zinc electroplated fasteners

[Jieve]

Hi guys,

Quick question. Was purchasing M8x1x70 8.8 fine threaded fasteners for a project at a local supplier yesterday and could only get them uncoated (actually black) and not zinc electoplated. I was told that it was because the zinc coat would interfere with proper fit, although are not hot dipped. I already had fine threaded zinc electoplated nuts for them, so was wondering if the supplier's story is legit. Anyone know about this?

Also, what exactly is the black coat? I thought the zinc electoplating was only in the single digit micrometers and didnt affect the tolerances much, but could be wrong about this. Anyone care to correct me?

Thanks!

 

[KENAT]

Is it black oxide? In which case it doesn't do much for corrosion prevention itself but does help absorb oil which helps with oxidizing a little.

If I remember correctly.

It is possible to get zinc plated fasteners in most common sizes etc. I forget the exact wording in the ASME B1.1 but there is some allowance made, at least on class 2 if I recall correctly.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[MintJulep]

It's possible to get zinc plated fasteners in just about any size.

It's possible to get any thickness (within reason) plating.

It's possible for the fastener manufacturer to roll the parts slightly under size to accommodate a known plating thickness.

The plating process can cause hydrogen embrittlement, which on grade 8.8 fasteners may lead to cracks and failure. Proper post-plating heat treatment can remove the hydrogen and alleviate the problem. However it's often not done, or not done correctly. So clued in buyers requires lots of extra certs and traceability.

You need to find a more knowledgeable supplier.

 

[TVP]

MintJulep is correct. Here is an example of an off-the-shelf catalog part with fine thread and zinc plating:

http://www.fastenal.com/web/search/...$|~ ~|attrdiameter:121100|~ ~|sattr06:^1.0$|~

 

[Jieve]

Guys,

thanks for the responses. Yeah I figured that it didn't make much sense. The supplier is a large fastener supplier based in a neighboring country (I'm in Europe) but they have a local store here about 15 mins from my work so I made the trek over there. They didn't have the M8x1x80 screws I was looking for with zinc plating, only 8.8 black oxide and stainless. The lady working there claimed that it was because the coating would be too thick and the parts wouldn't fit together - which didn't make any sense to me, but I went ahead and bought the black oxide screws. Another fastener supplier that we ordered from also did not have them available, it was the only part on our list that they couldn't get for us, and they will usually find the parts if they don't have them in stock. That's why I was curious if maybe these just don't exist, but obviously they do.

Thanks for the info.

 

[Cockroach]

On threaded fasteners, a coating such as zinc is only 0.0005 inches thick. We're talking haf mil. This would negligibly change threading geometry, which is why the industry uses zinc or phosphates coating all the time. So yeah, the vendor is giving you the story or chicky-poo has a poor understanding of the product line. I would bet the latter.

Regards,
Cockroach

 

[JohnRBaker]

Yes, zinc-plated fasteners are readily available since in applications like machinery designed for processing food products cannot use your normal 'hardware store' variety cadmium-plated nuts and bolts. I worked 14 years designing commercial bakery equipment and we had to use either stainless steel or zinc-plated hardware. In most cases we zinc-plated due to the cost difference from stainless. And we also had to make sure that when these machines were being erected in the field (most of what we made had to be shipped in modules and sub-assemblies which were erected in place in the bakeries as some of these machines were as large as a small house) that the millwrights didn't just run down to the local mon & pop hardware store if they needed some additional hardware.

Note that this was 30+ years ago so this is not something new, zinc-plated fasteners have been around for years.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA

http://www.siemens.com/plm

UG/NX Museum:

http://www.plmworld.org/p/cm/ld/fid=209

To an Engineer, the glass is twice as big as it needs to be.