Method of manufacturing a lining of polytetraflouroethylene (PTFE) for an expansion joint or similar flexible couplings, a PTFE lining and a tool for use in connection therewith

Abstract: The invention concerns a method of manufacturing an internal lining of polytetraflouroethylene (PTFE) for an elastomer expansion joint or similar flexible couplings, whereby one or more unsintered tapes of PTFE or a PTFE-based material is/are wound around a rotary-symmetrical, non-cylindrical, positive forming tool whereby the tapes form a lining comprising a number of PTFE layers in a form which essentially corresponds to the desired internal shape of the elastomer expansion joint or a similar flexible coupling member, whereafter the lining is sintered and subsequently removed from the form by collapsing the self-locking shell of the forming tool by removing at least one retention member of the forming tool. The invention also relates to a forming tool for use in connection with the method. Hereby, it is possible to manufacture the lining in any kind of rotary-symmetrical shape. The form removal after the sintering process takes place by taking the forming tool apart. According to the invention, it is not necessary to carry out a mechanical deformation of the PTFE material which means that by using a method according to the invention, a more stable lining in any rotary-symmetric shape and with significantly improved chemical barrier properties may be obtained.

Description: The present invention relates to a method of manufacturing an internal lining of polytetraflouroethylene (PTFE) for an elastomer expansion joint or similar flexible couplings, a PTFE lining manufactured hereby and a forming tool for use in connection with manufacturing. Flexible couplings, such as elastomer expansion joints, are used in a pipe line system for absorption of movements due to thermal expansions or mechanical loads on the pipe line system. In pipe line systems used in the chemical industry or power plants, the expansion joints are exposed to extremely aggressive mediums such as gas or fluids and are thus very exposed to corrosion. The form of and the movements in the flexible expansion joints combined with the pressure ranging from very low pressures to nominal pressures in excess of 25 bar make it quite difficult to treat the surface of the expansion joint with a durable protection. From EP-A-0 524 893, a method of manufacturing a cylindrical lining of polytetraflouroethylene (PTFE) or teflon is known. This material is advantageous since it is chemically resistant. According to this method, a number of strips of PTFE are manufactured and wrapped around a rod or cylinder in successive layers. After that, the tubular piece of PTFE is sintered and subsequently pulled off the cylindrical form around which it is manufactured. However, the internal geometry of a rubber expansion joint or a similar coupling is often non-cylindrical in shape. This means that a lining manufactured according to EP-A-0 524 893 must subsequently be mechanically deformed into a form which corresponds to the geometry of the internal opening in the expansion joint. The disadvantages of this known manufacturing method are that the manufactured lining must be cylindrical which requires subsequent treatment processes in order to provide the lining with the appropriate form. This mechanical deformation of the PTFE material weakens the strength of the lining which may lead to a weakening of the lining in the expansion joint since there is a risk that the lining does not possess the necessary chemical barrier properties. In addition, this method of manufacturing provides a relatively inaccurate lining whereby the risk of the expansion joint not being sufficiently protected on the inside is increased. A method of forming or coating articles by wrapping a thermoplastic material around them is known from British patent No. 1 371 337. The material, which may e.g. be PTFE, is wound around a core built by curved pieces placed around a central block. This form may be collapsed by removing the central block. However, this disclosure does not discuss the vital issue of how the forming blocks must be accurately fixed to the central block prior to the forming of a lining. This method and form assembly also result in a rather inaccurate lining which increases the risk of the expansion joint not being sufficiently protected internally. This is because the form must be manufactured with sufficient tolerances for the central block to be pulled out in an axial direction. The problem increases proportionately with the size of the form due to the enormous amount of friction between the abutment surfaces of the blocks towards the central portion. During this manufacturing process, the heat treatment of the lining can only take place from "the outside" since the massive core, which the forming tool represents in this respect, prevents good heat transfer to the inside of the lining. In this manner, there is a risk of non-uniform heat treatment which causes the inaccurate tolerances of the finished product. On this background, it is the object of the present invention to provide a method of manufacturing of a lining, which overcomes the disadvantages known from the prior art. This object is achieved by a method according to claim 1, a lining according to claim 10 and a forming tool according to claim 13. By a method according to the invention, it is possible to obtain a pre-manufactured, moulded and sintered lining in a predetermined design which fits a given connection piece, e.g. an elastomer expansion joint or a similar flexible coupling. Thus, the invention offers a manufacturing method of a lining for internal protection of an expansion joint, whereby the lining may be manufactured in any kind of rotary-symmetrical shape. The form removal after sintering takes place by taking the forming tool apart by collapsing it. Since the forming tool is provided with a self-locking shell, i.e. a hollow structure, a good heat conductivity is ensured to the inside of the lining during sintering whilst at the same time ensuring an accurate form which is both heat-resistant and by which a lining with precise dimensions may be obtained. By a lining according to the invention, it is not necessary to carry out a mechanical deformation of the PTFE material