Comments on: Avoiding piston micro-welding http://www.ret-monitor.com/articles/678/avoiding-piston-micro-welding/ Specific mission-critical info for professionals Fri, 18 May 2012 10:46:10 +0000 http://wordpress.org/?v=2.7.1 hourly 1 By: Terry http://www.ret-monitor.com/articles/678/avoiding-piston-micro-welding/comment-page-1/#comment-6168 Terry Sat, 22 Jan 2011 05:00:54 +0000 http://www.ret-monitor.com/articles/678/avoiding-piston-micro-welding/#comment-6168 I hope Dr. Randolph was misquoted in the second paragraph. The bottom face of the compression ring groove on an aluminum piston never gets anywhere near the melting point of aluminum (>1200degF). The ring groove microwelding effect described is a crude form of diffusion bonding, which can easily occur with aluminum at temperatures of only 300 or 400 degF. Similar to fretting, high local contact pressures and relative surface motion make the problem worse. Microwelding (as the name implies) is a phenomena that occurs at the micro level between tiny contacting surface asperity points. The mechanical bonding between asperities only occurs when the compressive strength of one (or both) of the materials has been exceeded. Even high performance piston aluminum alloys begin to lose mechanical strength above about 400degF. The most effective ways to prevent microwelding are to make the surfaces of very high strength materials like hard chrome or DLC, or use of some sort of inert surface coating that inhibits the welding. An oxide film on the surface is very effective, such as that produced on aluminum by anodizing, or that produced on steel surfaces by oil EP additives. I hope Dr. Randolph was misquoted in the second paragraph. The bottom face of the compression ring groove on an aluminum piston never gets anywhere near the melting point of aluminum (>1200degF). The ring groove microwelding effect described is a crude form of diffusion bonding, which can easily occur with aluminum at temperatures of only 300 or 400 degF. Similar to fretting, high local contact pressures and relative surface motion make the problem worse.

Microwelding (as the name implies) is a phenomena that occurs at the micro level between tiny contacting surface asperity points. The mechanical bonding between asperities only occurs when the compressive strength of one (or both) of the materials has been exceeded. Even high performance piston aluminum alloys begin to lose mechanical strength above about 400degF.

The most effective ways to prevent microwelding are to make the surfaces of very high strength materials like hard chrome or DLC, or use of some sort of inert surface coating that inhibits the welding. An oxide film on the surface is very effective, such as that produced on aluminum by anodizing, or that produced on steel surfaces by oil EP additives.

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