GB2065528A - Process for fixing cables to the top of a metal workpiece and equipment for carrying out the process - Google Patents

Abstract

The invention relates to a process for fixing cables or ropes to the surface of a metal workpiece, in particular electric conductors on track elements which carry wheels such as rails. A 1-5 mm thick metal base plate (7) is placed onto the workpiece (9), a layer of solder (8) being provided between the base plate and the workpiece, and the cable or rope (6) is then welded aluminothermically onto the top of the base plate with the solder being fused by the heat flow from aluminothermically produced reaction material (11). The invention also relates to equipment including a mould specific for carrying out the process. <IMAGE>

Description

SPECIFICATION Process for fixing cables to the top of a metal workpiece and equipment for carrying out the process The invention relates to a process for fixing cables or ropes to the surface of a metal workpiece, in particular electric conductors on track elements which carry wheels, such as rails, by soldering, and to equipment for carrying out the process.

It is frequently necessary, to make electrically conductive joints between cables or ropes and metal workpieces, such as girders or rails, in building and civil engineering, during the installation of equipment in process engineering or in track construction.

For making an electrically conductive joint between a rail and an electric conductor of, for example, steel or copper, it is known inter alia from Zeitschrift für Eisenbahnwesen und Verkehrstechnik, Glasers Annalen, Issue 1, No. 75, to use aluminothermically produced molten metals for a welded joint. To carry out the process, a graphite crucible is used which comprises a reaction cavity and a casting mould cavity, the two cavities being connected to one another by a casting channel.

This crucible also has an opening which is connected to the casting mould cavity and into which the cable which is to be welded on is inserted in such a way that one end protrudes into the casting mould cavity. For carrying out the weld, after cleaning the welding position, for example on the rail foot, the crucible with the electric conductor is placed onto the welding position in such a way that the casting mould cavity which is open downwards is located above the cleaned welding position. Subsequently, the casting channel between the reaction chamber and the casting mould cavity is covered by a small metal plate and the aluminothermic welding portion is filled in.After initiating the reaction, the hot molten, aluminothermically produced metal collects in the lower part of the reaction chamber, fuses through the small metal plate and flows into the casting mould cavity, as a result of which the electric conductor and the rail are welded up. The welding portion here consists of an aluminothermic composition, preferably based on copper oxide/aluminium or iron oxide/aluminium of copper oxide/iron oxide/aluminium, which composition reacts exothermically in a known manner after ignition and is converted to hot molten metal and aluminium oxide.

This known aluminothermic welding process which can be carried out within a very short time has, however, the great disadvantage that the fusion of the rail material during the welding process causes structural changes in the region of the welding position, which changes reduce the fracture safety of the rail.

As a result of the fusion of the rail material, which is connected with heating of the workpiece beyond the transition point, annealed structures, which should be avoided under any circumstances, are formed by the accelerated heat flow due to the cold base material surrounding the welding position. Moreover, copper diffuses into the base material, and this involves the known disadvantages. Attempts to delay cooling by preheating the welding position have not been successful since this welding process presupposes a bare metallic surface and even a slight oxidation of the surface suffices to prevent proper welding.

Autogenous or electric welding have the same disadvantage since cracks due to hardening can also be formed in this case.

Attempts have therefore been made, for example with rails, to solder such connectors on autogenously with silver solder, the surface of the rail being heated with the aid of a flame. However, it was also found in this case that due to carelessness -- local overheating can occur, as a result of which detrimental structures are formed.

The present invention relates to a process which reliably prevents a formation of detrimental structures in metal workpieces which undergo structural changes when correspondingly heated, since the welding position is covered by a small metal plate with the insertion of a solder, the melting point of which is below the transition point of the workpiece.

It is intended here to combine the advantages of the aluminothermic process, such as say the complete embodding of the end zone of the cable into the aluminotherically produced casting (casting all round), with the advantages of the soldering process, in parti cular the lower heat load.

According to the invention, this is achieved when a 1.0 to 5 mm thick metal base plate is placed onto the workpiece, a layer of solder being provided between the base plate and the workpiece, and the cable, rope or the like is then welded aluminothermically, in a manner which is in itself known, onto the top of the base plate, the solder being fused by the heat flow from the aluminothermically produced reaction material and the base plate being soldered to the workpiece.

The workpiece, for example the rail foot, is protected by the base plate from excessive heating which can lead to structural changes.

The heat flow from the base plate, howefer, reliably suffices for fusion of the solder and perfect uniform flat soldering. The low-melting solder, the melting point of which is in particular below the transition point of the workpiece, can here be present as a small plate or in the form of a paste or it is fused, on the side facing the workpiece, onto the small metal plate (base plate) covering the welding position.

The selection of the solder depends above all on the mechanical stress on the soldered joint and on the heating of the solder, which can take place when current passes through.

Both soft and hard solders can be used. A silver solder containing at least 5% by weight of Ag, in particular a solder having the com position of Ag = 39 to 41%, Cu = 18 to 20% and Cd = 18 to 22%, the remainder being Zn, has proved to be very suitable.

The base plate which can be round or square should have a thicknes of 1 to 5 mm, in particular in the case of steel workpieces, and should consist of steel. Below a thickness of 1 mm, there is a risk of fusing through; above a thickness of 5 mm, the heat transmission can be inadequate for reliable fusing of the solder metal. In the case of rails, a small steel plate of about 2-3 mm thickness has proved to be a particularly good base plate.

