GB2433560A

GB2433560A - Tilting thrust pad assemblies

Info

Publication number: GB2433560A
Application number: GB0626059A
Authority: GB
Inventors: Suren Advani
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-12-08
Filing date: 2006-10-31
Publication date: 2007-06-27
Anticipated expiration: 2026-10-31
Also published as: GB0626059D0; GB2433560B; GB0525014D0

Abstract

A tilting thrust pad assembly has a carrier ring 2 in which is formed an annular slot 3 into which a plurality of bearing members 1, generally known as thrust pads or thrust shoes, are received. Each thrust pad 1 is manufactured from a circular disc. The bearing surface of the thrust pad is of truncated circular shape and its boundary can be defined by four arcuate sides each separated by a straight side (fig 1), or three arcuate sides each separated by a straight side (fig 2), or two arcuate sides each separated by a straight side (figs 3 and 4). The resulting shape of the thrust pad permits the same thrust pad to be fitted into carrier rings of a wide range of sizes or curvatures.

Description

TILTING THRUST PAD ASSEMBLIES

THE DESCRIPTION

BACKGROUND OF THE INVENTION

This invention relates to tilting thrust pad assemblies which include a carrier ring in which is supported a circular array of thrust pads. Usually the total thrust bearing surface area of the array of thrust pads is between and 85 per cent of the annulus area available, the remaining area used for the lubricant to feed the thrust pads. Such assemblies are used to absorb axial thrust loads in a wide range of rotating machinery. The rotation of the collar or runner mounted on the shaft causes an oil film to be generated between the collar and the front face of the thrust pad. The pad is located in the carrier ring at its rear. The same thrust pad should preferably be capable of being used in carrier rings of different sizes or curvatures whereby the larger carrier ring has a greater number of thrust pads. This invention is concerned with the shape of the thrust bearing surface of the thrust pad. A Sector shaped pad has the disadvantage that if, for example, the same thrust pad from a carrier ring supporting eight thrust pads is put in a carrier ring supporting eighteen thrust pads and there is to be the same percentage of thrust area to annulus area, then the gap between the thrust pads at the outer radius of the thrust pads becomes too small. United States patent no. 3197264, Fig 12 discloses a bearing assembly including thrust pads which are capable of being accommodated in carrier rings of different sizes but the thrust pads are not sector shaped.

The thrust pads described therein have four sides all of them being arcuate convex outwards, two of the said arcuate sides being opposite each other and being of equal shape and the other two sides being opposite each other and of unequal shape, the thrust pad being symmetrical about an axis in the thrust pad surface between the equal arcuate sides.

It would be desirable, however, to have a thrust pad the shape of whose thrust bearing surface is of a simpler shape with its boundary not defined by arcs of differing shapes and sizes and still be capable of being accommodated in carrier rings of different sizes or curvatures, maintaining the total thrust area of a full compliment of thrust pads at 75 to 85 per cent of the annulus area available to the thrust pads.

DISCLOSURE OF THE INVENTION

According to the invention there is provided a thrust bearing assembly comprising a carrier ring in which is formed an annular slot into which a plurality of thrust pads are located and allowed limited movement for their proper functioning and the thrust pads are shaped so as to allow the the same thrust pad to be located in carrier members of different sizes or curvatures. In United States patent no. 3197264 Fig 12 this is achieved with the thrust pad boundary defined by arcs of differing shapes and sizes whereas in this invention the thrust pad boundary is defined by straight lines joined by arcs of the same circle so that the thrust pads can be manufactured cheaply from circular discs.

In the first case the shape of the thrust pad is an inverted isosceles trapezium having all its four corners rounded to produce four arcs, all of the same radius, defined by a circle whose centre lies on a line that joins the centres of the two parallel sides of the trapezium. The rear part of the thrust pad locates it in the carrier ring. In the radially outer surface of the thrust pad are two spaced regions making contact with the radially outer sidewall of the annular slot in the carrier ring, and in the radially inner surface of the thrust pad one region making contact with the radially inner sidewall of the annular slot in the carrier ring, said contacts being such as to limit for each thrust pad relative to the carrier ring, both radial movement and rotational movement about an axis through the thrust pad.

