Reasons and solutions for shortage of plastic products

1. Reasons for the shortage of plastic products

1. The injection molding machine has insufficient pressure and the injection time is too short.

2. Insufficient pressure in the injection mold means that the injection pressure loss during the injection cycle is too large.

3. Insufficient material fluidity.

4. Poor air escape from the cavity.

5. The gate is unbalanced (when one mold has multiple cavities).

2. Related knowledge

1. The lack of material is generally determined by the shape of the mold and the fluidity of the material. When the material shortage is caused by the setting of the molding conditions, the setting of the molding conditions should be set in the direction of good material fluidity, that is, increasing the mold temperature, the temperature of the barrel, and increase the injection speed and injection pressure.

2. When the exhaust design in the cavity is not clever, it is difficult for the air in the mold to escape. In addition to the lack of materials, it is also the cause of the product's battered spots and fusion marks.

3. the method to solve the shortage of plastic products

1. Immediately: Increase the temperature of the mold and the barrel, increase the injection pressure, and add a gas escape groove (depth 0.02~0.04mm) with a width of 5~10mm on the parting surface.

2. Short-term: increase the gate, increase the flow edge (overflow). In the case of a large number of shots per mold, the cavity of cavity is short of material to enlarge the gate of the cavity, and the configuration of the flow edge is changed, and the gas escape pin is added to improve the smoothness of the mold.

3. Long-term: avoid the difference in the thickness of the designed products, add gates where the thickness of the product is thick, understand the occasions where the product is used, and try to use materials with good fluidity if appropriate.


4. due to differences in materials

When the mold temperature is not high, the fluidity of the material is obviously deteriorated, such as polycarbonate PC, polyether PPO, polyethylene terephthalate, commonly known as polyester resin PETP, etc., which must heat the mold temperature to 80 Degree above (using mold temperature control machine).

5. References

1. The so-called material fluidity generally refers to measuring the weight of the material flowing into the injection hole at a certain time under a certain temperature and pressure. Indicates the flow properties of the material, such as the melting index of the material.

2. As a method of measuring the fluidity of the resin, a spiral flow (vortex) mold is used, and the length of the resin filling can be measured with this.

(1) The injection holding pressure time has nothing to do with the filling length over a certain time, but if it is too short, it will cause insufficient filling (lack of material).

(2) It has nothing to do with the time the material stays in the barrel.

(3) If the injection speed is too slow, the filling becomes insufficient, but the speed above a certain value will have little effect.

(4) The higher mold temperature is better, and the influence is also small.

(5) If there is a slight excess of the plasticizing stroke of the screw, the filling length becomes longer.

(6) The relationship between injection pressure and filling length is roughly linear.

(7) The material temperature is in the appropriate area of molding, and the temperature is roughly linearly proportional to the filling length.

(8) The thickness of the cavity is roughly proportional to the filling length.

3. The ratio L/T between the maximum filling length (L) and the thickness (T) of the cavity is used as the standard for the fluidity of the molding material.

Plastic product material L/T ratio

Polyvinyl chloride PVC (hard)

150-100

Polyvinyl chloride PVC (soft)

240-160

Polycarbonate PC

150-100

Polyamide or nylon PA6

320-200

Polystyrene PS

200-220

Polypropylene PP

280-160

Polyethylene PE

280-200