The process according to the invention can be carried out particularly advantageously with equipment which likewise represents a subject of the invention The equipment is characterised in that is consists of a preferably mirror-symmetrical, two-part casting mould which comprises a reaction chamber, a casting mould cavity located underneath the former, a casting channel which connects the reaction chamber and the casting mould cavity, and a bore which preferablg extends horizontally and leads into the casting mould cavity through the wall of the casting mould, and the reaction chamber can be closed by a small metal plate which can be fused by the aluminothermically produced metal melt, and either the casting mould has a recess, corresponding to the base plate, at the bottom in the lower region of the casting mould cavity or the casting mould is located on a fibre board which is formed from a heat-resistant fibre material and which, underneath the casting mould cavity, has a recess, corresponding to the base plate, the thickness of the fibre board corresponding to at least the thickness of the base plate.

The fibre board can consist of asbestos fibres or fibres of inorganic material which are commercially available under the names Fiberfrax or Kaowool and which are composed essentially of SiO2, Al203 and small amounts of B203 and Na2O. Advantageously, the thickness of the small fibre board is slightly greater than that of the small base plate. When the casting mould is placed on, the small plate is compressed and makes a seal against the workpiece.

If necessary, provision can be made for the base plate to be locked in the casting mould.

Thus, the base plate can engage with one or several projections in corresponding recesses in the casting mould. It can also have a lateral lug on the underside, which lug protrudes beyond the bottom of the casting mould and, bent at an appropriate angle, is fastened to the vertical outer wall of the casting mould.

The casting mould preferably consists of graphite.

The process according to the invention has proved to be particularly advantageous for fixing cables or metal ropes to rails.

Using the equipment according to the invention, the process according to the invention will be explained in more detail by reference to Figs. t to 3, in which: Figure 1 shows the casting mould according to the invention, in section, with the groove which receives the base plate, the casting mould being placed onto a rail foot, Figure 2 shows the casting mould accord ing to the invention with a fibre board between the casting mould and the rail, likewise in section, and Figure 3 shows the use of the process according to the invention and the combined soldered/welded joint of a cable on a rail foot, obtained by means of the equipment according to the invention.

According to Fig. 1, the graphite crucible (1) with the reaction chamber (2), casting channel (3), casting mould cavity (4), recess (5), cable (6). inserted into the bore (13) and the small steel plate (7) which is provided with solder (8), is placed onto the cleaned welding position on the rail (9) and advanta geously - but not shown - is clamped to the workpiece, in this case the rail foot. Appropriate clamping pliers are known. After the reaction chamber (2) has been closed by the small plate (10), the aluminothermic mixture (1 t), for example a mixture based on copper oxide/aluminium, is made to react and, after the reaction, the aluminothermically produced copper fuses the small plate (10) and pours onto the small steel plate (7). The heat of welding heats the solder (8) and rail (9) in the region of the welding position, as a result of which the small plate (7) is soldered on.

Fig. 2 shows the casting mould (1), according to the invention, which is placed onto the fibre board (14). The fibre board (14) has a recess (15) into which the base plate (7) is inserted. The fibre board (14) here makes a seal between the bottom of the casting mould (1) and the rail foot (9).

The finished joint is shown in Fig. 3, the joint between the electric conductor (6) and the small steel plate (7) being made by the aluminothermically produced welding material (12) and the joint between the small steel plate (7) and. the rail (9) being made by the solder (8).

Claims (9)

1. Process of fixing a cable or rope to the surface of a metal workpiece, in particular an electric conductor on a track element which carries wheels, such as a rail, by soldering, wherein a 1 to 5 mm thick metal base plate is placed onto the workpiece, a layer of solder being provided between the base plate and the workpiece, and the cable, rope or the like is then welded aluminothermically onto the top of the base plate, the solder being fused by the heat flow from the aluminothermically produced reaction material and the base plate being soldered to the workpiece.

2. Process according to claim 1, wherein the solder is fused onto the underside of the base plate or a solder in the form of a small plate or of a paste is provided between the base plate and the workpiece.

3. Process according to claim 1 or 2, wherein the solder used has a melting point which is below the transition point of the workpiece.

4. Process according to claim 1, 2 or 3, wherein a solder having a composition of 39-41% by weight of Ag, 18-20% by weight of Cu and 18-22% by weight of Cd, the remainder being Zn, is used.

5. Process according to any preceding claim, wherein the aluminothermic welding is carried out using an aluminotheric composi tidn based on copper oxide/aluminium or iron oxide/aluminium or copper oxide/iron oxide/ aluminium.

6. Equipment for carrying out the process of any preceding claim and comprising a twopart casting mould which preferably is mirrorsymmetrical and which comprises a reaction chamber, a casting mould cavity located underneath the reaction chamber, a casting channel which connects the reaction chamber and the casting mould cavity, and a bore which preferably extends horizontally and leads into the casting mould cavity through the wall of the casting mould, the reaction chamber being closable by a small metal plate which can be fused by the aluminothermically produced metal melt, with the casting mould either having a recess, corresponding to the base plate, at the bottom in the lower region of the casting mould cavity or being located on a fibre board which is formed from a heatresistant material and which, underneath the casting mould cavity, has a recess corresponding to the base plate, the thickness of the fibre board corresponding to at least the thickness of the base plate.

7. Equipment according to claim 6, wherein the casting mould is formed of graphite.

8. A process of fixing a cable or rope to a metal workpiece substantially as herein described with reference to the accompanying drawings.

9. Equipment for use in fixing a cable or rope to a metal workpiece constructed and arranged substantially as herein described with reference to and as illustrated in the accompanying drawings.