GB2456810A

GB2456810A - Production of seal, for aircraft, by coating fabric with polysulphide

Info

Publication number: GB2456810A
Application number: GB0801328A
Authority: GB
Inventors: John Rogers
Original assignee: James Walker and Co Ltd
Current assignee: James Walker and Co Ltd
Priority date: 2008-01-24
Filing date: 2008-01-24
Publication date: 2009-07-29
Also published as: GB0801328D0

Abstract

Uncured polysulphide 24 is applied to moving fabric 10. The fabric then passes past a doctor blade 18 that spreads the polysulphide into a coating. The coated fabric moves through a heated curing station 26. The at least partially cured polysulphide has a non-tacky surface. The spreading knife 18 is preferably used with a roller 20 coating remover 40 and solvent applier 42. The fabric is preferably differentially tensioned 14, and has two solvent containing coatings applied to it. The fabric may comprise woven glass, cotton, polyamide, carbon or metal cloth. The gaskets can be used to seal aeroplane fuselages or fuel tanks.

Description

1 2456810 Sealing material and the manufacture thereof This invention relates to sealing material comprising a fabric coated with polysulphide elastomer, for example as disclosed in EP1548083.

Sealing material of this type, in which the fabric may be a woven glass fibre cloth, is cut into gaskets for use for example in forming joints between parts of aircraft (eg. fuselage skin panels) or subassemblies thereof (eg. aircraft fuel tank panels).

Difficulty has been experienced in the past in manufacturing the sheets of sealing material with a consistent quality. Hitherto the sheets of sealing material have been made by hand, by manually spreading the polysulphide material onto a relatively small sheet of cloth, curing it and then grinding the polysulphide coating to the required thickness. The present invention is directed to providing at least in its preferred embodiments a more effective and reliable manufacturing method, and a more consistent product.

In one aspect the invention provides a method of manufacturing sealing material comprising the steps of applying uncured polysulphide material to a moving sheet of fabric, passing the fabric relative to a knife blade so as to spread the polysulphide material into a coating on the surface of the fabric, and moving the coated fabric through a heated curing station so that after passing through the curing station the coating of polysulphide material is at least partially cured and has a non-tacky surface.

Conveniently, the fabric is stored as a roll from which it is unwound and passed continuously through the above steps.

The method may include diluting the polysuiphide material with a solvent to aid the spreading thereof.

The solvent should be one which does not materially adversely affect the curing of the polysulphide material, nor its physical properties after curing. It also should be volatile, so that it can be evaporated-off during the curing step. Toluene, is preferred, but ethyl acetate and xylene may also be suitable.

Preferably the method comprises winding the coated fabric into a roll after it has passed through the curing station.

It further may preferably include interleaving at least one removable liner sheet with the coated fabric when winding it into a roll.

A central portion of the sheet may be differentially tensioned relative to the longitudinal edges thereof.

A curing environment may be provided at the curing station at a temperature in the range 100°C to 130°C, and preferably at approximately 1100 to 120°C.

Cloths (woven or unwoven) of glass fibre or other materials may be used, for example cotton, Kevlar� or other aramid, carbon fibre, polyamide, stainless steel, aluminium or other metal.

The thickness of the coated material may be from 0.15mm up to 4mm.

Preferably it is between 0.25mm and 0.5mm.

A preferred form of the method comprises defining a spreading gap between the knife blade and a backing roller, and removing adherent polysulphide material from the roller during the spreading step.

A second coating of polysulphide material may be applied to the fabric sheet by the method, either to the previously coated side or to the other side.

The or at least one said coated surface may be profiled or embossed.

Sealing gaskets may conveniently be cut from the coated sheet in relatively large numbers. Alternatively the sheets permit large and complicated gasket shapes to be cut in one piece.

The invention also provides a method of sealing a joint between structural parts, for example parts of an aircraft or a subassembly thereof comprising placing between those parts a sealing gasket manufactured as above.

