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"White film on 304 stainless after sanding"



December 18, 2015

Q. Hi guys, I am a machinist and am currently working with decorative sheets of Stainless steel type 304. The finish is supposed to be a variant of #6 architectural brushing. The sheets are run through a Timesaver up to 400 grit and then later on through fine grain non-woven abrasive (scotchbrite roller) on another Timesaver.

However, I am currently having difficulty with the current Timesaver sanded finish. The sheets are only 1/32 thick and after sanding (both sides) they are .022" thick. The Timesaver we have is not a wet machine so everything is run dry.

There is currently a white haze or film left behind after the sanding that is not easily removed. The haze only seems to appear when I run it on the dry machine and does not appear consistently if the sheets are run wet (though I've not run enough to fully validate this). I have ordered a new non-abrasive^non-woven abrasive roller to try to test if this works to remove the haze/film but wanted to see what you all thought about my particular problem as it is very detrimental to the overall finish right now.

Thanks for any advice/help.

Michael Myers
Machinist - Los Angeles California
^


December 28, 2015

A. Possible solutions;

Slow the feed--too much heat causes the atomic structure to capture particles from the abrasives.
Try feeding material from a different direction.
Clean the steel or what they call the passive solution--I have used acetone.
Have always wet sanded with soap solution but I always do high polish.

Attached a link about atomic structure that includes 304 series:
http://www.nickelinstitute.org/~/Media/Files/TechnicalLiterature/StainlessSteels_AnIntroductiontotheirMetallurgyandCorrosionResistance_14056_.pdf

Mark Moore
Marks Metal Art - Raytown, Missouri, USA
^


January 7, 2016

A. My curiosity has gotten the best of me. Did you get the non-abrasive rollers and try them? I think your white haze is the results of static electricity. Rig up something like a paint system or better yet try the wet process.

tony kenton
AF Kenton
Hatboro, Pennsylvania
^


January 11, 2016

Q. Dear Guys,

Thanks for your responses. One correction to my first post, I meant to say that I was getting a new Non-WOVEN Abrasive roller. Not a new Non-ABRASIVE roller. Sorry for the mix up. Basically, this is a a Scotch-Brite roller.

So far, Wet brushing with the new roller has produced the best product. However it is not perfect yet. I am toying with the feeds and speeds of the conveyor and the belt. Maybe this will change the heat build up, or even the static build up.

After posting my first question, I found an interesting article about stainless steel and sanding the surface of it which may be of interest to someone else who experiences the same problem.

The PDF is downloadable here:
www.ispeboston.org/files/july_2010_tech_talk.pdf

A lot of reference sites recommend using Electro polishing to clean the surface, but that is not an option in my case as I need a very certain reflectivity in the finish.

AF, if my problem is caused by a static build up on the part, is there any way to change/reduce the static on the part without spraying a lubricant? like static dissipating rollers or something? I have a dry machine and the mess of trying to make it wet would be difficult to dear with in my facility.

At this point unless someone has any other ideas, I guess it will just be a matter of trial and error.

Thanks for the insight, keep it coming.

Michael Myers [returning]
Machinist - Los Angeles, California
^


January 27, 2016

A. Personally I am not sure about grounding sheet; however, I am sure the manufacturer of your belt sander has experienced this issue. I suggest you contact them.

tony kenton
AF Kenton
Hatboro, Pennsylvania
^

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