FR2495981A1 - Electroslag welding of metals - includes maintaining weld metal in molten state after welding current is switched off - Google Patents

Abstract

Metals are electroslag welded by forming a flux bath, melting the electrode and the weld edges, filling the gap between the weld edges with molten metal and maintaining the metal in a molten state for a period after the weld current is switched off, the heat capacity of the flux bath being simultaneously raised. The period is pref. 10-15% more than the time required to degasify the weld metal. The heat capacity of the flux bath is raised pref. by increasing its vol. A pref. flux bath contains (in wt.%): BaF2 60.0-90.0, CaF2 5.0-15.0, LiF 1.0-5.0, NaF 1.0-10.0 and KF 1.0-15.0. The process is used for welding non-ferrous metals such as Al, Mg, Ti etc. and their alloys, in partic. Al bus bars and conductors. Welding process is stable and results in a high quality weld seam of low gas content since the rate of electrode melting is self-regulating and the degree of gas removal from the weld metal during and after welding is enhanced by slowing down the rate of crystallisation of the weld metal.

Description

The present invention relates to welding techniques and in particular relates to a process of welding under an electroconductive slag, in particular of light metals and of alloys whose density is lower than that of the slag, a flux of welding or stripper based on alkali and alkaline earth halides, and an installation for carrying out said process
The invention is applicable in particular to the welding of aluminum, magnesium, titanium or their alloys, as well as to the welding of other light metals. In particular, it can be applied in the case of welding of sheaths of electrically conductive bars. aluminum, in the metallurgy of non-ferrous metals, in the chemical and electrotechnical industries, etc.

 An electroconductive slag welding process is known (see BE Paton, "Elektroshlakovaya svarka", Mashgiz, 1959, pp. 90-149), which consists of preparing a slag bath, melting an electrode and the edges to be welded and filling the space between said edges with molten metal.

 It is well known that when light metal or their alloys are welded under electroconductive slag, using the fluxes known in this field for this purpose, the gas content of the metal of the solder increases with increasing thickness of the parts to be welded.

For example, there is known a flux flux (see the USSR author's certificate N 626913 published of March 28, 1977) intended for the welding, under electroconductive slag, of light metals and their alloys, which flux comprises halides of alkali metals and alkaline earth metals in the following proportions (5 # o by weight)
calcium fluoride 13 - 17
strontium fluoride 13 - 17
magnesium fluoride 10 - 14
lithium fluoride. .................. 16 - 20
potassium chloride (concentrated aqueous solution) ...

..... 36 - 44
The welded joint obtained using this flux and without resorting to current techniques for reducing the gas content of the metal of the weld, has a porous structure with a high gas content, which results in a significant deterioration of the mechanical characteristics of the welded joints obtained. The presence of potassium chloride in the form of a concentrated aqueous solution gives the flux in question a very hygroscopic character, hence the possibility of projections of the molten material and the instability of the welding process.

 The mentioned method of welding under electroconductive slag is implemented using a device comprising a bottom plate, ingot molds, outlet plates and a welding electrode.

 The welded joints obtained in the described manner and using the flux and the device mentioned are characterized by a high gas content and must undergo additional treatments aimed at improving their quality, necessary especially in the case of welding of parts playing a role. important.

 The complete degassing of the metal forming the welded point can be carried out by inhibiting the solidification process of said metal, by means of additional operations of preliminary, concomitant or subsequent heating of the metal of the welded joint.

 The heating in question of the metal forming the welded joint is only possible using complicated additional devices.

 Furthermore, said method requires the use of additional chemical elements which are introduced into the metal of the weld during welding to bond in the form of resistant compounds the components giving rise to gases, by forming resistant compounds, as well as additional protection of the welding area by inert gases.

 This use of additional technological operations increases the manpower necessary for implementing the welding process and increases its cost.

