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best surface grinding wheel for hot rolled sheet metal?


Aug 31, 2017
Looking to all you surface grinding experts

Have a job coming up that calls for 100 pieces of 12"X24" hot rolled sheet metal in varying 10, 12, 14, 16 gage thickness

i know that mill scale is problem and is not ideal, but given the circumstances, how would you attack this, meaning which wheel type would you use.

Surface grinder is a 12"x24" 3 axis automatic, with a wheel size of 2" wide, 14" diameter, 1800 rpm, full flood coolant.

many variables here for success, speeds and feeds, wheel type, coolant type and mix ratio,

I understand that there are other machines and methods to do this, but how would you get best results using a surface grinder of this size.

Goal is to quickly remove the mill scale and get down to clean bare steel with some what ok finish, does not need to be precise.
I would be very careful with thin sheet on a surface grinder. Trying to be too aggressive will result in trouble. Sheet will buckle up easily when it gets hot, may shoot out or cause wheel damage. The thinner the sheet, the less the magnet will get a grip on it. You might be better off with a handheld drum-style finisher.
I'll have to rummage around in my old shelf bins for the specifics, but the best thing I've found for removing mill scale abrasively is a coarse non-woven pad intended primarily for paint removal. Conventional abrasive belts and pads, either single disk or flap wheel, mostly just burnish the surface of the scale, generate a bunch of heat, and dull quickly. Angle grinder cutting wheels will cut through it, but don't work so well at a shallow angle, and the result needs a bunch of clean up.
A 6" to 10" convolute or unified non-woven wheel would probably work fine on either a buffer or a surface grinder, if you get the coarsest available grade. On the other hand, if you have full coolant, a conventional vitrified bond abrasive wheel with an open structure should work OK. Blanchards grind raw scaly plate as a routine operation. A surface grinder might not work that well, but it should work.
Having said all that, if you have or can improvise a suitable shallow tray, soaking overnight in 40% acetic acid (grocery store vinegar is only 5%, try the pool maintenance section of a big-box store) will probably strip the mill scale right off without any labor and without the rust-inducing fumes you'd get with muriatic acid (hydrochloric acid). If you need more aggressive action, dissolve a bunch of salt in the acetic acid but that increases the risk of corrosive fumes. To avoid flash rusting, rinse with water with baking soda or washing soda dissolved in it (or any other dilute alkali solution, like household ammonia).
To hold sheetmetal on a magnet you need one with a small pole distance
Also pick a material that grinds better as simple hot rolled St 52.3 for example grinds much better Also available in sheet over here

What would be your size and flatness allowances.
16 gauge .060" 12x24" would be darn hard to make dead flat.
I have set some parts on shim strips so to allow coolant to flow all around and under.
A Blanchard with in process dressing and a spotter to make +- .001 with not measuring would be good.
Surface grinding need be slow, and an overhead dresser handy. Wheel might try a 36 K or L with 50% concentration...I would call Radiac and ask for recommendation.
Seems like thin hot rolled likes to warp when one side is taken more than the other... likely have to straighten the part