Introduction to Polyurethane Pultrusion Process and Common Products and Applications

 

Pultrusion is a method for continuous production of composite material profiles. It is an automated production process that impregnates untwisted glass fiber roving and other continuous reinforcing materials on the creel, such as polyester surface felt, with resin, and then passes through a molding mold that maintains a certain cross-sectional shape, and solidifies and forms it in the mold before continuously ejecting it from the mold, thereby forming a pultruded product.

 

The tensile strength of products produced by pultrusion is higher than that of common metal materials such as steel and aluminum, and the material itself has good corrosion resistance. It is widely used in infrastructure, new energy, transportation, electrical engineering, chemical industry, ocean, boats and many other industrial and civil fields.

 

Pultrusion Molding Process

 

The pultrusion molding process is shown in the figure below. Therefore, it can be divided into several stages: glass fiber roving arrangement – impregnation – preforming – extrusion curing – traction – cutting.

 

 

Pultrusion composite materials can use a variety of resin matrices. In recent years, due to the many advantages of polyurethane resin, the market share has risen rapidly. The main advantages of glass fiber reinforced polyurethane pultruded composite materials are reflected in the following aspects:

 

1) High fiber content, the weight content can easily reach more than 80%. The fiber structure is simple, the profile performance is excellent, and the use of fiber felt or cloth is reduced or even eliminated, which greatly simplifies production and improves efficiency.

2) Profiles with complex cross-sections and thin walls can be produced without cracking.

3) The profile surface is smooth, and the material performance quality is stable and reliable.

4) Closed mold production process: closed loop mixing and impregnation. The proportioning, transportation, mixing and impregnation of the resin are carried out in a closed pipeline without contact with the environment, which avoids the influence of dust, moisture and other environmental factors on the product.

5) Clean and environmentally friendly production: polyurethane resin does not contain styrene, and there is no irritating odor in the production site, which minimizes the impact on the environment and workers’ health.

6) Fully automated production. All processes including raw material proportioning, mixing, conveying, fiber impregnation, traction, profile curing and molding, and cutting are completed by automatically controlled equipment to ensure the consistency of product quality.

 

Typical Mechanical Properties of Glass Fiber Reinforced Polyurethane Profiles

 

Polyurethane pultrusion products include various rods, flat plates, hollow tubes and profiles, which are widely used in the market.

 

1. Door and Window Profiles (Baydur® System)

• High Thermal Insulation:
• Like solid wood and PVC, polyurethane pultruded composite profiles have a very low thermal conductivity of 0.34 W/m•K at room temperature, which is only about 1/700 of aluminum alloy, and is an excellent thermal insulation material.

 

• Low Thermal Expansion:
• The linear thermal expansion coefficient of polyurethane pultruded composite profiles is about 7×10-6/K, which is much lower than that of aluminum alloy and is similar to the linear thermal expansion coefficient of the wall; therefore, when the temperature changes, the frame of the polyurethane pultruded composite profile will not have a gap with the wall, and the sealing is good, while ensuring the thermal insulation of the entire window in an environment with a large temperature difference.

 

· Corrosion Resistance:

Polyurethane pultruded composite profiles have strong corrosion resistance to most acids, alkalis, salts, organic matter, seawater, and humid air; they are also rust-proof and have better corrosion resistance than other door and window profiles. They are especially suitable for coastal, corrosive, and generally humid places.

 

 

2. Wind Turbine Blade Beam (Baydur® System)

The main advantages of using pultruded sheets to make blade beams are reflected in the following aspects:

· Mechanical properties · Compared with vacuum infusion process, pultrusion has the advantage of industrial production · High glass fiber content · More uniform arrangement of fibers in composite materials · Reduce risk factors in the production process · Pultruded sheets can be pre-inspected before entering the mold to minimize defects · The pultrusion process can minimize the impact and interference of human factors · Shorten mold occupation time

 

 

3. Cable Tray (Baydur® System)

• Historically, unsaturated polyester was used more frequently, but now it has basically switched to polyurethane pultrusion. Polyurethane pultrusion bridges have advantages in terms of ease of on-site construction and service life;

 

• Polyurethane bridges have high tensile strength, impact resistance and corrosion resistance. Compared with unsaturated polyester resins, polyurethane comprehensively improves the physical properties, strength and rigidity of the product.

 

• Fast pultrusion speed and high production efficiency.

 

• Polyurethane products have excellent toughness, and the edges after processing and punching show very few or even no microcracks. The surface is fine and smooth, the rigidity is strong, and the porosity is low, which is conducive to subsequent processing such as drilling, machining and assembly.

 

• Does not contain solvent styrene (toxic chemicals), no solvent volatilization will be generated during the production process, and no styrene emissions.

 

 

 

4. Pallets (Baydur® System)

· Due to the toughness of polyurethane composite materials, their impact resistance and shear strength are much higher than traditional materials. The service life of pallets can be 20 times more durable than traditional wooden pallets. Polyurethane pultruded pallets have a long cycle life and low single cycle cost, which has good economic benefits.

 

 

Compared with traditional wood-based materials, materials made with polyurethane pultrusion technology are 22% lighter, reducing fuel consumption and transportation costs for the entire ship and truck containers. While being lightweight, they also maintain sufficient toughness, which also reduces maintenance costs and increases the service life of containers. The service life of traditional container wood floors is only 5 to 10 years, while the service life of polyurethane pultruded floors can exceed 20 years. Its special properties include:

 

• Low weight, which can reduce energy consumption during transportation
• Strong durability (water, oil, odor, microorganisms) · Increase the service life of containers · Reusable and recyclable floor

 

6. Composite Solar Frame (Baydur® System and Desmocomp® System)

For a long time, photovoltaic power stations have used traditional metal frame components. Traditional metal frames will have PID effect under the action of high pressure for a long time, resulting in fatal power attenuation of components, extreme reduction in power generation, and huge economic losses. Therefore, the industry has conducted rounds of attempts to develop solutions to reduce the risk of PID effects, and non-metallic frames may be a good solution. Advantages of non-metallic solar panel frames:

 

• Non-metallic composite insulation frames give the panels excellent system-level anti-PID performance· Retain the convenience and reliable installation characteristics of the traditional frame system· Insulated frames do not require grounding· Suitable for various high-demand component systems and high-voltage systems

 

 

7. ThermoBracket Insulation Bracket (Desmocomp® System) Specially Developed for External Insulation Curtain Wall

 

fischer Benelux B.V. and FISCO GmbH jointly developed a facade component made of composite materials – ThermoBracket insulation bracket. In the process of selecting materials, they tested different resin technologies, and finally Covestro’s Desmocomp® resin was selected for its best flame retardant performance while also having mechanical load and thermal insulation performance.