Which substitute for hard chromium plating?

A. Dan,

A. You might want to consider some of the PVD hard coating options.

A. Dan: While you might want to look for a substitute on the environmental basis of trying to minimize chrome plating when possible, I strongly doubt that you will find PVD less expensive. And as long as you already have found chrome plating to be highly suitable for this function, I don't think you'll find anything that functions as well (or better).

When it comes to machinery with lubricated rubber seals, it's not solely a question of smoothness and coefficient of friction, but of oil-retention properties--and due to the "dried must-flat" topography of hard chrome plating, it excels at all of these.

A. Some thoughts,
Electroless nickel has many of the same properties that you are looking for and probably would be cheaper in the ones and twos quantities. Another plus is you would only have to pre grind, post grind would not be required. Drawback is thickness. The practical maximum thickness for EN is 0.0015". This probably will not have the length of service that the chrome will.

Also, you can regrind and rechrome the shaft a great number of times.

What probably is killing you is the minimum lot charge. You could very probably have two or possible even three shafts done for the price of one. This would mean that you would have to keep inventory longer than you might like because of several size shafts used.

Your shaft is about the easiest size and shape that there is to chrome plate if your plater is using conforming electrodes. A good plater, after a learning curve of a few parts, could cut your "for grind" thickness to one or two thousandths which would save you several dollars per part on the grinding operation.

If you had parts on the shelf, you could find an excellent plater and afford to ship anywhere in the USA, in lots of say 5, and have significantly cheaper per part plate and grind cost. My nickel says that you would have higher quality product also.

A. I agree with the previous responses. Indeed, EN or sulphamate Ni are less porous than chrome, although your problem might go beyond this and not be solved by switching to a different plating. Can you keep the stem dry by means of drying its surroundings? Can either be hot lamp, hot air, etc. This will be better approached using some sort of a jacket or sleeve. Then you might want to consider teflon (plain or impregnated in a plating) to cope with the possibility of problems due to lack of lubrication.

A. Mike,

A good deposit for this is electroless nickel as stated above; it is as deposited glass-like (amorphous), and can be baked to almost as hard as Hard Chrome.

A. When properly applied, adhesion of hard chrome to most low and mid alloy steels is around 20,000 psi or more. Vickers Hardness will be around 900-1100 HV (approx. 67-72 Rc). But if the gears are surface treated, specially nitrided, getting a good bond can be challenging even for most experienced platers. Remember that chrome is also brittle (less than 2% elongation). You can also consider nickel as an alternative.

A. Electroless Ni-P or Ni-B based composite coatings will be a useful alternative to hard chrome for plastic injection moulding dies. The performance of these coatings will be equally good as that of hard chrome.

According to some published literature, a 50 micron thick electroless Ni-P-SiC coating could improve the life of molds (usually last for 10000 moldings) for plastics, rubber etc., by 15 times. Electroless Ni-P-SiC coatings could prevent accelerated corrosion of abrasion molds in the plastics industry and in this respect it is superior to chrome plating. In foundries, electroless Ni-P-SiC coating enables an easy release of sand cores without breakage from core boxes.

Electroless Ni-P-PTFE coatings offer non-stick, non-galling, higher dry lubricity, low friction, good wear and corrosion resistant surfaces. Electroless Ni-P-PTFE composite coatings could also be used for molds for rubber and plastic components. The coatings can be used under a wide range of temperatures from cryogenic to 290 °C.

A. Vikram,

You should use electroless process. Then you do not have to worry about low throw, low & high current density areas, etc.

High Phos (9-12%) Electroless Nickel with post plating bake is what you should do.

Thanks

A. Very well answered by the other two respondents, I couldn't agree more. Only to add that electroless nickel, either composite with particles or heat treated, will require some special pre-plating techniques with some mold materials (like high alloy, stainless and copper alloys). Also special chemicals to strip it when required for modifications, repairs, etc. Chrome has been around for much longer, so it will be easier to find. Electroless nickel is a specialty that only found wide commercial use during the past 30 years in developed countries, composite EN maybe 20. So it will be harder to find in emerging regions.

A. These finishes have received "preliminary evaluation" as feasible alternatives by some US firms that have multiyear government contracts to investigate chromium alternatives for the military. But as I attend the presentations on chromium replacement technologies year after year I am reminded of a notepad block my brother-in-law gave me for Christmas a few years ago "Consulting: if you're not part of the solution there is good money to be made in prolonging the problem" :-)

They're probably actually trying, but I hope you find someone who is actually using these because I think we'll make little real progress until private enterprise starts widely applying these coatings to some non-military parts and getting some service history.

A. In certain applications and according to some specific and controlled testing, electroless nickel composite with diamond or other super hard particles with a subsequent heat treatment for maximum matrix hardness has demonstrated to be even superior to hard chrome. Being a plating process, makes it a promising candidate as opposed to other techniques that have limited adhesion and require a different surface preparation, such as HVOF. Only problem is that it is much more expensive and also in the line of fire of EPA.

A. Electroless nickel + synthetic round diamond is a more accurate description of this hard chrome competitor and, to my knowledge, is a proprietary process only offered by Surface Technology, Inc. in NJ. Maybe you could find platers doing EN with other types of hard particles. Fully hardened plain EN (preferably boron reduced) could modestly compete in some environments.

"Hard Chromium plating"
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A. Hi David.

4). Hard chrome plating is rarely done on aluminum because aluminum is not hard. Surface hardening procedures like chrome plating are of limited value on soft substrates because the plating may simply crack like an eggshell under heavy loads when there is no hard support under it. But it can be done.
3). For a quick intro, please see our on-line FAQ, "Introduction to Chrome Plating". For greater depth, Guffie's "Hard Chromium Plating" is good .
2). Aluminum is probably not a good bearing material because it galls badly, and aluminum on aluminum would be a horrible bearing. Aluminum is frequently electroless nickel plated, which is a hard coating which might possibly suffice for certain bearing applications, but the electroless nickel plating can be infused with teflon particles, which would probably make it a good bearing material.
1). Sorry, I don't know which is any local shops offer hard chromium plating on aluminum.

Good luck!

Regards,