SMC and GPO-3 are both composite materials widely used for electrical insulation, mechanical applications, and structural components. Though both materials are fiberglass-reinforced and polyester-based, their production processes differ slightly due to their end-use and material structure. Understanding how these sheets are produced helps illustrate why they are so valued in electrical and industrial applications.
 

1. SMC Sheet Production Process

SMC (Sheet Molding Compound) is a ready-to-mold fiberglass-reinforced thermoset material. The production of SMC sheets involves the following key steps:

a. Preparation of the Resin Paste

A resin paste is formulated using unsaturated polyester resin, fillers (such as calcium carbonate), initiators (for curing), and additives (for thickening, pigmentation, and flame resistance). This paste forms the matrix of the composite.

b. Sheet Forming

The resin paste is spread uniformly onto a plastic carrier film. Chopped glass fibers (usually 25–50 mm in length) are randomly distributed over the resin. A second layer of resin paste is applied on top, followed by another plastic carrier film. This creates a "sandwich" structure.

c. Maturation

The sheet passes through rollers to ensure proper impregnation of the glass fibers and to control sheet thickness. It is then rolled and stored in a controlled environment for a few days to allow the resin to thicken (a process called “maturation”) to a moldable consistency.

d. Cutting and Molding

After maturation, the SMC sheet can be cut into specific sizes or used directly for compression molding. However, when sold as sheet material, it is typically rolled and shipped to manufacturers who will mold or machine it into final parts.

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2. GPO-3 Sheet Production Process

GPO-3 is a rigid insulating sheet made by layering fiberglass mat with a polyester resin system. It is specifically engineered for flame, arc, and track resistance.

a. Impregnation of Fiberglass Mat

Continuous fiberglass mat (non-woven) is passed through a bath of thermosetting polyester resin, which may include flame retardants, fillers, and curing agents.

b. Layer Stacking

Several impregnated layers of fiberglass mat are stacked together to achieve the desired thickness. Each layer is carefully aligned to ensure consistent mechanical and electrical properties across the sheet.

c. Hot Pressing

The stacked layers are then placed in a heated hydraulic press, where they are compressed under high pressure and temperature. This process cures (hardens) the polyester resin and bonds the layers into a solid, homogenous sheet.

d. Cooling and Finishing

After curing, the laminate is cooled, trimmed to size, and sanded or surface-finished if necessary. GPO-3 sheets are typically produced in standard sizes and thicknesses but can also be machined into custom parts.

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Conclusion

While both SMC and GPO-3 are fiberglass-reinforced polyester composites, their production methods differ in structure and application. SMC is made in a semi-finished sheet form ideal for molding, while GPO-3 is a rigid laminate sheet formed through high-pressure compression. Each offers unique advantages in electrical insulation, flame resistance, and mechanical strength. Understanding their production processes highlights why these materials are trusted in critical electrical, automotive, and industrial systems worldwide.