What Are The Main Performance Parameters of A Single Screw Extruder?

Single screw extruder is mainly used in PE pipe production line, it is an important machine in the production.

The main performance parameters of a single screw extruder include screw diameter, screw aspect ratio, screw speed range, drive motor power, number of heating sections in the barrel, barrel heating power, extruder production rate, and extruder external dimensions.

1. Screw diameter (D, unit: mm): The outer diameter of the screw, which is commonly used to indicate the specifications of an extruder. The diameters of extrusion screws in China have been standardized and serialized. The currently published screw diameter series mainly includes specifications such as 30, 45, 65, 90, 120, 150, and 200. In production, the screw diameter is generally determined based on the cross-sectional size of the processed product, the type of plastic being processed, and the required production rate. There is an appropriate relationship between the size of the product cross-sectional area and the screw diameter. Generally speaking, larger screw diameters are selected for products with larger cross-sections, while smaller screw diameters are selected for products with smaller cross-sections. This is beneficial for product quality, equipment utilization, and operation.

2. Screw aspect ratio (L/D): The ratio of the length of the working part of the screw (i.e., the length of the threaded part) to its diameter generally indicates the strength of the screw. The larger the aspect ratio, the lower the strength of the screw. To some extent, the aspect ratio of the screw also characterizes its plasticizing capacity and quality. A larger aspect ratio and longer screw length result in a longer residence time of plastic in the barrel, leading to more thorough and uniform plasticization, thereby ensuring product quality. Under this premise, the rotational speed of the screw can be increased to enhance the extrusion output. However, a larger aspect ratio makes the processing and assembly of the screw and barrel more difficult and complex, with a corresponding increase in cost. Additionally, a larger aspect ratio increases the sagging of the screw, which can lead to uneven clearance between the screw and the barrel due to increased bending of the screw. Sometimes, this can cause the screw to scratch and wear the barrel, affecting the lifespan of the extruder. Therefore, it is essential to strive for high output and quality under the condition of a smaller aspect ratio. This is the most efficient and cost-effective approach, and one should never blindly increase the aspect ratio. Especially for screws with small diameters, when the aspect ratio is increased, the root diameter of the threads in the feeding section becomes smaller, leading to a decrease in screw strength. If the rotational speed of the screw is increased, its torque will inevitably increase, which can easily cause bending, deformation, or even breakage of the screw.

3. Range of screw speed n (rpm): It is generally expressed as nmin~nmax. nmax represents the maximum speed, and nmin represents the minimum speed. The 

screw speed, which refers to the speed at which the screw rotates inside the extruder barrel, is usually expressed in revolutions per minute (rpm). The range of screw speeds varies for extruders of different models and applications. In traditional extruders, the screw speed is generally set at 60 to 90 rpm. This setting is suitable for most conventional plastic processing tasks, ensuring product quality while maintaining relatively stable production efficiency. However, with technological advancements, the screw speed of modern extruders has been significantly increased. Currently, the screw speed of many modern extruders can reach 100 to 120 rpm or even higher. This high-speed setting helps to improve production efficiency, shorten production cycles, and thus reduce costs. However, as the screw speed increases, the service life of the screw decreases accordingly.

For certain specific applications, such as those requiring high output or high production efficiency, high-speed extruders may be used. The screw speed of such extruders can typically reach 150 to 180 revolutions per minute, or even higher. However, it is important to note that at high speeds, the torque applied to the screw increases, so the stability and reliability of the equipment must be ensured. For heat-sensitive materials such as PVC: it is recommended to use low speed (30-80rpm) to avoid overheating and degradation. For general-purpose plastics such as PE/PP: medium speed (80-120rpm) is commonly used to balance output and melt quality. For engineering plastics (such as PA, PC): higher speeds (100-150rpm) may be required to improve fluidity.

4. Drive motor power (N, unit: kW): The power required to drive the screw to rotate.

The power of the drive motor for a plastic extruder varies depending on its type, specifications, and application, with a common range from 1.1 kW to 160 kW. The specific value depends on the equipment model and design parameters. Below are some examples of motor power for typical models:

Small experimental equipment: such as laboratory single screw extruder, typically with a motor power of 1.1 kW or 1.5 kW

Medium-sized pipe extruder: For example, the SSJP series parallel twin-screw extruder, with a power range from 45 kW to 75 kW

High speed single screw extruder: It has a wide power range, such as 4-7.5 kW, 7.5-22 kW, 18.5-55 kW, etc., depending on the model, which are mainly used in small PE pipe production line.

Large industrial equipment: such as certain single-screw or twin-screw extruders, with main motor power reaching up to 55 kW, 75 kW, 90 kW, 110 kW, 132 kW, or even 160 kW, this models of extruder are mainly used for large diameter PE pipe production line.

5. Number of heating sections of the screw cylinder (B): The number of heating zones divided along the length of the screw cylinder, each of which can be independently controlled in temperature to ensure uniform plasticization of the plastic during the extrusion process. This parameter is a key indicator in the design of the extruder, directly affecting the accuracy of temperature control and product quality. Generally, the number of heating sections of the extruder screw cylinder should be more than three.

6. Barrel heating power (E, unit: kW): The power required to heat the barrel to the desired temperature. Generally, the greater the heating power of the barrel, the shorter the time it takes to heat it to the required temperature. Common heating power and number of heating sections for single-screw extruders

7. Extruder productivity (Q, unit: kg/h): Refers to the extrusion output per unit time. The higher the extruder productivity, the higher the output. Currently, the extrusion output on the market refers to the extrusion capacity under the condition of mold opening. The actual output may be partially reduced. To increase the output, one can redesign the screw structure (such as the current high-efficiency screw) or increase the screw speed (such as a high-speed screw).

8. Center height of the machine (H, in mm): The height from the centerline of the screw to the ground.

9. Overall dimensions of the machine: length, width, height, in mm.