| CLAIMS 1. A process for fusion welding rail ends of two adjacent rails, the process comprising the steps of - aligning the to-be-welded rails so as to define an inter-rail gap between the rail ends; providing a mould assembly comprising two upright side moulds that are fitted on either side of the inter-rail gap, each side mould including at least one elongate, open-ended down gate extending between a top part and a bottom part of the side mould and terminating in a down gate well; a base mould adapted for receiving the rail ends and for supporting the side moulds on either side of the inter-rail gap; the arrangement being such that the base mould and side moulds cooperate to define an enclosed mould cavity for receiving molten weld material; and receiving means for receiving molten weld material in at least one of the side moulds and arranged in flow communication with the down gate; and side-pouring molten weld material into the receiving means such that the molten weld material is transported from the receiving means, down the down gate of the side mould and into the base mould to form a rail foot, from where the molten weld material rises into the inter-rail gap to form the web and rail head of the rail weld. 2. The process according to claim 1 wherein the receiving means is a refractory receiving bowl which is removably located in the top part of a side mould and which terminates in a bottom diverting slot. 3. The process according to claim 2 wherein the receiving bowl is positioned in the side mould such that the diverting slot is arranged directly above the down gate of the side mould. 4. The process according to anyone of claims 1 to 3 comprising the step of pouring molten weld material from an overhead crucible, which is positioned above the side mould and off-centre from the rail head, into the receiving bowl, such that the molten weld material is transported via the down gate into the down gate well, which is located directly below the down gate of the side mould, the mould assembly being dimensioned such that upon entering the down gate well, velocity of the molten weld material is reduced so that the molten weld material enters the inter-rail gap with reduced velocity and no turbulence. 5. The process according to claim 1 wherein each side mould includes downwardly depending base mould engaging means extending from the base of the side mould, the base mould engaging means being dimensioned to engage complimentarily dimensioned side mould engaging means, which extend upwardly from the base mould, when the side moulds sit on top of the base mould. 6. The process according to claim 1 wherein the mould assembly is characterised therein that when the side moulds sit on top of the base mould, the base of the side moulds are level with the top of the rail foot. 7. The process according to claim 1 wherein the base mould defines a substantially central rail foot well in which molten weld material enters to form the rail foot; at least one down gate well laterally disposed relative to the rail foot well; and side mould engaging means extending upwardly from the base mould and dimensioned to engage complimentarily dimensioned base mould engaging means on the side moulds for supporting the side moulds. 8. The process according to claim 7 wherein the side mould engaging means are positioned on lateral opposite ends of the base mould, which ends extend beyond the rail foot such that the side moulds sit on top of the lateral opposite ends of the base mould. 9. The process according to claim 1 wherein the base mould includes two down gate wells located in lateral opposite ends of the base mould and positioned directly below the down gates of the side moulds, each down gate well being dimensioned to receive molten weld material from the down gate in the side mould, to reduce the velocity of the molten weld material and to direct a stream of molten weld material towards the rail foot well in such a way that it reduces turbulence of the weld material, the mould assembly being dimensioned such that the inter-rail gap is filled from the bottom upwards, through molten weld material that enters the rail foot well and rises not only to fill the inter-rail gap, but also the down gate of the opposite side mould. 10. The process according to claim 1 wherein the base mould defines two opposed rail receiving profiles on opposite sides of the base mould for snugly receiving the rail ends of the to-be-welded rails. 11. The process according to claim 7 or claim 10 wherein the rail foot well is defined intermediate the down gate wells, the side mould engaging means, and the rail receiving profiles. 12. The process according to claim 7 wherein the base mould includes a fracture rib between the rail foot well and each of the down gate wells, which allows, after solidification and at black heat, for the down gates and down gate wells to be removed with a hammer. 