which means that a manufacturing method according to the invention provides a more tough and stable lining with significantly improved chemical barrier properties. In a preferred embodiment of the invention, at least on layer of glass fibre fabric is wrapped around the outer layer. In this manner, a fixation of the unsintered PTFE material during the sintering process is obtained. In a particularly preferred embodiment of the invention, at least the outer layer is wound with an elongated PTFE tape. In this way, the glass fibre fabric may be avoided since at least the outer layer is elongated and does thereby provide a tightening around the forming tool whereby the PTFE layers are fixed during the subsequent sintering process. However, the glass fibre fabric may be advantageous anyway, potentially in combination with the elongated PTFE tape, in order to ensure uniform density in the lining, especially in relation to more complex geometrical shapes. The manufactured lining is sintered, preferably at a temperature between 325 and 425°C, for a period of time ranging from 30 seconds to over 1 hour, depending on the nature and the heat-conducting properties of the form. Subsequent to sintering and prior to the form removal, the lining may be provided with an adhesive and in a preferred embodiment of the invention, the outside of the lining may be provided with non-vulcanised rubber with contours corresponding to the desired final form of the elastomer expansion joint for a subsequent finishing moulding of the expansion joint. The PTFE tape or tapes, which is/are wound around the form, is/are an unsintered tape which may be provided with additives such as PFA, TFM and/or variants hereof and having a width ranging between 5 and 300 mm depending on the size of the lining to be manufactured. Typically, small forming parts ranging from 100 to 500 mm will be wound with a tape with a width ranging between 15 to 30 mm. The unsintered tape or tapes is/are preferably provided with a thickness of 0.05 to 0.5 mm. The tapes are wound in a helical form around the forming tool. Another advantage of this invention is that the manufacturing method is not sensitive to large variations in the accuracy of the laying pattern. The lining may consist of two windings to the number of windings needed, preferably between 10 and 20 windings. The layers may advantageously be wound at an angle of 1° to 90° degrees in relation to each other and have a fairly uniform thickness. Hereby, a tough and stable lining with accurate, predetermined dimensions is ensured. The forming tool used by a method according to the invention and which is suitable for manufacturing a lining according to the invention, comprises a number of forming elements assembled into an annular configuration and retained by assembly means, said forming elements each having an outer forming surface and two abutment surfaces for fixation, and the forming surfaces of the individual forming elements collectively forming a rotational-symmetrical forming surface which corresponds in shape and size to the desired internal geometry of an expansion joint making up a positive form for moulding around it, and the forming elements each being provided with an outer forming surface and two abutment surfaces for fixation, said forming elements assembling into a joint self-locking shell when assembled. The abutment surfaces on the majority of the forming elements are provided in a radial plane, but at least one forming element is provided with two abutment surfaces, which are different from a radial plane, and this at least one locking forming element is provided with a wedge-shaped cross-section which is oriented in another radial direction than the other forming elements, i.e. pointing outwards. Hereby, a self-locking mechanism of the forming elements is achieved and a demountable form with an accurate moulding surface is ensured. Moreover, a collapsible tool is achieved which can be taken apart and removed from the fully sintered lining irrespective of the kind of rotary-symmetric shape of the form, where it would otherwise be impossible to drag the lining off the form for the deforming of the lining. The forming tool is preferably made of a heat-resistant material which possesses good heat-conducting properties, such as aluminium. Hereby, the sintering period for the PTFE lining may be significantly reduced. In the following, the invention has been described in detail with reference to the accompanying drawings, in which fig. 1 shows a side view of a lining manufactured by a method according to the invention, fig. 2 shows a side view of an elastomer expansion joint with a lining manufactured by a method according to the invention, fig. 3 shows a cross-section of a forming tool according to the invention, and fig. 4 shows the manufacture of a lining according to the invention. Figure 1 shows a side view of a forming tool 10 for manufacturing a curved, rotary-symmetric lining 1 with the upper part showing a section of the forming tool 10. As can be seen in the figure, the forming tool 10 comprises a number of forming elements 11 ,11', 11" which are assembled by assembly means 12 including end plates between which the forming elements 11, 11', 11" may be restrained. The forming elements 11 create a forming surface 14 around which a PTFE lining 1 is formed. The lining 1 is formed by winding one or more layers of unsintered PTFE tape 3 (see fig. 4) depending on the size of the form around the desired dimensions of the lining 1. The tapes 3 are wound in a helical configuration around the form. Typically, the lining 1 will include two to twenty windings corresponding to the most common forms. The lining 1 will preferably have at thickness of 0.05 to 0.5 mm. The PTFE tapes 3 have a width of 5 to 300 mm, preferably 15 to 30 mm. After the tapes 3 are wound around the lining 1, the lining 1, whilst still on the form, is sintered at a temperature between 325° to 425° for a period of time ranging from 30 seconds to more than one hour depending on the dimensions of the lining and the heat-conducting properties of the form. In order to retain the unsintered PTFE lining during the sintering process, it may be provided with an outer layer of glass fibre fabric. Alternatively, at least the outer PTFE layer may be provided with an elongated PTFE