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Pultrusion Die

  • pultrusion mold
  • pultrusion mold
  • pultrusion mold
  • pultrusion mold


Pultrusion is a manufacturing technique employed to produce continuous lengths of fiber-reinforced polymer (FRP) composites with a consistent cross-section. This process involves pulling fiber-reinforced resin through a heated die, where the resin cures and solidifies into the desired shape. The die plays a crucial role in this process, as it determines the final product’s shape, size, and quality.

For optimal performance during the pultrusion process, the surface of the die cavity must be smooth and wear-resistant. This minimizes friction resistance, thereby extending the die’s service life. The selection of die material has a direct impact on the performance of the pultrusion die. The material must exhibit the following properties:

  • High strength, corrosion resistance, fatigue resistance, and wear resistance.
  • High thermal resistance and low thermal deformation.
  • Excellent machinability and surface polishing capabilities.
  • Low friction coefficient for minimal resistance and superior dimensional stability.

How To Machining And Design The Pultrusion Die?

Roughly Cutting
Step 1:Roughly Cutting

Afer confirmed the drawing,Incomepultrusion will cut the material with space.

Roughly Milling
Step 2:Roughly Milling

CNC center machining the space in first.

Preciousely CNC Machining
Step 3:Preciousely CNC Machining

Change the preciousely CNC center to 0.1mm feed at high cutting speed.

Roughly Grinding
Step 4:Roughly Grinding

Closed to the final size with preciously grinder.

High-Preciously Grinding
Step 5:High-Preciously Grinding

Use the “mm”Unit High-Precisouly Grinding to close the drawing toleraence.

Step 6:Chromplate

Hard chrome-plate

polish and close
Step 7:Polish And Close

Polish the surface with hand and machining the closed surface.

7 Products Found.

What's steel material could be choice in pultrusion die?

Pultrusion molds can be made from various materials, common ones include P20, 38CrMoAl, Cr12, 40Cr, and H13, with hardness levels generally ranging from HRC55 to HRC65. Through surface treatment techniques such as nitriding, chromizing, quenching, and polishing, the performance and durability of the molds can be further enhanced. Depending on the specific requirements of the product, molds can be designed with single or multiple cavities, with their service life extending from 50,000 meters to 200,000 meters, depending on the mold’s design, material, and maintenance condition. These factors together determine the efficiency of the mold and the quality of the product, making them critical elements that cannot be overlooked in the pultrusion manufacturing process.

  • P20 material
    P20 STEEL

    P20 steel is a pre-hardened plastic die steel with good machinability, better polishability and easy texturizing. It has been used widely for making injection molds and extrusion dies due to its superior mechanical properties such as excellent wear resistance, high compressive strength and toughness. In addition, it has very low shrinkage during heat treatment which makes it an ideal choice for intricate parts requiring tight tolerances. This steel also offers excellent corrosion resistance in humid environments as well as good weldability when welding with suitable techniques. Now in pultrusion technology, P20 can be easily machined into complex shapes since it is highly ductile in nature.

  • H13 material
    H13 Material

    H13 is ability to retain hardness and strength at elevated temperatures. In addition to its heat resistance attributes, H13 steel offers superior corrosion resistance making it an ideal choice in pultrusion technology that require protection from corrosive chemical elements.In additionally, H13 steel has excellent forging characteristics allowing for faster production rates when compared with conventional steels used.
    So we usually choice this material to increase the faster delivery time.

  • 12Cr-Mo-V STEEL
    12Cr-Mo-V STEEL

    12Cr-Mo-V is that it has a high tensile strength and good corrosion resistance. This makes it ideal for applications for epoxy system pultrusion. It can operate at elevated temperatures up to 500°C without any changes to its properties. Additionally, the steel contains molybdenum which helps increase creep strength and fatigue life as well as reduce wear from abrasive agents. The composition also includes chromium which improves oxidation resistance so 12Cr-Mo-V steel can be used even under harsh conditions where other steels would not last long. The combination of these elements gives this alloy great durability for extended periods of time making it an excellent choice for many industrial uses where reliability is important.

Key Considerations in Pultrusion Die Design

Resin Type

Different resins have varying curing times and viscosities, affecting how the material flows through the die

Size and Shape of the Final Product
Size and Shape of the Final Product

The die’s shape must match the desired final product shape, and its size must accommodate the volume of resin and fibers. Adequate clearance is necessary to ensure smooth flow without causing defects

Cooling System
Cooling System

Proper cooling is essential for the resin and fibers to cure correctly as they are pulled through the heated die. The cooling system must efficiently cool the entire cross-section of the product

Production Capacity
Production Capacity

For some simple products, we will design multi-cavity molds based on the needs of our customers to meet their production capacity requirements.


During the pultrusion molding process, after the reinforcing material is impregnated with resin (or while being impregnated), it must pass through a preform mold composed of a set of yarn guiding elements before entering the forming mold. The purpose of the preform mold is to further remove excess resin from the impregnated reinforcing material, eliminate bubbles, and gradually form a shape and size that approximates the forming mold cavity before entering the mold. Through preforming, the reinforcing material gradually achieves the required shape, and the distribution of the reinforcing material in the cross-section of the product meets the design requirements.

