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1. Principle and structural characteristics of screw conveyor
The working principle of screw conveyor is similar to that of a nut rotating on a screw which does not move axially. In the process of axially rotating movement, the rotating spiral blade in the material trough will push the material to move. The material is fed into the trough body from the feed port, and then sent to the other end along the screw, and discharged from the discharge port. The structure of screw conveyor mainly includes driving device motor, reducer, material chute, screw shaft, screw blade attached to screw shaft, support at both ends, inlet and outlet, discharge outlet and inspection port. The screw conveyor is simple in structure, easy to seal, and uses frequency converter to control the operation. The powder drop is relatively small, which can improve the accuracy of feeding control and measurement accuracy. It has a large adjustable range, good wear resistance and low operating cost. Therefore, it is widely used in concrete mixing station.
2. Analysis of common faults of screw conveyor
During the operation of screw conveyor, there are four common faults:
2.1 Spiral Shaft Stops Rotating
The main reasons leading to the stop of the spiral shaft may be as follows: 1) too much material is transported, resulting in greater resistance when it passes through the suspension bearing in the middle, which increases the load of the motor and finally stops the machine; 2) it may be because the seal of the intermediate bearing is damaged, which is subject to excessive resistance, and the material damages the bearing when it enters the bearing. (3) It may be due to the mixing of materials with large particle size in the process of conveying, which increases the resistance between the material and the machine slot, increases the load of the motor, and starts the automatic protection of the motor thermal relay.
2.2 Abnormal temperature rise, abnormal noise and abnormal vibration of reducer bearing
After driving, the bearings of reducer appear abnormal temperature rise, accompanied by abnormal noise, and the motor and reducer also appear abnormal vibration phenomenon. It may be caused by the following reasons: (1) The input shaft position of the reducer is normal, but the bearing temperature of the output shaft position is too high, which is due to the deviation of the center line of the helical shaft, or the burning of the bearing at the output shaft position of the reducer, or the loosening of the bearing seat at both ends. (2) It is also possible that the temperature of the output bearing is normal, but the temperature of the input shaft rises mainly because of loosening of the fixed bolt of the motor or burning of the output bearing of the reducer. (3) The temperature of output bearing and input bearing of reducer increases at the same time, mainly because the bearings at both ends of reducer are damaged at the same time, or the fixed bolts of reducer are loosened.
2.3 screw fracture
For the rodless screw conveyor, due to the lack of support and positioning of the central rod in its structure, under the action of the helical angle, once a helical surface of the blade is loaded, the force acting on the helical angle will be decomposed into two forces in two directions: one is along the axis direction, the other is mutual with the radius of the blade. Vertical direction. Under the action of different forces in these two directions, the helical blade will have two results: one is elongated by the axial direction, the diameter becomes smaller; the other is compressed blade pitch, the diameter becomes larger. After being restrained by the inner wall of the steel cylinder, the elastic deformation will be transmitted along the axis step by step until it reaches the front end of the transmission sleeve. If the material conveyed by the screw conveyor is of uniform quality, such as lime, in the course of operation, the force on the blades can be uniformly distributed, thus ensuring the normal use of the screw.
Life. Conversely, if the material conveyed by the screw conveyor has a larger particle size, or even a large block, the screw will be jammed out. If the screw blade is repeatedly subjected to large impact force in order to eliminate the faults, especially the front screw restrained by the transmission sleeve, it will suffer the greatest impact force. After reaching the fatigue limit, the front end of the rotating sleeve will begin to fracture.
2.4 other faults
Other faults of screw conveyor include: (1) abnormal noise of open gear drive. The main cause of abnormal noise in open gear transmission may be the loosening and offset of transmission device or support, which affects the distance between transmission gears, or the offset and loosening of bearings at the head and end of transmission gears. (2) Torsion crack of flange weld. The main reason is that the welding failure of connecting flange is caused by abnormal torque. (3) Cracks appear in the hollow coupling shaft. It is mainly due to long-term wear and tear, which reduces the strength of resistance, and eventually leads to cracks.
