In recent years, cement vertical kiln enterprises have widely adopted frequency converters to control the air supply system. Compared with traditional air valve control systems, it has many advantages: stable and sensitive adjustment of air volume and pressure; energy saving, no air leakage, and low noise; smooth motor starting. However, there are also some misconceptions: some users believe that vent valves can be removed when using frequency converters; and they believe that high temperatures in the main oil tank, auxiliary oil tank, and bearings are due to bearing or installation problems. One common issue is that after using frequency converters, many users, fearing that air leakage from vent valves will affect air supply efficiency and cause energy loss, remove the vent valves, creating a relatively closed air supply system. As is well known, Roots blowers are constant-volume blowers; their airflow does not change with air pressure, but air pressure increases with resistance. Because a certain resistance is always maintained inside the kiln, the air supply system contains high-pressure air that cannot be released before the blower is stopped. When the power to the Roots blower is cut off, the air pressure in the system will exert a reaction force on the blower impeller, forcing the blower to rotate in the opposite direction. As is well known, reverse rotation of Roots blowers is strictly prohibited because it will cause friction or knocking between the two impellers. Furthermore, during major overhauls of Roots blowers, to relatively extend the service life of the gear pair, when adjusting the clearance δ[sub]2[/sub] between the two impellers (see the diagrams), see Figure a: when adjusting δ[sub]2[/sub], adjust the value of δ[sub]2[/sub] to the upper limit of the permissible range, i.e., the maximum value. See Figure b: when adjusting δ[sub]2[/sub]': δ[sub]2[/sub]'. The value is adjusted to the lower limit of the permissible range, i.e., the minimum value (see table for details of Roots blower assembly clearance). Thus, as the working tooth surface of the blower gear pair wears, δ[sub]2[/sub] gradually decreases, and δ[sub]2[/sub]' gradually increases. However, at this time, the gear backlash c may exceed the permissible range. The Roots blower rotates forward without any abnormal noise. Due to the increase in tooth backlash, when the tooth backlash is greater than or equal to δ[sub]2[/sub]', when the blower rotates in the reverse direction, at best there will be friction or a slight knocking sound between the two impellers; at worst, the two impellers may be shattered. Secondly , some Roots blower gear lubrication uses immersion lubrication. The gear end bearings are lubricated by splashing oil during gear rotation, while the front bearing is lubricated by splashing oil from the oil slinger in the auxiliary oil tank. When a frequency converter is used, the blower cannot reach the operating speed, i.e., the motor cannot reach full-frequency operation, generally only between 24HZ-35HZ. Due to the reduced operating speed, the bearing lubrication is poor, the oil's heat dissipation capacity decreases, and high temperatures accumulate. III. Conclusions 1. When using a frequency converter to control the air supply system of a vertical kiln, a venting device must be installed, and venting must be performed before shutdown; 2. During the overhaul of the Roots blower, the working clearances δ₂ and δ₂' of the two impellers should be consistent; 3. The gear backlash Cn should be controlled according to technical requirements. When the sum of the tooth surface wear and the backlash Cn is close to δ₂, the gear should be replaced; 4. Increase the cooling water in the main and auxiliary oil tanks, modify the structure of the oil slinger in the auxiliary oil tank, and add a series water cooling pipe. [b][align=center]For more details, please click: Research on Frequency Converter Controlled Air Supply System of Vertical Kiln Roots Blower[/align][/b]