Pultrusion Mandrel for BWFRP pipe production

Customzied Pultrusion Mandrel

The mandrel is an essential component in the production and manufacturing of hollow profiles or tubes. In the pultrusion process, for some thick-walled products, heating rods can be added inside the mandrel to assist in the resin curing process. Typically, P20 material is chosen for mandrels due to its pre-stressed nature and ease of polishing, among other properties.

The length of the mandrel is generally determined based on the needs of the preforming process and is usually 600mm to 700mm longer than the mold length. For processes involving multiple layers of felt lamination, the length of the mandrel can extend to 2500mm to 3000mm. This extended length is necessary to accommodate the additional material and ensure that the entire profile is supported and heated evenly throughout the pultrusion process, facilitating the proper curing and consolidation of the resin.

  • Flat Pultrusion Mold
    Flat Pultrusion Mold
  • Ladder Pultrusion Mold
    Ladder Pultrusion Mold
  • Channel Pultrusion Mold
    Channel Pultrusion Mold
  • H Beam Pultrusion Mold
    H Beam Pultrusion Mold
Pultrusion Die Design

Pultrusion molds are typically assembled from several individually manufactured mold components. The number of components and the choice of parting lines depend on the cross-sectional structure of the pultruded product, mold machining processes, and usage requirements. To ensure the appearance quality of the pultruded products at the mold parting or mating lines is high, without the formation of burrs, it’s essential to minimize the number of parting lines under the premise of mold manufacturing, ensuring tight mold seams.

When glass fibers impregnated with resin enter the forming mold, the fiber bundles do so under the traction of the pultrusion machine. Due to the looseness of the fiber bundles at the mold entrance, they often accumulate and wrap around, leading to fiber breakage. Furthermore, long-term use of the mold can lead to significant wear at the entrance due to this accumulation and wrapping, affecting product quality. To address this issue, an elliptical section radius should be rounded around the mold entrance, and a conical entrance with an angle of 5° to 8° and a length of 50 to 100mm is advisable. This design can greatly reduce the occurrence of fiber breakage, thus improving the quality of the pultruded products.

In mold design, the determination of mold length should consider the raw materials used and the cross-sectional shape of the product. Currently, the standard mold length in domestic designs ranges from 900 to 1200mm, while the mold cavity size depends on the dimensions of the product and the shrinkage rate of the selected resin. Typically, the shrinkage rate for unsaturated polyester products is 2% to 4%, and for epoxy resin, it is 0.5% to 2%. For hollow products, special attention must be paid to the design of the mandrel; its effective length should be 2/3 to 3/4 of the mold length. Additionally, during the pultrusion process, the ease of fixing and adjusting the mandrel should be considered, along with the weighting and heating of larger mandrels to maintain horizontal balance and uniform heating. Taking all these factors into account, for molds around 900mm in length, the mandrel length can be designed to be around 1500mm.

How to polishing the Pultrusion mold?

To polish a mold, the following procedure should be followed: Begin with 600 grit waterproof sandpaper for initial sanding, and as progress is made, switch to finer sandpapers in the sequence of 600 grit → 800 grit → 1000 grit → 1200 grit → 1500 grit. Throughout the sanding process, it is imperative to continuously rinse the mold with aviation kerosene to remove the fine particles produced by the sanding, preventing scratches on the mold surface. After sanding with 1500 grit sandpaper, switch to a specialized electric polishing machine equipped with a wool polishing pad for polishing. Start polishing with a coarser abrasive polish while using a slightly harder wool pad, performing 2 to 3 rounds of polishing. Rinse the mold with kerosene to clean off the polished particles, then switch to a softer wool pad for further polishing of the mold. During polishing, move the polishing machine in one direction without pausing in one spot to prevent overheating and damaging the mold surface. This process should be repeated 2 to 3 times. After polishing, the mold cavity will be very bright, achieving a mirror finish, and it can continue to be used.

Are the pultrusion molds the same for different resin systems?

The length of the mold is generally designed to be 900~1200mm, and the size of the mold cavity is usually larger than the size of the product. The size depends on the dimensions of the product and the shrinkage rate of the selected resin. Generally, the shrinkage rate for unsaturated polyester products is 2%~4%, while for epoxy resin, it is 0.5%~2%. As for the material of the mold, P20 material is commonly used for unsaturated products, whereas for epoxy resin, GCR15 with overall quenching treatment is generally chosen.

What is the different between the seamless rod molds and seam rod molds?

There are generally two types of pultrusion tube molds: one is seamed, and the other is seamless. Seamless tube molds are usually processed by gun drilling, followed by chrome plating on the surface. Seamless molds are typically used for products where the final surface cannot have any seam lines. The cost of manufacturing seamless molds is lower than that of seamed molds.

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