• Topic 57493 "Zinc Plating Internal Threads: dimensional changes & coverage issues"

A. Hi, Rudi. Most thickness specifications only cover the area that can be touched with a 3/4" dia. ball; some may specify "coverage" of all areas, but not thickness. Alkaline zinc offers better coverage than acid zinc, so you might verify that your plater is using an alkaline process.

You can specify and obtain anything you want, including generous plating thickness inside blind holes, but it requires special procedures like internal anodes, holes up during plating and down during tank-to-tank transfer, etc., so it can be unaffordable for production parts.

Regards,

A. Hi Nanjund. Anything can be done, including getting full plating in a blind hole whose depth is twice its diameter. But when you say "on a production lot", I think you are trying to imply "without taking special measures" or "without special and exotic jigging". If it's a part that is barrel plated, it's not likely. You can do it in rack plating, with auxiliary anodes, and tilting the rack to eliminate air pockets and carryover of solutions, but probably not without these special measures. Best of luck.

A. If this is a blind hole, You will never get plating to the bottom of the hole. Typical plating will only go the depth of the hole that is equal to the width of the hole-Aspect ratio, and this does not hold for tiny holes.
If they insist, graciously tell them that it is an absolute impossibility, and pass on the job. You can help your cause if you can find a couple of specifications that have the coverage measurement in the QC section. The mill spec says something like coverage if it can be touched by a 3/4" ball.

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A. Sometimes it can be impossible to cover inside holes.

In general... I recommend the following to get maximum coverage...

1) use alkaline zinc process

2) keep the load size of the barrel as small as possible

3) apply the highest current densities that are possible without burning

4) pretreatment and activation can be critical as well to ensure that you have a clean and active surface that readily accepts the initial electroplating deposit.

A. Dear Jason,

In order to get Chromate on the zinc layer, you should have certain micron of Zinc layer then you will have chromate layer on it.

In your case your should find a good throw zinc plating (alkaline non cyanide zinc) and in this case I agreed with Thomas.

Just try Thomas recommendation (see above)

Good luck.

Best regards,

A. YES ALKALINE NON CYANIDE IS BEST ANSWER.
ASK THE CHEMICAL SUPPLIER TO PLATE FEW PIECES FIRST .
THEN THINK OF STARTING THE PROCESS.
REGARDS,

A. Again, if I read the post correctly, he is trying to plate a blind hole about 1" deep and 1/2" in diameter. Barring using an internal anode, I seriously doubt if any plating process will put enough metal on the bottom to allow the chromate to show color.

A. Hi santhosekumar. It is true that you cannot expect plating in these holes, but you can expect carryover of plating solutions.

You gave us the size of the block as 50 x 8 x 16 mm, and the depth of the blind holes as 8 mm. This means that if you moved to through-holes they would be dia M3 by 16 mm. That would reduce the carryover of zinc plating solution, but you would still not have plating inside the full length of the holes -- so it would offer an improvement, but not really a full solution.

If this is low volume production, it may be possible to plug those blind holes before plating to retain any rust-proofing solution in them rather than plating them, while also keeping the plating solutions out of them. If it is high production barrel plating where plugging won't prove practical, then through holes are probably you best bet.

Regards,

A. Hi Brad. Almost nothing is impossible, but the details of how to achieve this will depend on the material of the substrate, what metal you want to plate it with, and the actual dimensions, not just the 8D ratio.

Auxiliary anodes will surely be required if it's an electrolytic rather than electroless process; rotating the part to prevent air locks and solution carryover will probably be required, and some manner of solution exchange will probably be required to prevent depletion if the bores are tiny but probably not if they are large (because solution volume is proportional to the second power of the diameter).

Regards,

? Who designed that component?! -- rhetorical question :-)

If I'm understanding, you have blind bores about 3 mm in dia. by about 24 mm deep? As previously noted, almost nothing is impossible, but this is the closest thing to it. What is the substrate? Please don't tell me it's steel if you're trying to start with acid copper.

Regards,

A. Hi again. Sorry for apparently misunderstanding what you meant by "8d blind bores", which has resulted in 7 mostly wasted postings.

In that case what diameter are the bores which are approximately 3 mm deep? And they are just plain bores, not threaded holes? You seem to be implying that you are plating the parts anyway, including both rack & barrel plating, even though you don't get coverage in the bores?

Geoff Smith's point remains that it is entirely possible that the bores cannot be plated at affordable cost.

Regards,

 I have a small bet with myself that I know what these components are when we get an accurate description.

A. Hi Anoop. Although uneven plating in the threads can have a number of causes, getting no plating would seem to indicate that the steel is not clean and active in the thread area. Are you sure that no silicone lubricants are used in the thread rolling; silicone is for practical purposes impossible to remove sufficiently for plating.

Regards,

Q. Anoop,

No plating at threaded area looks to me like you make rack contact in this area; or threaded area not clean in your plating process.

A. Hi Dan. How deep are these blind holes, so we don't go down the rabbit hole as in previous entries on this thread? But why do you suspect poor cleaning as the reason the blind holes don't get plated -- I don't think I'd expect them to get plated regardless of how clean they are unless they're very shallow.

Regards,