Q&A: Tin Plate on Zinc/Nickel Deposit

By: Arthur S. Kushner 25. September 2012

 

Q. Our company produces components made from mild steel that are nickel/zinc plated. We have been asked to investigate the possibility of over-plating of a tin strip on these parts. Can this be done, and can it be done selectively? F.P.

 

A. The simple answer is that, yes, it can be done. You can plate tin over a zinc-nickel layer. The more complicated aspect of this is plating a layer selectively over the zinc-nickel deposit. Selective plating is very common in the electronics industry, but without knowing more details about the processes you are currently using, I cannot give you a more definitive answer.

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Plating Q&A: Can you color stainless steel?

By: Arthur S. Kushner 10. September 2012

Q. Can you color stainless steel? If so, how? N.L.

 

A. Yes, you can color stainless steel, but it is not a process that is typically performed in a plating shop. The basic process, which was developed by Inco (International Nickel) in the 1970s, is to immerse the stainless steel in a chromic and sulfuric acid solution at a temperature just below the boiling point of the solution. A thin layer of chrome oxide forms on the stainless steel, and by controlling the thickness of the oxide layer you can obtain colors that vary from bronze to blue, gold, purple and green. After treatment in this solution, the stainless steel is rinsed and given a cathodic treatment to harden the oxide layer. The layer can vary from 0.02 µm to 0.36 µm; the thicker the layer the darker the color. Most commonly, 304 grade stainless steel is used. The coating is reasonably robust but will scratch.

 

I am aware of one company that produces colored stainless steel, and you should be able to find others as well. Search the PFOnline.com database using the term “coloring stainless steel” to find an article about another recently developed process.

 

Some artists use a lacquer-based process for coloring stainless steel which is good for decorative purposes but will not stand up to heavy use.
 

Ask the Expert: Techniques For Copper And Tin Plating

By: Arthur S. Kushner 18. June 2012

 
Q. I am new to plating and want to learn more about the various processes used in our plating department. Please suggest some techniques for copper and tin plating and good plating techniques in general. H.K.
 
A. This is a question that I receive almost daily. It is good that you want to learn about the proper way of performing electroplating. The answer that I have given in the past is this: a good electroplater understands the processes and has hands-on experience. To learn about how the plating process works and what is required for various types of plating, you must take a training program of some type. There are two sources that I am aware of that offer training programs. The Kushner Electroplating School (with which I am no longer affiliated) offers both distance learning and on-site training (platingschool.com, 714-632-1374). Another source of training programs is the National Association of Surface Finishers, (nasf.org, 703-887-7235). You also can obtain a large amount of information about plating by reading articles that are on Products Finishing magazine’s website, PFonline.com. As far as hands-on experience, if you are not currently working in a plating shop you should attempt to obtain a position within one to learn the practical side of electroplating. Because of space limitations, I cannot supply you with a training manual on copper and tin plating.

ASK THE EXPERT: Solving 'Sandpaper Finishes' in Plating

By: Arthur S. Kushner 30. April 2012

 

 

Q. Our company produces oven racks. The base material is a low-carbon steel (SAE 1006/SAE 1008). The racks are nickel-chromium plated, and the process we use for the plating is as follows:

 

  • Hot degreasing
  • Acidic etch
  • Cathodic degreasing
  • Anodic degreasing
  • Acidic pickling
  • Semi-bright nickel plating
  • Bright nickel plate
  • Chromium activation
  • Chromium plating

 

After the process is completed, the plating has the feel and look of sandpaper, and we must have a bright, smooth finish. Can you give me any suggestions for solving this problem? F.A.

A. I agree that a sandpaper-type finish might have applications in certain areas, but not in decorative plating. Based on the information you provided, I can’t give you a definitive answer to your problem, but I certainly can give you some guidelines for troubleshooting.

The first thing I would do is inspect the parts after each step of the process. Are they smooth and not pitted after the degreasing and acid pickling steps? If yes, then these steps are not at fault. Do the same after each of the plating steps and, if you find the parts have roughness, for example, after the semi-bright nickel plating step, then that step should be investigated in more detail. If the roughness appears after your decorative chromium step, then the chromium plating bath must be investigated.

Assuming that by using this approach you can pin down the step that is giving you the roughness, you will now have to determine what the cause is. In most plating baths, roughness is usually caused by suspended materials in the bath. There are a number of possible causes for this. Start by looking at your filtration system. Filter cartridges do not last forever and must be changed on a regular basis. The cartridge you are using may not filter out the smaller particles that show up in plating baths.

If the baths are only used for short periods of time, they should be covered to keep out dust and grit that can fall into the tanks from the environment. Sometimes particulate matter is due to defective anode bags. The anodes should always be bagged and the bags inspected on a regular basis for tears. Another cause of particulate matter in the plating bath can be parts that have dropped into the tank or fallen off the rack during the plating process. If the drops are not removed promptly they may start dissolving, causing a rough deposit.

Other possible causes of rough deposits in your nickel baths are:

  • Current is too high.
  • Boric acid is too low.
  • pH is out of control.
  • Chlorides may be too low.
  • Organic impurities from decomposition of brighteners and wetting agents.

 

If you determine that the roughness appears after the chromium plating steps, there are a couple of possible causes: Your current may be too high or suspended particulate matter may be present. 

Plating: Trivalent Chromium Reduction

By: Arthur S. Kushner 2. December 2011

 

 

Q. I am trying to reduce the trivalent chrome in a hexavalent chrome tank. There was a method described in one of the directories a few years ago that I used, and it worked, but now I can't find the book it was in. I used copper rods hung in the tank, but, if I remember correctly, the length and placement of the rods was critical, as was the amount of amps used. A.R.K.
 

 

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