Overview of Composite Pultrusion Process

 

With the continuous development of the field of materials, the processing technology of composite materials is also increasingly optimized and updated. The following will introduce the relevant process technology of composite material pultrusion in the field of material process technology.

 

1. Definition of Pultrusion

Pultrusion refers to a method of continuously producing steel wire products of unlimited length by dipping, pultrusion, heating and curing, and cutting to fixed length of fiber roving or other fabrics of materials such as glass/basalt under external force traction (external force pulling and extrusion molding). This process is most suitable for the production of profiles of various cross-sectional shapes, such as rods, tubes, solid shapes (I-shaped, grooved, square profiles) and hollow profiles (door and window profiles, blades), etc.

 

2. Characteristics of Pultrusion

 

1. Advantages:

(1) Typical pultrusion speed is 0.5-2m/min, with high efficiency, suitable for mass production and manufacturing of long-sized products;

(2) Resin content can be precisely controlled;

(3) Mainly reinforced with untwisted roving, low raw material cost, multiple reinforcing materials can be used in combination, and the mechanical properties of the product can be adjusted;

(4) The fiber content in pultruded products can be as high as 80%, and the dipping is carried out under tension, which can give full play to the mechanical properties of continuous fibers and the product strength is high;

(5) The raw material utilization rate is above 95%, and the scrap rate is low;

(6) The longitudinal and transverse strength of the product can be adjusted arbitrarily to meet the use requirements of products with different mechanical properties.

 

2. Disadvantages:

(1) Non-continuous reinforcing materials cannot be used;

(2) The product shape is monotonous, and only linear profiles (non-variable cross-section products) can be produced, and the transverse strength is not high;

(3) The mold cost is relatively high;

(4) It is generally used to produce products with constant cross-sections.

 

3. Materials Required for Pultrusion

The materials used in the pultrusion process include resins, reinforcement materials, auxiliary materials, etc.

1. Resins used in pultrusion

The pultrusion process requires the resin used to have low viscosity, and mainly uses unsaturated polyester resins and epoxy resins or modified epoxy resins.

 

Unsaturated polyester resins used for pultrusion are basically o-phthalic and isophthalic types. Isophthalic resins have good mechanical properties, toughness, heat resistance and corrosion resistance. At present, o-phthalic type is more commonly used in China because its price is more advantageous than isophthalic type.

 

Compared with unsaturated polyester resins, epoxy resins have excellent mechanical properties, high dielectric properties, surface leakage resistance, arc resistance, and are excellent insulating materials. Commonly used resins for pultrusion are shown in Table 1, and the resin production formulas are shown in Table 2 and Table 3.

 

 

2. Reinforcement Materials used in Pultrusion

 

The fiber reinforcement materials used in pultrusion FRP are mainly E-glass fiber roving, which has the advantages of no draping, good bundling, easy to be impregnated by resin, and high mechanical properties.

 

According to the needs of the product, C glass fiber, S glass fiber, T glass fiber, AR glass fiber, etc. can also be selected. In addition, synthetic fibers such as carbon fiber, aramid fiber, polyester fiber, vinylon, etc. can also be selected for the needs of special-purpose products. In order to improve the lateral strength of hollow products, continuous fiber mats, cloth, belts, etc. can also be used as reinforcement materials. Table 4 shows the commonly used reinforcement materials for pultrusion.

 

 

Due to the development and exploitation of basalt in the field of materials in recent years, the use of basalt fiber as a reinforcing material in the pultrusion process has also been greatly improved. Its composite products will also be greatly developed in the field of materials in recent years and in the future due to their superior performance.

 

3. Auxiliary Materials Required for Pultrusion Process

 

(1) Inorganic Fillers

Appropriate addition of fillers can improve the heat resistance of the resin matrix, reduce the shrinkage of the resin, improve the surface properties of the pultruded products and reduce the cost. It can also give the pultruded products flame retardant, chemical corrosion resistance or electrical insulation functions. Commonly used inorganic fillers for pultrusion process are shown in Table 5.

 

 (2) Internal Release Agent

The pultrusion molding agent is shown in Table 6. In addition, there are initiators, curing agents, colorants, etc.

 

1. Overview of Typical Pultrusion Molding Processes

 

1. Pultrusion Process of Thermoplastic Composite Materials

Due to the high viscosity of thermoplastic resin melts and the difficulty of impregnation, the key point of improvement research work is concentrated on the impregnation technology, and the fundamental difference between different pultrusion processes lies in the difference between the impregnation method and the impregnation process. Generally, the thermoplastic composite material pultrusion process can be divided into two categories according to the impregnation technology: non-reactive pultrusion process and reactive pultrusion process. From the current application situation, the non-reactive process is the main body, widely used, and relatively mature. The following figure is a flowchart of the pultrusion process of two different thermoplastic composite materials

 

 

2. Pultrusion Process Equipment and Process Flow

 

Thermosetting pultrusion process: fiber supply – fiber guidance – resin impregnation – preforming – pultrusion – traction – cutting – pultruded products.

 

Thermoplastic pultrusion process: fiber roving arrangement – impregnation – preforming – extrusion molding and curing – traction – cutting – products.

 

 

Pultrusion Process Flow Chart

 

Pultrusion Process Diagram

 

 

Composition of Reinforcement Materials for Pultruded Products

 

Schematic Diagram of Winding

 

Pultrusion Winding Production Line

 

 

 

Schematic Diagram of the Pultrusion-Weaving-Winding Hybrid Process

 

Actual Diagram of The Reciprocating Drawing Mechanism

GoldWorthy Eng Annular Pultrusion Machine from the United States

 

 

 

 

Schematic Diagram of Injection Impregnation Method and Polyurethane Resin Pultrusion Production Line

 

Schematic Diagram of Pultrusion Technology for Core-Containing Material Products

 

 

Schematic Diagram of Prepreg Pultrusion Technology and Prepreg Pultrusion Machine

 

Prepreg Pultrusion for Large Aircraft Panels, Floor Beams and Space Station Trusses

 

Pultruded CFRP Channel Steel and Front End of Pultrusion Production Line

 

Thermosetting Composite Curved Profile Pultrusion Production Line Based on German Thomas Technology

 

Thomas in Germany Uses Reverse Pultrusion to Manufacture Cylindrical Helical Springs

 

Thermoplastic Curved Profile Pultrusion (ITV, Germany)

 

Pultruded CFRP Cluster Rods for Anchoring Mooring Cables in Deep-Sea Oil Fields

 

1. Conclusion

From the perspective of technological development, the pultrusion process of composite materials may be mature in all aspects. However, the field of materials is exploring and researching new superior performance materials at all times. When a new material is discovered, it means that various fields will undergo corresponding changes due to this material. This change may be insignificant or epoch-making. Therefore, no matter how mature the technology is, we should continue to explore new developments and continuously propose technological innovations according to changes in the market industry, rather than stagnate in pursuit of temporary stability. Only in this way can an enterprise be further developed, science and technology will continue to progress, and ultimately benefit all mankind.