Cleaning Method

Ask an Expert From: Products Finishing,

Posted on: 8/1/2004

Question: I had a local metal fabricator cut a shape out of a 7×10 ft ×1/2 inch thick out of cold roll steel to be used as a tabletop.

Question:

I had a local metal fabricator cut a shape out of a 7×10 ft ×1/2 inch thick out of cold roll steel to be used as a tabletop. I want to take the existing blackish-rust colored finish down to the silver metal color so I can use a blueing kit on the entire surface. Can you recommend a cleaning method, other than mechanical? Everyone keeps telling me to grind it down, but I really don’t want to do that if I don’t have to. I would rather use chemicals. K.E.

Answer:

The removal of the black and rust colored surface may not be very easy and is not something you can do on your own with any over the counter solution available. You will most likely have to find a local finishing shop that will pickle the steel in order to remove the rust and discoloration. Aggressive pickling is generally done in a tank (in your case a very large tank) of sulfuric acid, usually inhibited to minimize base metal attack. Phosphoric acid may also work, but could take longer and is a more expensive acid.

I am not sure, but based on your description and thickness of the material, are you sure you have cold rolled steel and not hot rolled? The finish of the hot rolled is poorer and used more for structural applications than cold rolled. About the only finish options you have available to you with hot rolled is pickled and oiled or blasted.

Unfortunately, it sounds a little late to ask now, but I would have verified with the sheet metal shop that what they gave you is indeed cold rolled. If you had it to do all over again, you should first find a shop that will give you the material in the condition you want it. A standard cold rolled material is available in a variety of finishes and is often specified as matte, commercial bright or luster finish (in decreasing order of surface roughness). ASTM A 109 defines the available finishes for cold rolled steel and the corresponding surface roughness as follows:

ASTM Designation
Number 1
Number 2
Number 2 ½
Number 3
Description
Matte (dull)
Regular Bright
Better Bright
Best Bright
Surface Roughness
20-80 microinches
< 20 microinches
< 10 micro inches
< 4 microinches

It would then only require the removal of a light rust preventative oil that could be taken off with mineral spirits. The blueing or another type of finishing could then be done to the surface.

 


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