Spray Molding Technology

Spray Molding Technology

Spray molding technology is an improvement over hand lay-up molding, and is semi-mechanized. It accounts for a significant proportion in composite material molding processes, with 9.1% in the United States, 11.3% in Western Europe, and 21% in Japan. Currently, the spray molding machines used in China and India are mainly imported from the United States.

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1. Principle and Advantages/Disadvantages of Spray Molding Process

The process involves spraying two types of polyester, mixed with initiator and promoter, from both sides of a spray gun, along with chopped glass fiber rovings from the center, mixing evenly with the resin and depositing onto a mold. After reaching a certain thickness, it’s compacted with a roller, then cured.

Advantages:

- Reduces material costs by replacing woven fabric with glass fiber roving.
- 2-4 times more efficient than hand lay-up.
- Products have good integrity, no seams, high interlaminar shear strength, and are corrosion and leak-resistant.
- Less waste of flash, cut cloth, and leftover resin.
- No restrictions on product size and shape.

Disadvantages:

- High resin content leads to lower product strength.
- Only one side of the product can be smooth.
- Potential environmental pollution and health risks for workers.
Suitable for large-scale manufacturing such as boats, and widely used for various products.

2. Production Preparation

Workspace requirements include special attention to ventilation. Main materials are resin (mainly unsaturated polyester resin) and untwisted glass fiber roving. Mold preparation involves cleaning, assembly, and applying release agents. Equipment types include pressure tank and pump supply.

3. Control of Spray Molding Process

Key parameters include controlling resin content at around 60%, spray pressure for uniform mixing, and the spray gun angle for effective coverage. Attention points include maintaining the correct environmental temperature, ensuring a moisture-free system, proper layering and compaction of sprayed material, and immediate post-use cleaning of the machine.