Preventive maintenance for screw barrels of injection molding machines

Excessive wear can cause serious losses to processors. Excessive clearance between the screw thread and the barrel surface will affect the performance, efficiency and energy consumption of the machine. In extrusion, the occurrence of wear may make the extrusion of the extruder screw barrel lower, so it requires higher screw speed and energy consumption. At the same time, this is usually accompanied by higher melting temperatures and more quality issues.

Through a good PM plan, careful inspection of critical screw / barrel clearances can ensure maximum processing extrusions without unplanned downtime. PM plans become even more important when producing quality-critical components, such as producing medical catheters and components for medical devices.

The detection process is to pull out the screw and thoroughly clean it, while checking the outer diameter (OD) of the thread and the inner diameter (ID) of the barrel while hot. The plastic material on the surface of the screw and barrel can be removed with a wire brush and copper wire mesh. Precision abrasion measuring instruments enable accurate measurements and are easy to use, with a variety of specifications and functions to choose from.

First, remove the plastic from the barrel, then insert an electronic aperture gauge into the barrel and read the ID data at each measurement position. The diameter and depth of the screw thread can be measured by a micrometer, and the digital tester provides LCD readings to record the data to a computer.

In order to be able to predict when the screw or barrel will need to be replaced or repaired and to schedule downtime at an advantageous time, regular measurements are required. For a new pair of screws and barrels with a size of 5.08cm, the recommended clearance range is 0.01016 to 0.01524cm.

A rule of thumb is that the reasonable clearance between screw and barrel is generally 1/1000 of the size. When the maximum allowable clearance is exceeded, the screw should be reassembled. Compared to complete replacement, repair services can bring worn parts back into service at a lower cost. In addition, the screw barrel of the injection molding machine can replace the bushing in the worn part, while the extruder barrel usually replaces the entire bushing, so the maintenance cost is more expensive and not cost effective.

Once the screw is worn at a certain point, the melt will return to the thread, causing further wear on the screw and barrel. Severe abrasion can result in a significant amount of resin being wasted and reduced productivity. However, through regular PM inspection, severe wear can be prevented. The best maintenance strategy is to keep the screw / barrel clearance within a reasonable range.