WO1997043080A1

WO1997043080A1 - Cutting device

Info

Publication number: WO1997043080A1
Application number: PCT/GB1997/001253
Authority: WO
Inventors: Stephen Turner; Paul Anthony Gunter
Original assignee: The Secretary Of State For Defence In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland
Priority date: 1996-05-09
Filing date: 1997-05-08
Publication date: 1997-11-20
Also published as: GB9609709D0; GB2312864A

Abstract

A device for cutting through resistant materials such as steel plates of upto around 5 mm thickness comprises a container for a thermite charge, the container having a linear slot in the form generally of the cut which it is desired to make, a closure for the slot which is rupturable by the action of the thermite burning and a means of igniting the thermite charge such as an electrical igniter/primer combination. The rupturable closure may be aluminium foil or a combustible material such as cardboard. By igniting the thermite charge at one end of the slot the charge burns progressively along the container and drives out a stream of hot particles through the aperture to progressively cut the resistant material along the desired line. A method of cutting may use the device or the like or, less preferably, a point source of thermite reaction products may be moved instead so as to direct and concentrate the hot products along a line across the surface which is to be cut.

Description

Cutting Device

The present invention relates to a device which utilises the burning of a thermite composition to cut through materials, particularly relatively hard and resistant materials such as metals.

The reaction of thermites to generate heat is well known. As a class of materials thermites generally comprise a mixture of a major proportion (typically around 70%) of powdered ferric oxide and a minor proportion (around 30%) of powdered or fine granular aluminium. When heated to a sufficient extent reaction between the components proceeds whereby aluminium oxide and metallic iron are formed. This reaction is highly exothermic and is capable of generating temperatures of upto 2200°C at which temperature the products are molten and can act as a heat reservoir. This gives rise to the use of thermites as a component in igniter compositions for magnesium bombs. In these applications thermites typically contain other components such as an oxidiser (usually sodium or barium nitrate).

A more widely known application of thermites is in welding, as for example the welding of lengths of railway track together (butt welding) to form continuous welded rail where the liquid iron product is retained in a mould surrounding the joint which is to be made, until it has solidified.

Devices have existed previously which have sought to use the heat generating capacity of thermites to cut through other materials. For example incendiary grenades have conventionally heretofore been constructed with a charge of thermite in a thin- walled aluminium alloy casing. On burning ofthe thermite the aluminium melts and the burning thermite will rest upon and progressively melt through the underlying surface which is to be cut. Although such devices are quite effective at penetrating mild steel sheets of upto 1.5mm thickness they are not capable of penetrating thicker sheets and they are only capable of producing a hole in one relatively restricted location. Thus, for example, to cut a line through a material a series of such devices would be required which would be both inefficient to operate and time consuming to set up. Moreover this would remove the advantage of speed and ease of use which provides the thermite cutting system with a significant advantage over alternative cutting systems such as the use, for example, of an oxyacetylene torch with all its attendant equipment such as gas cylinders, pressure tubing and torch to be moved around and set up.

It is therefore an aim ofthe present invention to provide a cutting device which is capable, using thermite as the active agent, of cutting through materials of either greater hardness or greater thickness which are not susceptible to cutting by currently available comparable devices. It is a further object ofthe present invention that the device should be relatively simple in both construction and use requiring no elaborate equipment infrastructure or operating technique. It is a yet further object to provide such a device which is readily capable of cutting through generally resistant materials along a line or indeed to a more complex pattern and requiring no especial efforts to set up.

Accordingly the present invention provides a cutting device which comprises a container, said container extending generally in the form ofthe cut which is to be made and having an aperture in the form of said cut and extending along one side ofthe container, closure means associated with and substantially sealing said aperture but which is rupturable on operation ofthe device, a thermite charge contained within the container and means for igniting said thermite charge in a region substantially adjacent to one end ofthe aperture.

In its simplest form the device according to the invention will comprise an essentially cylindrical container having a longitudinal slot cut through its wall to the dimensions ofthe cut which it is desired to make in an object to be cut. To cut more complex shapes however an extended container, for example of an essentially tubular form may be used, having generally the shape ofthe cut which is to be made.

