Jack Berg, president of Serfilco Ltd. (Northbrook, IL), has been preaching the gospel of proper filtration and organic contamination removal for platers for nearly 50 years. We recently
caught up with Berg and discovered that he hasn't lost his enthusiasm for discussing the topic.
What does carbon do for the metal finishing process?
J.B.: Carbon adsorbs oily contaminants such as release agents for plastic parts, machining fluids and sheet metal forming lubricants, which can adversely affect plating deposit adhesion if not properly removed. Carbon also removes other types of spent organic impurities that can reduce deposit ductility because of the internal stresses they create.
What forms of carbon are the most commonly used in metal finishing?
J.B.: Powdered carbon is quick-acting for fast adsorption, and is typically used in batch treatment or as pre-coated along with filter aid. Granular carbon is said to be slower to react than powdered but equal in adsorption capacity, more suitable for extended service life and with less tendency to release impurities once they have been adsorbed.
Why does granular carbon work if all the surface is compressed into the granules?
J.B.: First let's dispel a myth: granular carbon of different sizes is equal in adsorbency to powdered. Granular carbon is easier to work with compared to the powdered type, which is now considered to be carcinogenic. Granular carbon works because the flow of liquid runs throughout the carbon and impurities are attracted to its porous surface.
But will adsorbency be lower if solids block the outer surface of the granular carbon?
J.B.: Yes. That's why solutions must be pre-filtered to remove particles as small as 5 µm. This can be accomplished with a filter media employing filter aid or with a coarse cartridge filter relying on turnover to retain small solids while achieving a high turnover rate. Systems using a single cartridge for pre-filtration, a layer of carbon and a trap filter media are suitable for tanks up to 100 gal. Systems with multiple cartridges may be used on larger tanks.
How can users be sure that organic impurities are being maintained at very low levels?
J.B.: If users experience dull deposits, they should perform a routine Hull cell check and decrease or increase the volume of liquid diverted to the carbon chamber accordingly. Those using a high-pressure liquid chromatography (HPLC) instrument should see a straight line indicating the lack of organic impurities—and thus uniform deposit ductility day after day. "Working backwards" and filtering/coalescing the cleaner can continuously remove as much as 80% of organic contaminants before they reach the process tank. If heavy oils are present, a coalescing chamber may be required. But here again, pre-filtration is necessary and will extend cleaner life to reduce disposal costs.
Would users who neglect to change the carbon (hey, it happens) need to batch treat?
J.B.: Usually not. They should simply keep changing the carbon until their tank is back in balance. If users plan to drain a plating tank to inspect the lining or perform other maintenance, they can use less granular carbon, depending on the degree of contamination. A filter with optional carbon will increase dirt-holding capacity and extend time between cartridge changes to 2-3 months.