Dynamic screen is a common equipment in mining machinery, and its vibration is mainly realized by exciter.The exciter forms are diverse, and the widely used eccentric-block external structure has the characteristics of light weight, compact structure, lubrication concentration of transmission parts, convenient maintenance and low manufacturing cost.However, there is a general problem in this structure, that is, the bearing life in the exciter is short, and the bearing heating and burning loss often occur, which seriously affects the normal operation of the vibrating screen.
The operating condition of the exciter is harsh, not only the environment humidity is large, the dust is much, the speed is high (750~1400r/min), and there is a strong vibration impact.After practical experience, the main bearing damage is:
1.Design reasons
1) unreasonable selection of bearing type
Vibrating screen rolling bearing in the process of work by the impact load is bigger, the centrifugal force generated by the eccentric block high-speed rotating and centrifugal acceleration is bigger also, combined with the working environment of dust is more, so the use of the bearing type, speed limit, installation dimension, the demand is higher, such as clearance, lubricating general bearing under the condition of work is easy to damage.If the bearing is not selected properly at the initial stage of design, the service life of the bearing will be shorter.
Treatment method:
Special bearings for vibrating screen are selected.The commonly used vibrating screen bearings have two types: cylindrical roller bearing and aligning roller bearing.The cylindrical roller bearing has large radial bearing capacity, high bearing speed, strong bearing capacity for dynamic and static load, but high requirement for the coaxial degree of bearing pedestal hole.
Self-aligning roller bearing not only has large radial load capacity, and can withstand the direction of axial load, self-aligning performance is good, can compensate the coaxial problem caused by the bearing hole processing, but can't afford to pure axial load.
Because the vibrating screen is used in a bad environment,many bearing manufacturer for vibrating screen production special big clearance of bearing, bearing materials with special materials, structure more plain bearing have bigger difference, also has the bearing capacity is strong, impact resistant performance is good, the good characteristics of lubrication.
2)The lubrication seal structure design is not reasonable
Vibrator working process of the axial eccentric block under high speed rotation to produce larger radial force, due to the lubrication sealing structure design is unreasonable, inadequate bearing lubrication, is lead to deformation of the bearing heats, finally the main reason for the loss.At present domestic many vibrator bearing mainly adopts grease lubrication, sealing mainly adopts labyrinth seal structure, seal clearance generally in 1 ~ 2 mm, but in the actual use process as the vibrator inside the bearing temperature rise, grease viscosity reducing gradually, vibrator shaft high-speed rotation, grease in maze cover spilled from the labyrinth cover, eventually lead to bearing damage due to lack of lubrication.
Treatment method:
Use thin oil to lubricate, improve lubrication channel, lubricate circulation, make bearings get full lubrication.Improve the sealing structure, on the one hand to prevent the lubricating oil seepage in the box, on the other hand, to prevent the moisture and dust in the air from entering the tank to contaminate the lubricating oil.
3) improper selection of bearing and bearing pedestal holes
Bearing and bearing hole fit tolerance is the key point of design.If the bearing and bearing hole are selected to be larger than the interference fit, it will force the bearing raceway shape to produce geometric deformation, which will cause abnormal vibration when the bearing is running.If the large clearance fit is selected, the bearing outer ring will be produced relative sliding in the bearing hole, resulting in a sharp rise in the bearing temperature and the final bearing damage.
Treatment method:
Choose reasonable match tolerance.Because the radial force of the bearing inner ring is stationary when the exciter is working, the inner ring of the bearing is positioned in the axial direction.Therefore, the alignment of the inner ring and shaft of the bearing should adopt a loose transition fit or clearance fit tolerance.
4) the expansion of the shaft is not considered in the design.
Vibrator operating temperature is generally in the 60 ~ 85 ℃.Caused by heat bilges cold shrink shaft expansion amount can not be ignored, assuming that vibrator shaft 1 m long, temperature 40 ℃, the shaft so that temperature difference caused by the expansion amount to more than 0.45 mm.Such a large amount of deformation, if not considered enough to damage the bearing during design.
Treatment method:
Design will end bearing is designed to transfer or clearance fit, so that the vibrator shaft when heat bilges cold shrink can slide relative to the inner ring, avoid bearing under the effects of the axial force due to the heat bilges cold shrink.
