1、 Causes of material shortage:
1. Insufficient pressure of injection molding machine
2. Insufficient pressure in the mould
3. Lack of material fluidity
4. Poor air escape in mould cavity
5. Gate imbalance (when the number of each mold is large)
2、 Related knowledge:
1. The lack of material is generally determined by the shape of the mold and the fluidity of the material. When it is due to the setting of forming conditions
In case of blanking, the setting of forming conditions shall be in the direction of good material fluidity, i.e. increasing mold temperature
Barrel temperature, increase the injection speed and pressure.
2. When the design of the vent edge in the die cavity is not well-designed, the air in the die is difficult to escape, except for the lack of products
Besides the material, it is also the cause of paste spots and fusion marks.
1. Real time: increase mold temperature, feeding barrel temperature, increase injection pressure, add gas escape on parting surface
The groove (depth 0.02-0.04mm) is 5-10 mm wide.
2. Short term: increase the gate, increase the flow edge, and in the case of more than one die, the cavity will be enlarged due to lack of material
The gate of that mold cavity, as well as the configuration of changing the flow edge, plus the gas escape pin, improves the smoothness of the mold.
3. Long term: avoid different thickness of design products, add gates where the thickness of products is thick, and understand that
When using products, try to use materials with good fluidity if appropriate.
2、 Due to material differences
If the mold temperature is not high, the resin with obvious deterioration of material fluidity is like polycarbonate (PC) polymer
Ether (PPO) poly (ethylene terephthalate) (PETP), etc., which must be heated to 80 ° C
Above (use mold thermostat).
1. The so-called fluidity of materials generally refers to the determination of materials at a certain temperature and pressure
The weight of the flow into the orifice within the time. Indicates that the flow performance of the material has the melting index of the material. For example: gather
The melting index of ethylene is at 190 ℃ plus 2160 + - 10 ℃ for 10 minutes
The weight of the orifice.
2. As a method of determining resin fluidity, a spiral flow (vortex) mold is used, which can
The length of resin filling was measured.
(1) If the injection holding time is longer than a certain time, it has nothing to do with the filling length, but if it is too short, it will lead to
Insufficient starting and filling (lack of material).
(2) It has nothing to do with the retention time of the material in the barrel.
(3) If the injection speed is too slow, the filling becomes insufficient, but the speed above a certain value will affect
(4) If the mold temperature is high, the effect is small.
(5) If there is a little surplus of plasticizing stroke of screw, the filling length will be longer.
(6) The relationship between injection pressure and filling length is linear.
(7) The material temperature is in the proper area of molding, and the temperature is roughly in a linear proportion to the filling length.
(8) The thickness of the cavity is approximately in line with the filling length.
3. The ratio of filling length (L) to thickness (T) of the same cavity (L / T) is used as the standard of the fluidity of molding materials
Material L / T ratio
PVC (hard) 150-100
PVC (soft) 240-160