The finest paint treatment that provides the longest lasting protection for truck trailers is an E-coat primer followed by a powder coat finish, says Dr Bernard Krone. He is the owner of Bernard Krone GmbH, the third-largest trailer manufacturer in Germany. For the past three years, all the platform trailers assembled in the Krone plant have been shot-blasted, chemically cleaned in huge dip tanks, and then E-coated by cathodic immersion. After this primer is oven baked, the trailer goes through an automatic spray booth for the powder coating and baked again.
This $13-million investment in metal treatment is working so well that an even larger facility was opened last summer to paint Krone swap bodies (domestic containers). The dip tanks in this new facility are large enough to dip two swap bodies measuring 7.82 meters (25' 8") long at a time in each tank. In fact, the huge tanks can handle an entire bus body frame 15 m (49 feet) long.
The plant specializes in swap bodies, steel shipping containers, and the legs on which they stand while awaiting transfer from truck to rail. Trailer chassis for the swap bodies can load and offload the swaps by being backed under the swap body and raising the trailer frame by means of the air suspension so that the swap body legs can be removed. Swap bodies have the same twistlock corner fittings as ISO shipping containers, so they can be crane lifted onto rail cars.
Eliminating Paint Bottleneck "We increased our output 65% in the last year by eliminating our paint room bottleneck," says Bernhard Bruggen, owner of Bruggen Oberflachen- und Systemlieferant GmbH in Herzlake in the far northwestern part of Germany. The Bruggen company is an exclusive supplier of completely assembled and painted swap bodies to the Krone Group.
"We can increase our output another 65% this year because of the added capacity," says Bruggen. He wants to concentrate on the assembly and painting of swap bodies, purchasing the parts and weldments from other contract welding shops in the area. Marketing of the completed swap bodies is through the Krone organization.
This new plant can assemble and paint 60 to 100 swap bodies a day on three shifts, depending on the mix and complexity. However, the big leasing companies didn't buy last year, Bruggen says, and production was limited to 50 units per day. The plant is operating three shifts a day, six days a week.
Each of the 13 dip tanks in this newest facility is 17 m (56') long, 3.2 m (10 1/2') wide, and 4.8 m (15 3/4') high, with a 4.3 m (14') water depth. Each tank holds 62,000 gallons of liquid. While the facility has 13 tanks, three of them are buffer tanks or spares, for use when one of the 10 tanks must be serviced.
The first three tanks are for cleaning the welded steel boxes or frames: a chemical degreasing bath followed by two rinse tanks heated to 60 degrees to 70 degrees C (l40 degrees-160 degrees F). The next dip tank is a zinc phosphatizing solution followed by another rinse tank at 50 degrees to 60 degreesC (120 degrees-140 degrees F). The next tank is a passivating solution followed by yet another rinse.
Paint Tank Immersion The E-coating tank has 85% water and 15% paint, and the paint particles are charged positive by the anode in the electroconductive field. The steel swap body, as the cathode, is charged negative to attract the paint particles. With 3,000 amps of power, four minutes immersion in the E-coat tank is sufficient to coat 400 square meters (4,300 square feet) of metal surface. As the paint builds up on the metal surface, the paint layer acts as an insulator. The thickest paint layers insulate best, thus causing the paint particles to flow to the areas with the thinnest coating, such as in hidden pockets.
After the E-coat tank, the swap bodies are dipped into two successive rinse tanks. The first rinse tank is equipped to recycle any loose paint particles and return them to the E-coat tank.
Besides the huge size of the installation, with 13 dip tanks lined up, the most impressive sight is the automatic handling system that lowers each body into the appropriate tank, allows it to soak for the prescribed number of minutes, lifts it out again, one end higher than the other to get full drainage, and then moves it to the next tank. The entire procedure is controlled automatically. No operator watches the successive lifting and lowering actions or checks on the crane movement as it proceeds from tank to tank. The machine answers only to the supervisor.
Oven Baked After the E-coated body is twice rinsed and drip dried, it moves into the bake oven. There the gray prime coat is baked at 200 degrees C (400 degrees F) for 30 to 60 minutes. Instead of a long tunnel, the bake oven is a two-story block with eight slots for setting the prime coat on the second level and eight slots for baking the powder coat final finish on the ground level. The automatic conveyor moves swap bodies in and out of the slots according to a preset time schedule without any help from a human operator.
The layout of the plant puts the bake oven between the E-coat tanks for the prime coat and the powder coat spray booths for the finish coat so that the oven can serve both coating operations. The automatic crane that lifts and lowers swap bodies to the proper level also connects to a buffer conveyor where the steel bodies can cool down while suspended from conveyor rails.
This cool-down conveyor also acts as a buffer before bodies enter the powder coat operation. This buffer permits better scheduling of colors through the powder coat booths. Up to this point, the bodies can be more or less standard, regardless of customer. However, the color specified by the customer must be determined at this point, and scheduling of large numbers of the same color helps improve plant efficiency. It takes two hours to change colors. A total of 56 swap bodies can be stored on the cool-down and buffering conveyor.
Fifty percent of all the swap bodies are painted white for the final coat, and most of the rest are one of the standard colors: blue, red, or yellow. For custom colors beyond these four standard colors, the containers go through a "wet color" line where they are spray painted manually.
Four Standard Colors Standard colors go through one of the two side-by-side booths for powder coating. Reciprocating spray nozzles automatically apply the powder to the large flat surfaces, but a manual operator is also required in the booth to spray the hidden corners. After the powder coat is sprayed on, the swap bodies go to the bake oven, followed by another cool-down period.
After the finish coat is dry, the swap bodies go to one of the three assembly lines for completion. Some get FRP-plywood sidewall panels and rear doors. Others get dropsides and a framework for a fitted tarpaulin body or a curtainside body. Some have corrugated steel sidewalls and roof panels much like ISO containers. Others get full-opening accordion roofs to permit top-loading by overhead cranes. Most are fitted with wood floors such as the treated 22-ply birch floors supported by a steel framework common in ISO containers. Specialized heavy-duty floors equipped to tie down large rolls of newsprint are another specialty.
The Bruggen company is exclusive supplier to Krone for completed swap bodies. As an independent company, Bruggen also solicits other business, particularly in its specialty of E-coating and powder coating large structures. Possibly the largest structure so far is the body frame for a 15 m (49') bus.
Bruggen claims to be the market leader for swap bodies in Europe. With the capability of painting and assembling swap bodies at a rate up to sixper hour, few would dispute the claim or want to come up with the investment to challenge that capability.