GB1600991A

GB1600991A - Aluminothermic welding of rails

Info

Publication number: GB1600991A
Application number: GB12082/77A
Authority: GB
Original assignee: Thermit Welding GB Ltd
Current assignee: Thermit Welding GB Ltd
Priority date: 1978-05-26
Filing date: 1978-05-26
Publication date: 1981-10-21

Description

(54) ALUMINOTHERMIC WELDING OF RAILS (71) We, THERMIT WELDING (GB) LIMITED, Hammersmith House, London W6 9DX, England, an English company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a method for the aluminothermic welding of rails and to a set of pre-fabricated refractory units which are adapted to be assembled about a pair of rail ends to be welded together to form a mould for the aluminothermic welding of the rails.

It is known to weld rails by conducting an aluminothermic reaction to form molten steel, and introducing the molten steel to the cavity of the mould assembled from pre-fabricated refractory units about the ends of the rail to be welded together. The heat of the molten metal causes it to fuse with the ends of the rail as it solidifies. A weld between the rail ends is thus formed.

There is an increasing demand for (rail) track which is able to withstand trains travelling along it at high speeds, ie. those well in excess of 100 miles per hour. It is believed that a conventional foundation of gravel or like particulate material is sometimes inadequate to support rails over which "high speed" trains are to travel. Consequently, it has been proposed to lay (rail) track on concrete beams joined together end-to-end or on continuously slip-cast concrete, relatively thin rubber pads (typically 10mm thick) being interposed between the top surfaces of the beams and the feet of the rails. Such formations for supporting track may also be used in circumstances where there is no requirement for 'high speed' track. We have found that known moulds for the aluminothermic welding of rails are unsuitable when welding rails supported on concrete in their final positions. The main reason is that the clearance between the foot of the rail and the top of the beam on which the rail is supported is too small to accomodate underneath the rails prefabricated refractory units adapted to form the bottom portions of conventional moulds.

According to the present invention there is provided for the aluminothermic welding of rails supported in a thin flat longitudinally-extending member of uniform thickness positioned on top of a supporting base, a set of pre-fabricated units of refractory material which are capable of being assembled about two rail ends to be welded together to define a mould for the aluminothermic welding of the rail ends, the mould when assembled about the rail ends having openings through which the rails ends enter the mould, and a cavity for defining the dimensions of the weld, in which cavity the rails ends are, in use, received and which cavity communicates with a runner through which molten metal is introduced into the cavity in use of the mould, one of the units being adapted to define the bottom boundary of the cavity in the mould, when assembled, which unit has a maximum thickness equal to or less than 10 mm and is of a refractory material which in use of the mould, when assembled, to make the weld does not become distorted or allow molten metal to pass therethrough.

The invention also provides a method for the aluminothermic welding of rails supported on a thin flat longitudinallyextending member of uniform thickness positioned on top of a supporting base, which method includes the steps of assembling the mould for the aluminothermic welding of the rail ends from pre fabricated units of refractory material, the mould having openings through which enter the rail to be welded together and a cavity which defines the dimension of the weld, in which the rail ends are received and which has associated therewith a runner for introducing molten metal into it; conducting an aluminothermic reaction so as to form molten steel, and introducing the molten steel into the cavity whereby the molten steel as it solidifies welds the rail ends together, in which method one of the units which forms the base of the mould is fitted in place of a length of support member between the supporting base and the feet of the rails to be welded; which unit has a maximum thickness less than or equal to the thickness of the support member and is of refractory material which when making the weld does not become distorted or allow molten metal to pass therethrough.

Examples of suitable refractory materials for the bottom units are high alumina silimanite and zircon.

Desirable attributes for the refractory from which the bottom unit is fabricated are: 1. dimensional stability on firing 2. a high resistance to thermal shock 3. a 'refractoriness' capable of withstanding a temperature of the order of 2100"C to 2200"C 4. a relatively high density and compressive strength; 5. a chemical composition which does not result in the weld metal becoming contaminated with undesirable impurities; Chrome-magnesite types of refractory are unsuitable for use in making the bottom unit because the chromium they contain can be undesirable in the weld metal.

Fired silica refractories are unsuitable because of their poor resistance to thermal shock.

Fired magnesite refractories are also unsuitable in view of their brittle nature at the required thickness. However, the other units as they do not need to be especially thin may conveniently be made of a COr hardened refractory.

Although it is theoretically possible to use more than three units to define the cavity of the mould, it is very much convenient to use just three such units. In such an arrangement the bottom unit will cooperate with two other units. These two other units will cooperate together to define the openings through which the rail ends enter the mould.

