GB2067683A

GB2067683A - Synthetic plastics gaskets

Info

Publication number: GB2067683A
Application number: GB8101692A
Authority: GB
Original assignee: Carl Freudenberg KG
Current assignee: Carl Freudenberg KG
Priority date: 1980-01-22
Filing date: 1981-01-20
Publication date: 1981-07-30
Also published as: FR2474135B1; FR2474135A1; GB2067683B; DE3002140C2; DE3002140A1

Abstract

A one-piece, rotationally symmetrical gasket (4), of a synthetic plastics material having only slight resiliency such as polytetrafluoroethylene, is mounted in an annular gap (3) to be in sealing engagement with both a plate (1) and a tube (2). As viewed in radial section, the gasket (4) has a retaining part (7) of generally orthogonal profile and a sealing part (8) of generally circular profile. A diameter of the sealing part (8), which after mounting extends radially of the tube (2), is spaced from a facing part of a first leg (7a) of the retaining part (7) by a dimension 1.1 to 1.3 times the thickness of the plate (1). Said diameter itself has a dimension 1.1 to 1.6 times the width of the gap (3), measured radially of the tube (2). <IMAGE>

Description

SPECIFICATION Synthetic plastics gaskets This invention relates to synthetic plastics gaskets of the kind to be mounted in an annular gap formed between a tube-holding plate and a tube mounted in an oversized bore through the.

tube-holding plate.

A gasket of this kind is known from French patent 1,595,096 and consists of polytetrafluoroethylene, which is a material having only a limited capacity for adapting itself closely to uneven surfaces, besides having only slight resiliency. Flanges of that gasket which rest on the tube-holding plate are therefore not capable of fitting closely thereto in the manner as necessary with regard to good sealing. Fitting is also difficult, and in many cases intolerable damage occurs during insertion of that gasket into the tubeholding plate.

This invention is based upon the problem of developing a synthetic plastics gasket of this kind which is simple to fit and remove and guarantees excel lend sealing even when relative movements occur.

An assembly, in accordance with the present invention, comprises: a tube-holding plate, a tube mounted in an oversized bore through the tube-holding plate so that an annular gap is formed between the tube and the tube-holding plate, and a synthetic plastics gasket mounted in the gap; the gasket presenting a retaining part and an annular sealing part which, as viewed in a radial section, are respectively of generally orthogonal profile and generally circular profile: said generally orthogonal profile of the retaining part being formed by a first leg which extends transversely of the tube and a second leg which extends symmetrically of the sealing part, centrally within the gap and longitudinally of the tube; and said generally circular profile of the sealing part being such that a diameter thereof, considered before mounting by the gap but which after mounting by the gap extends radially of the tube, is spaced from a facing part of the first leg of the retaining part by a dimension 1.1 to 1.3 times the thickness of the tube-holding plate, with said diameter itself having a dimension 1.1 to 1.6 times the width of the gap, measured radially of the tube; the arrangement being such that the first leg of the retaining part abuts one face of the tubeholding plate to retain the sealing part in sealing engagement around the tube as well as around the junction between the bore and the other face of the tube-holding plate.

It will be appreciated that, because the second leg of the retaining part is always spaced from the adjacent surfaces of both the tube and the bore through the tube-holding plate, the retaining part possesses a certain mobility in relation to both the tube and the tube-holding plate.

Preferably, the width of the second leg of the retaining part, measured radially of the tube, is 0.4 to 0.6 times the width of the gap, measured radially of the tube.

After the gasket has been driven into the bore, it places itself with uniform pressure over the whole circumference of the adjacent junction between the bore and the tube-holding plate. This pressure increases after insertion of the tube through the gasket, and it can readily reach values at which a slight plastic deformation of the sealing part of the gasket can occur. However, such slight plastic deformation is not in itself disadvantageous, but on the contrary compensates for any irregularities to provide a good. sealing effect.

The gasket naturally presses on the tube with a pressure dependent upon the extent of the dimensional adaptation. However, as the point of contact between the gasket and the tube is situated in front of the tube-holding plate, this pressure can be supplemented by the pressure of a surrounding fluid which is being sealed-off. The superimposition of two pressures obviously leads to a particularly good sealing effect being achieved.

