JPH10274244A - Rolling bearing for supporting high speed rotary shaft - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a difference in temperature between inner and outer rings and also reduce the heating in a bearing. SOLUTION: A bearing 3 comprises an inner ring 3a close-fitted to the outer periphery of a main shaft 1, an outer ring 3b close-fitted to the inner periphery of a housing, multiple balls 3c arranged between the route surfaces of the inner ring 3a and outer ring 3b, and a cage 3d holding the balls 3c at specified peripheral intervals. Also the width dimension of the inner ring 3a is set larger than that of the outer ring 3b, and the pitch diameter PCD of the ball 3c is set so that the relation of PCD<(d+D)/2 is established with respect to the inner diameter (d) of the inner ring 3a and the outer diameter D of the outer ring 3b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling bearing for rotatably supporting a high-speed rotating shaft such as a main shaft of a machine tool.

[0002]

2. Description of the Related Art For example, in the field of machine tools, the rotation of a spindle is increasing at a high speed due to improvements in productivity and accuracy, processing of new materials (processing of ceramics, graphite, etc.), and complex processing. Tend to be Suppression of heat generation of the spindle bearing is a very important issue for such a high-speed spindle.

FIG. 6 illustrates a main shaft bearing portion of a machine tool using an angular ball bearing 13. A plurality of angular ball bearings 13 are used in combination, and a predetermined preload is applied to improve the rotational accuracy and rigidity of the main shaft 11. In order to lubricate and cool the inside of the bearing, a nozzle member 14 is disposed on the side of each bearing 13, and lubricating oil introduced through a passage (not shown) in the housing 12 is supplied from the nozzle member 14 to the bearing 13. It is injected toward the interior space. The lubrication system includes oil mist lubrication, air-oil lubrication, jet lubrication and the like, and is appropriately selected according to use conditions and the like.

Usually, the width L of the inner ring 13a and the width S of the outer ring 13b of the bearing 13 are the same (L = S).
In addition, the pitch circle diameter PCD of the rolling element 13c is equal to the inner diameter d of the inner ring 13a and the outer diameter D of the outer ring 13b by PCD ≒ (d +
D) / 2. The spacer 15 is arranged between the inner rings 13a adjacent in the axial direction.

The preload amount of the bearing 13 is set to a predetermined amount by tightening and adjusting the inner ring 13a in the axial direction via a labyrinth member 17 and a spacer 15 with a bearing nut 16 screwed to the shaft end of the main shaft 11. Is done.

[0006]

In the above-mentioned conventional bearing, the main shaft (inner ring) is in a high-speed region, particularly, dn value ｛bearing inner diameter d.
When rotating in a high-speed region where (mm) × number of rotations (rpm)} is 500,000 or more, the following problem occurs.

[0007] Heat generation inside the bearing increases, and the risk of seizure increases. Further, in a machine tool main shaft or the like, a change in temperature causes a decrease in processing accuracy.

[0008] The temperature difference between the inner ring and the outer ring increases (inner ring temperature> outer ring temperature), and the higher the speed, the more the preload increases, and the more dangers such as seizure and short life occur. The relationship is as shown in FIG. 4A.) On the other hand, if the preload is set so as not to generate an excessive preload in the high-speed region, the preload during low-speed operation becomes too small, resulting in insufficient rigidity of the main shaft (the state shown in FIG. 4B).

According to the present invention, the shaft (inner ring) is driven in a high speed region, in particular, d.
An object of the present invention is to solve the above-described problem when rotating in a high-speed region where the n value is 500,000 or more.

[0010]

According to the present invention, the width of the inner ring is made larger than the width of the outer ring, and the pitch diameter (PCD) of the rolling elements is set to the inner diameter (d) of the inner ring and the outer diameter of the outer ring. (D) was set so that PCD <(d + D) / 2.

[0011] The temperature difference between the inner and outer rings of the bearing is mainly caused by a difference in how heat generated inside the bearing escapes. Normally, heat is more easily dissipated on the outer ring side than on the inner ring side, so the temperature is higher on the inner ring side than on the outer ring side. By making the width of the inner ring larger than the width of the outer ring, heat diffusion from the inner ring to the shaft is improved, and the surface area of the inner ring that comes into contact with air is increased to improve heat dissipation. Therefore, the temperature rise of the inner ring is suppressed, and the temperature difference with the outer ring is reduced.

Further, by setting PCD <(d + D) / 2, even if the rotation speed of the shaft (inner ring) is the same, the rotation and revolving speed of the rolling elements are reduced, so that heat generation inside the bearing is reduced. Is done.

By providing a groove or a hole for heat dissipation at the end of the inner ring, the surface area of the inner ring that comes into contact with air is increased and the heat dissipation is further improved. Therefore, the temperature difference between the inner and outer rings is reduced more effectively.

[0014]

Embodiments of the present invention will be described below.

FIG. 1 shows the periphery of a bearing part which rotatably supports a main shaft 1 of a machine tool. The main shaft 1 is inserted through the inner periphery of the housing 2 and is rotatably supported by the housing 2 by a plurality of rolling bearings, for example, angular ball bearings 3.

