Method for mounting conical objects and hydraulic nut to be used in said method

Abstract: A method for mounting a hollow article which has a conically shaped opening, such as a conical ring, on a conical shaft comprises the following steps: installing the hollow article (2) on the shaft (6), in order to fit the conically shaped surfaces of said article and said shaft against each other, moving the hollow article (2) to a starting position (B), in order to provide an initial press fit, moving the hollow article over a predetermined distance (S s ) from the initial position to an end position (C), in order to provide a final press fit.

Description: The invention is related to the subject of mounting conically shaped objects together. An example in this field is the mounting of a bearing on a conical seating. In the process of mounting such objects, internal stresses are generated whereby an interference fit is obtained. The conical object is stretched, whereas the shaft is compressed. The objects concerned may comprise various engineering or machinery components, such as gears, bearings etc. Although high internal stresses lead to a correct interference fit, care should be taken not to overload the objects in order to avoid creep and the development of cracks. On the other hand, low stresses are to be avoided as well having regard to the problems of fretting or stress corrosion. According to a known method, the objects are mounted by applying a force of a certain magnitude. It is intended to thereby obtain the correct displacement of the objects with respect to each other so as to obtain the desired internal stresses. The disadvantage of this prior art method is that it brings inaccuracies emanating from the unpredictable friction between the objects. FR-A-2 619 428 and DE-C-597 408 disclose methods which differ from the subject matter of claim 1 substantially in that the predetermined force is not particularly specified. The aim of the invention is therefore to provide a method for mounting a hollow object having a conically shaped opening, such as a conical ring, on a conical shaft, or on a conical sleeve mounted on a shaft which provides a more predictable result. According to the invention, said method comprises the steps defined in claim 1. In driving the hollow object to its start position, any deviations in the shape or surface roughness of the objects, which deviations lead to an unpredictable, non-linear behaviour, are accounted for. Over the trajectory from the start position towards the final position, the behaviour of the objects appears to be well predictable, whereby an accurate mounting is obtained. The well-defined start position is obtained by exerting a predetermined axial force thereon. The force required to obtain said start position can be determined empirically. The method according to the invention is in particular suitable for mounting the inner, internally conically shaped race of a rolling element bearing on a shaft. Such bearing has a relatively large radial internal clearance between the rolling elements on the one hand, and the races on the other hand, in unmounted state, and a smaller, nominal radial internal clearance in mounted state. According to prior art practice, the clearance is usually checked by means of a feeler gauge. Such feeler gauge is inserted between a rolling element and a raceway, in order to establish the play. Upon driving the inner race up the shaft, this play is reduced. Obviously, this method is awkward and time-consuming, having regard to the fact that after each time the inner race has been driven up, the feeler gauge should be inserted. Continuous measurements are not possible since the mounting process has to be interrupted each time the feeler gauge is inserted. Moreover, this process could easily lead to overloadings in case the inner race appears to be driven up too far. Furthermore, the bearing space between the races and the rolling elements may not always be well accessible for insertion of the feeler gauge, in particular in a machine environment. Often, a hydraulic nut is applied in driving up the inner race, which nut further reduces the available access. This problem is further aggravated in case sealed rolling element bearings are employed. The seals on both sides prevent the insertion of a feeler gauge all together. Finally, incorrect readings might be obtained in case the races and rolling elements are not correctly centred. The object of the invention is therefore also to provide a method which does not have these disadvantages. According to the invention, this is achieved by driving up the inner race from the initial position to the final position over such a distance that the nominal radial internal clearance is obtained. The distance between the start position and the final position can be calculated accurately on the basis of the taper of the inner race and shaft. For all rolling element bearings in question, the force required for obtaining the start position, together with the distance between the start position and the final position, can be tabulated so as to provide a reference guide enabling a correct mounting procedure. Preferably, the start position is obtained by applying an axial force which induces a radial internal clearance reduction of 0,09 x 10 -3 x d (d=diameter of inner race). These forces can be determined empirically and tabulated. Furthermore, preferably, starting from the start position, the final position of the inner race is obtained by displacing the inner race over a distance which induces a radial internal clearance reduction of 0,6 x 10 -3 x d (d=diameter of inner race). The distances can be derived from the taper of the objects, and can be tabulated as well. The invention will further be explained with reference to several embodiments shown in the figures. Figure 1 shows an overall view of the subject of the invention. Figure 2 shows a scheme of the method according to the invention. Figures 3-6 show four different embodiments of a spherical roller bearings in the process of being mounted on the shaft. Figure 1 shows a spherical rolling bearing 1, comprising an inner race 2, which has a conically shaped inner surface, an outer race 3 with a spherical race way, as well as two rows of rollers 4. The spherical roller bearing 1 is being mounted on stub 5, comprising a conically shaped part 6, as well as a screw threaded part 7. A hydraulic nut 8 has been screwed onto the screw threaded part 7. This hydraulic nut 8 comprises a nut body 9 and which has a coaxial annular chamber 10. In said chamber 10 a ring-like piston 11 has been slidingly accommodated. By means of seals 12, the piston 11 has been sealed with respect to the cylindrical walls of chamber 10. By means of connector 13, chamber 10 is connected to a hydraulic hose 14, which in turn is connected to a hydraulic pump 15. The oil can be pumped from pump 15 by moving handle 16 up and down. Gauge 17 shows the oil pressure. As shown in figure 1, piston 11 rests against inner race 2 of spherical roller bearing 1. By pumping oil into chamber 10, ring 2 is driven up the conically shaped part 6 of stub 5. Piston 11 also has a radially outwardly pointing flange 18, against which measuring pin 19 rests. This pin forms part of distance measuring device 20, which contains a screw threaded housing 21 screwed into bore 22 provided in nut body 9. Dial indicator 23 is connected to the axially movable pin 19, so as to enable the measurement of the relative axial displacement between nut body 9 and piston 11. As mentioned, the system shown in figure 1 is used for carrying out the method according to the invention. For a description of this method, reference is made to both figure 1 and 2. In the process of mounting the spherical roller bearing 1 onto stub 5, bearing 1, in particular inner race 2 thereof, is slid over stub 5 until the conically shaped surfaces of inner race 2 and stub 5 abut each other. At that position, no or hardly any clamping action exists yet. This position of spherical roller bearing is indicated with A (zero position) in figure 2. Subsequently, the inner race 2 is driven up to the start position B, by pumping oil into chamber 10 of hydraulic nut 8. The force or pressure required to obtain this start position B can be read from a table in which for all relevant dimensions of roller bearing 1, these values have been tabulated. These values have been determinated empirically. It has been established that a start position, corresponding to a certain small initial interference, is reached when a reduction in the radial internal bearing clearance of 0,09 x 10 -3 x d has been achieved. The values related to such radial internal clearance reduction have been tabulated. Once the start position B has been reached, the inner race 2 is driven up over a distance S s towards final position C. The distance S s can be read from a table as well. These distances have been calculated on the basis of the taper of the object, in combination with the prescription that a reduction in radial internal bearing clearance of 0,6 x 10 -3 x d mm should be reached. With reference S, the distance between the position wherein the bearing is placed by hand, and the final position has been indicated. The axial drive-up distances required to obtain this condition can also be read from a table. It is to be noted that the reduction of 0,6 x 10 -3 x d mm occurs in driving up the inner race from the start position B to its final position C. As shown in figures 3 and 4, the method can both be applied in cases where there is only one sliding surface (figures 3 and 4), as well as in cases where two sliding surfaces exist (figures 5 and 6). Figure 3 corresponds to the case of figure 1; in figure 4 an auxiliary sleeve 24 has been provided. This sleeve 24 has a cylindrical bore, fitted on a cylindrical shaft 25. The outer surface of the sleeve 24 is partly tapered, and is partly cylindrical with screw thread so as to mount hydraulic nut 8 thereon. In the case of figure 5 the inner race 2 is in a fixed position. Inner racce 2 rests against a ring 26, which in turn rests against an abutment 27 of shaft 28. The auxiliary sleeve 24 is now sliding in the direction of the arrow 29, whereby it slides both over the inner race 2 as well as over the shaft 28. The same situation, wherein a sliding over two surfaces occurs, is shown in figure 6. Here as well, ring 30, which is cylindrical on the inside, and tapered on the outside, slides between inner race 2 and shaft 28. In the cases of figures 5 and 6, of course a larger force is required to obtain the start position B. The forces in these situations can be obtainned empirically as well, and tabulated.

