rgh0 wrote:Many many years ago as a vacation student I worked in a bolt making plant - the zinc plated bolts were silver in colour and the cadmium plates bolts a gold colour. Interesting that it can be the other way around depending on the process used I guess. In which case my Elan callipers may be cadmium plated originally
cheers
Rohan
The passivation process can change the colours to whatever you want............or the mixtures of silver, gold or lead even I believe with the cadmium may change the colour, however the cheap and cheerful coating used for callipers just gave nothing more than a surface 'shelf life'..........in jewelery cadmium was widely used for both silver and gold items.
http://www.thelaboratory.co.uk/legislation_cadmium.html For sure though I have never seen calipers hot dipped galvanised and I do not know of other ways to galvanise (Lotus Chassis were hot dipped galvanised) but as an 'oldy' I do appreciate modern techniques have moved on. My Brother in law specialises in Chrome on Plastic/Polymers and this has somewhat revolutionised components in the automotive and bathroom industry and his company plates plastic items in many different finishers for the leading European automakers but the volume business is the sanitary/bathroom parts..
Many metal fasteners since cadmium restriction have though been galvanised, especially in the building/fence industry. These fasteners have though to be treated with caution where torque settings may be critical.
One of the biggest problems with the plating process for metal fastenings is hydrogen embrittlement and unless fasteners are correctly baked to relieve this when plated they can shear easily........... something that has again been a big problem with cheap imported fasteners so always buy fasteners from an experienced company using experienced platers.
AHM........ not sure with todays modern changes but base zinc is white and turns yellow through the heat process if I recall from my chemistry 40 years ago, However you will see many items that are silver now stating 'zinc plated'....I am now retired on permanent vacation for the past 10 years but do appreciate how moden techniques and materials have changed things.
Traditionally galvanising and plating as terms were not quite considered the same thing back in my days anyway
http://www.azom.com/article.aspx?ArticleID=1380Regards
Steve