Guest Editorial -For Plateworld.com
Don Baudrand, Don Baudrand Consulting, e-mail:firstname.lastname@example.org
Filtering Electroless Nickel Solutions
Electroless nickel plating solutions require filtration. Filtration rate should be at least equal to 10 solution volumes per hour through 5 micron or 1 micron filters. For thick deposits and/or for extreme smoothness is required, I micron or less is suggested. Mild agitation is best for most Electroless nickel plating solutions. However there are proprietary EN solutions that require air agitation that act as a stabilizer.
Vertical pumps are commonly used for filtering EN solutions. They do not have seals or support bearings that require maintenance and repairs. They may be mounted inside the tank or outside the tank resulting in more plating area. Since they are not self priming, the impeller must be located at least 3 inched below the solution level. The vent hole must be above the highest working level of the EN solution. The hole must not be plugged. It is necessary to prevent fumes or solution reaching and damaging the pump motor. A valve in the intake line below the pump in the event that maintenance is necessary while the tank is full.
One of the most used with good success is wound polypropylene and other synthetic fabrics and using polypropylene cores that are supported with CPVC or Kynar chambers located outside the tank. The cartridges have longer life at a constant micron rating. They are available with complete retention as low as 0.1 micron.
Filter bag filters of woven polypropylene are the most commonly used for electroless nickel. The advantages are: They can be striped with nitric acid and reused several times. They are easy to inspect; easily changed; easy to dispose. Only propylene bags supported with stainless steel should be used for electroless nickel. They can be mounted over the tank or in the plating bath.
Filter bags made of polypropylene are the most used for filtering electroless nickel baths. They can be stripped using nitric acid, and reused several times. They can be mounted either in or out of the plating tank. They cause little back pressure on the pump. They are easy to clean.
Tanks for electroless nickel has been many over the years. Early on stainless steel type 304 was the material of choice. The disadvantage of using stainless steel is that they tend to plate, if touched by racks or items being plated, scratches or other imperfections start plating. The En solutions are too expensive to waste it on non production plating. The advantage is that it is easy to dissolve the plating areas using nitric acid. Using a small rectifier with the tank negative low current can be used to prevent plating on the tank. But rectifiers require frequent adjustment. It sometimes caused etching of the tank.
CPVC plastic is most common for piping and valves. It is used because it is strong and resistant to high temperature. It is also is easy to join by gluing and threading It is resistant to EN solutions and to plating out on the surface.
Pumps are required to have the capacity to turn over the EN tank volume 10 times per hour through one or more filters. A flow rate at least 8 feet per second through all the equipment, such as filters and piping is required. This rate is theoretical rate at which EN solutions cannot deposit.
Heating EN solutions is problematic, since it requires relatively high temperatures in the range of 185-195F (82.2 to87.8C) Electric immersion Heaters are the most used. Pressurized hot water or steam are likely the best but are more expensive. Agitation around and beneath the heater is required to prevent localized high temperature that could lead to "plate-out" on the heater, or spontaneous decomposition of the plating solution. Using agitation around the heaters would allow non-de-rated heaters resulting in faster heat up and closer control.
Thanks Ron Duncan
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