SMC Molded Parts

‌Excellent mechanical properties‌
SMC materials contain reinforcing materials such as glass fiber, which gives SMC molded parts high strength and rigidity, and can withstand large loads and impacts. ‌This material has a low thermal expansion coefficient, which ensures good dimensional stability and can maintain stable size and shape under different temperature conditions. ‌

‌Good corrosion resistance‌
The resin matrix of SMC materials usually uses unsaturated polyester resin or epoxy resin, which has good corrosion resistance and can resist chemical corrosion and atmospheric corrosion. ‌Therefore, SMC molded parts can be used for a long time in harsh environments without being damaged. ‌

‌Excellent insulation performance‌
Due to the high insulation performance of the resin matrix and the addition of reinforcing materials such as glass fiber, SMC molded parts are widely used in the electrical field. ‌It can be made into various insulating parts, such as transformer housings, insulation boards, etc.

Design flexibility
SMC compression molding offers designers a high degree of freedom in creating complex shapes and intricate geometries.

High strength-to-weight ratio
SMC parts exhibit excellent mechanical properties,including high strength, stiffness, and impact resistance, while being lightweight.

Corrosion resistance
SMC materials are inherently resistant to corrosion, making them suitable for outdoor and harsh environment applications.

Cost-effectiveness
SMC compression molding is a cost-effective manufacturing process especially for large production volumes, due to its high productivity and low material Waste.

Surface finish
SMC parts can achieve a smooth surface finish directly from the mold.Reducing the need for secondary fnishing operations.‌

1. Unsaturated polyester resin and crosslinking agents are the main body of SMC. Unsaturated polyester resins are usually polycondensed from unsaturated dicarboxylic acids (or anhydrides), saturated dicarboxylic acids (or anhydrides), and polyols. It has certain mechanical properties and strength, and the internal force is uniform. The crosslinking agent is mainly styrene. After the two are cross-linked, they are the main materials for the curing plasticity of the product, which play the role of connection, support, transmission balance, and protection.

2. The initiator causes the resin and crosslinker to cure and form in the resin paste stage. Its function is mainly to make the resin and the double bond in the cross-linking monomer such as styrene copolymerize so that the SMC can be solidified and formed in the mold cavity.

3. The filler occupies more than one-third of the sheet molding compound and can adjust the viscosity of the molding compound. It generally needs to have the characteristics of low specific gravity, low oil adsorption value, fewer pores, corrosion resistance, and low cost. The commonly used filler components are mainly CaCO3, Al(OH)3, and so on.

4. Thickeners give SMC a high-viscosity, non-sticky property. The preparation of sheet and bulk molding compounds requires a low viscosity of the resin to facilitate the impregnation of the glass fiber and filler by the resin. And compression molding requires a higher viscosity. Therefore, it is necessary to add a thickener before the molding process to convert the low viscosity of glass fiber impregnation into a high viscosity that is not sticky.

5. The release agent prevents the sheet molding compound from having an affinity with the metal mold surface. The release agent can prevent the unsaturated polyester resin from interacting with the surface of the metal mold during the plastic process of the resin mixture. Mainly long-chain fatty acids or salts represented by zinc stearate. Excessive use will easily reduce the performance of the product. The general usage accounts for 1~3% of the total product to ensure the quality of the product.

6. Glass fibers can enhance the corrosion resistance and insulation properties of SMC. Sheet molding compound usually chooses chopped glass fiber mats as reinforcement material. Excessive use will easily make the product too fluffy, and the use of too small a dose will not have an obvious strengthening effect on the product. The general usage is about 20%. In this way, the product can simultaneously meet the two processes of extrusion molding and compression molding.

Inhibitor increases the stability of SMC and prolongs the storage period. Since the initiator styrene will decompose slowly, causing the polymerization of the resin, adding an appropriate amount of free radical scavenger (polymerization inhibitor) can slow down the speed of styrene decomposition and prolong its storage period. Inhibitors are usually benzoquinones and polyvalent phenolic compounds.