GB2400893A - A method of manufacturing a sealing device - Google Patents

Abstract

A electromechanical method of manufacturing a sealing device (10 in Fig. 1) of the type having at least one support plate 12, 14 and a plurality of elongate elements 16, 28 extending from the support plate 12, 14. The method comprises the step of directing a jet of pressurised fluid 24 over the elements 16, 28 to cut the elements 16, 28 to a pre-determined size, forming a bore 20 through which a rotatable machine part passes when the sealing device is in use. The sealing deice may be a brush seal or a leaf seal.

Description

METHOD OF MANUFACTURING A SEALING DEVICE

This invention relates to improvements in the manufacture of sealing device.

In particular this invention relates to a method of machining elongate elements which form part of the sealing device.

Brush seals, leaf seals and the like are commonly used in applications such as gas turbine engines where they are used for maintaining effective seals between relatively rotatable components. Such seals for this type of application usually comprise a pair of annular side plates with a plurality of elongate elements sandwiched between the plates. The elongate elements are fixed and extend generally radially from the plates to define a central bore of the seal for sealing against a cylindrical surface of a component to be sealed, such as an engine shaft for example. In the case of brush seals the elongate elements are in the form of bristles. In the case of leaf seals the elongate elements are in the form of flexible leaves, or strips, arranged substantially parallel to the sealing direction.

A method of machining the bristles of a brush seal is disclosed in UK patent application GB-A-2, 196,705. An abrasive tip cutter is used to cut through the bristles in the axial direction of the seal. The radially outer perimeter of the cutter is provided with an abrasive coating of cubic boron nitride (CBN) which acts against the cut bristle ends to perform a grinding operation once the bristles have been cut by the tip of the rotating cutter. The bristles of an annular brush seal are cut by the annular tip of a cup shaped cutter. The brush seal is fixed on a mounting table with its central axis aligned coaxially with the rotational axis of the cutter so that the bristle elements are cut to a predetermined dimension of the seal, as determined by the dimensions of the cutter.

The method disclosed in GB-A-2, 196,705 has a number of disadvantages including the fact that a different diameter cutter is required for each different type of brush seal or different diameter seal. Another problem associated with this method is the high cost - 2 of the cutting tool which is due to the short life of the cutter before re-plating or re- coating is required. This method is also a relatively slow process, for instance depending upon the condition of the cutter a typical seal may require two hours or so of machining time to cut the bristles to the required diameter.

The method of the present invention seeks to reduce, and possibly eliminate, the problems associated with the above mentioned method by providing an improved method of machining the bristles of a brush seal, or the leaves of a leaf seal or the like, which is simple, accurate, quick and relatively inexpensive.

According to an aspect of the present invention there is provided a method of manufacturing a sealing device of the type having at least one support plate and a plurality of elongate elements extending from the said plate; the said method comprising the step of directing a jet of pressurized fluid over the said elements to cut the elements to a pre- determined size.

This method effectively eliminates the requirement for different tooling, in particular different size cutters for machining different diameter seals. This method provides a particular flexible approach to manufacturing brush seals, leaf seals and the like since a single machine tool can be used for machining many different types of such seals.

Since the method does not use cutting and grinding tools as in the previously mentioned method, the cost of machining is reduced and problems associated with relatively long lead times associated for the supply of new cutters can be substantially eliminated. The method of the present invention is capable of reducing machining time by 50% or so and therefore provides further cost benefits over the aforementioned known method.

In one preferred embodiment, the support plate comprises at least one, preferably two, annular support plates and a central bore with the elongate elements extending radially inwards from the support plates towards the bore, whereby the pressurized fluid is directed around the periphery of the bore to cut the elements to a predetermined bore diameter. This embodiment is particularly useful for machining annular ring-type brush - 3 seals or leaf seals and the like for applications in gas turbine engines where the elongate members extend radially inwards to define the periphery of the bore of the seal.

In other embodiments, the elongate elements may extend radially outwards from the annular support plate or plates such that the pressurised fluid is directed around the outer periphery of the seal to cut the elements to a predetermined outer diameter.

Thus the method of the present invention can be used to machine brush and leaf seals and the like where the elements extend radially inwards from an annular support ring or radially outwards therefrom, or seals having both radially inward and outward extending elongate elements.

