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Failure analysis and improvement of metal crusher bearings

Time:2018-10-25 Author:Hongyuan Machine

Failure analysis and improvement of metal crusher bearings

Metal crusher is a machine that utilizes the impact force to crush material by rotating the hammer at high speed inside the casing. The rotor is the main working part of the hammer breaker, and the main shaft is an important part supporting the rotor. It bears large cyclic impact force. Therefore, the material of the main shaft is required to have high strength and toughness, and bearings which can bear heavy impact load are selected. A single rotor hammer breaker is usually equipped with double row centripetal spherical roller bearings which can operate normally at high speed and have little friction. Hammer breaker rotor assembly balance (static balance and dynamic balance) higher requirements, because when the rotor has a small eccentricity, it produces a larger periodic inertial force acting on the bearing, can cause strong mechanical vibration, so that bearing wear faster. In practical work, the following experiences are summarized through observation and analysis of the reasons for early failure of bearings.

Failure analysis and improvement of metal crusher bearings

1. In the original condition, the metal crusher manufactured by our factory is taken as an example. The main shaft of the machine is 45# steel after quenching and tempering heat treatment, and 3628 double row centripetal spherical roller bearing is selected to support it. After the installation of equipment in normal production, bearing temperature often rises abruptly (temperature exceeds 80 degrees) too high phenomenon, serious accompanied by mechanical noise, affecting the normal production. Start to take shutdown cooling, intermittent work, to maintain the production of more than a month after the equipment has reached the normal operation of the situation, had to shut down inspection, in the inspection and repair found that the bearing ring and the main shaft neck with adhesion (adhesion) wear, the serious part of the adhesive neck was torn peeling. Two sets of rotor assemblies supplied by the original manufacturer were replaced successively, but after replacing the new bearings, similar phenomena appeared at the same time or so.
2. The possibility of observation first suspects that the above-mentioned problems are caused by the unbalance of the rotor and the inertia force, but the wear of the rotor keys is small and uniform, the static balance is good, and there is no great vibration in the work. During the inspection, it was found that the grease in the bearing block had dried up and failed. It was suspected that the failure of the grease caused by excessive temperature might cause the bearing to overheat and burn down. Therefore, the lubrication management of bearings will be strengthened, the grease will be added regularly and quantitatively, and the service cycle will be improved slightly, but it still can not effectively prevent the recurrence of the phenomenon of journal adhesion surface damage. Finally, the analysis may be due to improper assembly of bearings.
3. Analysis conclusion: Because the rotor of crusher bears heavy impact load and the bearing runs with friction heating, the temperature of the inner ring of the bearing is higher than that of the journal matched with it, which makes the matching of the inner ring of the bearing and the journal loose because of thermal expansion. In practical work, due to the different changes of temperature rise between bearing inner ring and journal, the matching properties of bearing inner ring and journal change constantly in different periods. The matching of bearing inner ring and journal is interference fit in the initial state (about 1 hour), clearance fit in the initial stage (about 2 hours) and transition fit in the later stage (about 2 hours). Therefore, the tolerance fit selected in the original design easily causes the bearing to expand due to friction heating, and the inner ring and journal slip relative to each other about 1-2 hours in the initial stage of work. The inner ring of the bearing crawls on the surface of the oil neck fit, and the metal surface peels off due to fatigue when the journal is subjected to high variable load stress. It will lead to early failure of bearing and wear of axle neck.
Improvement measures should be taken to change the tightness of bearing inner rings and journals. Considering the characteristics of hammer breaker under heavy cyclic impact load and the effect of working temperature rise, tolerance fit between bearing inner rings and journals should be selected. This fit property can ensure that the bearing inner rings and journals keep interference or excessive fit under high temperature rising conditions. No loosening will occur. In addition, spindle elongation after heating produces axial displacement, bearing inner and outer rings with the relative displacement of the bearing radial clearance reduction, or even the phenomenon of bearing stuck, should choose the bearing outer ring and bearing housing tolerance fit, and one of the bearings and bearing outer end of the pressure cover between the gap. The balance of the rotor will produce a lot of vibration when the mass of the rotor is large, the rotational speed is high, and a small amount of unbalance occurs, which will increase the power and cause bearing damage when serious. Therefore, the rotor must be balanced before it can be used. The important factor affecting the rotor balance is the hammer head. By changing the hammer head, the two hammers with equal mass are assembled in two symmetrical positions, and the gravity of the hammer head must be well matched so that the gravity of the hammer head is balanced, the gravity of each row of the rotor circumference direction is equal, and the axial gravity is uniformly arranged, so that the hammer breaker runs. The rotor can reach the balance requirement and avoid vibration. Special attention should be paid to the replacement of new hammers. Enhanced sealing lubrication and timely and correct lubrication can reduce friction resistance, cooling can remove friction heat and inhibit bearing temperature rise. Aiming at the characteristics of high speed, heavy load and high temperature rise of hammer breaker, aluminum disulfide compound calcium grease lubricating bearing should be selected. The grease is suitable for high temperature, high speed and heavy load occasions under 140 degrees. Its performance is superior to that of general compound calcium base grease. Its high temperature resistance, wear resistance and extreme pressure resistance, and service life is much better than that of ordinary calcium base grease. As the hammer breaker works in harsh environment, the grease has a great friction loss. It should be filled with grease every 8 hours, changed oil every three months, and washed bearing and seal sleeve and cover with gasoline or kerosene, and replaced labyrinth seal sleeve and cover with excessive wear gap on the bearing seat in time.
After being assembled and used according to the above measures, it is effectively prevented.

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