In operation the device is placed adjacent to but spaced apart from the material to be cut and the thermite charge is ignited. This causes the closure means adjacent to the end ofthe aperture where the thermite is ignited to rupture allowing hot particles of thermite slag (reaction products) to violently escape from the container and to impinge upon the material which is to be cut. As the thermite charge progressively burns along the container from the end where ignition began so the stream of reaction products exits from the container progressively along the length ofthe aperture therein and cuts through the adjacent material to form a generally linear cut therein.

It will be readily apparent therefore that the form ofthe cut which is made in the material placed adjacent to the device will generally replicate the form ofthe aperture in so far as that is sited to face towards the material to be cut. Other forms of the device and arrangements ofthe aperture therein to achieve specific forms of cut will be readily apparent to the skilled addressee. The width ofthe aperture may also be varied according to the particular arrangement and thermite composition to be used. Typically the width may be in the range from 2mm to 15mm.

It will also be apparent that because ofthe restraint placed upon the thermite reaction products within the container, pressure will be created therein such that the products will exit from the container through the aperture with a considerable force. To utilize this effect therefore it is important that the device should be employed at a small separation from the surface ofthe material which is to be cut rather than actually resting on or against that surface. Typically the separation to be employed will be of the order of from 5mm to 30mm, depending upon the nature ofthe material to be cut, the size ofthe device and the depth of cut required for example. To achieve the desired separation the device may either be supported by some independent structure in a spaced apart relationship from the material to be cut or the device may be provided itself with in-built spacing means such as-a flange around both ends in the case of a cylindrical container. However the former means will be generally preferred in order to ensure that the device remains in a fixed position whilst it is being operated for reasons of safety and maximum effectiveness.

Accordingly the present invention further provides a method of cutting a material which comprises placing a device according to this invention upon the material to be cut and in spaced apart relation thereto, igniting the thermite charge of the device and allowing said charge to react until all ofthe charge is consumed.

More generally, the invention provides a method of cutting a material which comprises concentrating a stream of hot reaction products from a source of burning thermite against the material to be cut and causing the said stream to move across a surface ofthe material in order to create a linear cut therein. Cutting may be achieved by either physically moving a point source and the consequential stream of hot particles across the surface or, which is preferred as being more readily controllable, by arranging that the source itself extends along the line which is to be cut and progressively burns along its length, the stream of hot particles being at the same time directed to move across the material surface and along the line ofthe desired cut.

Most conveniently the extended source is provided by the device ofthe present invention though other arrangements for the same may readily be envisioned by those skilled in the art.

As suggested previously, in order to provide the directed stream of hot particles which functions to cut through the object material, it is important that some pressure build-up should take place in the container prior to the ejection of material therefrom commencing. Consequently the container should be designed to withstand such pressure build-up and for this purpose a relatively thick-walled container may be used. Alternatively or indeed additionally thereto, a suitable pressure-relieving means may be incorporated into the device. While the primary control may be achieved by suitable selection ofthe type and strength ofthe closure means which is used, it may also be useful in some cases to leave a small portion ofthe aperture unsealed or to provide a separate small aperture through the container wall so as to allow thermite reaction products to begin to escape very soon after ignition ofthe thermite and so to limit the pressure which can develop in the container.

In general the selection of materials for the container and for the closure means will be easily determined in relation to the charge and type of thermite which is to be employed, which in turn will be determined in known manner by the depth and length of cut which it is desired to make in any given material. However, it may be stated that the container will often be most conveniently constructed of a suitable gauge of steel and the closure means of a material such as, for example, cardboard or aluminium foil. Where the container has a generally cylindrical foπn, the closure means may readily comprise a tube of combustible material lining the inner surface ofthe container.

The inner surface ofthe container may comprise a coating or lining of an insulating material. By providing an insulating material the container walls will be partly protected from the thermite reaction and therefore a thinner wall can be used. Thinner walls obviously result in a reduced mass which is important when the device is used as a portable cutting device. The insulating material also aids in focusing the energy ofthe thermite reaction towards the cut.

