What should be paid attention to when adjusting the barrel temperature parameters of different types of injection molding machines?

Different types of injection molding machines differ in structural design, screw form, heating system and application scenarios. When adjusting the barrel temperature parameters, it is necessary to optimize them in combination with the characteristics of the equipment. The following are the precautions for temperature adjustment of the main types of injection molding machines:
1. Classification by structural type (horizontal/vertical/right-angle injection molding machine)
1. Horizontal injection molding machine (most commonly used)
Features: The screw is placed horizontally, and the barrel aspect ratio (L/D) is usually 18~22, which is suitable for most general-purpose plastics.
Note on temperature adjustment:
Segmented temperature gradient: The temperature of the feeding section (rear end) is 10~20℃ lower than that of the compression section (to avoid slipping caused by melting of raw materials at the feed port), and the temperature of the metering section (front end) and nozzle is slightly higher than that of the compression section (to improve melt fluidity).
Thermosensitive materials (such as PVC): The temperature of the metering section needs to be reduced by 10~15℃ to avoid decomposition of the tail of the screw due to shear heat accumulation (the horizontal machine has a long screw and a strong shearing effect).
Transparent materials (such as PC): The nozzle temperature is 5~10℃ higher than the metering section to reduce the cooling stratification of the melt at the nozzle and avoid surface flow marks.
2. Vertical injection molding machine (mostly used for small parts and insert molding)
Features: The screw is vertically upward, the barrel capacity is small, suitable for multi-insert and small batch production, and raw materials are easy to be retained.
Note on temperature adjustment:
Prevent retention at the bottom of the barrel: The temperature of the feeding section should not be too high (5~10℃ lower than the horizontal machine) to avoid premature softening of granular materials at the bottom of the barrel, resulting in poor material discharge.
Quick color change/material change: Due to the small volume of the barrel and the rapid temperature fluctuation, the temperature of each section needs to be set to the lower limit of the material to be processed when changing materials, accelerate the discharge of residual materials, and reduce the risk of color mixing/decomposition.
Thin-walled products: The nozzle temperature can be increased by 10~15℃ to compensate for the gravity flow resistance during vertical injection and avoid material shortage.
3. Right-angle injection molding machine (horizontal screw + vertical injection, commonly used for side injection of mold)
Features: The nozzle direction is perpendicular to the mold injection port, suitable for three-plate molds, point gates, and a long melt flow path.
Note on temperature adjustment:
Nozzle temperature compensation: Due to the large number of turns and resistance in the flow channel, the nozzle temperature needs to be 10~20℃ higher than that of the horizontal machine to ensure that the melt passes smoothly through the right-angle flow channel.
Mold temperature matching: The barrel temperature needs to match the mold temperature (such as hot runner mold) to avoid premature solidification of the melt in the flow channel, resulting in cold material spots.
2. Classification by screw type (single screw/twin screw/plunger injection molding machine)
1. Single screw injection molding machine (most common)
Features: Plasticization is based on screw rotation, divided into gradual type (general material) and sudden type (crystallization material such as PE, PP) screws.
Note on temperature adjustment:
Gradual screw (long compression section): The barrel temperature can be set to a uniform gradient (such as 5~10℃ increase per section), and the screw shearing is used to assist plasticization. The temperature of the metering section of the crystallized material (such as PA) needs to be 20~30℃ above the melting point.
Sudden screw (short compression section): The compression section temperature needs to be 30~50℃ higher than the feeding section (fast melting of crystallized material), and the metering section temperature needs to be 5~10℃ lower than the compression section (avoid excessive shearing).
2. Twin-screw injection molding machine (mostly used for high filling and engineering materials)
Features: Twin-screw meshing mixing, strong shear force, uniform plasticization, suitable for glass fiber reinforcement and masterbatch dispersion.
Note on temperature adjustment:
Shear heat compensation: Due to the significant friction heat generation of the twin screw, the barrel setting temperature can be 10~15℃ lower than the single screw machine (such as PC from 300℃ to 285℃) to avoid overheating and decomposition of the melt.
