Finishing Systems for Truck Bodies and Trailers

Why Long Parts Favor Drive-Through Booths

Most trailer and body plants use drive-through booths with doors at both ends. The unit rolls in on its own wheels, on a dolly or on a floor conveyor, gets painted, and leaves through the far door toward cure or final assembly. Compared with a single-door booth, this avoids backing a trailer out across freshly coated surfaces and lets the next unit stage at the entry door. Airflow choices follow the building. Crossdraft booths move air lengthwise from the entry filters to an exhaust wall, which suits long parts but means the painter must work with the air at the far end. Side downdraft booths exhaust along the side walls near the floor, which keeps the painter in cleaner air along the full length. Full downdraft booths give the most uniform air but need a pit, which is a bigger commitment in an existing plant.

• Confirm the longest unit, including hitches, ramps and tailgates, before setting booth length.
• Allow walking room around the unit for painters and lifts.
• Plan door style around traffic: bi-fold, roll-up or swinging doors each affect sealing and floor space.

Building a Blast and Prime Sequence for Frames and Bodies

Steel frames and bodies typically need blasting to remove mill scale and weld residue before primer, while aluminum bodies may go through a different cleaning or etching process. For steel, an enclosed blast room long enough for a frame or body keeps media contained and lets a recovery floor return media to the blast pots. Many builders prime immediately after blasting so the clean steel does not flash rust, which argues for placing the primer booth right next to the blast room exit. Chassis and subframes are sometimes coated before the body is mounted, which allows smaller booths or even a powder coating line for the frame components while the body itself goes through a large liquid paint booth.

• Keep the path from blast exit to primer booth short and indoors.
• Place blast room dust collection where its exhaust cannot drift into booth intakes.
• Consider separate booths for primer and topcoat if volume justifies it.

Keeping Throughput Steady Through Paint and Cure

Paint lines for body builders usually bottleneck at cure. A unit that has to air dry in the booth blocks the next one, so many plants add a bake cycle in the booth or a separate cure oven or flash zone downstream. A combination spray and bake booth heats the air after painting so coatings set faster, and the heater and burner are part of the make-up air system. A separate cure room frees the booth immediately but adds a second enclosure, more heat, and one more transfer. Either choice depends on how many units per shift the plant needs and how much floor space is available. Masking, sanding and touch-up should happen at prep stations outside the booth so painting time is spent painting. Lighting along the full length of the booth and at low angles helps painters see coverage on side rails, undercarriages and fenders.

Utilities, Exhaust and Make-Up Air for Long Booths

Long booths move a lot of air. Every volume exhausted through the stack has to be replaced by filtered, tempered make-up air or the building goes negative, doors fight the operator and dust gets pulled in through cracks. That means the make-up air unit, the burner, the gas supply and the exhaust fans need to be planned together. Exhaust stacks and air intakes are usually on the roof, so roof structure, curbs and weather sealing become part of the job. Electrical work covers fans, lighting, heaters, controls and interlocks that keep spray equipment off unless the exhaust is running. Fire suppression coverage and electrical classification of the spray zone must be reviewed with your local fire code authority and insurer.

• Gas service sized for heated make-up air and any bake cycle.
• Electrical service for fans, controls, lighting and heat.
• Clean, dry compressed air for spray guns and blast equipment.
• Roof access and structure for stacks and rooftop units.

Maintenance Access on a Busy Body Line

A body plant cannot shut down the paint line every week to change filters. Design the booth so intake and exhaust filters can be reached from outside the work area, put the exhaust fan and make-up air unit where they can be serviced without a crane, and leave clearance around the blast room collector for filter changes. Planning these details at installation keeps maintenance quick and predictable.