The bearing 3 includes an inner race 3a fitted on the outer periphery of the main shaft 1, an outer race 3b fitted on the inner periphery of the housing 2,
It comprises a plurality of balls 3c arranged between the raceway surface of the inner ring 3a and the raceway surface of the outer ring 3b, and a retainer 3d for holding the balls 3c at a predetermined circumferential interval. As shown in FIG. 2, the width L of the inner ring 3a is set to be larger than the width S of the outer ring 3b (L> S), and the pitch circle diameter PC of the ball 3c.
D is P with respect to the inner diameter d of the inner ring 3a and the outer diameter D of the outer ring 3b.
CD <(d + D) / 2 is set.

In the bearing 3 adjacent in the axial direction, the inner ring 3
a and the inner ring 3a are in direct contact with each other. The spacer 15 as shown in FIG. 6 is not arranged. Therefore, the number of parts is small, and the assembling work is also facilitated. If the axial distance between the bearings 3 is large, a seat may be interposed between the inner rings 3a. Further, a nozzle member 4 is disposed between the outer rings 3b, and lubricating oil introduced through a passage (not shown) of the housing 2 is injected from the nozzle member 4 toward the bearing internal space, and the inside of the bearing is Lubrication and cooling are provided.

The amount of preload of the bearing 3 is determined by a bearing nut 5 screwed to the shaft end of the main shaft 1 and through a labyrinth member 6.
a is set to a predetermined amount by tightening and adjusting a in the axial direction. The labyrinth member 6 forms a labyrinth seal in cooperation with a labyrinth member 7 fixed to the end face of the housing 2.

In the embodiment shown in FIG. 3, a plurality of circumferential grooves 3a1 are provided on the outer periphery of both ends of the inner ring 3a in order to increase the surface area of the inner ring 3a which comes into contact with air and further enhance the heat radiation. Instead of the circumferential groove 3a1, modifications such as forming a spiral groove, forming a radial through hole or a bottomed hole, and forming an axial through hole or a bottomed hole are possible.

In the above embodiment, the width of the inner ring 3a is increased on both sides in the axial direction, but may be increased on only one side in the axial direction.

FIG. 5 shows a bearing having the structure shown in FIGS. 1 and 2 {Example product: L> S, PCD <(d + D) / 2}, and a comparative example product X {L <S, PCD = (d + D). The results of measuring the inner ring temperature and the inner and outer ring temperature difference at a predetermined number of revolutions are shown, using a comparative example product Y {L = S, PCD = (d + D) / 2}. Measurement conditions were as follows: lubrication method: air oil lubrication, rotation speed: 21000 rpm, inner ring inner diameter d: 100 m
m, Cooling: Housing cooling performed. As shown in the figure, it was confirmed that the inner ring temperature and the inner and outer ring temperature difference of the example product were smaller than those of the comparative example product X and the comparative example product Y. It is considered that this tendency becomes more remarkable when the bearing 3 having the configuration shown in FIG. 3 is used.

The present invention can be widely applied not only to the main shaft of a machine tool but also to a rolling bearing that supports a high-speed rotating shaft, particularly a shaft that rotates in a high-speed region where the dn value is 500,000 or more. Further, the bearing type is not limited to the angular ball bearing as illustrated, but can be similarly applied to a tapered roller bearing or the like.

[0023]

As described above, by making the width of the inner ring larger than the width of the outer ring, the heat diffusion from the inner ring to the shaft is improved, and the surface area of the inner ring that comes into contact with air is increased. As a result, the heat dissipation is improved, so that the temperature rise of the inner ring is suppressed (the temperature difference between the inner and outer rings is reduced). Further, by setting PCD <(d + D) / 2, the rotation and revolving speed of the rolling elements are reduced, so that heat generation inside the bearing is reduced. In this way, the temperature rise of the inner ring is suppressed (the temperature difference between the inner and outer rings is reduced), and the heat generation inside the bearing is reduced, so that the configuration shown in FIG. As a result, even if the shaft (inner ring) rotates in the high-speed region, there is less fear of entering the dangerous region.

Further, by providing a groove or a hole for heat dissipation at the end of the inner ring, the surface area of the inner ring in contact with air is increased and the heat dissipation is further improved, so that the above-mentioned effect is more remarkably exhibited. .

The rolling bearing of the present invention having the above-mentioned effects is suitable for use in a high-speed region where the dn value is 500,000 or more.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a periphery of a main shaft bearing according to an embodiment of the present invention.

FIG. 2 is a sectional view showing the bearing in FIG. 1;

FIG. 3 is a cross-sectional view illustrating a bearing according to another embodiment.

FIG. 4 is a diagram showing a relationship between a rotation speed and a preload amount.

FIG. 5 is a diagram showing a measurement result of a difference between an inner ring temperature and an inner and outer ring temperature.

FIG. 6 is a cross-sectional view showing the periphery of a conventional spindle bearing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main shaft 2 Housing 3 Bearing 3a Inner ring 3b Outer ring 3c Ball

Claims (3)

[Claims] 1. A rolling bearing which is preloaded and rotatably supports a shaft rotating at high speed with respect to a housing, wherein a width of an inner ring is larger than a width of an outer ring, and
A rolling circle for supporting a high-speed rotating shaft, wherein a pitch circle diameter (PCD) of the rolling element has a relationship of PCD <(d + D) / 2 with respect to an inner diameter (d) of the inner ring and an outer diameter (D) of the outer ring. bearing. 2. The rolling bearing for supporting a high-speed rotating shaft according to claim 1, wherein a groove or a hole for heat radiation is provided at an end of the inner ring. 3. The rolling bearing for supporting a high-speed rotating shaft according to claim 1, wherein the rolling bearing has a dn value of 500,000 or more.