GB2345144A - An apparatus for testing gaskets - Google Patents

Abstract

A pressure chamber 1 has pressurising fluid inlet and outlet means and an opening partially closed by a platen 5 which includes at least one aperture having means to locate a gasket 7 in position in use. A cover plate closes the aperture in the platen 5 and compresses the gasket between the platen 5 and the cover plate. The outer edge of the gasket 7 is viewable externally to the pressure chamber 1 to provide evidence of gasket performance, in particular the location and nature of any failure under pressure.

Description

An Apparatus and a Method for Evaluating and Developing Gaskets and Flanges The present invention relates to gasket-sealed flange interfaces and, in particular, to an apparatus and a method for evaluating and developing gaskets and their associated flanges under laboratory conditions.

There are a number of national standards describing tests for metallic and non-metallic gasket materials, the tests being particularly directed at the characteristics of compression and recovery (e. g. ASTM F36-A), tensile strength (e. g. ASTM F152 and DIN 52 910), stress relaxation (e. g. DIN 52 913) and hot compression (e. g. BS F125). These standards are commonly used in the gasket industry but have been found to be unsuitable for defining the sealability characteristics of gasket materials.

Materials providing similar results when evaluated to the tests prescribed in national standards have been found to have very different sealing characteristics when fitted to the flanges to be sealed. The tests are therefore considered to be suitable only for checking gasket material quality consistency after other means have been used to establish the sealability performance of a particular gasket and flange assembly.

Establishing gasket and flange sealability performance normally relies upon reference to past experience with similar media sealed under similar conditions. This provides a starting point which may need to be followed by experimentation with different gasket materials, constructions and thicknesses in association with different flange materials, flatness tolerances and surface finishes until a satisfactory result is found. This will not necessarily lead to the optimum result because it may prove uneconomical or too time-consuming to experiment with the large number of possible combinations.

The testing of gaskets under simulated operational conditions has long been practised but the fact that the gasket itself makes only a limited contribution to the total sealing performance at an interface has not been adequately recognised in the prior art.

For instance, patent US 3,400,572 discloses an apparatus and a method for evaluating the sealability and relaxation characteristics of gasket samples under different clamping loads but makes no reference to the attributes of the corresponding flanges and their contribution to the total sealing performance.

In another example, patent US 5,375,453 discloses an apparatus and a method for approximating the service life of a gasket. In use, a gasket sample is clamped into the apparatus and a chamber formed by an inner diameter of the gasket sample is filled with gas at a predetermined pressure. The amount of gas leaking by the gasket is measured following a predetermined number of temperature cycles. The pressure of the gas may also be cycled but no other variables are disclosed. There is not therefore provided a means to evaluate and develop the sealing performance of a complete gasket/flange interface.

A further disadvantage with the prior art is that no provision is disclosed for visually observing a gasket under test. The point at which a deterioration in sealing integrity commences, and whether leakage commences through a body of a gasket or across a face, can provide valuable information to aid the reformulation and development of materials and processes. The apparatus and method of US 5,375,453 provide for measurement of the amount of leakage but cannot indicate the precise manner of the leakage.

A further disadvantage with the apparatus and method of US 5,375,453 is that it provides only for gas as a testing medium.

In temperature cycling tests, a gas will not attain extremes of temperature as quickly as would a liquid medium and thermal shock loadings on the test piece will not therefore be as severe as might be seen where a gasket is required to seal an interface against liquid translocation.

Furthermore, use of liquid as a test medium might be considered as providing a better indication of the manner of leakage.

However, no provision is disclosed in any of the prior art for removing an intact gasket and flange assembly from the test apparatus which allows for expelling all traces of test media before release and inspection of the gasket. This can be a particular problem where liquid is used as the pressurising medium, since the release of a gasket from a test apparatus before removal of all liquid test media from the vicinity of the gasket will permit the liquid to creep onto areas which may have remained dry during the test. The perceived test results may therefore be inaccurate in providing an indication of the manner of leakage during testing.

