Views: 1 Author: Site Editor Publish Time: 2026-07-20 Origin: Site
1. What Are High Torque and Low Torque?
Low-Torque Extruders: Think of a low-torque extruder as a sports car. It can reach very high rotational speeds (RPM), but it lacks "pulling power" when faced with a heavy load or a steep hill. If the polymer melt is very stiff or highly viscous, a low-torque machine simply cannot push it forward.
High-Torque Extruders: Think of a high-torque extruder as a heavy-duty dump truck or a bulldozer. Its maximum speed might not be the highest, but it possesses massive raw power. No matter how tough the material is—whether it's high-viscosity, highly filled, or high-molecular-weight—it can chew right through it.
In actual production, the core differences between the two manifest in three main areas:
Material Handling Capability (The "Hard Stuff"): Low-torque machines are generally limited to processing conventional, easily melted plastics (such as standard PP or PE color masterbatches). High-torque machines are built for heavy lifting. They excel at processing engineering plastics with 50%+ glass fiber, highly loaded inorganic flame retardants, or sticky, high-resistance thermoplastic elastomers like EVA and TPU.
Throughput and Energy Efficiency: Many people mistakenly believe that higher RPM automatically equals higher throughput. This is false. Because low-torque machines are prone to motor overload, operators must be conservative with the feed rate, often leaving the machine "starved." High-torque machines, however, can handle aggressive feeding. At the same screw diameter, a high-torque machine offers significantly higher output and much better extrusion stability.
Equipment Cost: High torque requires the gearbox, splined shafts, and screw elements to withstand extreme torsional shear forces. Consequently, high-torque gearboxes are incredibly expensive. In some cases, a single imported high-torque gearbox can cost as much as half of a standard extruder line.
2. Strange Torque Phenomena on the Workshop Floor
During daily operations, every extruder control panel displays a "Torque %" meter. Whether you are running a high-torque or low-torque machine, an abnormal torque reading is the ultimate warning sign. Let's look at the two most common symptoms:
Symptom 1: Torque Spikes and Maxes Out (Overload)
This is an operator's worst nightmare. The machine suddenly shuts down with a loud bang, and the panel displays a 100% or 105% torque overload alarm.
Why does this happen?
Cold Starts (Unmelted Material): The barrel has not reached the proper temperature. The polymer inside is still solid, making it physically impossible for the screw to rotate.
Overfeeding (Material Blockage): The feeder is running too fast, and the screw cannot convey the material away quickly enough. The plastic accumulates in a specific zone—often near the vacuum or atmospheric vent—completely seizing the screws.
Formulation Changes: A sudden increase in the ratio of powder fillers or glass fiber causes the melt viscosity to skyrocket, exceeding the machine's mechanical capacity.
Symptom 2: Low Torque, but Output Won't Increase
Sometimes you may notice the torque is sitting comfortably at 30% to 40%, and the motor is spinning fast, but the die head is barely extruding any material.
Why does this happen?
Starve Feeding (Hopper Bridging): The feeder is not delivering material smoothly (e.g., powder bridging in the hopper). The screws are essentially running empty, meaning there is no flow resistance, resulting in low torque.
Excessive Barrel Temperatures: The plastic is being overheated into a watery consistency. The viscosity drops so low that the screws cannot impart any shear. This often means the polymer has already begun to thermally degrade.
Severe Screw Wear: The clearance between the screw flights and the barrel wall has become too large. The material is simply flowing backward over the flights instead of being pushed forward. The machine is failing to build pressure, doing "useless work."
3. Practical Solutions for Torque Abnormalities
When these problems arise on the production line, how should you adjust the process? Here are several proven troubleshooting tactics:
1. Fixing High-Torque Overload, Seizing, and Tripping
Feed Less, Spin Faster: If the torque is constantly hovering above 90%, the most direct solution is to reduce the feeder speed or slightly increase the main motor RPM. By putting less material in the screw and moving it out faster, you immediately relieve the internal pressure and resistance.
Fine-Tune Temperatures: If the resistance is occurring in the melting or conveying zones, increase the temperatures in those specific zones by 5 to 10°C. This helps the plastic melt more thoroughly and flow smoother. (Note: For highly shear-sensitive materials that melt via frictional heat, you might occasionally need to lower the temperature to increase viscosity—this depends entirely on the resin's rheology).
Clean and Inspect: Shut down the machine to verify if a foreign metal object has fallen into the barrel. Alternatively, if the machine sat idle at a high heat for too long, carbonized/degraded material may be locking the screws.
2. Fixing Low Torque, Low Output, and Vent Surging
Feed It More: If low torque is caused by underfeeding, check the hopper for bridging. Increase the feed rate until the screw fill-factor reaches an optimal state. A running torque of 70% to 80% is generally the "sweet spot" for most extrusion processes.
Screw Reconfiguration (The Last Resort): If temperature tweaks and feed rate adjustments do not work, your current screw profile (the arrangement of kneading blocks) does not match your formulation.
If the torque is too low and lacks shear, add restrictive elements or aggressive kneading blocks in the melting zone.
Conversely, if switching to a standard material causes the torque to max out, replace aggressive kneading blocks with narrower, forward-conveying blocks to let the material pass through more easily.
Conclusion
When purchasing equipment or designing a process, do not blindly assume that "higher torque is always better."
You must match the machine to the specific material you intend to run. If your core business is producing standard plastics or low-fill masterbatches on a daily basis, a standard or medium-torque extruder is more than sufficient. Why overspend on an ultra-high-torque gearbox when you could use those savings to buy more raw materials? Select the right tool for the job to maximize your ROI.
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