How to judge whether the injection molding machine barrel temperature setting is reasonable?

To judge whether the barrel temperature setting of the injection molding machine is reasonable, it is necessary to combine the characteristics of the plastic raw materials, product quality performance, equipment status and process parameters for comprehensive analysis. The following are specific judgment methods and steps:
1. Basic verification based on the characteristics of plastic raw materials
Reference material specifications
Each plastic (such as ABS, PP, PC, nylon, etc.) has a recommended barrel temperature range (melting point, processing temperature, decomposition temperature). For example:
ABS: The processing temperature is usually 200~250℃, and it may decompose if it exceeds 260℃;
PC: The processing temperature is 280~320℃, and plasticization may be poor if it is lower than 270℃.
Judgment point: Whether the temperature of each section of the barrel (especially the metering section and nozzle) is within the processing range allowed by the material and is lower than the decomposition temperature by more than 10~20℃.
Observe the melting state of the raw materials
When pre-molding manually, observe the appearance of the melt when the screw exits:
Reasonable temperature: the melt is uniform, glossy, and has no obvious particles or discoloration;
Temperature is too low: the melt is mixed with unmelted particles, the surface is rough, and the screw torque may increase;
Temperature is too high: the melt is yellow, has burnt spots, and even emits black smoke (decomposition).
2. Reverse verification through product defects
Irrational barrel temperature will directly lead to the following typical defects, and the temperature problem can be judged by the defect characteristics:
Defect phenomenon Possible temperature problem Verification method
Poor plasticization (material flowers, silver wire) The barrel temperature is too low and the raw material is not fully melted Check whether the temperature of the feeding section and compression section is lower than the melting point
Burning, black spots Local temperature is too high (such as nozzle or barrel dead corner) or the residence time is too long Reduce the temperature of the corresponding section and check whether the heating ring is abnormal
Flash, burrs The melt fluidity is too strong (high temperature leads to decreased viscosity) Reduce the temperature by 10~20℃ and observe whether the flash is reduced
Lack of material, insufficient filling The temperature is too low, resulting in poor melt fluidity Gradually increase 10℃ to test whether the filling is improved
Obvious surface flow marks and welding marks Uneven melt temperature or insufficient fluidity Check whether the temperature of each section is uniform and increase the nozzle temperature
Shrinkage, dents The melt cools too fast (too low temperature leads to uneven solidification) Increase the mold temperature or barrel temperature to improve the pressure holding effect
III. Check the consistency between the measured temperature and the equipment display
Thermocouple and heating ring status
Failure of the barrel temperature sensor (thermocouple) or damage to the heating ring will cause the actual temperature to be inconsistent with the set value.
Detection method:
Use an infrared thermometer to measure the barrel surface temperature and compare it with the controller display value (allowable error ±5℃, if exceeded, the sensor needs to be calibrated or replaced);
Observe the heating/cooling status: whether the current is normal during heating, and whether the temperature can be effectively reduced during cooling.
Melt temperature measurement
Detect the melt status through "injection sampling":
Stop production, manually inject glue into a clean container, and observe whether the melt is uniform, discolored or impurities;
If conditions permit, use a melt thermometer (such as an inserted thermocouple) to directly measure the melt temperature at the nozzle, which should be close to the set metering section temperature (allowable ±10℃ fluctuation).
4. Trial injection molding and process adjustment test
Step temperature test method
For new raw materials or unknown reasonable temperature, the following steps can be used for testing:
Set the initial temperature to the median of the recommended range of the material;
Trial injection molding 1~2 molds and observe product defects;
If the filling is insufficient, increase 5~10℃ each time (focus on adjusting the metering section and nozzle temperature); if flash or burning occurs, reduce 5~10℃ each time;
Record the temperature parameters corresponding to the best molding state.
Observe the screw load and back pressure
At a reasonable temperature, the torque is stable during screw pre-molding and the back pressure is moderate (adjusted according to the material, such as PC back pressure 5~10bar);
If the screw is difficult to rotate (torque is too high), the temperature may be too low; if the pre-molding speed is too fast and the melt is too thin, the temperature may be too high.
5. Stability verification in long-term production
Consistency of continuous production
At a reasonable temperature, the product size, weight, and appearance should be stable, without periodic defects (such as lack of material once every 10 molds, which may be caused by temperature fluctuations).
Check the key dimensions of the product regularly (such as every hour). If the fluctuation exceeds the tolerance, check whether the temperature control is stable (such as whether the PID parameters of the temperature controller are appropriate).
Barrel cleanliness and residue
After stopping, disassemble the screw and nozzle to observe whether there is carbonized residue on the inner wall:
A small amount of light-colored residue (not burnt) is normal;
Black scorch marks or lumps indicate that the temperature is too high or locally overheated (such as a short circuit in the heating coil).
VI. Precautions
Rationality of barrel segment temperature
Usually the temperature of the feed section is lower than that of the compression section and the metering section (to avoid slipping caused by premature melting of the raw materials), and the nozzle temperature is slightly higher than that of the metering section (to reduce flow resistance);
The upper temperature limit of heat-sensitive materials (such as PVC and POM) needs to be strictly controlled to avoid decomposition.
Environmental and equipment impact
When the room temperature is too low (such as in winter), the heat dissipation of the barrel is accelerated, and the set temperature needs to be appropriately increased;
The barrel wear of old equipment may cause melt retention, and the temperature needs to be slightly lowered to reduce the risk of decomposition.
Summary of judgment process
Initial inspection: confirm that the temperature setting meets the material specifications, and the sensor and heating ring are normal;
Mold trial: observe product defects and find the optimal temperature through step adjustment;
Measurement: verify the consistency between the melt state and the actual temperature and the displayed value;
Optimization: adjust parameters in combination with screw load, back pressure, and long-term stability.
Through the above methods, it is possible to systematically judge whether the barrel temperature is reasonable and solve the molding problems caused by improper temperature in a targeted manner.