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Ted Mooney, P.E. RET
Pine Beach, NJ

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Chrome plate can't reach roots and deep area

Q. RUSH! I get a problem in chrome plate. this is a 10" Dia screw 100" long, we used get good chrome surface with 3500A--4000A, 10V. but this time we can't power more than 2500A.so the screw's root and side of flight can't get chrome .Is it because the chromium activation solution is too old (I mean the conductivity is too little) ? we add BaCo3 adjust PH to 2.3g/L and Cr 230g/L. thanks!

Bob Cao
feed screws - Toronto, On, Canada
2005

A. I assume that you mean that your sulphate level is 2.3 g/L and not the impossible pH of 2.3 g/L. I would personally be very curious as to the level of tramp metals and the level of trivalent chrome in your tank. I used porous pots to keep it clean and never saw your problem.

James Watts
- Navarre, Florida

A. BOB !

CHROME MISPLATING PROBLEM, CHECK THE CHROME TANK SOLUTION ANALYSIS OF RATIO AND RECTIFIER RIPPLE, CATALYST CONCENTRATION AS WELL AS TEMPERATURE.

Popatbhai B. Patel
electroplating consultant - Roseville, Michigan

Q. Thanks for help!

This is the analysis test report:

Tank description: HCR-710 chromium plating solution.

Chromic acid 232.5 G/L. Sulphate 2.100G/L. Ratio 111.0:1. Chloride 0.015G/L. Copper 0.500G/L. Iron 0.800 G/L. Tank capacity 6360 L.

I agree with Mr. James Watts that there are high level of tramp metals and trivalent chrome in my tank. I want remove Cr3+ by electrolyzing the solution: anode-to-cathode ratio: 14~15:1 and electrolyze at 6 volts. 20 hours, again at 130F. Is it right process?

Now, I don't know how to remove Fe ,Ni, Copper and Chloride? thanks again.

BOB CAO [returning]
feed screws - Toronto, ON, Canada

A. I would strongly recommend you to get a good course on chrome plating or at least a good book. Chrome plating is very critical. Any person should be well trained before being given the responsibility to manage a chrome plating operation. Copper, nickel, iron, zinc and other metallic contaminants can be reduced by ion exchange or electrodialisis. In the past the only known way was to dump part of the solution and replenish with new which, today is unthinkable. Chlorides present less of a problem as they will slowly be oxidized and expeled as chlorine gas.

Guillermo Marrufo
Monterrey, NL, Mexico
2005

A. Porous pot technology. Removes copper, iron and some other metals. There is a high priced firm in Canada with an excellent product. Being frugal (cheap) I like the product from Hard Chrome Consultants in Cleveland ,OH. A considerably less expensive but fully adequate means without the bells and whistles. PS, this takes care of the trivalent at the same time.

James Watts
- Navarre, Florida
2005

Q. Thanks for help!

This is the analysis test report:

tank description: HCR-710 chromium plating solution.

Chromic acid 232.5 G/L. Sulphate 2.100G/L. Ratio 111.0:1. Chloride 0.015G/L. Copper 0.500G/L. Iron 0.800 G/L. Tank capacity 6360 L.

I agree with Mr. James Watts that there are high level of tramp metals and trivalent chrome in my tank. I want remove Cr3+ by electrolyzing the solution: anode-to-cathode ratio: 14~15:1 and electrolyze at 6 volts. 20 hours, again at 130F. is it right process?

now, I don't know how to remove Fe ,Ni, Copper and Chloride?

Thanks again.

BOB CAO [returning]
- ON.

A. Bob,

My previous post takes care of the metals. Chloride will normally come off as chlorine gas at the anode , so is somewhat self healing. Now, chloride is a very very strong catalyst for chrome plating, about 10 times that of sulphate, so keep the chloride out of the tank. Better rinsing or use DI or RO water.

James Watts
- Navarre, Florida

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A. Bob,

You do not say what your Cr(3+) level is. As far as I am aware, most hexavalent sulphate baths are reasonably tolerant of Cr(3+) levels, being able to cope with up to 5% the Cr(VI) level. Can I suggest you do a Hull Cell test to see if it is the solution that is the problem or something else. For the conductivity to suddenly decrease by almost 20% is quite dramatic, so it could be a simple dodgey connection. If it is not the electrolyte, it could be that the anodes have passivated and got coated with yellow lead chromate, assuming you use lead or lead/antimony anodes. Good active anodes should be purply brown. As far as anode: cathode ratios are concerned, the ratios between 2:1 and 1:2 are all possible, depending on the situation. To minimise the creation of Cr(3+) you should keep the anode: cathode ratio as high as possible. Removal of tramp cations is not easy - it is claimed that ion exchange will do it, but I have never tried it, so can't say one way or the! other. Good luck.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK

Q. Is there a "best" combination of Tin- lead- Antimony Anodes that work for Chrome baths?

Do the Anode alloy ratios have to be different for sulfur Catalyst Bright Chrome / Hard Chrome baths and different again for Silica Fluoride Catalyst containing Chrome baths?

Khozem Vahaanwala
Saify Ind

Bengaluru, Karnataka, India

The anode material does need to be an alloy because pure lead is too soft. Ages ago I was a plating line designer for M&T Chemicals (now Atotech), and I remember that we were told by the chrome processes department to use tin-lead for conventional chrome and antimony-lead for fluoride catalysts or maybe vice versa but I can't remember for sure which was which :-(

A tech data sheet from Atotech will tell you what anodes they suggest for their fluoride catalyzed and other proprietary processes though.

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

Thanks for everybody's help! There are 3 things that may cause the problem:
a): HCl(what is used for stripping chrome) maybe mixed in by accident.
b):operator add some old chrome solution(5-10 years? impurities in? oil in? soil mixed? I don't know. but it looks like black ink.) into our tank.
c):Rectifier got a shortage because operates mistake.than we fixed it by replaced 6 diodes.

I follow the suggestions and instructions from you :

1. First thing I get a technician inspection the rectifier equipment. he said it is ok.(?)

2. analysis test report from Atotech shows the chromium solution still ok. (see up Jan 8 post) or not? I don't know what Cr(3+) level is now.

3. We checked all electrical connections and all connections are clean and tight.

4. Replace all anodes(12pcs OD 2" X 150"L, 6% Tin-Lead rod)

5. We try remove Cr3+ by electrolyzing the solution: anode-to-cathode ratio: 14~15:1 and electrolyze at 6 volts. 20 hours, again at 130F. The colour of solution start changes from dark to red-dark, we keep working another 24 Hrs, it is close to red-wine colour (still a little dark)

6. We start chrome plating today: OD3.5"x100"L 9V 2000A 2Hours we got 0.0005" thickness chrome only, ice surface but too thin. On same screw we used to just set 6V than we can get 2000A, in 2 hrs get 0.002" thickness. So it is not good yet.

7.I'll order a porous pot now. but I don't know is it the last thing I can do before replace the rectifier(somebody recommend me, but I don't think it is resolvable.)

Thanks!

BOB CAO [returning]
- Toronto, ON, Canada

A. Bob, try moving your anodes a little closer to the part. Do not get gready. Try a 10% change. You will get a higher current for the voltage, less heat generated and more plate per hour. Unfortunately, a lot of the additional plate will go to the high current density areas.

James Watts
- Navarre, Florida
2005

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