In the gear transmission mechanical structure, the application of paired single-row tapered roller bearings has become more and more common. Because it can bear both radial and axial loads, it can be applied to a variety of bearing support structures. They have also explored a variety of support forms for tapered roller bearings. In order to facilitate assembly and adjustment, single-row tapered roller bearings are usually separated, that is, the inner and outer rings of the bearing can be assembled separately, which often requires the adjustment of the internal clearance of the bearing during assembly, and the requirements of the tapered bearing for the clearance. It is quite harsh, and whether the adjustment of its clearance is appropriate is directly related to the final running performance and service life of the bearing. This paper studies the characteristics of tapered roller bearings, the common layout structure, bearing clearance requirements and measurement methods, and the formation mechanism of the clearance, so as to deepen everyone’s understanding of the paired use of a single pair of tapered rollers, and guide workshop workers to better Good practice application.
1 Features of tapered roller bearings
Tapered roller bearings have tapered inner and outer raceways, with tapered rollers arranged between them. The projected lines of all tapered surfaces meet at the same point on the bearing axis, making tapered roller bearings particularly suitable for compound (radial and axial) loads. The axial load capacity of the bearing is mostly determined by the contact angle α. The larger the angle α, the higher the axial load capacity. The angle is represented by the calculation coefficient e. The greater the applicability of the axial load.
The outer circle (or inner circle) of the double row tapered roller bearing is a whole. Generally, the clearance has been set as required before leaving the factory, and no user adjustment is required. For single-row tapered roller bearings, due to their separable characteristics, the inner and outer rings are installed separately, and if they are used in pairs, the bearing clearance needs to be adjusted by the user during installation.
2 Common arrangement of paired single row tapered roller bearings
Paired single-row tapered roller bearings are supported independently, generally back-to-back or “O”-shaped support, as shown in Figure 1, because of its large load range and good support stability. The paired single-row tapered roller bearing is used as the fixed end and is used in conjunction with the cylindrical roller bearing. The single-row tapered roller bearings are distributed and supported at both ends of the shaft or gear. In order to ensure load balance, they are concentrated on the center line of the shaft, and are supported face-to-face separately.
3 Clearance requirements for paired single row tapered roller bearings
Bearings generally determine their working clearance according to the working conditions used. For ordinary transmission structures, users can query the clearance requirements according to the bearing catalog, but for structures with higher performance and more complex working conditions, such as wind power generation For speed-increasing boxes, etc., the application engineer of the bearing supplier shall formulate the clearance value of the bearing pairing and the technical requirements for assembly adjustment according to the calculation, and guide the user to complete the installation. Taking the speed increasing box as an example, in the speed increasing box structure where the paired single-row tapered roller bearings are located, the low speed stage has a low speed and a large load. In order to improve the bearing capacity, the bearing clearance is controlled in a small range; Higher, the calorific value is large, the oil demand is sufficient, and the clearance is controlled at a larger value; but the precise value should be given based on the comprehensive consideration of the expansion caused by the bearing temperature rise factor, the interference of the inner and outer rings, and the operating clearance requirements. final value.
