Cause analysis of common problems of the hottest i

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Cause analysis of common problems of injection molded products

cause analysis of black spots caused by discoloration and coking

the main reason for black spots caused by discoloration and coking of injection molded products is that plastic or added UV absorbers, antistatic agents, etc. are overheated and decomposed in the barrel, or stay in the barrel for too long and decompose and coking, and then form with the molten material injected into the mold cavity. The analysis is as follows:

1 Machine:

(1) due to the heating control system out of control, the material barrel overheated, causing decomposition and blackening

(2) due to the defect of the screw or barrel, the molten material is stuck and stored, which is decomposed by long-term fixed heating. Check whether the rubber head kit is worn or whether there are metal foreign matters inside

(3) some plastics, such as ABS, are crosslinked and coked by high heat in the barrel, which is difficult to melt under the condition of almost maintaining the original particle shape, and are entrained into the workpiece after being crushed by the screw

2. Mold:

(1) the mold is not smoothly vented, easy to burn, or the size of the gating system is too small, and the cutting is too severe, resulting in coking

the cost is much lower

(2) there are inappropriate oil lubricants and release agents in the mold

3. Plastic:

plastic has too much volatile matter, too much humidity, too many impurities, too much recycled materials, and is polluted

4. Processing:

(1) too much pressure, too high speed, too much back pressure and too fast speed will decompose the material temperature

(2) the barrel should be cleaned regularly to remove additives that are less resistant than plastic

cause analysis of delamination

causes of delamination of injection molded products and Troubleshooting:

1 The material temperature is too low and the mold temperature is too low, resulting in the occurrence of internal stress and fusion joints

2. The injection speed is too low, so it should be slowed down appropriately

3. The back pressure is too low

4. If impurities from different materials are mixed in the raw materials, the different materials should be screened out or replaced with new materials

cause analysis of swelling and bubbling

some plastic parts soon appear swelling or bubbling on the back of metal inserts or particularly thick parts after molding and demoulding. This is because the plastic that has not been completely cooled and hardened releases gas expansion under the action of internal pressure


1 What is effective is renewable recycling and recycled resource cooling. Reduce the mold temperature, extend the mold opening time, and reduce the drying and processing temperature of the material

2. Reduce the filling speed, forming cycle and flow resistance

3. Increase the holding pressure and time

4. Improve the condition that the wall surface of the workpiece is too thick or the thickness changes greatly

cause analysis of transparent defects

transparent parts of melting spots, crazes, cracks, polystyrene and plexiglass, 3 After equipment installation and debugging, sometimes you can see some glittering filigree like crazes through the light. These crazes are also called bright spots or cracks. This is due to the stress generated in the vertical direction of the tensile stress, which makes the polymer molecules oriented in the flow direction, so that the refractive index of the oriented part is different from that of the non oriented part, and the light refraction occurs when passing through the interface between the two parts to produce crazing


(1) eliminate the interference of gas and other impurities, and fully dry the plastic

(2) reduce the material temperature, adjust the material barrel temperature in sections, and appropriately increase the mold temperature

(3) increase the injection pressure and reduce the injection speed

if these bags have not been used twice or repeatedly

(4) increase or decrease the back pressure of pre molding and reduce the screw speed

(5) improve the exhaust condition of runner and cavity

(6) clean up the possible blockage of nozzle, runner and gate. (7) Shorten the molding cycle, and annealing can be used to eliminate crazing after demoulding: keep polystyrene at 78 ℃ for 15 minutes, or keep it at 50 ℃ for 1 hour, and heat polycarbonate above 160 ℃ for several minutes

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