3. Fault Prevention and Improvement of Screw Conveyor
In view of the common faults of screw conveyor, the following preventive measures can be taken:
3.1 Improving the Connection Strength of Bolts
The main factors affecting the strength of bolt connection include the load distribution of threaded teeth, the range of stress variation, the mechanical properties of materials, the degree of stress concentration and additional stress, etc. Through a lot of practice and theory, it can be proved that the tightened bolt connection is subjected to axial load. Based on the condition that the minimum stress is unchanged, the reliability of the connection is closely related to the stress amplitude. The smaller the stress amplitude, the smaller the possibility of fatigue damage of the bolt, thus improving the reliability of the connection. Because when bolts are connected, the total pulling force will be transmitted through the contact of thread teeth. Because of the different rigidity and deformation properties of bolts and nuts, the forces on the ring thread teeth are also different. When the connection is loaded, the bolt will be stretched to increase the pitch of the external thread, while the corresponding nut will be compressed to reduce the pitch of the internal thread. Therefore, the appropriate number of turns to choose the nut.
3.2 Improving the Quality and Strength of Components
In the structure of screw conveyor, there are strict requirements for the distance between helical blades and the guiding angle. If there are large errors between adjacent blades and the guiding angle, the equipment will increase the swing amplitude and vibration amplitude during operation, which will affect the reliability and safety of the blades. In addition, the screw conveyor usually has a lot of materials and a long running time, so the damage to the screw blade is relatively large, which leads to the problems of distortion, deformation and wear. In view of this situation, we should start from the source, improve the quality of the helical blades, strictly control the size error between the blades, improve the density and reliability of the weld, prevent slag inclusion or blowhole problems, and further ensure the strength of the helical shaft and the transmission shaft.
3.3 Guarantee Installation Quality
For screw conveyor, no matter which connection method is adopted, the accuracy of screw installation position should be guaranteed, and the problems of flange welding joint torsion crack should be avoided. After the installation of the equipment, wiring debugging should be carried out to ensure the correctness of the spiral steering, there should be no abnormal sound problems, and to ensure the flexibility and reliability of pneumatic butterfly valve action. After commissioning, the relevant indicators and parameters such as motor, reducer, bearing temperature rise should be checked to ensure that everything is normal and then open the manual screw silo gate, gradually feeding until the screw runs smoothly. During the operation of screw conveyor, the quality of materials should be strictly controlled to prevent excessive size of materials from being fed into the conveyor, and the driving device should be taken as a key maintenance item.
Daily Maintenance of 3.4 Spiral Conveyor
Specifically, the daily maintenance work of screw conveyor focuses on the following aspects:
(1) Regular inspection of the quality of helical blades, timely removal of abnormal wear, helical shaft deformation and other issues, once such problems are found, timely replacement; regular inspection of connectors, found that loosening should be tightened; if there are problems such as heating, noise and other problems in the operation of equipment, timely removal, spiral or chute repair or dimension. Protect.
(2) To do a good job of lubricating the head and tail bearing boxes, we can add lithium-based grease regularly every month, the amount of injection is 2/3 of the space in the bearing boxes; at intervals of 3-5, the suspension bearings and suspension shafts are immersed in the melted grease at the same time, and then re-assembled after cooling with the grease at the same time.
3. Maintenance of reducer should be done well. For rolling bearings, calcium-sodium base grease can be used. If the screw conveyor runs at a high frequency, it is best to replace the grease once every three months, or to extend or shorten it properly according to the actual operation of the equipment; to check the oil quantity in the reducer regularly; to make a good maintenance plan, a half-year minor overhaul and a two-year major overhaul, among which The main items of minor repairs include: replacing lubricating oil, checking the condition of transmission gears, sealing of rolling bearings, etc. In addition to the minor repairs mentioned above, the major items of major overhauls also need to disassemble all parts for inspection, and timely repairs or replacements should be made when problems are found. For transmission gears, if one of the following problems occurs, they should go ahead. For scrap replacement, cracks, pitting corrosion on the tooth surface is 1/3 of the bite surface, and the first bite gear is worn to 1/10 of the original tooth thickness.
