Method for joining at least two metal workpiece parts to each other by means of explosion welding

Abstract

The present invention relates to a method for joining at least two metal workpiece parts (2, 8) of a differing metal composition to each other by means of explosion welding, comprising the steps of: •—enclosing an inner workpiece part (2) at least partially with an outer workpiece part (89; •—arranging a mantle of explosive material (14) round the outer workpiece part; and •—detonating the explosive material in order to bring about a metallurgical connection between the two workpiece parts; •—wherein during the detonation of the explosive material the inner workpiece part is substantially wholly filled with and/or is at least partially enclosed by a dilatant non-Newtonian mixture (20). The invention further relates to a workpiece manufactured via this method.

Claims

1. Method for joining at least two metal workpiece parts of a differing metal composition to each other by means of explosion welding comprising: enclosing an inner workpiece part at least partially with an outer workpiece part; arranging a mantle of explosive material around the outer workpiece part; and detonating the explosive material in order to bring about a metallurgical connection between the two workpiece parts; wherein during the detonation of the explosive material, the inner workpiece part is one or both substantially wholly filled with and at least partially enclosed by a non-Newtonian mixture; and wherein the non-Newtonian mixture is a dilatant non-Newtonian mixture.

2. The method as claimed in claim 1, wherein the dilatant non-Newtonian mixture has a viscosity of between 10 and 100 mPa.Math.s.

3. The method as claimed in claim 1, wherein at a shear rate ′Υ of 30 to 100.Math.s, the dilatant non-Newtonian mixture has a viscosity value cP of between 10.sup.4 and 2.5.Math.10.sup.4 mPa.Math.s.

4. The method as claimed in claim 1, wherein the inner workpiece part encloses at least a hollow space which is substantially wholly filled with the dilatant non-Newtonian mixture during the explosion welding.

5. The method as claimed in claim 1, wherein the dilatant non-Newtonian mixture comprises cornstarch and a liquid.

6. The method as claimed in claim 5, wherein the ratio of cornstarch:liquid lies in the range of between 1.5:1 - 2.5:1.

7. The method as claimed in claim 5, wherein the ratio of cornstarch:liquid is substantially 2:1.

8. The method as claimed in claim 5, wherein the liquid comprises water.

9. The method as claimed in claim 5, wherein the liquid comprises one of glycol or glycerol.

10. The method as claimed in claim 5, wherein one or more solid substances are dissolved in the liquid.

11. The method as claimed in claim 5, wherein salt is dissolved in the liquid.

12. The method as claimed in claim 5, wherein sugar is dissolved in the liquid.

13. The method as claimed in claim 1, wherein the inner workpiece part comprises a metal tube filled with the dilatant non-Newtonian mixture prior to the explosion.

14. The method as claimed in claim 13, wherein the outer workpiece part is formed as a half of a tube cut through in longitudinal direction which has a greater radius of curvature than the outer radius of curvature of the inner workpiece part.

15. The method as claimed in claim 13, wherein the inner workpiece part comprises a succession of at least two metal tubes between which lies an intermediate connection, and the outer workpiece part is formed connecting thereto so as to form a wall after the explosion welding.

16. The method as claimed in claim 1, wherein the distance between the workpiece parts prior to the explosion lies in the range of between 0.5-3 cm.

17. The method as claimed in claim 4, wherein the hollow space is partially filled with a solid anvil prior to being filled with the dilatant non-Newtonian mixture, wherein the dilatant non-Newtonian mixture substantially wholly fills the remaining space.

18. Method for joining at least two metal workpiece parts of a differing metal composition to each other via explosion welding comprising: at least partially enclosing an inner workpiece part with an outer workpiece part; arranging a mantle of explosive material around at least a portion of the outer workpiece part; and detonating the explosive material in order to bring about a metallurgical connection between the two workpiece parts; wherein during the detonation of the explosive material, the inner workpiece part is substantially wholly filled with a dilatant non-Newtonian mixture.