4 Clearance measurement method of paired single row tapered roller bearings
As shown in Figure 4, according to factory practice, the matched bearings with back-to-back structure usually adjust the inner spacer to control the clearance, so the actual wear value of the inner spacer is A = H1 + H2 + C1 + ΔS,
H1 and H2 are the drop values when the inner and outer rings of bearings 1 and 2 are laid flat; C1 is the basic value of the outer spacer; ΔS is the required working clearance. In this way, the grinding method needs to measure multiple values, and each value needs to measure multiple points on the circumference, and finally calculate the average value, so the workload is large and the production efficiency is low; it can be used in the prototype trial production stage, but Not conducive to mass production. Based on the experience of the production plant, as shown in Figure 5, the following batch measurement methods are adopted:
The specific method is:
(1) Place a tapered roller bearing 1 on the flat plate after leveling, with the small end facing up, and place the machined outer spacer on the outer ring of bearing 1;
(2) Put another tapered roller bearing 2 on it with the small end facing down;
(3) Place a pressure block weighing about 100 kg (as shown in the figure, the pressure block is in the shape of a ring, hollow, which is convenient for the measuring ruler to enter and measure) on the inner ring of bearing 2, and start to rotate the outer ring of the two bearings for 10~20 circles to ensure that the two bearings are inner and outer ring with
Tapered rollers fit tightly;
(4) Measure the A1 value 4~6 times at the evenly distributed position on the circumference, and calculate the average value; then the wear distribution of the inner spacer to be processed is A=A1+ΔS (ΔS is the required value of the working clearance), and the tolerance control is ±0.025 mm; for the case where the single-row tapered roller bearings are arranged and used separately, the two bearings should be mounted on the component before adjusting the clearance, and the matching grinding value is obtained by measuring the distance from the end face of the outer ring of the bearing on the outside to the end face of the mounting hole . As shown in Figure 6, the method is as follows: First, the outer ring of the bearing should be compressed at multiple points in the circumferential direction of the pressure plate to ensure that the tapered roller and the inner and outer rings are fully fitted; secondly, the distance A2 in the circumferential direction is measured, and the average value is measured at multiple points. The grinding value A=A2+ΔS (±0.025 mm).
5 Formation mechanism of tapered roller bearing clearance
Working clearance calculation formula: ΔS = Sr – ΔSp – ΔST In the formula, ΔS is the radial working clearance (μm) of the normal warm bearing during operation; Sr is the internal radial clearance (μm); ΔSp is caused by the fit The reduction of radial clearance; ΔSp is the reduction of radial clearance due to temperature rise (μm). Reduction in radial clearance due to fit ΔSp: The reduction in radial clearance is due to the expansion of the inner ring and the contraction of the outer ring during installation. ΔSp = Δd + ΔD
Δd ≈ 0.9·U·d/F ≈ 0.8·U
ΔD ≈ 0.8·U·E/D ≈ 0.7·U
In the formula, Δd is the expansion of the inner ring (μm); ΔD is the expansion of the outer ring (μm); d is the inner diameter of the inner ring (mm);
U (μm) is the theoretical interference with tight fittings (theoretical interference refers to the maximum physical deviation of each fitting surface minus the
After 1/3 of its tolerance zone, the difference between these two dimensional deviations is obtained. It takes into account the value of the flattening of the contact surfaces during assembly). F is the diameter of the inner ring raceway (mm); E is the diameter of the outer ring raceway (mm); D is the outer diameter of the outer ring (mm); the decrease in radial clearance due to temperature ΔST: due to the temperature difference between the inner and outer rings Larger, the radial clearance change will be quite large.
ΔST = α·dM·1000·(υ’IR – υ’AR)
α(1/K) is the thermal expansion coefficient of steel:
α = 0.000011 · (1/K);
dM is the average diameter of the bearing (d+D)/2 (mm);
υ’IR (°C, K) is the inner ring temperature; υ’AR (°C, K) is the outer ring temperature (often there is a temperature difference between the inner and outer rings: 5 K to 10 K).
Axial clearance: The internal axial clearance ΔSa is the position at which a bearing ring moves from one limit position to another limit position in the axial direction of the bearing under no load condition,
For different types of bearings, the internal radial clearance ΔSr and the internal axial clearance ΔSa are related to each other. Table 1 shows the relationship between the two for some bearing types.
The application of paired tapered roller bearings, especially the control and adjustment of their clearance, needs to consider many factors, such as temperature rise, fit, speed, etc. Different bearing manufacturers have their own calculation and control methods. This article is a summary of the application of paired tapered roller bearings through the accumulation of work and some practices obtained in the actual workshop operation process. I hope to have some reference and help for everyone.