Tribology

Tec Star S.r.l.Viale Europa, 40 – 41011 Campogalliano (MO), Italy

Tel. +39059 526845 – Fax +39059 527000

Tribology: Case Histories

Dr. Alberto Borghi

Tec Star Srl - President | CEO

[email protected]

www.tec-star.it


Tel. +39059 526845 – Fax +39059 527000

Summary

Facilities Short description of analytical equipment used for problem solving.

Case HistoriesPolymer choice for low coefficient of friction and low wear rate applications;Wear rate induced by different synthetic lubricants;Polymer-steel coupling in alternate motion.


Tel. +39059 526845 – Fax +39059 527000

FACILITIESTribometerA tribometer is an instrument that measures tribological quantities, such ascoefficient of friction (COF), and wear rate (WR), between two surfaces incontact.

Physical parameters which can be varied: contact geometry vertical load (from 100mN to 1000N) sliding velocity (from 0,1 mm/s to 5 m/s) temperature (from -10°C to 250°C) presence of lubricant or grease humidity

This instrument can provide measurements on a wide range of materials(polymers, metals, thin coatings).If particular requirements are necessary, the instrument can be customized inorder to change contact geometry, to use real samples and to create particularenvironmental conditions.


Tel. +39059 526845 – Fax +39059 527000

Ball-on-Disk / Pin-on-DiskA ball or a cylindrical pin slides against a flat rotating sample; the instrumentmeasures the coefficient of friction during the whole duration of the tribo test.

After the test, a wear track usually appears on the sample surface: the volumeof the removed material is proportional to wear rate.

Due to its high degree of flexibility this technique allows comparison betweendifferent materials (polymers, metals, coatings, glass, sintered materials)under a wide range of testing parameters.


Tel. +39059 526845 – Fax +39059 527000

Block-on-RingA flat block is in contact on the side of a rotating ring; while a vertical load is applied on the block.

The coefficient of friction is measured during the whole test; at theend a typical wear scar is made on the block side, allowing thedetermination of wear rate.A small liquid container at the bottom of the ring is used for test inwet conditions. In this way the contact between block and ring iskept in constant lubrication and it is possible to measureperformances of fluids lubricants or greases.


Tel. +39059 526845 – Fax +39059 527000

Reciprocating ModeA ball or a cylindrical pin slides over a flat sample, which moves alternatively on a linear path.The instrument can reach high frequencies (60Hz) of motion.The coefficient of friction is measured during the test and characteristic wear tracks are produced on the sample.


Tel. +39059 526845 – Fax +39059 527000

Case HistoriesPolymer Coefficient of Friction

Issue The goal for this study is to measure static and dynamic coefficient offriction of four different technical polymers (PTFE with different formulations)for choosing the best material.

Analysis approach In order to simulate real conditions of work of these polymer items, a tribometer was chosen to measure coefficient of friction in pin-on-disk and ball-on-disk configuration.


Tel. +39059 526845 – Fax +39059 527000

Procedures The measurement of static and dynamic coefficient offriction requires two different instrumental configurations.The evaluation of wear track produced during dynamic measurementsallows the determination of wear rate.


Tel. +39059 526845 – Fax +39059 527000

Results The diagrams show friction and wear rate values obtained for thefour polymer samples.

The best material that combines low friction and high wear resistance isMaterial B


Tel. +39059 526845 – Fax +39059 527000

Wear Rate induced by different synthetic lubricants

Issue study of tribo performances of synthetic PAG lubricant for gear box. Wear rate of metallic counterparts (bronze-steel coupling), using two commercial lubricants and three pressure conditions, was recorded.

Analysis approach tribometer in Block-on-Ring configuration with the use of a specific liquid container to maintain the contact in lubrication.


Tel. +39059 526845 – Fax +39059 527000

Results Lubricant #2 showed a very low wear rate of Bronze surface, inparticular under 400 MPa of pressure.At higher pressure the behavior of two lubricants is almost the same.Coefficient of friction is similar for the two lubricants.

Wear Rate measured for twolubricants as a function ofcontact pressure.

Wear scar produced onBronze surface measuredby stylus profilometer.


Tel. +39059 526845 – Fax +39059 527000

Polymer-Steel coupling in alternate motion

Issue study of tribo properties of technical polymers during alternate sliding against a steel counterpart.We needed to reproduce the contact geometry and environment (temperature and relative humidity) of real working application.

Analysis approach tribometer in reciprocating configuration.Custimozation of sample geometry in order tosimulate the real contact geometry.


Tel. +39059 526845 – Fax +39059 527000

Results Tests on materials were made by varying both linear sliding velocityand environment temperature.For each material there is the possibility of drawing a 2D map of coefficient offriction and wear rate which shows its tribological behaviour in different testconditions.


Tel. +39059 526845 – Fax +39059 527000

Contacts

Dr. Alberto [email protected]

TEC STAR SrlViale Europa, 40

41011 Campogalliano (MO) - ItalyTel (+39)059.526845 Fax (+39)059.527000

Tribology

Documents

Transcript of Tribology