19. Method for joining at least two metal workpiece parts of a differing metal composition to each other via explosion welding comprising: at least partially enclosing an inner workpiece part with an outer workpiece part; arranging a mantle of explosive material around at least a portion of the outer workpiece part; and detonating the explosive material in order to bring about a metallurgical connection between the two workpiece parts; wherein during the detonation of the explosive material, the inner workpiece part is at least partially enclosed with a dilatant non-Newtonian mixture.

Description

(1) Preferred embodiments of the present invention will be further elucidated in the following description with reference to the drawing, in which:

(2) FIG. 1 is a schematic representation of an explosion welding process;

(3) FIG. 2 is a perspective and partly cut-away view of an initial stage of the method according to the invention;

(4) FIG. 3 is a cross-sectional view of an initial stage of the method wherein an alternative workpiece part is cladded;

(5) FIG. 4 shows a view of an initial stage for cladding a tube; and

(6) FIG. 5 is a cross-sectional view of the situation shown in FIG. 4.

(7) The principle of explosion welding is elucidated with reference to FIG. 1, wherein the inner workpiece part 2 is formed by a main part above which a cladding part which functions as outer workpiece part 8 is placed with a clearance 22. A layer of explosive material 14 is arranged on top of the outer side 12 of cladding part 8 remote from main part 2.

(8) The principle of explosion welding is based on the inner workpiece part 2 (the main part) and the outer workpiece part 8 (the cladding part) making contact with each other at very high velocity at an angle β.

(9) Cladding part 8 will accelerate due to the pressure wave from an explosion before striking main part 2 with a very great impact. In order to concentrate the impact in a small area the cladding part 8 must strike main part 2 at an angle.

(10) For acceleration purposes a distance is necessary between main part 2 and cladding part 8. This distance is formed by the clearance 22. The combination of the size of clearance 22 and the propagation velocity of the explosion determines the angle of impact. The ductility of cladding part 8 also has an influence here and a wave pattern will form to greater or lesser extent on the joining line 23.

(11) Because the air present between the two parts 2, 8 is displaced in that clearance 22 is closed by the explosion, a considerable pressure wave occurs in this space which greatly increases the temperature of plates 2, 8 locally and which will clean the surfaces 6, 10 by briefly exposing the microstructure. The Boltzmann equation predicts a gas temperature of 7270 kelvin at a propagation velocity of the explosion of 2500 m/s. Considering that steel becomes gaseous at about 3000 kelvin, but also the low enthalpy of air, it is assumed that the pressure wave is of crucial importance.

(12) In respect of the materials to be welded it has been found that the propagation velocity of the collision line between the two plates 2, 8 must lie below the speed of sound in the materials in order to make a neat weld. The process will hereby remain below the speed of sound, whereby the welding process will remain free of a supersonic boom, which would destroy the welding process.

(13) The kinetic energy of the impact between the two parts 2, 8 must be sufficiently great to cause the materials to enter into a connection at atomic level. It is important here that main part 2 is supported by a stable anvil 16 and will not therefore yield under the pressure of the explosion.

(14) For explosive cladding of for instance a flat plate the ground surface can as support fulfil this anvil function. While there will be some ‘recoil’ from the elasticity of anvil 16 and main part 2, whereby the angle α of FIG. 1 can result, in the case of a flat plate this can however be solved using a roller.

(15) FIG. 2 shows an application of a method in which a tubular inner workpiccc part 2 is provided via explosion welding with an outer workpiece part 8 which forms a cladding layer of high-alloy steel. According to the invention the function of a stable anvil 16 is provided herein by a non-Newtonian mixture 20 which is arranged in a tray 24. For the sake of clarity the front wall of tray 24 is not shown in FIG. 2. This mixture 20 is arranged at least in the volume enclosed by the tubular workpiece part 2 and is preferably also arranged around the lower part of outer wall 6 of the inner workpiece part 2.

(16) The upper half for cladding of outer wall 6 of inner workpiece part 2 protrudes above the non-Newtonian mixture 20. Located at some distance is an outer workpiece part 8 of for instance a high-alloy steel. The clearance 22 can for instance he guaranteed in that the outer workpiece part 8 is provided with several protrusions which form support points (not shown) with which the outer workpiece part 8 supports on outer wall 6 of the inner workpiece part 2.

