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pfonline.com/experts Stressed-Out Nickel Deposits Q. We receive parts requiring a "low stress" nickel deposit. Are there numerical ranges for high and low stress nickel deposits? A. I am not aware of any standard that specifies numeric values for high and low stress deposits, but this is a good opportunity to briefly discuss stress in nickel deposits. The plating bath composition affects residual stress in nickel deposits. The table below shows some stress values for different nickel plating baths: Typically when a low stress deposit is specified, sulfa- mate nickel is required. The conventional Watts nickel bath, which contains sulfate and chloride, gives a deposit with a high residual stress. Adding stress-reducing agents to the plating bath, which can be obtained from your chemical vendor, can lessen this stress. In some cases this is satisfactory, but if an additive-free deposit is required you will have to consider the sulfamate plating bath. Other factors like the temperature of the plating bath and the actual substrate itself, may influence the residual stress of the deposit. Barrel Plating and Nesting Q. We do a lot of plating in barrels and continually battle the problem of nesting of the parts. What are some of the methods recommended for reducing or hopefully elimi- nating this problem? A. This problem has been kicking around since the advent of barrel plating. I wish there was a cure-all for it, but in lieu of that, here are some of the classic solutions that partially solve the problem. Reduce the rotation speed of the barrel and the barrel loads. These two factors tend to interact with each other. I don't have a formula to determine the best rotation speed and barrel loads, so some experimentation on your part is required. Different shaped parts can be mixed together in the barrel. This is an effective approach, but leads to one major drawback: You have to separate the parts when the finishing process is completed. If it's a once in a while situ- ation, you may need to do that by hand, but larger volumes of parts will require some type of screening procedure for separation. A clever variation of this approach is to mix inert materials with your load of parts. For example, copper plated balls are mixed with the parts that you are plating in the barrel. The problem with this procedure is obtaining the inert parts. At one time there were a number of vendors who sold these, but I am not aware of any that sell these parts today. The third approach is to change the shape of the parts by adding a dimple or something that will make it more difficult for the parts to nest. The problem you have here is that the customer doesn't want to invest the time or money to do the redesign. Many of the engineers who are involved in designing of parts have minimal understanding of the requirements of the plating process. Hence, parts that nest. As an alternative to classic barrel plating of small parts, you should investi- gate vibratory plating. It has a number of advan- tages, but requires the purchase of new equip- ment. You can find more information on this type of plating by searching the Internet. Saving Money on Additives Q. The additives that we use in our plating operations are expensive. Where can I find less expensive additives for our plating baths? A. I have been asked this question many times over the years. I personally do not believe in "home-brew" plating addi- tives. Before you spend a lot of time trying to get around purchasing brighteners and other additives from your vendor, consider the following: • Is the plating bath performing the way you want it to? • Is the plating bath easy to control? • Do you get the sales and technical support required to maintain the bath and your production? If the answer to these three questions is yes, I believe the cost of the additives is justified. If the answer to any of these questions is no, then you might consider a new vendor. On the other hand, how many dollars will you really save by using a less expensive additive? Usually the time and effort involved in finding a new vendor is greater than the savings you will receive. As far as using a "home-brew" as a replacement for an additive, who is going to help you when you have problems with the plating bath? Many of the plating bath additives available today are materials that have been developed specifically for a given bath. While many of them are trade secrets some of them are patented. So unless you are planning to get into the commercial devel- opment of additives, I doubt this will be a significant item in the cost of your plating SOLUTION ANION RESIDUAL STRESS (PSI) Sulfamate 8,600 Sulfate 23,100 Chloride 33,000 46 NOVEMBER 2015 — pfonline.com p f o n l i n e . c o m / e x p e r t s ARTHUR S. KUSHNER Consultant platingclinic@pfonline.com PL ATING C L I N I C