Thread adhesive patches for Trivalent chrome applications 2

[baskargk]

CAn anybody faced a problem of thread adhesive patches poorly bonding on the surfcae of the trivalent chromium coated fasteners.

Whts is the root cause for this problem.? any soultions for the above problem.

Thanx inadvance for ur reply.

Baskar

 

[yates]

Never had bonding problems with thread patches, but then again, I have never done any chromme plating on threads before. What weird kind of product needs chrome plate on threads?

 

[MintJulep]

How about a mechanically inserted pellet or patch?

 

[CoryPad]

yates,

It is not chromium plating - it is chromate conversion coating of zinc plating. I haven't heard of any bonding problems with this.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[yates]

Cory,
Thanks for the correction. It did sound mighty odd to me. I have heard people complain that trivalent chromate conversion does not give the same friction coefficient and therefore a different torque/tension relationship. From a chemical or physical point of view, the responsible mechanism, (if proved to be true), beats me.

 

[CoryPad]

yates,

One possible explanation for friction coefficient changes may relate to thickness. Hexavalent chromate conversion coatings come in various thicknesses (and change color from yellow/gold to olive), but most trivalent chromate coatings are very thin.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[baskargk]

can somebody explain me wht's is the purpose of Trivalent chromate coating on ZINC plating? Whts Trivalent chromate coating?

regards,
baskar

 

[TVP]

Chromate conversion coatings delay the onset of corrosion of the zinc layer, thereby improving the overall corrosion resistance of the sytem. Chromium has a number of oxidation levels, including +3 (called trivalent) and +6 (called hexavalent). Hexavalent chromium rapidly bonds with oxygen, which explains why it is used in coatings to prevent corrosion. However, this same affinity for oxygen is what makes it a serious health hazard-- it accumulates in the lungs and prevents the normal oxygenation of the blood. Trivalent chromium also bonds with oxygen, but to a lesser extent. Hexavalent chromates are produced by dipping zinc plated parts in solutions containing chromium trioxide (CrO₃). Trivalent chromate are produced by dipping zinc plated parts in solutions containing chromic oxide {Cr₂O₃).