A Guide to Extruder Cleaning While Preventing Viscous Aging in Unexpected Situations!

There are many cleaning methods for extruders, and the following can usually be used:

Resin cleaning method

This method is done with a resin, such as a polyester resin or epoxy resin cleaner (professional cleaning resins are preferred). This method is generally used in the cleaning machine or extruder of the new equipment after a period of use, because part of the material remains on the screw or screw barrel gelatinization, the material extrusion speed slows down, and the color difference of the color change variety is large, this method can be adopted. After the resin is cleaned, the resin to be produced is used to add appropriate external lubrication and calcium powder to further clean the machine, and when the extrudate is considered clean, it can be officially put into production.

extruder

Non-resin cleaning method

This method is to use rice, corn, sawdust, toilet paper and other substances that have a certain friction force and are easy to crush, when the extruder is heated to the normal extrusion temperature, the friction between these substances and the screw and the screw barrel is used to remove the resin gelatinous matter attached to the surface of the screw and the screw barrel. Experience shows that the husk of rice has high hardness and great friction, and the effect of cleaning machine is more ideal in comparison. After cleaning the machine with this method, it is necessary to open the screw barrel to check the cleaning situation, and under normal circumstances, it is necessary to clean the machine with the resin cleaning material formula according to the above method before the production of formal products can be carried out.

Dismantling the screw and the screw barrel manual cleaning method

This method is to heat the extruder to the working temperature, and then use the manual or automatic ejection method to push out the screw to remove the material that is easy to remove while it is hot. After cooling, it is soaked in an organic solvent tank filled with acetone or cyclohexanone, and when the molten adherent attached to the screw swells, the adhesion is removed manually. The soaking time of the screw depends on the amount of buildup and the thickness of the gelatin. In order to reduce the use of solvents and facilitate the sealing of the container, it is sufficient to use a steel or stainless steel pipe that is slightly thicker than the diameter of the screw, and weld the seal at one end as a soaking tank. From the safety point of view, the container of the soaking screw must be stored in a cool, away from fire and power supply, and at the same time seal the mouth to prevent the solvent from volatilizing, and affix the safety mark.

If it is necessary to clean the machine thoroughly, the screw can also be opened while it is hot, and the gelatinization attached to the inner wall of the screw can be removed by manual method or solvent rubbing.

In order not to damage the surface finish of the screw and screw, you can only use something soft than the steel of the screw and the screw to remove the attachment with something like a hacksaw blade or copper brush, so as not to damage the screw and screw. Because the formula in the extruder stays in the extruder for a long time, it is easy to plasticize the gel and the extruder cannot be started. The standard of resin feeding amount is to ensure that all the powder coating materials retained inside the screw barrel can be pushed out of the screw barrel. In terms of the degree of removal of the extruded material, it is basically based on the fact that the color of the original product cannot be seen or there is no paste.

screw

When the extruder is used to start production, the material retained in the extruder is pushed out with the pre-mixed material according to strict procedures, and the extruded material can be used as a formal product only after the launch is confirmed to be clean.

When the extruder suddenly fails to power during normal operation, if the material inside the extruder barrel is not discharged out of the outside in time, the gel plastic will enter the viscos flow state, resulting in the inability to start the machine, and the materials in the extruder barrel need to be heated with electric heating or gas welding guns and other tools at high temperature, which is easy to damage the equipment. Therefore, after the power failure, the main engine switch of the extruder should be turned off immediately, and the extruder motor should be manually rotated with a handpan belt or a rocker rod to discharge the internal materials of the extruder as much as possible so that the residue in the screw barrel is minimal.

If the main motor of some extruders is directly connected to the gearbox, and there is no device for rocker to rotate the motor, the cooling water of the cooling system can also be increased to make the temperature of the extruder screw barrel and screw quickly cool down, so as to prevent the plasticizing viscosity aging of the material in the extruder.

Here are the specific cleanup tools and preparation steps:

1. Choose the right heating device

Burning or roasting to remove the plastic from the screw is the most common and effective method for plastic processing units, but acetylene flame should never be used to clean the screw. Acetylene flame temperatures can reach 3000°C, and cleaning the screw with acetylene flame will not only destroy the metal properties of the screw, but also significantly affect the mechanical tolerance of the screw.

If the acetylene flame turns a persistent blue color when baking a part of the screw, it means that the metal structure of that part of the screw has changed, which will lead to a decrease in the wear resistance of the part, and even the detachment of the anti-wear layer from the base metal. In addition, local heating with an acetylene flame can also cause one side of the screw to overheat, resulting in bending of the screw. Most screws use 4140. Made of H.T. steel, the tolerance is very tight, generally within 0.03mm.

The straightness of the screw is mostly within 0.01mm, and it is usually difficult to return to the original straightness when the screw is baked and cooled by acetylene flame. Correct and effective method: Clean the screw with a blowtorch immediately after use. Because the The screw has the heat in the machining process, the heat distribution of the screw is still uniform.

2. Choose the right detergent

Today, with the highly developed commodity economy, there is no shortage of all kinds of screw cleaners (screw cleaning materials) on the market, most of which are expensive and have different results. Whether to use commercial detergents depends on different manufacturers and production conditions ; Plastic processing enterprises can also use different resins to make screw cleaning materials according to their own production conditions, which can save a lot of money for the unit.

3. Choose the right cleaning method

The first step in cleaning the screw is to turn off the feeding plug plate, that is, to close the discharge port at the bottom of the hopper; The screw speed is then reduced to 15-25 r/min and this speed is maintained until the melt flow at the tip of the die stops. The temperature of all heating zones of the barrel should be set at 200°C. Once the barrel reaches this temperature, cleaning begins immediately.

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, as well as 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 the application of low-pressure dies, do not remove the die head for cleaning in the first place. Stop the machine and remove the die as soon as the extrudate is completely converted from the processing resin to the cleaning resin, and then restart the screw (within 10 r/min) so that the residual cleaning resin can flow out.

extruder

Cleanup steps

Cleaning the barrel is much easier than cleaning the screw, but it is also very important.

  1. When preparing the barrel for cleaning, the barrel temperature is also set at 200°C.
  2. Screw the drill pipe and electric drill with a round steel brush as a cleaning tool, and then wrap the steel brush with copper wire mesh.
  3. Before inserting the cleaning tool into the barrel, sprinkle some stearic acid into the barrel, or sprinkle stearic acid on the copper wire mesh of the cleaning tool;
  4. When the copper wire mesh enters the barrel, start the electric drill to rotate it, and at the same time artificially make it move back and forth until this forward and backward movement becomes no resistance;
  5. After the copper wire mesh is removed from the barrel, use a bundle of cotton cloth to wipe back and forth in the barrel to remove any cleaning resin or residue of fatty acid; After several such wipes back and forth, the barrel is cleaned. Thoroughly cleaned screws and barrels are ready to be assembled for the next production!

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