This method of location enables the same thrust pad to be located in carrier rings of vastly different sizes. To prevent the axial and circumferential removal of the thrust pad from the carrier ring the two non parallel sides of the thrust pad have slots into which engage the heads of screws inserted in the carrier ring. The said screws allow limited movement of the thrust pad for its proper operation.

In the second case the shape of the thrust pad is the same as the first case except that its radially outer straight side is replaced by an arc joining the two arcs either side of it to make one continuous arc so that the boundary of the thrust pad now is defined by three arcs of the same circle each separated by a straight side. The method for locating the thrust pad in the carrier ring is the same as that described above for the thrust pad in the first case.

In the third case the shape of the thrust pad is a circle with two segments of equal size removed both being equidistant from the centre of the circle so that the boundary of the thrust pad is defined by two unequal arcuate sides separated by two straight sides which meet at an acute angle. Again, the method for locating the thrust pad in the carrier ring is the same as that described above for the thrust pad in the first case.

In the fourth case the shape of the thrust pad is a circle with two segments removed, the said segments whose centres of area are diametrically opposite each other, so that the boundary of the thrust pad is defined by two straight and parallel sides each separated by an arcuate side, the said arcuate sides being equal in size to each other. Again the method for locating the thrust pad in the carrier ring is the same as that described above for the thrust pad in the first case.

Another aspect of this invention is that in all four cases the radial width of the thrust pad relative to its circumferential width can be varied within the circular envelope of the thrust pad.

In all the above four cases, as the boundary of the thrust pad is generated from a circle with two or more segments removed, its manufacture is simplified. The thrust pads are initially made as circular discs from which segments are machined off on conventional milling machines to provide the straight sides. Expensive numerically controlled milling machines that would be required to generate the profile of the thrust pads as described in US patent no. 3197264 Fig 12 may be used but are not essential.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig I is a front view of a thrust pad having its boundary defined by four arcs and four straight sides and located in a carrier ring Fig 2 is the side view of the pad in Fig I Fig 3 is a view of the thrust pad in Fig I looking at its rear face Fig 4 is a view of two carrier rings of different curvature supporting four of the same thrust pad shown in Figs I, 2 and 3 Fig 5 illustrates the same thrust pad as Fig I of alternative widths from the same circle Fig 6 is a front view of a thrust pad having its boundary defined by three arcs and three straight sides and located in a carrier ring Fig 7 is a front view of a thrust pad having its boundary defined by two arcs and two straight sides meeting at an acute angle, and located in a carrier ring Fig 8 is a front view of a thrust pad having its boundary defined by two arcs and two straight and parallel sides, and located in a carrier ring

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The first thrust bearing assembly is shown in Figs I to 4. This includes a thrust pad I located in a circular carrier ring 2 in the upper surface of which is formed a circular slot 3 having radially inner and radially outer sidewalls 4 and S respectively. The annulus available for the full compliment of thrust pads is the area between the outer circumference 5 and the inner circumference 6. For the size of the carrier ring shown there would be an array of 8 pads to fill the ring. With this shape of thrust pad it is possible to have the total thrust bearing surface area for the full array of thrust pads to be between 75 and 85 per cent of the annulus area available to them. The thrust pad can be made of various metals including steel, cast iron, gunmetal, bronze, copper chrome, etc and may be coated with a thin layer of whitemetal alloy or any other bearing material on the front face of the pad. The lower and opposite face of each pad I may be provided with a radial ridge or raised portion 7, also known as the pad pivot, as shown in Figs 1,2 and 3 and engaging with the base of the annular slot 3 to permit, on application of an axial load to the assembly, limited pivoting of the said pad about the said ridge. The profile of the front of the thrust pad I as shown in Fig I is obtained by removing four segments from a circular disc thereby having four straight sides separated by four arcs of the same radius and a common centre 24. The straight sides are numbered 8,9,10 and II and the four arcs are numbered 12,13,14 and 15. The straight sides 9 and 1.1 are parallel to each other and the angled sides 8 and 10 when extended meet at an acute angle. If the sides 8,9,10 and 11 are extended up to the points where they intersect they form an inverted isosceles trapezium. Also the thrust pad is symmetrical about an axis joining the centres of the sides 9 and 11. The rear of the thrust pad also has an additional straight side 16 also parallel to the sides 9 and 1 1.The rear of the pad locates it in the carrier ring and prevents the pad from dropping away from the carrier ring. The thrust pad 1 is located in the slot 3 of the carrier ring 2 in such a manner that allows small movements of the pad in all directions in order for the pad to function properly without the pad falling out from the carrier. The radial and rotational movement of the thrust pad is limited by three points of contact 19,20 and 21 between the thrust pad and the carrier ring and these are shown in Fig 3. The side 9 makes contact with the outer wall of the carrier ring at its two ends 19 and 20 and the side 16 makes contact with the inner wall of the carrier ring near its centre 21. To prevent the axial and circumferential removal of the thrust pad from the carrier ring the two sides 8 and 10 of the thrust pad have slots into which engage the stop screws 17 and 18 fixed to the carrier ring. These screws are headed and their heads locate in slots 22, 23 in the thrust pad which can also be seen in Fig 2. These screws permit limited movement of the thrust pad about its pivot 7 and also circumferentially and axially in the carrier ring 2.

