Refining of the charged scrap in an electric furnace is performed by arcs generated from electrodes. A lining on a wall or a bottom of a furnace is eroded by high temperature molten steel and slag during the melting process. The worn lining is mended by spouting sludgy lining material under the high temperature condition immediately after the tapping. In order to spout lining material an operator must insert a gunning nozzle attached to a long lance through a side opening of a furnace. Here, hard labor in a very severe operating condition with a high temperature is forced upon the operator. Moreover, it is not easy to mend the wide range of the lining and much more skillful technique is required.
A hot gunning machine 80 as shown in FIG. 17 has been used in order to release an operator from the direct operation of the long lance which is hard to handle. The hot gunning machine 80 comprises a main pole 81 disposed by an electric furnace 3, a shifting arm 82 which travels vertically along the main pole 81 and rotates around the main pole 81 and a nozzle carrier 83 which is equipped on the shifting arm 82. An exchangeable gunning nozzle 84 is attached to the lower end of the nozzle carrier 83 and the nozzle carrier 83 travels vertically along the center line of the furnace. Therefore, the gunning nozzle 84 can be transferred from the housing position shown by single-dot chain lines to the advanced position above the furnace shown by solid lines and then to the gunning position shown by double-dot chain lines. After the gunning nozzle 84 is revolved toward the required direction as shown by an arrow 85, lining material from a pneumatic transport hose 86 is spouted to mend the worn lining 3a. To mend the lining on the bottom of the furnace, the gunning nozzle 84 is retreated to the housing position and is exchanged for a gunning nozzle which has an angle suitable for gunning toward the bottom of the furnace.
The hot gunning machine described above facilitates machanical and remote operation under the high temperature condition and reduces the burden of the operator. Moreover, as the nozzle carrier can travel along the vertical center line of the furnace in an upright posture, when uniform mending over the inside of the furnace is required, it can be carried out easily by revolving the gunning nozzle 84.
However, there are difficulties as follows:
(1) When an electric furnace is large, the shifting arm 82 has to be long. In order to make the shifting arm 82 rotate in the circumference of the furnace, a large space must be maintained in a building where the electric furnace is installed.
(2) The machine is bulky in the housing position and occupies wide area so that the installation of other incidental equipments becomes restrictive.
(3) The gunning nozzle has to be exchanged in accordance with the portion to be mended. Therefore, a lot of manpower and time for the exchanging nozzle are necessary.
In order to solve the problem of the exchange for the gunning nozzle, for instance a swivel joint can be applied. As shown in FIG. 18, a known swivel joint 87 is attached to the lower end of the nozzle carrier 83 to facilitate tilting of the gunning nozzle 84. The swivel joint 87 has a swivel axis 88 and a horizontal path 90 is formed in a swivel shaft 89. The sludgy lining material passes through from a vertical path 91 to the horizontal path 90 and to a tilted path 92. however, as the lining material has to pass through two sharp bending parts, pressure loss becomes large and walls of the paths are heavily worn by the lining material. Moreover, the sludgy lining material stagnates at the bending parts and choking causes.