(17) Arranged on outer wall 12 of outer workpiece part 8 is explosive material 14 which, in accordance with the principle of explosion welding described with reference to FIG. 1, can cause the outer workpiece part 8 to collide with inner workpiece part 6, this resulting in the desired metallurgical connection between the two workpiece parts 2, 8.

(18) FIG. 3 shows how the method according to the invention is applied for the purpose of cladding a complex workpiece, such as a steam boiler wall part 26, in a single step. In the shown embodiment this steam boiler wall part 26 comprises two tube parts 28 between which lies an intermediate connection 30. Arranged on either side are flanges 32 with which a plurality of such steam boiler wall parts 26 can be connected to each other. The method according to the invention is thus also suitable for workpieces which are not rotation-symmetrical.

(19) FIGS. 4 and 5 show how all-round explosive cladding of a tube is possible. Because the explosive charge is arranged on the outer side, the inward directed force (pressure wave) of the explosion will be used for the welding.

(20) The two workpiece parts 2, 8 are inserted one into the other in tube form, wherein the inner workpiece part 2 functions as main part and wherein the outer workpiece part 8 functions as cladding part. The tube forming the outer workpiece part 8 has a larger inner diameter than the outer diameter of the tube forming the inner workpiece part 2. Half of the difference between these diameters forms the clearance 22 between outer wall 6 of inner workpiece part 2 and inner wall 10 of outer workpiece part 8.

(21) Shown in the cross-section of FIG. 5 is how the tubular workpiece parts 2, 8 are centred at the top and bottom using respectively an upper spacing ring 34 and a lower spacing ring 36. The pressure wave during the explosion will further centre the tubular workpiece parts 2, 8.

(22) The inner tubular workpiece part 2 is filled with a material which is impact-resistant, and thus forms a stable anvil 16. Used for this purpose according to the invention is a non-Newtonian mixture 20. This non-Newtonian mixture 20 is on the one hand sufficiently liquid to at least be poured into and to fill the volume enclosed by workpiece part 2. During an explosion the non-Newtonian mixture 20 will on the other hand function as stable anvil 16, while it can flow out of the inner workpiece part 2 again as liquid mixture afterwards. The lower spacing ring 36 also functions as a closing cap which closes the hollow space enclosed by the inner workpiece part 2 on the underside, whereby the non-Newtonian mixture 20 fills this enclosed hollow space and can function there as anvil 16.

(23) The assembly of the two tubular workpiece parts 2, 8 is centred in a sleeve 38 which thereby determines the layer thickness of the explosive charge 14.

(24) An igniter 40 with an initiating charge 42 is placed on the upper side in order to remotely initiate the detonation of the explosive material 14 arranged around the outer workpiece part 8. During the explosion the pressure wave will further centre the tubular workpiece parts 2, 8.

(25) As shown in FIG. 4, tubes can be suspended vertically. The whole assembly hangs clear of the ground with a free space such that the tube 2 for cladding, which will unavoidably be blasted out axially by the explosive 14, only hits the ground when the whole welding process has been completed. The welding process runs at a velocity of about 2500 m/s over a tube length of 6,000 mm and thus requires 2.4 msec; experience has shown that a free length between tube and ground of 500 mm is sufficient for this purpose.

(26) When a series of tubes are suspended, the individual tubes are preferably suspended vertically from a cable at a mutual distance of about 3 meters, and the igniters are set with a successive time delay of 5 ms.

(27) Although they show preferred embodiments of the invention, the above described embodiments are intended solely to illustrate the present invention and not to limit the scope of the invention in any way. When measures in the claims are followed by reference numerals, such reference numerals serve only to contribute toward understanding of the claims, but are in no way limitative of the scope of protection. It is particularly noted that the skilled person can combine technical measures of the different embodiments. The described rights are defined by the following claims, within the scope of which many modifications can be envisaged.