FRP pultrusion process
First, the introduction of pultrusion process
The pultrusion process is a molding method for producing FRP linear profiles. Under the driving of the traction device, the roving glass fiber roving and other continuous reinforcing materials are impregnated and preformed, and then solidified by a heated molding die. Thereby achieving continuous production of FRP products.
The pultrusion process was studied as early as 1948. In 1951, it was first registered in the United States, patented, and actually entered the field of structural materials or the early 1970s. After that, the pultrusion process became a widely used process technology, and gradually attracted the attention of all sectors of society. Along with the improvement of the raw material and equipment manufacturing level, many key technologies of the pultrusion process have made major breakthroughs and achieved rapid development.
Advantages of the pultrusion process:
(1) The physical and mechanical properties of composite products, especially the longitudinal specific strength and specific stiffness are quite prominent.
(2) The process is easy to achieve automatic control and the product quality is stable.
(3) There is basically no corner scrap in the process, and the effective utilization rate of raw materials is high.
(4) High production efficiency.
(5) The length of the product is limited only by the production space, and has nothing to do with the equipment capacity and process factors.
(6) With the gradual improvement of the variety and specifications of raw materials and the improvement of the technological level, any linear product with complex cross section can be formed.
Second, the pultrusion process
The typical process of pultrusion is:
Glass fiber roving arrangement - dipping - preforming - extrusion molding and curing - traction - cutting - products
The main raw materials of the pultrusion process:
Glass fiber (no roving, surface felt, plaid, etc.)
Curing agent (high-temperature curing agent such as TBPB/BPO and low-temperature curing agent such as methyl ethyl ketone peroxide)
Filler (calcium carbonate, aluminum hydroxide, glass beads, etc.)
Release agent, low shrinkage agent, etc.
1. Reinforced material conveying system: such as creel, felt spreading device, yarn hole, etc.
2. Resin impregnation: The straight tank dipping method is most commonly used. During the whole dipping process, the fibers and felts should be arranged neatly.
3. Pre-forming: The impregnated reinforcing material passes through the preforming device and is carefully conveyed in a continuous manner to ensure their relative position, gradually approaching the final shape of the product, and extruding excess resin before entering the mold. Molded and cured.
4. Mold: The mold is designed under the conditions determined by the system. According to the resin curing exotherm curve and the friction properties of the material and the mold, the mold is divided into three different heating zones, the temperature of which is determined by the performance of the resin system. The mold is the most critical part of the pultrusion process. Typical mold lengths range from 0.6 to 1.2 m.
5. Traction device: The traction device itself can be a crawler type puller or two reciprocating clamping devices to ensure continuous motion.
6. Cutting device: The profile is cut by a cutting saw with automatic synchronous movement according to the required length.
- Common defects and corrective actions in the pultrusion process
1. Peeling When the surface of the component has cured resin particles coming out of the mold, this phenomenon is called peeling or peeling off.
Corrective Actions: • Increase the temperature of the inlet end mold to allow the resin to cure faster. • Reduce line speed and allow the resin to cure earlier. • Line stop cleaning (30 to 60 seconds). • Increase the concentration of low temperature initiator
When blistering occurs on the surface of the part.
• Increase the temperature of the inlet end mold to make the resin cure faster
• Reduce line speed, the same as above
• Increase the level of reinforcement. Foaming is often caused by voids caused by low glass fiber content.
3, there are cracks on the surface
Surface cracks are caused by excessive shrinkage.
• Increase mold temperature to speed up cure
• Reduce line speed, the same as above
• Increase the loading or glass content of the filler to increase the toughness of the resin-rich surface, thereby reducing shrinkage, pressure and cracks
• Increase the level of low temperature initiator or use an initiator below the current temperature.
• Add a surface pad or veil to the part
4, internal crack
Internal cracks are often associated with excessive cross-sections that may occur in the center of the laminate or on the surface.
• Increase the temperature at the feed end to allow the resin to cure earlier
• Reduce the mold temperature at the end of the die as a heat sink to reduce the apex of the exotherm
• If the mold temperature cannot be changed, increase the line speed to reduce the temperature of the outer contour of the part and the apex of the heat release curve to reduce any thermal stress.
• Reduce initiator levels, especially high temperature initiators.
• Replace high temperature initiators with low exothermic but better curing agents.
5, color difference
Hot spots can cause uneven shrinkage, resulting in chromatic aberration (also known as color shift)
• Check the heater to make sure it is in place so that there is no temperature unevenness on the mold
• Check the resin mix to ensure that the filler and/or pigment does not settle or separate (color difference)
Third, NEWECO pultruded resin
NEWECO is one of the leading unsaturated polyester resin manufacturers and suppliers,widely used in automobiles, ships, rail transit, wind power generation, pipe cans, heat and corrosion protection, building materials, stone repair, sanitary ware, artificial stone and other industries. Suitable for hand lay-up, spray, pultrusion, winding, molding, vacuum introduction / RTM, casting and other molding processes. NEWECO Resin is committed to excellence and focuses on the application of composite materials to provide customers with comprehensive solutions.