The screw speed of a single screw plastic recycling machine is a key parameter affecting plastic melting efficiency and quality. Its mechanism of action permeates the entire material conveying, shearing, plasticizing, and molding process. As a core component in thermomechanical processing, the screw exerts shear and compression forces on the plastic through rotation, causing it to undergo three stages within the barrel: solid-state conveying, melting and compression, and homogenizing extrusion. Adjusting the screw speed directly alters the material's residence time and stress conditions in each functional section of the screw, thereby affecting the uniformity of melting efficiency, melt temperature stability, and the physical properties of the final product.
Increasing screw speed enhances shear heating. When the screw rotates at high speed, the friction frequency between the material and the screw surface and barrel inner wall increases. The shear force breaks the molecular chains and generates heat, accelerating the conversion of solid plastic to a molten state. This heat generation method is particularly important for heat-sensitive plastics, reducing reliance on external heating systems and minimizing the risk of localized overheating. However, if the screw speed is too high, the material's residence time in the screw is shortened, potentially causing some incompletely melted solid particles to be extruded, forming "unmelted spots" and reducing melting efficiency. Therefore, it's important to select a speed range that ensures sufficient melting while avoiding excessive shear, based on the plastic's melt index, thermal stability, and other properties.
Melt temperature uniformity is a key indicator of melt quality. Changes in screw speed significantly affect the axial and radial temperature differences of the melt. At lower speeds, the material resides in the screw for a longer time, allowing ample time for heat to diffuse through conduction and convection, resulting in a more uniform melt temperature distribution. At higher speeds, however, shear heat is concentrated on the screw surface, leading to excessively high temperatures at the center and low temperatures at the edges, creating a "temperature gradient." This unevenness can lead to problems such as varying shrinkage and internal stress concentrations in finished products. Especially when processing high-precision plastic products, optimized temperature distribution requires coordinated control of speed and back pressure.
Screw speed has a dual impact on the plasticizing quality of plastics. On the one hand, an appropriate increase in speed can enhance material mixing. Recycled plastics often contain raw materials and additives of varying grades and colors. High shearing speed effectively disperses these components, avoiding performance fluctuations caused by localized concentrations. On the other hand, excessively high speeds can cause excessive shearing, breaking long molecular chains and reducing the melt flow rate and tensile strength. For recycled engineering plastics such as PET and PA, excessive shearing can disrupt their molecular structure, leading to brittle or yellowing of the finished product. Adjusting the speed and screw geometry (such as flute depth and compression ratio) is crucial to balance mixing efficiency and molecular chain protection.
The matching of speed and screw structure is also a key factor influencing melt quality. The screw of a single screw plastic recycling machine is typically divided into a feeding section, a compression section, and a metering section, each with different functions. The feeding section must ensure stable material transport; excessively high speeds can cause material slippage or blockage. The compression section is the core melting zone, and the speed must be coordinated with flute depth to control the melt rate. The metering section requires a constant speed to maintain stable melt pressure and avoid extrusion fluctuations. Therefore, optimizing screw speed requires a comprehensive design based on structural parameters such as the overall screw length, aspect ratio, and flight width.
In actual production, the selection of screw speed also needs to consider the balance between energy consumption and production efficiency. While high speeds can increase output per unit time, they also increase motor load and energy consumption, accelerating wear on the screw and barrel. In recycled plastic processing, high speeds can also exacerbate equipment wear due to the potential for impurities in the raw materials. Therefore, it's necessary to determine the optimal speed range through experimentation to achieve the optimal balance between energy consumption and efficiency while ensuring melt quality.
The screw speed of a single screw plastic recycling machine is a key factor in determining the effectiveness of recycled plastic processing by influencing shear heat generation, melt temperature distribution, plasticization quality, and equipment energy consumption. Proper speed control requires a comprehensive consideration of plastic properties, screw structure, production efficiency, and energy requirements. Optimizing speed parameters through experimentation and simulation can achieve both improved melt efficiency and quality.
