For extruders used in the production of thermoset powder coatings, when changing the type of coating resin or type of color, it is necessary to clean the machine to prevent interference between types of powder coatings and ensure the quality of the output. If the extruder is not cleaned properly, the most obvious effect is on the color of the powder coating, which can be directly observed. In addition, in the previous production of artistic powder paint without a leveler, the extruder was not cleaned. When reproducing high-gloss powder paints, due to the interference of previous materials, the coating film of subsequent products is prone to shrinkage and other imperfections. Therefore, it is very important to clean the machine thoroughly when changing the type of paint resin, as well as the type of design and color. There are many methods for cleaning an extruder, generally the following can be used:
This method involves cleaning the machine with a resin such as polyester or epoxy. This method is usually used when cleaning new equipment or after the extruder has been in use for some time, because some of the material remains on the screw or barrel and thickens, the extrusion speed of the material slows down, and the color difference of the color-variable grade is large. Therefore, you can use this method. After cleaning the machine of resin, use the resin to make a powder coating and then clean the machine without adding a hardener or curable resin. Once the extrudate is found clean, it can officially be put into production. If the difference in color when changing the type of powder coating is small, and the time to thoroughly clean the machine is not too long, then it is necessary to clean the machine only with the resin that will be used for the production of powder coatings. To increase resin friction and make cleaning easier, some cleaning fillers can be added.
This method uses materials such as rice, corn, sawdust, toilet paper, which have a certain friction and are easily crushed. When the extruder reaches normal extrusion temperature, friction between these materials and the screw and barrel is used to remove them. Powder gel is applied to the surface of the auger and barrel. Experience shows that the outer shell of paddy rice has high hardness and high friction, and the cleaning effect of the machine is relatively ideal in comparison. After using this method of cleaning the machine, you need to open the auger barrel to check the cleaning situation. Under normal circumstances, before starting official production, it is necessary to use powder coating resin to clean the machine according to the above method.
Manual cleaning method when disassembling the screw and barrel
This method involves heating the extruder to operating temperature and manually or automatically ejecting the screw to remove easily removable materials while it is hot. After cooling, the screw is placed in a container with an organic solvent filled with
acetone or cyclohexanone and wet it. When the melted residue stuck to the auger swells, remove it by hand. The soaking time for the auger depends on the amount of sample and the thickness of the gel. To use less solvent and make it easier
To seal the container, use steel or stainless steel pipe slightly thicker than the diameter of the auger rod, and weld a seal on one end to use as a soaking container. From a safety point of view, the capacity for
The soaking screw should be stored in a cool place, away from fire and electrical sources. At the same time, it must be sealed to prevent evaporation of the solvent, and equipped with a safety sign.
If you need to thoroughly clean the machine, you can open the auger barrel while it is hot and remove any adhesive stuck to the inside wall of the auger barrel by hand or by wiping with a solvent.
To avoid damaging the surface of the auger and barrel, do not hit them with hard objects, but use a steel saw blade or a steel brush, which is softer than the steel of the auger and barrel, to remove the attachments to avoid damaging the auger and barrel.
Because thermoset powder coating is in the extruder for a long time, it is prone to polymerization reaction and gelation, and becomes particles on the coating film when powder coating is applied. If polymerization occurs, then The extruder can't even start. . Therefore, before stopping the extruder, it is necessary to use pure non-curing resin, that is, no hardener or curable resin, to eject the powder coating materials in the extruder so that
prevent these materials from remaining in the extruder and curing reaction. The standard for the amount of resin added is to allow the powder coating material held inside the auger barrel to be pushed out of the auger barrel to
preventing the material from hardening in the extruder. Regarding the degree of removal of extruded materials, the standard is basically that the color of the original powder coating should not be visible.
When starting production with an extruder, pre-mixed material must be used to push out the clean resin remaining in the extruder according to strict procedures. After ensuring that clean resin is expelled, extruded
the material can be used as a formal product. To prevent pure resin from entering the product, which may cause deterioration in the quality of the coated film product, the pure resin and part of the mixture pushed out when cleaning the machine can be
used in pre-mixing but cannot be used in the next fine grinding stage.
When the power of the extruder is suddenly cut off during normal operation, if the material in the extruder barrel is not discharged in time, some powder paints will undergo curing reactions and gels, which will even cure strongly after a long period of time.
time, which makes it impossible to start the machine. , It is necessary to heat the material in the extruder barrel with tools such as electric heater or gas welding torch, which is easy to damage the equipment. Therefore, after disconnecting
The power supply should immediately turn off the extruder main switch, manually crank the extruder motor using a hand belt or rocker, and unload the internal materials of the extruder as much as possible to minimize residues in the screw barrel. Pure resin
pushes out some of the remaining powder coating materials. Since only the waste heat of the extruder can be used at this time, the amount of pure resin added should not be too large.
If the main motor of some extruders is directly connected to the gearbox and there is no device to rotate the motor using a rocker, then you can also increase the amount of cooling water in the cooling system to quickly cool the temperature
extruder barrel and screw and prevent extrusion. The material in the machine undergoes a chemical reaction.
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