Classification of Plastic Recycling Equipment: The Roles of Crushers, Granulators, And Washing Lines

Against the backdrop of global "plastic bans" and circular economy policies, the plastic recycling industry is experiencing rapid growth. An efficient plastic recycling production line often consists of multiple pieces of equipment working together, with crushers, granulators, and washing lines known as the "three core devices." This article will detailedly explain the specific functions, applicable scenarios, and technical characteristics of these three types of equipment to help industry practitioners clarify equipment selection directions.

1. Crushers: The "First Line of Defense" in Plastic Recycling

Core Function: Break large or irregular waste plastics into uniform small pieces, clearing obstacles for subsequent processing.

Plastic waste comes in various forms - from complete PET bottles, large plastic sheets, to tangled films, automobile bumpers and other large products. If directly entering subsequent processes, the processing efficiency will be low due to their large volume. The emergence of crushers is precisely to solve this problem.

Working Principle: Through two or more sets of relatively rotating knives (blade material is mostly high-hardness alloy), the materials are sheared, torn and extruded, and finally broken into 5-10 cm fragments. According to different knife designs, it can be divided into single-shaft crushers, double-shaft crushers and four-shaft crushers:

• Single-shaft crushers: Suitable for processing flexible materials such as films and woven bags, with high knife speed and fast crushing efficiency;

• Double-shaft crushers: Generate strong biting force through the rotation of two shafts, can process hard materials such as thick-walled      pipes and plastic barrels, and the crushed particles are more uniform;

• Four-shaft crushers: Multi-shaft collaborative work, suitable for ultra-high hardness or mixed materials (such as plastic parts containing metal impurities), with higher crushing accuracy.

Key Advantages: Reduce the volume of materials (usually by 60%-80%), facilitate subsequent cleaning, transportation and granulation; at the same time, it can destroy the adhesion of pollutants on the plastic surface, improving the efficiency of the cleaning process.

2. Washing Lines: The "Core Link" Determining the Purity of Recycled Materials

Core Function: Remove oil, labels, sediment and other impurities on the surface of crushed plastics to ensure the quality of recycled materials.

Waste plastics often have a lot of pollutants attached before recycling - such as label glue on the surface of PET bottles, residual oil in edible oil barrels, and soil on agricultural films. If these impurities are not completely removed, they will directly affect the color, strength and market value of the final recycled materials. The performance of the washing line directly determines whether the recycled materials can meet different standards such as food grade and industrial grade.

Typical Composition and Division of Labor:

1.   Pre-washing tank: Remove easily falling sediment and large impurities on the surface through high-pressure water flushing;

2.   Hot washing cylinder: Add cleaning agents (such as caustic soda) and heat to 60-80°C to dissolve oil and label glue;

3.   Friction cleaning machine: Peel off stubborn stains through high-speed friction between materials;

4.   Rinsing tank: Rinse residual cleaning agents with clean water and adjust the pH value of materials;

5.   Dehydrator: Remove moisture on the surface of materials through centrifugal force (moisture content is usually reduced to below 5%) to prepare for granulation.

Technical Differences: For different raw materials, the configuration of the washing line needs to be "customized". For example, processing PET bottle flakes requires strengthening the label separation and degumming links; processing agricultural films needs to focus on sediment filtration; and medical waste plastics also need to add disinfection and sterilization modules.

3. Granulators: The "Final Step" to Achieve Plastic "Rebirth"

Core Function: Melt and plasticize the cleaned and dried plastic fragments, and process them into standardized particles to restore their processing performance.

The plastic fragments after crushing and cleaning finally need to be converted into "recycled plastic particles" commonly used in the market through granulators - this is the "ultimate product" of plastic recycling, which can be reused in injection molding, extrusion and other processing links to make new plastic products (such as pipes, films, turnover boxes, etc.).

Main Types and Characteristics:

• Single-screw granulators: Simple structure, low cost, suitable for processing high-purity single raw      materials (such as pure PE films, PP materials), with a general output of      100-500kg/h;

• Twin-screw granulators: Through the meshing and conveying of two screws, the mixing uniformity is better, and can handle scenarios of blending multiple raw materials or adding modifiers (such as filling calcium carbonate, toughening agents), with an output of up to 500-2000kg/h;

• Underwater pelletizers: Directly cool and cut the molten material with water after extrusion, the particles are round and uniform in size, suitable for the production of high-end recycled materials with high requirements on particle appearance.

Key Indicators: The temperature control during granulation (different plastics have large differences in melting points, such as PE is about 130°C, PET is about 260°C), the matching degree of screw speed and extrusion pressure will affect the density, strength and color of the particles. High-quality granulators can restore the performance of recycled materials to 80%-95% of that of virgin materials.

4. Synergistic Relationship of the Three Types of Equipment: An Indispensable "Recycling Closed Loop"

Crushers, washing lines, and granulators form the "golden triangle" of plastic recycling:

• Crushers "reduce the burden" for subsequent processes, and the crushing effect directly affects cleaning efficiency;

• Washing lines determine the "purity" of recycled materials, which is the key to accessing high-end markets;

• Granulators determine the "value" of the final product, and their process level affects the market price of particles.

In actual production, it is also necessary to match auxiliary facilities such as sorting equipment (such as color sorters, density sorters) and drying equipment according to the type of raw materials (such as PET, PE, PP, PVC, etc.) and production capacity requirements (from dozens of kilograms per hour to several tons) to form a complete recycling production line.

For example, the process of a production line for processing PET bottle flakes is:
Waste bottles → manual sorting → crusher crushing → label remover → hot washing line → dehydration and drying → granulator → PET recycled particles.