Aside from the Screw and Barrel, These Components are Equally Important When Choosing an Extruder!

Ningbo Fangli Technology Co., Ltd. is a mechanical equipment manufacturer with over 30 years’ experiences of plastic pipe extrusion equipment, new environmental protection and new materials equipment. Since its establishment Fangli has been developed based on user’s demands. Through continuous improvement, independent R&D on the core technology and digestion & absorption of advanced technology and other means, we have developed PVC pipe extrusion line, PP-R pipe extrusion line, PE water supply / gas pipe extrusion line, which was recommended by the Chinese Ministry of Construction to replace imported products. We have gained the title of “First-class Brand in Zhejiang Province”.

How do you usually go about purchasing an extruder? It requires not only analyzing your own needs but also gaining a thorough understanding of both the supplier and the extruder itself.

Most companies have a basic idea before purchasing a new extruder: whether they need a twin-screw or single-screw machine, and what material they need to produce. Depending on the product specifications and material consumption, they can refer to "Screw Diameter vs. Product Specification Dimensions" to first select the screw diameter, and then further determine the extruder's model and specifications based on that.

Once the extruder type and model are determined, another important consideration is how to choose an equipment manufacturer. This can be assessed from various angles such as product quality and after-sales service.

Screw Speed

This is the most critical factor affecting an extruder's production capacity. Screw speed not only increases the extrusion speed and output rate of the material but, more importantly, ensures good plasticization while achieving high output.

In the past, the main method to increase extruder output was to enlarge the screw diameter. While a larger screw diameter increases the amount of material extruded per unit time, an extruder is not a simple screw conveyor. The screw must not only convey the material but also compress, mix, and shear the plastic to achieve plasticization. With the screw speed unchanged, a large-diameter screw with deep flights has less effective mixing and shearing action on the material compared to a smaller-diameter screw.

Therefore, modern extruders primarily increase production capacity by raising the screw speed. For ordinary extruders, traditional screw speeds ranged from 60 to 90 rpm (revolutions per minute, same below). Now, speeds are generally increased to 100–120 rpm. Higher-speed extruders reach 150 to 180 rpm.

Increasing screw speed without changing the screw diameter increases the torque on the screw. When torque reaches a certain level, there's a risk of the screw twisting and breaking. However, by improving screw material and manufacturing processes, designing a rational screw structure, shortening the feed section length, increasing material flow velocity, and reducing extrusion resistance, torque can be reduced and the screw's load-bearing capacity enhanced. Designing the most optimal screw to maximize speed within its load-bearing capacity requires professionals to conduct extensive testing.

Screw Structure

Screw structure is a major factor influencing extruder capacity. Without a rational screw structure, simply trying to increase screw speed to raise output goes against objective laws and will not succeed.

High-speed, high-efficiency screw design is based on high rotational speeds. This type of screw may have a poorer plasticization effect at low speeds, but as the speed increases, plasticization gradually improves, reaching its optimal effect at the designed speed. This achieves both higher output and qualified plasticization.

Barrel Structure

Improvements in barrel structure mainly involve enhancing temperature control in the feed section and setting up feed grooves. This independent feed section is essentially a full-length water jacket, with its temperature controlled by advanced electronic control devices.

The appropriateness of the water jacket temperature is crucial for the stable operation and efficient extrusion of the extruder. If the water jacket temperature is too high, the raw material may soften prematurely, and even the surface of the pellets may melt, reducing the friction between the material and the barrel wall, thereby decreasing extrusion thrust and output. However, the temperature cannot be too low either. An excessively cold barrel increases the resistance to screw rotation; when this exceeds the motor's load capacity, it can cause difficulty starting the motor or unstable speed. Utilizing advanced sensors and control technology to monitor and control the extruder's water jacket allows the temperature to be automatically maintained within the optimal process parameter range.

Gear Reducer

Assuming the basic structure is similar, the manufacturing cost of a gear reducer is roughly proportional to its external dimensions and weight. A larger, heavier reducer means more material is consumed during manufacturing and larger bearings are used, increasing production costs.

For extruders with the same screw diameter, high-speed, high-efficiency extruders consume more energy than conventional ones. Doubling the motor power necessitates using a larger reducer frame size. However, higher screw speed means a lower reduction ratio. For reducers of the same size, one with a lower reduction ratio compared to one with a higher ratio has larger gear modules and a greater load-bearing capacity. Therefore, the increase in reducer volume and weight is not linearly proportional to the increase in motor power. If we use output as the denominator divided by reducer weight, high-speed, high-efficiency extruders yield a smaller number, while ordinary extruders yield a larger number.