In order to prevent damage to the sealing part of the gasket, while the tube is being inserted therethrough, it is preferred that the tube should have smooth-walled surface. Adequate surface quality exists in the copper, high-grade steel and glass tubes which are frequently used in heat exchangers. If such tubes are used, the use of lubricants is superfluous. Moreover, there is then adequate compensation for variations in length resulting from temperature changes.

Also preferably, the gasket further presents an annular groove which, as viewed in said radial section, extends symmetrically within the sealing part and parallel to the axis of the tube, with a bottom of said groove being spaced from said facing part of the first leg of the retaining part by a distance less than the thickness of the tubeholding plate.

This measure firstly improves the resiliency of the sealing part in relation to the sealed surfaces.

Moreover, the effective surface area of the sealing part is enlarged so that a surrounding fluid can further increase the application force of the sealing part upon those sealed surfaces. The bottom of the groove may have a generally arcuate profile which is concentric with the generally circular profile of the sealing part. This avoids any damage which might otherwise have been caused to the sealing part by notch effects.

The width of the groove, measured radially of the tube, may be 0.4 to 0.5 times said diameter of the sealing part, measured radially of the tube. It has been found that this latter feature is especially significant in the achievement of an excellent sealing effect.

A particularly preferred assembly in accordance with the present invention, incorporating a gasket which is formed in one-piece of a synthetic plastics material having only slight resiliency, will now be described, by way of example only, with reference to the accompanying drawing, which is a diametrical section through the tube, the gasket and the tube-holding plate shown in their assembled condition.

The drawing shows a tube-holding plate 1, a glass tube 2 mounted in an oversized bore through the plate 1 so that an annular gap 3 is formed between the tube 2 and the plate 1, and a synthetic plastics gasket 4 mounted in the gap 3, the gasket 4 sealing-off a low-pressure side 5 of the plate 1 from a fluid located on a high-pressure side 6 of the plate 1.

The gasket-4 is formed in one-piece of polytetrafluoroethylene, is rotationally symmetrical, and presents a retaining part 7 and an annular sealing part 8 which, as viewed in a radial section (e.g. the upper half of the drawing), are respectively of generally orthogonal profile and generally circular profile.

The generally orthogonal profile of the retaining part 7 is formed by a pair of legs. A first of the legs, 7a, extends transversely of the tube 2 and a second of the legs, 7b, extends symmetrically of the sealing part 8, centrally within the gap 3 and longitudinally of the tube 2. It is important to note that the second leg 7b has no contact of any kind with the plate 1 or the tube 2, thereby enabling the sealing part 8 to effect sealing engagement with both the plate 1 and the tube 2 in an optimum manner. The width of the second leg 7b, measured radially of the tube 2, is preferably 0.4 to 0.6 times the width of the gap 3, measured radially of the tube 2. The dimensions of the legs 7a and 7b may in fact be comparable.

The generally circular profile of the sealing part 8 is, of course, different when considered before and after mounting of the gasket 4. Before mounting, a diameter of the sealing part 8 (which after mounting extends radially of the tube 2) must be spaced from a facing part of the first leg 7a by a dimension 1.1 to- 1.3 times the thickness of the plate 1. Moreover, said diameter must itself have a dimension 1.1 to 1.6 times the width of the gap 3, measured radially of the tube 2. The gasket 4 further presents an annular groove 9 which opens to the fluid located on the high-pressure side 6 of the plate 1. As viewed in said above mentioned radial section, the groove 9 extends symmetrically within the sealing part 8 and parallel to the axis of the tube 2.The groove 9 has a bottom of generally arcuate profile which is concentric with said generally circular profile of the sealing part 8. Moreover, the distance between said bottom of the groove 9 and said facing part of the first leg 7a is less than the thickness of the plate 1. Preferably, the width of the groove 9, measured radially of the tube 2, is 0.4 to 0.5 times said above-mentioned diameter of the sealing part 8, measured radially of the tube 2. The provision of the groove 9 not only increases the resilience of the sealing part 8 with respect to the plate 1 and the tube 2, but also increases the effective surface area of the sealing part 8 so that the fluid located on the high-pressure side 6 of the plate 1 can press the sealing part 8 even more firmly upon both the plate 1 and the tube 2.Thus, good sealing engagement is achieved even for high pressures of said fluid, which can be either hydraulic or pneumatic.

