Core Summary of Composite Pultrusion Molding Process

Composite pultrusion molding is an automated process for the continuous production of fiber-reinforced plastic (FRP) profiles with constant cross-sections. Originated in the United States in 1948, it is characterized by high efficiency, stable product quality, low cost and high performance, and is widely used in mass production of profiles in various fields.

I. Core Definition and Advantages

Definition: It involves pulling continuous fibers through resin impregnation, mold heating and curing, and fixed-length cutting to produce profiles continuously.

Key Advantages:

• Automated continuous production with a linear speed of 0.2–1.5m/min (over 4m/min for high-speed molding), ensuring high efficiency.

• Fiber content can reach up to 80%, with excellent longitudinal mechanical properties and a raw material utilization rate of no less than 95%.

• Standardized cross-sections, stable product quality, no edge waste, saving materials and energy.

• Theoretically capable of producing products of any length, suitable for mass manufacturing.

II. Domestic Development History

• Started in 1968, when Beijing No. 251 Factory produced FRP pipes using the pultrusion method.

• Since 1985, more than 30 production lines have been introduced from abroad, and 70 production lines have been independently designed and processed by relevant units, with a total domestic production capacity of nearly 30,000 tons.

• In the early 1990s, sucker rods for oil extraction were developed through the combination of imported technology and independent research, which was recognized by the petroleum sector and put into practical production. FRP door and window profiles were also developed, leading to the rapid expansion of the industry.

III. Standard Process Flow

Fiber arrangement → Resin impregnation → Preforming → In-mold extrusion and curing → Traction → Fixed-length cutting.

IV. Key Equipment and Materials

Equipment: Fiber creel, resin impregnation tank, preforming mold, heating mold (three-zone temperature control), traction machine, cutting machine.

Materials:

• Resin: Unsaturated polyester resin is the main type (accounting for more than 90%), supplemented by epoxy resin, vinyl resin, phenolic resin, etc.

• Reinforcing materials: Glass fiber is the main material, with carbon fiber, aramid fiber, etc. optional to meet special performance requirements.

• Auxiliary materials: Release agent and filler.

V. Key Process Control Points

• The mold is divided into three zones: preheating, gelation and curing, with a temperature difference of 20–30℃ and a gentle temperature gradient.

• Core parameters: Mold temperature, pultrusion speed, curing degree and traction force need to be matched to ensure smooth surface and stable performance of products.

VI. Main Application Fields

It covers aerospace, automotive, construction, petrochemical, electronic and electrical, military and other fields, producing profiles, rods, pipes, structural parts, etc.