Friction and wear of guides and bearings. Friction reduction

Friction and wear of metals, ceramics,
trans-ceramics, plastics and seals

Because Lunac 2(hc)+ coatings are able to reduce the friction in many water lubricated axle-seal systems to a value as low as 0.009 ! we started up an extensive wear and friction research program. The following diagrams display the wear and friction of seals and bearings acquired from our tribo tester. The WMV tribo tests offer additional information about the influences of variation in counterparts as well as speed, pressure and lubrication. Many remarkable results proved that seal systems should be tested first, because surprising exceptions can often show up. Consequently we can offer specialized support in choosing the right material combinations.

Dry and wet friction

' Water lubricated ' and dry running systems follow essentially different tribo pathways. This picture represents two PA 12 pins that were tested on our tribo tester under equal condition apart from the surrounding medium. The left pin displays the effect of the prevailing tribo-oxidation in the dry running PA 12 stainless steel 1.4404 system. The right pin displays the effect of adhesive wear in the ' water lubricated ' PA 12 / stainless steel 1.4404 system. The wear rate of the right ' water lubricated ' system turned out to be a 7-fold higher. Conclusively; tribo-oxidation is not always unwanted. In the ' water lubricated ' system the stainless steel must be replaced or plated with an anti-galling coating for this system.

Water lubricated friction:

Tested on the WMV pin ring tribo tester according to the GLP norm.
Materials pin: Polyurethane, viton®, ecopur®, x-ecopur®, HT-HNBR, Fluoroloy 45, P6000, GUR 4120 PE, Duralion PE
Materials ring: Flame sprayed Cr2O3, Lunac 2+ trans ceramic, 1.8550 nitrided steel
Date: September 2007

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This picture displays the effect of a (coated) propeller shaft on 3 similar seals (HThnbr is a high temperature nbr version). Clearly visible is the low thermal conductivity effect of a full ceramic coating. A closer inspection revealed micro cracks in the black contact zone after bending. The high thermal conductivity of Lunac 2+ lowers the interface temperature. No leakage inducing micro cracks are developed on the Lunac 2+ coated shaft.

Dry friction:

Tested on the WMV pin ring tribotester, according to the GLP norm. Date: November 2007
Tested materials: Poly urethane, viton®, ecopur®, x-ecopur®, POM, PEEK, Ertalyte Tx®, PTFE, C-PTFE, Fluoroloy gold®, Fluoroloy 45®, HT-HNBR, GUR 4120 PE, epoxy-fenol.

Example of unexpected detrimental tribological behavior of Cr2O3 on HT-HNBR under dry conditions. The rubber wear is minor, but the Cr2O3 wear is severe and green dusty flakes are produced. In this case hard metal(lic) surfaces are in favor.

PEEK is a favorable material in metal-plastic bearing systems. Hardly known is that serious galling can show up despite the low coefficient of friction and initial low wear rate in this system. In our tests this galling always showed up within 2 hours! Conclusively, PEEK is able to tear the 18-8 stainless steel surface apart !! Hard (semi) ceramic coatings can effectively stop this PEEK issue.

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