A further aspect of the invention provides an apparatus for manufacturing sealing material comprising means for feeding fabric sheet material sequentially past a sealant applying station configured for applying polysulphide sealant to a surface of the fabric sheet, past a sealant spreading station configured for spreading the sealant into a coating on the surface, the spreading station comprising a gap defined between a knife blade and a roller through which gap the fabric sheet passes and means for removing sealant from the roller during spreading of the sealant, and past a curing station configured for heating the coated fabric sheet so that on exit from the curing station the coating of polysulphide is at least partially cured.

The means for removing sealant may comprise a scraper blade.

There may be means (for example a bow or "banana" roller for differentially tensioning a centre portion of the fabric sheet relative to the edges thereof.

The apparatus may comprise means for winding the coated fabric sheet as a roll.

There further may be means for interleaving at least one removable liner sheet with the coated fabric sheet during winding thereof.

The winding means may be configured to wind the coated fabric sheet into a roll at a location upstream of the polysuiphide-applying station, or otherwise convenient for re-passing the coated sheet through the apparatus.

The method can have the advantage of providing coated sheet material which is usable without grinding flat or other treatment. Thus in another aspect the invention provides gasket material instead to be cut into gaskets without further treatment, comprising a fabric sheet having thereon a spread layer of polysulphide material of predetermined thickness, the surface of the polysulphide layer being in its as-spread configuration.

The invention provides a gasket made from such gasket material, and a joint between structural parts (for example structural parts of an aircraft or a subassembly thereof) comprising a gasket as above.

The invention will be described merely by way of example with reference to the accompanying drawings, wherein: Figure 1 shows a side elevation, partially in section of one embodiment of apparatus according to the invention; and Figure 2 is a view on arrow 2 of figure 1.

Referring to figure 1, which at its left-hand end in a section on line 1-1 of figure 2, a sheet of woven glass fibre cloth 10 is unwound from a roIl 12 and passes via a tensioning roller 14 to a spreading gap 16 defined between a knife or doctor blade 18 and a roller 20. Just upstream of the doctor blade 18 is areciprocatingnozzle 22 which moves back and forth in the cross-machine direction to supply uncured polysulphide elastomer 24 across the width of the sheet 10 and builds a reservoir' of uncured polysulphide upstream of the knife 18 to provide a continuous supply to the spreading gap 16..

The sheet 10 passes through the spreading gap 16, the knife blade 18 acting as a dam or weir to permit only a defined thickness of polysuiphide material to adhere as a coating 19 to the sheet 10 and pass with it to a curing station 26.

This is an enclosed or semi-enclosed heated chamber maintained in this example at about 110°C so that the coated sheet emerges from the downstream end of the chamber 26 at least partially cured and with a skinned non-tacky surface.

The coated sheet then passes around a traction roller 28 and back beneath the machine to a rewind roll 30 on to which it is wound under substantially zero tension. The traction roller 28 is driven via a clutch which slips at a predetermined torque to prevent excessive tension being applied to the sheet 10.

A liner sheet 32 is interleaved under tension with the coated sheet via a braked roller 34 to prevent any tendency for adjacent turns of the coated sheet to adhere to each other. If desired, two liner sheets can be interleaved so that both sides of the coated sheet 10 are protected when it is subsequently unrolled. The rewind roll 30 is located at the upstream and of the machine, together with liner feed 32 and roller 34. This enables the once-coated fabric sheet to be fed again through the apparatus to coat the reverse side of the sheet 10, or to apply a further coating to the previously-coated surface.

After manufacture, the rolled-up coated sheet is dispatched for cutting into discrete gaskets. Curing of the polysulphide layer continues during storage and transport and normally is completely cured or substantially so within a few hours at room temperature.

In more detail, the tensioning roIl 14 provides tension according to conventional practice eg. by being mounted on a spring- loaded and damped pivoted arm, It also is braked to assist in promoting slow and even movement of the sheet 10 through the machine.

It may be found advantageous to replace the cylindrical rollers 14 with a bow or banana roller. This is a roller which is maintained in a slightly curved or bowed configuration as it rotates, for example by setting its bearings at a slight angle to the cross-machine direction so as to apply a bending moment to the roller. The banana roller tensions the centre of the sheet differentially relative to the edges.

