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Author: metal5192
Time: 05/28/07 09:35 PST
This is a reply to message no. 18801 by john2005
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Current Topic:
Request for help reducing friction and noise of a cam follower roller

John: Several points to be made:-

1.     flame hardening is not a preferred method to treat the A-2 due to decarburization caused by the temperature & exposure to air. This will result in a loss of carbon on the surface to probably 0.005" deep which in turn if not removed will cause pick-up and galling of the surface with extremely poor friction properties. The parts should be heat treated in vacuum at 1750F & tempered at 750F & 500F which will result in a hardness of Rc 57-59 and maximize the toughness value of the A-2

2.     The 4140 piece requires hardening from 1550F & tempered at 400F with resulting hardness of Rc 55-60 depending on chem analysis of the base material. To prevent galling and reduce friction both parts should be finished to 5-10 micron with no imperfections. Any marks in the contact areas will result in premature failure. 4140 is basically a machinery grade steel and is not intended for high wear conditions. If the finish on the cam surface is excellent requiring no finishing after heat treating, the have the 4140 carbonitrided to a depth of 0.020" which will result in a surface hardness of Rc 58-60 plus a thin nitride surface which is antifriction and slippery of 0.001-0.003" depending on process.

3.      Unless the dowel is hardened there will be excessive wear conditions evidentually with dimensional loss resulting in poor alignment. More expensive to machine but make the roller/dowel a one piece construction of A-2 heat treated to Rc 57-59

4.      No suggestions on non-metallic rollers. Your initial choice of materials is the norm in manufacturing except sometimes depending of the life requirements, the cam could be made from A-2 Rc 60-62 , D-2 Rc 60-62 or in corrosion applicatins 420C stainless steel to Rc 58-60

        Hope this is of use to you. By the way my name is Ron. Good luck!

         

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