GB2247723A

GB2247723A - Gasket to be arranged between two enameled flanges

Info

Publication number: GB2247723A
Application number: GB9118056A
Authority: GB
Inventors: Kapil Deo Swameye
Original assignee: Pfaudler-Werke GmbH; Pfaudler Werke GmbH
Current assignee: Pfaudler-Werke GmbH; Pfaudler GmbH
Priority date: 1990-09-01
Filing date: 1991-08-21
Publication date: 1992-03-11
Also published as: DE4027779A1; DE4027779C2; GB9118056D0

Abstract

A gasket to be arranged between two enameled flanges comprising an annular envelope 1 of corrosion-resistant envelope material open to the outside, and a combination of insert rings 2, 4, 5 of different materials, of which two steel insert rings 4 and 5 have a wedge-type cross section, in order to form by relative rotation of the insert rings a shim having a thickness varying along the circumference for compensation of angular deviations between the two flange surfaces to be sealed, wherein there are only two further insert rings 2 of uniform thickness, which are arranged on the two opposite sides of said metallic shim, 4, 5 and which consist of an elastic material. <IMAGE>

Description

GASKET TO BE ARRANGED BETWEEN TWO ENAMELED FLANGES This invention relates

to a gasket to be arranged between two enameled flanges of a pipeline, a heat exchanger, or like operating facilities which may be provided with a corrosion resistant enameling and which can be operated at a high temperature and/or a high pressure or vacuum.

It is generally known that, in the case of an enameled apparatus, flanges to be sealed deviate from the ideal shape, since the flanges of enameled equipment sometimes warp slightly during firing. For example, the flange of the agitator nozzle often does not remain horizontal. Since the slide ring unit or the stuffing box should be arranged in a vertical direction on the vessel, it is necessary to shim level differences at the agitator nozzle by inserting shimming elements into the respective gasket.

A method which has been used successfully for decades for making shimmed gaskets for enameled equipment comprises inserting segment-shaped shims or two insert rings having a wedge type cross-section, consisting of two Itgasket inserts (DIN 3754), between which a corrugated ring is arranged, and which are surrounded by an envelope of PTFE (Pfaudler Handbook BA 317-1, gaskets for equipment of Pfaudler-enameled steel, page 4). A proper shaping of such shim segments or wedge rings of It-material or of material which does not contain asbestos but has corresponding material properties is, however, rather cumbersome and timeconsuming, since working is necessary by means of a belt grinder. Additionally, pollution is caused by the dust produced during such grinding.

In addition a method for making of shimmed gaskets of this type is known, using a flowable resin mass which can be hardened, and to which an appropriate filler is added.

This mass is introduced into the outer envelope of the gasket and cured between the forming sealing surfaces, in order to form a shim (EP 0 079 448).

In order to allow adaptation to a warped enameled flange surface, and in order to avoid enamel damage in the case of sufficiently high contact pressure, it has already been suggested to provide for an envelope and a filler material of relatively hard non-metallic material, and to use a structure having several metallic corrugated rings arranged above each other (US-Patent 4 795 174). A compensation for angular deviations between the two flange surfaces to be sealed is not readily available for gaskets of this type.

It is therefore the primary object of the invention to improve a gasket of the above mentioned type, which can be arranged between enameled flange surfaces, in such a manner that on the one hand the gasket can be prepared and mounted in a rather simple manner, and on the other hand during the compensation of angular deviation a force distribution can be obtained which is as uniform as possible along the circumference of the gasket during tightening of the screws.

Accordingly the present invention provides a gasket to be arranged between two enameled flanges, comprising an annular envelope of corrosionresistant envelope material and open to the outside, and a combination of insert rings of different materials, of which two steel insert rings have a wedge-type cross section, in order to form by relative rotation of the insert rings a shim having a thickness varying along the circumference for compensation of angular deviations between the two flange surfaces to be sealed, wherein there are only two further insert rings of uniform thickness, which are arranged on the two opposite sides of said metallic shim, and which consist of an elastic material. Advantageously the further insert rings arranged on the opposite sides of the shim may be reinforced with a wire mesh.

It is already known to provide for a compensation of angular deviations between two plane metal surfaces, of which one is formed by the underside of a bolt head, using between the bolt head and the other metallic surface two identical washers having a wedge type cross section (USPatent 4 177 999). However, in this case sealing is performed by means of O- rings and by 'means of a sealing ring between the two wedge rings, so that from US Patent 4 177 999 no suggestion can be derived as to the manner in which a gasket could be designed so as to be usable between enameled flange surfaces in order to solve the above mentioned problem.

The invention is based on the recognition that, in the case of using a gasket in accordance with the invention, a uniform force distribution along the circumference of the gasket is made possible during tightening of the clampscrews. In the case of the known gasket mentioned at the beginning of the specification the insert can be considered I as an elastic spring, for which the formula F is applicable, where F = force, AI = pitch of the spring, 10 = original length of the spring, and M is a constant. In the case of the known gasket of the above described type the length 10 of the spring along the circumference varies, so that the force in accordance with the formula is different along the circumference. By contrast, in the case of a gasket in accordance with the invention the length 10 along the circumference is constant, since the two steel wedge rings can be considered as rigid. Therefore also the force along the circumference is constant, which is the reason for the substantial advantage that with this invention a uniform force distribution can be achieved. Surprisingly it became also apparent that if tightening of the screws was sufficiently strong to chip off the enamel this is no problem even though the insert consists primarily of steel and therefore of a material which can be considered as rigid in the case of such a gasket, and though the use of a 9 1 corrugated ring is not necessary, which use has previously been considered as necessary at least at higher operating pressures.

