Today we are go on with discussion to solutions and precautions for common problems of hot runner molds
5. Silver streak around the gate (area within 50mm from the center of the gate)
Reason: The plastic at the front of the needle core was punched into the mold cavity; the injection was started before the valve needle was fully opened (the injection speed is too fast).
Solution: Reducing the nozzle temperature; when the valve needle is opened, delay the injection for 0.2 seconds;

6. Welding marks near the gate
Reason: There is cold material in the nozzle or hot runner. After the gate is opened, the injection delay time is too long; there is an eccentric problem when the valve needle is installed;
Solution: Increase the temperature of the nozzle or hot runner. Shorten or cancel the injection delay time, check whether the hot runner is installed correctly.
7. White point near the gate
Cause: Air trapped at the tip of the valve needle. This phenomenon occurs due to the material ejection effect when the valve needle is opened, especially those with high viscosity; 
Solution: The end surface of the valve needle is designed as a spherical surface; reduce the injection speed; reduce the movement distance of the valve needle;

8. Irregular ring near the gate
Cause: The mold temperature near the gate is too high.
Solution: Reduce the temperature near the gate, the speed should be very slow at the beginning.
9. The surface of the gate is rough and ugly (affecting the appearance)
Reason: the valve needle is too rough; the temperature of the valve needle tip is too high (maximum value: 120C);
Solution: The surface of the valve needle needs to be well polished (sandpaper above 1600 mesh); use a special polishing paste (diamond paste) to polish the valve head