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Tips for plastic material change
Color change for the same material
In principle, when changing colors of the same material, it is easier to change from light-colored material to dark-colored material than from opaque material to transparent material.
The color change procedures :
(1) Close the feed door at the bottom of the hopper.
(2) shot to the air without material several times until the barrel is empty.
(3) feed new materials into the hopper
(4) Open the feed door; the screw moves forward and backward 10+ times until the color change is completed
When changing from opaque material to transparent material, it is necessary to dismantle the nozzle and remove the residual material.
It is necessary, at the same time, the screw must be pulled out and clean up; there must be no blind angle where residual materials can accumulate.
Color change of different materials
The replacement of different materials uses the different melting viscosity of the materials, and it also needs to control the barrel temperature.
Thermoplastic plastic materials adhere to barrel inner surfaces at high temperatures and do not stick at low temperatures.
The material change operation uses this property to make the raw materials to be replaced adhere to the cylinder wall so that the high viscosity cleaning materials passing through the cold screw can carry out the former material.
At this time, the temperature of the screw should be low so that the material to be replaced is not attached to the screw and could be removed. Therefore, the material for removing should be a material with high melt viscosity, such as high-density PE or PS, etc.
Note:
(1) Before the end of the material change, the temperature of the cylinder should be lower than the actual molding temperature.
If material A with low molding temperature is replaced by material B with high molding temperature, the temperature of material B to be removed should be lower than the molding temperature by 10℃ ~ 20℃.
If material B with high molding temperature is replaced by material A with low molding temperature, the temperature for removing material A should preferably be lower than the molding temperature of material A by 10℃~20℃.
(2) the screw speed should be low, reduce the screw back pressure, prevent friction heat lead to material temperature rise.
(3) For the raw materials to be replaced, try not to roll them onto the screw in the molten state.
(4) Make the screw advance with a short stroke, shot the material several times into the air, and the material change effect will be excellent.
(5) If there are scars or gaps on the inner wall of the cylinder or the groove on the screw, the molten material will stay there and make the change operation difficult.
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