Discoloration is when the color of the molded product becomes different from the normal color
1st、reasons for discoloration
Heat for too long
- Plunger, shunt shuttle, screw damage, defects, nozzle and mainstream jacket entrance anastomose, plunger or screw and barrel between the large gap, the barrel of each thread connection loosening, so that the molten material stuck in and accumulation, subjected to a long time fixed heating caused by decomposition.
- The nozzle channel is often in advection state because the wall material is heated for a long time, discoloration or the original color fades.
- The melted resin inside the barrel is often in a high temperature state. The higher the set temperature, the longer the retention time, the more severe the discoloration. In addition, the shear force applied during measurement is also one of the reasons for discoloration. The higher the screw speed, the greater the shear force, the easier it is to change color.
- If the injection speed is too fast, the shear force inside the mold will increase. When the gate or nozzle is small, the shear force will sometimes increase and cause discoloration.
- There is too much water in the plastic and it discolors the parts. For example, nylon or polycarbonate, if the moisture content exceeds the limit, will form colored hydrolysates, resulting in the color of the product.
- Molding injection pressure is too high, the time is too long, so that the parts change color.
- Remove improper oil lubricants and release agents in the material or mold, and clean the cylinder regularly if necessary.
- The equipment and raw materials themselves are unclean, dust and colorant powder in the air deposited in the hopper and other raw material containers without a tight lid so that the material is contaminated and discolored.
2nd、PMMA/PC Color-changing solution
1.Injection molding machine stand
►Test whether the actual temperature of the barrel has any error with the set temperature.
Check that the temperature controller is in the correct area to control the shooting cylinder.
Recalibrate temperature controller and check whether there is adhesive contact, etc.
►Incorrect thermocouple type is used.
Check that the type of thermocouple used is the same as that provided on the temperature controller, such as FeCon.
Check that all thermocouples are running smoothly.
►The retention time of plastic in the shooting cylinder is too long.
Check the injection weight, if less than 25% of the injection pressure of the injection molding machine, transfer the mold to a smaller injection molding machine.
If no smaller injection molding machine is available, the temperature of the injection cylinder will be reduced to the lowest value, which will produce injection parts that meet the quality requirements.
►The plastic stays in the shooting cylinder when production stops.
Stop production, to clean up the shooting cylinder, so that the screw in the first position.
►Somewhere in the cylinder the plastic “grounded" and degraded.
Look at the shooting cylinder and remove any residual stains on the closing surface.
drying：The measured temperature of PMMA is 80 ~ 90℃, and that of PC is 120℃
- If there is a thermometer, please measure the actual melting temperature and keep it stable
- Cartridge material retention time should not exceed 5 ~ 6 minutes
- The amount of the product should be greater than 50% of the total capacity of the machine barrel
Color changes during material production: May stop midway, stranded. Please empty the glue before production.
Machine stop processing
- Short stay (< 5 minutes) : For stays of less than 5 minutes, shoot the screw to the bottom
- Stay for a long time (> 5 minutes) : For more than 5 minutes, finish producing the raw material in the barrel and shoot the screw to the bottom
- Treatment within 1 hour of shutdown: stop resin feeding, empty the raw material in the screw, reduce the temperature of the material.
- Cleaning cylinder: empty the original material, clean at the water outlet at the appropriate temperature, and then clean with new material
- The injection speed should not be too fast
- Injection pressure should not be too high
- The screw speed decreases