A still further disadvantage with the prior art is that no provision is disclosed for simulating the vibration and harshness that a gasket-sealed flange interface may experience during inservice operating conditions and which may have a significant influence on the sealability performance.

It is an object of the present invention to provide an apparatus and a method for the laboratory evaluation of gasket-sealed flange interface integrity under representative in-service operating conditions.

It is a particular object of the invention to provide an apparatus and a method which provides some indication of the manner of leakage occurring during such an evaluation.

It is a further object of the invention to provide an apparatus and a method for the laboratory development of gasket-sealed flange interfaces under representative in-service operating conditions in respect of the association of gasket construction and materials with flange materials, surface flatness, surface finish and compressive loads.

According to a first aspect of the present invention, there is provided an apparatus for evaluating and developing gaskets and their associated flanges, comprising a pressure chamber having pressurising fluid inlet means and pressurising fluid outlet means, and provided with at least one opening; a platen for partially closing the opening in said chamber; said platen defining at least one aperture and being provided with means to locate a gasket in position over the at least one aperture in use; and a cover plate to effect closure of the aperture in the platen in use so as to engage a gasket in position over the aperture in the platen, with a first surface of the gasket engaging a surface of the platen and a second surface of the gasket engaging a surface of the cover plate.

In use, the gasket is engaged in place over the pressure vessel opening between the platen and the cover plate. The platen and cover plate cooperate to apply a suitable clamping load representative of service conditions and the container is pressurised to be similarly representative. The arrangement allows test conditions much more representative of those inservice to be applied than is possible with prior art devices where the gasket is merely clamped onto the pressure vessel.

This enables the whole gasket/flange interface to be evaluated, facilitating the optimisation of the characteristics of the gasket, and also the characteristics and design of the associated flanges. This is particularly the case if, as is preferred, the surface of the platen engageable to the first surface of the gasket is configured to be representative of the surface of a flange which would engage such first surface in service use, and also the surface of the cover plate engageable to the second surface of the gasket is configured to be representative of a flange which would engage such second surface in service use.

The surfaces may be configured to be representative of shape, material properties, surface finish or any like feature or combination of features.

Preferably the pressurising fluid is a liquid. The liquid may be water-based, for example engine coolant. Alternatively, the liquid may be oil-based, for example lubricating oil or fuel oil.

The arrangement of the invention facilitates removal of the pressurising fluid before removal of the gasket being evaluated, if required. Liquid is preferred in many cases for a number of reasons, not least since it may provide visible evidence of the gasket performance during and subsequent to the evaluation, and in particular, the location and nature of any failure under pressure.

The platen and cover plate are preferably arranged to engage the gasket such that a part of the gasket is visible externally in use. Preferably, the outer edge of the gasket is viewable externally of the pressure chamber in use. This permits the progress of the test to be monitored as it proceeds, and gives the observer the possibility of determining the failure mode of the gasket seal (e. g. whether leakage commences through the gasket body or across a face).

To simulate a range of service conditions, means may be provided to vary the temperature of the pressurising fluid during testing, preferably cyclically as the test progresses, conveniently in the form of a device for changing the temperature of the fluid located externally to the pressure chamber and a fluid feed system to receive fluid from the outlet means to the device and to return fluid from the device to the inlet means.

Preferably, this comprises a first fluid feed system communicating with a fluid cooling means, such as a heat exchanger, and a second fluid feed system communicating with a fluid heating means.

The fluid feed system may comprise means for pressurising the fluid in the chamber, to allow variation of the pressure during testing, preferably cyclically as the test progresses.

Conveniently, the pressurising means comprises a reservoir and a pump. The pressure of the fluid may be varied by conventional pressure control means such as an adjustable relief valve or a variable pressure pump. The fluid inlet means may comprise a closable inlet valve. The fluid outlet means may comprise a closable outlet valve. The closable valves may be used to isolate the platen and cover plate assembly from the fluid inlet means and fluid outlet means prior to and subsequent to the evaluation, allowing the pressure chamber to be evacuated of pressurising fluid prior to fitting or removing the platen and cover plate assembly.

