3. Fever caused by improper assembly of the bearing itself
(1) Improper cooperation
The inner hole of the bearing and the shaft are made by the base hole, and the outer circle of the bearing and the bearing hole are made by the base shaft. Generally, under normal load conditions, the shaft and the inner race of the bearing are matched by j5, js5, js6, k5, k6, m6, and the bearing seat hole and the bearing outer race are matched by j6 and j7. Rotating races, usually with an interference fit, can prevent the race from rolling and sliding on the shaft diameter and the mating surface of the housing bore under load.
However, due to the inaccurate measurement of the shaft diameter and the bearing housing hole or the roughness of the mating surface does not meet the standard requirements, the excessive interference fit is caused, and the bearing race is greatly squeezed, resulting in the radial clearance of the bearing itself. The reduction makes the bearing difficult to rotate, generates heat, and the wear is intensified or stuck. In severe cases, the inner and outer races of the bearing are cracked during installation.
The non-rotating seat often adopts a gap or a small interference, so that the rotation of the seat may cause a slight creep, and the contact surface of the race with the rolling element is continuously replaced, and the raceway of the race is evenly worn.
At the same time, it is also possible to eliminate the axial jam of the rolling elements in the bearing due to the thermal elongation of the shaft. However, if the gap is too large, the non-rotating seat will rotate together with the rolling elements, causing severe wear of the shaft (or the bearing housing hole) and the inner race (or the outer race), and the friction causes the bearing to heat and vibrate.
TH's cement grinding reducer was burned out after only two hours of operation after replacing the new bearing. Initially, the gap between the eccentric sleeve for fixing the bearing and the outer race of the bearing caused the vibration of the reducer. During maintenance, many pockmarks were found on the inner surface of the eccentric sleeve, and at the same time, the solid tooth glue was applied, which caused the bearing outer race to be unable to generate axial displacement, and thus could not be burned out if the shaft expansion requirement could not be satisfied.
(2) Improper assembly method
When the bearing and the shaft diameter or the bearing housing hole have a small interference, the press-in method is often used for assembly. The easiest way is to use a copper rod and a hand hammer to symmetrically tap the bearing with an interference fit in a certain order to make the bearing smoothly pressed in.
In addition, it is also possible to use a sleeve made of soft metal to be hammered in or pressed by a press. If improperly operated, the seat will be deformed and cracked, or the hand hammer will be hit on the non-interference fit seat, which will cause the raceway and the rolling element to be indented or the bearing to be indirectly damaged.
(3) Improper temperature control during assembly
When the rolling bearing is assembled, if it has a large interference with the shaft diameter, it is generally assembled by hot charging. The bearing is placed in the oil drum with organic oil. The outside of the oil drum is heated by hot water or flame. The temperature of the oil required for heating is controlled at 80 °C ~ 90 °C, generally not exceeding 100 °C, and not exceeding 120 °C.
After the bearing is heated, it is quickly taken out and placed on the journal. If the temperature is not properly controlled, the heating temperature will be too high, which will cause the bearing to temper and the hardness will decrease. During operation, the bearing will be prone to wear, peeling, excessive temperature rise and even cracking.
It should be noted that when oil is used to “boil” the bearing, the bearing should be placed flat in the oil drum, and a wooden block or steel bracket with a height of about 50 mm should be placed between the bearing and the bottom of the cylinder. The instrument or thermometer controls the oil temperature. Since the oil bath heating method is inconvenient for measuring the bearing expansion amount, temperature control, and installation, it is recommended to use an electromagnetic induction heater.
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