Low temperature in the feeding section: Keep the feeding section temperature lower than the softening point of the raw material (such as 180℃ for ABS feeding section to prevent the granular material from sticking at the screw meshing point).
Constant temperature in the metering section: The temperature fluctuation at the end of the twin screw is small, and the temperature of the metering section needs to be strictly controlled at the midpoint of the recommended range of the material (error ±5℃) to ensure stable melt viscosity.
3. Plunger injection molding machine (no screw, old equipment, for low viscosity materials)
Features: Relying on the plunger to push the material, poor plasticizing ability, easy retention of the melt, uneven shearing.
Note on temperature adjustment:
Avoid local overheating: The temperature of the front section of the barrel (close to the nozzle) is 5~10℃ lower than that of the rear section to reduce friction overheating when the plunger pushes the material (such as PVC set temperature does not exceed 190℃).
Fast injection: Due to low plasticizing efficiency, the nozzle temperature needs to be increased by 10~20℃ (such as 230℃ for PS nozzle) to compensate for the heat loss when the plunger pushes the material and avoid cold material blockage.
Frequent material cleaning: before each shutdown, lower the temperature to below the softening point of the material (such as PMMA to 180℃), clean the barrel with clean raw materials to prevent residual material from carbonizing.
3. Classification by clamping force/specification (small/medium/large injection molding machine)
1. Small injection molding machine (clamping force <500 tons, such as desktop machine)
Features: small barrel volume (≤50cm³), fast heating, fast heat dissipation, and large temperature fluctuations.
Note on temperature adjustment:
Set the lower limit of the temperature: set according to the lower limit of the recommended temperature of the material (such as PP set to 190~200℃) to avoid overheating of the melt due to the concentrated power of the heating coil in the small barrel.
Cooling time compensation: air cooling is required at the rear end of the barrel (feed port) to prevent the granular material from softening and agglomerating in the hopper (such as ABS rear end temperature ≤170℃).
2. Large injection molding machine (clamping force > 2000 tons, used for large products)
Features: long barrel (L/D ≥ 24), multiple heating sections (5~8 sections), uneven temperature distribution.
Note on temperature adjustment:
Segment refinement: set a section every 20~30cm according to the barrel length, and control the temperature difference between adjacent sections at 5~10℃ (such as 200℃ for the first section, 220℃ for the second section, and 240℃ for the third section) to ensure that the melt is heated evenly along the process.
Back-end insulation: install an insulation sleeve in the feed section to avoid heat loss caused by the cooling water jacket (such as the temperature of the PE feed section is 10℃ higher than that of the single-screw machine).
Melt temperature measurement: use an inserted thermocouple to measure the melt temperature in the middle of the screw (section 3), and ensure that the deviation from the set value is less than ±8℃ to avoid temperature control lag caused by too long a barrel.
4. Classification by heating method (resistance type / ceramic type / electromagnetic induction type)
1. Resistive heating (most traditional)
Features: The heating coil wraps the barrel, has large thermal inertia, slow heating (about 30 minutes), and a temperature difference of ±10℃.
Notes on temperature adjustment:
Preheating in advance: Start the machine 1 hour in advance before production, and preheat at 80% of the target temperature of each section to avoid burning the heating coil due to rapid heating.
Compensation cooling: The barrel temperature may drop by 5~15℃ after injection, and the set temperature needs to be increased by 5℃ (such as PC set at 300℃, the actual control is 295~305℃).
2. Ceramic heating (energy-saving type)
Features: high heating efficiency, fast temperature response (heating time is reduced by 50%), and uniform surface temperature.
Notes on temperature adjustment:
Precision control: The PID parameters of the temperature control table need to be set to "fast response" (proportional band 5~8℃) to avoid overshoot due to too fast heating (such as PA66 temperature overshoot does not exceed 10℃).
Avoid no-load heating: When there is no material in the barrel, the heating temperature must not exceed 50% of the material decomposition temperature (such as PVC is set below 150℃ when no load) to prevent the ceramic heating plate from burning dry and cracking.
3. Electromagnetic induction heating (high-end model)
Features: Heat is generated through induction of the barrel metal, heating is uniform, energy saving is more than 30%, and the temperature control accuracy is ±2℃.
