​Four reasons of insufficient filling of injection molding products

Four reasons of insufficient filling of injection molding products

1. Improper feed adjustment, lack of material or multiple materials

Inaccurate metering or improper operation of the feed control system, injection molding machine or mold or operating conditions, resulting in abnormal injection cycle, small pre-plastic back pressure or small density of material in the barrel may cause material shortage, for large particles, Plastics with large voids and crystallographic specific changes such as polyethylene, polypropylene, nylon, etc., and plastics with higher viscosity, such as ABS, should be adjusted to a higher amount. When the temperature is high, the amount of material should be adjusted.

When there is too much material stored at the end of the barrel, the screw consumes an extra injection pressure to compress and push the excess material in the barrel during injection, which greatly reduces the effective injection pressure of the plastic entering the cavity. The product is difficult to fill.

2. The injection pressure is too low, the injection time is short, and the plunger or screw is returned too early.

Molten plastics have higher viscosity at lower operating temperatures and poor fluidity and should be injected at higher pressures and speeds. For example, in the case of ABS color parts, the high temperature resistance of the colorant limits the heating temperature of the barrel, which is compensated by a higher injection pressure than usual and an extended injection time.

3. Slow injection speed

The injection speed has great significance for some products with complex shapes, large thickness and long process, long process, and plastics with high viscosity such as toughness ABS. When high pressure is not enough to fill the product, high-speed injection should be considered to overcome the problem of dissatisfaction.

4. The material temperature is too low

The temperature at the front end of the barrel is low, and the melt entering the cavity causes the viscosity to rise prematurely to the point where it is difficult to flow due to the cooling effect of the mold, which hinders the filling of the distal end; the plastic in the rear part of the barrel has a low temperature and a high viscosity. The difficulty of the flow hinders the advancement of the screw, and as a result, it appears that the pressure displayed by the pressure gauge is sufficient and actually the melt enters the cavity at a low pressure and a low speed;

If the nozzle temperature is low, it may be that the nozzle is in contact with the cold mold for a long time, and the heat is insufficient, or the nozzle heating coil is insufficiently heated or the contact temperature is low, which may block the feeding passage of the mold; if the mold does not have cold material Wells, with self-locking nozzles, using the post-feeding procedure, the nozzles can maintain the necessary temperature; when the nozzles are too cold, the nozzles can be heated externally to accelerate the nozzle temperature.