In this type of installation, the ladles containing the molten metal coming from the steel plant are brought near to the casting installation by means of a transport carriage or a travelling crane and are placed above a tundish, into which the molten metal pours via a taphole. The molten metal subsequently passes from the tundish to the bottomless mold, where the continuous strip of metal, namely a slab or a bar, is formed.
In order to make it easier to replace the ladles and reduce the downtime as much as possible, an appliance called a "ladle turntable" is often used as a ladle support.
Such appliances are known. They comprise at least one arm extending in an overhung manner from a barrel mounted rotatably about a vertical axis on a stationary base, for example the supporting stand of the installation. Each arm can support a ladle and, as a result of rotation, move it from a charging and discharging position into a casting position above the tundish.
The turntable is often equipped with two diametrically opposite arms, so that, while one ladle located above the tundish pours the steel which it contains, the previously emptied ladle can be removed from the other arm in order to replace it with a new full ladle.
In general, the taphole closed by means of a spout is extended downwards by a casting pipe, the function of which is to protect the jet of steel between the ladle and tundish from contact with the air and therefore from oxidation.
The protective devices are generally either a refractory pipe attached or retained under the ladle or a skirt made of asbestos or similar material, in which an inert atmosphere is maintained.
Because the ladle is brought above the tundish and then emptied as a result of the rotation of the arm of the support about its vertical axis, it was thought expedient to equip the ladle supports with lifting devices which make it possible to release the casting pipe during changes of ladles or tundishes. Lifting is also necessary when, in order to unblock the spout closing the taphole, it is necessary to blow into it, by means of a lance, pressurized oxygen which burns the steel solidified in the spout orifice.
The known devices for lifting the ladle-supporting arms can be of the hydraulic or the electromechanical type.
In devices of the mechanical type, lifting is brought about by means of elements of the winch and block and tackle, screws and nuts, connecting rod or crank type. These devices are heavy and bulky, and they sweep across a large space through the rotation of the turntable, thus creating dangerous zones at the workstations. Furthermore, they generally comprise a certain number of joints and guides which are exposed to the splashes of steel, and which therefore require frequent and difficult maintenance.
Moreover, the guides projecting above the arms require a greater lifting height on the crane and therefore a proportionate building height.
In devices of the hydraulic type, lifting is brought about by means of jacks. These devices are simpler and generate fewer stresses than the mechanical devices.
In this case, the lifting of the ladle is controlled by at least one hydraulic jack bearing on the supporting arm, the latter being mounted pivotally on the barrel about a horizontal axis.
The ladle is equipped with two journals engaging into suspension members which allow actuation by means of the travelling crane, and which rest on bearing parts formed at the end of the supporting arm and often having the form of a trapezoidal cup, into which fit the lower parts, of corresponding forms, of the suspension members. Thus, if the bearing parts are fastened rigidly to the end of the supporting arms, the pivoting of these during lifting determines a change of orientation of the supporting members and consequently an oscillation of the ladle about its journals. Consequently, it is often considered preferable to provide the bearing parts on two supporting stays connected to the barrel by means of an articulated system constituting a deformable parallelogram, of which they form an outer side moveable parallel to itself. For this purpose, each supporting stay is articulated about horizontal axes, respectively on the end of the supporting arm and on a connecting rod parallel to the supporting arm and articulated on the base, the vertex of the deformable parallelogram being formed by the respectively stationary and moveable axes of articulation of the supporting arm and of the retaining connecting rod respectively on the base and on the two supporting stays.
In such arrangements, which are described, for example, in EP-A-0,206,169 or FR-A-2,234,946, the lifting force is exerted on the supporting arm, which is therefore subjected to bending, and the force required from the jack is greater than the weight of the charge. For this reason, in order to support the articulated assembly more effectively during lifting, the latter is generally produced by means of two set-apart and synchronized jacks, each acting on one side of the supporting arm.