Winning the War on Filth – Part 2

I’ve encountered a lot of frustrations dealing with oxidation scale or scale from welding, heat treating, or laser cutting. The customer doesn’t communicate to the finisher that the new soil source is coming their way; then the temp worker hangs the part on the auto line; next thing you know the temp worker is reworking hundreds of parts due to blisters and poor plating coverage. So what system will work to help remove the standard soils you may be encountering and still survive the attack of a foreign scale? Here are some suggestions that have worked for some of my clients, as well as some additional options that may fit your process – we will be trying to stay within the typical soak, electroclean, acid stations; if one additional tank can be added, it will greatly increase your chance for success.
First, as we learned in the chemical warfare part 1 blog entry, we need to set up a multifunctional cleaner to attack the synthetic, the organic, and the petroleum based soils all in one tank in this case to help make room for the extra step needed to help with the unwelcomed new soil. The two options I recommend here would be a liquid additive cleaner system in which you can control the soap and caustic levels to combat the varieties of oil and grime. Consider selecting an LA (liquid additive) package that can also handle higher temps to assist in removal of some of the tough-to-temove chlorinated paraffin based soils. If you are uncomfortable using a liquid additive system, an all in one package that is closer to neutral in pH, but full of a variety of modern surfactants to attack the wide variety of soils (both foreign and domestic) we encounter nowadays may be the best fit for your system.

With a majority of the “easy” soils removed, we can now attack the more challenging stuff that caused the rework in the first place. A rinse is preferred between the first soak and the next step, this will rinse free from the surface of the part the oil-containing residue created in the first tank and help keep it in the first two tanks (soak cleaner and rinse tank). This rinse can be counter-flowed from the post electrocleaner rinse and also used to maintain the 1st soak tank solution level.

The next proprietary step can be one or two steps – working with your trusted advisor from Asterion you can determine the best choice. A caustic based descaling soak cleaner (these too can come in liquid additive version to help with costs) or a robustly formulated electrocleaner is the best next step to attack the hardened soil. Both of these options can be used as electrocleaners. Using the descaling soak cleaner as an electrocleaner may produce slightly more foam than your system is used to and will need to be tested to determine the best fit; but the advantages it brings as a scale renover and emulsifier of oil are superior to the basic electrocleaner. Also, depending upon the rinse options, the surfactants formulated into the soak/descaler option may help with oil control. It is important to mention here the advantage of rinsing between the 1st soak and this step is that you can use this step to strictly go after the oxidation/scale/laser dust and not be too concerned with oil residues. The days of eliminating rinsing between the soak and electrocleaner to save water are now creating larger issues with the effectiveness of removing soils. The common line designs without rinsing between the soak and electrocleaner are not the best option for attacking the modern day soils. Additional testing can be done on amperage and voltage levels, polarities, and dwell times; sometimes you may even interrupt the current, and let the chemistry work on the scale for a while, then reapply the current in the same step.

Finally, just like the basic electrocleaner may no longer suffice, the common 40% v/v HCl may no longer be the best choice. There are several additives we offer to provide additional fire power. These additives include fluoride salts, wetting agents, surfactants, amongst other ingredients. The additives are generally used at low concentrations, and do not need to be added during the times non-scaled work is processing. When choosing an acid additive, be sure to consider the tank construction, the efficiency of rinsing between the acid pickle and plating tank, and if this tank doubles for a strip tank (common place in Zn plating lines).

To summarize, for an increased chance of preventing the frustrations of reowork due to unforeseen scale try these steps: remove oils with a soak cleaner – rinsing prior to continuing to the electrocleaner, improve electrocleaner step with either an electrolytic alkaline descaler or alkaline descaler/soak cleaner used with an intermittent soak/electrolytic cycle, finally increase the effectiveness of a traditional HCl pickle with an additive. Other suggestions we can help with but not mentioned in this article and will most likely require additional tanks and equipment are electro-acids, chemical polishes, electrolytic acid descaling solutions – specifically formulated for scale removal, and permaganate based chemistries. Contact your Asterion rep for more information.