Heating and Cooling of Chrome Plating Tanks

A. Dear Mr. Najeeb,

As a hardchrome plating company with many years of experience, we feel that we might be able to help you. There are many different solutions for your problem, but in order to be able to help you, we would like to receive more detailed information, such as:

Tank size,

catalyst condition (density, Fe, Cr3+, etc.)

Rectifier capacity

If you give us this information, we will work out a detailed plan for you.

Kind regards,

A. Hi Nageeb,

I guess that you have 3 options: 1. Use a much larger tank; 2. Use a cooling coil (PVDF should be ideal) which is the normal approach, I believe; 3. Use what I call 'evaporative control'.

Back in 1980 I encountered exactly the same problem. The customer in Vancouver, EBCO, was plating very large diameter rolls and the heat became excessive which, possibly (I am not a plater!) might lead to a poor finish.

EBCO still have this system. However, at that time in 1980 they wanted to do something about the air pollution, too.

That's where I came in. I suggested what I call an ordinary 12 micron chromic 'dry scrubber' mist eliminator (fairly sophisticated internal design!) which has two banks of PVC blades. I suggested (but I had never every heard of this being done before) that the eliminator would have the second blade bank separated and with its own washdown bank ... and that they use a pump to spray the first blade bank with the hot chrome. (I have over 300,000 cfm of hard chrome scrubbing fully annotated).

What happens then is that the ambient air (Boyle's law?) draws off the heat from the tank's hot liquid which is returned, definitely cooler!, via gravity back to the tank.

If you wanted to corroborate this, let me know and I could give you the address & contact at EBCO. OK? Last year they did replace one of the blade banks -- not bad for 20 years service)

Cheers!

A. Best practice is certainly to include heating because the bath operates at 110 to 140 °F. (depending on exactly what you are doing) and you do not want to use your rectifier and your chrome plating solution as a heater. Best practice is also to include cooling coils. The air would be used for solution mixing rather than cooling, particularly if the tank is deep.

A. Hi Bojan. You are trying to operate the chrome plating tank at 45 °C, so you must do what is necessary to keep it at 45 °C. That means providing heat if the bath falls below 45 °C, and removing heat (providing cooling) if the bath exceeds 45 °C ...

If the bath runs 24 hours a day, and it processes a reasonable amount of production, it is possible that separate heating provision may not be required because the rectifier will provide more than enough heat (but it's still desirable). If the bath operates frequently or constantly, it will probably be necessary to remove heat with cooling coils, or the tank will overheat. Stopping production to let the tank cool off is rarely a satisfactory answer. Good luck.

Regards,

A. Hi. The temperature must be constant while you are plating: all the time and at every depth.

It is not true that having the heating on while plating will necessarily cause a problem. But it is true that the plating generates so much heat that additional heating may not be required during that time, and cooling may be required to keep the temperature from climbing. If you multiply the plating Amps you are using times the plating Volts you are using, you know the Watts of heat you are adding to the bath.

A range of 42 - 46 °C is too much variation. I think you should not exceed the range of 43-44 °C for the most consistent plating. You probably have insufficient sparging/agitation if the temperature is lower down deeper in the tank. Good luck.

Regards,

A. Hi Jagdish. The thumb rule is that all of the power introduced to the tank will be converted to heat, and all of it must be removed. That means you multiply Amps x Volts to arrive at the Watts of heat you are inputting, and convert this to BTUs/hour (multiply it by 3.41) or Calories/hour (multiply by 859.8) which must be removed.

If the bath operates at 130 °F (54.4 °C), you can estimate the heat lost from the walls and surface of the tank and deduct this from the cooling requirement. Good luck.

Regards,

A. Hi Garrett. It is isn't clear to me whether you are saying that the tank is getting too hot or not staying hot enough. Sorry, I also don't know quite what you mean by agitation depth -- are you referring to mechanical vertical agitation during plating, or something to do with the air agitation coils at the bottom of the tank? 140 °F is more typical of hard chrome plating than decorative plating, so I assume that's what you are doing.

Obviously the rectifiers add a great deal of heat to the tank, especially in hard chrome plating.

Regards,

A. If you can't get to the root cause for the excess sulphate, then consider making the barium adds in an auxiliary tank instead of in the plating tank. Then, filter the chrome solution back to the plating tank. You wouldn't need to move the entire solution to the auxiliary tank, just move enough to take the sulphate near to zero for a calculated portion that, when returned, gets your sulphate back to the proper ratio.