Winona Corporation, Winona Lake, Indiana, is a custom powder coating job shop that coats products for the orthopedic industry, recreational vehicle shades, trailer fenders, ladders, truck tool boxes and more. The 20 million parts coated annually range in size from small anodes to vehicle bumpers.
The company uses Nordson powder spray equipment and fluidized beds for powder coating. Powders are applied 1.5 to 3.0 mils thick. Coated parts cure in a gas-fired convection oven for 10 min at 400F.
For pretreatment, Winona had multiple three-stage washers and was having a problem meeting customers' increasingly stringent neutral salt spray performance criteria. Winona diligently followed its chemical supplier's technical recommendations to no avail. It appeared that equipment modifications were necessary to increase the performance of the three-stage washers.
Prior to switching, line one had been dumping its rinse waters daily, while adding seven different chemicals to the other stages of the washer. Line speeds were drastically reduced to increase dwell time for problem parts. Line two was operating at a pH of 3.7 to 4.2 in order to increase cleaning ability and obtain better etch on the aluminum parts.
Goals. Winona had four goals.
- Increase neutral salt spray results to greater than 240 hrs.
- Decrease operator involvement by reducing the number of chemical and manual chemical additions on an exceedingly frequent basis.
- Minimize temperatures of the line to conserve natural gas.
- Operate at a more neutral pH to extend washer and equipment life.
The Process. Winona attended a phosphating seminar by BetzDearborn. Working with a local representative, it conducted an engineered line survey and reviewed case histories.
A comparison was run in the plant with CRS oiled panels. A portable washer was brought in and run against one of the three-stage washers. Neutral salt spray testing showed that the pretreatment program fell short of the required neutral salt spray hours. The portable washer with the new cleaning chemicals passed more than 500 hrs.
Considering this marked improvement, Winona implemented the new cleaning program, which uses Permatreat® 377M cleaner and iron phosphate conversion coating. The cleaner combines a robust surfactant package for cleaning with a high-end phosphating chemistry. The result is a single treatment that gives a tightly adherent coating. Winona is also using Permatreat 604A sealer to enhance corrosion resistance. The chromium-free sealer also requires no special waste handling.
The cleaning system helped Winona consistently obtain 40 plus mg/sq ft of phosphate coating weight on line one and 60 mg/sq ft on line two. The supplier helped Winona regularly test coating weight and salt spray results during start-up. Winona was able to obtain more than 1,000 hrs neutral salt spray results using only a cleaner/coater and a sealer.
An additional controller was added to the sealer stage. Winona's first line was already using a pH controller on the cleaner/coater stage. Line two automated its cleaner/coater stage and sealer stage with pH control equipment. Operator involvement was dramatically reduced. Operator testing was changed from every 30 min to twice per shift, while maintaining a more consistent bath chemistry and producing a better quality product. The improved control allowed Winona to eliminate manual additions of chemicals and reduce the number of chemicals used from seven to two.
Both lines had been running excessive temperatures (135 and 160F) in the cleaner/coater baths in order to sufficiently clean parts. Now the baths are run at 120F for almost all parts. Difficult parts with excessive oil and grease occasionally require the temperature to be increased to 135 to 140F. Reducing stage temperatures saves money in natural gas costs by minimizing the fuel consumed by the washers.
Both lines operate at a pH of 4.8 to 5.2 on all parts. This is 1 pH unit higher than line two was running. By operating at a higher pH for everyday production, Winona lowers the corrosivity of the bath and extends the life of the steel washer and recirculating equipment.
Results. The success at Winona resulted in immediate improvement in bath chemistry. Line one increased stage one bath life by 50 pct and extended sealer stage bath life by 200 pct. Line two increased stage one bath life by 50 pct with less than half the amount of sludge, which was much easier to clean.
The new process also decreased overtime hours, water consumption and chemical consumption by extending bath life. It also greatly improved neutral salt spray results, exceeding customer requirements. Line speed was also increased for problem parts.
The new system helped decrease minimum operating temperatures for everyday production, lowering natural gas consumption. The automated control reduced operator involvement, allowing operators to focus on production issues and provide confidence and reliability in the quality of the pretreatment applied to all parts.
The improvement shown by switching saved the customer money while improving performance, consistency and production capacity.