EP1853829A1

EP1853829A1 - High-speed movable bearing in particular for the mounting of a main spindle of a machine tool

Info

Publication number: EP1853829A1
Application number: EP06706010A
Authority: EP
Inventors: Willi Albert
Original assignee: Schaeffler KG
Current assignee: IHO Holding GmbH and Co KG
Priority date: 2005-03-04
Filing date: 2006-02-24
Publication date: 2007-11-14
Also published as: CN101133255A; DE102005009921A1; JP2008536059A; US20080247698A1; WO2006092120A1

Abstract

According to the invention, the high-speed moving bearing (1) is embodied as an automatically-compensating movable ball bearing with several adjacent races of balls (6, 7, 8, 9, 10) with operation-dependent radial thermal expansion of the bearing rings (2, 3), the bearing rings (2, 3) of which are only in supporting contact with one ball race (8) in the cold state for the high-speed movable bearing (1), by means of a convex embodiment of the running surfaces (5) for the roller bodies (4) on the inner bearing ring (2). With increasing thermal expansion and expansion due to centrifugal force of both bearing rings (2, 3), the further ball races (6, 7, 9, 10) come sequentially into such a contact position with both bearing rings (2, 3) as a result of an elastic radially-flexible embodiment of both bearing rings (2, 3), that the bearing rings (2, 3) at the operating temperature for the high-speed moving bearing (1) are in supporting contact with all ball races (6, 7, 8, 9, 10).

Description

Name of the invention

High-speed loose bearing, in particular for supporting the main spindle of a machine tool

description

Field of the invention

The invention relates to a high-speed floating bearing according to the preamble of forming features of claim 1, which can be used in particular advantageous for storage of the main spindle of a machine tool or storage of other fast rotating machine parts.

Background of the invention

It is generally known to the person skilled in the art of rolling bearing technology that at least two bearings arranged at specific distances from one another are required for guiding and supporting a revolving machine part. If the support of the shaft in the usual way takes place in two radial bearings, the problem arises that the distances of the bearing seats on the shaft and in the housing only coincide within the framework of the manufacturing tolerances. In addition, the shaft usually warms under operating conditions stronger than the housing, so that the temperature-related differences in length of the shaft must be compensated in the bearings. The longest proven way to compensate for these manufacturing tolerances and differences in length is therefore to guide the shaft only in a fixed bearing in the axial direction, while at the other bearing by a floating bearing the different distances either at the seating position of the inner ring, at the seating position of the outer ring or be balanced in the bearing itself by moving the bearing rings to each other. While have proven to be particularly suitable as a bearing of such a shaft bearing depending on the required accuracy of the axial guidance of the shaft deep groove ball bearings, spherical or tapered roller bearings or double row or two single row angular contact ball bearings, floating bearings are most easily realized by cylindrical roller bearings or needle roller bearings, as in these A shift of the RoII- corona is possible on the track of each bordlosen bearing ring or shaft.

Especially when using cylindrical roller or needle roller bearings as a floating bearing of a water-cooled machine tool main spindle, it has proved to be disadvantageous that these bearings usually have a high radial stiffness, resulting in different temperatures between inner and outer ring or shaft and spindle housing Thermal expansion in an increasing radial tension in the bearing makes noticeable. The ever-increasing by this temperature-induced radial stress friction between the bearing rings and the rolling elements can be so strong that the permissible operating temperature of the bearing is exceeded by the resulting frictional heat and the required lubricating film between the rollers and the bearing rings to the partial burning of the lubricant and the premature failure of the camp breaks down locally. Although a known possibility for avoiding such a premature bearing failure is to preset the radial play of the bearing accordingly, such a radial play adjustment via a costly conical seat of the inner bearing ring on the main machine tool Spindle very time consuming and also requires very costly enveloping circle gauges.

Another possibility for realizing a movable bearing in the storage of a machine tool main spindle is also disclosed in EP 926 368 A2 single row ball bearings, in which the outer race is formed with a groove-shaped ball raceway and the inner race with a longitudinally planar ball track and the arranged between the races bearing balls made of ceramic. Due to the design of the bearing with a defined radial clearance to be achieved that the bearing has both a sufficient seat on the shaft and in the housing and a favorable operating clearance, while the movable bearing function by the possibility of axial displacement of the inner bearing ring in the region of its flat tread is guaranteed.

