Grinding VS Lapping wear rates 1

[rambobugman]

Currently at my office, we have a piece of equipment that acts like a mechanical directional control valve. I works by sliding a plate from one location to another. This device incorporates three steel plates that are approximately 12in L X 3in W X 1 in Thick (440 HT) with holes drilled through in all plates in different locations. All three plates are stacked on top of each other. The top and bottom plates are stationary. The middle plate is slid in and out (about 1 in from one location to the other) at a rate of 300 cpm. This plate acts as a directional valve. Also, middle plate is lubricated by the use of mineral oil. Currently we grind & lap the touching surfaces to an 8 RA finish. My question is this: Under all the same conditions, what type of surface wears quicker assuming both are coated with mineral oil as a lubricant. Does a better surface finish decrease the shear force created between the mineral oil thus decreasing the wear rates of the plates?

 

[unclesyd]

We ran different 440 material components against each other and found that lapping was far superior to any type of grinding we could do.
The components were first ground as flat as possible on a dedicated Blanchard, then "Diamond Lapped", finally polished with a diamond polish. The biggest improvement came when we went from SiC & Al2O3 lapping media to the diamond media. It has a decided advantage in that it also leaves a square edge hole instead of a radiused edge.

Can you use anything besides mineral oil as a lubricant?

 

[profengmen]

unclesyd has it right, I'll only add some comments.

yes, the smoother the surface, the less coefficient of friction, and thus less wear.

The "shear forces" you ask about are always the same. It is the fore multiplied by the coefficient of friction that does the wear.

Lapping after you blanchard grind will give you the best results, but you have to remember that removing material while lapping affects the thickness of your plates, and therefore increase the gap between parts. There are very few accurate micro-lapping-machines that will utilize controlled material removal.

Silicon Carbides and Aluminum Oxides, as Unclesyd mentioned, come in different "grits". They do not last as long as the diamond compounds and thus rounded edges do not cut as well. Applied liberally and often they will polish as well as diamond, but will take longer.

It's the same as sanding wood, you start with heavy paper and move down to the finer grit. The smoother the surface, the less friction, the less wear. Also, the less mineral oil you need. Hardness of the material is also a factor.