MOLDING KIT FOR ALUMINOTHERMAL WELDING OF RAILS AND PROCESS FOR ALUMINOTHERMAL WELDING OF RAILS

FIELD OF THE INVENTION

The present invention relates to a thermite weld molding assembly and a thermite weld process for metal profiles, in particular rails, using such a molding assembly.

STATE OF THE ART

Thermite welding of two metal profiles consists in aligning the two metal profiles so that their ends are opposite each other, then in pouring a molten metal in the space between the ends in order to weld the profiles.

To carry out the welding, a mold is used comprising several parts which grip the metal profiles, thus forming a molding cavity containing the ends of the metal profiles to be welded and intended to receive the molten metal.

This type of weld is most often used for welding metal rails, and in particular railroad rails.

Due to the structure of the mold in several parts, and the dimensional differences existing between the metal rails to be welded and the mold, the joints between the parts of the mold on the one hand, and between a part of the mold and the metal rails of on the other hand, are not perfect, and it is therefore necessary to seal the mold before casting the metal.

This operation, called "luting", is conventionally carried out by applying a paste or a coating, sand, or even a binder applied with an extruder gun, in interstices to be filled, before or after setting. place the mold around the metal rails to be welded. These luting products have refractory properties, that is to say they are able to resist contact with molten metal when the latter is poured into the mold cavity, and generally give good sealing results. .

However, the application of these luting products is long and laborious since they need to be deposited with great precision to ensure optimum sealing of the mold. This also generates an additional financial cost for carrying out the weld, due to the purchase and transport of the lute product, sometimes going as far as representing several kilograms per weld.

Lighter products also generate a certain amount of waste that needs to be removed and treated, which has a negative impact on the environment.

DISCLOSURE OF THE INVENTION

The aim of the invention is therefore to remedy the drawbacks of the prior art by proposing a molding assembly comprising a thermite weld mold for metal rails, the wrenching of which is carried out easily and quickly.

Another object of the invention is to provide such a molding assembly in which the molding of the mold is carried out at a reduced financial cost and generates a lower quantity of waste, compared with the molds of the state of the art.

Another aim of the invention is to provide a process for thermite welding of metal rails which uses such a molding assembly.

To this end, the invention relates to a mold assembly for thermite welding of metal rails, comprising at least one mold part configured to come into contact with at least one other mold part and rails to be welded in order to form a mold part. mold cavity in which the ends of the metal rails to be welded are arranged and in which a molten metal is poured to perform the welding of the metal rails, the mold assembly being mainly characterized in that each mold part comprises a configured seat to be placed in contact with at least one of said rails, said bearing surface comprising a groove in which is applied a luting product made of an intumescent material.

Optionally, the molding assembly according to the invention can comprise the following characteristics:

the throat includes:

an internal border, configured to close the mold cavity, an external border configured to separate the groove from the outside of the mold,

a base which extends opposite the rails to be welded, and which connects the internal edge and the external edge,

the lutage product is set back relative to the span, relative to the rail; the bearing surface is provided with a compressible refractory lining capable of coming into contact with the rail during assembly of the mold, the leaching product being applied to said compressible refractory lining;

the mold part comprises a bottom part;

the luting product is in the form of a strip;

the strip is a thermoformed strip or a strip obtained by molding; - the strip is conformable to the mold part;

the intumescent material is selected from one or more of the following chemicals: sodium silicate, calcium silicate, ammonium phosphate, and extruded co-graphite.

Another object of the invention relates to a process for thermite welding of metal rails, in which the ends of the metal rails to be welded are arranged in a mold cavity of a thermite welding mold, said mold comprising at least two mold parts. configured to come into contact with one another and the rails to be welded to form said mold cavity, each mold part comprising a bearing surface configured to be placed in contact with at least one of said rails, said bearing surface comprising a groove, the method comprising a step of casting a molten metal in the molding cavity, the method being mainly characterized in that it comprises, prior to the step of casting the metal in the molding cavity, an application step ofa luting product made from an intumescent material in the throat.

