PROCESS OF AND EQUIPMENT FOR FENDER AND BODY ENAMELING1 240019
Recent improvements in the mechanical equipment and the processes employed in the various car-assembling plants of a large motor-car-building company are described. As a result of the changes these departments have been transformed from the most unsightly parts of the factory into the cleanest, most comfortable and least dangerous. The processes to which special attention is devoted are those for the enameling of fenders and sheet-metal parts and such small parts as various stampings, forgings and malleables and cover the application of two coats of an asphaltic-base enamel and a subsequent baking at about 450 deg. fahr.; in body enameling they cover the application of three coats of similar material and baking at from 290 to 350 deg. fahr.
The course of the various parts is followed from the time of their receipt to that of their delivery to the assembling department to which they belong. When first received from the stamping department or from outside sources they are carefully inspected. They are protected from rust at the source with an outside coating that may be easily removed later by a washing process that precedes enameling. Successive improvements in the fender-enameling ovens consisted of replacing the original box-type ovens, which were open at one end and in which the dipping was done by hand, with those of the semi-continuous type, open at both ends and arranged in line in such a manner that certain parts could be dipped and hung on the conveyor bars while other parts previously dipped and run into the ovens were baking; these ovens in turn were superseded by those of the continuous type in which the parts are hung on the conveyors at one end, are automatically dipped, allowed to drip and baked and not handled again until they finally emerge at the discharge end completely finished with a double coating of enamel. The body-enameling ovens likewise were changed from the original square-box type with doors in the front to the tunnel-type equipped with power conveyors. The last three batteries built by the company were further improved by being suspended overhead with the ends inclined to the floor, thereby forming a seal at each end and completely trapping the oven.
The ideal oven-wall should have low thermal-conductivity, low thermal-capacity and the minimum amount of through metal, should contain the minimum amount of metallic materials, form a rugged construction, be designed, if possible, to allow the ready removal of the ovens without waste of material, provide a smooth inner surface to facilitate cleaning, be completely dust-tight and non-dusting and have a reasonably low first cost of construction. The ideal conveyor should carry the body through all three coats without the necessity for removing it from the conveyor after each bake and mounting it again to flow-on the succeeding coat; but with large production this would require an unreasonably long building.
A system of handling enamel is described that ensures absolute cleanliness and safety, prevents waste and provides centralized and economical operation.
Indirect gas heaters were superseded by electric heaters so that electric heating became standard throughout, with the exception of one bank of body ovens in which electric heaters were used in the central zone to supplement high-pressure steam-coils. Electric heating was satisfactory so far as ease of operation and accuracy of control was concerned, but was found to be costly and the cause of numerous fires in the ovens. As a result, the electric heaters have been discarded in favor of indirect oil-fired hot-air heaters, each oven having its own individual heater of the multiple-unit type. Compared with electric heaters, the first cost of the equipment is favorable, the cost of maintenance is negligible, the labor operation cost about the same and the fuel cost per unit much less.
In addition to arrangements for automatically emptying the tanks in case of fire, the dip-tanks and drain-boards are protected with automatic Foamite extinguisher heads and the fender ovens are equipped with open-end high-pressure steam lines for smothering the fire with steam. Body-oven flow-rooms are protected by water-sprinkler heads.
Special attention is devoted to cleanliness, not only of the materials but of the equipment, tanks, conveyors, floors and the like. A ventilation system injects washed air into the rooms, which creates a static pressure and a flow of air currents outward through the doors and the windows. This prevents dust-laden air from entering.
Distribution of the finished enameled parts to the various assembling departments is done by overhead conveyors that reduce the labor cost of handling, minimize the rejections on account of injury, occupy less floor space and at the same time provide means of carrying a small stock of finished parts ahead of the assembling operations.