How to quickly clean the extruder

How to quickly clean the extruder

How to quickly clean the extruder

Extruders often change raw materials when producing different products, and it often takes a long time to completely replace the previous raw material by throwing away a lot of raw materials. Especially when replacing high melt index raw materials with low melt index products, such as replacing EVA, EAA, ionic polymers, HEPE, PP, and metallocene polymers with LDPE, it is especially difficult. There are common replacement method and special screw cleaning agent cleaning method for cleaning the screw. The former method will use a lot of resin .

1. Cleaning method

1. Water cleaning method

Water cleaning method, using a small amount of water to clean the screw can reduce the cleaning time and avoid crystal points during production. The specific steps are as follows (the following quantities are set based on a typical extruder with a screw diameter of 90mm and L/D=28) .

① Set the screw to rotate at a low speed, generally 10r/min.

② Add the cleaned material head with coating grade LDPE.

③ The screw runs at high speed for about 10 minutes, so that LDPE completely replaces the original material.

④Insert a plastic tube into the material in the hopper, close to the screw and slowly and continuously inject 100~200ml of water.

⑤ After a few minutes, foaming starts from the middle of the melt curtain , and then develops to full foaming,

⑥When the foaming process is over, the melt becomes clear and clean again. After 15~20 minutes, reduce the screw speed and add new material.

⑦ Complete the operation and start production.

2. Variable speed washing method

Another commonly used screw cleaning method is the variable speed flushing method, commonly known as the disco flushing method, the steps are as follows:

① The screw runs at a medium speed to remove the material stored in the machine;

② Change the flow sequence, as shown in the table below.

Table 1 Variable flow operation sequence

③ If they are not rinsed clean, they have crystal points and sundries, continue the above sequence until they are clean.

2. Selection of cleaning resin

Replace the light-colored resin with high-viscosity resin; maintain the equipment in time; keep the material handling equipment clean; use an intermediate resin to fill the difference in processing temperature (for example, when replacing PA with POM, PS can be used as cleaning material), etc.

Generally, powdered or pulverized cast acrylics and polyvinyls are the primary clears. In fact, cast acrylics are suitable for cleaning with any resin. For the cleaning of the extruder, special cleaning materials are usually required, and sometimes the die head, filter screen, etc. need to be disassembled. Polyvinyl compounds usually contain a release agent and are often used to clean "soft" thermoplastics (polyolefins, benzene, etc.) ethylene and polyvinyl chloride, etc.). For extruders, this is sometimes not possible due to many requirements and limitations. The following table shows the cleaning materials selected for different materials.

3. EVOH cleaning

1. Cleaning

Switching from LDPE to EVOH can be used directly without other changes; switching from HDPE, PP, LLDPE to EVOH, first replace it with LDPE and then use EVOH to extrude. Especially after using PA and PVC, be sure to completely replace the resin in the barrel and die with LDPE before extruding with EVOH.

2. Resin temperature

Please note that the temperature setting of the barrel and die head should not exceed 240°C, and the speed of the screw should be controlled.

3. Residence time

Based on 30 minutes, if the operation is interrupted for a long time, please select the low-speed rotation of the screw to keep running.

4. Cleaning after operation

If it is replaced with LDPE, it can be cleaned effectively in a short time.

5. Attention points for cleaning resin

Please do not use PP or HDPE when pre-cleaning or using for cleaning. If these resins come into contact with EVOH, problems sometimes occur, it is difficult to clean, and clumping sometimes occurs.

In addition to regular and preventative maintenance cleaning, shutdown storage seals should be done with a heat-stable screw cleaning agent, especially on weekends or holidays. During downtime, oxygen in the barrel can cause residual polymer to degrade and carbonize, leading to prolonged machine downtime and even scrapping the machine. Screw cleaners do a good job of protecting the screw and barrel from contamination during downtime and getting the extruder back into production mode quickly after the holidays.