How to dull a stainless steel finish

A. Nap finish on a knife. I suspect the temp/hardness of the blade is very resistant to any resurfacing system. Since you do not have a blast system I suggest deburring via a small vibratory system using a very coarse ceramic media shape. If this doesn't accomplish task, try adding a little acidic compound and retry.

A. Unless you need to be selective, You can achieve a dull matte finish in a number of ways. Probably the most common is to abrasive blast the part. It can also be accomplished using mass finishing equipment and chemically. For selective areas, you may have to mask off or protect the polished areas against these processes, but this presents other problems. The way your question is worded, it sounds like you would save time and money by leaving the polishing of the part until after the matte finish.

A. Sorry but this is a bad idea. The HCl will leave the SS in a corrosion sensitive condition. May look good now but wait a while and the calls will be a coming. Consider an abrasive blasting means, then passivate the parts.

A. Hi.

I have to agree with John that all but the most exotic stainless steels are subject to chloride corrosion and that hydrochloric acid is not a good way to dull it. Bead blasting can create a beautiful matte finish if that's what you seek.

Regards,

A. Have you experimented with any bead blasts, Jim?

A. Pickling in a mixture of 35% nitric acid/4% hydrofluoric acid will produce a gray finish.

A. Suggest substituting Ammonium Bifluoride instead of liquid hydrofluoric acid. Same % but safer handling.

Geoffrey Whitelaw
- Port Melbourne, Australia

A. You can achieve almost the same identical appearance of an abrasive blast finish, without the dimple pattern, by using a dry organic abrasive media in a mass finishing system.

A. You can achieve the same grey, non-reflective finish as found on architectural Titanium by dry blasting with #220 Aluminum Oxide.

A. Hi Nirav. If it's just one part, there are jobshops who can probably do this for you without a lot of lost effort on experimentation. "Antireflective" covers a pretty wide range from a matte bead blast to an optical black chrome finish or specialty black paints. Can you offer more detail please?

Regards,

A. Hi again Nirav. I see nothing wrong with any of the three ideas suggested by Jeffrey, AF, and Ken. But since it's a mass product of small size, I probably find AF's suggestion of mass finishing the most promising for economy and simplicity. Are these blades one-time use or are they sterilized and re-used?

Regards,

A. I have worked extensively with surgical blades. I think the only way you'll be able to reduce the reflectivity of the blade without ruining the edge is to apply a PVD black coating. The coating has to be very thin or you'll dull the edge, and done at low temperature or you'll over-soften the metal.

Hi Nirav. I'm perhaps a pessimist, but I'm having a hard time thinking an acid or electrolytic process can simultaneously remove burrs and provide an aesthetically pleasing non-reflective matte appearance for the blades.

I would suggest deciding whether you will remove the burrs mechanically or electrolytically, and properly solving that problem before addressing the final appearance issues. Good luck.

Regards,