The preventive maintenance of injection molding machine screw barrel
Excessive wear will cause serious loss to processors. The excessive clearance between the screw thread and the cylinder surface will affect the performance, efficiency and energy consumption of the machine. In extrusion, wear may result in lower extrusion of the extruder screw barrel and hence higher screw speeds and energy requirements. At the same time, this is usually accompanied by higher melting temperatures and more quality problems.
Careful inspection of key screw / cylinder clearances by a good PM plan ensures maximum processing extrusion and no unscheduled downtime. The PM program becomes more important when producing components of high quality, such as the manufacture of medical catheters and components for medical devices.
The test procedure is to pull the screw out and clean it thoroughly, while checking the outer diameter (OD) of the screw and the inner diameter of the cylinder (ID) by heat. The plastic material on the surface of the screw and barrel can be removed by wire brush and copper wire mesh. Precision wear measuring instruments are available for accurate measurement and easy to use, with a wide range of specifications and functions to choose from.
First, remove the plastic from the barrel, then insert an electronic aperture meter into the cylinder and read the ID data at each measuring position. The screw thread diameter and depth can be measured by the micrometer thread, and tester digital models provide LCD readout, recording data to a computer.
Regular measurements are required to predict when the screw or cylinder will need to be replaced or repaired, and the downtime scheduled at an advantageous time. For a pair of new screw and barrel sizes of 5.08cm, the recommended clearance range is 0.01016 to 0.01524cm.
One rule of thumb is that the gap between the screw and the cylinder is generally 1/1000 of the dimension. The screws shall be reassembled when the maximum clearance is allowed. With respect to complete replacement, the repair service enables the wearing parts to be re put into use at lower cost. In addition, the injection machine screw barrel can be replaced in the wearing part of the liner, and the extruder cylinder is usually replaced by the entire bushing, so the cost of maintenance is more expensive, so as not to cost effectiveness.
Once the screw is worn at a certain point, the melt will return to the thread, leading to further wear of the screw and barrel. Severe wear can cause a large amount of resin to be wasted and reduce productivity. However, severe wear can be prevented by regular PM testing. The best maintenance strategy is to keep the screw / cylinder clearance within a reasonable range.

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