What is the clearance between screw and barrel?

Jun 12,2024

The clearance between the screw and the barrel in a screw extruder (commonly used in plastic processing, injection molding, and extrusion) is a critical parameter that affects the efficiency and quality of the extrusion process. The clearance is the small gap between the outer diameter of the screw and the inner diameter of the barrel.



Typical Clearances


General Guidelines:

For most extrusion processes, the clearance is typically in the range of 0.001 to 0.002 times the screw diameter.
For example, if the screw diameter is 100 mm, the clearance would typically be between 0.1 mm and 0.2 mm.

Injection Molding Machines:

The clearance can be slightly tighter, often ranging from 0.001 to 0.003 times the screw diameter.
This tight clearance ensures better control over the material being processed, which is critical for producing high-quality molded parts.

Factors Affecting Clearance:

Material Type: Different materials require different clearances due to their varying flow characteristics and thermal expansion properties.
Wear and Tear: Over time, the screw and barrel wear down, increasing the clearance. Regular maintenance and replacement of parts are necessary to maintain optimal clearance.
Operating Conditions: High pressures and temperatures can affect the clearance due to thermal expansion.



Importance of Proper Clearance


Efficient Melting and Mixing: Proper clearance ensures efficient melting, mixing, and conveying of the material.

Minimized Leakage: Too large a clearance can lead to material leakage, reducing the efficiency of the process.

Reduced Wear: An optimal clearance minimizes wear and tear on both the screw and the barrel, extending their operational life.

Quality of Output: Consistent and optimal clearance helps in maintaining the quality of the extruded or molded product, ensuring uniformity and reducing defects.



Maintaining the correct clearance between the screw and barrel is crucial for the performance and longevity of the extrusion or injection molding equipment, as well as for the quality of the processed material. Regular inspection and maintenance are essential to ensure that the clearance remains within the recommended range.

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