Optionally, the method according to the invention can comprise the following characteristics:

the method comprises a step of preheating the mold prior to the step of pouring the metal into the molding cavity, the luting product being applied before said preheating step;

the luting product is applied before the assembly of the mold parts with the rail to form the mold cavity;

the luting product is applied so as to be set back from the bearing, relative to the rail;

the bearing surface being provided with a compressible refractory coating capable of coming into contact with the rail during assembly of the mold, the leaching product is applied to said compressible refractory coating;

the luting product is in the form of a strip, the method comprising a step of shaping the strip prior to its application to a mold part;

the strip is a thermoformed strip or a strip obtained by molding; the strip is conformed to the mold part during its application;

the luting product is in the form of a liquid, preferably chosen from mastic or coating;

the method further comprises, before the casting of the molten metal in the molding cavity, a step of applying the liquid to said at least one surface of the mold part facing the rail;

the application of the liquid is carried out by means of a brush, a knife, an extruder gun, or a high pressure piston;

the intumescent material comprises sodium silicate.

DESCRIPTION OF FIGURES

Other advantages and characteristics of the invention will become apparent on reading the following description given by way of illustrative and non-limiting example, with reference to the appended figures which represent:

FIG. 1, a perspective diagram of a part of a mold for thermite welding of metal rails, according to one embodiment of the invention; Figure 2, a perspective diagram of the mold part shown in Figure 1, which is provided with a ligation product made of an intumescent material, which is in the form of a thermoformable strip;

Figure 3, a diagram of a thermoformable strip of intumescent material; Figure 4, a side view diagram in section of a mold formed by assembling two parts identical to that of Figure 2 on either side of the ends of the two rails to be welded in order to grip said rail ends , according to one embodiment of the invention;

FIGS. 5A to 5C, schematic diagrams of the successive steps of placing a mold part provided with a compressible refractory lining of the felt type on a rail;

FIGS. 6A to 6D, block diagrams of the successive steps of placing a mold part without a compressible refractory lining on a rail; FIGS. 7A to 7D, schematic diagrams of the successive stages of placing a mold part without a compressible refractory lining, the bearing surface of which comprises a groove,

Figures 8A to 8D, diagrams of grooves of different shapes,

Figure 9, a perspective diagram of a mold part, the seat of which includes grooves as shown in Figures 7A to 7D.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

A first object of the invention relates to a molding assembly comprising a thermite weld mold of metal profiles, and more particularly of metal rails.

Such a mold 100 consists of two mold parts 1 having a substantially identical structure, one part of which is shown in Figure 1 according to one embodiment, and a bottom part 50. The two parts 1 are adapted to be assembled with each other, as well as to the bottom part 50, in order to form the mold 100 containing the ends 31 of the rails to be welded 30.

Referring to Figure 1, each mold part 1 comprises an upper face 2, a lower face 3, and side faces 4, 5 joining the upper 2 and lower faces 3. The mold part 1 consists of a part upper 6 configured to be assembled to the corresponding upper part of a second mold part, and a lower part 7 configured to come into contact with the ends 31 of the rails in order to grip them.

The mold parts 1 and 50 are made of a rigid and refractory material, that is to say a material having good mechanical strength and which is able to withstand very high temperatures, and in particular, the temperature of the weld metal in the liquid state with which it comes into contact.

The mold part 1 is hollowed out in its entire length, from its upper face 2 to its lower face 3, so as to delimit two internal lateral surfaces 9 facing each other with respect to a longitudinal plane P1 , and connected by a bottom 10. The internal side faces 9 are themselves hollowed out so as to form, with the bottom 10, one half of a pouring chamber 101 (shown in Figure 4) of the weld metal. liquid state, the latter conventionally coming from a crucible of refractory material arranged above the pouring channel.

Directional and positioning terms such as in particular “above”, and

“Below”, “top”, “bottom”, “upper”, or even “lower” refer to the arrangement of the various constituent elements of the mold parts, or of the elements which cooperate with the mold parts, according to a conventional use of the mold, in which the mold parts are mounted on a rail whose shoe rests on a support (generally the ground) transverse to the longitudinal plane P1 of the mold parts.

The front face 4 of the mold part 1 is provided with two contact surfaces 8 intended to come into contact with the two corresponding contact surfaces of the second mold part 1 during assembly of the mold 100.

The lower part 7 of the mold part 1 comprises two edges 1 1, called internal edges, which extend from the lower end of the contact surfaces 8 where they form slope breaks 12, to the lower end of mold part 1. The internal borders 1 1 are delimited laterally by the internal lateral surfaces 9 and by the external lateral surfaces 5 of the mold part.