13. The process according to claim 2 wherein the mould assembly includes a knock-off core which is removably positioned between the two side moulds and centrally above the rail head and which is adapted to receive molten weld material to form a head metal riser section, the mould assembly being dimensioned such that the receiving bowl at least partially overlaps the knock-off core from above, forcing the knock-off core downwardly towards the rail head. 14. The process according to claim 13 including the steps of - preheating the enclosed mould cavity with a preheating burner; inserting the knock-off core between the two side moulds and centrally above the rail head; inserting the receiving bowl in the top part of one of the two side moulds above the knock-off core, such that it at least partially overlaps with the knock-off core from above, thus forcing the knock- off core downwardly towards the rail head; side-pouring molten weld material into the receiving bowl such that the molten weld material is transported from the receiving means, down the down gate of the side mould and into the base mould to form the rail foot, from where the molten weld material rises upwardly into the inter-rail gap to form the web and head of the rail weld and at least partially to fill the knock-off core, the arrangement being such that the receiving bowl sits firmly against the knock-off core, holding it in position and preventing the knock-off core from rising when the molten weld material fills the inter-rail gap and the knock-off core. 15. The process according to claim 14 including the step of removing the knock-off core with a hammer, together with the down gates and mould refractories, after solidification and when the molten weld material in the inter-rail gap has reached a black heat. 16. The process according to claim 1 including the further step of sealing the side moulds and base mould where they engage each other and the rails by firmly placing luting putty within luting grooves defined between the side moulds, base mould and the rail ends. 17. The process according to claim 1 wherein the side moulds define a head rising room in an upper part of the side moulds for receiving molten material rising from the inter-rail gap and the down gates, the head rising room being dimensioned to contain all slag in the head rising room and on top of the molten weld material. 18. A mould assembly for use in fusion welding rail ends of two adjacent rails, the mould assembly comprising - two upright side moulds that are fitted on either side of an inter-rail gap defined between the rail ends, each side mould including at least one elongate, open-ended down gate extending between a top part and a bottom part of the side mould and terminating in a down gate well; a base mould adapted for receiving the rail ends and for supporting the side moulds on either side of the inter-rail gap; the arrangement being such that the base mould and side moulds cooperate to define an enclosed mould cavity for receiving molten weld material; and receiving means for receiving molten weld material in at least one of the side moulds and arranged in flow communication with the down gate. 19. The mould assembly according to claim 18 wherein the receiving means is a refractory receiving bowl which is removably located in the top part of a side mould and which terminates in a bottom diverting slot. 20. The mould assembly according to claim 18 wherein each side mould includes downwardly depending base mould engaging means extending from the base of the side mould and dimensioned to engage complimentarily dimensioned side mould engaging means, which extend upwardly from the base mould, when the side mould sits on top of the base mould. 21. The mould assembly according to claim 18 characterised therein that when the side moulds sit on top of the base mould, the base of the side moulds are level with the top of the rail foot. 22. The mould assembly according to claim 18 wherein the base mould defines a substantially central rail foot well in which molten weld material enters to form the rail foot; at least one down gate well laterally disposed relative to the rail foot well; and side mould engaging means extending upwardly from the base mould and dimensioned to engage complimentarily dimensioned base mould engaging means on the side moulds for supporting the side moulds. 23. The mould assembly according to claim 22 wherein the side mould engaging means are positioned on lateral opposite ends of the base mould, which ends extend beyond the rail foot such that the side moulds sit on top of the lateral opposite ends of the base mould. 24. The mould assembly according to claim 18 wherein the base mould defines two opposed rail receiving profiles on opposite sides of the base mould for snugly receiving the rail ends of the to-be-welded rails. 25. The mould assembly according to claim 22 or claim 24 wherein the rail foot well is defined intermediate the down gate wells, the side mould engaging means, and the rail receiving profiles. 26. The mould assembly according to claim 22 wherein the base mould includes a fracture rib between the rail foot well and each of the down gate wells. 27. The mould assembly according to claim 19 wherein the mould assembly includes a knock-off core which is removably positioned between the two side moulds and centrally above the rail head and which is adapted to receive molten weld material to form a head metal riser section, the mould assembly being dimensioned such that the receiving bowl at least partially overlaps the knock-off core from above, forcing the knock-off core downwardly towards the rail head. 28. The mould assembly according to claim 18 wherein the side moulds define a head rising room in an upper part of the side moulds for receiving molten material rising from the inter-rail gap and the down gates. 29. A process for fusion welding rail ends of two adjacent rails according to claim 1 substantially as herein described and exemplified. 30. A mould assembly for use in fusion welding rail ends of two adjacent rails according to claim 18, substantially as herein described and exemplified. |
BACKGROUND TO THE INVENTION
The invention relates to fusion welding of rails to form substantially
continuous railway tracks. In particular, it concerns a new process and
mould assembly for use in aluminothermic intercast welding of rail ends.