Although a ball bearing designed in this way counteracts operational radial thermal expansion of the bearing rings by its defined radial clearance, it has the disadvantage that it has only a low load capacity and thus in so-called crash cases, in which the bearing is suddenly exposed to extremely high point load, to material damage and ultimately to total failure tends. In addition, it has been found in practice that even the defined radial clearance of the bearing is not sufficient to avoid overloading the bearing with a larger heat gradient from the bearing inner ring to the bearing outer ring, so that it is not possible with such a bearing even in a double-row design, to ensure a uniformly precise radial spindle guidance in every operating condition of the bearing.

Object of the invention

Based on the stated disadvantages of the solutions of the known prior art, the invention is therefore based on the object, a Hochgeschwindigkeitsloslager, in particular to support the main spindle of a machine tool to design, with which it compensate in addition to the function temperature-related differences in length of the main spindle relative to the fixed bearing is also possible from operational radial thermal expansion of the bearing rings resulting overloading of the bearing to avoid and at each temperature and operating state of Bearings ensure a uniformly precise radial spindle guide.

Description of the invention

According to the invention, this object is achieved in a high-speed floating bearing according to the preamble of claim 1 such that the high-speed floating bearing is formed as operational radial thermal expansion of the bearing rings self-balancing ball bearing with several juxtaposed rows of balls whose bearing rings in the cold state of the high-speed ball bearing by a convex design of the tread for the rolling elements on the inner bearing ring via only one row of balls are in contact with each other, with increasing thermal expansion and centrifugal expansion of both bearing rings by a radially elastic compliant design of one or both bearing rings successively enter the other rows of balls in such a contact position with two bearing rings that the bearing rings at operating temperature of High-speed loose bearing over all rows of balls in supporting contact with each other.

In an expedient development, the inventively designed high-speed bearing preferably has five juxtaposed rows of balls with diametrically identical steel or ceramic balls as rolling elements, of which only the rolling elements of the middle row of balls in the cold state of Hochgeschwindigkeitsloslagers are in bearing contact with both bearing rings. The arrangement of five rows of balls next to each other has the advantage that external radial loads almost uniformly on the individual ball be distributed in rows and that the camp is a lot more robust than known single or double ballless ball bearings. However, depending on the application, it is also possible to form the high-speed floating bearing with fewer or more than five rows of balls. In the selection of the material and the shape of the rolling elements, especially the use of ceramic balls has proven to be advantageous because balls are due to their ideal shape produce more precise than, for example, cylindrical rollers and with these results in excellent smoothness of the floating bearing. In addition, ceramic balls are compared to cylindrical rollers made of ceramic similarly inexpensive to produce as the alternative also usable known balls from a bearing steel or the like.

In order that a movable bearing designed with such a number of rows of balls does not require much more axial space than conventional movable bearings, it is further proposed as an advantageous embodiment of the inventively designed Hochgeschwindigkeitsloslagers, the rolling elements of the individual rows of balls each circumferentially evenly spaced apart in a common bearing cage nested to arrange so that the axial width of the high-speed loose bearing is less than the sum of the diameters of a transverse row of five rolling elements. In practice, it has been found that the axial width of a floating bearing formed with five nested rows of balls corresponds approximately to twice the width of the single-row ball bearing described in the prior art and that this is not disadvantageous due to the axial space available in most applications effect.

The nested arrangement of the rows of balls can be realized in such a way that the rolling elements of the middle and the axially outer rows of balls and the rolling elements of the two ball rows adjacent the middle ball row each arranged on common, circumferentially alternately successive transverse axes become. It is between the arranged on a transverse axis rolling elements of the middle and the axially outer rows of balls only one of their ball pockets in the bearing cage delimiting web arranged, while also separated only by a ball pockets in the cage cage limiting web of separate rolling elements of the two of the central ball row adjacent rows of balls between the transverse axes the middle and the axially outer rows of balls are arranged at the height of the ball pockets of these rows of balls limiting webs.

