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Recycled plastic granulation technology
After waste plastics are thoroughly cleaned and dried, they are typically processed into pellets based on the specific characteristics of the resin and the molding conditions prior to forming. This granulation process can be broadly categorized into two main types: cold-cut granulation and hot-cut granulation. Different plastic varieties often require distinct granulation methods, and even the same type of plastic may employ various granulation techniques depending on the molding equipment and process used.
1. **Cold Cut Granulation of Sheets and Strands**: In this method, the molten plastic is either extruded as strands using an extruder or shaped into sheets via a two-roll mill. These strands or sheets are then cooled in a water tank, dehydrated, and fed into a pelletizer at a controlled speed. The traction speed usually doesn’t exceed 60 to 70 meters per minute, with no more than 40 strands being processed simultaneously. The length of the resulting pellets depends on both the pulling and feeding speeds. Quality checks for the granulation, including surface quality, gloss, color, and air bubble presence, can be conducted continuously during the process. A key advantage of this method is its simplicity in operation, with pellets that rarely stick together. However, it requires a relatively large operational space.
**Pelletization Methods**:
| Pelletization Method | Yield (kg/h) | Applicable Materials | Pellet Diameter (mm) | Length (mm) | Pellet Shape | Main Features |
|----------------------|--------------|----------------------|----------------------|-------------|--------------|---------------|
| Cold Cut Granulation - Sheet | 5~1000 | PE, PP, ABS, PVC, PA, etc. | 1~6 | 1~6 | Cubes | Easy to start, but poor cutting shape and pellet flowability. |
| Cold Cut Granulation - Cylinder | 5~1000 | PE, PP, ABS, PS, PA, etc. | 1~6 | 1~6 | Cylinder | Suitable for multiple resins, high output, no need for post-drying. |
| Hot-Cut Pelletizing - Center Pelletizing Air-Cooled | 20~100 | PE, PP, etc. | 4~6 | 1~2.5 | Cylinder | Easy operation, good pellet shape, low pelletizing power, limited to PVC or high-viscosity materials. |
| Hot-Cut Pelletizing - Center Cut Granular Water-Cooled | 20~600 | PE, etc. | 2.5~6 | 1~3 | Gogo-shaped cylinder | Prone to pellet splicing, simple operation, good working environment. |
| Hot-Cut Pelletizing - Eccentric Pellet Water Cooling | 20~3000 | PE, etc. | 2~6 | 1~3 | Chess piece cylinder | Small head size, high yield, larger cutter, milling tooth ring cutter. |
| Hot-Cut Pelletizing - Water Ring Pellets | 500 to 5000 | Almost all thermoplastics | 1.5~6 | 1~3 | Go pellets | High-volume applications, suitable for all thermoplastic materials. |
In summary, the choice of granulation method largely depends on the specific requirements of the plastic being processed and the desired end product. Each method offers unique advantages and limitations, making it crucial to select the most appropriate technique for the intended application.