Fusion welding of rail ends, and in particular aluminothermic welding, is one of the established, internationally accepted procedures for in situ welding of rails and utilises the high affinity of aluminum for oxygen for the reduction of iron oxide. In general, the procedure comprises aligning rails to be joined together, leaving a prescribed inter-rail gap between adjacent rail ends, and
fitting preformed refractory moulds around the inter-rail gap between the rail ends to form an enclosed mould cavity. An especially designed preheating burner is used to preheat the refractory moulds and the enclosed mould cavity for removal of all water vapour and to preheat the rail ends. Superheated molten steel is then intercast into the mould cavity from a refractory crucible located above the refractory moulds, and allowed to solidify in the mould cavity to form a rail weld in the inter-rail gap between adjacent rail ends. After solidification, refractory materials and surplus steel are removed from the rail weld, and after further cooling, rail fastenings are replaced and rail heads are grinded back to profile.
The quality of the rail weld between the rail ends is of critical importance when it comes to wear resistance of railways and their ability to handle increasing rail traffic and axle loads. In particular, rail welds need to be homogenous, with fine grained, hard weld material concentrated in the rail head, and as little as possible slag-losses of alloying additives. Moreover, intimate thorough mixing of the casting steel within the mould cavity must be avoided at all costs, otherwise a concentration of alloying additives in the rail head cannot be achieved. In some countries, the weld is ultrasonically and radiographically tested. However, radiographic testing of rail welds is not permitted in all countries and in such cases only ultrasonic testing of the rail welds is performed.
Most commonly-used processes for aluminothermic welding of rails employ top-pouring refractory moulds having a diverting plug, made from silica sand and bound with sodium silicate. One such a process is described in patent number US 6,227,282, which includes the steps of surrounding to- be-welded rail ends with a refractory mould, which includes a diverting plug fitted in an upper region of the mould covering a rail head of the to-be- welded rail ends. A metal stream is top-poured from an overhead reaction crucible into the refractory mould over the diverting plug, such that it impinges on the diverting plug. The metal stream is transported into the mould cavity from the top and subsequently fills the mould cavity to form a rail foot, web and rail head, with two risers extending upwardly from the rail foot.
Top-pouring processes incorporating a diverting plug suffer from two major disadvantages. The first disadvantage is that during the top-pouring operation the metal stream is dispersed, causing turbulence in the mould cavity. Due to the high temperature of the metal stream, the dispersed liquid metal droplets oxidise. These oxidised liquid metal droplets must then reform a complete metal liquid before arriving at the bottom of the mould cavity, but this often does not happen, resulting in unwanted gas becoming entrapped in the rail weld. This undesirable gas generation resulting from the pouring process can cause gas holes in the weld metal after solidification and leads to ultrasonic and/or radiographic examination failure.
After solidification, the refractory moulds and risers are broken away from the rail weld. The next step is to shear off excess riser material from the rail head. The excess material on top of the rail head cannot be removed at the same time when the moulds and risers are broken away because of the particular designs of currently available moulds. It is here where the second disadvantage lies, because of the critical temperature at which the excess material must be sheared. It must be sheared after partial solidification, because the weld material becomes extremely hard and difficult to remove after complete solidification. Expert on-site knowledge is required to know exactly when sufficient partial solidification is achieved for the shearing step of each rail weld.
There is therefore a need for an in situ fusion welding process which consists of a single process step characterised in providing metals or metalloids in a controlled manner into the mould cavity with the least amount of turbulence so as to concentrate these alloying additives in a weld head, thereby to produce a rail weld that includes a rail head of hard weld material, and a rail foot that is less prone to breakage.