These two units will also cooperate together to define head and web portions of the cavity and will together cooperate with the bottom unit to define the foot position of the cavity.

In general, the two units will also cooperate to define together at least one runner and at least one riser (or channel) each of which at one of its ends terminates at the top face of the assembled mould and at its other end in the cavity. The purpose of the or each runner is to provide a passage for molten steel formed by an aluminothermic reaction to run into the cavity. The purpose of the or each riser is to enable excess molten metal to pass out ofthe cavity. After having made the weld, any excess metal which is solidified in the riser and the runner may be cut away by, for example, a rotary cutter or a cutting torch (for example, an oxy-acetylene welding torch) and the collar of the weld around the top and sides of the heads of the welded rail removed by grinding.

The bottom unit preferably has a maximum thickness of about 8mm if the support member is 10mm thick. It preferably has in what is intended to be its top face a shallow recess which defines the base of the collar of the weld.

The weld is desirably made by the method described in the complete specification of our copending cognate British patent applications 12083/77, 3929/78 and 3930/78. Serial no. 1600992.

When assembling the mould from the refractory units, the part of the rubber pad (or other support member) underneath the rail ends to be welded together may be cut away and the bottom unit inserted in its place. Any space between the concrete support and the bottom of the base may be filled with refractory sand so as to ensure that the top face of the bottom unit is hard up against the feet of the rails to be welded.

If the mould is to be formed from three units, the other two units may be fitted over the rail ends and brought together to define the cavity.

The apparatus and method according to the present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a schematic side view of the two rails to be welded together, the rails being supported on a concrete beam; Figure 2 is a section through an assembled mould for the aluminothermic welding of rails; Figure 3 is a plan view of the bottom refractory unit of the mould; Figure 4 is a side view of the bottom refractory unit; Figure 5 is a plan view of the assembled mould; Figure 6 is a side view of the refractory units forming the moulding showing the opening through which the rail end enters the mould; Figure 7 is a tranverse section through a welded rail, Figure 8 is a side view of the weld shown in Figure 7.

Referring to Figure 1 of the drawings, two rails to be welded together are indicated by the references 2 and 4. The ends of these rails are spaced apart. Each rail has a foot 6, of web 8 and a head 10. The rails are supported on a concrete beam 12 and may be fastened thereto by pins or other means (not shown). Interposed between the rails 2 and 4 and the beam 12 is a continuous rubber pad 14. This rubber pad may typically be 10mm thick.

In Figure 2 is shown an assembled mould 15. The mould 15 is formed of three pre-fabricated refractory units. There are two side units 16 and 18, both of CO2 hardened refractory. These cooperate with a bottom unit 20 of the same thickness as the rubber pad 14 (or having a slightly smaller thickness). The unit 20 is of zircon. The units 16 and 18 are adapted to define together openings 22 for receiving the rails 2 and 4. The openings are contiguous with a mould cavity 24 which defines the size and shape of the weld.

The unit 20 has recesses or grooves 42 which receive complementary projections from the other units when the mould is assembled.

Mould shoes 38 are fitted around the sides of the mould and are clamped. Luting or refractory sand is then applied. The mould is then pre-heated for a short period to drive off all moisture. The core plug 25 is positioned in the mould and engages a land (not shown). Thermit (registered trade mark) powder is then ignited in a crucible (not shown) held above the runners 34. Molten steel formed by the aluminothermic reaction may then be tapped from the bottom of the crucible into the runners 34. It will then flow into the mould cavity 26, any excess molten steel passing into the risers 36. The molten metal may then be allowed to solidify forming the weld shown in Figures 7 and 8.

Excess weld metal which solidifies in the risers 36 is then removed after cooling. This can be done by means of a sharp blow or by cutting using a cutting torch or cutting tool (eg. a rotary cutter). This is done after the mould shoes 38 are unbolted and removed and the mould broken open. The head portion of the collar 32 shown in Figure 7 is ground away using a rotary cutter. Finally the section of the rubber pad that had been removed is then replaced underneath the welded rails.

In making the weld it is desirable that in the assembled mould the cavity has a shape such that the thickness of the collar of the finished weld on the undersurface of the feet of the welded rails is say 2mm less than is for a weld made by the method according to our copending cognate applications Nos. 12083/ 77, 3929/78 and 3930/78. Serial no. 1600992.