2.Process reasons
1)the machining precision of the bearing hole is not enough, and the two bearing holes of the same shaft are different.
Treatment method:
The concentric precision of two bearing holes is guaranteed by machining with high machining accuracy.In CNC boring and milling machine or machining center, one cutting of two bearing holes is completed.
2) uneven force during bearing assembly.
As in the process of cold assembly, the inhomogeneity of the inner ring of the bearing causes a certain deflection of the inner ring of the bearing, and the inner ring of the bearing will wear out faster during operation.The outer ring of bearing is not evenly applied, and the outer ring of the bearing can also produce a certain deflection, which causes the outer ring of the bearing to wear faster.
Treatment method:
The special assembly is made for bearing assembly, so that the inner ring or the outer ring are uniformly pressurized and assembled in place during bearing assembly.Prevent the force of the inner and outer ring during assembly.
3) when the bearing is installed, it is not clean, or the lubricating oil is not clean, which causes the bearing roller to wear out, the friction of the rolling body increases, the temperature rises, and finally the bearing is damaged.
Treatment method:
Clean the bearing before assembly.In the process of using the shock absorber, the lubricating grease should be replaced regularly.For the first time, after 150h of equipment use, the equipment must be replaced after 1000h.
4)there is a large Angle error between the mass difference of the group eccentric block and the installation Angle of the eccentric block, which causes the vibration of the vibration source center and causes the bearing heating.
Treatment method:
Adjust the quality and Angle of eccentricity block so that its quality and Angle are symmetrical.If the vibrator in the two groups of counter weight Angle or different quality is different, the vibrating direction Angle and vibration power would be different, can produce the phenomenon such as sieve body torsional vibration, the vibrator influenced by load.
Therefore, when making eccentric blocks, the eccentric block should be guaranteed to be the same material with the same density.At the same time, to ensure the center of eccentricity, the geometric shape of eccentric block should be strictly required.In addition, when installing or adjusting the excitation force, the Angle of the eccentricity block on the same axis should be consistent, and the eccentricity block on the parallel axis should be symmetric.
3.Use and maintenance reasons
1)due to the improper installation of the base or spring seat, the abnormal motion of the sieve is caused, resulting in the rotation or distortion of the vibrating screen, causing the bearing heat of the exciter to be damaged.
Treatment method:
When the vibrating screen is installed and adjusted, the basic level of the foundation is first measured with the level.If the foundation is found to be adjusted by adding a pad on the base, it can be measured and adjusted to the base level.
2)the center of gravity of the vibrating screen is large, which causes the abnormal motion of the sieve, which causes the heat damage of the exciter bearing.
Treatment method:
Ideal working state of the vibrating screen should be smooth machine operation, various amplitude is consistent, but because do not have a unified benchmark design, processing and installation accuracy is low, or the material not equal reason often exciting force caused by deviation from the center of gravity, resulting in vibrating screen rotation or distorted, vibrator is abnormal loading, causing damage bearing heating.Therefore, only by strictly controlling the precision of production and installation during design, manufacture and installation can the center of gravity position of excitation force be guaranteed.At the same time, when using shaker, try to achieve uniform material.
3)the fixed bolts of the vibration exciter are loose or not added to the spring washer, causing the vibration of the vibration source center, causing the vibration of the exciter bearing to be damaged.
Treatment method:When the exciter is connected, the elastic gasket is added, and the exciter is used for the first time. After running 2h and 50h, it is necessary to re-examine the mounting bolts of the fastening vibration device and find that the looseness is immediately tightened.The bolts and nuts of the exciter can only be used once and must be replaced after fastening.
4)improper selection of lubricating oil, filling too much or too little, resulting in heat damage of the exciter bearing.
Treatment method:
Excessive grease injection, resulting in heat, normal should be filled with 2/3 of the lubricating cavity, and must use the exhaust bolts exhaust.But lack of grease or grease aging, dry also can cause the bearing heat.General in the case of not leak vibrator 0 ~ 100 h filling a lubricating oil, a charging less than 1 kg, to see how many filling oil, and timely get rid of waste oil, to get the normal lubrication bearing.
The exciter is the source of vibrating screen excitation.Improving the design and processing quality, proper use and careful maintenance are the prerequisites for the good operation of the exciter bearing.
No comments:
Post a Comment