In the drawings there is shown an embodiment of the invention which shall be described below in a more detailed manner. In the drawings:- FIGURE 1 shows a cross-section through the two wedge rings in a gasket in accordance with the invention; and FIGURE 2 shows a cross-section of the gasket of Figure 1.

As shown in Figure 2 the gasket in accordance with the invention has an envelope 1 of PTFE or similar corrosion-resistant envelope material. This envelope may, if desired, be reinforced along the inner diameter in a manner known per se. In the illustrated embodiment of the invention there are two insert rings consisting of an elastic material such as a soft material comprising asbestos with rubber as a binder and with mineral additives, or asbestos-free material having material properties corresponding with those of the asbestos containing material. Preferably the two insert rings 2 are reinforced by a wire mesh 3 in order to avoid early failure because of brittleness of the elastic material, which brittleness occurs earlier in the case of insert rings 2 free of asbestos than in the case of insert rings containing asbestos.

The two insert rings 2 are provided on opposite sides of a shim formed by two steel shin rings 4,5. The two shim rings 4,5 preferably have a common shape and have a form resembling a steel tube in the form of a circular cylinder and divided by a plane cutting surface which is inclined to the dashed line axis of the steel tube. Such wedge rings to serve as the insert rings 4,5 can be prepared in a simple manner in mass production and do not need specific working. The wedge rings can for example be made of mild steel or of stainless steel.

For a compensation of angular deviations of warped flange surfaces, the two insert rings 4,5 can be rotated relative to each other, so that the shim formed by the two steel wedge rings has a thickness varying along the circumference depending on the rotational position and the angle of cut. Since it is not necessary to carry out work on either the steel wedge rings 4,5 or the insert rings 2 of elastic material for the purpose of a compensation of angular deviations between the two flange surfaces to be sealed, and since also it is not necessary to work the PFTE envelope I for adaptation purposes, mounting can be performed in a time-saving and simple manner not only during the manufacture of enameled equipment provided with gaskets of this kind, but also during replacement of gaskets of this kind at the place of operation.

The insert rings or gaskets 2 are of a soft material such as asbestos with rubber binding material and mineral additives although they may alternatively be comprised of asbestos-free material. These asbestos containing gaskets serving as gaskets for enameled apparatuses are sometimes known as "high pressure (rubberised asbestos) packing sheets".

The two adjusting inserts formed by the insert rings 4, 5 are of steel and the additional two insert rings 2 comprise the elastic sealing material.

Enameled reactors have at their upper ends an enameled contact support face. For the reasons given at the out set in this application, seal rings for use at this location which have equilibration inserts are of special interest.

According to construction and application of use of contact reaction containers etc., the working pressure may be anything from a few bars to 20 or more bars. Higher temperatures with contact reaction containers are temperatures between about 100 and 250C. Reaction - 6 containers of several hundreds or even thousand litres capacity are used for several different purposes in the chemical industry. Seals which are compatible with such temperatures and pressures are required for such an application. With reaction containers there are special sealing problems even if these are for example intended for a maximum of 10 bars, although the operating pressure can be widely different from this, in particular if also working under vacuum. Furthermore, there is a higher risk of corrosion if the operating temperature is more than 100 or even 2000C.

1

Claims

1. A gasket to be arranged between two enameled flanges comprising an annular envelope of corrosionresistant envelope material open to the outside, and a combination of insert rings of different materials, of which two steel insert rings have a wedge-type cross section in order to form by relative rotation of the insert rings a shim having a thickness varying along the circumference for compensation of angular deviations between the two flange surfaces to be sealed, wherein there are only two further insert rings of uniform thickness, which are arranged on the two opposite sides of said metallic shim, and,which consist of an elastic material.

2. A gasket according to claim 1, wherein the two insert rings of elastic material are reinforced with a wire mesh.

3. A gasket according to claim 1 or 2, wherein said outer envelope is of polytetrafluoroethylene.

4. A gasket according to any one of claims 1 to 3, wherein said elastic material is a material comprising asbestos bound with a rubber binder and containing mineral filler.

5. A gasket according to any one of claims 1 to 3, wherein said elastic material is an asbestos-free heat resistant material.

6. A gasket according to any one of the preceding claims when installed between the flanges of a pipeline, a heat exchanger or the other similar operating facilities provided with a corrosion resistant enameling, which facility can be operated at a high temperature and/or a high pressure or vacuum.

7. A gasket substantially as hereinbefore described with reference to, and as illustrated in the accompanying drawings.

Published 1992 at 7be Patent Office, Concept House, Cardiff Road, Newport. Gwent NP9 IRH Further copies may be obtained from Sales Branch. Unit 6, Nine Mile Point, Cwmfelinfach. Cross Keys, Newport. NPI. 7HZ. Printed by Multiplex techniques lid, St Mary Cray, Kent.