The methods of cleaning the screw include ordinary replacement method and special screw cleaning agent cleaning method. The former method will use a large amount of resin.
Extruder screw
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 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 rotates at high speed for about 10 minutes, so that LDPE completely replaces the original material.
④ Insert a plastic tube into the hopper material, 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 all foaming,
⑥ When the foaming process is over, the melt becomes clear and clean again. After 15~20min, reduce the screw speed and add new material.
⑦Complete the operation and start production.
2. Variable speed flushing method
Another common screw cleaning method is the variable speed flushing method, commonly known as the disco flushing method. The steps are as follows:
①The screw runs at medium speed to remove the material stored in the machine;
②Change the flow order, as shown in the table below.
Fractional ratio of screw maximum speed/%
Screw rotation time/min
③If they are not rinsed clean, they have crystal points and debris, continue the above sequence until they are clean.
Choice of cleaning material:
1) Replace light-colored resin with high-viscosity resin;
2) Timely maintenance of equipment;
3) Keep the material handling equipment clean;
4) Use a certain intermediate resin to fill the difference in processing temperature (for example, when replacing PA with POM, PS can be used as cleaning material), etc.
Supplement cleared material
Recommended cleaning material
Polyolefin
HDPE
PS
Cast acrylic resin, PS
PVC
General purpose PS, ABS, cast acrylic resin
ABS
Casting polypropylene resin, PS
PA
PS, HDPE with low melt flow rate, cast polypropylene resin
PET
resin to be processed
PBT
PS, HDPE with low melt flow rate, cast polypropylene resin
PC
Casting acrylic resin or PC return material, can not use PA or ABS
POM
PS, avoid any resin containing PVC
Engineering resin
PS, HDPE with low melt flow rate, cast acrylic resin
Fluoropolymer
Cast acrylic resin, PE
Polyphenylene Sulfide
Cast acrylic resin, PE
Polysulfone
PC return material, extrusion grade PP
Polysulfone/ABS
PC return material, extrusion grade PP
Polyphenylene ether
General purpose PS, cast acrylic resin
Thermosetting polyester
Similar mixture materials without catalyst
Add fillers or reinforcements
Cast acrylic resin
Flame Retardant Compounds
Direct use of natural resin without flame retardant, mixed with 1% sodium stearate
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Generally, powdered or pulverized cast acrylics and polyethylene-based materials are the main clearing materials. 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, filter screen, etc. need to be dismantled. ethylene and polyvinyl chloride, etc.). For extruders, this is sometimes not applicable due to a number of requirements and limitations.
EVOH cleaning
1. Cleaning
Switching from LDPE to EVOH can be used directly without any other changes; switching from HDPE, PP, LLDPE to EVOH, first replace it with LDPE and then use EVOH for extrusion. 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 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 in a short time and effectively.
5. Notes on cleaning resin
Please do not use PP or HDPE when pre-cleaning or using cleaning. If these resins come in contact with EVOH, problems sometimes occur, they are difficult to clean, and sometimes caking occurs.
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