Green chromate vs. Gold chromate
Green chromate vs. Gold chromate
(OP)
I am experiencing a problem with a Green chomated brake nut and its mating characteristics with an aluminum body. I am getting false torques during the assembly of the two components. I am not getting false torques with a similar Gold chomated brake nut and aluminum body.
Green nut/aluminum body - the aluminum body is Gravity die cast and goes through a T-5 Heat treat process and is Anodized.
Gold nut/aluminum body - the body is extruded, no idea if heat treated or if coated
The nut is made on the same equipment, but plated differently.
HELP !?!?!?!?!?!
Green nut/aluminum body - the aluminum body is Gravity die cast and goes through a T-5 Heat treat process and is Anodized.
Gold nut/aluminum body - the body is extruded, no idea if heat treated or if coated
The nut is made on the same equipment, but plated differently.
HELP !?!?!?!?!?!





RE: Green chromate vs. Gold chromate
Without additional details, this will just be speculation. The first thing I would do is confirm alloy and heat treatment for the extrusion. Next, what are the differences in the chromates? By green, do you mean the thick, dark olive drag coating? Or is it a faint green that is basically a clear chromate with a dye added to it? The OD green is a much thicker chromate, and may be affecting the tightening process. More likely, some type of lubricant is integral with the gold chromate, which reduces friction and therefore improves resistance to galling. You should confirm this with your vendor.
Have you verified the thread characteristics of the aluminum components (dimensions, integrity, etc.)? Any damage? Other than this, my first guess is the friction aspect, as many chromates for fasteners have friction modifiers added for better tightening performance. Post more info if possible.
RE: Green chromate vs. Gold chromate
RE: Green chromate vs. Gold chromate
The green chomate is the dark olive green coating.
I have confirmed the threads of the nut and both aluminum bodies. The AL bodies are okay.
The green nut will not thread completely on M10 x 1.0 Class II Ring Gage. But it measures okay with an optical comparator.
Currently we are using a Marathon brand 'flushing oil'
CoryPad,
What type of 'friction modifiers' are you talking about ? Can you give me some examples ?
RE: Green chromate vs. Gold chromate
http://www.themagnigroup.com
RE: Green chromate vs. Gold chromate
I do not know much about thick zinc electroplating plus chromate coating, but I have painful experience with chromate conversion coatings on aluminium.
Aluminium has a very high coefficient of friction, and the untreated stuff binds easily. The chromate conversion has no effect on this. We had to have a telescope taken apart by a machine shop a few years ago, and we learned our lesson. If something has to fit accurately, you do not use chromate conversion. Anodize works much better. If the interface has to be conductive, you cannot rely on the coating.
I think this reinforces the comments above about the zinc electroplating. When finishers prepare to anodize or coat something, they clean it by etching. This means that anodized or alodined parts actually lose material in the coating process, and clearances increase.
JHG