tape. Hereby, the elongated tape will retract around the form and thereby the other layers of PTFE tape 3. After sintering, non-vulcanised rubber 2 is applied around the lining 1, e.g. while the lining 1 still remains on the forming tool 10, as shown in fig. 2. Hereafter, the form is removed from the lining 1 by collapsing the forming tool. The elastomer expansion joint, i.e. the lining with the applied rubber may then be placed in a rubber moulding form on an expanding silicone core or the like, wherein the layer of rubber 2 is vulcanised. Finally, the elastomer expansion joint may subsequently be processed at the end surfaces for the formation of special end geometries. The forming elements 11 make up a hollow shell. The shell provides the forming surface and is hollow since the forming elements 11 make up a tubular form. The forming elements 11 are restrained at each end by a retention member, e.g. an end plate 12. Each forming element 11 is provided with two radially oriented abutment surfaces 13. In order to achieve the self-locking effect, one of the forming elements 11" is provided with a wedge-like shaped cross-section pointing outwards so that this locking forming element 11" may be mounted and dismounted on the annular shell from the inside and wedged into place between two neighbouring forming elements 11' which are shaped with an oppositely disposed radial abutment surface 13 and an adjacent, angled abutment surface 13", said adjacent abutment surface being adjacent and angled similarly to the corresponding abutment surface of the locking element 11", see fig. 3. Hereby, the forming elements 11 may be pushed into place in an annular configuration and accurately locked in this position forming a forming surface 14. The form 10 may be dismounted inside the finished lining 1. The forming elements 11 may be released from the restrained position by removing the retention member, i.e. the end plates of the assembly means 12, whereby the forming elements 11 are loose and no longer retained in their annular positions. Consequently, the form is allowed to collapse inside the lining and the form elements may be removed from the inside of the lining. By the invention, it is realised that other variations and equivalents than those described are possible without departing from the scope of the invention as set forth by the accompanying claims.

Claims: Method of manufacturing an internal lining of polytetraflouroethylene (PTFE) for an elastomer expansion joint or similar flexible coupling members, whereby one or more unsintered tapes of PTFE or a PTFE-based material is/are wound around a rotary-symmetrical, non-cylindrical, positive forming tool whereby the tapes form a lining comprising a number of PTFE layers in a shape which essentially corresponds to the desired internal shape of the coupling member, whereafter the lining is sintered and subsequently removed from the form by collapsing the self-locking shell of the forming tool by removing at least one retention member of the forming tool. Method according to claim 1, whereby the outer layer is wrapped with at least one layer of glass fibre fabric. Method according to claim 1 or 2, whereby at least the outer layer is wound with an elongated PTFE tape. Method according to claims 1 to 3, whereby the lining is sintered at a temperature between 325 and 425° C for a period of time ranging from 30 seconds to over one hour. Method according to any of the preceding claims, whereby the lining subsequent to the sintering process and prior to the form removal may be provided with an adhesive and whereby the lining is supplied with a non-vulcanised layer of rubber around the lining with a contour corresponding to the desired shape of the elastomer expansion joint for moulding thereof. Method according to any of the preceding claims, whereby the PTFE tape or tapes is/are provided with a width ranging between 5 to 300 mm, preferably between 15 to 30 mm. Method according to any of the preceding claims, whereby the PTFE tape or tapes is/are provided a thickness in the range of 0.05 to 0.5 mm. Method according to any of the preceding claims, whereby the tapes are wound in a helical form around the forming tool. Method according to any of the preceding claims, whereby the lining comprises at least two windings, preferably between 10 and 20 windings. PTFE lining for an elastomer expansion joint or a similar flexible coupling manufactured according to a manufacturing method according any of the preceding claims, whereby the lining is provided with two or more layers of PTFE tape provided in a helical configuration and with a rotary-symmetric, non-cylindrical shape. Lining according to claim 10, wherein the PTFE tape or tapes is/are provided with a width ranging between 5 to 300 mm, preferably between 15 to 30 mm. Lining according to claim 11, wherein the PTFE tape or tapes is/are provided with a thickness ranging between 0.05 to 0.5 mm. Forming tool for use in connection with a manufacturing method according to any of claims 1 to 9 comprising a number of forming elements mutually arranged in an annular configuration building a rotational-symmetric forming surface which corresponds in shape and size to a desired internal geometry of a expansion joint and thus constitutes a positive form for moulding around it, said forming elements being restrained by assembly means, characterised in that the forming element each is provided with an outer forming surface and two abutment surfaces for fixation, said forming elements being assembled for forming a self-locking, hollow shell. Forming tool according to claim 13, wherein the abutment surfaces on a majority of forming elements are disposed in a radial plane. Forming tool according to claim 14, wherein at least one forming element is provided with two abutment surfaces different from a radial plane and wherein this at least one locking form element is provided with a wedge-shaped cross-section oppositely directed from the majority of forming elements. Forming tool according to claims 13 to 15, wherein the forming tool is made of a heat resistant material with high heat-conducting properties, such as aluminium.

Inventors: JACOBSEN FINN ERIK, JACOBSEN, FINN ERIK
Applicants: KE BURGMANN AS, KE-BURGMANN A/S
Application year: 2001
Main classification: B29C67
IPC codes: B29C67, B29C53, B29C43