When the thrust pad is fitted to a carrier ring of a larger curvature 4' and 5' as shown in Fig 3 its straight sides 9 and II make contact with the inner and outer walls of the carrier ring again at 19,20 and 21 and this is possible because the sides 9 and II are linear. So a thrust pad can be assembled in carrier rings of vastly different sizes and curvatures, the only difference in the thrust assemblies being that the larger carrier ring has a greater compliment of thrust pads. By example Fig 4 shows half carrier rings of two different sizes with four thrust pads assembled in both carrier rings. For carrier rings comprising of two halves, a maximum of 1 8 pads can be supported in the larger carrier ring and a maximum of 8 pads in the smaller carrier ring.

Another aspect of this invention is that the aspect ratio of the thrust pad ie its radial width relative to its circumferential width can be varied within the circular envelope of the thrust pad. This is illustrated in Fig 5 where for the pad shown in dotted lines the ratio of the circumferential width to the radial width is greater than the pad shown in full lines although the circular envelope 25 of the two pads is the same.

The second thrust assembly is shown in Fig 6. The shape of the thrust pad 26 is the same as the thrust pad in Figs 1,2,3 and 4 except that the radially outer straight side is replaced by an arc joining the two arcs either side of it to make one continuous arc 27 so that the boundary of the thrust pad is defined by three arcs of the same circle each separated by a straight side.

The location of the thrust pad in the carrier ring is the same as in the first assembly shown in Figs 1,2,3 and 4.

The third thrust assembly is shown in Fig 7. The shape of the thrust pad 28 is the same as the thrust pad in Fig 6 except that the radially inner straight side is replaced by an arc joining the two arcs either side of it to make one Continuous arc 30 so that the boundary of the front of the thrust pad now has two arcuate sides 29 and 30 each separated by a straight side.

The shape of the thrust pad can also be defined as a circle with two segments removed both being equidistant from the centre of the circle leaving two arcuate sides separated by straight sides which meet at an acute angle. The location of the thrust pad in the carrier ring is the same as in the first assembly shown in Figs 1,2,3 and 4.

The fourth thrust assembly is shown in Fig 8. The shape of the thrust pad 3 1 is circular with a segment removed from the top and another from the bottom giving radially outer and inner straight and parallel sides, and two equal arcuate sides 32 and 33. The location of the thrust pad in the carrier ring is the same as in the first assembly shown in Figs 1,2,3 and 4.

So, in all four thrust assemblies described above the final shape of the thrust pad is generated from a circle thereby enabling the initial stages of its manufacture to be in the form of a circular disc.

The manufacture of the thrust pad in all four cases when compared against the thrust pad with four arcuate sides all of different sizes and shapes, as described in the US patent no. 3197264 Fig 12, is much simpler and therefore cheaper to produce. The thrust pads faced with the bearing material can now be made as circular discs shown by the chain dotted line in Fig 5, following which segments are then removed or machined off on conventional milling machines in order to provide the straight sides depending on the design selected from the four cases described above.