Thus, this thickness will typically be 3mm and not 5mm as is normally preferred, there being a corresponding recess 40 with a maximum depth of 3mm in the bottom unit 20. In order to compensate for this reduction in the volume of the collar it is desirable that the assembled mould has a shape such that the thickness of the collar on the top surface of the feet of the welded rails is greater than is generally preferred. Typically, it may be thicker by an amount equal to that by which the thickness of the collar on the under surface of the feet of the welded rails is reduced in comparison with the aforesaid generally preferred weld. Thus, the collar at the said top surface may be 2 mm thicker than it is in the aforesaid generally preferred weld.

WHAT WE CLAIM IS: 1. A method for the aluminothermic welding of rails supported in a thin flat longitudinally-extending member of uniform thickness positioned on top of a supporting base, which method includes the steps of assembling a mould for the aluminothermic welding of the rail ends from pre fabricated units of refractory material, the mould having openings through which enter the rail ends to be welded together, and a cavity which defines the dimensions of the weld, in which the rail ends are received and which has associated therewith a runner for introducing molten metal into it; conducting an aluminothermic reaction so as to form molten steel, and introducing the molten steel into the cavity via the runner whereby the molten steel as it solidifies welds the rail ends together, in which method one of the units which forms the based of the mould is fitted in place of a length of support member between the supporting base and the feet of the rails to be welded, which unit has a maximum thickness less than or equal to the thickness of the support member and is of a refractory material which when making the weld does not become distorted or allow molten metal to pass therethrough.

2. A method as claimed in claim 1, in which the base unit is of high-alumina sillimanite.

3. A method as claimed in claim 1, in which the base unit is of zircon.

4. A method as claimed in any one of the preceding claims in which the support member is 10mm thick and the base unit of the mould has a maximum thickness of 8mm.

5. A method as claimed in any one of the preceding claims in which there are three prefabricated refractory units.

6. A method as claimed in any one of the preceding claims in which the longitudinally-extending member is a rubber pad.

7. A method as claimed in any one of the preceding claims, in which part of the longitudinally-extending member under the rail ends to be welded together is cut away or removed, the prefabricated refractory unit which forms the base of the mould, when assembled, is inserted in place of the cut away material.

8. A method as claimed in claim 7, in which refractory sand is inserted between the base and the refractory unit which forms

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. and 4 and the beam 12 is a continuous rubber pad 14. This rubber pad may typically be 10mm thick. In Figure 2 is shown an assembled mould 15. The mould 15 is formed of three pre-fabricated refractory units. There are two side units 16 and 18, both of CO2 hardened refractory. These cooperate with a bottom unit 20 of the same thickness as the rubber pad 14 (or having a slightly smaller thickness). The unit 20 is of zircon. The units 16 and 18 are adapted to define together openings 22 for receiving the rails 2 and 4. The openings are contiguous with a mould cavity 24 which defines the size and shape of the weld. The unit 20 has recesses or grooves 42 which receive complementary projections from the other units when the mould is assembled. Mould shoes 38 are fitted around the sides of the mould and are clamped. Luting or refractory sand is then applied. The mould is then pre-heated for a short period to drive off all moisture. The core plug 25 is positioned in the mould and engages a land (not shown). Thermit (registered trade mark) powder is then ignited in a crucible (not shown) held above the runners 34. Molten steel formed by the aluminothermic reaction may then be tapped from the bottom of the crucible into the runners 34. It will then flow into the mould cavity 26, any excess molten steel passing into the risers 36. The molten metal may then be allowed to solidify forming the weld shown in Figures 7 and 8. Excess weld metal which solidifies in the risers 36 is then removed after cooling. This can be done by means of a sharp blow or by cutting using a cutting torch or cutting tool (eg. a rotary cutter). This is done after the mould shoes 38 are unbolted and removed and the mould broken open. The head portion of the collar 32 shown in Figure 7 is ground away using a rotary cutter. Finally the section of the rubber pad that had been removed is then replaced underneath the welded rails. In making the weld it is desirable that in the assembled mould the cavity has a shape such that the thickness of the collar of the finished weld on the undersurface of the feet of the welded rails is say 2mm less than is for a weld made by the method according to our copending cognate applications Nos. 12083/ 77, 3929/78 and 3930/78. Serial no. 1600992. Thus, this thickness will typically be 3mm and not 5mm as is normally preferred, there being a corresponding recess 40 with a maximum depth of 3mm in the bottom unit 20. In order to compensate for this reduction in the volume of the collar it is desirable that the assembled mould has a shape such that the thickness of the collar on the top surface of the feet of the welded rails is greater than is generally preferred. Typically, it may be thicker by an amount equal to that by which the thickness of the collar on the under surface of the feet of the welded rails is reduced in comparison with the aforesaid generally preferred weld. Thus, the collar at the said top surface may be 2 mm thicker than it is in the aforesaid generally preferred weld. WHAT WE CLAIM IS:

1. A method for the aluminothermic welding of rails supported in a thin flat longitudinally-extending member of uniform thickness positioned on top of a supporting base, which method includes the steps of assembling a mould for the aluminothermic welding of the rail ends from pre fabricated units of refractory material, the mould having openings through which enter the rail ends to be welded together, and a cavity which defines the dimensions of the weld, in which the rail ends are received and which has associated therewith a runner for introducing molten metal into it; conducting an aluminothermic reaction so as to form molten steel, and introducing the molten steel into the cavity via the runner whereby the molten steel as it solidifies welds the rail ends together, in which method one of the units which forms the based of the mould is fitted in place of a length of support member between the supporting base and the feet of the rails to be welded, which unit has a maximum thickness less than or equal to the thickness of the support member and is of a refractory material which when making the weld does not become distorted or allow molten metal to pass therethrough.

3. A method as claimed in claim 1, in which the base unit is of zircon.

the base of the mould, when assembled.

9. A method as claimed in any one of the preceding claims, in which the weld is made in accordance with the method of our copending cognate applications Nos 12083/ 77, 3929/78 and 3930/78. Serial no 1600992.

10. A method as claimed in any one of the preceding claims, in which the prefabricated refractory unit which forms the base of the mould, when assembled, has a recess in what in the assembled mould is the top face of the unit, which recess is adapted to define the foot of the weld.

11. A method as claimed in claim 10, in which the collar of the finished weld has at the feet of the rails a thickness of 3mm.

12. A method as claimed in any one of the preceding claims in which the prefabricated refractory unit which forms the base of the mould, when assembled, has recesses or grooves in its sides which recesses or grooves receive complementary projections from the other units.

13. A method for the aluminothermic welding of rails supported on a thin flat longitudinally-extending member of uniform thickness positioned on top of a supporting base, substantially as herein described with respect to the accompanying drawings.

14. For use in the aluminothermic welding of rails supported on a thin flat longitudinally-extending member of uniform thickness positioned on top of a supporting base, a set of prefabricated units of refractory material which are capable of being assembled about two rail ends to be welded together to define a mould for the aluminothermic welding of the rail ends, the mould when assembled about the rail ends having openings through which the rail ends enter the mould, and a cavity for defining the dimensions of the weld, in which cavity the rail ends are, in use, received and which cavity communicates with a runner through which molten metal is introduced into the cavity in use of the mould, one of the units being adapted to define the bottom boundary of the cavity in the mould, when assembled, which unit has a maximum thickness equal to or less than 10 mm and is of a refractory material which in use of the mould, when assembled, to make the weld does not become distorted or allow molten metal to pass therethrough.

15. A set of prefabricated refractory units as claimed in claim 14, in which the unit defining the bottom boundary of the cavity is of high alumina sillimanite.

16. A set of prefabricated refractory units as claimed in claim 14, in which the unit defining the bottom boundary of the cavity is of zircon.

17. A set of prefabricated refractory units as claimed in any one of claims 14 to 16, in which the unit defining the bottom boundary of the cavity has a maximum thickness of 8 mm.

18. A set of prefabricated refractory units as claimed in any one of claims 14 to 17, in which the aforesaid unit has a recess in one of is faces, which recess defines the bottom boundary of the cavity in the assembled mould.

19. A set of prefabricated refractory units as claimed in any one of claim 18, in which the recess has a maximum depth of 3mm.

20. A set of prefabricated refractory units as claimed in any one of claims 14 to 19, in which the set comprises three prefabricated refractory units, one unit defining the bottom boundary of the cavity as aforesaid, the other two units each receiving, in use of the assembled mould to make a weld, a rail end.

21. A set of prefabricated refactory units as claimed in claim 20, the aforesaid other two units are of a carbon dioxide hardened refractory.

22. A set of prefabricated refractory units as claimed in claim 20 or 21, in which the unit defining the bottom boundary of the cavity has recesses or grooves which receive complementary projections from the other units when the mould is assembled.

23. A set of prefabricated refractory units as claimed in any one of claims 14 to 22, from which a mould suitable for use in the mould according to our copending cognate applications Nos. 12083/77, 3929/78 and 3930/78 Serial no. 1600992 is capable of being assembled.

24. For use in the aluminothermic welding of rails supported on a thin flat longitudinally-extending member of uniform thickness positioned on top of a supporting base, a set of prefabricated refractory units substantially as described herein with reference to, and as shown, in Figures 2 to 6 of the accompanying drawings.