SUMMARY OF THE INVENTION
According to the invention there is provided a process for fusion welding rail ends of two adjacent rails, the process comprising the steps of - aligning the to-be-welded rails so as to define an inter-rail gap between the rail ends;
providing a mould assembly comprising
two upright side moulds that are fitted on either side of the inter-rail gap, each side mould including at least one elongate, open-ended down gate extending between a top part and a bottom part of the side mould and terminating in a down gate well;
a base mould adapted for receiving the rail ends and for supporting the side moulds on either side of the inter-rail gap; the arrangement being such that the base mould and side moulds cooperate to define an enclosed mould cavity for receiving molten weld material; and
receiving means for receiving molten weld material in at least one of the side moulds and arranged in flow communication with the down gate; and
side-pouring molten weld material into the receiving means such that the molten weld material is transported from the receiving means, down the down gate of the side mould and into the base mould to form a rail foot, from where the molten weld material rises into the inter-rail gap to form the web and rail head of the rail weld.
The receiving means may be a refractory receiving bowl which is removably located in the top part of a side mould and which terminates in a bottom diverting slot. The receiving bowl may be positioned in the side mould such that the diverting slot is arranged directly above the down gate of the side mould. The process may comprise pouring molten weld material from an overhead crucible, which may be positioned above the side mould and off-centre from the rail head, into the receiving bowl, from where the molten weld material may be transported via the down gate into the down gate well, which is located directly below the down gate of the side mould. Upon entering the down gate well, velocity of the molten weld material is reduced, thus allowing the molten weld material to enter the inter-rail gap with reduced velocity and no turbulence.
Each side mould includes downwardly depending base mould engaging means extending from the base of the side mould. The base mould engaging means is dimensioned to engage complimentarily dimensioned side mould engaging means, which extend upwardly from the base mould, when the side moulds sit on top of the base mould.
The mould assembly is characterised therein that when the side moulds sit on top of the base mould, the base of the side moulds are level with the top of the rail foot. This differs from prior art mould assemblies where the base of the side moulds are usually level with the bottom of the rail foot. The applicant has found that with the new arrangement, improved close fitting is achieved when the two side moulds are clamped together against the rails. The base mould defines a substantially central rail foot well in which molten weld material enters to form the rail foot; at least one down gate well laterally disposed relative to the rail foot well; and side mould engaging means extending upwardly from the base mould and dimensioned to engage complimentarily dimensioned base mould engaging means on the side moulds for supporting the side moulds.
The side mould engaging means are positioned on lateral opposite ends of the base mould, which ends extend beyond the rail foot such that the side moulds sit on top of the lateral opposite ends of the base mould.
In a preferred embodiment of the invention, the base mould includes two down gate wells located in the lateral opposite ends of the base mould and positioned directly below the down gates of the side moulds. Each down gate well is dimensioned to receive molten weld material from the down gate in the side mould, so as to reduce the velocity of the molten weld material and in turn to direct the stream of molten weld material towards the rail foot well in such a way that it reduces turbulence of the weld material. The inter-rail gap is filled from the bottom upwards, through molten weld material that enters the rail foot well and rises not only to fill the inter-rail gap, but also the down gate of the opposite side mould.
The base mould also defines two opposed rail receiving profiles on opposite sides of the base mould for snugly receiving the rail ends of the to- be-welded rails.
The rail foot well is defined intermediate the down gate wells, the side mould engaging means, and the rail receiving profiles.
The base mould further includes a fracture rib between the rail foot well and each of the down gate wells, which allows, after solidification and at black heat, for the down gates and down gate wells to be removed with a hammer.
The mould assembly further includes a knock-off core which is removably positioned between the two side moulds and centrally above the rail head and which is adapted to receive molten weld material to form a head metal riser section, the arrangement being such that the receiving bowl at least partially overlaps the knock-off core from above, forcing the knock-off core downwardly towards the rail head.
The process includes the steps of - preheating the enclosed mould cavity with a preheating burner; inserting the knock-off core between the two side moulds and centrally above the rail head;
inserting the receiving bowl in the top part of one of the two side moulds above the knock-off core, such that it at least partially overlaps with the knock-off core from above, thus forcing the knock- off core downwardly towards the rail head;
side-pouring molten weld material into the receiving bowl such that the molten weld material is transported from the receiving means, down the down gate of the side mould and into the base mould to form a rail foot, from where the molten weld material rises upwardly into the inter-rail gap to form the web and head of the rail weld and at least partially to fill the knock-off core,
the arrangement being such that the receiving bowl sits firmly against the knock-off core, holding it in position and preventing the knock-off core from rising when the molten weld material fills the inter-rail gap and the knock-off core.
