303 SS Galling Problems

[mdb2346]

I am having problems with a slight galling issue with a 303 SS body with a 12L14 heat treated piston. The fit is very tight but it is lubricated. The piston will cycle for a while then it will begin to wear into the 303 SS and then start galling. What can I do to solve this? I would rather change the piston material or possibly coat the piston than change the 303 SS body material. Any ideas?

 

[ApC2Kp]

mdb2346,

The surface finish is probably the first question. Also if the fit is tight, how is the tolerance controlled?

Is the 303 SS I.D. finished with a reamer or something better? An engine cylinder has a honed finish. Perhaps a roller burnished I.D. is better for your application. The piston finish could be evaluated also. There were some articles describing surface finish left after rigid honing tools versus the flexible honing carbide 'brush' tools of Engineered brush co. when applied to both I.D. and O.D. of wear surfaces. Their findings supported use of a micro texture controlled finish with cross helical pattern for lubricant distribution on the wear surfaces.

Is a change of lubricant possible? Is the lubricant picking up any contaminants? What is maintaining the supply of lubricant, or is it being diluted or breaking down from heat? Or maybe it is high moly grease, or even a dry film lube?

 

[mdb2346]

We are currently using a diamond cross-grinding honing tool on the 303 SS after the bore is drilled and reamed. The part is actually a valve that is always filled with oil. Changing the lubricant is not possible because we cannot control what the end user decides to use. As far as surface finish, the pistons are around a 2 and the bores are around 8-9. Unfortunately I do not have a profilometer to measure this accurately.

 

[EdStainless]

There is no contact profilometer that can measure down in your range. You can do it optically.

Roller burnish is a great idea. It will harden the surface and assure that there are no peaks in the surface texture. I would also suggest that you look at coating the 303 with a dry film lube such as tungsten disulfide.

SS has such poor wear properties I am surprised that you only have some problems.

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Plymouth Tube

 

[TVP]

I agree roller burnishing is a great idea. Cogsdill and Ecoroll both have good technical content on their websites. I also agree that using some type of dry film lubricant on the Type 303 stainless part is a good idea. If you have a more-or-less partnership arrangement with the end user(s), then you should discuss the issue of lubrication with them. It may only require a slight modification to one of the additives, such as adding an EP-additive or adding more of it to the current formulation.

 

[MikeMet]

Make your body from Nitronic stainless steels which have excellent galling resistance or ion nitride the surface, which also imparts very good galling resistance. You could also ion nitride your piston for added galling resistance.

 

[dgallup]

Nitronic will be a bear to machine compared to 303. I would look into hard chrome plating the bore. There are a bunch of more exotic specialty platings available just for cylinders.

 

[unclesyd]

In line with the post by MikeMet I would go with Nitronic 60 or Gall-Tough from Carpenter.

I would Liquid Nitride the 303 SS part in lieu of ion nitriding. After liquid nitriding 303 SS is one of the best wear and galling resistant materials around.

http://cartech.ides.com/datasheet.aspx?i=103&e=250&c=TechArt