Tips for Plastic Material Change for Injection Molding

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 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 especially 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 it 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 need 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 wall of the cylinder, 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 material change, the temperature of the cylinder should be lower than the actual molding temperature.

If the material A with low molding temperature is replaced by the material B with high molding temperature, the temperature of the material B to be removed should be lower than the molding temperature by 10℃ ~ 20℃.

If the material B with high molding temperature is replaced by the material A with low molding temperature, the temperature for removing the material A should preferably be lower than the molding temperature of the 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 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.

PC to ABS(1) Shoot all the PC materials in the cylinder
(2) Remove PC resin from the cylinder by HDPE at PC molding temperature. "
(3) Reduce the temperature of the cylinder below 220 °C, and then remove the HDPE with ABS.
PC to POM(1) Shoot all the PC materials in the cylinder
(2) Remove PC resin from the cylinder by HDPE at PC molding temperature. "
(3) Reduce the temperature of the cylinder below 190 °C, and then remove the HDPE with POM.
PC to PMMA(1) Shoot all the PC materials in the cylinder
(2) Remove PC resin from the cylinder by HDPE at PC molding temperature. "
(3) Reduce the temperature of the cylinder below 240 °C, and then remove the HDPE with PMMA.
ABS to PC(1) Shoot all the ABS materials in the cylinder
(2) Remove ABS resin from the cylinder by HDPE at ABS molding temperature. "
(3) raise the temperature of the cylinder to 290 °C, and then remove the HDPE with PC.
ABS to POM(1) Shoot all the ABS materials in the cylinder
(2) Remove ABS resin from the cylinder by PS at ABS molding temperature. "
(3) reduce the temperature of the cylinder to 190 °C, and then remove the PS with POM.
ABS to PMMA(1) Shoot all the ABS materials in the cylinder
(2) Remove ABS resin from the cylinder by PS at ABS molding temperature. "
(3) Raise the temperature of the cylinder to 240 °C, and then remove the PS with PMMA.
POM to PC(1) Shoot all the POM materials in the cylinder
(2) Remove POM resin from the cylinder by PE at POM molding temperature. "
(3) Raise the temperature of the cylinder to 290 °C, and then remove the PE with PC.
PP to PC(1) Shoot all the PP materials in the cylinder
(2) Raise the temperature of the cylinder to 290 °C, and then remove the PP with PC.
PP to POM(2) Shoot all the PP materials in the cylinder
(2) Keep the temperature of the cylinder to 190 °C, and then remove the PP with POM.
PP to ABS(3) Shoot all the PP materials in the cylinder
(2) Keep the temperature of the cylinder to 240 °C, and then remove the PP with ABS.
PP to PMMA(4) Shoot all the PP materials in the cylinder
(2) Keep the temperature of the cylinder to 240 °C, and then remove the PP with PMMA.
PP to HIPS(5) Shoot all the PP materials in the cylinder
(2) Keep the temperature of the cylinder to 240 °C, and then remove the PP with HIPS.
HIPS to PC(1) Shoot all the HIPS materials in the cylinder
(2) Remove HIPS resin from the cylinder by HDPE at HIPS molding temperature. "
(3) Reduce the temperature of the cylinder below 290 °C, and then remove the HDPE with PC.
HIPS to POM(1) Shoot all the HIPS materials in the cylinder
(2) Remove HIPS resin from the cylinder by PS at HIPS molding temperature. "
(3) Reduce the temperature of the cylinder below 190 °C, and then remove the PS with POM.
HIPS to ABS(1) Shoot all the HIPS materials in the cylinder
(2) Remove HIPS resin from the cylinder by ABS at HIPS molding temperature. "
HIPS to PMMA(1) Shoot all the HIPS materials in the cylinder
(2) Remove HIPS resin from the cylinder by dried PMMA at HIPS molding temperature. "
HIPS to PP(1) Shoot all the HIPS materials in the cylinder
(2) Remove HIPS resin from the cylinder by PP at HIPS molding temperature. "
POM to ABS(1) Shoot all the POM materials in the cylinder
(2) The cylinder is heated to 220 °C, and repeat this several times
POM to PMMA(1) Shoot all the POM materials in the cylinder
(2) Remove POM resin from the cylinder by PS at POM molding temperature. "
(3) Keep the temperature of the cylinder below 240 °C, and then remove the PS with PMMA.
PMMA to PC(1) Shoot all the PMMA materials in the cylinder
(2) Remove PMMA resin from the cylinder by PE at PMMA molding temperature. "
(3) Keep the temperature of the cylinder 220 °C, and then remove the PE with PC.
PMMA to ABS(1) Shoot all the PMMA materials in the cylinder
(2) Remove PMMA resin from the cylinder by ABS at PMMA molding temperature. "
(3) Keep the temperature of the cylinder 220 °C, and repeat several times.
PMMA to PP(1) Shoot all the PMMA materials in the cylinder
(2) Remove PMMA resin from the cylinder by PP at PMMA molding temperature. "
(3) Keep the temperature of the cylinder 190 °C, and repeat several times.
PMMA to POM(2) Shoot all the PMMA materials in the cylinder
(3) Remove PMMA resin from the cylinder by PS at PMMA molding temperature. "
(3) Keep the temperature of the cylinder 190 °C, and repeat several times.
PMMA to HIPS(1) Shoot all the PMMA materials in the cylinder
(2) Remove PMMA resin from the cylinder by HIPS at PMMA molding temperature. "