Each internal edge 1 1 comprises a bearing 13 which extends along said edge, configured to come into contact with a rail end 31 during assembly of the mold 100. The bearing surfaces 13 define, with the internal side surfaces 9 and the bottom 10 of the mold, once said assembled mold shown in Figure 4, a molding cavity 102, or molding chamber, containing the ends 31 of the rails to be welded and the space between the rails 30, and intended to receive the liquid metal from the casting chamber 101.

The staves can be covered with a felt. The felt is a material well known in itself, consisting of refractory and compressible fibers bound by a refractory binder, applied to the bearing surfaces of the mold parts by means of a suitable glue,

in order to close the mold cavity. Reference may be made to document WO 2007/031528 for a description of such a mold provided with felt.

In the remainder of the description, P2 denotes the longitudinal plane of symmetry separating the rails 30 in their length into two sides of rails situated on either side of this plane, the plane P2 being perpendicular to the plane P1 and transverse to the plane of the rail support 30.

Each of the two bearing surfaces 13 is hollowed out, so as to define a high bearing surface 14 whose shape corresponds to that of one side of the head 33 of the rail 30, an intermediate bearing 15 whose shape corresponds to that of one side of the web 34 of the rail, and a low bearing surface 16, the shape of which corresponds to that of one side of the shoe 35 of the rail.

The high bearing 14 is in the form of a recess. It comprises a high portion 14a whose shape corresponds to the top of the head 33 of the rail 30, an intermediate portion 14b whose shape corresponds to a lateral edge of the head 33, and a lower portion 14c whose shape corresponds to the base of the head 33 .

The intermediate bearing surface 15 is in the form of a projection, the shape of which corresponds to that of the web 34 of the rail 30.

The low span 16 is in the form of a recess. It comprises a high portion 16a whose shape corresponds to the top of the shoe 35 of the rail 30, and a low portion 16b whose shape corresponds to a lateral edge of the shoe 35.

An internal edge 1 1 defines an external recess 20 in the corresponding external side face 5 of the mold part 1, at said edge 1 1. The external recess 20 extends along the edge 1 1, it is that is to say from the lower end of the contact surfaces 8 to the lower face 3 of the mold part 1.

The outer recess 20 is itself formed of a first outer surface 21 which extends from the bearing 13 perpendicular to said bearing, and a second surface 22 which extends from the first surface 21 perpendicular to said first surface, and therefore substantially parallel to the bearing 13.

A chamfer 23 is produced in the angle joining the surface of the upper part 6 of the part and the upper bearing surface 14. The shape of the chamfer 23 corresponds to the top of the head 33 of a rail end.

The mold part 1 further comprises a cooling pipe 24, one end of which opens onto the upper face 3 of the mold part towards the outside of the mold 100, and the other end opens into the molding cavity. 102, at the level of the top surface 14. Cutouts are advantageously made in the contact surfaces 8 and in the internal lateral faces 9, and constitute passageways for the circulation of the solder metal in the liquid state between the casting chamber 101. metal and cooling pipes 24.

In order to mount the mold 100 shown in FIG. 4 and proceed with the welding of the two ends of the rails, two mold parts 1 such as that described above are assembled on the bottom part 50.

The contact surfaces 8 of the two mold parts 1 come into contact with one another, on either side of the plane P2, thus forming the casting chamber 101 for the metal.

For each part of the mold, the bearing surfaces 13 of the lower part 7 come into contact with one side of the two ends 31 of the rails 30 to be welded.

In this configuration, the bottom 10 of the mold parts is located opposite the space between the two rail ends.

In detail, a first bearing 13 covers a first side of the first rail end, a second bearing 13 covers the first side of the second rail end, in a manner analogous to the first bearing.

The same applies respectively to the second mold part mounted on the second side of the two rail ends.

When the two mold parts 1 are mounted on the ends 31 of the rails to be welded, the two surfaces 13 of the first mold part mounted against each of the two rail ends on a first side of said rails, and the two surfaces of the second mold part mounted against each of the two rail ends on a second side of said rails, form a molding impression 102 which extends around the ends 31 of the rails and the space separating said rail ends. The molding cavity 102 is preferably closed by the bottom part 50 able to be connected to the lower surface 3 of each mold part 1, so that the surfaces of said bottom part 50 are connected to the respective surfaces 13. first and second mold parts 1.