The aperture may also be preferably lined or lined with an insulating material. This will help prevent degradation ofthe aperture during operation ofthe cutting device resulting in a more accurate cut.

Any convenient form of igniting means which is able to produce a sufficiently high temperature to start the thermite reaction can be employed. For example, an electrical igniter may be used in conjunction with a suitable primer but if it is preferred to avoid the complication of an external power source an appropriate fuzing means and primer may be used instead. Such arrangements will be readily apparent to the skilled person.

The invention will now be more particularly described with reference to the following examples and to the accompanying drawings in which:

Figure 1 is an exterior view of a cutting device according to the present invention;

Figure 2 is a cross section along AA ofthe device of Figure 1, and Figure 3 is a cross section of an alternative embodiment of a cutting device according to the present invention.

In Figure 1 , a cutting device shown generally at 1 comprises a casing 2 for the thermite charge (not shown), the casing being in the form of a cylinder the open ends of which are sealed with end caps 3, 3'. These end caps are of larger diameter than the cylinder so as to provide a space between the cylinder and any relatively flat surface upon which the device may be placed. The end caps and cylinder ends are conveniently screw threaded so as to enable the caps to be tightly secured to the cylinder. Alternatively the caps may be secured to the cylindrical body with a strong adhesive for example.

A longitudinal slot 4 is formed in the cylinder and is sealed with a closure 5, conveniently made of cardboard, arranged in this case internally ofthe slot. An additional small aperture 6 is formed in the cylinder adjacent the end 3 where an igniter (not seen) is positioned. Leads 7 to an electric igniter pass through the end cap 3. For convenience the igniter may be attached to the inside of cap 3 prior to screwing the cap onto the cylinder. For some applications the device may be fuzed and the fuze and igniter could conveniently form an assembly incoφorated with the end cap 3. In this embodiment no external leads are of course required.

In Figure 2 the nature ofthe closure means 5 is more readily understood as being a cardboard tube 5 which lines the inside ofthe casing 2 ofthe device. The thermite charge 8 is contained within the tube and on ignition will burn away the cardboard tube and allow reaction products to exit the casing 2 through the slot 4.

Figure 3 shows a cutting device similar to that shown in Figures 1 & 2, where like numerals indicate like components, but wherein the internal surface ofthe casing 2 has a coating of insulating material 9. The insulating material, which may be treated cardboard or a ceramic material, allows the casing to have thinner walls than it otherwise would do and also helps to focus the energy generated in the thermite reaction. Example 1

An incendiary device according to the invention was made up using a cylindrical body of steel 7.5mm thick and 50mm in outer diameter; the length ofthe cylinder was 150 mm. End caps of diameter 60mm were screwed onto the ends ofthe cylindrical body. A longitudinal slot 5mm wide and 90mm long was cut in the cylinder and, separated from the slot but along the same longitudinal line, an aperture of 5mm diameter was also cut. This hole was left uncovered but the main slot was closed with a tubular sleeve made of cardboard 2 mm thick, placed inside and stuck to, the cylindrical body.

Prior to affixing the end cap nearest to the aperture, the cylinder (with the tubular sleeve and the other end cap already in place) was charged with a thermite material comprising aluminium powder, ferric oxide ("hammerscale"), barium nitrate and boric acid. This composition was pressed into the cylinder under a pressure of 60 kN.

After filling the cylinder as described, a Type 100 electric igniter (ICI Explosives Ltd.) was loosely placed into the end of the cylinder and in contact with the primer consisting of a gunpowder mixture which was itself in contact with the thermite charge. The leads to the igniter were passed through the small hole in the cylinder body and to a suitable switch for controlling the supply of current to the igniter. The second end cap was then fitted onto the cylinder.

The device was placed in a horizontal position on a steel plate 5mm thick and the thermite charge then ignited. It was found that a slot 20 mm wide and 35 mm long was cut in the plate.