To simulate a full range of operational conditions, the apparatus may be located in an environment wherein means are provided to controllably vary the ambient temperature within the environment in which the apparatus is situated.

The invention further comprises a system for evaluating and developing gaskets and their associated flanges, comprising the above apparatus mounted on a table having vibration means to vary vibration and harshness characteristics.

The apparatus may be mounted on the table with a normal attitude to the table, or alternatively with a normal to the perpendicular attitude to the table.

Means are preferably fitted to the platen and/or cover plate to measure and control vibration levels.

A mass may be attached to an extension fixed to the cover plate to vary vibration and harshness characteristics, by intensifying the effect of the vibration means.

In a further aspect, the invention is a method of evaluating and developing gaskets and their associated flanges, comprising: engaging a platen in position over an opening of a pressure chamber so as to partially close the chamber, said platen defining at least one aperture; locating a gasket in position over said aperture; engaging a closure plate onto the platen in position over the gasket so as to engage the gasket in position over the aperture in the platen and apply a clamping load thereon; introducing pressurising fluid into the chamber to pressurise the chamber; and monitoring the behaviour of the gasket under pressure.

The pressure and/or temperature of the pressurising fluid may be varied cyclically, preferably by means located externally to the chamber.

The clamping load may be varied to simulate different in-service conditions, for example by means of adjusting screws. Optionally, the clamping load is monitored during testing using pressure sensors.

The performance of the gasket is preferably monitored by visual observance.

In a further aspect, the invention comprises the use of the above apparatus or method in the evaluation and development of gasket and/or flange surface treatments or finishes.

By way of example, the embodiments of the invention will be described with reference to the accompanying drawings: Figure 1 is an isometric view of a pressure chamber which forms part of the apparatus of the present invention; Figure 2 is an isometric view of the pressure chamber to which has been attached a platen; Figure 3 is an isometric view of the pressure chamber and platen onto which a gasket to be tested has been positioned; Figure 4 is an isometric view of the pressure chamber and platen onto which a cover plate has been fastened to clamp the gasket for testing; Figure 5 is an isometric view of a six-hole cover plate; Figure 6 is an isometric view of a two-hole cover plate; Figure 7 is an isometric view of the apparatus mounted on the table of a shaker inside an environmental enclosure with its axis in a perpendicular attitude and with an additional mass fastened to the cover plate; Figure 8 is an isometric view of the apparatus mounted on the table of a shaker inside an environmental enclosure with its axis in an attitude normal to the perpendicular and with an additional mass fastened to the cover plate.

The embodiments of the invention will be described with reference to evaluating and developing flanges and gaskets for sealing liquid media such as oils and water-based coolants, for which it is particularly suitable.

Referring to the drawings, figure 1 shows a cylindrical pressure chamber 1 incorporating a circular peripheral flange 2 at an end.

The chamber 1 is provided with closable inlet and outlet valves 3 through which a pressurising liquid will be pumped. A further closable valve 3 is provided at a lower point for drainage of the apparatus. Adjacent to, but spaced apart from, a centre hole in the peripheral flange is a groove 4 into which is fitted an O-ring.

Figure 2 shows the pressure chamber 1 to which a platen 5 has been fastened so that it seals against the O-ring of figure 1.

The platen 5 carries a shaped hole 6 and is designed to replicate a first flange against which a gasket to be evaluated would be fitted in service. The design of the platen 5 will vary according to the gasket profile. The platen 5 also carries holes 8 positioned to match the fastener holes 9 in the gasket.

Figure 3 shows a gasket 7 placed in position around the perimeter of the shaped hole 6 on the platen 5. The gasket 7 may have a sealant or other surface treatment applied if this will be the case in service but a major benefit of the present invention is the ability to evaluate and develop gaskets and their interfaces to a level where sealant or other surface treatment should not be necessary.

