What problems will the twin-screw extruder cause if it is not cleaned for a long time?
The twin-screw extruder is the main machine in the field of blending, and its superior performance and customizability are its advantages in this position. It can combine different additives and fillers to achieve different particle shapes and properties with different properties.
While a variety of additives and fillers can be processed for extrusion, certain methods of obtaining these products can also lead to contamination issues and low flow or low pressure in many areas throughout the barrel.
In a continuous process like extrusion, contamination can have a detrimental effect. Purge in extrusion tends to be more challenging compared to other processes, and a twin-screw extruder presents a greater challenge because the system is more complex than a single-screw extruder.
How to clean the twin screw extruder, what are the methods?
Let’s take a look at the cleaning methods of the twin-screw extruder.
1. Resin cleaning
Use polyester resin or epoxy resin for cleaning, which is generally used for cleaning new equipment or after the extruder has been used for a period of time. This method can be used when part of the material remains on the screw or screw barrel to gel, the extrusion speed of the material is slow, and the color difference of the color-changing varieties is large. Today, with the highly developed commodity economy, there are many kinds of screw cleaners (screw cleaning materials) on the market, most of which are expensive and have different effects.
Whether to use commercial detergents depends on different manufacturers and production conditions; Plastic processing enterprises can also use different resins as screw cleaning materials according to their own production conditions, which can save a lot of money for the unit.
The first step in cleaning the screw is to turn off the feeding plug, that is, close the feeding port at the bottom of the hopper; Then reduce the screw speed to 15-25r/min, and maintain this speed until the melt flow at the front end of the die stops flowing. The temperature of all heated zones of the barrel should be set at 200°C. Cleaning begins as soon as the barrel reaches this temperature.
Depending on the extrusion process (the die may need to be removed to reduce the risk of excessive pressure at the front of the extruder), cleaning must be done by one person: The operator observes the screw speed and torque from the control panel, and also observes the extrusion pressure to ensure that the system pressure is not too high. During the whole process, the screw speed should be kept within 20r/min. In low pressure die applications, do not remove the die for cleaning first. Immediately when the extrudate was completely converted from process resin to clean resin, the machine was stopped and the die was removed, followed by restarting the screw (within 10 r/min) to allow the remaining clean resin to flow out.
1. Manually add the washing machine material from the feeding port until the color of the extruded strip is the same as that of the washing machine material pellets, stop feeding, empty the material, and stop the screw rotation of the twin-screw extruder;
2. Open the die head of the screw extruder and start cleaning;
3. Rotate the screw of the twin-screw extruder and take out the orifice plate, discharge the residual washing material in the barrel, and clean the orifice plate;
4. Stop and pull out the screw to observe whether it is cleaned, and manually remove the residual material on the screw. Reinstall the screw; add new material to flush the residual washing material in the barrel, and stop the rotation of the screw;
5. Install the orifice plate and die head of the twin-screw extruder to complete the cleaning operation of the twin-screw extruder.
2. Fire cleaning
Using fire or fire to remove the plastic fixed on the screw is the most common and effective method for plastic processing units. Immediately after the screw is used, a blowtorch is used to clean it. Since the screw has heat in the processing experience at this time, the heat distribution of the screw is still uniform. But never use an acetylene flame to clean the screw. The temperature of acetylene flame can reach 3000°C. Cleaning the screw with acetylene flame will not only destroy the metal characteristics of the screw, but also significantly affect the mechanical tolerance of the screw.
If the acetylene flame turns into a persistent blue color when baking a certain part of the screw, it means that the metal structure of this part of the screw has changed, which will result in reduced wear resistance of the site, and even delamination of the anti-wear layer from the base metal. In addition, the local heating of the acetylene flame will also cause overheating of one side of the screw, which will cause the screw to bend. Most screws are made of 4140.H.T. steel with very tight tolerances, generally within 0.03mm.
The straightness of the screw is mostly within 0.01mm. When the screw is baked and cooled by the acetylene flame, it is usually difficult to return to the original straightness. Correct and effective method: use a blowtorch to clean the screw immediately after use. Because the screw has heat during processing at this time, the heat distribution of the screw is still uniform.
3. Water cleaning
Screw washing; The fully automatic screw washing machine utilizes the kinetic energy of hydraulic rotation and cooperates with the reaction force of screw rotation to achieve 360-degree peeling without dead ends. It has high working efficiency and does not damage the physical structure of the screw. It is suitable for forced peeling and removal of various polymer materials, so it is a green processing technology with good cleaning effect.
What are the suggestions for the maintenance of the machine after use?
