Rivets, because of their small diameter and blind holes, are difficult to clean. Detroit Tubular Rivet, Inc. manufactures a variety of rivets in many sizes and lengths. These rivets carried excessive oil into plating process tanks and the waste treatment system causing headaches and expense for the company. A new, automated vapor degreaser solved the problem and cut costs as well.
Before the system was installed, the automatic barrel plating system included two hot alkaline soaks and one electrocleaning station. Each station was also equipped with oil skimming and removal. Although this was recommended as an adequate cleaning system, it was not.
Oil was carried into subsequent process tanks, causing many problems. Various types of precleaning processes were researched. None of the aqueous or semi-aqueous processes, whether spray, rotation or immersion was effective. The only cleaning process that eliminated oil from process tanks was vapor degreasing.
Before vapor degreasing, so much oil accumulated in the cleaning tanks that each Sunday, when alkaline cleaning tanks were cold, oil was skimmed off and transferred to a holding tank. pH was reduced to two and the waste treated with a coagulant. Three 55-gal drums of oil were skimmed off each Monday. Since installing the new degreaser, the company has not had to do this.
As a result of the study, the company purchased a chlorinated solvent vapor degreaser from Finishing Equipment, Inc. The system uses methylene chloride as the solvent. This automated, enclosed system handles up to 500 lbs of rivets at one time.
Since installation, no oil has been carried into the plating process, resulting in a significant improvement in quality. Oil is recovered and reused in manufacturing process, saving $50,000 annually.
Detroit Tubular has reduced use of alkaline cleaners by one-third and acids by 70 pct. The acid savings are made because acids cannot work on oily surfaces; it retards their function. Removing the oil allows the acids to work more effectively. Also, less rinse water is required.
Another benefit results from the degreaser cooling system. It is cooled with an air-cooled chiller. In the summer, the chiller's heated air is discharged outside and the extra ventilation keeps the shop cool. In the winter, heated air contributes to heating the shop.
Explosions on the plating and electrocleaning tank were eliminated. The hydrogen and oxygen generated at the zinc tank and in a surface foam commonly caused explosions. Oil in the plating tank made the explosions more violent, to the extent of actually burning the ceiling over the plating tank. These explosions have been reduced to zero from the previous 15 to 20 per day.
The waste treatment system now functions properly. Flocculation, settling and filtering of plating sludge proceeds on schedule. Prior to this, oil prevented these systems from functioning properly. Zinc sludge in the sludge dryer is no longer ignitable. The sludge is suitable for sale and recycling.
The system uses only five gal of methylene chloride per day to clean 40,000 lbs of rivets daily. There are other intangible benefits with this machine. Solvent degreasing has minimized energy costs and wastes.
The degreasing system has been permitted by Wayne County and Michigan under their regulations and toxic rules. Methylene chloride is exempted as a VOC by EPA, does not deplete the ozone, and personnel exposure and shop conditions are acceptable.
No other cleaning system could accomplish for Detroit Tubular what the new methylene chloride degreasing system has done.