2-7 What is the reason why single-screw air compressors cannot be promoted on a large scale?
Single-screw air compressors feature one screw rotor and two planetary gears, but face challenges: moving parts deformation affects meshing accuracy and volumetric efficiency; planetary gear material needs improvement for better sealing and durability; and screw profile optimization is needed for efficiency and cost-effectiveness.
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Answer: From the name, the characteristic of this type of air compressor is that it has only one screw rotor. But in fact, a single-screw air compressor has three rotating shafts, namely, it consists of a screw rotor and two planetary gears perpendicular to the screw rotor. It has not been promoted on a large scale because of the following problems that are difficult to solve in industry.
(1) There are many moving parts. Single-screw air compressors have three rotating shafts, and the rigidity of the screw and the planetary gears is quite different. They are prone to uneven deformation during movement, so it is difficult to ensure the mutual meshing accuracy, so the volumetric efficiency is low. In the single-screw compressors currently sold on the market, the planetary gears are all made of non-metallic materials with poor wear resistance. During high-speed operation, due to large wear, the internal leakage increases, so the flow rate has a large attenuation after working for a period of time. In addition, the meshing accuracy caused by uneven deformation is difficult to ensure, which will also reduce the mechanical stability of the whole equipment and limit its scope of use.
(2) The material of the planetary gear needs to be further improved. As one of the core components of a single-screw air compressor, the planetary gear is mainly used for sealing. If a steel planetary gear is used, a large gap must be left between the planetary gear and the screw due to the large expansion coefficient and volume of steel. This will not only cause more leakage and low efficiency, but will also cause seizure and cause major failures. If composite materials are used, although the above problems can be solved, due to the low strength and poor wear resistance of the current composite materials, they will not only be quickly damaged under the shear force and mechanical friction during operation, causing increased internal leakage and reduced efficiency, but also require frequent maintenance, increasing the labor intensity and maintenance costs of maintenance personnel.
(3) The single screw profile needs further optimization. The conventional profile rotor is round and single-headed, with mature technology and low production cost. The new profile rotor is elliptical and double-headed. The new profile rotor is efficient, saves materials, and can improve the efficiency and life of the pump, but has high processing precision and high production cost.
The structure diagram of the single screw air compressor is shown in Figure 2-2.
Figure 2-2 Structure of a single screw air compressor
