Mechanically galvanized

[bluedog225]

What do folks think of mechanically galvanized fasteners?

I’ve come down on the side of hating them. But I could be encouraged to hate them more.

Was there something wrong with hot dipped? I’ve got an ongoing 40-50 year test running and they seem to be holding up.

 

[PCustoms]

First time I've heard the term....

 

[Coasterbuilder]

Mechanical Galvanized​

Mechanical galvanizing is a process in which parts are tumbled in a drum with chemicals, zinc powder, and glass beads. During the tumbling, the beads cold-weld a uniform coating of the zinc powder onto the surface of the part. Offers superior corrosion resistance, a more uniform coating thickness, and no chance of hydrogen embrittlement as compared to electro-zinc. Post plating dichromate dip can be added for yellow mechanical zinc.

Application: Commonly used on high strength parts where hot dip galvanizing is not possible due to hydrogen embrittlement concerns. Hardened lockwashers are typically are finished with mechanical zinc and yellow dichromate.

 

[PCustoms]

@Coasterbuilder thanks.

I dealt with a hydrogen embrittled issue a few years ago, had to dust off my metallurgy knowledge and dig deep to figure out why we kept popping the heads off cap screws. Fun.

 

[PLUM72]

One reason to mechanically galvanize a fastener is to reduce the chance of hydrogen embrittlement if that fastener is heat treated. Those Simpson screw anchors have a case harden operation on them. Adds hardness to the threads as it cuts into the concrete. A typical grade 2 hardware store bolt is electro-zinc plated and may have a clear chromate finish over the top. This is that “shiny” silver color you see on this stuff. Use an electro plate zinc on a heat treated fastener, and you need a bake operation to remove any trapped hydrogen. By going to mech zinc, the manufacturer saves a bit on the plating operation by not having the time and expense to do the added bake. Platings and coatings are a true science. Different thicknesses of zinc will give different corrosion protection. A triple mechanical zinc is often equated to hot dipped galvanized.

 

[LopezBart]

Acid etching & then plating traps hydrogen... heating the parts after acid etch drives out the hydrogen again. Typically a problem w/ higher carbon steels.

 

[whateg01]

What do folks think of mechanically galvanized fasteners?

I’ve come down on the side of hating them. But I could be encouraged to hate them more.

Was there something wrong with hot dipped? I’ve got an ongoing 40-50 year test running and they seem to be holding up.

And why do you not like them? Just because they aren't "the way we've always done it"?

 

[bluedog225]

I get the hydrogen embrittlement deal with higher grades.

I think they offer lower/shorter protection. Could be wrong.

Don’t see triple coat mentioned.

I like to build things for the long haul.

 

[bluedog225]

Looks like maybe they can be expected to have a good service life. Would like to see some testing.

 

[mike93lx]

I get the hydrogen embrittlement deal with higher grades.

I think they offer lower/shorter protection. Could be wrong.

Don’t see triple coat mentioned.

I like to build things for the long haul.

Maybe reach out to Simpson, they may have some info to share

 

[mv213]

Learned something new! TIL