There are two transmission modes of screw air compressors, one is gear transmission and the other is belt transmission. Both transmission modes have their own advantages and disadvantages. The following will introduce the difference between the two in detail.
Gear Drives vs. Belt Drives
In the transmission system of the air compressor, it can be generally divided into direct drive and belt drive. For a long time, which of the two transmission methods is better has been one of the focuses of debate in the industry. The direct drive of the screw air compressor refers to the fact that the main shaft of the motor drives the rotor through the coupling and gear box speed change, which is not actually a direct drive in the true sense. Direct drive in the true sense means that the motor is directly connected to the rotor (coaxial) and both have the same speed. This is obviously very rare. Therefore, the view that direct drive has no energy loss is wrong.
Another transmission method is belt transmission, which allows the rotation of the rotor to be changed through pulleys of different diameters. The belt drive system discussed below refers to an automation system representing the latest technology that meets the following conditions:
1. The belt tension in each running state reaches the optimal value
2. By avoiding excessive starting tension, the working life of the belt is greatly extended, and the load of the motor and rotor bearing is reduced at the same time;
3. Always ensure the correct pulley connection;
4. It is very easy and fast to replace the belt, and it is not necessary to adjust the original setting;
5. The entire belt drive system operates safely and without failure.
Comparison of gear drive and belt drive
1. Efficiency
Excellent gear transmission efficiency can reach 98%~99%, and excellent belt drive design can also reach 99% efficiency under normal working conditions (see Professor Heinz Peeken's research report published in "Transmission Technology" in December 1991. ). The difference between the two does not depend on the choice of transmission mode, but 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 2.5bar, and some even as high as 4bar to ensure the lubrication of the gearbox.
For belt drive, the no-load pressure can theoretically be zero because the oil sucked in by the rotor is sufficient to lubricate the rotor and bearings. Generally for safety reasons, the pressure is maintained at about 0.5bar.
Taking a 160kw gear-driven air compressor as an example, it works 8,000 hours a year, of which 15% (ie 1,200 hours) is no-load. This machine will consume 28,800kwh more than a belt-driven air compressor of the same power every year. The electricity bill (assuming the no-load pressure difference between the two machines is 2bar, about a 15% difference in energy consumption), will be a lot of money in the long run.
3. Oil loss
Experienced actual users know that the gear box will be the first to suffer in the event of a loss of oil. Belt drive systems do not have this safety issue at all.
4. Design working pressure according to user requirements
Usually the working pressure required by the user is not exactly the same as the pressure of the manufacturer's standard model. For example, the user requires a pressure of 10bar. Depending on the condition of the post-processing equipment, the length of the piping and the degree of sealing, the required working pressure of the air compressor may be 11 or 11.5bar. In this case, an air compressor with a rated pressure of 13bar is generally installed and the outlet pressure is set to the required working pressure on site. At this point the displacement will remain essentially the same because the final working pressure is reduced but the rotor speed is not increased. The belt drive design manufacturer representing modern technology only needs to simply change the diameter of the pulley and can design the working pressure to be exactly the same as the user's requirement, so that the user can obtain more air volume with the same power motor. For wheel drive, it is not so convenient.
5. Installed air compressor - pressure change
Sometimes due to the change of the user's production process conditions, the design pressure of the originally purchased air compressor may be too high or too low, and it is hoped that it can be changed, but for the gear-driven air compressor, this work will be very difficult and expensive. But for the belt-driven air compressor, it's a breeze, just replace the pulley.
6. Install new bearings
When the rotor bearing needs to be replaced, for the gear-driven air compressor, the gearbox and the gearbox main shaft bearing need to be overhauled at the same time, and the cost is unacceptable for the user. For belt drive air compressors, there is no such problem at all.
7. Replace the shaft seal
Any screw air compressor uses an annular shaft seal, which needs to be replaced after a certain life. For gear-driven air compressors, the motor and coupling must be separated before the shaft seal can be accessed, which makes this work time-consuming and labor-intensive, thereby increasing maintenance costs. For belt-driven air compressors, it is much easier to just remove the pulley first.
8. Motor or rotor bearing damage
For geared air compressors, when the motor or rotor bearing is damaged, it often affects the connected important components and causes both direct and indirect damage. This is not the case for belt-driven air compressors.
9. Structure noise
For a geared air compressor, due to the rigid connection between the motor and the rotor, the vibration of the rotor in the compression chamber will be transmitted to the gear box and the motor bearing, which not only increases the wear of the motor bearing, but also increases the machine noise.