A versatile material known as sheet moulding compound, or SMC, is a pre-mixed, glass fibre-reinforced polyester product that is mainly used in compression moulding processes. This material is supplied in large rolls, weighing up to 1000 kg, or can be custom-mixed on-site to allow manufacturers to have combines a manufacturing process with a reinforced composite, created by combining long strands of chopped fibres, typically glass or carbon, with a thermoset resin, such as polyester, vinyl ester, or epoxy. The use of longer fibres in SMC gives it superior strength properties compared to standard bulk moulding compounds. As a result, SMC is commonly used in a range of demanding applications, including electrical components, corrosion-resistant parts, structural components that require low cost and high performance, as well as in the automotive and transit industries.
A composite material known as sheet moulding compound (SMC) is a pre-fabricated, glass-fibre reinforced polyester product that is specifically designed for use in compression moulding processes. It is typically supplied in large rolls, weighing up to 1000 kg, although some manufacturers may opt to mix the resin and other components on-site to achieve greater control over the chemical composition and filler content. SMC is a unique material that combines a manufacturing process with a reinforced composite product, created by dispersing long strands of chopped fibres, such as glass or carbon, in a bath of thermoset resin. The resulting material boasts superior strength properties compared to bulk moulding compound (BMC) products, making it an ideal choice for a range of applications, including electrical components, corrosion-resistant products, structural components, automotive parts, and public transportation systems.
Manufacturing begins with the application of a precise amount of resin paste onto a plastic carrier film from a reservoir. A chopper then cuts fibers onto fully coated as the fibers settle. A second sheet is applied on top, encasing the fibers in resin, and the layers are compressed before being wound onto a storage roll for maturation. The carrier film is later removed, and the material is cut into custom shapes using a steel die. The shaped material, known as a charge, is then subjected to heat and pressure in a mould, resulting in a fully cured product. The addition of fillers, such as glass microspheres or fibers, can enhance strength while reducing weight. However, production can be challenging, particularly when working with fillers that require specific wetting, die temperature, and pressure adjustments to achieve the desired shape and properties.
SMC stands out from comparable methods due to its exceptional capacity for mass production, outstanding consistency in part quality, and cost efficiency resulting from minimal labor needs and significantly reduced waste. Additionally, SMC offers the advantage of weight reduction, achieved through reduced material requirements and the ability to integrate multiple components into a single part. Furthermore, its flexibility surpasses that of many alternative processes.
The characteristics of these materials differ based on the type of filler and resin used, with those containing oriented fibers (particularly long directional dependence. Typical property ranges are as follows.
The material density range of 1.1 to 2.0 grams per cubic centimeter, equivalent to 69 to 125 pounds per cubic foot. Its impact resistance varies from 4 to 11 joules per square centimeter, or 7 to 21 foot-pounds per square inch. The material’s flexural strength falls between 120 and 230 megapascals, or 17 to 33 kilopounds per square inch, with a flexural modulus of 10 to 15 gigapascals, or 1,500 to 2,200 kilopounds per square inch. Tensile strength ranges from 55 to 125 megapascals, or 8 to 18 kilopounds per square inch, with a tensile modulus of 7 to 14 gigapascals, or 1,000 to 2,000 kilopounds per square inch. Compressive strength is between 130 and 220 megapascals, or 19 to 32 kilopounds per square inch. The material’s heat deflection temperature under different loads ranges from 200 to 260 degrees Celsius, or 392 to 500 degrees Fahrenheit, at 1.82 megapascals, and from 115 to 180 degrees Celsius, or 239 to 356 degrees Fahrenheit, at 0.455 megapascals. The curing temperature is between 80 and 150 degrees Celsius, or 176 and 302 degrees Fahrenheit.
