Join Date: Sep 2000
Location: Washington, Michigan USA
E-Coat is short for "Electrophoretic Deposition" of primer, which is the process used by all assembly plants worldwide to prime complete raw bodies after they're hot-cleaned and coated with iron phosphate (to provide "tooth" for the primer).
The complete body, hung from a moving overhead conveyor, is submerged in a 60,000-gallon tank of water-based primer, with the body positively charged and the tank and primer negatively charged (high voltage, low amperage) for about five minutes, then drained, rinsed, and baked. The attraction of the opposing electrical charges ensures that the primer film build thickness is even everywhere on the body, even in enclosed box sections.
Surfacers, sealers, and color and clear are done later in sealed, temperature- and humidity-controlled downdraft booths by robotic spray machines using high-voltage electro-static "bells", not spray guns, which spin the paint off a 4"-diameter disc spinning at 10,000 rpm, where the body is charged one way and the disc is charged the other way to attract the paint directly to the body surface and minimize overspray losses.
All paint (except the clearcoat) is water-based, so all the miles and miles of paint plumbing, pumps, valves, and tanks is solid stainless steel. All of this operates at about 80 bodies per hour - an assembly plant paint shop is the most expensive real estate on the planet (about $750 million for a typical assembly plant paint shop).
This E-Coat process (just the primer portion) is now done on a small scale (tank just big enough to hold one car body) by an increasing number of small aftermarket shops, usually in combination with a chemical stripping process first, like the shop in Detroit.
'69 Z28 Fathom Green