Analysis of Pultrusion Process Parameters for Composite Insulating Core Rods

Process Overview

The pultrusion process for insulating core rods involves non-twisted fiberglass rovings being impregnated with resin in a dip tank at a controlled traction speed. After being pre-formed by specialized equipment, the materials enter the mold cavity. The final product is formed through complex physical and chemical reactions as it passes through specific zones: cooling, preheating, gelation, and curing.

The fundamental solidification of the core rod occurs within the mold cavity. Therefore, the process parameters for each zone must be strategically selected based on the continuous movement and phase transitions of the impregnated fibers inside the mold.

Zone Analysis within the Mold Cavity

• Cooling Zone: The setup of a cooling zone at the mold entrance is crucial to prevent the backflowing resin from curing prematurely at the mouth, ensuring the smooth passage of the impregnated fibers.

• Preheating Zone: A sufficiently long preheating zone utilizes resin backflow and migration to achieve thorough re-impregnation of the straightened and precisely positioned fibers. This stage also leverages the low thermal conductivity of the resin to create an inward heat flow, forcing the fibers to aggregate toward the center of the mold.

• Gelation Zone: As temperatures continue to rise, the combined effects of fiber aggregation, decreasing resin viscosity, and volume expansion lead to a gradual accumulation of pressure against the mold walls. This pressure peaks at the gel point.

• Curing Zone: Beyond the gel point, the exothermic curing reaction triggers a sharp temperature spike. This causes a rapid increase in resin viscosity, swiftly transforming the material into a hardened solid. The entire forming process is a synergy of resin flow under traction, pressure distribution, heat transfer, and curing kinetics.

Determining Process Parameters

Given the overlapping variables within the mold cavity, it is impractical to use every single factor to define the pultrusion parameters. Instead, the focus must be on the direct causal relationship of the resin’s transition from liquid to solid.

The “Exothermic Curve” of the resin’s solidification is the most practical reference for reflecting the reaction process. Therefore, the parameters for each mold zone should be primarily based on this curve, while also accounting for secondary factors such as traction speed, surface friction, and fiber-to-resin bonding. Optimization is key to ensuring peak performance of the finished core rod.

Batch Production Stability

In large-scale production, factors such as fluctuations in raw material quality, changes in resin viscosity due to ambient storage temperatures, and the periodic addition of new resin can cause parameters to deviate from the optimal design. Such deviations directly impact the performance consistency of the pultruded rods.

Consequently, fine-tuning the parameters in each zone based on real-time production conditions is essential to maintaining the high-performance stability of every batch.