This will reduce any tendency for the edges of the sheet 10 to cockle or curl-over, and result in significantly better behaviour of the sheet as it passes through the apparatus.

The polysulphide material 24 is prepared as needed from a two-part formulation, the two constituents being kept in separate tanks and mixed only immediately before dispensing. A suitable mixer/dispenser is supplied by Metermix Systems Limited. By way of example, a specific polysulphide material which was found satisfactory in a pilot plant was DeSoto grade 1776 or 1770, with a 30 minute usable upot life" after mixing. The 1770 grade was sufficiently fluid to be used as-mixed; the 1776 grade required the addition of some toluene to reduce its viscosity, in the amount of approximately lOg per bOg of mixed polysulphide material.

Although figures 1 and 2 show the polysulphide as being applied through a reciprocating nozzle, it may be found adequate for short runs to apply it by a hand-scoop given the relatively slow progress of the sheet 10 through the machine. Thorough mixing however is important.

Cheek blades or wings 36 are provided on the ends of the roller at each side of the fabric to remove excess polysuiphide which may escape from the edges of the sheet. The blades 36 are adjustable in the cross-machine direction so that they can be positioned close to the edge of the sheet 10.

Alternatively, fixed cheek blades may be provided at the ends of the knife blade 18 similarly to control the width of the spread polysuiphide. Then there may be a narrow uncoated margin down each edge of the sheet. Whatever the arrangement, it is important to keep the cheek blades 36 clean of any cured or curing elastomer, otherwise pieces may detach and become clogged under the knife blade, resulting in patches of uneven or missing coating on the sheet, or even tearing of the sheet 10.

The position of the knife blade 18 is adjustable relative to the roller 20 so as accurately to define the spreading gap 16. The blade is provided at each end with a 40:1 ratio anti-backlash screw actuator to adjust the blade to within an accuracy of 0.025mm (0.001"). The actuators may be controlled by a process controller which receives feedback from a thickness measuring sensor. The controller also may control the speed of the sheet 10. However, we have found it adequate to set the spreading gap using feeler gauges. Provided that the machine is adequately engineered, the tolerance can be maintained. Thus, in the pilot plant, the roller 20 is of steel, hard chromium plated and mounted in precision taper roller bearings.

Although the method of the invention avoids applying substantial pressure to the elastomer as it is coated onto the sheet, nevertheless there will be some seepage of elastomer through the glass-fibre weave onto the surface of the roller 20.

Therefore there is provided a scraper blade 40 which removes any elastomer which has adhered to the roller surface. The operation of the scraper blade may be assisted if the surface of the roller 20 is kept dampened by a suitable solvent such as toluene eg. via a pad 42 fed with solvent from a reservoir.

The curing station 26 comprises a 1 Om long oven having a hot plate 44 which has a non-stick eg. Teflon� surface and which is the pilot plant was maintained at 110-120°C.

As used in the pilot plant, the sheet 10 was Fothergill Y0336, 0.08mm thick with a plain weave, although other thicknesses (eg. 0.25mm) and weaves may be used.

It was coated with a 0.25mm layer of DeSoto 1776 and was passed through the oven at 4m/min. On exit from the oven the sheet had a non-tacky touch-dry surface. Curing of the polysuiphide by heating it was contrary to the manufacturers recommendations, but it showed no evidence of blistering or other degradation.

Any toluene or other volatile organic compounds present in the uncured elastomer will be driven-off during the curing step, and if above allowable amounts, must be recovered.

Thus at least in the described embodiment the invention can provide a coated sealing material which can be used in the condition in which it leaves the apparatus with its polysulphide layer in its as- spread condition. Although as described the layer is of even thickness, in principle it is possible to profile the layer in the cross-machine direction by appropriately shaping the knife blade 18.

The different parts of the profiled section then each have their own predetermined thickness. Alternatively the coated sheet may be passed through a pair of rollers, one or both of which has a patterned surface, whilst the polysulphide coating is still only partially cured but with a touch-dry surface. Thereby an embossed pattern may be imparted to one or both surfaces. Conveniently this pair of rollers may be located immediately upstream or downstream of the traction roller 28.