After solidification and when the molten weld material in the inter-rail gap has reached a black heat, the knock-off core is removed with a hammer, together with the down gates and mould refractories. Known fusion welding processes all require a hydraulic rail shearing machine to remove excess head metal from the rail head. With the proposed invention this step is not required.
The process includes the further step of sealing the side moulds and base mould where they engage each other and the rails by firmly placing luting putty within luting grooves defined between the side moulds, base mould and the rail ends.
The side moulds are further characterised therein that they define a head rising room in an upper part of the side moulds for receiving molten material rising from the inter-rail gap and the down gates.
In use, the overhead crucible, containing an aluminothermic welding mixture, is positioned above the top of at least one side mould. Once all the mould parts have been positioned and clamped around the inter-rail gap between the two rails to be welded, and the knock-off core and receiving bowl have been inserted into position, the aluminothermic welding mixture is ignited. After expiration of the appropriate reaction time, molten metal is released from the crucible and directed into the refractory receiving bowl. All the liquid metal falling into the receiving bowl is discharged through the diverting slot into the down gate of the side mould. The metal flow is received in the bottom down gate well of the base mould and is diverted into the inter-rail gap, filling the inter-rail gap from the rail foot well upwards and rising to the rail head and further upwards to fill the knock-off core.
Alumina slag, which also forms during the reaction of the aluminothermic welding mixture in the crucible, is discharged from the crucible directly after the discharge of the molten metal. As a result of the lower specific gravity of the alumina slag, liquid alumina slag floats on top of the molten metal after the inter-rail gap and down gates have been filled.
The side moulds are so constructed to contain all the alumina slag in the head rising room and on top of the molten metal. This alumina slag acts as an insulator and assists in keeping the top head riser section liquidous for a longer period, thus facilitating progressive solidification to take place from thinner sections in the rail foot through the rail web area and lastly in the thicker rail head.
According to a further aspect of the invention there is provided a mould assembly for use in fusion welding rail ends of two adjacent rails, the mould assembly comprising - two upright side moulds that are fitted on either side of an inter-rail gap defined between the rail ends, each side mould including at least one elongate, open-ended down gate extending between a top part and a bottom part of the side mould and terminating in a down gate well;
a base mould adapted for receiving the rail ends and for supporting the side moulds on either side of the inter-rail gap; the arrangement being such that the base mould and side moulds cooperate to define an enclosed mould cavity for receiving molten weld material; and
receiving means for receiving molten weld material in at least one of the side moulds and arranged in flow communication with the down gate.
The receiving means may be a refractory receiving bowl which is removably located in the top part of a side mould and which terminates in a bottom diverting slot.
Each side mould may include downwardly depending base mould engaging means extending from the base of the side mould and dimensioned to engage complimentarily dimensioned side mould engaging means, which extend upwardly from the base mould, when the side mould sits on top of the base mould. The mould assembly may be characterised therein that when the side moulds sit on top of the base mould, the base of the side moulds are level with the top of the rail foot. The base mould may define a substantially central rail foot well in which molten weld material enters to form the rail foot; at least one down gate well laterally disposed relative to the rail foot well; and side mould engaging means extending upwardly from the base mould and dimensioned to engage complimentarily dimensioned base mould engaging means on the side moulds for supporting the side moulds.
The side mould engaging means may positioned on lateral opposite ends of the base mould, which ends extend beyond the rail foot such that the side moulds sit on top of the lateral opposite ends of the base mould.
The base mould also may define two opposed rail receiving profiles on opposite sides of the base mould for snugly receiving the rail ends of the to- be-welded rails.
The rail foot well may be defined intermediate the down gate wells, the side mould engaging means, and the rail receiving profiles.
The base mould further may include a fracture rib between the rail foot well and each of the down gate wells.
The mould assembly further may include a knock-off core which is removably positioned between the two side moulds and centrally above the rail head and which is adapted to receive molten weld material to form a head metal riser section, the arrangement being such that the receiving bowl at least partially overlaps the knock-off core from above, forcing the knock-off core downwardly towards the rail head.
