeds, but our model has eliminated the need for an air bearing which requires its own
air supply to be functional. The price for air consumption is difficult to quantify, it will depend
on a variety of factors ranging from the efficiency of the air compressors used to power the
device to the method of how the electricity is supplied to the building.
Comparing our cost to the Ransburg air turbine, the current model on the market, we see that our
model is very cost effective. Our air turbine design manufacturing cost is a fraction of the
manufacturing cost for the Ransburg air turbine. The retail cost of our turbine is unknown at the
moment but it will certainly be cheaper than the $3,785 retail price tag on the Ransburg. While
there are performance differences between the two designs, our air turbine has proved that it is
able to produce a less expensive functional product. Our turbine does have a smaller life
expectancy but even purchasing up three of our product versus one of the Ransburg air turbines
the customer would still be saving money.
3.3 Environmental Impact Statement
Purpose and Need: The current products on the market are very expensive and are over-
engineered for the type of applications that our turbine assembly is designed for. Our pneumatic
air turbine provides a low cost yet high performing alternative to the high priced turbines on the
market now. The current product is designed to help apply a very high quality finish for the
automotive industry; this quality of a finish is not needed for all applications. For customers
who still want a fine finish but are not worried about it looking like a brand new Lexus and don’t
want to spend a fortune each time the turbine needs replacing, our product provides the perfect
alternative.
Impact to Environment: Through the life of our product the turbine will impact the
environment in a few different ways, the first and most important is what will happen with the
assembly when the product is deemed no longer good enough to perform. There are few
different options that one could take, the first being to recycle all the metal parts of the assembly,
the housing can be completely separated from the parts and is made out of aluminum, which
could be melted down and made into recycled aluminum stock. The same can be done with the
shaft and bearings, the stainless steel used to make the shaft can be melted down similarly to the
aluminum and recycled back into raw material stock, the bearings could go through the same
process. The rotor, which is made out of HDPE, can also be recycled and turned back into raw
material stock. Another option for recycling the components of the turbine could be to reuse the
housing entirely. We do not anticipate the housing being the component that limits the life of the
35
assembly, if this is the case and the bearings fail for instance, the housing could be returned and
the reloaded with new bearings. The biggest help to environment that our product offers over the
old versions is that it is easily interchangeable with a new assembly so the entire paint arm would
not have to be replaced. In this case the only thing being exchanged is the turbine, not the bell
cup, not the paint hoses, nor the plastic casing of the paint arm. There is another indirect way
our product impacts the environment and that is through the paint transfer rate. The higher the
paint transfer rate the less paint that will be floating around polluting the atmosphere. Our
turbine will provide the bell cup with a speed that will produce a high paint transfer rate allowing
for the paint to attach to the intended surface.
Alternatives to Design: Our PDS call for such a high performing part that the materials used to
make our product must be of the highest quality. It is difficult to create such a high performing
device and use materials that are meant to degrade over time or are not as strong as the metals we
have chosen. With that being said there is one key alternative that can be explored, the first
being going with a plastic housing rather than aluminum. The difference would be the plastic
case could be easier to make once there is a mold made for it but of course that requires a
production of a mold. The other advantage could be in the ease of recycling the housing, plastic
recycling is a hot topic and there is a vast infrastructure in place for the recycling of plastics.
Plastics on the other when not recycled correctly can cause major environmental issues so we
would consider an end-of-life reclamation program. The program could call for all the end life
products to be shipped back to distribution and determined the main cause for their failing. If the
main cause was the bearings, as mentioned above, the bearings could possibly be replaced and
the housing could be reused. If the reason for failing is something else, like a housing or rotor
malfunction the part could then be disassembled and sent off to the appropriate recycling centers.
A biodegradable lubricant would only be applicable to the bearing component of our assembly,
we are outsourcing the bearings and finding a lubricant that can handle the speeds, temperatures
and pressure that our assembly will see is a difficult and expensive task.
Discussion: The big alternative in the housing material would potentially add to initial
manufacturing cost of the part but may drop the long run cost. The additional cost would come
from need to manufacture a mold for the plastic housing as opposed to machining the part on the
lathe with the aluminum housing. The initial cost of making a mold would be expensive but the
raw plastic material would cost less than the raw aluminum material so we could save money in
the long run. There is another issue that comes into play with a plastic housing, the tolerances
required to fit the shaft and bearings into place could be an issue. We plan to press fit the
bearings into the aluminum housing which requires tight tolerances and with a plastic mold the
tolerances may not be what we need. All in all our product impacts the environment in different
ways good and bad, but by providing a product at a low cost and continuing with such high paint
transfer rates our product is providing a good solution to society.
3.4 Regulatory and Safety Considerations
The product must conform to various UL and OSHA safety standards for explosive atmospheres.
It will be used in environments containing heavy paint fumes. To meet these standards, we used
almost all conductive metal components in our design. The components that are non-metals are
in constant close contact with metal surfaces, eliminating any chance of static electricity buildup.
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Our only safety concern for the product is the amount of noise the device emits while operating.
While in use in industry, the device will rarely be operating in the same room as personnel,
which makes it a minor concern. But if humans are in the area, ear protection will be required.