Example 2

A second incendiary device according to the present invention was made up using a cylindrical steel body 150mm in length, 50mm in outside diameter and having a wall thickness of 4mm. Similarly to Example 1 end caps of diameter 60mm were screwed onto the ends ofthe cylindrical body.

The cylindrical body had a longitudinal aperture 5mm wide and 100mm long and also a separate circular aperture 5mm in diameter. The internal surface ofthe cylindrical body was lined with an insulating material and a tubular sleeve of cardboard 2mm thick was secured inside the cylindrical body using adhesives.

The cylindrical body was filled with a thermite composition and fitted with an igniter the same as in Example 1.

The device was placed in a horizontal position on a steel plate 5mm thick and the thermite charge was then ignited. It was found that a slot 50mm long and 20mm wide was cut in the steel plate.

Claims

1 A cutting device which comprises a container, said container extending generally in the form ofthe cut which is to be made and having an aperture substantially in the form of said cut and extending along one side ofthe container, closure means associated with and substantially sealing said aperture but which is rupturable on operation ofthe device, a thermite charge contained within the container and means for igniting said thermite charge in a region substantially adjacent to one end ofthe aperture

2. A cutting device according to claim 1 characterised in that the container is cylindrical in form and has a longitudinally extending aperture therein

3. A cutting device according to claim 1 or claim 2 characterised in that the container incorporates also means for spacing apart the aperture from a surface of an object which is to be cut.

4 A cutting device according to claim 3 when dependent on claim 2 characterised in that said spacing apart means comprises flanges located at each end ofthe cylinder.

5. A cutting device according to any of claims 1 to 4 characterised in that the container also possesses a hole separate from the said aperture and located adjacent the end ofthe container at which the means for igniting the thermite charge is located.

6. A cutting device according to any ofthe preceding claims characterised in that the means for igniting the thermite charge comprises an electrical igniter acting on a primer material.

7. A cutting device according to any ofthe preceding claims characterised in that the closure means comprises a combustible material lining the interior ofthe container.

8. A cutting device according to claim 7 characterised in that the closure means comprises a layer of cardboard.

9. A cutting device according to any ofthe preceding claims characterised in that the inner surface ofthe container comprises a lining of insulating material.

10. A cutting device according to any ofthe preceding claims characterised in that the aperture has a lining of insulating material.

11. A cutting device substantially as hereinbefore described with reference to Figure 1 ofthe accompanying drawings.

12. A method of cutting a material which comprises placing the device according to any one of claims 1 to 11 upon the material to be cut and in spaced apart relation thereto, igniting the thermite charge ofthe device and allowing said charge to react until all ofthe charge is consumed.

13. A method of cutting a material which comprises concentrating a stream of hot reaction products from a source of burning thermite against the material to be cut and causing the said stream to move across a surface ofthe material in order to create a linear cut therein.

14. A method according to claim 13 characterised in that the source extends along the line which is to be cut and is arranged to burn progressively along its length, the stream of hot particles thus generated being directed to move across the material surface and along the line ofthe desired cut.

15. A method according to claim 14 characterised in that the stream of hot particles is directed to move across the surface by providing the source with a linear aperture in substantially the form ofthe line which is to be cut.

16 A method of creating a linear cut in an object which comprises placing on the object a cutting device comprising a container, said container extending generally in the form ofthe cut which is to be made in the object and having an aperture substantially in the form of said cut and extending along one side ofthe container, said container further having closure means associated with and substantially sealing said aperture but which is rupturable on operation ofthe device, a thermite charge contained within the container and means for igniting said thermite charge in a region substantially adjacent to one end ofthe aperture, igniting said thermite charge and allowing it to burn until substantially the whole ofthe charge is consumed.

17 A method as claimed in claim 15 or claim 16 characterised in that the aperture is arranged to lie at a small distance from the surface ofthe object to be cut

18. A method as claimed in claim 17 characterised in that the separation between the aperture and the surface ofthe object to be cut is between 5 and 30mm