 There was a vertical welding process for aluminum (US Pat. No. 3,585,343, published June 15, 71), which consists in preparing a slag bath of the following composition (% by weight) potassium chloride 45 soduim chloride ... ....................... soduim 27 sodium cryolite (3t '# aF.AlF3) 22 lithium chloride .......... ................. lithium 6 to melt an electrode and the edges to be welded, and to fill with molten metal the space between said edges.

 This flux ensures the stability of the welding process under electroconductive slag, well neutralizes the oxide film present on the parts to be welded, without however allowing dense or compact welded joints to be obtained without carrying out the abovementioned operations intended to reduce the content of metal gas from the welded joint.

 The process in question is implemented using a device comprising a shell, graphitic ingot molds, current supply elements and a solid section electrode provided with a guide sleeve ensuring the rotation of said electrode in the slag bath. The current supply elements are arranged outside the melt.

 The elimination of gases from the welded joint is carried out by means of the use of graphite ingot molds which reduce the extraction of heat from the molten bath, and by virtue of the rotation of the electrode in the slag bath.

 The known method described above does not make it possible to completely eliminate the gases from the metal of the welded joint, which is due to the high speed of solidification of said metal and to the fact that during welding the rotation of the electrode n 'exerts a mechanical action only on the slag bath.

 The implementation of the process of welding under electroconductive slag using the flux and the device described requires the use of a complicated control or slaving apparatus to ensure the stability of the welding process by monitoring the availability. tion of the electrode in the welding bath, which complicates and makes costly the welding process, without however allowing the complete elimination of the gases from the metal of the joint had its solidification, due to the low melting temperature of the flux used.

 The invention therefore relates to a method of welding under an electroconductive slag, in particular of light metals and their alloys, a welding flux or stripper and a device for implementing said method, which would ensure the stable progress of the welding process and would allow to obtain welded joints with minimum gas content thanks to the self-regulation of the electrode melting speed, the elimination of gases both during the welding process and after the interruption of the current welding, by inhibiting the solidification process of the metal of the welded joint and by modifying the quantitative and qualitative composition of the flux used.

 The subject of the invention is therefore a welding process under lai-vf f - electroconductive in particular of light metals and their alloys, of the type consisting in preparing a ia5 # er bath, in melting an electrode and the edges to be welded and filling the space between said edges with molten metal, this process being characterized in that the metal of the joint is kept in the liquid state, after the interruption of the welding current, by increasing the thermal capacity of the bath slag, said maintenance of the seal in the liquid state taking place for a period of time greater than that necessary for degassing of the metal due to it; in a proportion of 10 to 15%, the said degassing time required being chosen experimentally before welding.

 A process allows you to obtain dense or coLQDacû # - welds.

 To increase the thermal capacity of the slag, it is possible, according to the invention, to increase its volume, which makes it possible to reduce the cooling rate of the metal of the joint during welding.

Said heat capacity can also be increased by using a welding flux or stripper of the following composition (% barium fluoride eCl, c; - 0.0 calcium fluoride ............. ........... calcium 5.0- 15.0 lithium fluoride ....., .................. lithium 1s0 - 5 .0 sodium fluoride * 1.0 - 10.0 potassium fluoride 1.0 - 15.0
The introduction, within the proposed stream, of the mentioned quantities of barium fluorite allows the density of said stream to be increased to a value exceeding the density of the metal to be welded, which facilitates the separation of the molten metal from the slag when welding under electroconductive slag and ensures the stable progress of the welding process.

 When the content of barium fluoride in the proposed stream is reduced below the aforementioned lower list, the separation of the molten metal from ave # the slag takes place in an unsatisfactory manner and harms its stability; IF, on the contrary, the upper limit is exceeded, the activity of the flux decreases and the deoxidation of the edges to be welded takes place in an unsatisfactory manner, which ultimately leads to the formation of defenders in the welded joint.

 Introducing the mentioned quantities of calcium fluoride into the claimed flow makes it possible to increase the activity of the flow and to improve, thanks to the decrease in surface tension at the dairy-molten metal interface, the combination , during the electroconductive slag welding process, individual drops of molten metal in a single metal bath.