Each feature disclosed in this specification (which term includes the claims) and/or shown in the drawings may be incorporated in the invention independently of other disclosed and/or illustrated features. ln particular but without limitation the features of any of the claims dependent from a particular independent claim may be introduced into that independent claim in any combination.

Statements in this specification of the "objects of the invention" relate to preferred embodiments of the invention, but not necessarily to all embodiments of the invention falling within the claims.

Claims

Claims 1. A method of manufacturing sealing material comprising the steps of applying uncured polysulphide material to a moving sheet of fabric, passing the fabric relative to a knife blade so as to spread the polysuiphide material into a coating on the surface of the fabric, and moving the coated fabric through a heated curing station so that after passing through the curing station the coating of polysulphide material is at least partially cured and has a non-tacky surface.
2. A method according to claim I comprising diluting the polysulphide material with a solvent to aid the spreading thereof.
3. A method according to claim 1 or 2 comprising winding the coated fabric into a roll after it has passed through the curing station.
4. A method according to claim 3 comprising interleaving at least one removable liner sheet with the coated fabric when winding it into a roll.
5. A method according to any preceding claim comprising differentially-tensioning a central portion of the sheet relative to the longitudinal edges thereof.
6. A method according to any preceding claim comprising providing a curing environment at the curing station at a temperature in the range 1000 to 130°C, and preferably at approximately 1100 to 120°C.
7. A method according to any preceding claim wherein the thickness of the material is between 0.15mm and 4mm.
8. A method according to any preceding claim comprising defining a spreading gap between the knife blade and a backing roller, and removing adherent polysulphide material from the roller during the spreading step.
9. A method according to any preceding claim comprising applying a second coating of polysuiphide material to the sheet of fabric by the said method, either to the previously-coated side thereof or to the other side.
10. A method according to any preceding claim comprising profiling or embossing the or at least one said coating.
11. A method of manufacturing a sealing gasket comprising cutting it from a sheet of sealing material manufactured according to any preceding claim.
12. A method of sealing a joint between parts of an aircraft or a subassembly thereof comprising placing between those parts a sealing gasket manufactured according to claim 11.
13. Apparatus for manufacturing sealing material comprising means for feeding fabric sheet material sequentially past a sealant-applying station configured for applying polysuiphide sealant to a surface of the fabric sheet, past a sealant spreading station configured to spreading the sealant into a coating on the surface, the spreading station comprising a gap defined between a knife blade and a roller through which gap the fabric sheet passes and means for removing sealant from the roller during spreading of the sealant, and past a curing station configured for heating the coated fabric sheet so that on exit from the curing station the coating of polysulphide is at least partially cured.
14. Apparatus according to claim 13, wherein the means for removing sealant comprises a scraper blade.
15. Apparatus according to claim 13 or 14 comprising means for differentially-tensioning a centre portion of the fabric sheet relative to the edges thereof.

II
16. Apparatus according to claim 15, wherein the differential tensioning means is a banana roller.
17. Apparatus according to any of claims 12 to 15 comprising means for winding the coated fabric sheet as a roll.
18. Apparatus according to claim 17 comprising means for interleaving at least one removable liner sheet with the coated fabric sheet during winding thereof.
19. Apparatus according to claim 17 or 18, wherein the winding means is configured to wind the coated fabric sheet into a roll at a location upstream of the polysuiphide-applying station or otherwise convenient for re-passing the coated sheet through the apparatus.
20. Gasket material intended to be cut into gaskets without further treatment, comprising a fabric sheet having thereon a spread layer of polysuiphide material of predetermined thickness, the surface of the polysuiphide layer being in its as-spread configuration.
21. A gasket made from material according to claim 20.
22. A joint between structural parts, for example parts of an aircraft or a subassembly thereof comprising a gasket according to claim 21.
23. A method, apparatus, fabric sheet material, a gasket or an aircraft joint substantially as herein described with reference to the accompanying drawings.