GB2290999A

GB2290999A - Repair of labyrinth seals

Info

Publication number: GB2290999A
Application number: GB9413900A
Authority: GB
Inventors: Dennis Steel
Original assignee: National Power PLC
Current assignee: National Power PLC
Priority date: 1994-07-09
Filing date: 1994-07-09
Publication date: 1996-01-17
Anticipated expiration: 2014-07-09
Also published as: GB2290999B; GB9413900D0

Abstract

Labyrinth seals for use in milling or grinding apparatus are repaired by removing the worn seal and/or region adjacent thereto; providing a piece of seal material 6 whose size and shape correspond to the size and shape of the new seal; fixing said seal material to the region where the seal is to be located using bolts and/or adhesive; and, machining said seal material, including bolts where provided, so as to provide an undulating surface 7. Furthermore a bolt is provided for use in the method comprising a relatively deep head having a shallow tool mating indentation whereby the head of the bolt can be machined to remove the indentation and enable the remaining portion of the head to form part of an undulating surface. <IMAGE>

Description

IMPROVEMENTS RELATING TO LABYRINTH SEALS The invention relates to a method for maintaining a labyrinth seal for use particularly, but not exclusively, in milling apparatus.

Labyrinth seals are typically used where one environment, or part of an apparatus, is to be sealed from a neighbouring environment, or part of an apparatus. Notably, where small particulate contaminants are likely to pass between environments, or parts of an apparatus, such labyrinth seals are provided. Thus, such seals are to be found in milling apparatus and specifically in the gear box of a milling apparatus so as to safeguard against pulverized material such as pulverized fuel entering the gear box.

The integrity of a labyrinth seal relies, in part, on the size of the labyrinth provided, typically increases in size of the labyrinth due to wear of the seal signifies a reduction in sealing ability. For example, in a milling apparatus working 10,000 hours between services a labyrinth seal having a clearance of thirty thousandth of an inch (0.030) would normally have a life expectancy of 20,000-30,000 hours before it was considered ineffective.

At this ineffective stage, the clearance would have usually increased to one hundred and fifty thousandth of an inch (0.150). Ineffective labyrinth seals are typically replaced at considerable cost. We have therefore devised a maintenance system which can half the cost of replacement of a labyrinth seal and extend the life expectancy of the article including the labyrinth seal.

According to a first aspect of the invention there is therefore provided a method for maintaining a labyrinth seal comprising: a) removing the worn seal and/or a region adjacent thereto; b) providing a piece of seal material whose size and shape corresponds to the size and shape of the new seal; c) fixing said seal material to the region where the seal is to be located; and d) machining said seal material so as to provide an undulating surface.

In a preferred embodiment of the invention the fixing is undertaken using a suitable adhesive.

According to a second aspect of the invention there is provided a method for maintaining a labyrinth seal comprising: a) removing the worn seal and/or a region adjacent thereto; b) drilling the area to receive a new seal with a pre-determined number of boit-receiving apertures; c) providing a sheet of seal material whose size and shape corresponds to the size and shape of the new seal; d) drilling said sheet of seal material, with a plurality of apertures whose number and positioning corresponds to said apertures provided in b) above; e) fixing said sheet of seal material on the area prepared to receive the new seal using bolt means; and f) machining said sheet of seal material so as to provide an undulating surface.

In a preferred embodiment of the invention the sheet of seal material is machined in the region of said bolts whereby said bolts are machined so as to form1 in part, said undulating surface.

Preferably said undulating surface comprises a plurality of alternating ridge and recess members so as to provide a number of spaced upstanding projections.

Preferably still the area to receive the new seal is first treated with an adhesive before the seal is affixed thereto. This not only enhances the bonding of the new seal in position but also safeguards against pockets of air being trapped behind the seal.

Preferably further still said bolt is provided with a relatively deep head which is further provided with a relatively shallow outer tool or screw driver mating indentation such that when the sheet of seal material, including the bolt, is machined the outer most shallow tool or screw driver mating indentation is removed and the contour of the undulating surface is therefore provided by the inner relatively deep head of the bolt.

It follows from the above that the maintenance method involves the removal and replacement of a labyrinth seal surface which surface can be repeatedly removed and replaced using the apertures provided in the area prepared to receive the new seal and the bolts fashioned in accordance with the invention.

It therefore follows that according to a third aspect of the invention there is provided a bolt for use in the method of the invention comprising a relatively deep head which is provided with an outer relatively shallow tool mating indentation region whereby the head of the bolt can be machined so as to remove said shallow indentation region and so as to enable said remaining region of said head to form a part of an undulating surface.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying Figures wherein: Figure 1 represents a sectional view of a gear box air seal; Figure 2 represents a section along the line D-D of Figure 1; Figure 3 represents a section along the line C-C of Figure 1; Figure 4 represents a section through a part of the labyrinth seal prior to machining; Figure 5 represents an eniarged section of part of a machined labyrinth seal; Figure 6 represents a side sectional view of a bolt in accordance with the invention prior to machining; and Figure 7 represents a side sectional view of a bolt in accordance with the invention after machining.

Referring to the Figures and firstly to Figure 1, there is shown, in section, a circular gear box air seal 1 which is provided on its inner most side 2 with a labyrinth seal. Figure 2 shows a section along the line D-D. The seal has been machined so that the worn labyrinth seal has been removed and a cavity X which is 4.125 inches in depth has been provided. This cavity X extends about the entire inner most surface of gear box air seal 1.

Once this cavity X has been created a pre-determined number of apertures of a pre-determined size and pitch are provided in rear wall 3 defining cavity X. For instance, as shown in Figure 1, forty eight apertures 4 are provided in wall 3 and essentially spaced in a pair-like manner.

