Time : Settembre 28, 2021
Hammer crusher is mainly used to crush limestone and clinker matched with grate cooler in cement plant. One of the main faults in its production is bearing heating. Some of the heating phenomena occur in the initial running in period and become normal after running for a period of time. Some phenomena lasts for a long time and has a great impact on production. The main causes of heating are: improper bearing design and selection, poor processing quality of equipment parts, unqualified installation, improper selection or filling amount of lubricant, improper use, maintenance and repair, resulting in loose vibration and fit, failure to replace the bearing in time after wear, and high ambient temperature due to improper operation. This paper makes a detailed analysis of the causes and maintenance of the crusher hammer, and gives the corresponding precautions for the use of the crusher hammer.
1. Improper Bearing Design and Selection
1.1 Improper Selection of Bearings
Hammer crusher belongs to heavy load equipment. It is started with heavy load when starting, and the load is heavy and has impact load when running. Therefore, two aspects should be paid special attention to when selecting rolling bearing:
(1) Load selection of bearing. If the selected bearing has low rated load and serious bearing wear during operation, it will cause bearing heating and shorten its service life.
(2) Selection of bearing clearance. Too small clearance is not conducive to the formation of oil film and the elimination of thermal expansion. Especially when the ambient temperature is high, too small original radial clearance will make the clearance of the bearing smaller or even zero due to the expansion of temperature rise during operation, which is easy to cause bearing heating.
The clearance of rolling bearing is divided into radial clearance and axial clearance. Radial clearance is divided into original clearance, installation clearance and working clearance. The selection of clearance should consider the fit between bearing and shaft and bearing seat, the change of original clearance caused by working temperature and load. The reasonable selection of bearing clearance should be based on the original clearance and consider the change of clearance caused by fit, temperature difference between inner and outer rings and load, so as to make the working clearance close to the best state.
Most of the hammer crushers are equipped with tight sleeve bearings, inner ring tapered holes, which can adjust the clearance during installation or operation. The radial clearance of tapered bore spherical roller bearings with tight sleeve is slightly larger than the radial clearance of cylindrical cylindrical roller bearings with the same group. However, for hammer crusher, with heavy load and impact load, the ring of rolling bearing is easy to deform, resulting in uneven stress on the mating surface and loose mating. Therefore, the larger the load, the larger the interference should be selected. Due to the increase of interference, the reduction of radial clearance caused by interference during assembly should be larger. In addition, the clearance is further reduced due to the temperature rise during operation. Therefore, for heavy load equipment such as hammer crusher, C3 clearance group with larger clearance than the basic group should be selected.
1.2 Improper Design Fit Between Bearing and Shaft or Hole
The rolling bearing is not properly matched with the shaft or hole. When the bearing works, due to the influence of friction heating and other heat sources, the temperature of the ferrule will be higher than that of the matched parts. The thermal expansion of the inner ring will lead to the looseness of its fit with the journal, while the thermal expansion of the outer ring will lead to the tightening of its fit with the shell hole, which will lead to the heating of the bearing. For example, a PC1010 hammer crusher uses 3628 double row centripetal spherical roller bearings, and the bearing temperature rises frequently, resulting in adhesive wear of the journal. The reason is the improper fit between the bearing and the shaft, and the tolerance of the original design main shaft journal ϕ 140k6 is low, the temperature rises after operation, and the bearing inner ring and journal change from interference fit to clearance fit, resulting in relative sliding.
The tolerance K6 of ϕ140 axis is selected when it belongs to light load, and M6 tolerance shall be selected even under normal load. For the heavy-duty equipment such as hammer crusher, the diameter is ϕ140 shaft should be selected ϕ140p6 or slightly larger interference ϕ140r6。
Of course, the above bearings are ordinary cylindrical hole self-aligning roller bearings. For Hammer Crushers, more rolling bearings with tight set sleeve are used. The tolerance of shaft is H9, and the tolerance of bearing seat hole is H7. The interference fit between shaft and bearing is realized by tightening the tight set sleeve.