Figure 4 shows a cover plate 10 fastened to the platen 5. A conduit 11 and tap 12 is fitted to the cover plate 10 as an air bleed means. The cover plate 10 replicates a second flange against which a gasket 7 to be evaluated would be fitted in service. Electronic load cells 13 may be fitted between the cover plate 10 and each of the fasteners 14 retaining the cover plate 10 and gasket 7 to the platen 5 to enable the clamping load to be measured, hence gasket clamping loads can be varied to simulate both different size fasteners and different flange areas. Also fitted to the cover plate 10 and platen 5 are accelerometers 15 to enable measurements to be taken when the apparatus is used under vibration conditions. An outer edge of the fitted gasket 7 is viewable externally of the apparatus.

The temperature of the pressure chamber 1 and the gasket 7 is varied by varying the temperature of the test liquid externally of the chamber 1. This is achieved by the use of two feed systems (not shown) for each of the media to be tested, each feed system including a reservoir and a pump. The first feed system also includes a heater and the second feed system also includes a chiller unit (heat exchanger). Each feed system is controlled by electrically managed solenoid valves.

The temperature variation may be cyclic and thermal shock may be induced by allowing the chamber 1 to be purged by fluid at a different selected temperature for a predetermined time.

Typically, a change in temperature between 0 C and 120 C can be achieved in ten minutes but, when required, the apparatus can be used for tests outside of this temperature range. Cyclic pressure variation may also be introduced where this will replicate conditions which may be seen in service.

Figure 5 shows the reverse side of the cover plate 10 shown fitted to the apparatus of figure 4. This example cover plate 10 has six fastener holes 16 and a shape typical of a six-hole flange. Figure 6 shows a typical two-hole cover plate 17 which could be fitted to a corresponding two-fixing-hole platen (not shown). It will be clear that the shapes of platens, gaskets and cover plates are not restricted to the shown examples. However it may not be necessary to exactly replicate an in-service gasket profile because the combination of gasket shapes, between fixing holes, of the two examples will replicate a wide number of flange/gasket profiles.

The cover plate 10 may be made from any material that is likely to be suitable for the flange which is being simulated, e. g. steel or aluminium, and it may be given a surface finish and texture which will be economical for the flange to be used in service, e. g.'2, 0-3,2 Ra milled'or'0, 8-1,6 Ra ground'.

The selected surface finishes and textures may be provided over the whole of the cover plate 10 or restricted to one or more specific areas. Alternatively, more than one surface finish and/or texture can be applied to different parts of the cover plate 10 to provide directly comparable results.

The cover plate 10 may also be configured with alternative degrees of flatness, e. g.'0-0, 10 mm concavity'or'0, 10-0,15 mm concavity'and the material from which it is formed may have different directions of lay (i. e. machining direction or material grain flow). Predetermined degrees of flatness may be simulated by machining channels 18 of the selected out-of-flatness measurement.

It is envisaged that a stock of cover plates will be held, each having a selected variation in material, surface finish, surface texture, flatness and/or lay. Operator experience may permit a short-list to be drawn up of the most suitable cover plate configurations for testing and these can each be tested in turn in an assembly which includes the gasket.

The gaskets 7 to be evaluated may be short-listed from past experience or manufacturers'recommendations. They may vary primarily in material, construction and thickness but it should be noted that the manner of manufacture may also have an effect on gasket performance. It has been found, for example, that gaskets manufactured by the calendering process can have different sealing capabilities between one side of the gasket and the other.

Certain gaskets 7 have been found to perform differently in service dependant upon the direction of grain presented to the associated flange. It is therefore recommended to prepare and test gasket samples with perpendicularly opposing grain direction in order to access both conditions.

It has been found that, in cut sheet gaskets, progressively softer and more conformable materials are required as out-offlatness of the interfacing flanges is increased. This may result in an undesirable increase in torque relaxation of the assembly fasteners. To minimise this effect, it is beneficial to develop a range of materials to meet incremental increases in flange out-of-flatness following which an appropriate selection for specific applications may be made.

Visual examination of the gasket 7 under test will reveal important information regarding the source and form of any leakage. Initial signs of any deterioration in gasket sealing integrity will, especially in the case of soft cut gaskets, be generally visible as a discoloration of the edge of the material.

