Letter 38047

Horizontal hard chrome plating bath or vertical bath  

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Hello,

My name is Neel. I am a part time researcher. We are a team of 4 researchers. We are helping a small entrepreneur in his research. He is a manufacturer of hard chrome plated bars and tubes.

1) We wanted to know the advantages and disadvantages of horizontal hard chrome plating over vertical hard chrome plating. The length of shafts is around 3-3.5 metres and plating thickness desired is 20 microns.

2) In the conventional vertical bath, we are getting plating taper at the bottom end. What is the reason for that?

3) Will there be any time saving in the horizontal bath?

Please help me with these 3 questions.

Regards,

Neel Pandya
researcher - Pune, India

Neel,
As a researcher you will know that it makes a job easier when you are in posssession of all the facts. Unfortunately, you are very vague as to what is being done by way of materials and processes. As far as your points are concerned, regarding the orientation of a tank, horizontal tanks of this size will take up more floor space and will be more prone to solution evaporation. You will also have increased issues with extraction using horizontal tanks. In practical terms, the lower the exposed surface area of a tank, the easier it is to reduce losses, but there may be other effects you may want to minimise, such as foaming; a small surface area but high charge density per unit area could result in an unacceptable foaming level. With regard to the second point, I assume you are using hexavalent chromium and therefore suspect you have a problem with jigging - a 3.5 metre tube is one hell of a length to throw with chromium. You should consider using mutlipe connections onto the tube. As far as time is concerned, like all electroplating, Faraday's Laws dictate how much metal is deposited; the trick to success is to use Faraday's Laws to your advantage and to maximise deposit uniformity and minimise any electrochemical losses and wastage.

Trevor Crichton R&D practical scientist - UK

One potential advantage of horizontal plating is partial submersion so that you can measure the plating thickness and spot some gross defects as the plating is progressing.

Ted Mooney, P.E.  finishing.com Brick, New Jersey

Neel,
I read the Trevor and Ted's answer, they are good, but I would like you know some practical points for this problem.
At first, There are some different between this two procedure base on cr(VI)plating,I can guess how do you it, but i don't know your equipment level. If i assume your solution was refined and with a normal condition,
1-Did you could balance the temperature between bottom and top of the bath during your plating? for this tank ,it's more important to getting a good result in the vertical and with this deep.
Did you have a fixture for prevent of 'near the anodes with the shaft' at the bottom of tank or another mechanism for this?
3-At this vertical procedure,you had anodes about 3.5 meter minimum, did your anodes were clean at the all of these surface (for example at the end of it).
Rgds;

Hamed Shams
- Karaj, Iran

Neel:
Based on the answers you have received and the absence of this problem on the Internet.......I can only conclude the parts can be plated vertically without taper. With a single connection at the top we had the same problem and after checking everything we concluded the taper was due to voltage drop and thus less current density from top to bottom. However....like you we are not certain. Copper core anodes possibly help but resistance in the part is still present with no practical way of multiple connections..
Can't see horizontal improving taper except anode current distribution potentially improved.
I hope we hear more on this.
Cliff Smith

Cliff Smith
- Oklahoma City, Oklahoma