(1) Lubricant Selection Issue: The rotor bearing uses Mobil EP2 grease, and all grease specifications meet the requirements for stable bearing operation. The grease selection is correct, and this issue can be ruled out.
(2) Lubricant Contamination Issue: Upon inspection, the bearing end cover was found to be clean, with no dust or other impurities present. This issue is ruled out as a cause of bearing overheating.
(3) Excessive Grease Addition: Generally, excessive grease can lead to poor heat dissipation and bearing overheating. Each bearing housing end cover of the crusher rotor has an oil drain hole. Excessive grease addition can cause a short-term temperature increase, but the bearing temperature will return to normal after the old grease is drained. This crusher bearing operates at a high temperature of around 85℃ year-round, so this is unlikely to be the cause.
(4) Bearing Assembly Issue: Upon inspection, the outer end cover of the free end bearing was opened. The distance from the outer ring of the bearing to the side of the bearing housing was measured to be 26.3 mm, and the length of the bearing end cover stop was measured to be 30 mm. Comparing the two sets of data confirmed the bearing overheating problem. The issue stemmed from the excessively tight pressure of the outer end cap on the free end bearing. The end cap's stop was pressed firmly against the outer ring of the bearing, preventing thermal expansion of the rotor shaft and causing the bearing to overheat.
(5) Calculation of rotor shaft thermal expansion: With a center distance of 3400mm between the two bearings and a working temperature difference of 100℃, and an expansion coefficient of 1.2×10⁻⁵/℃ for ordinary carbon steel, the expansion amount is 4.08mm (3400mm×100℃×1.2×10⁻⁵/℃).