Reasons of secondary waste products in thermoplastic injection molding

Insufficient plastic parts: mainly due to insufficient material supply, poor melt filling flow, inflated too much and poor exhaust and other reasons leading to poor filling melt filling flow, inflated too much and poor exhaust and other reasons leading to filling cavity dissatisfaction, incomplete shape of plastic parts or multi-cavity individual cavity filling dissatisfaction.

Reason analysis:

1. Improper injection amount, insufficient feeding amount, insufficient plasticizing ability and insufficient surplus material

2. Plastic tensile degree is different or uneven

3. Plastic in the hopper "bridge"

4. Too much lubricant in the material, large clearance between the screw or plunger and the material barrel, and too much melting backflow

5. Poor balance of feed port in multi-cavity

6. The nozzle temperature is low, the plug or the aperture is too small, and the cylinder temperature is low

7. The injection pressure is small, the injection time is short, the pressure holding time is short, the screw or plunger is returned too early

8. Injecting too fast or too slow

9. Plastics have poor fluidity

10. Excessive overflowing material on the fly edge

11. Low mold temperature, fast plastic cooling

12. Mold gating system has large flow resistance, improper inlet position, small section, bad form, long and tortuous process

13. Poor exhaust, no cold hole or improper cold hole

14. Excessive release agent, moisture in the mold cavity, etc

15. The plastic wall is too thin, the shape is complex and the area is large

Plastics contain much moisture and volatiles

17. Inflate too much in melting material

Dimension instability: mainly due to the poor mold strength, poor accuracy, injection machine work is not stable and forming conditions are not stable, so that the size of the plastic parts is not stable.

Reason analysis:

1. Electrical or hydraulic system of the machine is not stable

2. The forming conditions are not stable (temperature, pressure, time change) and the forming cycle is not consistent

3. The mold strength is insufficient, the positioning rod is bent and worn

4. Poor mold accuracy, unstable movement of moving parts and inaccurate positioning

5. When the mold is unstable, it is loose and tight, and it is easy to fly out

6. The gate is too small or uneven, and the multi-cavity feed port is not well balanced

7. Uneven plastic particles or feeding quantity

8. Improper performance or uneven plasticization of the injection machine should be replaced

9. The cooling time of plastic parts is too short, and the cooling is uneven after demoulding

10. Improper ratio of recycled material and new material

11. Plastic shrinkage is not stable,

Crystallinity of crystalline materials is unstable

12. Bad rigidity of plastic parts, uneven wall thickness

13. Unstable post-processing conditions of plastic parts

Bubble: due to the excess aeration in the melting material or poor exhaust resulting in residual gas in the plastic parts, and a small volume or string of holes (note that should be distinguished from vacuum bubble).

Reason analysis:

1. The raw material contains water, solvent or volatile matter

2. High material temperature, long heating time, plastic depolymerization decomposition

3. Low injection pressure

4. Piston or screw back too early

5. Bad mold exhaust

6. Mould temperature is low

7. The injection speed is too fast

8. There is moisture, grease in the mold cavity, or improper release agent

9. Bad plastic parts, poor flow channel gas storage dead Angle collapse pit (dent) or vacuum bubble: due to poor pressure retaining material, uneven cooling of plastic parts, uneven thickness and large plastic shrinkage

1. The flow channel and feed port are too small, or the quantity is not enough

2. The wall of the plastic parts is too thick or uneven in thickness (the back is prone to collapse in the thick wall)

3. Improper position of the feed port is not conducive to feeding and feeding

4. High material temperature, high mold temperature, short cooling time, easy to dent

5. Low mold temperature, easy to vacuum bubble

6. Low injection pressure and slow injection speed

7. Short injection and pressure holding time

8. Insufficient feeding quantity, insufficient material supply, insufficient surplus material

9. Poor material flow or excessive material overflow

The flicking edge is too large: because of the bad mold closing, the gap is too large, the plastic fluidity is too good, the feeding is too much, the plastic parts are extruded along the edge of the excess sheet.

Reason analysis:

1. The sealing of parting surface is poor, and the gap between the sliding parts of cavity and core is too large

2. Bad mold strength or rigidity

3. Poor mold parallelism

4. There is no pressing during unidirectional force or installation of the mold

5. The injection pressure is too large, the clamping force is insufficient or the clamping mechanism is bad, and the mould of the injection machine is not parallel

6. The projection area of the plastic parts exceeds the molding area allowed by the injection machine

7. Plastic fluidity is too large, material temperature is high, mold temperature is high, injection speed is too fast

8. Excessive feeding quantity

Bad welding: due to the low temperature of the material when the material is shunting and confluence, the resin does not dissolve with the compound and other reasons, so that the material is fused in the confluence, bad welding, along the surface or internal plastic parts produce obvious fine seam line.

Reason analysis:

1. Low material temperature and low mold temperature

2. The injection speed is slow and the injection pressure is small

3. There are too many inlet, improper position, improper form of gating system, long process, large material flow resistance, and fast drop of material temperature

4. Improper mold cooling system

5. Bad shape of plastic parts, too thin wall, too many embedded parts and uneven wall thickness, so that the material confluence in the thin wall

6. Low embedded temperature

7. Plastics have poor fluidity and fast cooling speed

8. There is too much moisture, lubricant and melting material in the mold, and too much mold release agent

9. Bad mold exhaust

10. There is insoluble material in the material infiltration, improper release agent, and insoluble oil

11. Use aluminum foil and other thin-sheet colorants

12. Poor distribution and fusion of fiber fillers

13. Have a cold

Plastic parts surface ripple: because the melt material along the surface of the mold is not neat flow to fill the cavity, but into a semi-solidified wave flow in the cavity surface or the melt material has the phenomenon of stagnant flow.

Reason analysis:

1. Low material temperature, low mold temperature and low nozzle temperature

2. Low injection pressure and slow injection speed

3. Cold material hole improper, there is cold material

4. Plastics have poor fluidity

5. Improper mold cooling system

6. The gating system has long flow, small section, small size of feed port and improper form and position, which make the flow resistance of melting material and fast cooling

7 plastic parts thin wall, large area, complex shape

8. Insufficient material supply

9. The flow channel is tortuous and narrow with poor finish

Bad demoulding: due to the filling effect is too strong, the mold demoulding performance is poor and other reasons, so that the plastic parts demoulding difficult or after demoulding plastic parts deformation, rupture, or plastic parts residual direction does not meet the design requirements.