Improvements in or relating to filament coating

Abstract: Known methods of melting Titanium and its alloys for the purpose of sheathing a ceramic filament includes the pre-melting of the metal in a crucible, which results in contamination of the metal. The present invention obviates the crucible and instead, positions a rod of solid Titanium or an alloy thereof adjacent the filament and locally heats the end thereof. The melt continuously coats the filament which is then traversed laterally of the rod. The method is employed in an inert atmosphere and contamination is thus avoided.

Description: This invention relates to a method of making a composite material from which a composite structure can be formed. Endeavours are being made worldwide, to replace metal structures with metal/ceramic composite structures. This is particularly the case in the gas turbine aero engine industry, so that at least equally strong, but much lighter weight engines may be built. Titanium and alloys thereof are examples of strong, lightweight metals and are used in the construction of casings and compressor aerofoils ie blades and stators. Ways and means have been examined, to further reduce the weight and at the same time, at least maintain the strength of articles normally made from e.g. metals such as Titanium or its alloys. Ceramics such as Silicon Carbide have been found to give the required properties when sheathed in Titanium. Titanium and its alloys, along with other lightweight metals such as magnesium have a drawback however, in that they are highly reactive on contacting other materials when at their melting temperature. This is particularly so if the contact is over a time period exceeding more than several seconds. When Titanium has been melted in a pouring pot, the reaction of the Titanium with the material of the pot has been observed, even where the pot material is ceramic, and contamination has resulted. Efforts have been made to reduce the contamination of the Titanium to be poured, for example, by lining the pot with Titanium and maintaining the lining in a solid state by local cooling. The Titanium melt thus only contacts a material with which it shares a common identity. The present invention however, seek to provide an improved method of applying Titanium or other reactive metal to a ceramic filament. According to the present invention a method of applying a sheath of reactive metal to a ceramic filament comprises the steps of movably supporting a rod of said reactive metal above and with one end adjacent the ceramic filament, arranging heating means around said adjacent rod end in spaced relationship therewith, melting said rod end and on said melted end extending downwards and enveloping the adjacent portion of the filament, simultaneously causing the filament to move through the melt in a direction laterally of the rod and moving the rod towards the filament at a rate corresponding to the rate of transfer to the filament, all of said steps being effected in an inert atmosphere. The invention will now be described by way of example and with reference to the drawing which is a diagrammatic illustration of apparatus with which the method is effected. Referring to the drawing. A container 10 has an inert atmosphere within it. The atmosphere may be inert by way of being a vacuum or preferably, it may consist of one of the noble gases e.g. argon. A pair of drums 12 and 14 are positioned one at each end of the container. The drum 12 is a magazine of Silicon Carbide in filament form and is rotatable. The drum 14 has an end of the filament, identified by the numeral 16 fastened to it and is rotated by a co-axially mounted motor 18. A rack 20 is fastened to the roof of the container 10 and projects downwardly, towards the central portion of the filament 16. The rack 20 carries a saddle 22 in both sliding and driving manner i.e. the track is trapped between a 'U ' shaped strap 24 and a sprocket wheel 26 which in turn is supported for rotation by a motor 27, between the legs of the strap 24. The other end of the legs of the strap 24 are adapted so as to enable clamping of a rod of Titanium 28 therebetween, in an attitude which is parallel with the rack 20. A heating coil 30 surrounds the end of the Titanium rod 28 which initially, is positioned close to and above the filament 16. Operation of the apparatus described in connection with the present invention is effected as follows. The speeds at which the filament 16 and Titanium rod 28 must be moved in order that a constant volume of melted Titanium is deposited on the filament, are first assessed. An appropriate computer programme is then devised and utilised to operate a computer 32. The computer 32 is connected to a control box 34 which in turn, is connected to the motor 27 which drives the sprocket wheel 26, to the motor 18 which drives the drum 14 and to the heating coil 30. In operation, the computer 32 instructs the control box 34 to activate the heating coil 30. The control box then senses the heat achieved by the coil 30 and on sensing that heat which achieves melting of the Titanium, the control box informs the computer32 which then instructs the control box 34 to activate the motors 27 and 18. During the operation, the control box 34 constantly monitors the temperature of the heating coil 32 and the speed of movement of the Titanium 28 and the filament 16. If any of the respective values is incorrect, the control box sensors this and informs the computer 32 by way of appropriately generated signals, whereupon the computer 32 instructs the appropriate steps that the control box should take, to correct that value. The control box 34 may be provided with a timing device which, when a pre-selected time has expired after initiation of the process, switches off the power to the device. The time will be related to the maximum length of filament 16 which may be unwound, without emptying the drum 12. The Titanium may be stored in wire form on a further drum (not shown) thus obviating the rack 20. This may only be the case where the diameter of the wire is sufficiently small as to allow winding and yet sufficiently large as to provide sufficient melt to sheath the filament. If those criteria are met, then such a drum may also be motor driven under the control of the control box 34. Titanium alloys are also suitable for sheathing ceramic filaments as described hereinbefore.

Claims: A method of applying a reactive metal or reactive metal alloy sheath to a ceramic filament characterised by the steps of movably supporting a rod of Titanium or Titanium alloy (28) above, and with one end adjacent the ceramic filament (16), surrounding said one end with heating means, melting said one end and on said melted end extending downwards and enveloping the adjacent portion of the filament (16), simultaneously causing the filament (16) to move through the melt in a direction laterally of the rod (28) and moving the rod towards the filament (16) at a rate corresponding to the rate of transfer of metal to the filament (16), all of said steps being effected in an inert atmosphere. The method of applying a reactive metal or reactive metal alloy sheath to a ceramic filament as claimed in claim 1 characterised by the step of supporting the reactive metal or reactive metal alloy (28) in a saddle (22) which engages a rack (20)and is driven therealong via a sprocket wheel (26). The method of applying a reactive metal or reactive metal alloy sheath to a ceramic filament as claimed in claim 1 characterised by the step of producing the reactive metal or reactive metal alloy (28) in wire form and supporting said wire on a rotatable drum. A method of applying a reactive metal or reactive metal alloy sheath to a ceramic filament as claimed in any previous claim characterised by the step of effecting the method in a vacuum. A method of applying a reactive metal or reactive metal alloy sheath to a ceramic filament as claimed in any of claims 1 to 3 characterised by the step of effecting the method in an atmosphere comprising an inert gas. The method of applying a reactive metal or reactive metal alloy sheath to a ceramic filament as claimed in claim 5 characterised by the step of effecting the method in an atmosphere of Argon gas. A method of applying a reactive metal or reactive metal alloy sheath to a ceramic filament as claimed in any previous claim and characterised by the step of controlling the operation by an appropriately programmed computer.

Inventors: DOORBAR PHILLIP JOHN, DOORBAR, PHILLIP JOHN
Applicants: ROLLS ROYCE PLC, ROLLS-ROYCE PLC
Application year: 1990
Main classification: C23C26
IPC codes: C04B41, C23C26, C22C47