NZ204903A - Explosive welding using charge positioned eccentrically in inert surrounding material - Google Patents

Description

2049 03 17 //, .n .o? ■'\! 1xt• i 11ic11on Filod: •»••••*••* ft?M**/.PSr. t'f-M/p.K. .t*!t.$n(.Q° E'8*MJG't986V" Publication Date: P.O. Journal, No: .... /.+l NEW ZEALAND PATENTS ACT, 1953 Dale: COMPLETE SPECIFICATION METHOD OF SPLICING METAL ELEMENTS BY MEANS OF EXPLOSION-WELDING NITRO NOBEL AB, a Swedish company, of 710 30 Gyttorp, Sweden hereby declare the invention for which I / we pray that a patent may be granted to me/us, and the method by which it is to be performed, to be particularly described in and by the following statement:- * (followed by page la) . ..... ■ . . 1 .frW—VH-V 2 049 03 METHOD Of SPLICING METAL ELEMENTS BY MEANS OF EXPLOSION WELDING Metal elements such as sheet-metal and tubes can be spliced by various known methods of explosion-welding.

Figure 1 shows schematically some such arrangements.

The explosive charge 1 accelerates either a splice plate 2 towards the elements 3 and ^ to be joined, or a part of one of the elements.

Since a relative large explosive charge must be used in relation to the thickness of the elements or the splicing strip, in order to achieve satisfactory cohesion, the splicing method according to Figure 1 causes considerable deformation of the elements even if they are supported during the procedure.

In the arrangements shown in a and b where an explosive charge with low detonation speed must be used, the overlap must be made wider than is necessary for the strength of the joint. This is because the pressure relief from the edges of the charge affects the welding process in long, narrow charges so that with decreasing width, only edge effects are finally obtained. Even if the width is increased unjoined edge zones are obtained, see Fig.2. In some cases such unjoined edge zones may give rise to gap corrosion.

In cases c and d in Fig.l, a more rapid explosive charge can be used due to the angular arrangement, and a narrower overlap is obtained with satisfactory cohesion. However, these arrangements require great accuracy in preparing the joint and the elements must be fixed together in the correct position so that the angle set is correct along the entire 'joint. This entails practical difficulty in the case of long joins.

The object of the present invention is to eliminate these difficulties. 204903 Description The explosive charge is given the simplest and most ideal shape, i.e. cylindrical, and is entirely encased in an inert medium so that the pressure relief and spread of fumes will be delayed until the explosion-welding process is complete.

. The overlapping splicing material is also cylindrical so that even if the elements to be Joined are somewhat irregular or placed slightly incorrectly, a region will always be obtained where the collision angle is correct for.satisfactory adhesion. The relief of the pressure which still occurs with increasing distance from the centre of the charge through the inert medium is compensated by the increase in the angle set, due to the cylindrical shape. The arrangement is shown in Figure 3- In the cross-section shown 1 is the charge, 2 the splicing material, 3 and 4 the elements to be joined and 5 the inert material surrounding the charge 1.

In Figure 3 the splicing material has greater inner than outer radius. However, this is by no means necessary in principle, but facilitates adhesion of the edges and improves the appearance of the join (Fig.3b).

The shock wave through the inert medium 5 has even further to go due to the eccentric location of the charge in relation to the surface of the splicing material and their different curvatures. Together with the curvature of the splicing material in relation to the metal elements, this determines the speed, both at right angles and parallel to the surface of the elements, at which the collision takes place. The explosion-welding process is thus not directly dependent on the detonation speed of the explosive, but on the detonation pressure, the material properties of the inert medium transmitting the shock wave, the splicing material and the geometry.

Explosives can thus be selected which have favourable properties with respect to slight critical diameter, manufacture, sensitivity, etc. 3 As for the inert material, practically any material may be selected which does not react with the explosive. In practice a material easy to make into rod form and favourable from an economic point of view is selected. Various types of plastic have been found to fulfil these requirements.

It is clear to anyone with experience of explosion-welding that component 2 in Fig.3 may provide the drive plate for one or more plates beneath, being flat, for instance, or it may even consist of the part of the inert medium below the charge. This may be advantageous if thin or brittle material is to be joined. Fig.H.

