Four Ball Accelerated Wear Tester

Department of Mechanical EngineeringFall Semester 2014

Mechanical System Design CONTROLS TEAM STRUCTURES TEAM FABRICATION TEAM

Ana Dungan Whitney Stregles Daniel Griffin

Kelsey Kaht Robert Nalecz Colin Holliday

Steve Soto Riley Shay Casey Sheppard

John Willis Jordan Ansley Michael Spaulding

Ibrahim Ahmed

Background and Design Development

Four Ball Tribometer❖ Tests a lubricant’s extreme pressure properties under high contact

in pure sliding or pure rolling motion❖ In this design, a ½ inch diameter ball is pressed against three

similar balls at a set force. The top ball will spin against the three lower balls creating wear scars on the balls.

❖ The force and torque applied to the system are measured and this data, along with the appearance of wearscars, enables the user to concludewhich lubrication is the most efficient

Example Set-Up

Note: This is not our 4-Ball Tribometer

ObjectivesSuccessfully design and fabricate a four ball accelerated wear tester:

➢ Thoroughly research and develop major concepts and compare constraints

➢ Develop a design that rotates a top ball under a force causing friction and wear on the bottom 3 balls

➢ Develop a prototype to test major concepts

➢ Develop methods for measuring wear, torque, load, and temperature

➢ Establish a budget for the project

ASTM StandardsASTM D2266 ASTM D4172 ASTM D5183

Value Tolerance Value Tolerance Value Tolerance

Force Applied40 kgf 0.2 kgf 15 kgf 0.2 kgf 40 kgf Not Given

392 N 2 N 147 N 2 N 392 N Not Given

Lubricant Temp

75 C 2 C 75 C 2 C 75 C 2 C

167 F 4 F 167 F 4 F 167 F 4 F

Speed 1200 rpm 60 rpm 1200 rpm 60 rpm 600 rpm Not Given

Duration 60 min 1 min 60 min 1 min 60 min Not Given

Oil Level very top of cup 3mm above top of balls 3mm above top of balls

[1]

Design Process❖ The design of the 4-ball tribometer was changed several times.❖ The initial design involved a lever and an inline motor.❖ The second design included the drill press that was donated to

our team and the previous lever idea.❖ The final design utilizes a pneumatic cylinder and was

upgraded from the use of a manual regulator to the integration of a data acquisition concept and force sensor components to control the applied force.

Initial Design❖ Basic Concept

➢ Not technologically advanced❖ Inline Motor❖ Lever Arm

➢ Strategically placed fulcrum➢ Force applied to the bottom

❖ Wear Measurement➢ Microscope and Volume Displacement

Second Design❖ Lever arm design incorporated onto

the drill press❖ Existing platform mount retains

translating shaft ❖ Two Cups Inside One Another

➢ Increase Repeatability❖ Weights used to apply load❖ Wear Measurement via Camera

Second Milestone Design❖ Air cylinder with manual

regulator to apply force from the top

❖ Thrust bearing under the cup for self-alignment

❖ Fixed bottom plate for improved repeatability and accuracy

❖ Force sensors implemented on the cup

❖ Wear measurement camera❖ Hot plate for heating the lubricant

to the test standard

Concerns After Milestone Two❖ Pneumatic Cylinder:

➢ Manual Air Regulation Accuracy

➢ Air Cleaning

❖ Data:

➢ No Way to Directly Calculate Normal Load

➢ Controlling Motor Speed

❖ Cup:

➢ Dual Cup Design for Repeatability Created an Extra Moment to Consider

❖ Force Application:

➢ Not Constant Over Time

➢ Weights Capability to Fall Decreased Safety Factor

❖ Heating and Cooling:

➢ Overheating would lead to welding of balls

➢ Maintaining the temperature at the standard without overheating

❖ Safety:

➢ Temperature Intensity and Ball Welding Concerns Over Time

Controlling Applied Force❖ Manual Regulator

➢ Budget-friendly➢ Not accurate➢ Needs to be controlled better

❖ Controls Loop➢ Continuously checks and displays data ➢ Maintains desired force output➢ Costly

Final Re-Design ConceptsDesign Changes:❖ Added Filter to the Pneumatic Cylinder

❖ Added Electronic P-Valve

➢ Controls loop feeds data to constantly regulate pressure

❖ Redesigned for Addition of Axial Transducer

➢ Input Data relays to the DAQ for direct normal force measurement

❖ Self-Alignment Plate Design for the Axial Transducer

❖ Replacement 3-Phase Motor to Allow for the Addition of Variable Speed Drive

❖ Added Heating Elements and Temperature Controller

❖ Added Auto-Stop Controlled by the Temperature Controller

Final Design❖ Drill press was further modified❖ Pneumatic cylinder added to apply force❖ Axial Transducer incorporated for direct

force measurement❖ Auto-Stop Controller incorporated for

increased safety❖ Addition of plate to platform for mounting

cup and axial transducer

Theoretical Testing and Equations

Theoretical Testing❖ Finite Element Analyses (FEA) were performed to determine the

theoretical stresses and deformation results based on the designed components under the standard conditions determined.

