Pultrusion Process and Solutions

Advantages:

(1) The mechanical properties of the product are excellent, especially the longitudinal strength.

(2) The process is automated and the quality is stable.

(3) There is no scrap and the raw materials are effectively utilized.

(4) Continuous production, no limit on the length of the product.

(5) The resin impregnation area can be closed to limit the emission of volatile substances.

Disadvantages:

(1) It is limited to a constant cross section;

(2) The mold and heating costs are relatively high, and it is difficult to recover the cost due to low output.

Pultrusion refers to a method of continuously producing FRP linear products by pulling prepreg tapes, fibers or fabrics under external force, through dipping, extrusion molding, heating and curing, and fixed-length cutting.

The characteristics are that the prepreg tapes, dipped fibers or fabrics are pulled by external force, extruded through a heated mold, and cured to form FRP linear profiles, which are used to produce composite products with fixed cross-sectional shapes.

2 Reinforcement Materials

Prepreg Tape

Carbon Fiber Prepreg Tape

Fiber

Carbon Fiber

12K, 24K, 48K

Glass Fiber (usually direct yarn)

1200Tex, 2400Tex, 4800Tex, 9600Tex…

Fabric

Chopped mat

Stitched mat

Fiber cloth

Surface mat

3 Matrix Materials

Common Resins:

Epoxy resin
Epoxy vinyl ester resin
Unsaturated polyester resin
Polyurethane resin
Function of Matrix Materials

Bond the reinforcement materials into a whole, and play the role of transferring and balancing the load. Give the composite material basic properties:

Tensile properties: depends on the reinforcement material;

Bending and compression properties: partly depend on the matrix material;

Interlaminar shear properties: depends on the matrix material;

Functionalities such as heat resistance, corrosion resistance, flame retardancy, weather resistance, electrical properties, bio-resistance and light transmittance: depends on the matrix material.

Basic Requirements for Matrix Materials

Low viscosity: Below 1000mPa·s in the production environment, the resin should have good fluidity and wettability.

Long gel time, short curing time, high activity and low heat release.

Low curing shrinkage: Fillers can be introduced into the formula to reduce the curing shrinkage while reducing costs.

Good adhesion, certain toughness, and not easy to crack during molding.

4 Curing System

Epoxy Curing System

Epoxy curing agents are mainly anhydrides

The supplier provides (A+B) two-component or (A+B+C) three-component formula materials, and no third party is required to provide them.

Polyurethane Curing System

The supplier provides A+B two-component formula materials, and no third party is required to provide them.

Epoxy Vinyl Ester Resin, Unsaturated Polyester Resin

Generally two or three initiators are added

Common Curing Systems

BPO (benzoyl peroxide) is commonly used as the starting initiator

TBPB (tert-butyl peroxybenzoate) is commonly used as the termination initiator

Lm-P (curing agent for pultrusion), which works better with BPO

Akzo Nobel:

TRIGONOX HMS starting initiator: 0.8-1.2%

TRIGINOX C termination initiator: 0.3-0.5%

Shuojin:

Pulcat AW starting initiator: 0.6-1.2%

Norox TBPB termination initiator: 0.1-0.2%

Norox 500 intermediate initiator: 0.1-0.4%

5 Demolding System

Epoxy resin: INT-1846N INT-1890M Epoxy vinyl ester resin, unsaturated polyester resin: INT-PS125 INT-PUL524M Zinc stearate (commonly used) Release agent addition amount: Initial addition amount: 1%, Effective addition amount: 0.75-2%

6 Fillers and Additives

Inorganic Fillers:

Purpose: reduce cost, reduce shrinkage, improve flame retardancy Commonly used: calcium carbonate, aluminum hydroxide Particle size: 150-1200 mesh, addition amount: 10%-50% of resin Organic fillers:

Color paste, color powder, diluent, etc., Additives:

Toughening agent, etc.

7 Mold System

Preforming mold: The function is to gradually form a preform with a shape and size similar to the molding cavity according to the configuration form of the profile section, and then enter the molding mold, so as to ensure that the yarn content of the product section is uniform.

Forming Mold:

Mold length: 500 ~ 1500 mm mold material: mold steel mold form: integral, combined type heating device: electric heating plate, electric wave heating, hot oil circulation

Process Control

Reinforced fiber arrangement → Dipping → Preforming → Pultrusion molding and curing → Traction → Cutting → Product → Packaging

Mold Analysis

The mold is generally divided into three areas, namely the heating area, gelling area and curing area. Three sets of heating plates are used on the mold for heating. During the heating process, the temperature of the resin gradually increases and the viscosity decreases. After passing through the heating area, the resin system begins to gel and cure. At this time, the viscous resistance at the interface between the product and the mold increases, the boundary conditions are broken, and the resin has a sudden change in speed at the separation point. The basically cured profile moves at a uniform speed on the mold surface and is basically cured after leaving the mold.

Temperature Control

The cavity temperature is generally set high in the middle and low at both ends.

The temperature of the heating zone can be lower, and the temperature of the gelling zone is similar to that of the curing zone. The temperature distribution should make the curing exothermic peak appear in the middle of the mold, and the gelling and curing boundary point should be controlled in the middle of the mold. Generally, the temperature difference between the three sections is controlled at about 20-30℃, and the temperature gradient should not be too large. The temperature setting is closely related to the formula, traction speed, mold size and form. (Practical experience is more important).

The initial temperature setting of the middle section is determined by the peak value and related conditions of the DSC curve of the resin curing system. It is generally 20-30℃ higher than the peak temperature.

In fact, the faster the pultrusion speed, the higher the temperature needs to be set.

For example, epoxy: 160-180-160℃

Epoxy vinyl ester (unsaturated): 130-150-130℃