Significance and Use
5.1 This test method is designed to rank material couples, surface treatments, and lubricants by CFT and in their resistance to adhesive wear. Since adhesive wear is a complex phenomenon and stochastic in nature, it is essential to evaluate surfaces to confirm the presence of adhesion.
5.2 This test method should be considered when evaluating the impact of changes in a process or application that is prone to adhesive wear, including any combination of scoring, galling, and plowing. These modes of failure commonly occur under sliding contact, at high contact stress, and, when applicable, at lubricant starvation.
5.3 The TCT is often used to evaluate the ability of material couples, surface treatments, coatings, and lubricants to prevent or reduce adhesive wear in metalworking operations including deep drawing, extrusion, and pipe bending. Other applications in which the test may be effective are loader bucket bushings, gear teeth at startup, and low-clearance pumps.
5.4 This test method is best used as a comparative screening tool. The ranking of performance produced by the TCT correlates well with the ranking in many applications.3 However, since the test is a bench test and not directly reproducing any specific application, TCT results should be only used as an indicator of the tendency for adhesive wear to occur. TCT is a useful screening test for comparing the effectiveness of material couples, surface treatments, coatings, and lubricant formulations before process testing and field trials.
Scope
1.1 This test method covers laboratory procedures for determining the coefficient of friction (COF) and resistance of materials to adhesion under flat sliding using the twist compression test (TCT). This test method ranks material couples, surface treatments, coatings, and lubricant combinations by COF and their resistance to adhesion.
1.2 The time until adhesion for the materials under the test conditions are reported and used to quantify the tribocouple’s adhesion resistance and susceptibility to galling or scuffing. Systems of higher adhesion resistance will give longer time until failure.
1.3 The coefficient of friction values averaged between the test reaching full test pressure and the time of the onset of adhesion or the end of tests run for a predetermined time period are recorded. Systems are ranked by their average coefficients of friction before adhesion occurs.
1.4 Units—The values stated in SI units are to be regarded as the standard. No other units of measurement are included in this standard except psi and pounds in Table 1.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