In other embodiments the support plate may comprise an elongate plate with the elongate elements extending from one or both sides of the plate to define a linear seal.

In preferred embodiments the pressurised fluid comprises water and the cutting apparatus comprises a water jet cutter. The present inventor has found that, in the case of brush seals, acceptable bristle tip finish and tolerances can be achieved using water jet cutters of the type available from SE Huffman Corporation.

In preferred embodiments the pressurised fluid may comprise an abrasive cutting agent, for example an abrasive grit. In one example the grit may have a mesh size of 220.

Preferably the elongate elements are held together prior to cutting. The elongate elements may be held together over their entire length, for example by using a binder, or the tips of the elongate elements may be spot welded so that they are held together for mutual support during the water jet cutting operation. In one particular embodiment the binder comprises a wax or a wax type material which is capable of holding the elongate elements in a matrix type structure during cutting of the bristle tips.

Preferably the working pressure of the pressurised fluid is greater than 2000 bar, and more preferably in the range 2500 to 3500 bar. In one particular example bristles made from Haynes 25 stellite wire were cut to acceptable tolerances and surface finish using a water jet cutter having a working pressure of 3100 ban The method of the present invention also contemplates embodiments of brush seals where the bristles are cut in such a way that adjacent elements have progressively greater length dimensions in a direction normal to the plane of the seal. This is particularly useful for applications where a tapered bore is required in an annular ring type brush seal, that is to say where the bore tapers inwards or outwards in the axial direction of the seal. The method also contemplates embodiments of leaf seals where the leaves are cut in such a way that the length of the leaf progressively increases in a direction normal to the plane of the seal.

The invention will now be more particularly described by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a view of an annular ring-type brush seal having an internal bore of bristles suitable for use in a gas turbine engine; Figure 2 is a crosssection view in the axial direction of the seal of Figure 1 positioned for machining by water jet cutting apparatus; and Figure 3 is a cross- section view similar to Figure 2 with the exit of the water jet cutting apparatus inclined with respect to the longitudinal axis of the seal for cutting a tapered bore.

Referring to Figure 1, an annular ring-type brush seal comprises a pair of annular side plates 12 and 14 with a plurality of bristle elements 16 fixed to the annular side plates by welding or other means. The bristle elements 16 are sandwiched between the side plates 12 and 14 and extend radially inwards from the radially inner side of the side plates to form an annular arrangement of bristles on the internal side of the side plates so as to define an internal periphery 18 of a central bore 20. \ - 5

As can be seen in the cross-section view of Figure 2, the seal 10 comprises a stack of bristle elements 16 arranged side-by-side in the axial direction of the annular seal.

This stack type arrangement of bristle elements provides the seal with an axial dimension 22 through which the jet 24 of a high pressure water jet cutter apparatus is required to cut during machining of the bore periphery 18. In the drawing of Figure 2 only the nozzle exit section 26 of the water jet cutting apparatus is shown, the remaining parts of the water jet cutting apparatus are well known in the art and are therefore omitted from the drawing of Figure 2 for the purpose of clarity.

The water jet cutting apparatus is preferably of the type having at least two axes of motion so that the nozzle exit 26 can be directed around the periphery 18 of the bore to cut the tips 28 of the bristle elements to the required bore diameter of the brush seal.

In other embodiments, the cutter may be held stationary and the brush seal rotated about its longitudinal axis so that the cutter moves relative to the seal about its periphery 18 to cut the tips to the predetermined dimension.

In the drawing of Figure 2 the nodule 26 is directed such that the water jet 24 is substantially perpendicular to the longitudinal direction of the bristle elements such that a cut is made around the periphery of the bore that is substantially parallel to the longitudinal axial direction of the seal. This type of cut may be required where the tips of the cut elements are to be positioned in close proximity to, or engagement with, the surface of a constant diameter rotating shaft, for example a shaft in a gas turbine engine.