The side moulds further may be characterised therein that they define a head rising room in an upper part of the side moulds for receiving molten material rising from the inter-rail gap and the down gates. SPECIFIC EMBODIMENT OF THE INVENTION
The invention will now further be described and illustrated with reference to the following non-limiting example only, wherein -
FIGURE 1 is an exploded perspective view of a mould assembly according to the invention;
FIGURE 2 is an assembled perspective view of the mould assembly of
Figure 1 ;
FIGURE 3 is the base mould only of the mould assembly;
FIGURE 4 illustrates the manner in which the mould assembly of the invention is fitted around an inter-rail gap of two to-be- welded rail ends;
FIGURE 5 is a sectional view of the mould assembly of Figure 4;
FIGURE 6 illustrates the manner in which a side mould and base mould of the mould assembly of the invention is fitted around an inter-rail gap, showing the location of the knock-off core and receiving bowl; and
FIGURE 7 is a partially filled mould assembly of Figure 6, illustrating a filled down gate and knock-off core.
The invention relates to a new in situ fusion welding process for welding adjacent rail ends [6] to form a substantially continuous railway track, and to a mould assembly for use in such a process. The process consist of a single process step and is aimed at introducing molten welding material into an inter-rail gap [8] between the to-be-welded rails [6], in a controlled manner and with the least amount of turbulence and velocity, so as to concentrate alloying additives in a weld head.
The process incorporates the use of a mould assembly [10] which comprises two upright side moulds [12], a base mould [14], and receiving means [16] for receiving molten weld material in at least one of the side moulds [12]. The side moulds [12] are fitted on either side of the inter-rail gap [8], while the base mould [14] is adapted for receiving the rail ends [6] and for supporting the side moulds [12] on either side of the inter-rail gap [8]. The side moulds [12] and base mould [14] cooperate to define an enclosed mould cavity [22] for receiving molten weld material.
Each of the side moulds [12] includes at least one elongate, open-ended down gate [18] extending between a top part [12.1] and a bottom part [12.2] of the side mould [12], and terminating in a down gate well [20], which is arranged directly beneath the down gate [18] of the side mould [12].
The receiving means [16], which is a refractory receiving bowl [16], is removably located in the top part [12.1] of a side mould [12] and is arranged in flow communication with the down gate [18]. The receiving means [16] terminates in a bottom diverting slot [24] and is positioned in the side mould [12] such that the diverting slot [24] is arranged directly above the down gate [18] of the side mould [12],
Each side mould [12] includes downwardly depending base mould engaging means [26] extending from the base [12.3] of the side mould [12]. The base mould engaging means [26] is dimensioned to engage complimentarily dimensioned side mould engaging means [28], which extend upwardly from the base mould [14], when the side moulds [12] sit on top of the base mould [14].
The mould assembly [10] is characterised therein that when the side moulds [12] sit on top of the base mould [14], the base of the side moulds [12] are level with the top [32.1] of a rail foot [32].
The side moulds [12] also include a head rising room [46] in an upper part of the side moulds [12] for receiving molten material rising from the inter-rail gap [8] and the down gates [18].
The base mould [14] defines a substantially central rail foot well [30] in which molten weld material enters to form the rail foot [32]; at least one down gate well [20] laterally disposed relative to the rail foot well [30]; and side mould engaging means [28] extending upwardly from the base mould [14] and dimensioned to engage complimentarily dimensioned base mould engaging means [26] on the side moulds [12]. The side mould engaging means [28] are positioned on lateral opposite ends [14.1; 14.2] of the base mould [14], which ends extend beyond the rail foot [32] such that the side moulds [12] sit on top of the lateral opposite ends [14.1 ; 14.2] of the base mould.
In a preferred embodiment of the invention, the base mould [14] includes two down gate wells [20] located in the lateral opposite ends [14.1 ; 14.2] of the base mould [14] and positioned directly below the down gates [18] of the side moulds [12]. Each down gate well [20] is dimensioned to receive molten weld material from the down gate [18] in the side mould [12], so as to reduce the velocity of the molten weld material and in turn to direct the stream of molten weld material towards the rail foot well [30] in such a way that it reduces turbulence of the weld material. The inter-rail gap [8] is filled from the bottom upwards, through molten weld material that enters the rail foot well [30] and rises not only to fill the inter-rail gap [8], but also the down gate [18] of the opposite side mould [12].
