Ensuring Uniform Mixing of Materials in The Production Process of PE Ground Protection Mats

I. Raw Material Preparation Stage

1. Precise Measurement System

• During the raw material preparation, high-precision metering equipment is employed to guarantee the accurate addition of different raw materials in specific proportions. For the main raw material, polyethylene (PE), whether it is high-density polyethylene (HDPE) or low-density polyethylene (LDPE), its weight or volume is precisely measured. For instance, electronic scales or volumetric metering pumps are used, with an error range typically controlled within a very small margin, such as ±0.5%. This ensures that the proportion of different batches of PE raw materials and other additives remains consistent.

• The metering of additives (such as antioxidants, UV stabilizers, fillers, etc.) is equally strict. Take antioxidants as an example. The addition amount is usually determined based on a certain proportion of the weight of the PE raw material. For example, 0.1 - 0.5 kilograms of antioxidants are added per 100 kilograms of PE. Through precise metering equipment, the accuracy of this proportion can be ensured, laying the foundation for subsequent uniform mixing.

2. Pre-mixing Treatment

• Before the raw materials are fed into the extruder, a pre-mixing process is carried out. The PE raw materials and various additives are placed into a specialized mixing device, such as a high-speed mixer. The blades of this mixer rotate at high speed, causing the raw materials to tumble vigorously within a closed container. For example, the rotation speed of the mixer can reach 1000 - 2000 revolutions per minute, and the duration usually ranges from 10 to 30 minutes, depending on the quantity and properties of the raw materials.

• During the pre-mixing process, the smaller additive particles are evenly dispersed among the PE raw material particles. For example, calcium carbonate as a filler can evenly coat the surface of PE particles, enabling these additives to be more uniformly incorporated into the PE matrix during the subsequent processing.

II. Extrusion Process

1. Extruder Screw Design

• The structure of the extruder screw plays a vital role in the uniform mixing of materials. The screw is usually divided into different functional sections, namely the feeding section, the compression section, and the metering section. In the feeding section, the screw pitch is relatively large, and its main function is to smoothly convey the raw materials to the next section.

• As the raw materials enter the compression section, the screw pitch gradually decreases, exerting a compression effect on the raw materials. This design causes the raw materials to be gradually compacted during forward conveyance, reducing the gaps between different raw materials and facilitating mixing. For example, the compression ratio can be designed between 2 and 4 to ensure that the raw materials are sufficiently compressed and the various components are brought closer together.

• The screw in the metering section is mainly responsible for precisely controlling the output of the raw materials and further mixing the materials. The rotation of the screw generates shear forces, which can break up the agglomeration of raw material particles and mix them more evenly.

2. Temperature Control and Melting

• Different temperature zones are set in the extruder to achieve the gradual melting and uniform mixing of the raw materials. In the feeding section, the temperature is generally lower, for example, 150 - 180°C. This temperature allows the PE raw materials to be fed in a solid particle state. As the raw materials are conveyed forward, the temperature gradually rises. In the melting section, the temperature can reach 190 - 220°C, ensuring the complete melting of the PE raw materials.

• The additives are better dispersed during the melting process of the PE raw materials. For example, antioxidants and UV stabilizers are evenly distributed in the liquid PE as it melts. When the temperature reaches the appropriate range in the metering section, such as 200 - 230°C, the liquid raw materials and additives are fully mixed to form a uniform melt, preparing for the extrusion molding.

III. The Auxiliary Role of Subsequent Processing Steps

1. Mixing Promotion during Cooling and Tempering

• During the cooling process, for example, when the freshly extruded PE protection mat material is cooled through cooling rollers or a water-cooling trough, the molecules inside the material are still in a somewhat active state. If there are some minor non-uniform parts during the mixing stage, the slow and uniform cooling process can further promote the diffusion and mixing of the components inside the material.

• For some processes that involve tempering, where the protection mat material is heated to a temperature below the melting point and held for a certain period, this process also helps the molecular movement inside the material, further homogenizing any possible non-uniform components.

2. Mechanical Action during Processing

• In the subsequent calendering process, the protection mat material is flattened and smoothed through a set of rollers. The pressure and friction between the rollers exert a certain mechanical action on the material, further mixing the components inside. For example, when the material passes through the rollers of the calendering machine, the pressure difference between the upper and lower rollers makes the component distribution in the thickness direction of the material more uniform.

• In the cutting and final processing steps, although the main purpose is not mixing, the mechanical forces and movements involved can also have a certain impact on the overall uniformity of the material. For example, during cutting, the vibration and stress on the material can cause some microscopic adjustments in the material structure, which may contribute to a more even distribution of components in a very limited extent.