By close inspection, it will be possible to observe whether commencement of any leakage is through the body of the material or across a face of the gasket 7. Tracer dye may be added to the pressurising liquid to emphasise any leakage indications in situations where, for example, the gasket colouring or texture may not readily show wetting.

Further leakage may be detected by pressure decay measurements using high accuracy transducers (not shown). The test liquid feed system (not shown) may be fitted with level switches to shut down the equipment in the case of gross loss of pressurising liquid.

The configuration of the main body of the apparatus as three separable parts, chamber 1, platen 5 and cover plate 10, as shown in figures 1 to 4, provides for the platen 5, gasket 7 and cover plate 10 to be taken off the chamber 1 as an assembly so that virtually all of the liquid can be removed from the vicinity of the gasket 7 before it is separated from the assembly for posttest examination. This provision prevents the liquid creeping onto areas which may have remained dry during the test and thus ensures reliable interpretation of sealing performance after disassembly of the test apparatus.

A further key feature in the laboratory evaluation and development of a gasket-sealed interface is vibration and harshness simulation. Figure 7 shows the apparatus mounted in a perpendicular attitude on a table 19 of a conventional shaker test device 20. Random, sine wave or shock vibrations to a predetermined programme can be input to the shaker table 19. Accelerometers 21 may be fitted to the platen 5 and cover plate 10 to measure and control vibration levels.

Also shown in figure 7 is an environmental cabinet 22 enclosing the test apparatus. The cabinet 22 serves to controllably vary the ambient temperature around the apparatus and its use helps ensure realistic simulation whether or not vibration and harshness simulation is being undertaken as part of the tests.

An additional mass 23 may be added to the apparatus in order to vary the vibration and harshness characteristics. The additional mass 23 may be fixed to an extension 24 to the cover plate 10 and may be varied in order to provide different characteristics at the cover plate to simulate in-service conditions. An accelerometer 21 may be fitted to the mass 23 to monitor vibration levels.

Figure 8 shows the apparatus, fitted with the additional mass 23, mounted via a bracket 25 onto the shaker table 19 within the environmental enclosure 22 in an attitude normal to the perpendicular. The apparatus may, of course, be mounted at any other angle to simulate in-service conditions.

The apparatus and method of the present invention may be used initially to develop a range of gasket types to meet specific defined conditions of flange shape, fastener end load, surface finish and flatness for each. It may then be used to aid defining the minimum required clamping stress in the area of maximum out-of-flatness. This is achieved by fitting a new gasket sample, of the same type as tested, in conjunction with pressure sensitive paper and then applying the previously defined fastener end loads. The colour change of the paper is measured using a densitometer. The resulting clamping stress is then determined by comparison with values previously obtained by applying known loads to standard test disc samples (not shown).

At the conclusion of the development of a range of gasket types, a list can be drawn up which can be in a format similar to the example shown as Table 1. When considering a specific interface for sealing, a preliminary choice may be made from the developed range of gasket types using the fluid to be sealed and either expected or measured flange out-of-flatness as the prime selection criteria. Having selected a gasket type that is likely to match the criteria, its suitability may then be confirmed by making checks with pressure sensitive paper in conjunction with a gasket prepared from the preliminary selected material and fitted to the actual interface to be sealed.

The present invention may be used to evaluate and develop interfaces sealed with various types of gasket, including cut soft sheet, crimped metal sheet, elastomer coated metal, moulded elastomeric and liquid dispensed.

Type Fluid to be Sealed Out of Flatness Code (max) A1 Low pressure oil 0, 050 mm A2 Low pressure oil 0, 075 mm A3 Low pressure oil 0, 100 mm A4 High pressure oil 0, 075 mm A5 Coolant 0,075 mm A6 Coolant 0,100 mm Table 1

Claims (29)

Claims

1. An apparatus for evaluating and developing gaskets and their associated flanges, comprising a pressure chamber having pressurising fluid inlet means and pressurising fluid outlet means, and provided with at least one opening; a platen for partially closing the opening in said chamber; said platen defining at least one aperture and being provided with means to locate a gasket in position over the at least one aperture in use; and a cover plate to effect closure of the aperture in the platen in use so as to engage a gasket in position over the aperture in the platen, with a first surface of the gasket engaging a surface of the platen and a second surface of the gasket engaging a surface of the cover plate.