Expensive numerically controlled milling machines that would be required to produce the profile of the thrust pads as described in the US patent no. 3197264 Fig 12 may be used but are not essential anymore. Also as most of the manufacture of the thrust pads including the addition of the bearing material to their front faces is carried out when they are in circular disc form, it is easier and more economical to manufacture them.

Claims

CLAIMS

I. A thrust pad, the shape of whose thrust bearing surface is an inverted isosceles trapezium having all its four corners rounded to produce four arcs, all of the same radius, defined by a circle whose centre lies on a line that joins the centres of the two parallel sides of the trapezium so that the boundary of the thrust pad is defined by four arcuate sides each separated by a straight side.

2. A thrust pad, the shape of whose thrust bearing surface is the same as defined in claim I except that the upper straight side is replaced by an arc joining the two arcs either side of it to make one continuous arc so that the boundary of the thrust pad is defined by three arcuate sides each separated by a straight side.

3. A thrust pad, the shape of whose thrust bearing surface is a circle with two segments of equal size removed both being equidistant from the centre of the circle so that the boundary of the thrust pad is defined by two unequal arcuate sides separated by two straight sides which meet at an acute angle.

4. A thrust pad, the shape of whose thrust bearing surface is a circle with two segments removed, the said segments whose centres of area are diametrically opposite each other, so that the boundary of the thrust pad is defined by two straight and parallel sides each separated by an arcuate side, the said arcuate sides being equal in size to each other.

5. A thrust pad as claimed in claims 1, 2, 3 and 4 in which the thrust pad due to its shape may be manufactured from a circular disc.

6. A thrust pad as claimed in claims 1, 2, 3 and 4 where its radial width relative to its circumferential width can be varied within the circular envelope of the thrust pad.

7. A thrust bearing assembly comprising a carrier ring defining therein an annular slot having radially inner and radially outer sidewalls, and a plurality of similar thrust pads as claimed in claims 1, 2, 3 and 4, each thrust pad including a rear portion for location in said slot and having a shape which allows the same thrust pads to be positioned in carrier rings of wide range of curvatures or sizes.

8. A thrust bearing assembly as claimed in claim 7 in which the carrier ring locates the thrust pads as claimed in claims 1, 2, 3 and 4 permitting the thrust pads small movements for their proper functioning.

9. A thrust bearing assembly as claimed in claims 7 and 8 in which the front surface of each thrust pad receives an applied load and a radial ridge is formed on the lower surface of the thrust pad in the annular slot of the carrier ring and engaging the base of the slot to permit limited pivoting of the thrust pad about the said ridge relative to the carrier ring.

Amendments to the claims have been filed as follows:

CLAIMS

I. A thrust pad, the shape of whose thrust bearing surface is an inverted isosceles trapezium having all its four corners rounded to produce four arcs, all of the same radius, defined by a circle whose centre lies on a line that joins the centres of the two parallel sides of the trapezium so that the boundary of the thrust pad is defined by four arduate sides each separated by a straight side.

2. A thrust pad as claimed in claim 1 in which the thrust pad due to its shape may be manufactured from a circular disc.

3. A thrust pad as claimed in claim I where its radial width relative to its circumferential width can be varied within the circular envelope of the thrust pad.

4. A thrust bearing assembly comprising a carrier ring defining therein an annular slot having radially inner and radially outer sidewalls, and a plurality of similar thrust pads as claimed in claim 1, each thrust pad including a rear portion for location in said slot and having a shape which allows the same thrust pads to be positioned in carrier rings of wide range of curvatures or sizes.

5. A thrust bearing assembly as claimed in claim 4 in which the carrier ring locates the thrust pads as claimed in claim I permitting the thrust pads small movements for their proper functioning.

6. A thrust bearing assembly as claimed in claims 4 and 5 in which the front surface of each thrust pad receives an applied load and a radial ridge is formed on the lower surface of the thrust pad in the annular slot of the carrier ring and engaging the base of the slot to permit limited pivoting of the thrust pad about the said ridge relative to the carrier ring. a a * .** a a. **

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