Nonmetallic Coating. Coil-coated finishes are available in several varieties. Common problems with coil-coated materials can be the abrasion of the coated surface, its sensitivity to pressure, and cracking of certain types of paints at the bend lines.
Today, paints usually have excellent surface characteristics for roll forming. Typically, lubrication is not required because paints are relatively soft compared with the metals. Operators must ensure that the gap between the rolls is sufficient and that no undue pressure is applied on the coated surface. The surface finish of the rolls and other tooling should be good and free of chips and cracks. A rough roll surface may pick up paints and/or mar the surface.
Paint cracking may occur if less ductile paint or plastic is used. A larger bending radius can overcome this problem. If the bending radius must remain small, then preheating of the bend lines in front of the forming rolls can make the paint flexible and elastic enough to be formed without making it too soft. Depending on the type of paint or laminate used, the surface temperature may be raised to 130 to 230 degrees.
On the other hand, paint is less flexible at low temperatures. Painted coils that are transported and/or stored below the freezing point may develop paint cracks if they are roll formed shortly after bringing them inside the plant.
Exposed surfaces must be checked carefully for paint cracks. Almost invisible small cracks at the bend lines allow water and corrosive atmosphere to pass through, and corrosion may start during storage and/or after installation. Correcting problems caused by paint cracking is extremely expensive.
In the case of laminated material, the thickness of lamination should be added to the thickness of material when rolls are designed and installed. For example, rolls designed for 0.036-inch-thick material will not be able to process 0.034-inch-thick steel with 0.010-inch-thick laminate.
