How to set the temperature parameters of each section of the injection molding machine barrel?

Setting the temperature parameters of each section of the injection molding machine barrel needs to be combined with the characteristics of the plastic, the equipment structure, the product requirements and the molding process. The following are the systematic setting steps and key principles:
1. Basic preparation: clarify the material characteristics
Obtain the basic temperature range of the material
Check the technical data sheet (TDS) provided by the plastic supplier, focusing on:
** Melting temperature (Tm)** or glass transition temperature (Tg): For example, the melting point of crystalline plastic PA66 is 260℃, and the melting temperature of non-crystalline ABS is 220-260℃.
Thermal stability temperature: avoid exceeding the decomposition temperature of the material (such as PVC is easy to decompose when it exceeds 180℃, and PC will carbonize when heated for a long time when it exceeds 320℃).
Recommended barrel temperature range: Usually the supplier will give the recommended temperature range for the feeding section, compression section, metering section and nozzle.
Differentiate material types
Crystalline plastics (such as PA, PE, PP): The barrel temperature must be 10-30℃ higher than the melting point to ensure sufficient melting, while avoiding excessively high temperatures that lead to abnormal crystallinity (affecting shrinkage and mechanical properties).
Non-crystalline plastics (such as ABS, PC, PS): The temperature must be higher than Tg by 30-50℃, and the focus is on ensuring melt fluidity to avoid poor plasticization due to low temperature.
Thermosensitive plastics (such as PVC, POM): The temperature setting strictly controls the upper limit, and the segmented temperature gradient is small to prevent local overheating and decomposition.
Hygroscopic materials (such as PA, PC, PET): The raw materials must be dried first (water content meets the standard), and then the temperature is set to avoid water vaporization and bubbles at high temperatures.
2. Principles of barrel segment temperature setting (taking the three-stage type as an example)
1. Feeding section (near the feeding port, the first section)
Function: convey solid particles to avoid premature softening of materials (prevent "bridging" or slipping).
Temperature setting:
10-30℃ lower than the melting point or softening point of the material (such as ABS feed section is set at 200-220℃, which is lower than its melting lower limit of 220℃).
Crystalline plastic: The temperature is slightly higher than room temperature or close to the softening point (e.g. PP feed section 180-200℃, lower than the melting point 165℃? No, this needs to be corrected: PP melting point 160-170℃, the feed section temperature should be lower than the melting point, set below 160℃ to avoid premature softening of the particles).
Note: If the feed section temperature is too high, the particles are easy to slip when the screw rotates, resulting in poor feeding; if it is too low, the screw friction increases and energy consumption increases.
2. Compression section (middle section, second section)
Function: Compact the material, melt the plastic through shear heat and external heating, and remove gas.
Temperature setting:
Gradually increase to close to or slightly higher than the material melting temperature (20-30℃ higher than the feed section).
Example: ABS compression section is set to 220-240℃, close to its lower melting limit; PA66 compression section is set to 260-270℃, slightly higher than the melting point 260℃.
Key: Ensure that the material starts to melt in this section to prevent unmelted particles from entering the metering section.
3. Metering section (melting section, third section)
Function: Make the melt evenly mixed and plasticized, and control the melt temperature and density.
Temperature setting:
The highest temperature section of the barrel is 10-20℃ higher than the melting temperature of the material (to ensure complete melting).
Example: PC metering section is set to 290-310℃ (melting temperature 280-300℃); PVC metering section is set to 170-180℃ (avoid exceeding the decomposition temperature of 180℃).
Note: The metering section temperature of heat-sensitive materials (such as POM) needs to be strictly controlled to avoid long retention time of the melt and cause decomposition.
4. Nozzle temperature (additional section)
Function: Control the melt outflow speed to avoid cold material blockage or drooling.
Temperature setting:
Usually 5-10℃ lower than the metering section (reduce the risk of high-temperature melt retention and decomposition at the nozzle).
Thin-walled products or complex structures: the temperature can be the same as or slightly higher than the metering section temperature (to improve fluidity).
