The transmission system of screw air compressors can generally be divided into direct drive and belt drive. For a long time, the superiority of the two transmission methods has been one of the focus of debate in the industry. The direct drive of screw air compressors refers to the motor main shaft driving the rotor through the coupling and gearbox speed change, which is not actually a true direct drive. The true direct drive means that the motor and the rotor are directly connected (coaxial) and the two have the same speed. This situation is obviously very rare. Therefore, the view that there is no energy loss in direct drive is wrong.
Another transmission method is belt drive, which allows the rotor speed to be changed by pulleys of different diameters. The belt drive system discussed below refers to an automated system representing the latest technology that meets the following conditions: The belt tension in each operating state reaches the optimized value. By avoiding excessive starting tension, the service life of the belt is greatly extended, while the load on the motor and rotor bearings is reduced. Always ensure the correct pulley connection. Replacing the belt is quite easy and quick, and there is no need to adjust the original settings. The entire belt drive system operates safely and trouble-free. It is worth mentioning that some manufacturers who advocate direct gear transmission also use belt drive for some of their products.
Comparison parameters between gear transmission and belt transmission:
1. Efficiency
The efficiency of excellent gear transmission can reach 98%-99%, and the efficiency of excellent belt transmission design can also reach 99% under normal working conditions (see the research report published by Professor Heinz Peeken in "Transmission Technology" in December 1991). The difference between the two does not depend on the choice of transmission method, but mainly depends on the design and manufacturing level of the manufacturer.
2. No-load energy consumption
For direct gear transmission, the no-load pressure is generally maintained above 2.5 bar, and some are even as high as 4 bar to ensure the lubrication of the gearbox.
For belt transmission, theoretically, the no-load pressure can be zero, because the oil sucked into the rotor is sufficient to lubricate the rotor and bearings. Generally, for safety reasons, the pressure is maintained at around 1.5 bar. Take a 160kw gear-driven air compressor as an example. It works 8,000 hours per year, of which 15% (i.e. 1,200 hours) is no-load. This machine will consume 28,800kwh more electricity per year than the belt-driven Liuzhou Fuda screw air compressor of the same power (assuming that the no-load pressure difference between the two machines is 2bar, about 15% difference in energy consumption). In the long run, this will be a considerable expense.
3. Oil loss
Experienced actual users know that the first victim of oil loss will be the gearbox. There is no such safety problem in the belt drive system.
4. Design working pressure according to user requirements
Usually, the working pressure required by the user is not completely consistent with the pressure of the manufacturer's standard model. For example, if the user requires a pressure of 10bar, the working pressure of the Liuzhou Fuda screw air compressor may be 11 or 11.5bar depending on the condition of the post-processing equipment, the length of the piping and the degree of sealing. In this case, a compressor with a rated pressure of 13 bar is generally installed and the outlet pressure is set to the required working pressure on site. At this time, the exhaust volume will remain basically unchanged, because the final working pressure has been reduced but the rotor speed has not increased.
Belt drive design manufacturers, which represent modern technology, only need to simply change the diameter of the pulley and design the working pressure to be exactly the same as the user's requirements, so that the user can get more air volume with the same power motor. For gear drive, it is not so convenient.
5. Pressure change of installed air compressor
Sometimes, due to changes in the user's production process conditions, the design pressure of the original screw air compressor may be too high or too low, and it is hoped that it can be changed, but for gear-driven air compressors, this work will be very difficult and expensive, while for belt-driven air compressors, it is a piece of cake, just replace the pulley.
6. Install new bearings
When the rotor bearing needs to be replaced, for gear-driven air compressors, the gearbox and the gearbox spindle bearing need to be overhauled at the same time, and the cost is unacceptable to users. For belt-driven air compressors, this problem does not exist at all.
7. Replacement of shaft seal
Any screw compressor uses an annular shaft seal, which needs to be replaced after a certain lifespan. For gear-driven compressors, the motor and coupling must be separated before the shaft seal can be approached, which makes this work time-consuming and laborious, thereby increasing maintenance costs. For belt-driven compressors, it is much easier to remove the pulley first.
8. Damage to motor or rotor bearing
For gear-driven Liuzhou Fidelity screw compressors, when the motor or rotor bearing is damaged, it often affects the connected important parts and causes direct and indirect double damage. This situation does not exist for belt-driven compressors.
9. Structural noise
For gear-driven compressors, due to the rigid connection between the motor and the rotor, the vibration of the compression chamber rotor will be transmitted to the gearbox and motor bearings, which not only increases the wear of the motor bearings, but also increases the machine noise.