Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Black Zinc or Black Oxidation process for stainless steel screws
Q. I need to have about 50 different screws made black. Our company makes medical instruments. We can not have our screws rust. However, we also need them black. The problem is that we do not have large quantities.
I have been quoted anywhere from $18 to $60 dollars per line item, or lot, up to 25 pounds. One promising quote was 50 pounds of screws for $150 dollars. However I don't know if I would have to put all of my screws in together. If I did that I would have to sort them out, which would be almost impossible.
I only have about half a pound of each screw. So at the $18 per screw type I would need to pay $900 dollars to have only 25 pounds processed. One option may be to keep my screws separated in a metal mesh. I have been told that this would work in a powder coating process.
I would like to hear from people who are willing to explain their pricing scale.
Michael Earl Laub- Boise, Idaho
2001
A. I do not think that black oxide would be acceptable for most medical instruments. Since that is a terribly broad area, it might be OK.
I would look at black chrome. It is jet black and is used on numerous decorative and jewelry items.
You might be able to find a vapor deposition process that would give you a black finish, possibly on the head only, that is very durable and affordable.
Most black oxide setups are quite large and are not really setup to handle small quantities. They also work at very high temps. There are very small barrel plating setups that would easily handle 1/2 pounds of screws.
Consider mixing large with small screws that you could easily separate as a cost savings measure. Have people separate them on their coffee breaks.--Free coffee.
I think that you can probably buy the screws, or some of them, already black from someone.
James Watts- Navarre, Florida
2001
Q. Mr. Watts:
In your response to Mr. Laub, you suggest a "black chrome" finish for (I assume) steel screws. Are you referring to "black rhodium" or "black nickel" plating, or something else? I am very interested in finding a way to put a black matte finish on iron or steel jewelry that is durable enough for reasonable wear. Gunsmith "bluing" treatments scratch and wear quite easily, so that's out. Baked on polymer sprays like "Aluma-Hyde" don't wear well either. Any suggestions?
Thanks in advance!
Wayne EmeryJewelry Design Studio - Tacoma, Washington, USA
2001
A. Mil-Std-792, Type II marking methods might be helpful for small quantities. The specification is available from the US Government site: astimage.daps.dla.mil/quicksearch
The depth of penetration of the markings is required to be greater than 0.0005" and typically the color is described as black, although that may vary to brown or bluish tones depending on the chemistry of the metal and the etching compounds.
A quick look using your favorite search engine for "electrochemical etch" should give you commercial sites where the electrical equipment and chemicals are available. The equipment purchase (or perhaps rental?) is the largest cost, but that's one-time only and a little chemical goes a long way. The only challenge is getting a marker head that is flexible enough to get into the threads of the screws, but if all you are concerned with is the visible screw-heads, that may not be a problem.
Dave Hass- Oklahoma City, Oklahoma, USA
2002
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