GB2169361A

GB2169361A - An adjustable bearing mounting for a rotor

Info

Publication number: GB2169361A
Application number: GB08531950A
Authority: GB
Inventors: Arvid Holm
Original assignee: Thomas Ths Sabroe and Co
Current assignee: Johnson Controls Denmark ApS
Priority date: 1985-01-02
Filing date: 1985-12-31
Publication date: 1986-07-09
Also published as: DK585D0; GB8531950D0; JPS61185694A; GB2169361B

Abstract

In a bearing mounting for a rotor (2) of a screw compressor the bearing (8) is rigidly mounted on a rotor shaft (6) while being axially slidably received in a stator bore. A spring (44) biases the outer race (14) of the bearing axially outwardly of the bore, while adjustment screw means (46) in a rigid bore cover (34) are operable to displace the outer bearing race inwardly, thereby enabling a fine axial adjustment and separation of the rotor from a position in which an end surface (24) of the rotor is in engagement with a cooperating internal stator wall portion (26) to a position in which the gap is of predetermined small size eg 50-70 mu m. <IMAGE>

Description

SPECIFICATION An adjustable bearing mounting for a rotor The present invention relates to an axially finely adjustable bearing mounting for the rotor of a rotary machine, primarily a screw compressor, whereby the rotor is adjustable to a position, in which an end surface thereof is spaced a predetermined distance from an adjacent interior wall surface of the stator of the machine. Due to the surrounding stator the said distance is not, in practice, accessible for direct measuring, so some kind of indirect determination of the distance will have to be used.This is particularly relevant for screw compressors, in which the axial gap between th end surfaces of the rotors and the cooperating internal stator end walls should be very small, but not too small, e.g. some 60,um with a tolerance of some 30cm. The gap occurs by the juxtaposition of several, rather heavy machine parts, which should be machined with extreme accuracy for fulfilling the required total tolerance, and it is an important simplification, therefore, that the bearing means of the rotor and therewith the rotor itself may be finely adjustable in the axial direction, as the said machine parts may then be produced with coarse tolerances.

It is already known in the art that the axial adjustability of the rotor is achievabie by effecting an axial adjustment of the outer race of a thrust bearing mounted rigidly on a protruding shaft portion of the rotor, inside a bearing receiving bore in the stator, and it is even known that such an adjustment can be effected by forcing a pressure element against the outer end of one outer race of the thrust bearing, when the rotor or the inner end of the outer race of the thrust bearing is subjected to an outwardly directed spring action relative the stator.

The relevant arrangements according to the prior art, however, have suffered from certain drawbacks, and it is the purpose of the present invention to provide an improved arrangement, which combines a simple construction with the possibility of a very accurate measuring out of the desired location of the rotor.

According to the invention the Bellville or similar spring is inserted directly between the outer race of the thrust bearing and a shoulder portion of the rotor shaft receiving bore of the stator, and the means for axially adjusting the position of the rotor are constituted by one or more screw members engaged in a primary screw connection with a threaded hole in a rigid cover element arranged rigidly associated with the stator over the outer end of the bearing receiving bore therein, said screw or screws being operable to axially displace the said outer bearing race against the action of the said spring member.

With this arrangement it is possible to ern- pirically find the rotor position in which the rotor just slips the stator end wall surface, whereafter the rotor is easily further displaced as required, based on a simple and accurate measurement of the displacing thereof.

In the following the invention is described in more detail with reference to the drawing, in which: Figure 1 is a sectional view of a bearing mounting according to the invention, and Figure 2 is a partly schematic sectional view of a modified mounting.

Fig. 1 shows a section through the discharge or high pressure end of a known screw compressor having to cooperating rotors 2, of which only one is visible in the Figure. Each rotor 2 has an axially projecting shaft 6 provided with a roller bearing 8 comprising an inner race 10, rollers 12, and an outer race 14. The inner race 10 is secured to the shaft 6 by means of an outer clamp plate 16, which is held against the end of the inner race by means of a bolt 18 screwed into a central, threaded hole in the shaft 6. The inner race 10 is hereby held'rigidly abutting a ring member 20, which is supported against a shoulder 22 on the shaft 6.The ring member 20 is a so-called balancing piston, an outwardly projecting portion of which serves as a labyrinth tightening element between the roller bearing 8 and the opposed portion of the rotor 2, whereby th oil pressure on the rotor side of the ring member 20 will be oppositely directed relative the axial forces on the rotor as created by the compression work.

The adjacent end surface of the rotor is designated 24. It is located immediately outside an inwardly facing wall surface 26 of a rigid stator portion 28 having at its opposite side a wall surface 30 and in front of that a recess, in which is received a.o. the ring member 20 as projecting from the shaft. The bearing 8 is received in a stator bore, the outer end of which is closed by a sealed cover or plug 32, which is retained by means of an outer cover 34 secured to the stator by means of screws. The plug cover 32 has an outer flange portion 33 which engages the outer end of the outer bearing race 14, the opposite end of this race 14 engaging a distance ring 40, which surrounds the ring member 20 and projects inwardly, to the left, towards a shoulder 42 of the said recess in front of the wall surface 30.In the space between the wall surface 30 and the shoulder 42 is mounted strong Belleville spring 44, which abuts the wall surface 30 and seeks to force the distance ring 40 outwardly, when the latter is tightened by means of the covers 32 and 34 so as to abut the shoulder 42.