In the embodiment of Figure 3, the nozzle exit 26 of the water jet cutting apparatus has been inclined with respect to the axis of the seal so that an angled cut 32 is produced along the axial length of the seal with axially adjacent bristle elements having slightly different dimensions. By inclining the pressurized cutting jet in this way it is possible to machine the brush seal with a tapered bore with the angle of the taper being determined by the inclination of the nozzle 26 during cutting of the bristle element tips. - 6

In the method of the present invention it has been found particularly effective if the bristle elements 16 are covered in wax, and in one particular example with the wax built up approximately 1.5mm either side of the seal in order to improve the structural integrity and strength of the wax. The wax acts to prevent, or substantially reduce, movement of the bristle elements during cutting by the water jet cutting apparatus and preferably to prevent or reduce abrasive grit contained in the pressurized water exiting the nozzle 26 becoming embedded in the seal, that is to say in the interstercies between adjacent bristles.

In one particular example bristles made from Haynes 25 stellite wire were machined by a water jet cutting apparatus having an operational working pressure of 3130 bar using a garnet 220 mesh abrasive grit. A brush seal having a diameter of approximately 30 cm was machined to a tolerance of + or- 0.125 mm in a cycle time of less than 10 minutes.

In the above examples brush seals have been described, however it will be appreciated that the method of manufacture is equally applicable to leaf seals and the like.

Although aspects of the invention have been described with reference to the embodiments shown in the accompanying drawings, it is to be understood that the invention is not limited to the precise embodiments shown and that various changes and modifications may be effected without further inventive skill and effort. For example, the bristle tips may be positioned on the radially outer side of the seal so that the water jet cutting apparatus cuts the outer diameter of the seal rather than an inner diameter on the radially inner side of the support plates. The method of the present invention may also be used for cutting the bristle tips of a linear type brush seal. The invention also contemplates embodiments where cutting fluids other than water are used. t - 7

Claims (1)

1 A method of manufacturing a sealing device of the type having at least one support plate and a plurality of elongate elements extending from the said plate; the said method comprising the step of directing a jet of pressurised fluid over the said elements to cut the elements to a predetermined size.

2 A method as claimed in Claim 1 wherein the said support plate comprises at least one annular support plate and a central bore with the said elongate elements extending radially inwards from the said plate to define the said bore, whereby the said pressurised fluid is directed around the bore of the seal to cut the elements to a pre-determined bore diameter.

3 A method as claimed in Claim 1 wherein the said support plate comprises at least one annular support plate and with the said elongate elements extending radially outwards from the said plate, whereby the said pressurised fluid is directed around the outer periphery of the seal to cut the elements to a pre determined outer diameter.

4 A method as claimed in Claim 1 wherein the said support plate comprises at least one elongate plate, and the elongate elements extend from the said plate to define a linear seal.

A method as claimed in any one of the preceding claims wherein the said pressurised fluid comprises water.

6 A method as claimed in any one of the preceding claims wherein the said pressurized fluid comprises an abrasive cutting agent.

7 A method as claimed in Claim 6 wherein the said cutting agent comprises an abrasive grit. - 8

8 A method as claimed in any preceding claim wherein the said elongate elements are held together prior to cutting.

9 A method as claimed in Claim 8 wherein the elongate elements are held together by a binder.

A method as claimed in Claim 9 wherein said binder is set around the said elongate elements.

A method as claimed in Claim 9 or Claim 10 wherein the said binder comprises a wax or wax type material.

12 A method as claimed in any one of the preceding claims wherein the working pressure of the said pressurised fluid is greater than 2000 bar.

13 A method as claimed in Claim 12 wherein the said working pressure is in the range 2500 - 3500 bar.

14 A method as claimed in any one of the preceding claims wherein the said elongate elements are cut so that adjacent elongate elements have progressively greater lengths in a direction normal to the plane of the seal.

A method as claimed in any one of the preceding claims wherein the said elongate elements are cut so that the length of the elongate elements is progressively increased in a direction normal to the plane of the seal.

16 A method as claimed in any one of the preceding claims wherein the sealing device is a brush seal and the elongate elements are bristles.

17 A method as claimed in claim 1 to claim 15 wherein the sealing device is a leaf seal and the elongate elements are in the form of flexible strips.

18 A sealing device manufactured in accordance with the method of any one of the preceding claims.

19 A method substantially as hereinbefore described and/or with reference to the accompanying drawings.