A further feature of the inventively designed Hochgeschwindig- Klosslosloslagers it is beyond that in the preferred planar inner surface of the outer bearing ring according to the number of rows of balls five juxtaposed grooves are incorporated as a guide for the rolling elements. These, due to the Wälzkörperschmiegung a slightly larger radius than the radius of the rolling elements having grooves are formed in cross section in each case with the same width and the same depth and go directly into each other, so that the rolling elements are guided in the grooves with about a quarter of its circumference ,

In a further embodiment of the inventively designed Hochgeschwin- digkeitsloslagers it is finally proposed that due to the particularly high heat gradient between the main spindle and the spindle housing of a machine tool preferably both bearing rings for radially elastic compliant training on their outer surfaces are each formed with a concave cross-section annular recess, the extends almost over the entire axial width of the bearing rings and their greatest depth corresponds to about half the thickness of the bearing rings. These circumferential depressions in the outer surfaces of the bearing rings thus cause a reduction in the material cross section of the bearing rings, through which the stiffness of the bearing rings decreases towards the axial center and through which simultaneously increases the radial elasticity of the bearing rings to the axial center. It has proven to be advantageous in addition to process the surfaces of the concave annular recesses by fine grinding to a possibly from the notch effect of Surface roughness resulting in overload fracture of the bearing rings to avoid. The adjoining the concave annular recesses axial edge regions of both bearing rings, however, again flat and preferably formed without fine grinding, so that the bearing rings can be easily fixed in the spindle housing or on the main spindle over this designed as an annular bearing seats edge regions. In applications with less high heat gradient between the bearing rings, however, it is also possible to design radially elastic only the outer or only the inner bearing ring in the manner mentioned, so that in each case formed in a conventional manner bearing ring resulting from the notch effect of surface roughness risk of breakage ,

The inventively designed high-speed floating bearing, in particular for supporting the main spindle of a machine tool, thus has the advantage over the known from the prior art bearings that it is due to the special design of its bearing rings and training as a multi-row ball bearing in addition to the ability temperature-related differences in length of the main spindle be able to compensate their fixed seat and is able to compensate for operational radial thermal expansion and centrifugal expansion of the bearing rings automatically and thus to ensure a uniform and precise spindle guide at each operating and temperature condition of the camp. Due to the convex design of the tread for the rolling elements on the inner bearing ring and a corresponding design of Lagerradialluft a precise spindle guide is initially ensured in the cold state of the bearing via the middle, standing with two bearing rings in contact bearing ball row. With increasing centrifugal forces and operational thermal expansions of the bearing rings, the two rows of balls adjacent to the middle row of balls then come into bearing contact with both bearing rings. When the high-speed idler bearing designed according to the invention finally reaches its operating temperature, the two axially outer rows of balls then come into bearing contact with both bearing rings due to the radially elastic design of the bearing rings Ball row is not overloaded and in any temperature condition of the bearing sufficient bearing stiffness is given. Although the design of the inventively designed Hochgeschwindigkeitsloslager as five-row ball bearings is compared to known single-row ball bearings cause of a slightly increased bearing friction, the high speed suitability of this camp remains. At the same time it is thus achieved, for example compared to double-row cylindrical roller bearings, that the high-speed endless bearing according to the invention is much less sensitive to tilting of the inner bearing ring to the outer bearing ring. Furthermore, the inventively designed high-speed floating bearing is characterized by the possibility of using non-contact sealing disks for lubricant storage by maintenance freedom and by the use of inexpensive producible ceramic balls instead of expensive ceramic rolls by low production costs.