During the casting of the metal in liquid form in the mold 100, the metal flows along the casting chamber 101 to the mold cavity 102 where it fills the space between the ends 31 in order to weld the ends. rails 30 by thermite reaction. The metal vapors and the products of the thermite reaction are discharged from the mold via the cooling pipes 24.

A luting product 40, made of an intumescent material, is applied to one or both of the mold parts 1. It can be applied to the mold parts before their assembly on the rails to be welded or directly on the assembled mold 100.

The material is said to be “intumescent” in that it is able to swell under the effect of the heat caused by an increase in the temperature of the mold, in particular within the mold cavity, so as to form a system. foam which is for example in the form of a foam or a solid shell. In practice, the intumescent material is configured to expand during the implementation of a so-called preheating step carried out before the metal is poured into the mold, and allowing a gradual rise in temperature of the mold and the rail in order to facilitate melting the metal and removing moisture from the mold. The expansion of the intumescent material is triggered when it is subjected to a temperature called "threshold temperature", depending on its physical and chemical properties.

Preferably, the intumescent material is selected from one or more of the following chemicals: sodium silicate, calcium silicate, ammonium phosphate, and extruded co-graphite.

According to a first embodiment, the luting product 40 is in the form of a strip 41 shown in FIG. 3. The strip 41 is shaped so that its shape corresponds to that of the surface of the mold part. to which it must be applied later.

The strip 41 can be thermoformable in that it is shaped at high temperature, prior to its mounting on the mold part 1 or 50, the forming temperature of the strip being a function of the physical and chemical characteristics of the material. intumescent, and being in practice much lower than its threshold temperature.

Alternatively, the strip 41 can be molded in order to have the desired shape, and then be applied to the mold part.

The strip 41 can be flexible or rigid depending on the nature of its constituent material and its dimensions. However, a flexible strip will be preferred in order to facilitate the shaping of the strip to the mold part.

This first embodiment offers the advantage of providing a “ready-to-use” luting product, in that it suffices to apply the strip 41 already formed on the surface concerned, in particular by gluing for example, which is quick and easy to do.

According to a second embodiment, the luting product 40 is in the form of a liquid product to be applied to the mold part. The term "liquid" refers to a liquid of low viscosity (for example a viscosity close to that of water, that is to say approximately 1 * 10 "3 Pa.s) or of high viscosity (for example a viscosity close to that of water). motor oil, i.e. approximately 0.2 Pa.s). However, a sufficiently high viscosity to be able to easily apply the product to the surface (s) concerned, while preventing the product from flowing, is preferred. on other surfaces to which it is not intended to be applied.Also make sure to choose a liquid product which requires a reduced drying time compared to that of the

The liquid product is preferably mastic or filler.

This second embodiment offers the advantage of providing a wringing product 40 which can be applied to areas of complex shapes, without leaving areas to be protected which are not yet covered with the product.

The luting product isolates the mold cavity 102 from the outside environment, preventing liquid metal from exiting the mold cavity during the molding operation.

The luting product is positioned on at least one surface of the mold part 1 or 50, this surface being configured to be placed facing the rail 30 to be welded.

The wrench tends to deteriorate when exposed to too much heat, especially over a long period of time. Thus, the luting product is preferably positioned at a distance from the rail ends, so that it expands during the preheating step, while preventing it from being too exposed to heat and from degrading. Too rapid degradation of the physicochemical structure of the intumescent material constituting the luting product would in fact lead to an inability of the luting product to seal the mold until the metal solidifies.

The luting product is applied to the mold parts so as to be in the vicinity of the mold cavity 102, and preferably outside said mold cavity. This ensures the sealing of the molding cavity 102 while avoiding direct contact between the metal and the luting product during the casting of the metal in the mold 100 which could cause burrs at the junction between the rail. and the bearing surface of the mold against the rail.

However, provision can be made to position the luting product at the junction between the rail and the bearing surface of the mold against the rail (in particular on a bearing surface 13, possibly coated with a felt). In this case, the luting product is liable to come into contact with the molten metal. We therefore choose a luting product capable of structurally resisting contact with the molten metal.

The lute expands in the junction during the preheating step, then filling said junction, and then the metal comes into contact with the expanded lute during the molding step.

When the stave is covered with a felt, the expansion of the luting product compresses the felt even more. This offers the advantage of allowing the felt to compensate for the shrinkage of the wrenching product when said wrenching product is at the end of its life.

