1 force balance
Single screw: The radial and axial force of the screw is automatically balanced. The gas force of the planetary gear requires the planetary gear to have sufficient strength and rigidity.
Twin screw: The screw rotor is subjected to large radial and axial forces, and the screw rotor is required to have sufficient strength and rigidity, and finally the bearing needs to bear a large load.
The single-screw star wheel and twin-screw bearings are the flaws of these two models in China. These two factors can only be solved by the industry, and it is necessary to improve the overall technical level of materials from machine to machine to process.
2 noise and vibration
Single screw: good balance of force, low noise and vibration, generally 60~68dB(A);
Twin screw: Poor force balance, high frequency noise when the rotor is engaged, generally 64~78dB(A).
3 reliability
Single screw: The star wheel is a wearing part. Because of the material problem, the domestic star wheel usually only has a life of several thousand hours. If it is regarded as a consumable, there is no other reliability problem;
Twin screw: Due to the large bearing load, most screw machines have overhaul time of 20,000 to 50,000 hours. Bearings need to be replaced and the value is high.
4 processing equipment
Single screw: At present, single screw processing equipment is extremely difficult to obtain in China, so most of the domestic use of general machine tool processing, product quality is unstable, accuracy and efficiency are not good;
Twin screw: There are already mature rotor processing batch production equipment (milling machines, grinding machines, etc.) and have been introduced to China.
5 efficiency
Basically, both the twin screw and the single screw are highly efficient. From the national standard, the fuel injection single and the double screw were combined and implemented according to the unified energy efficiency standard. It can be inferred that the efficiency of the two is actually similar. It depends mainly on the material, precision and process of a certain plant or type.
Single screw: the highest efficiency at 1500~3000r/min;
Twin screw: the highest efficiency at 3000~6000r/min;
Objectively speaking, in terms of performance persistence, the current single screw can not compete with twin-screw (speaking is a common phenomenon), mainly because of the problem of star wheel wear, involving material and processing accuracy (currently still pain in China) ).
If you only talk about the efficiency of the new machine, not the performance is long-lasting, the efficiency of the piston machine is already high enough. however...
6 easy to manufacture
Single screw: Basic type is not difficult to manufacture, and high performance models require high equipment and materials;
Twin-screw: Before the introduction of screw-specific processing equipment in China, the gap is very large in terms of quality and quantity. Therefore, most of the twin-screw production enterprises are reassembled by imported heads and the price is high. Therefore, most of the single-screw manufacturing enterprises on the market have developed at that time.
7 maintenance, repair
Single screw: Basic maintenance and repair is not difficult, high-performance models still need factory maintenance.
Twin screw: The maintenance of twin screw is very simple. At the same time, because of the wide range of use of twin screw, there are more and more technical personnel for overhaul of the mainframe. It is no longer necessary to return to the factory or support the manufacturer.
8 scope of application
Single screw: Due to the complete balance of the screw force, the single screw can work under high pressure and is suitable for high exhaust pressure applications. Low vibration and low noise are of great significance to the military. Moreover, the single-screw rotor and the star wheel are contact-type seals, making it easier to achieve oil-free operation at low speeds.
Twin screw: Due to rotor stiffness and bearing load limitations, twin screw can only be used in medium and low pressure applications, power, refrigeration and gas delivery, generally less than 4.5MPa. Due to the inability to directly mesh between the twin-screw rotors without oil lubrication, high speeds (usually above 10,000 rpm) are required, and the efficiency is low, especially for bearings.
