Cleaning Screws and Barrels

Screw and barrel systems are the most sensitive parts of plastic processing machines. For this reason, cleaning and maintenance is extremely important in order for the screw and barrel to work with the precision and efficiency of the first day.

Screw and barrel must be cleaned before periodical maintenance checks during raw material changes or during long-term stops and must be kept by coating with appropriate protective oils.

Screw and barrel can be mechanically or chemically washed. In the chemical cleaning of the screw and barrel, the screw and barrel are cleaned with the help of a cleaning agent fed into the screw barrel in the system operating under normal process conditions, without being removed from the system and separated from each other. When processing sensitive polymers, chemical cleaners should be used at every opportunity, and there should be no degraded burnt polymer in the places where the polymer comes into contact and passes.

If the mechanical cleaning of the screw and barrel are; It is applied while the screw and barrel are on the machine -by feeding a different raw material-with a suitable solid cleaning compound or by removing them from the machine and separating them from each other. As much as possible, raw materials should not be left on the screw and barrel during short or long-term stops. If possible, the raw material in the hive should not be emptied immediately, even during short stops while polymers such as PET, PA, OC, PVC are working.

The points to be considered in mechanical cleaning are as follows:

• When removing the screw and barrel from the machine, the screw and barrel should be removed as much as possible without leaving any raw materials in the machine.

• Immediately after disassembly on the machine -if possible while the screw and barrel are hot- the screw and barrel should be separated from each other.

• Screw barrel that are separated from each other should never be placed on metal or hard ground. Wooden or plastic floor should be preferred.

• The screw should not be cleaned with hard objects such as a file. Brass should be cleaned with a brush, bronze brush, spatula, copper felt or cloth. No dust should be left on the screws.

• Dirt and rust on the screw barrel that cannot be cleaned with simple methods should be cleaned by a specialist with polishing.

• If there are burrs on the screw, only the burr area should be carefully softened with sandpaper and polished as much as possible.

• It should not be forgotten that the screw and barrel should be as bright as possible and there should be no burrs, cracks and damaged surfaces on which the raw material can be attached.

Bimetallic Coating on Screws

The increase in the variety of plastic materials in the processes and the use of additives with high abrasive - corrosive effect shorten the life of screws and barel very quickly.

Screws, which are made bimetallic by coating the screw threads, have higher abrasion and corrosion resistance and a longer life.

Thanks to this technique, which can be applied to all screws, standard nitration-hardened screws have a hardness depth of 0.2 mm-0.6 mm, while this layer is at least in bimetallic screws.

It is 2-3 mm and their life is 3-5 times longer than standard screws.

Screws, which are generally made of high-capacity alloy steels, are made bimetallic in CNC controlled special PTA benches by coating the tooth tops using wear and alloys.

Periodic Maintenance on Screws and Barrels

In order to ensure the healthy operation of the barrel and screws and to continue the healthy operation, both periodic maintenance and instant maintenance should be applied. Although the periodic maintenance timing varies according to each process, the operations to be performed are similar.

For periodic maintenance of screws and barrels;

• The screw and barrel should be visually inspected to ensure that there are no burrs, injuries, cracks, burnt material or rust on them.

• The necessary document should be prepared to measure the deformations and wear on the screw and barrel, and the controls made with appropriate measuring instruments should be recorded.

• If the cooling systems in the screw and barrel can be removed, they should be disassembled and cleaned. If it cannot be removed, it should be cleaned by using solutions that can remove sediment and lime deposits that may occur in cooling systems.

• Any grazes or injuries to the screw shaft connection should be reported.

• The straightness of the screw and the barrel should be checked.

• It should be checked whether the gap between the sleeve and the screw exceeds the predetermined gap value according to the system being worked on.