❖ Theoretical Calculations were used to determine the dimensions of the air cylinder

Given:➢ Lever Arm Length= 4 in.➢ Bore Size= 7/16 in.➢ Gear Ratio= 13:1➢ Pinion Diameter= I in.➢ From ASTM D2266 Standards, Applied Force= 88.18

lbf

Collet FEA

Thermal FEA

Thermal analysis determined that no

insulation is necessary.

Theoretical Calculations❖ Tangential Force at Pinion:

➢ By considering the relationship between forces and the mechanical advantage of the gear ratio, Ft was calculated.

❖ The Moment about Pinion, M :

Theoretical Calculations❖ Required Force Output from Air Cylinder:

➢ Using the Equation for Moment at the End of a Rotating Rod as a Result from the Air Cylinder Force, FA:

➢ Working Area of Cylinder, A:

❖ Required Internal Pressure of 7/16 in. Bore Air Cylinder:➢ From Pascal’s Law, P:

Budget

Budget

❖ The initial budget presentation was estimated at $1,575.31

❖ The budget was re-presented based off of the concerns presented by Dr. Vlcek and Dr. Molina at $3,538.70

Original Total Budget:

$1,575.31

Proposed New Budget:

$3,538.70

Difference:

$1,963.39

Force Components Budget

Control’s Budget

Fabrication Components Budget

Final Budget

Technical DrawingsComponents Designed by the Group:

❖ Chuck/Collet Set-Up:➢ Chuck➢ Stopper

❖ Cup Set-Up:➢ Cap➢ Retainer➢ Cup

Stopper

**Note: All Dimensions are in Inches

Chuck

**Note: All Dimensions are in Inches

Cap

**Note: All Dimensions are in Inches

Retainer

**Note: All Dimensions are in Inches

Cup

**Note: All Dimensions are in Inches

Centering Plate

**Note: All Dimensions are in Inches

Fabrication Issues❖ Collet Design Problem 1: Threads caused DA collet to become

non-concentric ➢ Solution: Eliminated threads that tighten down on collet

❖ Collet Design Problem 2: Not enough friction to keep DA collet from turning during operation➢ Solution: Use dowel to hold collet in place with a hex cap

screw that will pull DA collet into chuck

Fabrication Images

Cup/Transducer/Plate Assembly

Cup/Transducer/Plate Assembly

Pneumatic Piston Set-Up

Chuck Set-Up

Instrumentation/Controls

Review:❖ Block Diagram❖ Temperature ❖ Torque❖ RPM❖ DAQ❖ Power Supplies

Instrumentation and Controls

Recent Additions:❖ Axial Force❖ New Motor❖ RPM Control❖ Emergency Stop

Instrumentation block diagram

Instrumentation and Controls

Force/Torque Controls

Torque Transducer

Force Controller

Pressure Valve

DAQ

❖ Single Phase Induction Motor❖ No Control Available❖ Encoder would be counting

total revolutions

Original RPM Controls

New RPM Control

❖ New 3 Phase, ½ hp motor will reach speed specified in standards➢VFD controller will maintain constant RPM AC Motor 0.5 HP

Emergency Stop

❖ Arduino controller and programming were used to implement this feature Arduino Controller

Measuring Torque and Axial Force

❖ Thrust and torque load cell simplifies torque and axial force measurement

❖ No longer rely on calculated axial force and torque

Thrust and Torque Load Cell

Force/Torque Controls

Temperature Controls

Temperature sensor Temperature controller Temperature actuator

Temperature Controls

❖ Torque and Thrust Biaxial Sensor❖ Thermocouple❖ Microcontroller❖ Power Relay❖ Miniature Relay

Power Supply Controls

Power Supply Controls

Calibration and Testing

❖ Signal Conditioning❖ Force❖ Temperature❖ Auto-shutoff❖ RPM

Calibration and Testing❖ Signal Conditioning

➢ Built three inverted op-amp circuits to amplify temperature, torque, and force signals

❖ Force Sensor➢ Calibrated by using calibration charts➢ Tested by listening to pressure change as actuator

or valve is activated by controller

Calibration and Testing❖ Temperature

➢ Tested by boiling water and observing heating element activation

Calibration and Testing❖ Auto-shutoff

➢ Tested auto-start by observing activation of drill➢ Tested auto-stop by boiling water and

observing deactivation of drill❖ RPM

➢ Ordered three-phase motor and VFD controller➢ Encoder temporarily set-up for RPM counting

until new motor arrives

ResultsThe Results of the tribometer were unfortunately not

able to be recorded due to the DAQ set-up being incomplete.