According to this embodiment, the structural and mechanical characteristics of the mold parts, and when the felt is present, are adapted so as to avoid any detachment of the bearing surfaces from the rails which could lead to poor sealing of the mold.

According to a preferred embodiment of the invention, with reference to Figures 2 and 3, the luting product 40 is applied in the external recess 20 delimited by an internal border 11 of the mold part. It is applied to the second surface 22 of the recess so as to cover said second surface. In addition, depending on the thickness of product applied, it also covers, at least partially, the first surface 21 of the recess. In the case where the luting product is a thermoformable strip 41 as shown in FIG. 3, the upper portion 42 of the strip has a shape corresponding to that of the upper bearing 14, and is applied thereto. Likewise,

It is of course possible if necessary to apply the luting product 40 in the external recess 20 so as to cover only part of the second surface 22, that is to say a part of its length which s 'extends from the slope break 12 to the underside 3 of the part, and / or a part of its width which extends from the first surface 21 to the outer side surface 5 of the mold part. This may be appropriate if the luting product is only intended to isolate only a part of the mold cavity 102, and in fact reduces the time required for the application of said luting product as well as the amount of product needed.

During the step of preheating the mold 100, the temperature within the mold increases to a preheating temperature close to the temperature of the molten metal cast subsequently. The preheating temperature can in particular be equal to the temperature of the liquid metal. The rise in temperature of the mold during preheating causes an increase in temperature in and outside the mold cavity 102, in particular near the mold cavity. When the threshold temperature is reached, the luting product 40 expands and then occupies the entire volume of the external recess 20, preventing the metal from leaving the mold cavity 102 via the junction between the surfaces 13 of the mold parts and the rails 30.

What has been described above concerning the application of the luting product to a surface of a mold part 1 also applies to the bottom part 50. The luting product can thus be applied in particular on the surfaces 18 of the bottom part 50, in accordance with what has just been described, the surfaces 18 optionally comprising a felt.

Figures 5A-C and 6A-D illustrate the behavior of the wringing product during its application to a mold part according to the previous embodiment, and during the subsequent molding operation. The luting product 40 is applied in the external recess 20 delimited by an internal border 11 of the mold part.

Referring to Figures 5A, 5B, and 5C, the mold 100 is a mold with felt. The presence of a felt 17 overcomes a sometimes laborious step of shortening the thickness of the internal border 1 1, in particular by scraping the excess sand when the part is agglomerated sand, in order to '' adjust the distance between part 1 of the mold and the rails 30.

In accordance with FIG. 5A, a certain quantity of the luting product 40 is applied in the external recess 20, prior to the assembly of the mold. The felt 17 constitutes an edge of the mold part, the bearing surface 13 of which is intended to come into contact with a rail 30 to be welded. The felt 17 is in the free state (uncompressed) and has a predetermined thickness denoted E F o- The scope 1 1 of the felt 17 and the surface 45 of the luting product facing the rail are offset with respect to one another. the other of a withdrawal noted R 0 .

In accordance with FIG. 5B, mounting the mold part on the rail causes compression of the felt 17, the thickness of which is reduced, from E F o to E F i. The shrinkage R 0 decreases as a function of the compression of the felt up to a value Ri. The preheating of the mold, prior to the casting of the metal, causes the expansion of the luting product 40 which then fills the volume of the recess 20 and overflows slightly outside the recess, as illustrated in FIG. 5C.

In addition to preserving its structural integrity, the positioning of the luting product 40 outside the molding cavity 102, and the presence of the internal border 1 1 provided with a felt separating the luting product and the imprint molding, makes it possible to prevent the luting product 40 from expanding in the junction between the bearing surfaces 13 and the rails 30, which could lead to an effect opposite to that sought, namely a slight detachment of the bearing surfaces 13 by compared to the rails 30 and poor sealing of the mold.

The shrinkage R 0 between the bearing surface 13 of the felt 17 and the surface 45 of the luting product is advantageously chosen so as to allow good compression of the felt. In other words, the felt 17 must be able to be compressed in the desired state of compression, without, however, the wringing product 40 coming into contact with the rail 30 before expansion. When the felt 17 is compressed, the luting product 40 therefore remains separated from the rail 30 by withdrawal

The shrinkage R 1 remaining after compression of the felt allows the leaning product to expand properly throughout the volume of the recess 20, without overflowing too much outside said recess.