The twin-screw extruder requires necessary daily maintenance and regular maintenance in daily use. During the operation of the twin-screw extruder, it is necessary to maintain and maintain the extruder according to certain technical performance, which is not only conducive to the operation of the twin-screw extruder equipment, but also can effectively ensure the safety of the equipment and personnel. The screw extrusion system is maintained in two ways: daily maintenance and regular maintenance:
Common sense of daily maintenance of twin-screw extruder
1. Routine maintenance is a regular routine work, which does not account for the operating hours of the equipment, and is usually completed during driving. Mainly clean the machine, lubricate the moving parts, fasten the loose threaded parts, check and adjust the motor, control instruments, working parts and pipelines in time.
2. The screw is only allowed to start at low speed, and the idling time should not exceed 3 minutes.
3. After the machine is used for a period of time, an inspection should be made to check the tightness of all screws.
4. When opening the barrel cover or the air extraction cover, be careful to prevent foreign objects from falling into the host.
5. After the extruder has been used for 500 hours, there will be iron filings or other impurities from the gear grinding in the gear box. Therefore, the gear should be cleaned and the gear box lubricating oil should be replaced.
6. If the steering fullness of the instrument and pointer is found, check whether the contact between the thermocouple and other side lines is good.
7. No sundries are allowed in the material, and hard objects such as metal and sand are strictly prohibited from entering the hopper and extruder.
8. In case of power failure during production, the main drive and heating stop. When the power supply is restored, it is necessary to reheat each section of the barrel to the specified temperature and keep it warm for a period of time before starting the extruder.
9. There must be enough time for preheating and heating up, and the manual cranking should be brisk before driving. Generally, it should be kept at a constant temperature for 2 hours after reaching the process set temperature.
10. Designate a person to be responsible for equipment maintenance. And the detailed records of each maintenance and repair are listed in the factory equipment management file.
Regular maintenance of twin-screw extruder
1. Regular maintenance is generally carried out after the extruder runs continuously for 2500-5000 hours. The machine needs to be disassembled to check, measure and identify the wear of main parts, replace the parts that have reached the specified wear limit, and repair the damaged parts.
2. It is not allowed to run empty, so as to avoid rolling of the screw and barrel.
3. If abnormal sound occurs when the extruder is running, it should be stopped immediately for inspection or repair.
4. Strictly prevent metal or other sundries 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 part or a magnetic frame can be installed at the feeding port of the material entering the barrel, to prevent the debris from falling into the material, the material must be sieved in advance.
5. Pay attention to the cleanliness of the production environment, and do not allow garbage impurities to be mixed 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. When the extruder needs to be stopped for a long time, anti-rust grease should be applied to the working surfaces of the screw, barrel and head. The small screw should be suspended in the air or placed in a special wooden box, and should be leveled with a wooden block to prevent the screw from being deformed or bruised.
7. Regularly calibrate the temperature control instrument to check the correctness of its adjustment and the sensitivity of the control.
8. The maintenance of the reducer of the extruder is the same as that of the general standard reducer. It is mainly to check the wear and failure of gears, bearings, etc. The gearbox should use the lubricating oil specified in the machine manual, and add the oil according to the specified oil level. Too little oil, insufficient lubrication, reducing the service life of parts; Excessive oil, high heat, high energy consumption, easy deterioration of oil, also make lubrication failure, resulting in damage to parts. The oil leakage part of the gearbox should be replaced in time to ensure the amount of lubricating oil.
9. The inner wall of the cooling water pipe attached to the extruder is easy to scale and the outside is easy to corrode and rust. Careful inspection should be done during maintenance. Excessive scale will block the pipeline, and the cooling effect will not be achieved. If the rust is serious, water will leak. Therefore, scale removal and anti-corrosion cooling measures must be taken during maintenance.
10. For the DC motor that drives the screw to rotate, it is necessary to focus on checking the wear and contact of the brushes. It should also be frequently measured whether the insulation resistance value of the motor is above the specified value. In addition, check whether the connecting wire and other parts are rusted, and take protective measures.
11. Designate a person to be responsible for equipment maintenance. And the detailed records of each maintenance and repair are listed in the factory equipment management file.
Kairong Group, headquartered in Nanjing, China, is a global manufacturing and trading company in the field of high-performance plastics and rubber processing equipment, extrusion solutions, masterbatch, and compounding, etc.
Its unit Nanjing Haisi Extrusion Company is a professional manufacturer of twin screw extruder, single screw extruder, two stage extruder,equipment for dryer and its related auxiaries. We tailor solutions from raw materials, materials processing equipment, to injection for different customers.
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