When the calcium fluoride content is reduced or increased below or above the above limits, the efficiency of the flow decreases.

 The aforementioned quantities of lithium fluorides, sodium and potassium - c in the claimed flux also contribute to improving its activity.

 The claimed proportions of the components forming fl-a) in cuesticn contribute to increasing the melting temperature of said flux above the melting temperature of the metal to be welded, which has the effect of slowing the solidification of the molten metal which finds it. in the space between the edges to be welded, this promoting the degassing of said metal and obtaining a quality weld. These advantages provided by the claimed flow make it possible to significantly raise the quality and reliability of the welded assemblies obtained.

 To increase the thermal capacity of the slag bath and to maintain the metal of the joint in the liquid state until the complete elimination of the gases, it is necessary to have recourse to a device of the type comprising a shell with a bottom plate, ingot molds, a current supply element and a welding electrode, said device being characterized according to the invention in that the welding electrode is mounted through an orifice located in the center of the bottom plate, and in that that in the melting zone of said electrode is a low resistance current supply element.

 Such a device contributes to the stable progress of the welding process thanks to the self-regulation of the melting speed of the welding electrode, because in case of fusion of the tip of the electrode below the upper surface of the element current supply, the active spot passes from the electrode to the current supply element, where a decrease in the melting speed of one electrode.

 The current supply element placed in the melting zone of the electrode can, according to the invention, be made either of a solid material whose melting temperature is higher than the welding temperature, or of a liquid material whose boiling point is higher than said welding temperature.

 The material (or material) thus chosen of the current supply element does not arm during welding.

 In addition, when the current supply element consists of a liquid material, the density of the latter is chosen to be greater than the density of the slag bath so that the material in question does not mix with the metal. the electrode does not dissolve in it.

 The material of the current supply element thus chosen prevents pollution of the metal of the joint by said material during welding.

 Advantageously, the electrode of the electroconductive slag welding device can be provided with internal, longitudinal and transverse channels, filled with a material laissezpass ## - g'zeccommunicating with an analogous channel made in the bottom plate of the shell.

The presence of the channels in question makes it possible, during welding, to eliminate the gases from the molten bath, and the fact that said channels are filled with a material leaving
screwing the gases allows the material to drain out from flowing out of the space between the edges.

 One of the internal channels of the welding electrode can be arranged along said electrode and communicates with the other channels, which are formed transversely to the electrode along the entire length of the latter.

The invention will be better understood and other objects, details and advantages thereof will appear better in the light of the explanatory description which follows, to differ. ts embodiments given solely by way of nonlimiting examples with reference to the attached nonlimiting drawings in which
- Figure 1 illustrates the welding process under electroco slag: conductor of light metals and their alloys, when using a solid state current supply element
- Figure 2 illustrates the process of electro-conductive slag welding of light metals and their alloys, when the current-supply element is in the licuid state
FIG. 3 illustrates the process of maintaining the liquid metal of the joint on a hearth at high temperature after the interruption of the current
- Figure 4 shows the welded joint after solidification of the metal of said joint.

 Below are described concrete but nonlimiting examples of embodiment of the invention.

Example 1
The parts are welded under electroconductive slag using a device prepared as follows.

 On a shell or crucible 1 (FIG. 1) are placed samples of aluminum to be welded 2 isolated from the latter, 500 mm long and whose section is 50 μm, so that the edges to be welded are separated by a space. 60 mm.

 Then ~ # 1. has 2 graphitic connection plates on the samples to be assembled3. We cover laterally - gotiF-es 4, isolated from the parts to be welded 2, the space between the edges to be welded.

 Through a hole made in the center of the bottom plate 5, an aluminum electrode whose cross section is 20 x 40 mm is introduced into the space between the edges to be welded.

