Thermoset plastic industrial laminates are identified in process by three stages: A, B and C.
A-stage refers to the key raw materials described earlier - reinforcing substrates and resin binders.
B-stage refers to the product produced when reinforcing substrates and resin binders are brought together but not fully cured. The reinforcing substrate is unwound from a large master roll and dipped into a bath of liquefied resin binder. The reinforcing substrate becomes either saturated, as is the case with absorbent papers and cotton cloths, or coated, as is the case with glass and graphite cloths. Once the wet resin binder is joined with the reinforcing substrate in this method, it is slowly drawn through a long conveyorized oven where the liquefied resin binder is dried (see sketch below). The result leaves dry semi-cured resin bind in and/or on the reinforcing substrate. Once joined and dried in this fashion, the product is referred to as B-stage or prepreg, and the process described is called B-staging, prepreging or treating.
C-stage refers to sheet, rod, tube, angle or other in their "cured stage".
Sheets - B-stage is sheeted into plies then laid on top of each other into predetermined stacks that will render a given thickness. These stacks are placed into the hydraulic laminating press between two flat surfaces and pressure is applied. While under pressure, heat is introduced to begin the bake cycle. The resin in the B-stage product is re-activated by the heat to a sticky state which moves slowly, filling and bonding the layers together until it eventually hardens and cures. Once plies bond to each other and cure, they are referred to as C-stage laminate sheet and the process described is called laminating or pressing.
Rods - The B-stage is convolutely wrapped under tension onto itself, much like a roll of paper towels is wound. Once the B-stage is rolled to form a rod, it is placed into a laminating press which has upper and lower half round mold cavities. A full round is formed when the two half-round molds close and meet each other. The size of the mold cavity determines the diameter of the finished rod. Once pressure is applied, the layers are pressed together filling all voids. Similar pressures and heat cycles employed for making sheets are used. When the layers bond to each other and cure, they are referred to as C-stage laminate rods or rolled and molded rods.
Ground plastic rods are made from square bars of thermoset composite sheets that are ground into circular outside diameters, and then cut into lengths. Sheet rod is best utilized when the application needs to be completely free of voids, while rolled and molded rods are best when “hoop strength” is required. Sheet rods are also generally less expensive than rolled and molded rods.
Each method has its advantages and drawbacks. We’ll work with you to help choose the option that best suits your project.
Tubes - Rolling tubes is nearly identical to rolling rods with the exception that a steel rod called a mandrel is employed to size and form the inside diameter of the tube. B-stage rolled tubes are usually placed into an oven chamber as opposed to a press. Tube bake cycles compare to those of sheet and rod. Once cured, the center mandrel is extracted. The final cured product is referred to as C-stage laminate tube or rolled tube.
Angles - This process is nearly identical to that of sheets except the mold cavities are "V" shaped rather than flat surfaces. The final cured product is referred to as C-stage laminate angle or molded angle.
Other shapes - Once cured, the end product is referred to as C-stage.