What are the causes and repair methods of the damage to the screw and barrel of the plastic extruder? (2)


Repair of the barrel The inner surface of the barrel is […]

Repair of the barrel
The inner surface of the barrel is harder than the screw, and its damage comes later than the screw. The scrap of the barrel is the increase in the inner diameter due to time wear. Its repair method 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 to a thickness of 1~2mm, and then finished to size.
3. Under normal circumstances, the homogenization section of the barrel wears faster. This section (take 5~7D length) can be trimmed by boring, and then equipped with a nitrided alloy steel bushing. The inner hole diameter refers to the screw diameter and stays Normally fit the clearance and process and prepare.
I emphasize here that the two important parts of screw and barrel, one is a slender threaded rod, and the other is a relatively small and long hole. Their machining and heat treatment processes are more complicated, and it is difficult to ensure accuracy. Therefore, whether to repair or replace these two parts after wear must be analyzed from an economic perspective. If the repair cost is lower than the cost of replacing a new screw, it is decided to repair. This is not necessarily the correct choice. The comparison between repair cost and update cost is only one aspect. In addition, it also depends on the ratio of repair cost to the time of using the screw after repair to the cost of updating and the time of using the updated screw. It is economical to adopt a scheme with a small ratio, which is the right choice.
4. Materials for screw and barrel manufacturing
The manufacturing materials of screw and barrel in imported extruder, commonly used alloy steels are 34CrAINi7 and CrMoV9. The yield strength of this material is about 900MPa. After nitriding, the hardness is above 1000HV, which is both abrasion-resistant and corrosion-resistant.
5. The impact of the working problems of the extrusion system on product quality
(1) The assembly gap between screw and barrel is too large
1. There are horizontal wrinkles;
2. The cross-section geometry and size error are large;
3. There are focal spots on the surface
4. Production decline
(2) The heating temperature of the barrel is unstable
1. The surface is rough with water lines;
2. The section size is unstable and the geometric shape error is large;
3. The product strength is not good and it is easy to be brittle;
4. There are lumps on the surface
(3) The screw speed is unstable
1. Large changes in cross-sectional dimensions;
2. There are horizontal wrinkles;
3. When the speed is too fast, the surface will be rough, brittle and hard.