Causes of problems with screw barrels and some treatment methods

Update:25 Oct 2021

There are probably several reasons:
1. Too much regrind is added to the plastic.
2. The screw and barrel are covered with glue-the plastic wraps the screw and rotates together.
3. The screw and the barrel are worn out, or the abrasion of the rubber ring causes the plastic to leak and not be transported to the front end of the barrel.
4. Inaccurate temperature control, the temperature of the rear end of the barrel is too high, adjust the temperature setting, and check whether the cooling water circuit is blocked.
5. The feeding port of the barrel is blocked. Check whether there is any melted plastic block sticking here.
6. The plastic particles are too large, causing bridging, and the plastic can be crushed again.
7. Too much oil is added to the plastic, causing the screw to slip.
8. If the newly replaced screw does not feed, it may be that the design of the screw and barrel discharge port is not appropriate. For the screw, the screw groove of the feeding section of the screw barrel is too shallow, which causes the screw to not drive the plastic forward when it rotates. The conveying, or the conveying amount of material is very small; for the barrel, it is the design of the discharge port.

Solution:
Because the twin screw is a hungry extrusion, the phenomenon of unfeeding is rarely seen. The following methods are more commonly used: set an eccentric feeding port, use a large pitch and deep groove threaded element (SK) in the feeding section, and ensure that the joint cylinder is often cooled. The feeding is smooth, and for some difficult feeding, a forced feeding device can be added. According to your situation, the main reason is that the pitch is too small, and you should consider replacing the larger pitch component.

The repair method of screw barrel is as follows:
1. For the barrel with increased diameter due to wear, if there is a certain nitriding layer, the inner hole of the barrel can be directly bored and ground to a new diameter size, and then a new screw can be prepared according to this diameter.
2. The inner diameter of the barrel is machined and trimmed to re-cast the alloy, the thickness is between 1~2mm, and then finished to size.
3. Under normal circumstances, the homogenization section of the barrel wears quickly. This section (take 5~7D long) can be trimmed by boring, and then equipped with a nitrided alloy steel bushing. The diameter of the inner hole refers to the diameter of the screw. Normally fit the clearance, and carry out processing and preparation.

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