Hard chrome plating thickness variation problems

A. Hi prakash. Please attach a picture of the item in e-mail to mooney@finishing.com for posting here, and tell us the dimensions, etc. Getting hard chromium plating on the inside of a bore without auxiliary anodes in the bore is probably hopeless.
Luck & Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Hi Manoj. You didn't mention the thickness of the plating yet, so we don't know what the percentage variation is. And you didn't mention anything about the fixturing, so it's hard to say how to improve it. But, in general, chromium plating is more efficient at high current densities than at low current densities, so a high current density area will get much more plating than a low current density area. You need to be doing something fixture-wise to fix this (thieves, shields, anodes which conform better, rotation during plating, etc.) There is no solution adjustment that will cause the efficiency in the LCD area to even reach the efficiency of the HCD area, let alone exceed it. Good luck.

A. Hopefully someone with substantial hands-on hard chrome plating experience will speak up if something sounds wrong, but this sounds to me like a reasonable variation in plating thickness for the conditions. Without rotating the parts, which would presumably be a very big problem, I doubt that you'll reduce that variation around the circumference. But slight changes in the shields, and making sure you have good agitation, may reduce the end to end variation.

A. Manoj,

I think the thickness variation you describe for a hard chrome solution can't give you a better metal distribution then you have. If you like to have a better metal distribution change to electroless nickel.

Regards,

A. Dear Mr Manoj,

If your spec says 5-12 microns, and you already have a tolerance of 7 microns and are achieving a variation of just four, everything seems to be working for you, the variation is within reasonable limits.

A. Dear Mr. KV,

I think you got it wrong tolerance and variation are two different things. The specs demand coating of 5-12 microns, which means that the coating can be minimum 5 microns and maximum 12 microns but does not say that it can vary from 5 to 12. I think you can get me. As far as the initial question is concerned, I think job rotation, fixture design and robbers can solve your problem. We plate rods 8 to 20 mm dia 7 to 14 microns, both parallel and true within 2 microns. Go ahead try a better job holding design.

ALL THE BEST

Vikram Dogra
Irusha India - Chandigarh, India

A. PLATING THICKNESS VARIATION DEPENDS ON
1. SURFACE PREPARATION
2. CONTROL OF BATH CONDITIONS
3. UNIFORMITY OF THE POWER SOURCE
4. ANODE PLACEMENT
5. SHIELDS, THIEVES
6. TANK DESIGN, etc.,
Practically variation is there .

A. Manoj,

I agree with many here about your question about thieves & shields. To get a better metal distribution you must think about this. How long is your anode, because the anode must be a little shorter than the part. Are the anodes active. Is the anode arrangement so that it goes around the part. Sulphate ratio to the chrome, trivalent chrome metal contamination, temperature. Also a low current density will help you with a better metal distribution.

Regards,

A. Hi cousin. Your question is too brief. Are you saying that you can't get 50 microns even if you plate for two days? Or are you saying that you don't achieve it in the arbitrary time period that you wish?

Let's start with a Faraday's Law calculation to determine what efficiency you are achieving -- What is the total surface area of the plated parts, the plating time, and the amperage reading of the ammeter on the rectifier?

Regards,

A. Hi. If the minimum allowable final size is 168.917 and it has the minimum of 20 µm of chrome, the diameter will increase by only .04 mm, so before plating it must be 168.877 mm or more before plating. If the maximum allowable final size after plating is 168.957 and it has the maximum of 30 µm on it, the diameter will increase by .06 mm, so it must be no larger than 168.897 before plating.

Regards,

A. Hi Orlando. A sketch or photo of the arrangement would probably be worth a thousand words. Although I've seen shields successfully employed in plating, I have personally never seen them used in chrome plating and am not optimistic about it. I think the most straightforward solution would be a properly shaped conforming anode rather than a shield or a robber.

Regards,

A. Hi Anil. It is fairly common to keep shafts and rollers rotating during chrome plating, so that is one approach. It is necessary to maintain very consistent anode-to-cathode spacing, so that's another approach. If you are plating shafts vertically, it's possible that the plating solution at the bottom of the tank is colder than near the top of the tank.

You might want to have a hard chrome plating consultant, or at least a representative from your chrome plating solution provider take a look -- or forward photos and full details, and maybe a kindly reader can help. Good luck.

Regards,

A. HI. I'm not doing chrome plating. Sharing my experience in cadmium and zinc- nickel plating regarding thickness issue: 1) Temperature of the solution, Tank needs proper circulation so that temperature always same throughout the tank. 2) Dimension/ drawing of the parts. 3) Parts need to be rotated in interval time. For example, taking A as a side of your part and B is another side of your part. After 20 minute A is facing anode, you need to change B to facing the anode for 20 minutes. So that you can reduce the thickness difference between both sides. 4) Distance between anode and cathode. Try to make it always constant. 5) Current density and location of contact points. Thank you Izzuddin Jaafar Asahi Aero Malaysia Sdn Bhd - Selangor, Malaysia January 8, 2020

? How did you hang the parts in your racks? Did you use thieves or in it the bottom of the parts there will be a thicker deposit?
Regards

A. Hi Anil,
You should check the distance between anode to cathode.
It must be same from both sides as well as not more than 5 to 6 inches every side as chrome has very less conductivity 12% to most effective 24% only.

And also you can make the arrangement of round moving cathode movement which would help you to balance the thickness distribution on the surface of component, as well by mild agitation -- it maintains the temperature of whole solution.