What is Blue Chromate Plating?

A. Hi Praveen. Both doubtless have a clear or bluish chromate because bare zinc plating without chromate is almost unheard of. If you would introduce your position in the supply chain, where these tubes came from, and your actual issue, it would be much easier to answer more directly, but some zinc plating processes do produce a brighter finish than others, but plating is relatively thin such that mechanical treatments before plating (like sanding, polishing, bead blasting) can show through and produce different apparent brightness as well. It looks to me like one of the tubes was scratch brushed before plating and the other was polished, but an acid zinc plating finish is significantly brighter than a cyanide zinc or alkaline zinc plating.

Zinc plating is usually considered a functional finish rather than a decorative one, and brightness is usually not part of the specification.

Luck & Regards,

A. "Blue chromate plating" is an example of somewhat misleading lingo or trade vernacular, Kevin, and it can indeed be hard to get your bearings in such cases. As a young engineer involved in surface finishing, please give strong consideration to attending a local AESF meeting (www.nasf.org) if possible. You do not need to be a member, you will be welcomed, and you will rub shoulders with "old hands" who will be delighted to answer your every question in whatever detail you need. If you can get to "Sur/Fin" this year, you can attend the industry's largest exhibition and conference.

To answer your question without misleading you can be tricky, but I'll try. Many steel components, including the majority of nuts & bolts, are zinc plated for corrosion resistance and an acceptable appearance. But the zinc in turn will quickly "white rust". To deter this, zinc plated components are almost always chromate conversion coated, and that chromate can be of several colors -- black, iridescent yellow, and blue being examples. The blue is a slightly blue toned bright metallic finish, it is certainly not blue in the sense of blue paint. Traditionally these chromate coatings have involved hexavalent chromium. These days they are usually trivalent to comply with RoHS requirements.

So what does "blue chromate plating" mean? Almost surely it means zinc plating followed by a blue-toned chromate conversion coating, hopefully trivalent chromate. Our "must have" booklist is more targeted towards these processes than simply starting at ASM. Good luck!

A. Hi Ron. Zinc plating with blue chromate is the least expensive electroplating of all, and although stainless steel construction might be better in some ways, it would be extremely rare for solid stainless steel to be less expensive than zinc plated and blue chromated steel.

As for conductivity, there are usually two issues, the bulk conductivity/resistivity and the surface resistance. For example, copper and silver have excellent bulk conductivity, but steel and titanium and stainless steel have poor bulk conductivity. Gold has excellent surface conductivity because it doesn't tarnish, whereas a painted steel item would have extremely poor surface conductivity if any.

Neither zinc plated steel nor stainless steel has really good surface conductivity, so neither is suitable as a surface for electrical contacts, so you are probably thinking of bulk conductivity (if the item must carry a ground current for example). The conductivity of carbon steel is about 10% of the conductivity of silver; the conductivity of stainless steel varies according to type, but it is about 1/4 that of steel. Good luck.

Regards,

A. Hi Patrick. Hopefully a supplier will contact you in private. There are numerous competing industrial suppliers, but it is true that many are unwilling to sell to individuals over liability concerns and the lack of economy of scale. Maybe google for "hobby plating suppliers"?
Sorry that we can't suggest suppliers for a number of reasons ( huh? why?), but one of those reasons is that while google is for live searches, this site has attempted to be a permanent technical reference since 1989, and offering supplier names & links across 60,000 threads either turns it into a wasteland of dated info & broken links or an impossible game of whack-a-mole :-)

Good luck, and regards,