Analysis on the Causes of Sliding Bearings Holding Axle

(1) The lubricating oil and sliding bearing oil pool have impurities, dirt, and poor oil cleanliness. When the oil ring rotates with the main shaft, the oil supply system starts to work. Impurities and dirt enter between the main shaft and the sliding bearing along with the lubricating oil. The gap between the main shaft and the sliding bearing is generally 0.03-0.04mm. When impurities and dirt pull the main shaft or sliding bearing, non-liquid friction is prone to occur, resulting in shaft holding.

(2) The grinding head lubrication system is malfunctioning. The plain grinding sliding bearing is lubricated by an oil ring. This lubrication method has the advantages of simplicity, automaticity, and low oil consumption. 16 small holes of 5mm are evenly distributed on the circumference of the oil ring. When the oil ring rotates with the main shaft, the small hole on the oil ring splashes the lubricating oil in the oil pool, and the lubricating oil splashes on the main shaft. The spiral oil groove on the main shaft inputs the lubricating oil between the main shaft and the sliding bearing. When the lubrication system of the grinding head does not supply oil or the oil supply is unstable, the phenomenon of shaft holding will occur.

After shaft seizure occurs, the reasons can be found from several aspects:

①Whether there is oil leakage in the grinding head.

②Whether the oil pool is short of oil, and whether the oil level is lower than the indicator line on the oil mark. There is a kind of flat grinding lubricating oil which is prepared with kerosene, which is volatile. When the grinder is in normal use, the operator should always pay attention to the oil mark. When the lubricating oil in the grinding head is lower than the indicator line on the oil mark, add lubricating oil in time.

③ Before assembling the grinding head, the grinder manufacturer must check the ovality of the inner hole of the oil ring (ovality≤0.05mm) and whether the 16 5mm holes on the oil ring are evenly distributed. The oil ring is sleeved on the main shaft, the inner circle of the oil ring is close to the outer circle of the main shaft, and the lower end of the oil ring is placed under the oil surface. When the main shaft rotates, the oil ring is driven to rotate synchronously by static friction. When the ellipse of the inner hole of the oil ring is too large, the contact surface between the main shaft and the oil ring will be large and small, or even not in contact, so the friction force will be large and small, or even without friction, causing the oil ring to rotate quickly and slowly , The oil supply is normal and abnormal momentarily and the shaft is hung.

(3) The lubricating oil of the grinding head sliding bearing does not meet the specified requirements. There are two types of lubricating oil for flat grinding heads: one is N7/GB3141 machine oil, and the other is 1 part of N23 machine oil and 9 parts of kerosene. Some users purchase new flat grinders and directly inject other types of mechanical oil without reading the instruction manual, which causes the shaft to lock.

(4) The radial clearance between the main shaft and the sliding bearing is too small, the lubricating oil is not easy to input, and the temperature rise between the main shaft and the sliding bearing is too high, resulting in the shaft holding.

(5) The scraping method of the sliding bearing is incorrect, and the contact point does not meet the requirements. Incorrect scraping method of sliding bearing, uneven contact points or too few contact points will make the bearing oil film unstable and poor oil film rigidity. If the grinding wheel is being ground, it is easy to cause shaft holding.

(6) The coaxiality of the rear bearing seat and the grinding head body and the perpendicularity of the end surface, as well as the deviation of the parallelism of the outer spacer between the two rolling bearings, and the inner spacer are too large. When this happens, the front end of the spindle, that is, the cone of the spindle contacting the grinding wheel chuck, has a relatively large runout. When the spindle is rotating, the runout and position of the spindle cone are extremely unstable and fluctuate. In fact, this is a superficial phenomenon, which reflects that the spindle axis is drifting and unstable, which leads to unstable bearing oil film and poor oil film rigidity. If the grinding wheel is grinding, it is very easy to produce shaft holding.

(7) The vertical feed is too large, and the cutting is overloaded. At this time, the speed of the grinding wheel decreases, the rigidity of the bearing oil film decreases, and non-liquid friction is formed between the main shaft and the sliding bearing, which eventually causes the shaft to hold. There are many factors for flat grinding heads to hold the shaft. When looking for the cause of the shaft, you must not grasp the point and eliminate the fault from multiple perspectives and all-round.

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Repair of sliding bearing after embracing shaft and measures to prevent embracing shaft

(1) It is matched with the radial ball bearing 210, the outer spacer ring and the inner spacer ring between the D grade (when two 46210, D grade angular contact ball bearings are used, the spacer ring is not required), and the 20kg is applied to the bearing. The axial force determines the height difference between the inner and outer spacers, and the parallelism of the two ends of the inner and outer spacers is less than or equal to 0.003ram.

(2) Install the rear bearing seat, rolling bearing, bearing outer spacer and inner spacer on the main shaft, and then install the above-mentioned assembly into the grinding head body.

(3) Place the grinding head body vertically (the spindle cone face up) without sliding bearing, and measure the radial runout of the spindle ≤0.1mm. Attach the dial indicator holder to the end of the spindle with the needle pointing to the inner diameter of the front bearing seat, and measure the coaxiality between the spindle and the front bearing seat ≤0.02mm. If the measured value is out of tolerance, the inner and outer spacers of the bearing should be readjusted, and the rear end of the grinding head body should be ground until the requirements are met.

(4) The main shaft and sliding bearing are equipped with scraping. Attention should be paid to the scraping: ①The red lead powder or red ink oil applied should not be too thin. It should be evenly applied. ②When scraping the sliding bearing with a scraper, the radial force is 10kg, and the gap between the main shaft and the sliding bearing seat is adjusted to 0.02—0.025mm.

(7) The sliding bearing is filled with lubricating oil as required, and silk cloth should be used to filter the filling.

(8) Place the grinding head body horizontally and run it idling for 4 hours to allow the main shaft and sliding bearing to get full running-in, and measure the temperature rise of the bearing ≤30℃.

(9) Drain all the lubricating oil in the grinding head body. Refill lubricating oil as required. Silk cloth should be used for filtering when filling oil. It is necessary to spot check the cleanliness of the lubricating oil. According to the weight method, the impurities and dirt should not exceed 200mg.

(10) Adjust the gap between the main shaft and the sliding bearing seat to 0.03~0.04mm, and start a test run. To measure the radial runout of the spindle cone and the axial movement of the spindle, the old machine tools should be less than 0.01ram, and the new ones should be less than 0.005mm.