Bearing and shaft and hole tolerance and selection of bearing clearance

1. Question 1) In mechanical design, see how to select the bearing and the shaft and hole tolerance, as to how to select the bearing clearance, is more or less vague. The original clearance, installation work clearance, clearance exactly how to choose? 2) Ordinary mechanical design, the journal of normal load, 120 mm, all choose the m5 tolerance ( + 0. 013, + 0. 028). The average + O. 0205; Basic clearance group ( + 0. 015 ' + 0. 041). , the average + 0. 028; Bearing inner hole tolerance ( 0, - 0. 02) , the average - 0. 01. So after installing the average interference becomes + O. 0305, compared to the bearing clearance only + 0. 028, became a negative clearance at work, it is ok for you? 3) Continuous load, a motor, 600 kw, 120 mm diameter of axle, using 6324 bearing. If choose shaft tolerance n6, C3 clearance, do you think small clearance? Whether should choose C4 clearance or choose the m5, C3 clearance? After installation clearance whether to thermal expansion of the space? Should have how old? 2. Answer 1) Don't choose clearance suggestion, in the manual is reasonable. This is because the bearing clearance is set in production, so when use is to cooperate with its clearance to choose the appropriate tolerance matching, not the other way round. Because according to your tolerance and fit to the selected bearing. That is the essence of the clearance choice, is to choose the appropriate tolerance to cooperate. Under normal circumstances, bearing the internal clearance at work should be a very small positive ( Yu except taper roller bearings and angular contact ball bearing) 。 As for how much, different types of bearings, have different scope. Usually temperature conditions, for example, general of small and medium-sized deep groove ball bearings work clearance in 4 ~ 1 l recommend microns. 2) You said bearing clearance changes, said only the change of the influence of tolerance, but there is another aspect to note that is the temperature change, heat bilges cold shrink caused by clearance changes. It must also want to consider when calculating. Select clearance is the original clearance minus caused by tolerance matching clearance decreases, and subtracting the clearance variation due to temperature changes, the resulting work clearance conform to the basic operation condition is good. 3) Put you on your request of the bearing has made the following calculation: because you did not give the temperature distribution ( Shaft, bearing chamber) , so I only tolerance was calculated ( Assumes that the bearing chamber of tolerance for H7) 。 If is the diameter of axle n6, if choose 6324 / C3 bearings, internal residual clearance is 0. 005-0. 049mm。 If you fit into the m6, remaining clearance to 0. 003-0. 057mm。 From here you can see, in fact is not a problem you need to choose C4, but you need to look at their own tolerance matching problem. In addition, you said white space for thermal expansion and I think that need to be considered. Because, the so-called thermal expansion of space, inside the bearing, the biggest effect should be a clearance. Cooperate and clearance to choose by the way, here are the natural, don't own the other left. Finally a general suggestion: for industrial motors, general health, it is recommended to use. Clearance ( Except for small motor) 。 Tolerance matching according to the manual selection ( Should believe manual, because the Numbers are closely calculated) Unless have special temperature load change. Even in my personal work at ordinary times, only the temperature or operating conditions have special requirements to do clearance. In general, in accordance with the manufacturer directly provide the manual option.