Common bad phenomena in plastic injection molding

Common bad phenomena in custom plastic injection molding

The following is the analysis and countermeasures of the causes of defects in the plastic injection molding process under the main science popularization.

(1) Short shot (unsaturated mode)

(1) Short shot (unsaturated mold); that is, the phenomenon that the molten plastic fails to completely fill the corners of the molding space (mold cavity)

(2) Reasons and improvement measures (see the table below)

Reasons for improvement

1. Material temperature and mold temperature are too low. Increase the temperature of the material tube and mold temperature.

2. The size of nozzle, main channel and irrigation point is too small. Increase the size of nozzle, main channel and irrigation point appropriately.

3. Poor mold venting. Keep the mold surface clean and open vent holes

4. The nozzle is cold or blocked. Remove debris from the nozzle and appropriately increase the temperature of the nozzle

5. Material pipe and check valve are worn and leaked internally. Replace check valve and material pipe

6. The injection speed and pressure are not enough. Increase the shooting speed and pressure

7. Different sizes of plastic particles cause uneven melting. Adjust the back pressure and screw speed to make the plastic evenly mixed.

(2) Raw edges

(1) Flash; that is, the film-like or burr-like excess rubber that appears on the parting surface, around the runner and in the gap between the mold inserts

(2) Reasons and improvement measures (see the table below)

Reasons for improvement

1. The mold clamping force is insufficient, and the mold is supported during injection to increase the clamping pressure of the machine or adjust a larger machine

2. The parting surface does not match or there is debris

Clean the mold surface, re-match the mold to make the male and female molds match 3, the mold inserts have gaps, and the inserts are reconfigured to have no gaps

4. The mold temperature is too high. Adjust the mold temperature

5. The material temperature is too high, reduce the temperature of the material pipe

6. Excessive injection pressure, reduce injection pressure

7, the shooting speed is too fast, slow down the shooting speed

8. Holding pressure time, improper pressure setting Adjust the holding pressure and time

9. The back pressure is too high and the screw speed is too fast. Reduce the back pressure and screw speed

10. The finished product area is too large or the location of the filling point, the quantity is set to use a larger machine, the filling point position is corrected, the quantity is not calculated properly

Silver wire

(1) Silver bars (silver lines) are radial silver-white stripes on or near the surface of the molded product along the plastic flow direction-reasons and improvement measures

1. Too much water in the plastic, fully dry the molding material before molding

2. There are volatile components or impurities in the material. Use as little raw material as possible to use volatile additives to ensure the purity of the material

3. The mold temperature is too low, increase the mold temperature appropriately

4. Poor mold exhaust. Dredge the exhaust ditch or add an exhaust hole

5. There is oil, water or mold release in the mold cavity. Clean the water, oil and mold release in the mold cavity.

6. The horizontal runner and inlet are too small to enlarge the runner and inlet

7, the injection pressure is too high, the shooting speed is too fast, reduce the shooting pressure and slow down the shooting speed

8. The remaining material in the material tube is overfired, reducing the remaining material in the material tube and reducing the nozzle temperature to shorten the molding cycle

9, the material is too decomposed in the material pipe, reduce the temperature of the back section of the material pipe, appropriately increase the back pressure, and slow down the screw speed

 Low gloss of finished product 

(1) Low gloss of finished product means that the surface gloss of the finished product does not meet the quality requirements, and the surface has no refractive index-reasons and improvement measures

1. The injection speed and pressure are too low. Increase the injection speed and pressure.

2, the material temperature is too low, increase the temperature of the material pipe appropriately

3. Too much residual material in the material pipe, reduce the residual material in the material pipe

4. The mold temperature is too low, increase the mold temperature

5. The nozzle aperture is too small. Increase the nozzle aperture (usually the aperture is between 2.0-3.0)

6. The screw rotation time is too low. Slow down the screw rotation speed and increase the rotation time

7. Poor mold exhaust to improve mold exhaust

8. Poor plastic fluidity Improve plastic fluidity

9, the size of plastic particles is not uniform, use plastic with the same particles in the daytime weight

10. The plastic has high moisture content, and the plastic raw materials are thoroughly dried

Deformation

(1) Deformation can be divided into two types: diagonal distortion and parallel edge warping, which are finished products.

Irregular bending phenomenon that occurs in the process-causes and countermeasures

1. Insufficient cooling time for molding, extend the cooling time appropriately

2. Overfilled, adjust the molding conditions to avoid overfilling

3. Uneven or too high mold temperature control, adjust mold temperature

4. The finished meat is uneven

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