Brass sheets or plates 6 of seal material are then sized and shaped so as to accommodate the cavity provided by removal of the old labyrinth seal.

In the embodiment shown in Figure 1 two brass plates, each of equal size and each adapted to fill one half of the cavity shown in Figure 1, are provided. However, it is within the scope of the invention to provide a single plate or indeed any number of connecting plates. These brass plates 6 are further provided with apertures 4b which are sized and shaped to accommodate bolts in accordance with the invention, which bolts will be described hereinafter. The number and nature of these bolt receiving apertures will be determined by the corresponding apertures provided in the rear wall 3 of the gear box air seal 1.

Adhesive is applied to the rear wall of cavity 3, with a view to preventing air entrapment, before brass plates 6 are applied to the rear wall 3 and attached thereto using bolts 5.

A side elevation view of bolt 5 is shown in Figure 6. It can be seen that bolt 5 comprises an elongate shank member 5a, a bevelled upper most neck member 5b and an outer upstanding annular member 5c. The outer most surface 5d of annular member Sc is provided with an indentation 5e sized and shaped to accommodate the head of a driving means such as a screw driver. However, the depth of indentation 5e is relatively shallow compared to the depth of members 5b and Sc for reasons which will become apparent during the following description.

Referring now to Figure 4, it can be seen that plates 6 have been attached to rear wall 3 such that apertures 4 in wall 3 are aligned with apertures 4b provided in plates 6. Moreover, bolt 5 has been positioned within said aligned apertures 4, 4b and driven into position using indentation 5e and a suitable tool. A nut 10 is provided on shank member 5a of bolt 5.

With the sheet of seal material or brass plate 6 positioned inside the cavity X provided by the removal of the old labyrinth seal, the structure is now ready for machining.

Using conventional machine tools, the inner most surface 2 of the new labyrinth seal provided in Figure 4 is machined to a depth represented by X. Moreover, during machining, the depth represented by Y is discarded.

The nature of the machining is such that a series of upstanding spaced members or fins 7 are provided. Both the sheet of seal material or brass plate 6 and the bolts 5 of the invention are machined so as to provide a surface having a continuous series of fins provided therealong.

Figure 7 shows in greater detail the nature of the machining in the region of bolt 5. It can be seen that the outer most part of the sheet of seal material and the bolt represented by depth Y is discarded during machining and fin like structures 7 are provided in the remainder of the sheet of seal material 6 and bolt 5. Moreover, the size of fin 7 is such that a plurality of fins are provided by a single head of bolt 5.

Once the above machining is completed, the seal is in place and ready for use. After a prolonged period of use the seal can be replaced and using new bolts, which bolts are manufactured in accordance with the invention, a new seal plate can be inserted into the cavity provided by removal of the old seal plate and fixed into position, using bolts 5, prior to machining. Thus, the invention provides for a maintenance system which can be repeatedly applied to seals so as to prolong the life of equipment bearing such seals.

Claims

1. A method for maintaining a labyrinth seal for use in a milling or grinding apparatus comprising: a) removing the worn seal and/or a region adjacent thereto; b) providing a piece of seal material whose size and shape corresponds to the size and shape of a new seal; c) fixing said seal material to the region where the seal is to be located; and d) machining said seal material so as to provide an undulating surface.

2. A method according to Claim 1 wherein the fixing is undertaken using a suitable adhesive.

3. A method for maintaining a labyrinth seal for use in a milling or grinding apparatus comprising: a) removing the worn seal and/or a region adjacent thereto; b) where a pre-determined number of bolt receiving apertures have not hitherto been provided, drilling the area to receive a new seal with a pre-determined number of bolt-receiving apertures; c) providing a sheet of seal material whose size and shape corresponds to the size and shape of the new seal; d) drilling said sheet of seal material with a plurality of apertures whose number and positioning corresponds to said apertures provided in b) above; e) fixing said sheet of seal material on the area prepared to receive the new seal using bolts; and f) machining said sheet of seal material so as to provide an undulating surface.

4. A method according to Claim 3 wherein the sheet of seal material is machined in the region of said bolts whereby at least one of said bolts is machined so as to form, in part, said undulating surface.

5. A method according to any proceeding Claim wherein said undulating surface comprises a plurality of alternating ridge and recess members so as to provide a number of spaced upstanding projections.

6. A method according to any proceeding Claim wherein the area to receive the new seal is first treated with an adhesive before the seal is affixed thereto.

7. A method according to Claims 3 to 6 wherein the method comprises providing a bolt with a relatively deep head which bolt is further provided with a relatively shallow outer tool or screwdriver mating indentation such that when the sheet of seal material, including the bolt, is machined, the outermost shallow tool or screwdriver mating indentation is removed and the contour of the undulating surface is therefore provided by the inner relatively deep head of the bolt.

8. A method according to Claims 4 to 7 wherein the machining of said sheet of seal material, including the bolt, is such that a plurality of fins are provided by a single head of the bolt.

9. A method according to any preceding Claim comprising repeating the steps of said method.

10. A method for maintaining a labyrinth seal substantially as described herein with reference to and/or as illustrated in the accompanying Figures.

11. A bolt for use in the method of the invention comprising a relatively deep head which is provided with an outer relatively shallow tool or screwdriver mating indentation region whereby the head of the bolt can be machined so as to remove said shallow indentation region and so as to enable said remaining region of said head to form a part of an undulating surface.

12. A bolt according to claim 11 wherein a plurality of fins forming an undulating surface are provided by the head of the bolt.

13. A bolt substantially as described herein with reference to and/or as illustrated in figures 4, 6 and/or 7.

14. A milling apparatus incorporating a seal provided using the method of the invention.