How to Do Preventive Maintenance for the Screw and Barrel?

Excessive wear can cause serious losses to processors. Excessive gaps between the screw threads of the extruder and the surface of the extruder barrel will affect the performance, power and power consumption of the machine. In extrusion, the generation of abrasion may make the extrusion volume of the extruder screw and barrel lower, so a higher extruder screw speed and power consumption are required. At the same time, this is usually accompanied by a higher melting temperature and more quality problems.


1. The process of extruder screw inspection


After a good PM plan, careful inspection of the key extruder screw and barrel gaps can ensure a larger processing and extrusion volume, and at the same time, there will be no downtime for non-planning. When producing high-quality components, PM solutions become increasingly important, such as the production of medical catheters and components for medical devices.


The inspection process is to pull out the extruder screw and clean it thoroughly, while checking the outer diameter (OD) of the thread and the inner diameter (ID) of the barrel while it is hot. The plastic material on the surface of the extruder screw and barrel can be removed with a steel wire brush and copper wire mesh. The fine wear measuring instrument can achieve accurate measurement and is easy to use, and there are various specifications and functions to choose from.


Remove the plastic in the barrel of the extruder, then insert an electronic aperture meter into the barrel, and read the ID data at each measurement position. The thread diameter and depth of the screw can be measured by a thread micrometer. At the same time, the digital type tester provides liquid crystal readings and records the data in the computer.


2. Wear of extruder screw and barrel


In order to be able to predict when the extruder screw or barrel needs to be replaced or repaired, and to schedule the shutdown at a favorable time, timing measurements are required. For a new pair of screw and barrel with a scale of 5.08 cm. The recommended gap size is 0.01016~0.01524cm.


There is a rule that the reasonable gap between the screw and the barrel is generally 1/1000 of the scale. When the allowable large gap is exceeded, the screw should be assembled from the beginning. Compared to complete replacement, repair service can make the worn parts put into use from scratch at a lower cost. In addition, in the worn part of the screw barrel, the bushing can be replaced from the beginning, while the extruder barrel usually replaces the entire bushing, so the maintenance cost becomes more expensive, which is not cost-effective.


Once the extruder screw is worn at a certain point, the melt will return to the thread, causing the wear of the screw and barrel to further accelerate. Severe wear will cause a lot of resin to be wasted and reduce productivity. However, regular PM detection can prevent serious wear. A good maintenance strategy is to keep the gap between the screw and the barrel within a reasonable scale.

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