A well developed field exists in the art of coating machines for continuous coating of strip materials
. A common application of this is in the area of applying paint or primer to a strip of sheet metal which is initially in the form of large coils. In a typical industrial setting, the material is uncoiled and delivered to a machine which applies the coating to both faces of the strip. After exiting the coating machine the strip progresses through a drying oven. As the wet strip cannot be handled while it progresses through the oven, the strip has the form of a catenary suspended by the coating machine at the entrance to the oven and by a coiler, take-up bridle, or other receiving device at the exit. In certain ovens a part of the weight of the strip may be supported by gas flotation.
A typical coating machine applies a coating to the top face of the strip prior to applying a coating to the bottom face. A strip enters the machine and is held between a backup roll and a top applicator roll which applies the coating machines to the top face of the strip. A transfer roll adjacent to the top applicator roll is partially immersed in a coating material reservoir. The thickness of the coating applied to the top face of the strip can be varied by varying the pressure between the applicator and backup rolls. Similarly the amount of coating delivered to the applicator roll can be controlled by varying the pressure between the transfer and applicator rolls. Relative speeds of the rolls and strip can also be used for control.
One problem that is encountered in obtaining uniform film thickness of coating machines is oscillation of the strip in the drying oven. Such uncontrolled oscillations may occur in a strip supported entirely between the bottom applicator roll and a take-up bridle at the end of the oven, or may occur in a strip partly supported by flotation. When an oscillation occurs, there may be variations in the contact between the strip and the bottom applicator roll. These variations may be seen as slight streaks in the coating. It would be highly desirable to avoid such streaks.