2. The Machining Accuracy of Equipment Parts can not Meet the Requirements
In the causes of bearing heating of hammer crusher, the machining accuracy of equipment parts can not meet the requirements, especially the machining accuracy of bearing seat can not meet the requirements, which is also an important factor. The tolerance, roughness and cylindricity of the bearing seat hole shall be ensured during the processing. If the hole tolerance is too small, the bearing clearance will be too small during fitting, and if it is too large, the fitting will be loose. Both of these conditions will cause bearing heating.
3. Poor Installation Quality
The poor installation quality is mainly reflected in the non levelness of the bearing seat, the misalignment of the coupling and the lack of sufficient thermal expansion of the bearing.
Improper installation causes misalignment of the coupling and uneven bearing seat. The alignment of the coupling or split bearing seat is not adjusted well, and the alignment accuracy is poor. The bearing is in a distorted state in the initial state.
The alignment of the coupling shall be in accordance with the requirements of the general code for construction and acceptance of mechanical equipment installation engineering (GB50231-2009), and the maximum allowable value of radial displacement and inclination shall be determined according to the diameter of the coupling, and corrected according to this value.
During installation, the free end bearing does not leave enough thermal expansion, so that this end bearing cannot extend freely during operation, resulting in the bearing standing large axial force, heating and even burning out.
The two rolling bearings of hammer crusher are generally installed with one end fixed and one end free. In this way, when the temperature rises during operation, the shaft can swim freely without blocking after thermal expansion. Therefore, pay attention to the calculation and reservation of this thermal elongation during installation, and make the axial clearance between the bearing end face and the bearing seat end cover greater than the thermal elongation of the shaft. If the reserved clearance value is insufficient, the end face of the bearing will be pushed against the end cover of the bearing seat after the shaft is heated and expanded, resulting in bearing heating or even burning out.
4. Poor Lubrication
Poor lubrication includes improper lubricant selection, improper filling amount or oil level of grease, deterioration of oil (grease) or lack of oil (grease).
(1) The lubricant selection and lubrication method are unreasonable. The rolling bearing lubricant shall be selected according to the bearing operating temperature, speed index, load characteristics, lubrication method and other factors. The improper lubricant selection and the too low or too high viscosity, which will make the heat generated in the bearing operation unable to be taken away, resulting in bearing heating.
(2) Improper amount of oil (grease)
Too little or too much oil (grease) will cause fever due to lack of oil or too much oil and large agitation.
(3) Failure to change oil on time, deterioration of lubricating oil and impurities such as iron filings in lubricating oil lead to deterioration of lubrication condition.
(4) The bearing is short of oil, hot and invalid due to oil leakage of bearing seat and other reasons.
As the hammer crusher belongs to heavy-duty equipment, there are some misunderstandings in the selection of lubricants, and there is a tendency to blindly pursue high viscosity.
For the selection of lubricant for hammer crusher in cement industry, L-HM68 anti-wear hydraulic oil (GB11118.1-2011) should be selected for thin oil centralized lubrication or oil immersion lubrication. For oil cup lubrication, 2 Extreme Pressure Lithium Grease (GB/T7323-2008) can be used. For the hammer crusher equipped with grate cooler, when grease is used for centralized lubrication, the grease can be No. 1 extreme pressure lithium grease (GB/T7323-2008). For oil cup lubrication, 2 Extreme Pressure Lithium Grease (GB/T7323-2008) can be used.
As for the selection of filling amount or oil level, for oil immersion lubrication, the oil level should be in the middle of the upper and lower red lines of the oil mark, and the oil level height of the rolling bearing is not allowed to exceed the center of the lowest roller. For concentrated oil supply of thin oil, pay attention to the oil supply pressure. For grease lubrication, the grease filling amount should be 1 / 3 ~ 1 / 2 of the inner cavity volume of the bearing seat.
5. Vibration Factors
The vibration of hammer crusher also affects the wear and temperature rise of bearing. Vibration sources include rotor imbalance, installation misalignment, loose connecting bolts of bearing seat and vibration transmitted by motor. In particular, the imbalance factor of the rotor is more prominent. Due to the large mass and high circumferential speed of the rotor, a large centrifugal force will be generated after losing balance, which will cause strong vibration of the crusher, which will accelerate the wear of the bearing and cause the heating of the bearing.
