Silver grain is mainly raw material is not completely dry, caused by moisture or volatile components .When silver, first of all to use a thoroughly dried pellet molding experiment, if so can not be eliminated, you can check for other reasons.
Silicone generated specific reasons are as follows:
1, injection molding machine:
(1) barrel, screw wear or over the plastic head, the apron has a stream of dead ends, long-term heating and decomposition.
(2) If the heating system runs out of control and causes the temperature to be too high to decompose, check if there are any problems with the heating elements such as thermocouple and heating ring, etc. Improper screw design may result in improper exhaust or easy air intake.
2, mold:
(1) poor exhaust;
(2) mold, runner, gate, cavity friction resistance, resulting in local overheating and decomposition;
(3) gate, cavity distribution is not balanced, the cooling system is irrational will result in uneven heating and local overheating or blocking the air channel;
(4) Leaking cooling water enters the cavity;
(5) There are some unplasticized plastic cold materials on the injection-molded parts to increase the size of the cold-material holes; the tail part of the flow channel is expanded to form additional plastic cold-material holes; the nozzle and the injection nozzle jacket are heated by electricity;
(6) The runner and gate are too small or too long, causing the plastic to condense during transport, increasing the runner diameter and gate depth, if required.
3, process:
(1) set the temperature, pressure, speed, back pressure, melt motor speed is too high cause decomposition, or pressure, speed is too low, injection time, packing is not sufficient, too low back pressure, due to failure to obtain high pressure and density Not enough to melt the gas and appear silver grain, should set the appropriate temperature, pressure, speed and time and the use of multi-injection speed.
(2) low back pressure, speed, easy to make air into the barrel, with the melt into the mold, the cycle is too long when the melt in the barrel is heated too long and there decomposition, plastic stranded in the shot tank for too long, reducing The total cycle time; injection molding injection molding requirements is too small (recommended machine injection volume of 20% to 80%).
(3) lack of material, feeding buffer is too large, the material temperature is too low or too low mold temperature will affect the material flow and molding pressure, to promote the formation of bubbles.
(4) melt surface temperature is too high, reducing the shooting cylinder temperature; melt temperature is too low to cause mold filling time instability, increasing the shooting cylinder temperature; increased nozzle temperature; increased mold filling speed
(5) mold surface mold release agent too much, with a white sprinkler thoroughly clean the mold surface
4, plastic aspects:
(1) plastic humidity, add too much proportion of renewable materials or contain harmful crumbs (crumbs easily decomposed), should be fully dry plastic and eliminate debris.
(2) Moisture absorption from the atmosphere or moisture absorption from the colorant, the colorant should also be dried, it is best to install the dryer on the machine.
(3) Too much or uneven mixing of lubricants, stabilizers, etc. added to plastics, or plastics with volatile solvents, which can cause decomposition when the degree of heat mixing is difficult to achieve.
(4) plastic contaminated, mixed with other plastics.