The gap between the rotor end surface 24 and the stator wall surface 26 should be adjusted to show a width, b, of a predetermined small size, e.g. 50-70,um.

The outer cover 34 is provided with in wardly projecting pointed screws 46, which are operable from outside to produce a more or less pronounced inward displacement of the inner cover 32, and it is possible to hereby displace the outer race 14 of the bearing a short distance against the action of the spring 44, or in the direction of this action, respectively. The shoulder 42 is located such that by the tightening of the outer ring members 14 and 40 against this shoulder the gap width b is known for sure to be larger than the desired, optimal, small gap width, the production tolerances of the elements in the described mechanical row of elements.

When the screws 46 are screwed outwardly from the associated entirely screwed in position the spring 44 will force the outer bearing race 14 outwardly, whereby the gap width b will be reduced until it goes to zero, i.e. until the rotor end surface 24 gets in touch with the stator wall surface 28. This situation is easily provided for or experienced by causing the rotor to rotate, by rotating it at its opposite free end, while operating the screws 46 to effect an axial displacement of the roller bearing and therewith of the entire rotor.

It is possible to hereby adjust the pin screws 46 in such a manner that the rotor will be displaced a desired short distance inwardly from the position in which its end surface 24 is in direct mechanical touch with the inner wall surface 26 of the stator element 28, inasfar as this free spacing will be directly perceptible by the attempt to rotate the rotor and even directly measurable or adjustable with the aid of a dial gauge in operative connection with an opposite free end of the rotor. It is possible to hereby adjust the gap width b with a very high accuracy, since for well machined surfaces 24 and 26 a rotor displacement of less than 10ism will be sufficient to bring the surfaces frictionally free of each other. Thus, the gap width is easily adjusted to e.g. 50-60,um by means of the dial gauge.

It will be appreciated that an essential possibility is the fixable, finely graduated displaceability of the outer race of the pressure bearing against the action of the interposed spring member as effectable by suitable adjustment means, since it is possible to hereby empirically determine the displacement position in which the rotor is just free of the stator wall surface 26 and to measure out, from this position, the displacement which will correspond to the desired gap width b. The invention comprises the corresponding mounting method.

With the use of the said pin screws 46 for the adjustment of the bearing covers 32 the desired fine adjustability will require these screws to be provided with a fine or low-pitch threading, which is principally undesirable when the same screws should resist a considerable axial pressure.

On this background Fig. 2 shows a preferred arrangement, in which a centrally disposed adjustment screw 48 is in thread connection with both the outer cover 34 and the inner cover 32. However, the respective two thread connections are provided with mutually slightly different threading pitches, such that the screwing out or in of the the screw in the outer cover 34 will result in a very small displacement of the inner cover 32. A desired fine adjustability is hereby achievable without the thread connections themselves having to show any small pitches, i.e. without the connections having to be of the finely threaded type. Thus, the adjustment screw 48 may easily be designed to resist the relevant high axial pressure.

With the use of the illustrated inner bearing covers 32 it will be sufficient to utilize but a single, centrally mounted adjustment screw 46 or 48.

The Belleville spring 44 may of course be substituted by other types of spring means operable to exert an outwardly directed pressure on the outer race 14 or on the distance element 40. The spring means, of course, should be strong enough to resist operational forces acting on the rotor in the direction in which the spring is compressible.

The bearing shown in Fig. 1 is a combined axial and radial bearing, and it may well be substituted by juxtaposed separate bearings for radial and axial forces, respectively.

Claims

CLAIMS:

1. An axially finely adjustable bearing mounting for the rotor of a rotary machine, primarily a screw compressor, comprising a bearing or bearing assembly rigidly mounted on a rotor shaft and having its outer race slidingly received in a core in the stator, spring means being provided for biasing the rotor in the outward direction of the rotor shaft, and adjustable pressure exerting means being provided for urging the outer race of the bearing in the opposite direction, characterized in that said spring means are arranged between the outer race of the bearing and a shoulder portion of the said bore, and that the pressure exerting means are constituted by one or more screw members engaged in a primary screw connection with threaded hole means in a cover element rigidly mounted on the stator over the outer end of the bore, said screw or screws stepping on the outer bearing race being operable to urge the rotor a well defined distance from a position, in which an end portion of the rotor body is just leaving a frictional engagement with an adjacent interior wall surface of the stator.

2. A bearing mounting according to claim 1, in which the said screw or screws engage the outer bearing race by intermediate of a cover element slidingly arranged inside the bore.

3. A bearing mounting according to claim 2, in which the screw or screws, preferably a single, centrally disposed screw, are in threaded engagement with both the rigid and the slidable cover element, viz. through respective threadings having a slight mutual pitch difference.

4. A method of adjusting the position of a rotor, substantially as herein described.