 The hole through which the electrode is introduced is sealed, for example by a cord of amia: lte 7. Around the welding electrode and the lining 7 is located, inside the shell 1, urs grapeitic current supply element 8 placed on the bottom plate 5.

 JIn the plate # bottom 5 and in the electrode r- are formed lime 11, 12, 13 for the evacuation, during melting, of the gases coming from the melt, said channels being filled with a mixture of crushed metallic material and grains of flux 14, a mixture serving for the flow of the flow of the molten bath through said channels.

 So that the melting temperature of flux 14 is higher than that of the metal to be welded (L-00C), a flux of the following composition (% by weight) barium fluoride is chosen .......... .............. barium 60.0 calcium fluoride ........................ calcium 15.0 fluoride lithium ......................... lithium 5.0 sodium fluoride ................ .......... sodium 10,0 potassium fluoride ........................ potas 10,0.

 The delsity of the flux in question is 3.1 g / cm3, its melting temperature is 9000C.

 The flux 14 is poured into the space between the welding parts 2 so that the upper part of the electrode 6 exceeds the level of the flux, for example by 10 mm.

 The connection plates 3 and the welding electrode U are connected using cables 15 to a welding transformer 16.

 Then the mass of flux 14 poured into the space between the edges to be welded is covered with previously melted flux.

 Thus, the device for implementing the welding process under electroconductive slag is ready to operate.

 The welding speed is the following no-load running voltage (Um.v.) - 38V welding current (they) ....................... ... 4.5 HA.

 The welding circuit being closed, the edges to be assembled of samples 2 and the electrode 6 are melted and form a metal bath 17, while the stream 14, also in fusion, gives rise to a slag bath 18, the metal bath 17 being sheltered from the atmosphere using an inert gas consisting, in this case, of argon.

 During the welding, we are witnessing the fusion of the electrode, the metal of which fills the space between the edges to be welded, until the omission where the molten end of the electrode is below the surface. top of the current supply element 8.

 Once the electrode in this position, its melting slows down because the active spot passes from the tip of the electrode to the upper surface of the current supply element 8, so that the tip of the electrode is at a higher level than the upper surface of # '' current supply element 8, i.e. there is a self-regulation of the melting speed of the electrode c.

 The gases released from the weld pool during welding are discharged through the channels 11, 12, 13 of the electrode 6 and of the fold plate 5.

 Once the space between the edges to be welded is filled with molten metal 17, the welding current is cut.

 The slag bath 18 solidifies and a sole 19 is formed at high temperature (9000C).

 During 1.5 mint the temperature of the sole 19 and of the liquid metal 17 drops from 9000C to the solidification temperature of the metal to be welded 2, which in this case is GtS00C. Losing this time, the metal bath 17 d-Feure in the liquid state, which contributes to a maximum evacuation of the gases #### g of the metal forming the joint. The degassing of the metal of the joint ends at the end of this 1.2 min (the degassing time is determined experimentally before welding).

 After solidification of the liquid metal, a welded joint made of a compact metal is obtained.

 The resistance of the metal of the joint is 90-92% that of the metal to be welded, that is to say greater than that obtained in the ace of the known process.

 Metallographic analysis shows the absence of pores in the metal of the vehicle.

 One can also have recourse to a current supply element 20 constituted by a liquid material (FIG. 2).

 Welding is carried out in this case in a manner analogous to that described in the cmsid example of embodiment of the invention.

The nonlimiting exemplary embodiments 2, 3, 4, 5 below are similar to Example 1, the materials used being indicated in the following table
Material material Flow composition,% in
Example of full weight soldering electrode ------------------------------ BaF, CaF2 Si aF KF
BaF2 CaF2 51F NaF KF 2. Titanium Titanium 90.0 5.0 2.0 2.0 1.0 3. Magnesium Magnesium 75.0 10.0 3.0 2.0 10.0 4. Aluminum Aluminum 50.0 20.0 5.0 5.0 20.0 5. Aluminum Aluminum 95.0 2.0 1.5 1.0 0.5
In the case of welding under an electroconductive slag according to Examples 2 and 3, welded assemblies are obtained, characterized by a compact gasket metal. The strength of the metal of the joint is 90.0 and 75.0%, respectively, of that of the metal to be welded.