Summary

❖ Completed:➢ Concept Development➢ Multiple Design Changes➢ Final Design Approval➢ All Fabrication

❖ Incomplete:➢ Three Phase Motor➢ VFD Controller➢ Auto-Stop Controller➢ DAQ Output Results➢ Final Set-Up and Wire

Organization

References

[1] ASTM Standards:ASTM D2266-01(2008), Standard Test Method for Wear Preventive Characteristics of Lubricating Grease (Four-Ball Method), ASTM International, West Conshohocken, PA, 2008, www.astm.org

ASTM D4172-94(2010), Standard Test Method for Wear Preventive Characteristics of Lubricating Fluid (Four-Ball Method), ASTM International, West Conshohocken, PA, 2010, www.astm.org

ASTM D5183-05(2011), Standard Test Method for Determination of the Coefficient of Friction of Lubricants Using the Four-Ball Wear Test Machine, ASTM International, West Conshohocken, PA, 2011, www.astm.org

Gantt Timeline

Concept Comparison Results

Comparison Constraints: Ease of Use, Cost, Size, Safety, Accuracy, Maintenance, Repeatability

Table 1: Concept Comparison Group Totals

QFD

Air Cylinder Set-Up

Figure 15: Air Cylinder Model (Side View)

Air Cylinder Set-Up

Figure 16: Air Cylinder Detail Drawing

Air Cylinder Set-UpTable 3&4: Air Cylinder Calculations and Possible Scenarios

Rough Calculations

Total Needed Downward Force 150 lb

Tang. Force from Pinion (1" Diam) 11.53 lb

Moment Produced at Pinion 5.765 lb*in

Rack/Pinion Gear Ratio 13:01

Air Cylinder Set-Up

Table 5: Air Cylinder Details

Air Cylinder Set-UpTable 6: Air Cylinder Set-Up Parts List

Temperature Measurement

ASTM D2266, D4172, and D5183 Standards require a

lubricant temperature of 75 ℃maintained within 2 .℃

Figure 18: Omega Thermocouple [3]

Temperature Measurement

LabVIEW writes Excel file that contains time and

temperature data.

Figure 19: Temperature Output

Temperature Measurement

Manufacturer Price Specifications QuantityOmega $35.00 -200 to 1250 ℃

1McMaster-Carr $35.00 -200 to 1250 ℃TEMPCO $35.00 -200 to 1250 ℃

Table 9: Thermocouple Manufacturer Comparisons

Temperature Control

PID control provides more accuracy

Figure 20: AUTONICS temperature controller [4]

Temperature Control

Manufacturer Price Specifications Quantity

AUTONICS $143.00 +/- 1 ℃1

Omega $195.00 +/-0.5 ℃

Table 10: Temperature Controller Manufacturer Comparisons

Heating

Manufacturer Price Specifications QuantityOmega $25.00 10W/in2

2McMaster-Carr $26.00 10W/in2

Table 11: Heating Element Manufacturer Comparisons

RPM Measurement

Real time RPM:❖ LabVIEW program

creates Excel file❖ Excel file contains time,

encoder counts, and RPM

  

Encoder

Figure 23: Encoder Motion Schematicω = (θ2-θ1)/( T2-T1)

RPM Measurement

The max RPM required by the three standards used is up to 1200 rpm

and the smallest accuracy required is ±60

rpm.

Figure 24: Karlsson Robotics Rotary Encoder [7]

RPM Measurement

Figure 28: Display of LabVIEW Data

RPM Measurement

Manufacturer Price Specifications QuantityKarlsson Robotics $50.00 up to 6,000 RPM 1Automation Direct $90.00 up to 5,000 RPM

Table 13: Rotary Encoder Manufacturer Comparison

Data Acquisition

❖ Sampling rate is an important factor for DAQ selection.

❖ Digital counter required for easier RPM measurement.

Figure 30: National Instruments DAQ [8]

Data Acquisition

Manufacturer Price Specifications QuantityNational Instruments $300.00 48 kS/s 1LabJack $114.00 50 kS/s

Table 14: DAQ Manufacturer Comparison

Power❖5 Volts provided to the

encoder and force sensors by a DC power supply.

Figure 34: Power Supply [11]

Power

Manufacturer Price Specifications QuantityTDK-Lambda $18.00 5V 1CUI $28.00 5 V

Table 16: DC Power Supply Manufacturer Comparison