Claims: Method for mounting a hollow object (2) having a conically shaped opening, such as a conical ring, on a conical shaft (6) or on a conical sleeve (24, 30) mounted on a shaft (25, 28), comprising the steps of: installing the hollow object on the shaft or the conical sleeve so as to bring the conically shaped surfaces of said object and the shaft or the conical sleeve into abutting relationship in a zero position (A), applying a predetermined axial force on the hollow object (2) so as to drive the hollow object from said zero position (A) to a start position (B) for providing an initial interference fit, driving the hollow object over a predetermined distance (S s ) from said start position (B) to a final position (C) for providing a final interference fit, wherein said predetermined force is defined as the force required to create an elastic expansion of the hollow object in the start position (B) amounting to 5%-20% of the elastic expansion in the final position (C). Method according to claim 1 for mounting the inner, internally conically shaped race (2) of a rolling element bearing on a shaft (6), which bearing has a relatively large radial internal clearance between the rolling elements (4) on the one hand, and the races (2, 3) on the other hand, in unmounted state, and a smaller, nominal radial internal clearance in mounted state, wherein the inner race (2) is driven from the initial position (B) to the final position (C) over such a distance that the nominal radial internal clearance is obtained. Method according to claim 2, wherein the start position (B) is obtained by applying an axial force which induces a radial internal clearance reduction of 0,09 x 10 -3 x d (d=diameter of inner race). Method according to claim 2 or 3, wherein, starting from the start position (B), the final position (C) of the inner race (2) is obtained by displacing the inner race over a distance which induces a radial internal clearance reduction of 0,6 x 10 -3 x d (d=diameter of inner race).

Inventors: KELLSTROEM MAGNUS, PETTERSON KENNETH, RYDIN MAGNUS, KELLSTROEM, MAGNUS, PETTERSON, KENNETH, RYDIN, MAGNUS, Kellström, Magnus
Applicants: SKF MAINTENANCE PRODUCTS BV, SKF MAINTENANCE PRODUCTS B.V.
Application year: 1995
Main classification: F16C35
IPC codes: F16D1, F16B4, F16C35, F16C25