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Reventive protection of screw barrels of injection molding machines

Update:06 Sep 2019

Excessive wear can cause serious damage to the processo […]

Excessive wear can cause serious damage to the processor. Excessive clearance between the screw threads and the barrel surface can affect the machine's power, power and energy consumption. In extrusion, the onset of wear may result in a lower extrusion of the extruder screw barrel, thus requiring higher screw speeds and energy usage. Together, this is generally accompanied by higher melting temperatures and more quality issues.

After a good PM solution, careful inspection of the critical screw/barrel clearance ensures maximum machining throughput, and there is no non-planned downtime. PM solutions are becoming increasingly important when producing parts that are of high quality, such as medical catheters and components for medical devices.

The process of testing is to pull the screw out and thoroughly clean it together and look at the outer diameter (OD) of the thread and the inner diameter (ID) of the barrel. The plastic material on the surface of the screw and barrel can be removed with a wire brush and a copper wire mesh. The Precision Wear Measurement Instrument is accurate and easy to use, and is available in a variety of sizes and functions.

First, the plastic in the barrel is removed, and then an electronic aperture gauge is inserted into the barrel to read the ID data in each measurement orientation. The thread diameter and depth of the screw can be measured by a thread micrometer, together with the digital type of tester supplying liquid crystal readings and recording the data to a computer.

In order to be able to guess when the screw or barrel will need to be replaced or repaired, and to schedule the shutdown at a favorable moment, the demand is measured periodically. For a new pair of screws and barrels with a size of 5.08 cm, the recommended void size is 0.01016 to 0.01524 cm.

One rule of thumb is that the reasonable clearance between the screw and the barrel is typically 1/1000 of the scale. When exceeding the maximum clearance allowed, the screw should be assembled from the beginning. Compared to a complete replacement, the repair service enables the wear parts to be put into service at a lower cost. In addition, the screw barrel of the injection molding machine can replace the bushing from the head in the worn part, and the extruder barrel generally replaces the entire bushing, so the repair cost is more expensive, and then there is no cost benefit.

Once the screw is worn at a certain point, the melt returns to the thread, causing the screw and barrel to wear further. Severe wear can cause a lot of resin to be spoiled and the yield to drop. However, after periodic PM detection, the onset of severe wear can be avoided. The best protection strategy is to keep the screw/barrel gaps within a reasonable size.