The base mould [14] also defines two opposed rail receiving profiles [34] on opposite sides of the base mould [14] for snugly receiving the rail ends [6] of the to-be-welded rails. The rail foot well [30] is defined intermediate the down gate wells [20], the side mould engaging means [28], and the rail receiving profiles [34].
The base mould [14] further includes a fracture rib [36] between the rail foot well [30] and each of the down gate wells [20], which allows, after solidification and at black heat, for the down gates [18] and down gate wells [20] to be removed with a hammer.
The mould assembly [10] further includes a knock-off core [38] which is removably positioned between the two side moulds [12] and centrally above a rail head [40] and which is adapted to receive molten weld material to form a top head metal riser section [38.1], the arrangement being such that the receiving bowl [16] at least partially overlaps the knock-off core [38] from above, forcing the knock-off core [38] downwardly towards the rail head [40]. The process comprises the steps of preheating the enclosed mould cavity [22] with a preheating burner (not shown); inserting the knock- off core [38] between the two side moulds [12] and centrally above the rail head [40]; and inserting the receiving bowl [16] in the top part [12.1] of one of the two side moulds [12] above the knock-off core [38], such that it at least partially overlaps with the knock-off core [38] from above.
An overhead crucible [42], containing an aluminothermic welding mixture, is positioned above one side mould [12] and off-centre from the rail head [40]. Once all the mould parts are clamped around the inter-rail gap [8] between the two rails to be welded, the aluminothermic welding mixture is ignited. After expiration of the appropriate reaction time, molten metal [46] is released from the crucible [42] and directed into the refractory receiving bowl [16]. All the liquid metal [46] directed into the receiving bowl [16] is discharged through the diverting slot [24] into the down gate [18] of the side mould [12]. The metal flow is received in the bottom down gate well [20] of the base mould [14] and is diverted into the inter-rail gap [8], filling the inter- rail gap [8] from the rail foot well [30] upwards and rising to the rail head [40] and further upwards to fill the knock-off core [38]. At the same time the metal flow fills the down gate [18] of the opposite side mould [12], rising from the bottom upwards and into the head rising room [46]. Upon entering the down gate well [20], velocity of the molten weld material [46] is reduced, thus allowing the molten weld material to enter the inter-rail gap [8] with reduced velocity and no turbulence. During the casting process, the receiving bowl [16] remains firmly against the knock-off core [38], holding it in position and preventing the knock-off core [38] from rising when the molten weld material [46] fills the inter-rail gap [8] and the knock-off core [38].
After solidification and when the molten weld material [46] in the inter-rail gap [8] has reached a black heat, the knock-off core [38] is removed with a hammer, together with the down gates [18] and mould refractories. When the mould assembly [10] is hit with a hammer, the side moulds [12] and down gates [18] fracture at the fracture rib [36].
The process includes the further step of sealing the side moulds [12] and base mould [14] where they engage each other and the rails by firmly placing luting putty within luting grooves [44] defined between the side moulds [12], base mould [14] and the rail ends [6] .
Alumina slag [48], which also forms during the reaction of the aluminothermic welding mixture in the crucible, is discharged from the crucible [42] directly after discharge of the molten metal [46]. As a result of the lower specific gravity of the alumina slag [48], liquid alumina slag floats on top of the molten metal [46] after the inter-rail gap [8] and down gates [18] have been filled.
The side moulds [12] are so constructed to contain all the alumina slag [48] in the head rising room [46] and on top of the molten metal [46]. This alumina slag [48] acts as an insulator and assists in keeping the top head riser section [38.1] liquidous for a longer period, thus facilitating progressive solidification to take place from thinner sections in the rail foot [32] through the rail web [50] and lastly in the thicker rail head [40]. The step of collecting all the alumina slag [48] in the head rising room [46] within a top part of a side mould [12] differs from all other aluminothermic processes, where the liquid alumina slag [48] is channelled off the refractory mould top sections into slag trays. These metal slag trays are attached to a side of the refractory side moulds [12] for receiving the alumina slag [48], and are removed with care after solidification of the alumina slag [48] has taken place. Not only is it safer to have all the alumina slag [48] contained within the top part of the two side moulds, but also less equipment is required and ease of operation is accomplished. It will be appreciated that other embodiments of the invention may be possible without departing from the spirit or scope of the invention as defined in the claims.