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PensacolaFred (Mechanical) (OP)
3 Oct 06 20:55
Our vendor switched from Hexvalent to Trivalent plating and were having all kinds of issues ie. pushing up hoses on to the end fittings, threads to tight. Any advice or help you can give me to shed some light on this situation!!
BillPSU (Industrial)
3 Oct 06 22:34
The trivalent coating should not be impacting threads or fittings as the coating is very thin. The hexavalent and trivalent coatings are protecting the zinc plating  and if properly applied would have little effect.

The trivalent coatings needs to be thicker to give the same corrosion protection as hexavalent coatings. There are two different approaches to achieve this. The first approach is to make the coating thicker the second approach is to maintain the thickness and add an organic sealer. The different companies using this approach may have poor control of this process and you may be required to verify your supplier's performance. Your supplier may also just be adding more zinc.

Trivalent coatings are primarily required in EU automotive applications which is why the change is being done. The US will probably follow suit but not as of right now. The organic coatings are typically proprietary and application experience is minimal at this time. The only people who seem to have a good handle on this technology at this time is Parker but I am sure many other companies will bring their coatings to similar performance levels quickly.
TVP (Materials)
4 Oct 06 15:23
PensacolaFred,

What is the plating being specified?  Chromium plating is deposited out of hexavalent or trivalent baths.  Chromate conversion coatings used on top of zinc plating are deposited out of hexavalent or trivalent baths.

The information provided by BillPSU is related to the latter.  There are a number of plating chemical vendors that have robust trivalent chromate products such as Dipsol, MacDermid, SurTec, and Atotech.  I am not sure about Parker-- is this referring to the former Parker Amchem that is now Henkel Surface Technologies?
BillPSU (Industrial)
4 Oct 06 23:31
TVP
The Parker I was referring to is the hydraulic company which coats their fittings and hydraulic hose ends. Pensacola was referring to end fittings of hydraulic hoses. There are companies such as Gates Rubber, Alfagomma, and Aeroquip which compete in the metal braided hose market which are going through the same conversion to meet EU standards. The hydraulic fitting business has many other players including Airway and Piper. There is also off-shore manufacturers which produce these same components with varying degrees of quality.
NoDakEng (Mechanical)
30 Oct 06 17:57
PensacolaFred,
I have just been informed that my company is experiencing similar issues as we migrate to Trivalent chromate conversion coatings.  There is speculation that this may be a tolerance issue with the threads since you need more zinc elecroplating for silimar corrosion protection.  

Have you found the root cause of the issue?  I'm meeting with Gates Hose and Piper reps separately within the next couple weeks, however, I do not expect them to have a full understanding of the issue.

Does anyone else ave any experience with the transition to trivalent chromium on hydraulic fittings and tube ends?

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