HVOF coating on Extursion Ram peel off

[raviswanadha]

Hi all ,
recently we have have recently coated an extrusion ram of diameter 500mm and length 4000mm with HVOF WC/Co/Cr . The Ram is used to power another main ram for extruding Steel Tubes. The Coating thickness 500microns and sealed the coating with Dichtol thermal spray sealer. We ground the ram with 3m trizact diamond belts to the required surface finish. When the ram was put into service within 10 days of operation, it was observed at some portions coating was peeling off especially at the bottom surface. They are presently using gun metal bush and cotton packing. The ram is operated at 350 bar pressure( 5000 psi). There is some jerking of the ram while starting and stopping.Also they are using glass powder mixed with water as a lubricant for extruding Steel pipes. Any suggestions on what could be the reason for peeloff and what coating is best suited for this application.
Best Regards

[MichiganMan]

Sorry to answer your question with questions, but the following might help to illuminate root cause.

Was this a newly made piece, or a piece that had been in service prior?

What steps did you take to eliminate oil contamination in the piece? Other surface prep?

Which Dichtol product did you use? There may be temperature issues or chemical compatability issues with the hydraulic fluid. Presumably they are using a flame retardant hydraulic oil, and many of these are known to degrade organic polymers (if I recall dichtol is at least partially organic).

When you say "bottom surface" what do you mean? Do you mean to indicate that the failure is primarily in the area that the packing is riding on the ram?

[raviswanadha]

Sorry to answer your question with questions, but the following might help to illuminate root cause.

Was this a newly made piece, or a piece that had been in service prior?
Ans: The Ram was in service prior to coating.

What steps did you take to eliminate oil contamination in the piece? Other surface prep?
Ans: intially we preheated the ram then cleaned the surface with IPA( iso Proply alcohol) and then grit blasted the surface.

Which Dichtol product did you use? There may be temperature issues or chemical compatability issues with the hydraulic fluid. Presumably they are using a flame retardant hydraulic oil, and many of these are known to degrade organic polymers (if I recall dichtol is at least partially organic).
Ans: We have used Dichtol WFT 1532

When you say "bottom surface" what do you mean? Do you mean to indicate that the failure is primarily in the area that the packing is riding on the ram?
Ans: Yes the failure is primarliy in the area that the packing is riding.

[MichiganMan]

Possible Root Causes:

Verify that service temp of the ram is in range of the Dichtol product. Depending on the temp of the ram in service you may need to go to the HTR product. Also Note that the temperature in the area of the packing may be elevated with respect to the rest of the piece, particularly if the configuration of the ram has a packing gland that is manually tightened. Over tightening increases friction often causing chattering as you described (jerking motion). This in turn increases heat in the area and accelerates wear in that area as well. Was there noticably more wear in the area that corresponds to your problem area when you took the piece out?

I suppose it is possible that there was still oil trapped in the piece that the pre-heat and wash did not drive out. It may be necessary to bake the piece in order to eliminate the impregnated hydraulic oils prior to surface prep and coating application.

I suspect that one or the other of the above would be your cause, and the chattering in operation leads me to believe that the former is slightly more likely than the latter (about 50-40 with 10% being some other cause).

Good luck.