Referring to Figures 6A, 6B, 6C, and 6D, the mold is a non-felt mold. The inner edge 1 1 is therefore made of the same material as the rest of the part 1 of the mold.

In accordance with FIG. 6A, a certain quantity of the luting product 40 is applied in the recess 20, prior to the assembly of the mold.

In accordance with Figure 6B, the internal edge 1 1 is then shortened, for example by scraping off the excess sand when the part 1 is made of agglomerated sand, in order to adjust the contact between the mold part 1 and the desired manner. rail 30. In doing so, the thickness of the edge 1 1 changes from E B o to E B i, and the shrinkage R 0 between the span of the edge and the surface of the recess 20 facing the rail decreases to a value

Similar to the previous embodiment with the felt mold, the internal border 1 1 separates the luting product 40 from the molding cavity 102, thus avoiding any direct contact between the metal and the luting product during a subsequent step of pouring the metal into the mold.

Furthermore, the withdrawal R 0 between the bearing surface 13 and the surface 45 of the luting product is advantageously chosen so as to allow a predetermined shortening of the internal edge 1 1 in order to position the mold part 1 at a desired distance from the rail 30 In other words, the edge 11 must be able to be shortened as desired, without however the luting product 40 coming into contact with the rail before expansion.

When the edge 1 1 is shortened, the luting product 40 therefore remains separated from the rail

30 by withdrawal

It goes without saying that the invention is not limited to the structure of the mold as illustrated but that it applies to any thermite welding mold, whatever the number and the shape of the mold parts constituting it. . In addition, the intumescent luting product can be applied to all of the mold parts, or to only some of them.

Figures 7A, 7B, 7C, and 7D illustrate the behavior of the wringing product during its application to a mold part as described above, and during the subsequent molding operation. Unlike the previous embodiment described in support of Figures 6A to 6D, the bearing 13 comprises a groove 60 separated from the outside of the mold. According to the embodiment shown, the groove 60 is delimited both by the internal edge 1 1, but also by an external edge 61 which is arranged adjacent and at a distance from the internal edge, relative to the length of the rail and which separates said groove 60 from the outside of the mold.

In accordance with FIG. 7A, a certain quantity of the luting product 40 is applied in the groove 60, prior to the assembly of the mold. The luting product can be applied to one or more of the surfaces of the groove 60 which are the first surface 21, the second surface 22 which forms the bottom of the groove, and the third surface 63 of the outer rim 61.

According to Figure 7B, the inner edge 1 1 and the outer edge 61 are then shortened, for example by scraping the excess sand when the part 1 is agglomerated sand, in order to adjust the contact between the sand as desired. mold part 1 and the rail 30. In doing so, the thickness of the internal edge 1 1 and of the external edge 61 changes from E B o to E B i, and the withdrawal R 0 between the bearing 13 and the surface 45 of the luting product 40 opposite the rail decreases to a value Ri. For a good fit of the mold with the rail, the inner edge 1 1 and the outer edge 61 are shortened to the same thickness E B i.

Referring to Figures 7C and 7D, the mold part 1 is then mounted on the rail 30 and the preheating of the mold, prior to the casting of the metal, causes the expansion of the luting product 40 which then fills the volume of the groove 60.

The outer rim 61 separates the luting product 40 from the outside of the mold, thus avoiding any overflow of the luting product out of the groove 60, outside the mold, during its expansion.

The inner edge 1 1 separates the luting product 40 from the molding cavity 102, thus avoiding any direct contact between the metal and the luting product during a subsequent step of casting the metal in the mold.

The withdrawal R 0 between the bearing 13 and the surface 45 of the luting product is advantageously chosen so as to allow a predetermined shortening of the internal edge 1 1 and of the external edge 61 in order to position the mold part 1 at a desired distance of the rail 30. In other words, the inner edge 11 and the outer edge 61 must be able to be shortened as desired, without however the luting product 40 coming into contact with the rail before expansion. When the inner edge 1 1 and the outer edge 61 are shortened, the luting product 40 therefore remains separated from the rail 30 by the withdrawal Ri.

