Disassembly and maintenance of lab extruder
- Screw
(1) Screw disassembly: In order to adapt the extruder to different process requirements, several different screws are often installed on one extruder. Therefore, considering the need to replace the screw and repair it, when designing the structure of the transmission system, attention should be paid to the connection between the transmission part and the screw to facilitate the disassembly of the screw.
Some lab extruders are also equipped with a special screw assembly and disassembly mechanism. The long bolt used for screw disassembly is shown in the figure. When disassembling the machine, the operating procedures should be followed; when disassembling, the screw should be removed first and then the barrel; when installing, the barrel should be installed first and then the screw. The following points should be noted when disassembling the screw:
① Confirm that the material in the barrel is completely melted, remove the head and pull out the screw. For a general single-screw extruder, the screw cooling water inlet and outlet rotary joints can be removed first (the screw needs to be cooled), and then a copper rod can be used from one side of the reducer through the gear transmission hollow shaft to the tail of the screw, and the copper rod can be hit with a hammer to gradually push the screw out of the barrel, or a special tool can be used to push the screw out. For twin-screw extruders, special tools are required to pull out both screws at the same time.
② During the process of pulling out the screw, the screw should be prevented from deformation and bruising. The steel wire rope used should be covered with a rubber hose. Operators should pay attention to safety and avoid being burned.
③ Clean the material on the surface of the screw. The tools used in the cleaning process are copper tools or bamboo tools, etc. It is not allowed to use tools such as steel materials to knock.
④ Measure the outer diameter of the screw. Generally, the wear does not exceed the allowable limit.
⑤ For screws that have been running for a long time, non-destructive detection inspection can be carried out when necessary.
(2) Cleaning and maintenance of the screw: After the screw is pulled out, place it on a flat ground and use a copper wire brush to remove the residual material on the screw. Use a release agent or mineral oil when cleaning to make the cleaning work faster and more thorough. After cleaning, observe the wear of the screw. For small scars, use sandpaper or oilstone to polish it smooth. For obvious scars, the cause should be found out. When the screw cools down to room temperature, wipe off the dirt on the screw surface with solvent, carefully observe the surface quality of the screw ribs and screw grooves, then measure the basic parameters of the screw and analyze the wear of the screw.
(3) Precautions for screw maintenance:
① When the material cools in the screw groove, it must not be forcibly peeled off, otherwise the screw surface (surface chrome plating, surface roughness) may be damaged.
② Only bamboo or copper materials can be used to clean the screw. When using solvent to clean the screw, be careful of the solvent contacting the human skin to avoid injury.
③ When the screw is not used for a long time, it should be coated with anti-rust oil on the surface and wrapped, and hung vertically.
2. Disassembly and maintenance of the barrel
(1) Clean the inner surface of the barrel and check the inner surface wear and scratches.
(2) The horizontal deviation of the front and rear ends of the barrel should not exceed 0.05mm/m, and the tilt direction should be consistent.
(3) When assembling the barrel, the flange bolts should be tightened and hot-tightened. If necessary, perform non-destructive testing or replace the bolts.
3. Filter replacement device
(1) Disassemble, inspect, repair and replace the filter.
(2) The mechanism is flexible, the stroke is moderate, there is sufficient clamping force between the barrel and the head flange, and the filter plate and the barrel have appropriate assembly tolerances.
(3) The surface of the inner wall of the hydraulic cylinder (or cylinder) is smooth. If the seal is severely worn and leaks oil (or air), it should be replaced.
(4) Disassemble and inspect the hydraulic oil pump.
4. Repair of the barrel
The inner surface hardness of the barrel is higher than that of the screw. Generally, the condition of the barrel is less than the wear of the screw. First, based on the wear of the barrel, decide whether it is worth grinding the inner hole of the barrel. Generally, when the wear of the barrel does not exceed 0.5mm, you can consider finishing. Its repair method is as follows.
(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 size, and then a new screw can be prepared according to this diameter.
(2) The inner diameter of the barrel is machined and recast with alloy, with a thickness of 1~2mm, and then fine-machined to the required size.
(3) In general, the homogenization section of the barrel wears faster. This section (5~7D long) can be bored and trimmed, and then matched with a nitrided alloy steel bushing. The inner hole diameter refers to the screw diameter, leaving a normal matching clearance for processing and preparation.
