Working principle of PE greenhouse film woven bag plastic granulator

The working principle of a plastic granulator (also known as a plastic pelletizer) involves processing waste plastics or raw materials into standard granules through steps such as heating and melting, extrusion and plasticization, cooling and solidification, and granule cutting.

1. Core workflow

The operation of a plastic granulator is a continuous process, primarily consisting of the following key stages:

Feeding

The dry plastic raw materials (such as PP, PE, PVC, etc.) or recycled materials that have been crushed and cleaned are fed into the main machine screw system through the hopper. Some models are equipped with automatic metering and feeding devices to ensure uniform feeding.

Plasticization and mixing

The material is conveyed forward by the screw, and simultaneously subjected to the heat generated by the external heating ring and the shear friction of the screw, gradually melting into a viscous flow state.

Single screw extruder: The screw is divided into a feeding section, a compression section, and a homogenization section, which achieve material conveying, compaction, melting, and homogenization.

Twin-screw model: It boasts stronger mixing and kneading capabilities, making it ideal for demanding applications such as filling modification and color masterbatch. Featuring a "building block" screw design, it allows for flexible adjustment of functional zones.

Extrusion molding

Molten plastic is extruded through a die (mold) under high pressure, forming strips, sheets, or ropes. The temperature of the die needs to be precisely controlled to ensure stable discharge and the absence of bubbles.

Cooling and setting

The extruded hot plastic strip needs to be quickly cooled and solidified. Common methods include:

Water-cooled stretching: It cools down through a cooling water tank and is suitable for most general-purpose plastics;

Air-cooled conveyor belt: used for heat-sensitive materials (such as PVC) to avoid moisture residue;

Underwater pelletizing: The material is directly cooled and cut by water flow at the outlet of the die, resulting in round pellets with high automation.

Granulation and screening

The cooled plastic strips are cut into uniform particles by a high-speed rotating cutter, and then passed through a vibrating screen to remove fine powder and irregular particles, resulting in recycled plastic particles that meet specifications (common size φ3×3mm).

Collection and packaging

The finished granules are blown into the storage bin or automatic packaging system through a fan, completing the entire production process.

II. Key Technical Features

Temperature control: A multi-zone PID temperature control system is employed to monitor the temperature of each section in real-time, ensuring the error is controlled within ±2℃ to guarantee the quality of plasticization.

Screw design: The aspect ratio (L/D) is typically 20:1 to 40:1. The larger the L/D, the longer the material residence time, resulting in more thorough plasticization.

Energy-saving technology: Modern equipment commonly employs electromagnetic heating and variable frequency speed regulation, achieving energy savings of over 30%.

The core parameters of a plastic granulator directly affect its applicable materials, production efficiency, and granule quality. Therefore, when selecting a granulator, it is necessary to comprehensively match its specifications with material characteristics, production capacity requirements, and process requirements.

1. Detailed explanation of key parameters and industry standards

Screw Diameter

Common range: Φ125mm ~ Φ260mm

Impact: The larger the diameter, the stronger the extrusion force, making it suitable for high-filling or high-output scenarios. For example, although the screw size of the medium PVC granulator is not specified, its output of ≤600kg/h requires a screw with a diameter of Φ75 or above; while the screw diameter of the Xingyuan 220 model reaches 215mm, specifically designed for large-scale waste plastic recycling.

Aspect ratio (L/D Ratio)

Standard value: 20:1 ~ 40:1

Function: The higher the L/D ratio, the longer the material plasticization time, and the more thorough the mixing. For example, double-stage mixing granulators often adopt an L/D ratio of 30:1 or higher to ensure the uniformity of recycled materials.

Motor power (Main Motor Power)

Industrial-grade equipment typically has a power rating of over 45 kW. The Binda granulator is labeled with a power of 200W, which may indicate that it is a small experimental machine or due to data anomalies. In actual production, models like the 220 require high-power drive for the three-screw system to handle high-resistance materials.

Heating and temperature control system

Heating power: 28kW ~ hundreds of kW (e.g. heating power of 28kW)

Energy-saving technology: Electromagnetic heating can save 30%-70% energy compared to resistance coils, and it heats up faster. High-end models are equipped with a multi-level temperature control system, which achieves precise temperature control through front, middle, and rear temperature measurement blocks to prevent material decomposition.

Output Capacity

Small machine: 80-150kg/h (for example)

Medium-sized machine: 300-600kg/h (such as PVC granulator)

Large machine: >800kg/h, suitable for continuous production line

Screw type and configuration

Single screw: simple structure, low cost, suitable for general-purpose plastics (such as PP, PE)

Twin-screw extruder: strong self-cleaning ability, uniform mixing, suitable for color masterbatch and modified materials

Granulation method and cooling system

Strand granulation: water cooling and solidification, low equipment cost, easy operation

Air-cooled hot cutting: avoids moisture residue, suitable for heat-sensitive materials such as PVC

Underwater pelletizing: High degree of automation, round particles, suitable for high-end modified materials