Referring to Figures 8A, 8B, 8C, and 8D, the groove 60 can be in different forms, as long as there is a continuity of the internal borders 1 1 and external 61 defining the groove, it being understood that the height of said edges internal and external is likely to vary along the groove depending on the thickness of sand to be removed to adjust the mold.

The groove 60 may for example be rounded, polygonal, or else angular.

FIG. 9 illustrates a mold part, the bearing surface 13 of which comprises two grooves 60, each being separated from the molding cavity by an internal edge 1 1 and separated from the outside of the mold by an external edge 61.

The luting product 40 is applied in the grooves 60, prior to mounting the mold. The luting product 40 covers the bottom 22 of the groove, and partially covers the first surface 21 of the inner edge 1 1 and the third surface 63 of the outer edge 61.

CLAIMS

Molding assembly for thermite welding of metal rails (30), comprising at least one mold part (1, 50) configured to come into contact with at least one other mold part (1, 50) and rails (30 ) to be welded in order to form a molding cavity (102) in which the ends (31) of the metal rails to be welded are arranged and in which a molten metal is poured to carry out the welding of the metal rails (30), the assembly mold being characterized in that each mold part (1, 50) comprises a bearing surface (13) configured to be placed in contact with at least one of said rails (30), said bearing surface (13) comprising a groove (60) in which is applied a luting product (40) of an intumescent material.

A molding assembly according to claim 1, wherein the groove (60) comprises:

an internal border (1 1), configured to close the molding cavity (102),

an outer edge (61) configured to separate the groove (60) from the outside of the mold,

a bottom which extends opposite the rails (30) to be welded, and which connects the inner edge (1 1) and the outer edge (61).

Molding assembly according to one of claims 1 or 2, in which the wringing product (40) is set back relative to the bearing surface (13) relative to the rail (30).

A mold assembly according to any preceding claim, wherein the mold part (1, 50) comprises a bottom part (50).

A molding assembly as claimed in any one of the preceding claims, in which the luting product (40) is in the form of a strip (41).

6. A molding assembly according to claim 5, wherein the strip is a thermoformed strip or a strip obtained by molding.

7. Molding assembly according to one of claims 5 or 6, wherein the strip is conformable to the mold part.

8. A molding assembly according to any preceding claim, wherein the intumescent material is selected from one or more of the following chemicals: sodium silicate, calcium silicate, ammonium phosphate, and extruded co-graphite,

9. A method of thermite welding of metal rails (30), in which the ends (31) of the metal rails to be welded are arranged in a mold cavity (102) of a thermite welding mold (100), said mold (100). ) comprising at least two mold pieces (1, 50) configured to come into contact with each other and rails (30) to be welded to form said mold cavity (102), each mold piece (1 , 50) comprising a bearing surface (13) configured to be placed in contact with at least one of said rails (30), said bearing surface (13) comprising a groove (60), the method comprising a step of casting a metal into it. melting in the molding cavity (102), the method being characterized in that it comprises, prior to the step of casting the metal in the molding cavity (102),a step of applying a luting product (40) made from an intumescent material in the throat (60).

10. The method of claim 9, comprising a step of preheating the mold (100) prior to the step of casting the metal in the molding cavity (102), the luting product (40) being applied before said step of preheating.

1 1. A method as claimed in claim 9, in which the luting product (40) is applied before the assembly of the mold parts (1, 50) with the rail (30) to form the mold cavity (102).

12. The method of claim 9, wherein the luting product (40) is applied so as to be set back relative to the bearing (13), relative to the rail (30).

13. Method according to one of claims 9 to 12, wherein the luting product (40) is in the form of a strip (41), the method comprising a step of shaping the strip (41). prior to its application to a mold part (1, 50).

14. The method of claim 13, wherein the strip is a thermoformed strip or a strip obtained by molding.

15. Method according to one of claims 13 or 14, wherein the strip is conformed to the mold part during its application.

16. A method according to any one of claims 9 to 12, wherein the wrenching product (40) is in the form of a liquid, preferably chosen from mastic or coating.

17. The method of claim 16, further comprising, before casting the molten metal in the mold cavity (102), a step of applying the liquid to said at least one surface (21, 22) of the part. (1, 50) of the mold facing the rail (30).

18. The method of claim 17, wherein the application of the liquid is carried out by means of a brush, a knife, an extruder gun, or a high pressure piston.

19. Method according to one of claims 9 to 18, wherein the intumescent material comprises sodium silicate.