Hard Chrome Alternative 1

[Haz88]

Hi All,

I have been looking into how we can drop the costs on a component we need at work. Basically its a mild steel tube with hard chrome plating on the OD as it is a sealed and bearing surface.
I got a little excited about the potential of Nitride (ONC black) but have since found out it is achieved using high temperatures and will most likely warp our tubes. even the "low temperature" plasma nitride is still approx 400 deg C.
I have had a small look into High Velocity Oxy-Fuel (HVOF) but i can only find information on suppliers pages therefore i am skeptical it isn't biased.
Question:
Does anyone know of any good quality alternatives to hard chrome plating? especially if its cheaper?
(wall thickness is 3mm)
much appreciated.
Josh

 

[metengr]

What material contacts the hard chrome plating in service?

 

[Haz88]

essentially it runs on two Teflon dry universal bearings, the system runs much like a hydraulic ram. the guide which holds the bearings is 6061 AL with an oring and scraper .

 

[TVP]

Ferritic nitrocarburize + oxidation (ONC black, Kolene QPQ, Arcor, etc) should be cheaper. This process can be and is routinely performed on tubular components for hydraulic cylinders. What is the diameter and wall thickness of these tubes?

 

[Haz88]

thanks TVP, its a 50mm OD 44mmID tube, so relatively thin wall. My suppliers of hard chrome say the high temperatures involved will warp the tube... not having any previous experience in this situation i don't exactly disagree, yet it is good to get more than one opinion.

 

[tbuelna]

I would agree with TVP. A liquid salt bath nitrocarburize process, such as Melonite QPQ, will provide a smooth hard case and corrosion resistance on mild steel. The process temperatures involved are typically around 1075degF max. But there is no quench involved, and the parts are carefully pre-heated to around 900degF prior to being placed in the liquid salt bath, so there is no significant distortion resulting from the process. The intermediate polish operation used with Melonite QPQ produces a very smooth final surface that should not require any finish grinding/honing that hard chrome plating often does.

Based on your description, the Melonite QPQ process (or something similar) should cost less overall than using hard chrome. The only advantage that hard chrome has versus LSB nitrocarburize is that the hard chromed part can be reworked if the plated surface is damaged.

 

[Haz88]

Fantastic,
I will look into it. Thank you very much.

 

[WKTaylor]

Haz88.

What is Your 'mild steel' strength requirement? 95-KSI? 125-KSI? etc?

What is Your current ASME B46.1 surface roughness requirement [before and after plating]? 8-microinches RA, 16-mi RA, etc?

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
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[btrueblood]

"My suppliers of hard chrome say the high temperatures involved will warp the tube."

So, the supplier of a current process is claiming that an alternative process (that they likely can't do) won't work? Ever hear the line "trust but verify"?