Polyurethane pultrusion injection molding machine and fiberglass pultrusion molding process

In the realm of Fiber Reinforced Polymer (FRP) manufacturing, the pultrusion process holds a vital position due to its unique advantage of efficiently producing continuous, constant-cross-section profiles. The traditional pultrusion of fiberglass (typically using unsaturated polyester or epoxy resins with glass fibers) has been a mature technology for decades. However, with ever-increasing demands for material performance, an emerging technology utilizing polyurethane (PU) resins and specialized injection machines is sparking a revolution. This article delves into both technologies, analyzing their core processes and equipment innovations.

Part 1: The Fiberglass Pultrusion Process

Pultrusion is a continuous process for manufacturing composite materials with a constant cross-section. The basic principle is analogous to "pulling" fibers and "extruding" them through a die where they cure.

1.1 Process Flow:

1. Creel:Glass fiber roving and other reinforcements are fed from a creel rack.

2. Resin Impregnation:The fiber strands are guided through an open resin bath (or dip tank), where they are saturated with a formulated resin system (typically unsaturated polyester or vinyl ester).

3. Pre-forming:The wet fibers then pass through a pre-forming die, which removes excess resin and roughly shapes the material before it enters the main die.

4. Curing:This is the core step. The pre-formed profile enters a heated, precision-machined steel die. Under controlled temperature, the resin undergoes a curing (cross-linking) reaction, hardening into a solid profile that matches the die's cavity shape.

5. Pulling & Cutting:A continuous puller system grips and pulls the cured profile from the die at a constant speed. Finally, a cut-off saw automatically cuts the profile to the required length.

1.2 Characteristics:

• Advantages:High production efficiency, high material utilization, consistent product quality, and suitability for automation.

• Limitations:Relatively slow curing speed of traditional polyesters limits line speed; mechanical properties (especially toughness and transverse strength) have room for improvement; Styrene emissions during production can be an environmental concern.

Part 2: The Polyurethane Pultrusion Injection Machine and Process Innovation

To overcome the limitations of traditional fiberglass pultrusion, the polyurethane pultrusion technology emerged. The heart of this technology is the specialized Polyurethane Pultrusion Injection Machine.

2.1 Advantages of Polyurethane Resin:

• High Reactivity:Cures significantly faster than traditional resins, allowing for greatly increased pultrusion speeds (often by 50% or more).

• Superior Mechanical Properties:Renowned for exceptional toughness and impact resistance, alongside excellent interlaminar shear strength and transverse strength.

• Environmental Friendliness:Typically Styrene-free, resulting in very low Volatile Organic Compound (VOC) emissions.

• Excellent Fatigue & Durability:Products exhibit a longer service life.

2.2 Core Functions of the PU Pultrusion Injection Machine:
This machine is the "heart" of the PU pultrusion process and is fundamentally different from a traditional resin bath:

• Precise Metering & Mixing:The machine features high-precision metering pumps that deliver the PU resin's A (polyol) and B (isocyanate) components in a strict ratio to a static mixer.

• High-Pressure Injection:The thoroughly mixed resin is injected under pressure directly into a closed injection chamber or block, not an open bath.

• Efficient Impregnation:Inside the injection block, the fiber reinforcements are uniformly and thoroughly wetted from all sides as they pass through. This closed design minimizes resin exposure, virtually eliminates VOC emissions, and ensures optimal fiber wet-out.

Part 3: Key Comparison and Conclusion

The traditional fiberglass pultrusion process remains a mature and reliable technology that will continue to serve many applications effectively. However, the Polyurethane Pultrusion Injection Machineand the technology it enables represent the future direction of the composite pultrusion industry towards higher efficiency, superior environmental performance, and exceptional material properties. For manufacturers seeking top-tier mechanical performance, increased production throughput, and greener manufacturing, investing in polyurethane pultrusion technology is a strategic choice to maintain a competitive edge.