 Metallographic analysis shows the absence of pores in the metal of the joint.

 When welding l mple 4, the metal of the welded joint has inclusions of solidified slag resulting from the small difference in density between the slag and the metal to be welded.

 In the case of welding according to Example 5, the welded joint has partial weld gaps between the metal of the joint and the edges, due to the insufficient activity of the flux.

 On the basis of the results obtained, it can be concluded that the claimed process of welding under electroconductive slag, the welding flux or stripper and the device for its implementation make it possible to obtain a dense or compact welded joint metal having good mechanical characteristics.

 Of course, the invention is in no way limited to the embodiments described and shown which have been given only by way of example. E; particular, it includes all the means constituting technical equivalents of the means described as well as their combinations, if these are executed according to the spirit and implemented in the context of protection as claimed.

Claims (9)

R E V E N D I C A T I O N S  1. Welding process, under electroconductive slag, in particular of light metals and their alloys, of the co type: - # si. # While preparing a slag bath (18), melting an electrode (U) and the edges to weld and fill with a molten metal the space between said edges, characterized in that, after interruption of the welding current, the metal of the joint is kept in the liquid state by increasing for this purpose the thermal capacity of the slag bath (18).  2. Welding method according to claim 1, characterized in that the metal of the joint is maintained in the liquid state for a period of time greater than that necessary for degassing of the metal of the joint in a proportion of 10 to 15 9 / 0.  3. Welding method according to one of claims 1 and 2, characterized in that, to increase the thermal capacity of the slag bath (18), it increases the volume thereof.  4. Welding method according to the use of claims 1 and 2, characterized in that the increase in the thermal capacity of the slag bath (18) is obtained by using a flux whose melting temperature is higher than that of the metal welding.  5. Welding flux for implementing the method according to one of claims 1, 2 and 4, of the type comprising lithium fluoride and sodium fluoride as well as a potassium salt, characterized in that it further comprises barium fluoride and calcium fluoride, and in that said potassium salt is potassium fluoride.  6. Welding flux according to the dream; dication 5, characterized in that it contains (% by weight) barium fluoride ....................... barium 60.0-90.0 calcium fluoride 5.0-15.0 lithium fluoride 1.0- 5.0 sodium fluoride 1.0-10.0 potassium fluoride ......... ............. potassium 1.0-15.0  t. Welding device for implementing the method according to one of claims 1, 2, 3 and 4, of the type comprising a shell (1), a bottom plate (53, molds (4), a welding electrode (6) and a current supply element (&, characterized in that  the welding electrode is arranged through a hole made in the center of the bottom plate (5), and in that in the gun zone of said electrode is arranged a current resistance element (8) of low resistance .  8. Welding device according to claim 7, characterized in that the current supply element (s) consists of a solid material do t the melting temperature is higher than the welding temperature.  9. Welding device according to claim 7, characterized in that the current supply element (20) consists of a liquid material whose boiling point is higher than the welding temperature and whose density is higher than the density of the slag bath (18), said liquid material of the feed element -e ran (20) and the liquid metal of the electrode (c) ntétart not miscible with each other and being insoluble one in the other.  10. Welding device according to; one of claims 7 and 9, characterized in that the bottom plate () of the shell (i) and the welding electrode (t) comprising internal channels (11, 12, 13) for the evacuation of gases, said channels communicating with each other and being filled with a material allowing the gases to pass.  11. welding device according to claim 10, characterized in that one (12) of the internal channels of the welding electrode is disposed along said electrode and communicates with the other channels (13), formed across said electrode along the entire length thereof.  12. Welded joints characterized in that they are obtained by the process which is the subject of one of the claims 1, 2, 3 and 4.