Hot runner mold: the nozzle temperature needs to match the flow channel temperature to avoid solidification or carbonization of the melt in the flow channel.
III. Initial parameter setting steps
Preset according to the recommended value of the material
Based on the middle section (compression section) temperature recommended by the supplier, the feed section is 20-30℃ lower, the metering section is 10-20℃ higher, and the nozzle is 5-10℃ lower.
Example: ABS recommended temperature is 220-260℃, then the segment setting is:
Feed section 210℃ → Compression section 230℃ → Metering section 250℃ → Nozzle 245℃.
Fine-tune in combination with product structure
Thin-walled/long-flow products: Increase the metering section and nozzle temperature by 5-10℃ to enhance fluidity and avoid short shots.
Thick-walled products: Appropriately reduce the metering section temperature (to reduce the risk of shrinkage and water shrinkage), but ensure that the melt is uniform.
Complex structure (with inserts/thin wall + thick wall): nozzle temperature is slightly higher than metering section to prevent cold material from affecting filling.
Injection test verification
Manual injection to observe material strips:
Qualified: smooth surface, no particles, no bubbles or burn marks.
Abnormal:
Particles/material flowers → increase the temperature of compression section or metering section by 5-10℃.
Bubbles/black spots → reduce the temperature of metering section or nozzle by 5-10℃ to check whether it is decomposed.
IV. Dynamic adjustment and monitoring in production
Temperature gradient inspection
Under normal circumstances, the barrel temperature should gradually increase from the feeding section to the metering section (3-5℃/section) to avoid "temperature inversion" (such as the metering section is lower than the compression section).
Exception: For some low-viscosity materials (such as PE) or high-speed molding, the temperature of the compression section and the metering section can be close to reduce overheating caused by shear heat.
Consider equipment characteristics
Screw design: Screws with a large length-to-diameter ratio (L/D) have higher shear heat, and the external heating temperature can be appropriately reduced; short screws require increased external heating compensation.
Heating coil status: Regularly check whether each section of the heating coil is damaged (such as the temperature of a certain section cannot be increased or is out of control) to avoid local overheating or overcooling.
Mold temperature matching
Barrel temperature needs to be coordinated with mold temperature:
High mold temperature (such as PC product mold temperature 80-100℃): The barrel temperature can be slightly lower to avoid slow melt cooling and prolonged molding cycle.
Low mold temperature (such as PS product mold temperature 40-60℃): The barrel temperature must ensure that the melt does not solidify prematurely when filling the mold.
Handling abnormal situations
Difficulty in feeding: Reduce the temperature of the feed section by 10-15℃ to increase the friction of the particles.
Nozzle drooling: Reduce the nozzle temperature by 5-10℃, or increase the screw loosening distance (anti-drooling function).
Plasticizing time is too long: appropriately increase the temperature of the metering section, or increase the back pressure (to enhance mixing efficiency).
5. Common misunderstandings and pitfall avoidance guide
Blindly pursue high temperature to solve filling problems
If short shots are caused by low temperature, you should first check whether the compression section and metering section have reached the melting temperature, rather than directly increasing the nozzle temperature (which may cause salivation or decomposition).
Ignore the state of raw materials
Wet raw materials (such as undried PA) will cause the water in the barrel to vaporize, and bubbles will be generated even if the temperature is correct. It is necessary to dry it until the moisture content meets the standard.
The temperature difference between sections is too large
The temperature difference between adjacent sections is recommended not to exceed 30℃ to avoid local overheating or uneven melting of materials due to large temperature differences between sections (especially heat-sensitive materials).
VI. Summary: Core formula for temperature setting
Barrel temperature = material properties (melting/decomposition temperature) + product structure (thin wall/thick wall) + equipment status (screw/heating coil) + actual measurement verification (injection material strip)
Through the closed-loop process of "preset → test → adjust → monitor", combined with material technical parameters and actual production feedback, the temperature of each section can be set efficiently to ensure uniform plasticization of the melt and stable mold filling, reducing product defects (such as material shortage, decomposition, dimensional deviation, etc.) from the source.