Composite Materials Technology Lecture: A Brief introduction to the History, Manufacturing Process and Characteristics of Fiber Pultrusion Technology

 

Pultrusion is a common manufacturing method for fiber composite materials. It is a continuous process that uses fiber reinforcement and resin matrix to produce a constant cross-sectional profile. This article will introduce the history, main manufacturing process and characteristics of pultrusion.

 

 

01 A Brief History of the Pultrusion Process

 

One of the main figures in the invention and development of composite technology, a man named Brant Goldsworthy invented the pultrusion process. While working for an aircraft company that supplied the U.S. Army during World War II, he came up with the idea of ​​combining various materials together to make stronger plastics.

 

His experiments were so successful that he eventually decided to open his own company, making several advances in the field of composites and creating some plastics that were generally stronger than any plastic seen before.

 

02 Manufacturing Process of Pultrusion

 

The pultrusion process refers to the manufacturing process of producing continuous lengths of fiber-reinforced polymers with a constant cross-section. During this process, reinforcing fibers, liquid pultrusion resins, pigments, and other raw materials are usually stretched through a heated die to transform them into FRP composite products. The main process includes 4 steps:

 

 

Step 1: Feeding the raw materials into the guide channel The pultrusion process involves pulling the necessary raw materials through a heated die, which means that the reinforcing fibers need to be in continuous form. In most cases, either filament rolls called rovings or continuous strand mats are used. They provide the required tensile strength to pull the rest of the fiber reinforcement through the die.

 

 

That said, the first pultrusion process step involves feeding continuous filaments or mats into the machine through a yarn guide. In the yarn guide, the roving filaments are usually passed through a tensioner and then formed into the finished product. Therefore, it is crucial for manufacturers to maintain maximum precision when feeding the rovings into the guides, as this determines the strength and quality of the final profile.

 

Step 2: Impregnating the Fibers in a Resin Bath

 

The reinforced fibers or mats pass through a wet-out tank for resin impregnation. The forming guides can be placed before, in, or after the resin bath. The wet-out bath usually contains a resin, most commonly polyester or vinyl ester, pigments, fillers, and a catalyst to aid in curing.

The most common one is an open resin-filled tank, which usually has a separator bar inside the tank, so the rovings are guided above and below the impregnation bar. It is considered the standard resin impregnation method because it is cost-effective and produces high-quality profiles.

 

 

Another type of wet bath also involves an open filling bath; the only difference is that the reinforcement does not move up and down. Therefore, it is more suitable for vertical reinforcements such as mats and veils, as they remain in a horizontal position throughout the process and are ideal for producing hollow pultruded composite products.

 

Step 3: Heating/Curing

 

The resin-impregnated reinforcement fibers then pass through a heated mold. This step is also critical because it is where the final profile is formed. When the impregnated reinforcement is exposed to the heated mold, the cross-linking process begins and gradually cures.

 

It is important to note that the cross-linking process is exothermic. This means that once it is initiated, it causes the temperature of the resin to exceed that of the mold. This usually happens near the end of the heating process, and in turn, the resin will naturally be drawn out of the mold.

 

 

Therefore, it is very important to maintain the optimal temperature. If the temperature is too high, cracks will appear in the composite material. On the other hand, if the temperature is not hot enough, the resin will not achieve complete cross-linking. Either way, the result is a composite profile of poor quality.

 

Step 4: Separation

 

As mentioned earlier, separation begins at the end of the heated mold process using a pulling mechanism. For this purpose, many manufacturers usually use a reciprocating hydraulic clamp puller.

 

 

After separation, the cured profile is usually cut to the required length using an automatic saw. This is usually the last pultrusion process step, after which the cured profile can be either processed again at the factory or packaged and shipped to the customer.

 

03 Characteristics of Pultrusion

 

In general, the pultrusion manufacturing process is more economically attractive, convenient, and efficient than other types of manufacturing technologies currently on the market.

 

Pultrusion also produces high-quality, error-free composite materials, which ensures that the products produced have a longer service life than other old-fashioned products. Because of this, it has become increasingly popular and in high demand in recent years.