Fitting is carried out in the following sequence of steps (a) the gasket 4 is inserted, starting from the low-pressure side 5, into the above mentioned bore through the plate 1, insertion being continued until the first leg 7a of the retaining part 7 firmly abuts the adjacent face of the plate 1; and (b) the tube 2 is then itself inserted through the gasket 4, the direction of insertion of the tube 2 being immaterial be#cause of said generally circular profile of the sealing part 8 of the gasket 4.

In the final assembly, the abutment of the first leg 7a of the retaining part 7 with one face of the plate 1 serves to retain the sealing part 8 in sealing engagement around the tube 2 as well as around a junction 10 between the oversized bore and the other face of the plate 1.

The generally circular profile of the sealing part 8 not only assists insertion of the tube 2, but subsequently avoids leakages that might otherwise have resulted from a tilted position of the tube 2, and further reduces any leakages that might have otherwise resulted from different thermal expansions of the components of the assembly.

Apart from simple fittability, the use of a synthetic plastics gasket leads to an especially good seal, and it is an advantage to be emphasized that as regards satisfactory dimensional tolerances for the parts to be sealed, no higher demands are made than usual hitherto.

The assembly of the present invention does not hinder the use of additional anti-corrosion agents, for example the arrangement of a foil of polytetrafluoroethylene on the high-pressure side of the plate facing the fluid to be sealed-off.

The synthetic plastics material from which the gasket is formed is preferably polytetrafluoroethylene but could be for example polypropylene.

Claims

1. An assembly comprising: a tube-holding plate, a tube mounted in an oversized bore through the tube-holding plate so that an annular gap is formed between the tube and the tube-holding plate, and a synthetic plastics gasket mounted in the gap; the gasket presenting a retaining part and an annular sealing part which, as viewed in a radial section, are respectively of generally orthogonal profile and generally circular profile; said generally orthogonal profile of the retaining part being formed by a first leg which extends transversely of the tube and a second leg which extends symmetrically of the sealing part, centrally within the gap and longitudinally of the tube; and said generally circular profile of the sealing part being such that a diameter thereof, considered before mounting by the gap but which after mounting by the gap extends radially of the tube, is spaced from a facing part of the first leg of the retaining part by a dimension 1.1 to 1.3 times the thickness of the tube-holding plate, with said diameter itself having a dimension 1.1 to 1.6 times the width of the gap, measured radially of the tube; the arrangement being such that the first leg of the retaining part abuts one face of the tubeholding plate to retain the sealing part in sealing engagement around the tube as well as around the junction between the bore and the other face of the tube-holding plate.

2. An assembly according to claim 1, in which the gasket further presents an annular groove which, as viewed in said radial section, extends symmetrically within the sealing part and parallel to the axis of the tube, with a bottom of said groove being spaced from said facing part of the first leg of the retaining part by a distance less than the thickness of the tube-holding plate.

3. An assembly according to claim 2, in which said bottom of the groove has a generally arcuate profile which is concentric with said generally circular profile of the sealing part.

4. An assembly according to claim 2 or claim 3, in which the width of the groove, measured radially of the tube, is 0.4 to 0.5 times said diameter of the sealing part, measured radially of the tube.

5. An assembly according to any preceding claim, in which the width of the second leg of the retaining part, measured radially of the tube, is 0.4 to 0.6 times the width of the gap, measured radially of the tube.

6. An assembly according to any preceding claim, in which the gasket is formed in one-piece of a synthetic plastics material having only slight resiliency.

7. An assembly according to claim 1 and substantially as hereinbefore described with reference to the accompanying drawing.