The characteristic of the contact low-pressure molding process is to manually lay the reinforcement material and impregnate the resin, or use simple tools to assist the placement of the reinforcement material and resin. Another feature of the contact low pressure molding process is that it does not need to apply molding pressure (contact molding) or only a lower molding pressure (0.01-0.7MPa pressure is applied after contact molding, and the maximum pressure does not exceed 2.0MPa).
Contact low-pressure molding process|: First, the material is made into a design shape on the female mold, male mold or counter mold, and then cured by heating or normal temperature, after demolding, the product is obtained by auxiliary processing. This type of molding process includes hand lay-up molding, injection molding, bag compression molding, resin transfer molding, autoclave molding, and thermal expansion molding (low pressure molding). The first two are contact molding.
Among the contact low pressure molding processes, the hand lay-up molding process is the first invented in the production of polymer-based composite materials, and has the widest application range. Other methods are the development and improvement of the hand lay-up molding process. The biggest advantage of the contact molding process is simple equipment, wide adaptability, low investment and quick results. According to statistics in recent years, the contact low pressure molding process still occupies a large proportion of the composite material industrial production in countries around the world, such as the United States accounting for 35%, Western Europe accounting for 25%, Japan accounting for 42%, and China accounting for 75%. This illustrates the importance and irreplaceability of the contact low pressure molding process in the industrial production of composite materials, and it is a process that will never decline. But its biggest disadvantage is low production efficiency, high labor intensity, and poor product repeatability.
1. Raw materials: The raw materials that come into contact with low-pressure molding include reinforcing materials, resins, and auxiliary materials.
(1) Reinforced materials
Contact molding requirements for reinforcement materials: ①Reinforcement materials are easy to be impregnated by resin; ②Sufficient deformability to meet the molding requirements of complex shapes of products; ③Bubble is easy to deduct; ④The physical and chemical performance requirements of the product use conditions can be met; ⑤Reasonable price (as cheap as possible) and abundant sources.
The reinforcing materials used for contact molding include glass fiber and its fabric, carbon fiber and its fabric, aramid fiber and its fabric, etc.
(2) Matrix material
The requirements of the contact low-pressure molding process for the matrix material: ① It is easy to penetrate the fiber reinforced material under the condition of hand lay-up, easy to remove bubbles, and has a strong adhesion to the fiber; ② It can gel and solidify at room temperature, and requires small shrinkage and volatilization Less material; ③Suitable viscosity: generally 0.2～0.5Pa·s, no glue flow phenomenon; ④Non-toxic or low-toxic; ⑤Reasonable price and guaranteed source.
Commonly used resins in production are: unsaturated polyester resin, epoxy resin, phenolic resin, bismaleimide resin, polyimide resin and so on.