Maintenance And Repair of Extruder Screws And Barrels

Since its introduction, twin-screw extruders have been widely used in the field of plastic modification and are the core equipment in the field of modification. Every modification factory takes good care of the twin-screw extruder, but in daily work, it is inevitable to encounter equipment loss and repair. So in order to avoid or reduce loss, how to repair it after a failure, the editor will introduce to you some tips on extruder maintenance and repair.

1. Maintenance of twin screw extruder

In order to ensure the safe and stable production of the twin-screw extruder and extend its service life, it is necessary to strengthen the maintenance of the twin-screw extruder. The basic contents are as follows:

Maintenance during equipment operation

No foreign matter is allowed to be carried in the material, and hard materials such as metal and sand are strictly prohibited from entering the hopper and barrel. When opening the vacuum chamber cover, foreign matter should be prevented from falling into the barrel. The extruder should be kept warm for a sufficient time after heating up, and should be turned lightly before starting. The screw is only allowed to start at a low speed, and the idling time should not exceed 2 minutes. The feeder should gradually increase its speed only after feeding in a hungry manner.

Daily maintenance of host

The engine oil and lubricating oil should be replaced after every 4000 hours of operation. If the main motor is a DC motor, the motor carbon brushes should be checked once a month and records should be kept. The carbon brushes should be replaced when necessary; the electric control cabinet should be purged once a month, and the wear of the screw and barrel should be checked every quarter and records should be kept; the gears, bearings and oil seals of the gearbox should be checked once a year; when the machine is shut down for a long time, anti-rust and anti-fouling treatments should be carried out.

2. Repair of twin screw extruder

Causes of damage to the screw and barrel

① The screw rotates in the barrel, and the friction between the material and the two causes the working surfaces of the screw and the barrel to gradually wear: the screw diameter gradually decreases, and the inner diameter of the barrel gradually increases. In this way, the matching diameter gap between the screw and the barrel increases little by little as the two gradually wear. However, since the resistance of the head and the diverter plate in front of the barrel has not changed, this increases the leakage flow of the extruded material when it moves forward, that is, the flow of the material from the diameter gap to the feed direction increases. As a result, the production of the extruder decreases. This phenomenon also increases the residence time of the material in the barrel, causing the material to decompose. In the case of polyethylene, the hydrogen chloride gas produced by the decomposition strengthens the corrosion of the screw and the barrel.

② Fillers such as calcium carbonate and glass fiber in the material can accelerate the wear of the screw and barrel.

③ Because the material is not plasticized evenly, or metal foreign matter is mixed into the material, the torque of the screw suddenly increases, and this torque exceeds the strength limit of the screw, causing the screw to break. This is an unconventional accident damage.

Screw repair

1. The broken screw should be considered according to the actual inner diameter of the barrel, and the outer diameter deviation of the new screw should be given according to the normal clearance with the barrel for manufacturing.

2. After the thread surface of the worn screw is treated and thermally sprayed with a wear-resistant alloy, it is then ground to size. This method is generally processed and repaired by a professional spraying factory, and the cost is relatively low.

3. Overlay wear-resistant alloy on the threaded part of the worn screw. Overlay 1~2mm thick according to the degree of wear of the screw, and then grind the screw to size. This wear-resistant alloy is composed of materials such as C, Cr, Vi, Co, W and B, which increases the wear and corrosion resistance of the screw. Professional overlay welding factories charge a high fee for this processing, and it is rarely used except for screws with special requirements.

4. The repair screw can also be repaired by hard chrome plating. Chromium is also a wear-resistant and corrosion-resistant metal, but the hard chromium layer is easier to fall off.

Barrel repair

The inner surface hardness of the barrel is higher than that of the screw, and its damage comes later than that of the screw. The scrapping of the barrel is when the inner diameter increases due to wear and tear over time. Its repair methods include:

1. For barrels with increased diameter due to wear, if there is still a certain nitriding layer, the inner hole of the barrel can be directly bored and ground to a new diameter, and then a new screw can be prepared according to this diameter.

2. The inner diameter of the barrel is machined and re-cast with alloy, the thickness is between 1~2mm, and then fine-machined to size.

3. In general, the homogenizing section of the barrel wears out quickly. This section (5~7D long) can be repaired by boring and then equipped with a nitrided alloy steel bushing. The inner hole diameter refers to the screw diameter, leaving a normal matching clearance for processing and preparation.

Here is a small tip for everyone, the screw and barrel are two important parts, one is a slender threaded rod, and the other is a small diameter and long hole. Their machining and heat treatment processes are relatively complicated, and it is difficult to ensure the accuracy. Therefore, whether to repair or replace the two parts after wear and tear must be fully analyzed from an economic perspective.

If the cost of repair is lower than that of replacing a new screw, it is not necessarily the right choice to repair it. The comparison between the cost of repair and the cost of renewal is only one aspect. In addition, the ratio of the cost of repair and the time of using the screw after repair to the cost of renewal and the time of using the renewed screw should also be considered. The solution with a smaller ratio is economical and is the right choice.

NANJING HAISI is professional manufacturer of screw and barrel for extruder, we supply Twin Screw Extruder, Single Screw Extruder, Plastic Recycling Extruder, Two Stage Extruder, Lab Scale Extruder, Mixing and Feeding Machine, Cooling and Pelletizing Machine, Crushing Machine and so on.