The national standard of hammer crusher stipulates that the vibration amplitude of the bearing seat of hammer crusher shall be ≤ 0.2mm. If the vibration exceeds the standard, it shall be handled.
6. Bearing Wear and Fit Failure
The wear of bearing is the most important fault in the use of bearing. Continuous wear will change the size of inner ring, outer ring, rolling element and cage of bearing, and even produce pitting or peeling. The matching clearance of bearing will increase and the surface roughness of running elements will increase, which will reduce the running accuracy of bearing and therefore the running accuracy of machine, This will cause the temperature rise, vibration increase and noise increase of the bearing. In serious cases, it will lead to heating, vibration increase, bearing burning and even shaft bending.
In addition, during the operation of the bearing, there will be failure such as loose fit, which will also cause bearing heating.
7. Excessive Tension of V-belt
When the hammer crusher adopts V-belt drive, if the tension of V-belt is too large, it will also cause bearing heating and accelerated wear of V-belt and bearing.
8. Improper Maintenance Method
In the use of the bearing with tight sleeve of hammer crusher, due to improper maintenance methods, the bearing is too tight or loose while tight, which will also cause bearing heating and bearing wear. The bearing with a set sleeve is characterized in that the clearance of the bearing can be adjusted through the set sleeve, but improper adjustment will cause the rupture of the set sleeve or the loosening of the fit. For example, the bearing of a grate cooler hammer crusher is 22338K + H2338. When the bearing is heated and the shaft moves, the treatment measures are improper. Only the method of fastening the fixed sleeve at the non transmission end is used to deal with the fit between the shaft and the bearing. The shaft shifting indicates that the fit between the two bearings and the shaft is loose. Only one bearing is fastened. Although the shaft shifting problem is temporarily solved, the fit of the other bearing is still loose, which will cause the bearing wear and heating at the loose part, and make the bearing at the fastening part bear all the axial force, so it becomes easy to loosen. Therefore, the actual result is that the bearing heating and shaft shifting are becoming more and more frequent. The correct method is to tighten the set sleeve of two bearings at the same time.
The tightening of the bearing with the fixed sleeve is generally judged by measuring the reduction of the radial clearance of the bearing, because after the interference fit is formed during tightening, the radial clearance of the bearing will be reduced on the basis of the original clearance, and the reserved radial clearance should consider the influence of the temperature difference between the inner and outer rings when the bearing is working.
9. The Ambient Temperature is Too High
For the hammer crusher matched with the grate cooler, when the process operation is normal, the temperature of the clinker is + 65 ℃, but when the operation is abnormal, the temperature of the clinker is high, and the high ambient temperature will also increase the temperature of the bearing. Therefore, it is necessary to pay attention to the requirements of the crusher for the working environment. For example, the grate cooler hammer crusher of a 5000t /d line was started up after one overhaul. Due to the failure to discharge the high-temperature air in the grate cooler in time and the high clinker temperature (up to 200 ℃ on average), the bearing temperature of the crusher increased rapidly.
10. Conclusion
There are many reasons for the heating problem of the rolling bearing of the hammer crusher. When dealing with the heating problem of the bearing, we should comprehensively analyze and consider from the aspects of design, processing, installation, lubrication, use, maintenance and repair, find out the main reasons and take corresponding measures to deal with it. For the grate cooler hammer crusher with high ring temperature, give full play to the role of the cold air blade on the shaft and strengthen the cooling role; For the general hammer crusher without cold blade, when the bearing is hot and the cause cannot be found for the moment, temporary methods can be used to reduce the temperature of the bearing, such as welding the cooling blade blade on the flywheel to reduce the temperature of the bearing.
More about Hammer Crusher：
There are two forms of hammer crusher: single rotor crusher and single rotor crusher. It is a crusher for directly crushing materials with a maximum particle size of 600-1800 mm to 25mm or less. Hammer crusher is suitable for crushing medium hardness materials in cement, chemical industry, electric power, metallurgy and other industrial sectors, such as limestone, slag, coke, coal and other materials. Single rotor is divided into reversible type and irreversible type. Single rotor hammer crusher and ring hammer crusher are widely used.
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