2. An apparatus as claimed in claim 1, wherein the pressurising fluid is a liquid.

3. An apparatus as claimed in any preceding claim, wherein the platen and cover plate are arranged to engage the gasket such that a part of the gasket is visible externally in use.

4. An apparatus as claimed in claim 3, wherein the outer edge of the gasket is viewable externally of the pressure chamber.

5. An apparatus as claimed in any preceding claim, wherein means are provided to vary the temperature of the pressurising fluid during testing.

6. An apparatus as claimed in claim 5, wherein the means to vary the temperature of the fluid comprises a temperature control device for changing the temperature of the fluid located externally to the pressure chamber, and a fluid feed system to receive fluid from the outlet means to the temperature control device, and to return fluid from the temperature control device to the inlet means.

7. An apparatus as claimed in claim 6, comprising a first fluid feed system communicating with a fluid cooling means and a second fluid feed system communicating with a fluid heating means.

8. An apparatus as claimed in claim 7, wherein the cooling means comprises a heat exchanger.

9. An apparatus as claimed in any one of claims 6 to 8, wherein the fluid feed system comprises means for pressurising the fluid in the chamber.

10. An apparatus as claimed in claim 9, wherein the pressurising means comprises a reservoir and a pump.

11. An apparatus as claimed in any preceding claim, wherein means are provided to adjust the pressure of the fluid.

12. An apparatus as claimed in any preceding claim, wherein closable valves are provided to isolate the platen and cover plate assembly from the fluid inlet means and fluid outlet means.

13. A system for evaluating and developing gaskets and their associated flanges, comprising the apparatus as claimed in any of the preceding claims, mounted on a table having vibration means.

14. A system as claimed in claim 13, wherein means are fitted to the platen and/or cover plate to measure and control vibration levels.

15. A system as claimed in claim 13 or 14, wherein a mass is fixed to an extension to the cover plate to vary vibration and harshness characteristics.

16. A method of evaluating and developing gaskets and their associated flanges, comprising: -engaging a platen in position over an opening of a pressure chamber so as to partially close the chamber, said platen defining at least one aperture; -locating a gasket in position over said aperture; -engaging a closure plate onto the platen in position over the gasket so as to engage the gasket in position over the aperture in the platen and apply a clamping load thereon; -introducing pressurising fluid into the chamber to pressurise the chamber; and -monitoring the behaviour of the gasket under pressure.

17. A method as claimed in claim 16, wherein the pressure of the pressurising fluid is varied cyclically.

18. A method as claimed in claim 16 or 17, wherein the temperature of the pressurising fluid is varied cyclically.

19. A method as claimed in any one of claims 16 to 18, wherein the temperature of the pressurising fluid is varied by means located externally to the chamber.

20. A method as claimed in any one of claims 16 to 19, wherein the clamping load is varied to simulate different inservice conditions.

21. A method as claimed in claim 20, wherein the clamping load is varied by adjusting screws; said clamping load being monitored using pressure sensors.

22. A method as claimed in any one of claims 16 to 21, wherein the performance of the gasket is monitored by visual observance.

23. Use of the method as claimed in any one of claims 16 to 22, in the evaluation and development of gasket surface treatments or finishes.

24. An apparatus substantially as hereinbefore described with reference to figures 1 to 5.

25. An apparatus substantially as hereinbefore described with reference to figures 1 to 4 and 6.

26. An apparatus substantially as hereinbefore described with reference to figures 1 to 5 and 7.

27. An apparatus substantially as hereinbefore described with reference to figures 1 to 4,6 and 7.

28. An apparatus substantially as hereinbefore described with reference to figures 1 to 5 and 8.

29. An apparatus substantially as hereinbefore described with reference to figures 1 to 4,6 and 8.