Like many manufacturers, Mack Trucks Inc. (Macungie, PA) faced a problem when production volumes increased. The equipment used to recover paint sludge from its paint booths no longer kept up with production volume. With a little help, Mack has implemented a new sludge-recovery system that has dramatically reduced costs in labor, water consumption and chemical use.

Mack paints its chassis with a high-solids tow-component coating in one of two paint spray booths, each with a 30-foot-long upper section for painting the top of the chassis and a 15-foot-long lower section for painting the underside. The downdraft booths were installed in 1975. The upper and lower sections of each spray booth have separate water pits, and the combined capacity of all four pits is approximately 21,000 gallons.

These spray booths were originally designed for painting approximately 50 chassis per day, but the increased demand for Mack trucks has pushed the company's output to 76 chassis per day. This volume produced more solids than the recovery system could capture.

Mack was using a traditional tank-agitation system. Each recirculation pit had an agitation manifold around its perimeter. A side stream flow went to a centrifuge, which alternated among the four pits. A portion of the water was then delivered to the centrifuge for separation, and the rest of the water was blown through nozzles at the bottom of the pit to keep the solids in suspension.

Tim Litzenberger, Mack's plant maintenance manager, says the company was draining and cleaning the pits every 8 weeks. The system also required pump back-flushing once a day due to sludge accumulation.

At first, Litzenberger considered adding more pumps and centrifuges to the existing system. However, the installation of additional centrifuges was cost-prohibitive, and the goal of continuously clean water probably would not have been achieved.

Litzenberger then investigated float-and-skim systems. For large systems with high volumes of paint, this is probably the most common type of system used. In this system, detackifying chemicals are added to the water to coagulate the paint and cause it to float the surface, making it easier to collect. A pump draws off the floating solids and water mixture and transfers it to another tank where the solids float to the top again. A skimmer then rakes the solids out of this tank and into containers for disposal.

Although float-and-skim systems are popular, they have a few drawbacks. Because only the top portion of the pit water is being drawn off, some settling inevitably occurs and causes downtime while the pits are drained and manually cleaned. This type of system also creates a very high volume of waste and requires a very high concentration of detackifying chemicals that cannot be recovered. Mack's pits are located directly below the spray area, making it nearly impossible to implement a successful floatation system.

In the end, Litzenberger opted for a new technology, the Mss Flow system from Water Wash Technologies (Chicago). The footprint of the new system is the same as the system that it replaced. The patent-pending Mass Flow design provides a uniform cross-sectional movement of paint-laden water through the tank to avoid dropout to the bottom, and confines the paint particles to be extracted within the consolidator. The consolidator absorbs the tank water at the rate of the circulation pump.

Mack's 30-foot booth has two circulating pumps rated at 1,100 gallons per minute each, and the tank capacity is 7,000 gallons of water. The consolidators uniformly turn over the entire capacity of the tank in approximately 3.5 minutes. A total of 640 gallons of water is extracted at the end of both consolidators with a separate pump, driving 40 gallons through the centrifuge and returning 600 gallons back to the agitation headers in the tank. This process prevents the highly contaminated water from migrating and settling out in other areas. This short-circuiting of the contaminated water to each of the consolidators builds up a higher concentration of paint particles to be extracted at the end of each consolidator, thereby increasing the efficiency of recovery.

The consolidator delivers the water to a centrifuge, supplied by US Centrifuge (Indianapolis). The centrifuge alternates between the two sections of the booth. The cost-effective use of only one centrifuge per booth is possible because the system delivers highly concentrated water to the feed stream of the centrifuge. The centrifuge separates out nearly 1.5 pounds of solids per minute (700 pounds per 8-hour shift per booth) when running at peak efficiency.

This high degree of separation is obtained as a result of US Centrifuge's "Smart Machine" technology, which senses the load in the unit and automatically activates the machine's clean cycle. The unit's control system allows in to stop in only 30 seconds, perform a clean cycle in 2 minutes and get back on line quickly. This makes it possible to perform multiple clean cycles every hour. Other features include the "Centri-Lock" plow clutch for increased separating efficiency.

Mack implemented the new system in less than 3 months. It only took a few hours to get the system up and running. Although the piping and installation were done by Mack personnel, Litzenberger credits the teamwork of Water Wash Technologies, US Centrifuge and Texo Chemical (Cincinnati), the chemical supplier, for the successful startup. US Centrifuge added some additional control functions that Mack required. Texo provided startup assistance and operator training. In addition, a Texo representative monitors the chemical consumption weekly, making adjustments as needed to maintain peak efficiency.

After more than 7 months on-line, the Mass Flow system has eliminated all traces of sediment in the water pits. This has exceeded Litzenberger's ambitious goals of reducing the pit cleaning task to once every 6 months. With the new system, Litzenberger expects to clean annually, if needed.

In addition to labor savings because of reduced cleanup, Mack has also saved money on chemicals. "The centrifuge is so efficient, we don't need a lot of extra chemicals to coagulate the paint," Litzenberger says.

The new system has virtually eliminated clogging, according to Litzengerger. "Many times, the old system was down because of clogs," he explains. "The Mass Flow process had additional filters and screens, so clogging is not a problem."

An initial cost analysis at Mack has shown potential savings of nearly $100,000 per year. Water Wash Technologies and US Centrifuge estimate that a typical system could generate cost savings in excess of $1 million over the life of the system.