Notes on temperature adjustment:
Matching screw material: If the screw is stainless steel (non-magnetic material), the set temperature needs to be lowered by 10~15℃ (because the induction heat is mainly concentrated on the inner wall of the barrel, and the center of the screw heats up slowly).
Avoid barrel scaling: Clean the carbonized layer on the inner wall of the barrel regularly (once every 2000 hours) to ensure induction efficiency and prevent local overheating (such as cleaning with a special cleaning agent after POM production).
V. Special types of injection molding machines (precision/high speed/multi-material/hot runner)
1. Precision injection molding machine (high-precision products, such as optical lenses)
Note on temperature adjustment:
The temperature difference of the entire section is ≤5℃: The temperature difference between the metering section and the nozzle is controlled within 3℃ (such as PC metering section 300℃, nozzle 302℃), to avoid dimensional deviation caused by melt viscosity fluctuations.
Barrel insulation layer: Add insulation cotton (thickness ≥20mm) to reduce the impact of ambient temperature (such as room temperature 25℃, the deviation between the barrel surface temperature and the set value is <3℃).
2. High-speed injection molding machine (thin-wall products, such as disposable lunch boxes)
Temperature adjustment notes:
Supercritical heating: The temperature of the metering section is 15~20℃ higher than the normal temperature (such as PP set to 230℃), and the shear heat during high-speed injection is used to further reduce the melt viscosity and achieve rapid filling.
Nozzle heating power enhancement: Equipped with an independent heating ring (power 20% higher than the normal one) to ensure that the nozzle temperature is stable during high-speed injection (fluctuation <±5℃) to avoid drawing or cold materials.
3. Multi-material injection molding machine (two-color/three-color molding)
Temperature adjustment notes:
Compatible with different materials: The temperature of the main injection table (first component) and the auxiliary injection table (second component) is independently controlled, and the temperature difference between the two materials must be ≤30℃ (such as ABS main injection table 230℃, PC auxiliary injection table 290℃, it is necessary to check whether the joint surface is cracked).
Alternating injection protection: When the auxiliary injection table is not working, the barrel temperature drops to the softening point of the material + 10℃ (such as the standby temperature of the PA6 auxiliary injection table is set to 210℃) to prevent degradation caused by long-term high temperature.
4. Hot runner injection molding machine (no runner waste)
Temperature adjustment note:
Runner plate and barrel synchronization: The hot runner temperature needs to be 5~10℃ higher than the barrel metering section (such as barrel 240℃, runner plate 250℃), compensate for runner heat dissipation, and avoid melt solidification at the gate.
Thermocouple position: The barrel temperature sensor needs to be close to the nozzle (distance ≤5cm) to ensure that the nozzle and hot runner temperatures are consistent (deviation <±3℃) to prevent cold material from clogging the gate.
VI. General precautions
Material compatibility: When changing materials, the full-section temperature needs to be reset according to the melting point and decomposition temperature of the new material (such as changing from PE to PVC, the barrel temperature needs to be reduced from 200℃ to 180℃, and the screw needs to be thoroughly cleaned).
Screw wear compensation: For old screws (with reduced compression ratio), the barrel temperature needs to be increased by 5~10℃ to compensate for the insufficient plasticization efficiency (for example, for screws that have been used for more than 3 years, the PP temperature is adjusted from 190℃ to 200℃).
Ambient temperature correction: In winter, the temperature of each section of the barrel needs to be increased by 5~8℃ (for example, when the room temperature in the north is 0℃, ABS is adjusted from 220℃ to 225℃), and in summer, it can be reduced by 3~5℃ to offset the difference in equipment heat dissipation.
Summary
The core of temperature adjustment of different types of injection molding machines lies in matching equipment structure (screw/heating method), material properties (melting point/thermal sensitivity) and product requirements (precision/wall thickness). When adjusting, you need to first confirm the type of equipment, refer to the material specification, combine the actual melt state (such as injection sampling) and product defects (such as lack of material/flash), and gradually fine-tune (5~10℃ each time) to finally find the best matching point between temperature and equipment to ensure uniform plasticization, smooth flow, and no decomposition risk.