Comments on: Camshaft surface finish http://www.ret-monitor.com/articles/1131/camshaft-surface-finish/ Specific mission-critical info for professionals Fri, 18 May 2012 08:57:54 +0000 http://wordpress.org/?v=2.7.1 hourly 1 By: Terry http://www.ret-monitor.com/articles/1131/camshaft-surface-finish/comment-page-1/#comment-5873 Terry Sun, 09 Jan 2011 06:41:20 +0000 http://www.ret-monitor.com/articles/1131/camshaft-surface-finish/#comment-5873 John Coxon's conclusions are mostly correct about DLC's and superfinishing of cam lobes and tappets. During operation, the continuous sliding velocity and relatively low contact stress at the cam lobe and tappet interface, means that it has hydrodynamic conditions. Since the contact is hydrodynamic in nature, the cam lobe and tappet surface materials are not relevant with regards to friction. Having a super-smooth surface will only be helpful in that it will extend the limits of operation the parts will maintain hydrodynamic contact, due to more favorable lambda ratios. With regards to DLC's, they have been shown to be beneficial with regards to fatigue life. When these super-hard coatings are applied to one of the surfaces in a journal or roller bearing, during periods of mixed or boundary contacts they can actually polish and mechanically rework the mating surface, which has the effect of improving its fatigue life. John Coxon’s conclusions are mostly correct about DLC’s and superfinishing of cam lobes and tappets. During operation, the continuous sliding velocity and relatively low contact stress at the cam lobe and tappet interface, means that it has hydrodynamic conditions. Since the contact is hydrodynamic in nature, the cam lobe and tappet surface materials are not relevant with regards to friction. Having a super-smooth surface will only be helpful in that it will extend the limits of operation the parts will maintain hydrodynamic contact, due to more favorable lambda ratios.

With regards to DLC’s, they have been shown to be beneficial with regards to fatigue life. When these super-hard coatings are applied to one of the surfaces in a journal or roller bearing, during periods of mixed or boundary contacts they can actually polish and mechanically rework the mating surface, which has the effect of improving its fatigue life.

]]> By: Ray Fontana http://www.ret-monitor.com/articles/1131/camshaft-surface-finish/comment-page-1/#comment-3972 Ray Fontana Wed, 18 Aug 2010 17:45:02 +0000 http://www.ret-monitor.com/articles/1131/camshaft-surface-finish/#comment-3972 In most cases the new oils used will give friction coefficients of around 1.0 to 1.2. This is around the area that most DLC and ADLC coatings have as friction coefficients. The coating does provide a low friction low wear surface in the absence of oil but will be as affective as oil if it is present. As you mentioned in the article the surface finish plays a very important role because most of these coatings if deposited on a mirror surface < 1 micro inch will be as smooth as this or smoother as deposited. If they are deposited onto rougher surfaces they become the roughness of that surface and can become very good files. In most cases the new oils used will give friction coefficients of around 1.0 to 1.2. This is around the area that most DLC and ADLC coatings have as friction coefficients. The coating does provide a low friction low wear surface in the absence of oil but will be as affective as oil if it is present.
As you mentioned in the article the surface finish plays a very important role because most of these coatings if deposited on a mirror surface < 1 micro inch will be as smooth as this or smoother as deposited. If they are deposited onto rougher surfaces they become the roughness of that surface and can become very good files.

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