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What are the solutions and avoidance methods for screw slippage in twin-screw granulator?

by:TENGDA     2022-12-15

Frequent routine work will lead to failure of the twin-screw granulator, such as too high back pressure, overheating or overcooling in the second half of the barrel, wear of the barrel or screw, improper hopper planning, etc. will cause the twin-screw granulator to malfunction. The screw slips, so what solution do we have? How can we avoid screw slipping and similar failures? Next, TENGDA Plastic Extruder Machine Manufacturers will give you a brief introduction.

The solution to the screw slippage of the twin-screw granulator:

1. The back pressure is too high: If the back pressure is set too high, the screw may not be able to generate enough pressure to transport the melt forward to overcome the back pressure of the back pressure, and the screw will rotate in a certain direction without retreating, so Will do more work on the melt and significantly increase the melt temperature, which can adversely affect the quality of the finished product and cycle time.

2. The second half of the barrel is overheated or overcooled: At the rear of the feeding section, the material forms a thin layer of molten polymer during the heating and shrinking process, and the molten film layer is attached to the barrel. If there is no such thin layer, the particles will It is difficult to transport the material forward, and the material in the feeding section must be heated to a critical temperature to form a critical molten film.

However, it is often that the residence time of the material in the barrel is too short to allow the polymer to reach this temperature. The occurrence of this situation may be due to the small scale of the equipment and the corresponding equipment with smaller barrels and screws. If the residence time is too short, it is easy to cause polymer melting or insufficient mixing, which will cause the screw to slip or stall.

3. Cylinder or screw wear: Same as the feeding section, when the resin melts in the screw compression section, it adheres to the barrel wall. When the screw rotates, the material breaks away from the barrel wall and is transported forward after being sheared. If there are wear areas on the screw and barrel, the screw will not be able to move material forward effectively.

4. Improper design of the hopper: The correct design of the hopper is the key to ensure the stable transportation of materials. Generally speaking, new pellets of uniform size work well in square hoppers with abrupt constriction zones. However, this is not the case when adding recycled materials. The shape and size of the pellets are very different by breaking again, which affects the uniformity of the feed. Incoherent feeding means that the screw cannot maintain a uniform delivery pressure on the melt, and slippage occurs.

5. When processing hygroscopic materials: Improper material drying will significantly reduce the viscosity of the material in the barrel and generate water vapor, making it difficult for the screw to transport the material forward.

6. Failure of the non-return ring: When the screw is rotating and plasticizing the material, the non-return ring should be in the front position and contact the fixed ring seat. If the non-return ring is in the backward position, or in a position between forward and rearward, the molten polymer will have resistance as it passes through the gap between the non-return ring and the ring seat. If you suspect that there is a problem with the check ring, you should replace it immediately.

How to avoid screw slippage in twin-screw granulator

The most effective way to avoid screw slippage in the twin-screw granulator is to start with its maintenance.

1. Since the electrical control system has high requirements on ambient temperature and dust prevention, the electrical system should be isolated from the production site, and ventilation or ventilation fans should be installed. It is recommended to place the electrical control cabinet in a simple room to keep the room clean and Ventilation, so that the indoor temperature is not higher than 40 ℃.

2. The extruder is not allowed to run empty, so as to prevent the screw and the machine from rolling. It is not allowed to exceed 100r/min when the host starts idling; when starting the host, first start at a low speed, check whether there is any abnormal noise after starting the host, and then slowly increase the speed of the host to within the allowable range of the process. When the new machine is running in, the current load should be 60-70%, and the current in normal use should not exceed 90%.

3. Turn on the oil pump first when starting up, and then turn off the oil pump after shutting down; the water pump keeps working during the whole production process, and the operation of the water pump cannot be stopped to avoid the decomposition and carbonization of the materials in the barrel due to the temperature rise of the barrel. The asbestos wind cover of the main motor fan needs to be Clean it frequently to avoid excessive dust adhesion to block the windshield, resulting in insufficient heat dissipation of the motor and tripping due to overheating.

4. Prevent metal or other debris from falling into the hopper, so as not to damage the screw and barrel. In order to prevent iron debris from entering the barrel, a magnetic component or a magnetic frame can be installed at the feeding port of the barrel when the material enters the barrel. To prevent debris from falling into the barrel, the material must be screened in advance.

5. Clean up the dust, tools and sundries on the surface of the unit in time. Pay attention to the cleanness of the production environment, and do not let garbage and impurities mix into the material to block the filter plate, which will affect the output and quality of the product and increase the resistance of the machine head.

6. The gearbox should use the lubricating oil specified in the machine manual, and add oil according to the specified oil level height. Too little oil will lead to insufficient lubrication, which will reduce the service life of parts; It is easy to deteriorate, and also makes the lubrication invalid, resulting in the consequence of damaging the parts. The oil leakage part of the reduction box should replace the gasket in time to ensure the amount of lubricating oil. s consequence. The oil leakage part of the reduction box should replace the gasket in time to ensure the amount of lubricating oil.

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