How is the metal extrusion processed controled to make a consistent extrusion.

In my limited exposure to Chemilling, The surface finish will get slightly better. As the acid eats way at the high points on the surface, it's also eating at both sides of the peak and thins the high point till it's gone. But that would only happen if and when you have a very very rough surface to start with and you have a lot to remove. The acid will eat every exposed surface eaqually. Holes get bigger and outside diameters (OD's) will get smaller, but at the same rate. A surface finish of 250 is pretty rough, the standard for a machined surface is 125, extrusions I've delt with were around 32. I'd be interested to know where your 250 is coming from, maybe the tooling needs to be looked at or repaired.

An engineer at a large coal-burning

facility needs high-performance

instrumentation to detect high ash

levels in hot-ash bins.

The high-sulfur coal ash can reach

temperatures up to 427°C (800°F)

and is highly abrasive. The typical

life expectancy of probes in this

environment is limited, and an

extremely rugged, high-temperature

level switch is required

Did you read the post before you made your answer I think you got confused.