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How to do smut-free mid temp black oxide on wood screws


Q. My name is Vivek and I have a question for all the experts: how to produce black oxide at mid temp conditions without any rub off or smut on wood screws? Also it is free from oil as I got some samples from China where they are manufacturing screw and coating it with black oxide in such a manner that there is no oily touch or smell on the pieces and it is black free from any rub off or smut.

Vivek sharma
- Mumbai and Maharashtra, India
December 8, 2022

? Hi Vivek. How do you know it was a mid-temperature process, or that it's even black oxide as opposed to black zinc or e-coating or QPQ nitriding?
Luck & Regards,
pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

Q. Sir,
Thanks for your reply.
I speculated it to be black oxide as the coating thickness is below 5 micron whereas in CED coating the thickness range from 10 to 20 micron
Also when I dipped the component in HCl acid it immediately turned into bare metal pcs; there was no reaction observed.
Within seconds I was able to see the bare metal
In case of CED generally we can observe paint flakes stripped off from the surface.
Also in case of black zinc because of zinc it shows some reaction which was not seen either.

Vivek sharma [returning]
Employee - Mumbai
December 15, 2022

Q. I am also looking for that. Like how is China supplies black oxide finished dry wall screws without oil. And they have a nice corrosion resistance.
Please guide me through.
As i have installed a black oxide plant but for screws my cost is going much higher than thought.
I have quantity of 50-70 tons per month for black oxide.

Kishan Patel
Electroplating company owner - Ahmedabad, Gujarat.
December 25, 2022

A. Hi. I have no idea what your Chinese competitor is doing, but have you tried baking the screws after hot black oxiding in order to try to dry the oil onto them? Black oxide with no oil can flash rust in 15 minutes.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

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