Brief description of the drawings

A preferred embodiment of the inventively designed high-speed floating bearing will be explained in more detail with reference to the accompanying drawings. Showing:

1 shows a cross section through the drive of a machine tool with a main spindle mounted in a fixed bearing and in a high-speed endless bearing according to the invention;

Figure 2 is an enlarged view of a half of a cross section through an inventively designed high-speed floating bearing. Detailed description of the drawings

FIG. 1 schematically shows the drive of a machine tool, which consists essentially of an electric motor 26 and of a main spindle 27 driven by it. This main spindle 27 is clearly visible with one end mounted in two angular contact ball bearings 29, 30, which are formed as a fixed bearing seat 31 within a spindle housing 28. The other end of the main spindle 10, however, is mounted in a movable bearing seat 32, which is formed by an inventively designed high-speed floating bearing 1. As can be seen from FIG. 2, this high-speed loose bearing 1 consists essentially of an inner bearing ring 2 fastened to the main spindle 27 and an outer bearing ring 3 fastened in the spindle housing 28 and a number of rolling elements 4 arranged between these bearing rings 2, 3 and has a floating bearing function the possibility of axial displacement of the inner bearing ring 2 in the region of its tread 5 for the rolling elements 4.

In addition, it is clear from Figure 2 that the high-speed floating bearing 1 according to the invention as operational radial Wärmedehnun- conditions of the bearing rings 2, 3 automatically compensating ball bearing is formed, which five juxtaposed rows of balls 6, 7, 8, 9, 10 with the same diameter ceramic balls as rolling elements 4 has. Only hinted at Figure 2 it can be seen that the bearing rings 2, 3 of the high speed loose bearing 1 in the cold state of the bearing by a convex design of the tread 5 for the rolling elements 4 on the inner bearing ring 2 only via the central ball row 8 are in contact with each other, while With increasing thermal expansion and centrifugal force expansion of both bearing rings 2, 3 by a radially elastic compliant design of both bearing rings 2, 3, the further rows of balls 6, 7, 9, 10 successively in such a contact position with both bearing rings 2, 3 occur that the bearing rings 2, 3 at operating temperature of the high-speed loose bearing 1 over all rows of balls 6, 7, 8, 9, 10 are in contact with each other. The rolling elements 4 of the individual rows of balls 6, 7, 8, 9, 10 are arranged for this purpose, as also only hinted at Figure 2, each circumferentially evenly spaced from each other in a common bearing cage 11 nested, so that the axial width of the Hochgeschwindigkeitsloslagers 1 is less than the sum of the diameters of a transverse row of five rolling elements 4. For the nested arrangement of the rows of balls 6, 7, 8, 9, 10 while the rolling elements 4 of the middle and the axially outer rows of balls 6, 8, 10 are arranged on a common transverse axis, while the rolling elements 4 of the two adjacent the middle row of balls 8 Ball rows 7, 9 are also arranged on a common transverse axis, which are arranged in the circumferential direction between the transverse axes of the rolling elements 4 of the middle and the axially outer rows of balls 6, 8, 10. The axial guidance of the fixed in the bearing cage 11 rows of balls 6, 7, 8, 9, 10 between the bearing rings 2, 3 is also about five juxtaposed and clearly visible in Figure 2 grooves 13, 14, 15, 16, 17, in the newly formed inner surface 12 of the outer bearing ring 3 are incorporated and each have the same width and the same depth in cross-section and are formed with a slightly larger radius than the radius of the rolling elements 4.

Likewise, in FIG. 2, it can finally be seen that both bearing rings 2, 3 of the high-speed loose bearing 1 are designed for radially elastically yielding design on their outer surfaces 18, 19, each having a concave annular recess 20, 21, which extends almost over the entire axial width of the bearing rings 2, 3 and whose greatest depth is about half the thickness of the bearing rings 2, 3 corresponds. These concave annular recesses 20, 21 in the outer surfaces 18, 19 of the bearing rings 2, 3 cause a reduction in the material cross section of the bearing rings 2, 3, by the stiffness of the bearing rings 2, 3 decreases towards the axial center and through which the radial Elasticity of the bearing rings 2, 3 increases towards the axial center. The axial edge regions 22 adjoining these annular recesses 20, 21, 23, 24, 25 of both bearing rings 2, 3, however, are flat and each form annular bearing seats, via which the bearing rings 2, 3 are fixed in the spindle housing 28 and on the main spindle 27.

