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blackening screws
- Thread starter dian
- Start date
- Replies 27
- Views 7,786
crossthread
Titanium
- Joined
- Aug 5, 2004
- Location
- Richmond,VA,USA
rons
Diamond
- Joined
- Mar 5, 2009
- Location
- California, USA
Are you willing to use a hot caustic bath to soak the parts? I used stuff from Electrochemical Products (EPI).
Have also done work with cold black solutions. It's easier but not as durable.
Have also done work with cold black solutions. It's easier but not as durable.
Peter from Holland
Diamond
- Joined
- Jan 15, 2005
- Location
- The Netherlands
You can buy zinc plated black passivated nuts and bolts
Peter
Peter
When I need to replace a screw or bolt in something old and the currently available plated fasteners do not look right, I heat them red hot which burns the plating off and leaves them black. I can't say how durable a "finish" it is but it looks right. A quick soak in muriatic acid will dull them and eventually remove the plating and then you can use the tool black.
jbacc
Hot Rolled
- Joined
- May 5, 2009
- Location
- New Jersey
I have heated them and quenched them in used motor oil, turned them a nice black color.
cyanidekid
Titanium
- Joined
- Jun 4, 2016
- Location
- Brooklyn NYC
heating the fastener to a red heat will soften the steel, and a quench will not reliably restore temper without a proper heat treat. generally a bad idea unless you are nowhere near the strength limits of the fastener.
If you are only doing a small batch, the blackener (I usually go with the Birchwood Casey products) will remove the zinc just fine. if you are doing some quantity, I would use a sodium bisufate "pickle" such as Spearex brand to strip off the zinc. safer to work with.
If you need enough parts, just ordering them "black zinc" should do it.
You need to make sure they know how black you want..... we had sme batches that were a dark brownish before the supplier got the message that "black" means deep black.
Ther is also a more expensive "marine" coating that is black and very good against corrosion.
The heating will "screw up" the bolts and screws, not recommended. Blackening solutions should be OK, although not as durable.
You do not need them red hot for the oil blackening, they should work just as well if heated to just the "gray" oxide just past blue. That still will soften them significantly, and the plating will mean they do not show the temper colors, and may not allow the blackening either.
You need to make sure they know how black you want..... we had sme batches that were a dark brownish before the supplier got the message that "black" means deep black.
Ther is also a more expensive "marine" coating that is black and very good against corrosion.
The heating will "screw up" the bolts and screws, not recommended. Blackening solutions should be OK, although not as durable.
You do not need them red hot for the oil blackening, they should work just as well if heated to just the "gray" oxide just past blue. That still will soften them significantly, and the plating will mean they do not show the temper colors, and may not allow the blackening either.
You will need to remove the zinc before blackening. Here's an easy procedure to get a true black oxide. I haven't tried it yet myself.
My peculiar nature: Quick rust bluing--- Back in black!
My peculiar nature: Quick rust bluing--- Back in black!
steve-l
Titanium
- Joined
- Mar 2, 2012
- Location
- Geilenkirchen, Germany
It is much less expensive to buy your fasteners black. As others have said, plated fasteners cannot be blued. Blueing (or blacking) is easy to do, you just need a stainless tank, a gas heater and a mixture of sodium hydroxide (lye) and a bit of ammonium nitrate mixed in water. The ratio is readily found on line. Heat the mixture to about 290F and dunk your cleaned fasteners in and watch. If the fasteners are heat treated, the blackening takes a bit longer. Soft steel is pretty fast. Unfortunately, buying the ammonium nitrate may be a bit difficult, because you will immediately be assumed to be a terrorist. Ask me how I know!
rons
Diamond
- Joined
- Mar 5, 2009
- Location
- California, USA
One of my first attempts with a EPI hot bath. You shouldn't heat the solution on the top of a kitchen range. If it splashes on the range top the enamel is etched away.
We bought millions of fasteners that were blackened, AND zinc plated. It is done routinely by most fastener providers.
Shop-done blacking is maybe not possible on plating, at least easily
Gordon Heaton
Titanium
- Joined
- Feb 19, 2007
- Location
- St. George, Utah
Zinc plated hardware reacts fine with Birchwood Casey 'SuperBlue'. Like all cold blues, it isn't very durable.
Please tell me the heat treatment used on small fasteners. What alloys are used to make them?
Perhaps the op could have been more specific in his intended use of blackened fasteners and their grade. Certainly, there are many applications where a properly heat treated fastener is required but the op's post does not reflect this. If I go to the local industrial supply house and ask for a box of 1/4-20 screws, what are the chances they will be anything but plated mild steel with a list of possible countries of origin.
donie
Diamond
- Joined
- May 17, 2003
- Location
- Walla Walla Wine and Wild Turkey
Down and dirty, I do it also, it leaves a durable finish. Just be sure to fully immerse the part in the oil, or you could have a fire.
yes, i need the strength (automotive application) and even more if they are sheet metal screws. i usually only need a few of a kind, so no way of buying them. my blackening solution (two different ones actually) does nothing to zink plated screws. so the only solution would be to strip them and blacken them, right? then they will rust fast.
rons
Diamond
- Joined
- Mar 5, 2009
- Location
- California, USA
Blackening is a form of rust. Instead of brown the color is black.
CarbideBob
Diamond
- Joined
- Jan 14, 2007
- Location
- Flushing/Flint, Michigan
Yes you have to strip first so why buy zinc plated to start with?
The life of cold black, warm black, homemade recipes and true hot black are very different even if you get a nice finish on day one with any of these.
Environment involved and life span desired.
Bob
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