Letter 7049

Rotating Hard Chrome Plating 

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Our company is about to start a Hard Chrome Plating (HCP) project, which needs to design & construct (or purchase) a "Rotating" HCP machine. The product part is a Piston Crown, whose shape is cylindrical, has a diameter up to 1 meter and weigh up to 1500 kg. Such piston crown has 4 Ring Grooves, whose width is in the range of 8 mm ~ 28 mm, and 0.4 mm thickness of chromium is expected to be deposited only onto the surface of the Ring Grooves, not the whole piston crown.

Our company is currently using the traditionally dipping method, but the quality cannot be easily controlled. We have heard that a "Rotating" chrome plating approach (i.e. holding the piston crown in a bath and allow it to spin) is a good way to obtain a more even chromium distribution. We would like to have your opinion on whether such "Rotating" approach is popular one, and any information that could help us to explain our objective needs would be deeply appreciated. Thank you.

Andrew Ning
- Hong Kong

Dear Andrew,

Have you considered the Selective Electroplating method for this application, which you may find has several advantages?

Regards,

Bryan McCrystal
Brooktronics - Perth,WA,Australia

Have you ever tried to use the auxillary anode so as to have a better metal distribution over the LCD region. Also, Sergent bath is not as good as the catalytic type in metal evenness.

Jason Wu
- Hong Kong SAR

Its an excellent process but the plant will cost you !!

Be sure to use mesh titanium anode which are curved to the cylindrical shape of your roller below the roller and if possible on the sides covering at - least 50 % of the area.

Khozema Vahanwala Saify Ind   Bangalore, Karnataka, India

I do not know if it is a popular one, but sure it works, and you do not need titanium anodes, just use lead.

You will have to make a lot of different anodes for all possible diameters and types of piston crowns (usually from 350 to 900 - Mitsubishi, Pielstick, Sulzer etc.) and adjust them precisely every time.

Keep in mind that it is difficult (or shall I say impossible?) to get a uniform coating, especially for such a thickness as 0.4mm, and the coating would be thicker from the bottom of the groove to the edge. Also, it takes a great deal of time in the bath and of course the grooves require subsequent grinding.

Hope you make it and get the best out of it.

Christos Sigalas
- Athens, Greece

Thanks to Bryan, Jason, Khozema and Christos for your help.

Bryan, we think that brush plating is not very appropriate towards our application because (1) the area to be brush is quite large (2) the plating outcome (such as the evenness of chromium distribution) very much depends on the operatorís skill (3) the width of the ring groove is very small (between 8mm to 28mm), so it does not help (4) the plating time will be long since more than 0.4mm chromium is to be deposited, so it will be tough for a person to operate continuously throughout.

Jason & Khozema, we are already using ëhalf-circleí shape anode. Also, we are currently investigating the possibility of using plating additive. Any suggestion?

Christos, we do have to keep stock of different size of anodes for all possible diameters and types of piston crowns. That is still fine since we do have space available to store them. The main problem for us is the long plating time, which can be more than 60 hrs.

Thanks again for your help.

Andrew Ning
- Hong Kong

I worked for a U.K.company which plated ships pistons for sultzer and doxford. We partially submerged the pistons and fitted auxillary anodes. The piston was rotated whilst plating. There is obviously a lot more to the plating of pistons which cannot be easily written down.

Norman Evans
- U.S.A.

Thanks for your response, Norman.

I agree that there are many parameters that can affect the plating outcome. In order to find out the range of operating conditions, did you use a small scale experimental setup or through trial-and-error method? (For example, what is your opinion on the rotary plating speed for a Sulzer RND90M piston?)

In terms of plating time & evenness of chromium distribution, what is the difference between rotary & non-rotary process? And apart from the piston rotary action, any extra agitation is needed?

Your experience would be deeply appreciated & valued.

Andrew Ning
- Hong Kong

Dear Andrew,

It's been a long time but if you read this it would be interesting to exchange opinions. I want to ask you what you have done till now and if it worked.

Since in the company I work we face the same problems (very long deposition time, uneven distribution of the chrome layer etc.) I am curious to know if you have found a proper solution for solving these.

Thank you

Christos Sigalas
- Athens, Greece

Dear Christos Sigalas,

Our company only started the rotary plating investigation in January 2001. A rotary machine has been constructed. Numerous trials have been performed and the results showed that chromium has been deposited in a more even manner. However, the hardness of the such deposited chromium only is between 700HV ~ 800HV Vickers, where our requirement is between 760HV ~ 960HV. It may be down to the error of the measuring equipment, but we don't know. Any suggestion to increase the hardness?

Andrew Ning
- Hong Kong

We are doing marine diesel piston repair and we do the grooves by welding. My question is whether piston groove plating technology and equipment available.

Ismail Ozalp
- Istanbul, Turkey

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