创建于02.06

WHAT IS PULTRUSION PROCESS?

Pultrusion process is to form and solidify continuous glass fiber bundles, strips or cloth impregnated with resin glue under the action of traction through an extrusion die, and continuously produce FRP profiles of unlimited length. This process is most suitable for producing FRP profiles of various cross-sectional shapes, such as  rods, tubes, solid profiles (I-shaped, H-shaped, grooved, square profiles) and hollow profiles (door and window profiles, blades, etc.).

Pultrusion is a special process in the composite material forming process. Its advantages are:

① The production process is fully automated and the production efficiency is high;

② The fiber content in the pultruded product can be as high as 80%, and the impregnation is carried out under tension, which can give full play to the role of the reinforcing material and the product strength is high;

③ The longitudinal and transverse strength of the product can be adjusted arbitrarily to meet the use requirements of products with different mechanical properties;

④ There is no scrap in the production process, and the product does not need post-processing, so it saves labor, raw materials and energy consumption compared with other processes;

⑤ The product quality is stable, the repeatability is good, and the length can be cut arbitrarily.

The disadvantage of pultrusion is that the product shape is monotonous, only line-shaped profiles can be produced, and the lateral strength is not high.

(1) Raw materials for pultrusion

① Resin matrix In the pultrusion process, the most commonly used is unsaturated polyester resin, which accounts for more than 90% of the resin used in this process. In addition, there are epoxy resin, vinyl resin, thermosetting methacrylate resin, modified phenolic resin, flame retardant resin, etc.

② Reinforcement material The reinforcement material used in pultrusion is mainly glass fiber and its products, such as untwisted roving, continuous fiber mat, etc. In order to meet the special performance requirements of the product, aramid fiber, carbon fiber and metal fiber can be selected. Regardless of the type of fiber, when used in the pultrusion process, its surface must be treated so that it can be well bonded to the resin matrix.

③ Auxiliary materials The auxiliary materials of the pultrusion process mainly include release agents and fillers.

(2) Pultrusion die

The die is an important tool for pultrusion technology, generally consisting of a preforming die and a forming die.

① Preforming die In the pultrusion process, after the reinforcement material is impregnated with resin (or while being impregnated), before entering the molding die, it must pass through a preforming die composed of a group of yarn guide elements. The function of the preforming die is to gradually form a preformed body with a shape and size similar to the molding die control according to the cross-sectional configuration of the profile, and then enter the molding die, so as to ensure that the yarn content of the product section is uniform.

② Molding die The ratio of the cross-sectional area of the molding die to the cross-sectional area of the product should generally be greater than or equal to 10 to ensure that the mold has sufficient strength and rigidity, and the heat distribution is uniform and stable after heating. The length of the pultrusion die is determined according to the traction speed and the curing speed of the resin gel during the molding process to ensure that the product reaches the demoulding curing degree when it is pulled out. Generally, steel chrome plating is used, and the cavity surface is required to be smooth and wear-resistant to reduce the friction resistance of pultrusion molding and increase the service life of the mold.

(3) Pultrusion molding process

The pultrusion molding process consists of yarn feeding, impregnation, preforming, curing and shaping, traction, cutting and other processes. After the untwisted roving is drawn out from the creel, it passes through the yarn dispensing device and enters the impregnation tank to be soaked in the resin glue liquid, then enters the pre-molding mold to discharge the excess resin and bubbles, and then enters the molding mold to gel and solidify. The solidified product is continuously pulled out of the mold by the traction machine, and finally cut to a fixed length by the cutting machine. In the molding process, each process can have different methods: for example, in the yarn feeding process, continuous fiber mats can be added, hoop-wound yarn or three-way fabric can be used to improve the lateral strength of the product; the traction process can be a crawler traction machine or a manipulator; the curing method can be in-mold curing or curing with a heating furnace; the heating method can be high-frequency electric heating or molten metal (low melting point metal), etc.

(4) Other pultrusion molding processes

In addition to vertical and horizontal units, pultrusion molding processes also include curved product pultrusion molding processes, reaction injection pultrusion processes, and filler-containing pultrusion processes.