"Time to dump the cleaner." These five words usually helped Martin Straus, owner of Chem-Plate Industries in Elk Grove Village, Illinois, out of trouble, but not for very long. "Dumping the cleaner usually got us out of trouble with the cleaning and rejects," noted Mr. Straus, "but it got us in a lot of trouble from the waste treatment standpoint. You cannot dump cleaners often and expect the waste treatment system to handle it."
The company's waste treatment system, as with most, was designed to handle the normal daily flow through the zinc barrel plating line. Dumping the cleaner dumped a lot of oil into the system. Oil in a waste treatment system can stop the precipitation process.
"We saw two problems related to one area, cleaning. We were tired of dealing with it the `same old way' and decided to see what we could do to correct the situation permanently," stated Mr. Straus.
Chem-Plate decided that its number-one priority was maintaining a cleaner that cleaned the parts it plated for GM, Chrysler and Ford. The company wanted a cleaner that cleaned for a long time and could handle a heavy oil loading. Unfortunately, it only had two cleaner choices.
One type of cleaner is an emulsifier that holds oil in solution so that it is not dragged into subsequent rinses and finishing baths. This type of cleaner has a short life; once you reach five to 10 g/liter of oil, the cleaner can no longer be used, according to Mr. Straus. However, it is a relatively simple cleaner to use.
A second type of cleaner is a "splitting cleaner." This type of cleaner displaces the oil. It works well in a controlled environment; it does not work well in a barrel operation that operates 24 hrs a day, seven days a week, such as at Chem-Plate. Other aspects of the cleaner that Chem-Plate was not happy with included: cleaner was highly caustic; operated at 170 to 190F; and any zinc entering the cleaning solution killed it.
"We wanted to find a way to combine the dirt-holding capacity of the emulsifying cleaners with the best properties of a splitting cleaner," stated Mr. Straus. In cooperation with Straus Chemical Corporation, Chem-Plate developed a microdisplacement cleaner that holds up to 80 g/liter of oil and still cleans the parts.
"We put the cleaner on-line, assuming it would last eight times longer than the present cleaner that held only 10 g/liter of oil. We were wrong," admitted Mr. Straus. As oil built up in the cleaner and the barrels were lifted out, the cleaner and oil in the rinse tank would separate out. The oil would end up in the plating baths and water treatment system.
"So, we had this super cleaner, but it looked like we could not do anything with it. We had to get to work to solve this problem," stated Mr. Straus. It was not an emulsifying cleaner, but as long as there was movement, the cleaner microemulsified the oil. When movement stops, the solution separates into cleaner, transitional zone and oil. This occurs at the actual cleaning temperature, not an elevated temperature.
As a solution, Chem-Plate removed a small slip stream from the cleaning bath and pumped it into a holding tower. This occurred continuously during the day. The holding tower provided a quiet zone where the oil could rise to the top and metals and other contaminants could fall to the bottom. Oil is decanted off the top using a variable speed pump.
"The cleaner operates 24 hours a day at 120F," stated plating manager Paul Sullivan. "Each day the supervisor titrates the bath and makes the necessary additions by adding the powder directly to a barrel that contains 300 to 500 lb of parts. Operators also calculate how much liquid caustic to add with the cleaner. "With a 1,000 gal tank running 24 hrs a day, we add about one-and-one-half gal of liquid caustic," noted Mr. Sullivan. "Cleaner makeup is 19 lbs for 100 gal water. We used to used 3,100 lbs of cleaner a month and we now use 800."
Solution samples are removed weekly from the top and bottom of the holding tower. The sludge removed from the bottom of the tank, the bottom of the oil separator and what is skimmed off the top equals approximately 115 gal per month. With the old "dump" method, Chem-Plate generated 700 gal of sludge a month.
The cleaner, 110 FS, is a heavy-duty powder soak cleaner that contains no fillers or caustic soda. It operates at 120F and does not lose its cleaning ability even when loaded with oils and/or metals. Even if there is an oil film on the cleaner tank it does not stick to the parts or the barrel rater. It is dispersed in a subsequent rinse.
The cleaner takes oils and forms a microdispersion. Oils are dispersed in the bath as long as there is some solution movement. The movement of the plating barrels provides all the agitation necessary. When the bath stops moving, oils float to the surface. This requires eight hours.
The cleaner can be removed from the tank periodically and skimmed. A holding tower may be installed that allows oil to float to the top and then be skimmed off. Solids and other materials sink to the bottom of the holding tank and eventually are removed.
The real test of the cleaner is whether or not the zinc plate adheres to the part. Within an hour of plating, most work is baked at 400F for four to eight hours. If cleaning is poor, the plating may crack or delaminate. So far, Chem-Plate has not had a problem.
Chem-Plate has used the same cleaner since October 1995, without dumping it. The soak tank with the oil/water separator is approximately 1,000 gal. Although the company has used the same cleaner since October 1995, it had been using the cleaner for eight years before that without realizing its full potential of no dump. "It was a good cleaner to start with," stated Mr. Straus, "now it's an even better one."