LIST OF REFERENCE NUMBERS

1 high speed bearing 18 outer surface of 2

2 inner bearing ring 19 outer surface of 3 3 outer bearing ring 20 ring recess

4 rolling elements 21 ring recess

5 tread of 2 22 edge area of 18

6 ball row 23 edge area of 18

7 ball row 24 edge area of 19 8 row of balls 25 edge area of 19

9 Ball row 26 Electric motor

10 ball row 27 main spindle

11 bearing cage 28 spindle housing

12 Inner surface of 3 29 Angular contact ball bearings 13 Raceway 30 Angular contact ball bearings

14 Raceway 31 Fixed seat

15 raceway 32 floating seat

16 raceway

17 raceway

Claims

claims

High-speed loose bearing, in particular for supporting the main spindle of a machine tool, which essentially consists of an inner bearing ring (2) fastened on the main spindle (27) and an outer bearing ring (3) fastened in a spindle housing (28) and of a number between these bearing rings ( 2, 3) arranged rolling elements (4) and which as a floating bearing possibility of axial displacement of the inner bearing ring (2) in the region of its tread (5) for the rolling elements (4), characterized in that the high-speed loose bearing (1) as operational radial heat expansions of the bearing rings (2, 3) self-compensating ball bearing with a plurality of juxtaposed rows of balls (6, 7, 8, 9, 10) is formed whose bearing rings (2, 3) in the cold state of the high-speed loslagers (1) by a convex design of the running surface (5) for the rolling elements (4) on the inner bearing ring (2) via only a ball row (8) are in bearing contact with each other, with increasing thermal expansion and centrifugal force expansion of both bearing rings (2, 3) by a radially elastic compliant design of one (2 or 3) or both bearing rings (2 and 3) the other rows of balls (6, 7, 9, 10) successively in such a contact position with both bearing rings (2, 3) occur that the bearing rings (2, 3) at operating temperature of the high-speed loose bearing (1) over all rows of balls (6, 7, 8, 9, 10) standing in contact with each other.

2. high-speed loose bearing according to claim 1, characterized in that it preferably has five juxtaposed rows of balls (6, 7, 8, 9, 10) with diametrically identical steel or ceramic balls as rolling elements (4), of which only the rolling elements (4) of middle ball row (6) in the cold state of the high-speed loose bearing (1) with two bearing rings (2, 3) are in bearing contact.

3. high-speed loose bearing according to claim 2, characterized in that the rolling elements (4) of the individual rows of balls (6, 7, 8, 9, 10) in the circumferential direction uniformly spaced from each other in a common bearing cage (11) are arranged nested, so that the axial width of the high-speed loose bearing (1) is less than the sum of the diameters of a transverse row of five rolling elements (4).

4. high-speed loose bearing according to claim 3, characterized in that for the nested arrangement of the rows of balls (6, 7, 8, 9, 10), the rolling elements (4) of the middle and the axially outer rows of balls (6, 8, 10) and the rolling elements ( 4) of the two rows of balls (7, 9) adjacent to the middle row of balls (8) are each arranged on common, mutually successive, transverse axes in the circumferential direction.

5. high-speed loose bearing according to claim 1, characterized in that in the preferably flat inner surface (12) of the outer bearing ring (3) corresponding to the number of rows of balls (6, 7, 8, 9, 10) five juxtaposed running grooves (13, 14, 15, 16, 17) are incorporated, which each have the same width and the same depth in cross-section and are formed with a slightly larger radius than the radius of the rolling elements (4).

6. high-speed loose bearing according to claim 5, characterized in that preferably both bearing rings (2, 3) for radially elastic compliant training on their outer surfaces (18, 19) each having a cross-sectional con Kaven annular recess (20, 21) are formed, which extends over almost the entire axial width of the bearing rings (2, 3) and whose greatest depth is about half the thickness of the bearing rings (2, 3).

High-speed loose bearing according to Claim 6, characterized in that the axial edge regions (22, 23, 24, 25) of the two bearing rings (22, 23, 24, 25) adjoining the concave annular recesses (20, 21) in the outer surfaces (18, 19) of the bearing rings (2, 3) ( 2, 3) are formed flat and the bearing rings (2, 3) are mounted only on these as annular bearing seats formed edge regions (22, 23, 24, 25) in the spindle housing (28) or on the main spindle (27).