Calculated per unit of output, the smaller motor power and reducer weight of high-speed, high-efficiency extruders mean their manufacturing cost per unit output is lower than that of ordinary extruders.

Motor Drive

For extruders with the same screw diameter, high-speed, high-efficiency extruders consume more energy than conventional ones, so increasing motor power is necessary. A high-speed 65 extruder requires a 55 kW to 75 kW motor. A high-speed 75 extruder requires a 90 kW to 100 kW motor. A high-speed 90 extruder requires a 150 kW to 200 kW motor. This is one to two times the motor power configured on ordinary extruders.

During normal extruder operation, the motor drive system and heating/cooling systems are continuously working. Energy consumption from the motor and gearbox and other transmission parts accounts for 77% of the machine's total energy consumption; heating and cooling account for 22.8%; and instrumentation and electrical components account for 0.8%.

An extruder with the same screw diameter fitted with a larger motor might seem to consume more electricity. However, calculated based on output, high-speed, high-efficiency extruders are more energy-efficient than conventional ones. For example, an ordinary 90 extruder with a 75 kW motor and an output of 180 kg consumes 0.42 kWh of electricity per kilogram of material extruded. A high-speed, high-efficiency 90 extruder with an output of 600 kg and a 150 kW motor consumes only 0.25 kWh per kilogram, which is only 60% of the former's energy consumption per unit output, showing significant energy savings. This comparison only considers motor energy consumption. If we also consider the electricity used by heaters, fans, and other devices on the extruder, the difference in energy consumption is even greater. Extruders with larger screw diameters require larger heaters and have increased heat dissipation areas. Therefore, for two extruders with the same output capacity, the new high-speed, high-efficiency extruder has a smaller barrel, and its heater energy consumption is less than that of a traditional large-screw extruder, resulting in considerable electricity savings in heating as well.

Regarding heater power, high-speed, high-efficiency extruders compared to ordinary extruders with the same screw diameter do not require increased heater power despite higher output. This is because the extruder's heater mainly consumes electricity during the preheating stage. During normal production, the heat for melting the material primarily comes from the conversion of motor electrical energy. The heater's duty cycle is very low, so its electricity consumption is not significant. This is even more evident in high-speed extruders.

Before inverter technology became widely applied, traditional extruders with large outputs generally used DC motors and DC motor controllers. It was previously believed that DC motors had better power characteristics and a wider speed regulation range than AC motors, offering more stable operation in low-speed ranges. Additionally, high-power inverters were relatively expensive, which limited their application.

In recent years, inverter technology has developed rapidly. Vector-type inverters achieve sensorless control of motor speed and torque, with significant improvements in low-frequency characteristics, and their prices have dropped considerably. Compared to DC motor controllers, the biggest advantage of inverters is energy savings. They make energy consumption proportional to motor load: consumption increases under heavy load and automatically decreases under light load. The long-term energy-saving benefits are very significant.

Vibration Damping Measures

High-speed extruders are prone to vibration. Excessive vibration is very harmful to normal equipment operation and the service life of components. Therefore, multiple measures must be taken to reduce extruder vibration and improve equipment lifespan.

The parts of an extruder most susceptible to vibration are the motor shaft and the gear reducer's high-speed shaft. First, high-speed extruders must be equipped with high-quality motors and gear reducers to avoid the motor rotor or reducer high-speed shaft becoming sources of vibration. Second, a good transmission system must be designed. Paying attention to improving the rigidity and weight of the frame, as well as the quality of machining and assembly, are also important aspects of reducing extruder vibration. A good extruder can be used without being fixed by anchor bolts and will have basically no vibration. This relies on the frame having sufficient rigidity and self-weight. Additionally, quality control in the machining and assembly of various components must be strengthened. For example, controlling the parallelism of the frame's upper and lower planes during machining, the perpendicularity of the reducer mounting surface to the frame plane, etc. During assembly, careful measurement of the motor and reducer shaft heights, strict preparation of reducer shim blocks to ensure concentric alignment between the motor shaft and reducer input shaft, and ensuring the reducer mounting surface is perpendicular to the frame plane are crucial.

Instruments and Gauges

Extrusion production operation is essentially a "black box"; it's impossible to see inside directly, so we rely on instruments and gauges for feedback. Therefore, precise, intelligent, and easy-to-operate instruments and gauges allow us to better understand the internal conditions, enabling faster and better achievement of production results.

If you need further information, Ningbo Fangli Technology Co., Ltd. welcomes your inquiry. We will provide professional technical guidance or equipment procurement suggestions.