To position the charge system according to Fig.3 the splicing piece may be provided with an abutment index inserted between the edges of the metal elements as shown in Fig.5- Figure 6 shows a method of simultaneous explosion-welding from both sides of the elements, which can very well be done according to the method of the invention by using charges with high detonation speed and thus high precision. Firing from both sides of the element may be advantageous when splicing large-diameter elements such as pipe-lines above and below water where the application of supports to impede deformation is difficult and expensive. Another such case is the splicing of compound material where both the basic material and the plating material on one side thereof must be joined.

The explosive charge may also be given other shapes having a cross-section converging in the direction of the joint, such that the distance from the charge through the insert material to the netal elements increases as the lateral distance from the joint increases. In particular, a charge which is triangular in cross-section may be used, in which one apex of the triangle is directed towards the joint.

Claims (21)

WHAT WE CLAIM IS:-

1. Method of explosion welding to join together metal elements with the aid of a charge above the joint and a splicing element placed between the charge and the joint, characterised in that the charge is located in an inert material extending further above the charge than below it and that the charge is so shaped in relation to the inert material and the metal elements that the distance through the inert material for the compression increases as the distance from the joint increases.

2. Method according to claim 1, characterised in that the charge and the inert material are elongate.

3. Method according to claim 2, characterised in that the charge has a cross-section converging in the direction of the joint.

4. Method according to claim 3, characterised in that the charge has a triangular cross-section with an apex directed towards the joint.

5. Method according to claim 3, characterised in that the cross-section of the charge is substantially circular.

6. Method according to any one of the preceding claims, characterised in that the inert material has substantially circular cross-section.

7. Method according to any one of the preceding claims dependant on claim 2, characterised in that the charge placed eccentrically in the inert material is supported by the splicing element in such a way that the symmetry lines of the charge, the inert material and the splicing element coincide in cross-section and are located immediately above the joint between the metal elements and where thus the explosion-welding process is determined by the detonation pressure, the geometry of the cross-section and the material properties of the inert material and the splicing element, and runs at right angles to the longitudinal direction of the charge and the joint. 204905 - 5 -

8. Method according to claim 7, characterised in that the splicing element comprises a tube segment which is arranged so that the inert material with the charge therein is supported in the concave recess of the splicing element.

9. Method according to any one of the preceding claims characterised in that splicing is performed from one side of the metal elements.

10. Method according to any one of claims 1 to 8, characterised in that splicing is performed simultaneously from both sides of the metal elements.

11. Method according to any one of the preceding claims, characterised in that the metal elements comprise flat sheets.

12. Method according to any one of claims 1 to 10, characterised in that the metal elements are tubular; forming part of one tubular piece or being two separate tubular elements.

13. Method according to any one of the preceding claims, characterised in that the splicing element is used as drive body to accelerate one or more splicing elements beneath, said element(s) in turn being designed to hold together the metal elements to be joined.

14. Method according to any one of claims 1 to 12, characterised in that the part of the inert material which, seen from the charge, is directed towards the metal elements, constitutes a drive body.

15. A method of explosion welding substantially as herein described with reference to any embodiment shown in Figures 3 to 6 of the accompanying drawings.

16. Metal elements joined by the method of explosion welding as claimed in any one of the preceding claims. 27 tf/Vn986 | : „ s 204S03 - 6 - i

17. An explosive device for use in a method of explosion welding as claimed in claim 1, the device comprising a shaped explosive charge located eccentrically within an inert material such that the device can be placed above the joint with a splicing element therebetween such that the inert material extends further above the charge than below it and the distance through the inert material for the compression increases as the distance from the joint increases.

18. A device as claimed in claim 17 wherein the charge and the inert material are elongate.

19. A device as claimed in claim 18 wherein the charge has a substantially circular or a substantially triangular cross-section.

20. A device as claimed in any one of claims 17 to 19 including the splicing element which is shaped as a tube segment in the concave recess of which the device can be supported.

21. An explosive device substantially as herein described with reference to any embodiment disclosed in Figures 3 to 6 of the accompanying drawings. NOG6C AS r.y t™' i..!" c»!.irrcc! Arcnts, A. J. FAnX u COM, per ,,