Max. Hard chrome plating Thickness

A. The process that you refer to is Brush Plating. There are numerous vendors of the solutions and equipment. Brush chrome historically is a "cap", very thin applied over nickel or cobalt or other choice of metal. Liquid Development Corporation has a trivalent chrome gel that requires flow thru technology that is capable of a thicker coating of chrome. It is not capable of thicknesses from a chrome tank, but is quite a bit thicker than "regular" brush chrome.

An engine lathe is an expensive device to use if you are using the lathe as the negative source. It does the bearings no good. Nearly every brush plate vendor sells a rotating device that can be mounted on a table top, making drip collection a lot simpler and the equipment significantly more portable.

Solutions other than the trivalent chrome are sold by many vendors, so shopping can save money if you are going to use it a lot; and buy from a well known company.

You may not need chrome. Hardened nickel or cobalt may be enough.

A. I want to add (many years later) that we have successfully repaired industrial engine's crankshafts using chroming processes. OEM do not recommend this practice but, instead of buying a new crankshaft, which usually takes 8 to 10 weeks to be delivered from factory, we can in eight days rebuild the damaged bearing surfaces back to original specs. For any industrial process this means equipment availability and up-time for achieving production targets.

A. Theoretically yes, but hard chrome is too brittle (less than 1%) compared to 15% or more for steel and may spall or chip. For that thickness it will also be cracked. The cracks may be thin and shallow but, depending on process parameters, they may penetrate into the base material allowing for corrosion products to undermine it. Nickel (particularly from a sulfamate bath) can be deposited to that thickness and even more. Its elongation matches that of steel. Other options: thermospray (less adhesion), press fit of another bushing.

A. Guillermo is right. Most aircraft repairs usually call out a chrome thickness between .003-.005 inches (.076-.127 mm). Once chrome gets thicker than this the part starts to take on the metallurgical properties of chrome rather than the base metal. Nickel plate and grind to a thickness that will allow a subsequent chrome plate and grind to the final dimension leaving the .003-.005 inches of chrome.

A. Hi Asim. Chrome plating should be okay, but electroless nickel plating or brush plating with nickel may be easier (and probably better). When you say "compensate the reduction in thickness", though, I hope you are referring solely to restoring the dimensions; you cannot neck down a shaft and then compensate for the loss in strength by chrome plating it. Good luck.

Regards,

A. Perhaps there is a confusion with the term "unbalanced".
Balance refers to mass distribution around a center or axe, not dimensions. Dimensional variations are usually referred to as "run-out".

A. Chrome for bearing shaft repair should be put on at 0.005" minimum and ground to no less than 0.003" per side.

Grinding requires lots of coolant and the proper wheel. The wrong choice of resin and grit will lead to failure! It requires very thin passes or it will peel from the heat.

QC is what your customer wants. Normally if it is sort of bright with no white areas, it probably is good IF it lives thru the grind operation.

Judging from your last post, the machinist is loading the part off center, both times, probably in the same direction with the part rotated 180. Off center is definitely a machinist problem.

A. Sir: If your shaft was hard chrome plated, and was not ground properly, it is probably "off center". This means that your shaft is not completely round after plating and grinding; this will make your shaft vibrate after installation. I will recommend that you take a digital micrometer or caliper and measure the area that was plated all around, see if you find different readings. Thanks.

A. I don't mean to start a discussion about geometry or mechanics here but I have to disagree with Mr. Cordero's comment about roundness. A diameter could be perfectly round and still run out. In situations of very tight tolerances, this is generally a consequence of part distortion or different machining operations using different surfaces or items of the part (i.e., between centers or resting on journals). Regards,

A. Hi Ahmad. I've never heard of anything of the nature of trying to squeeze a shaft longitudinally to make it bigger in diameter. But it probably can be nickel or chrome plated. Good luck.

Regards,

A. Usually, it is not a problem to have 50-150 microns (0.002"-0.006") of hard engineering Chrome per side on a round part. To prevent peeling, surface has to be properly activated (depends on base material: for regular carbon steel or low alloy steel - reverse etch in Cr plating solution). It's recommended to plate a little over required size and grind the deposit to size. Also Hydrogen embrittlement relief bake is critical immediately after the plating.

A. Hi Sarah. We appended your inquiry to a thread on the subject, and pending additional replies it looks like nickel plating before chrome plating is a sounder approach as suggested by Guillermo and Tim. Good luck.

Regards,

A. Hi, Sarah. We repair a lot of parts to restore their dimensions after wear/erosion. According to our experience, maximum chrome layer thickness recommended is 0.010-0.012 inch. Thicker chrome layer could crack during the grinding process. The best practice is to plate low stress sulfamate nickel layer (any thickness you need), to machine it to 0.004-0.007" less than the final dimension needed, plate chrome and grind it to the final dimension.
Good luck.