1. Field of the Invention
The present invention relates to a heating furnace of various types, such as a furnace employed in a hot rolling process in manufacturing steel, a reheating furnace or a hardening furnace employed for manufacturing a seamless steel pipe and a heating or heat-treating furnace used in manufacturing a copper alloy. The invention relates more particularly to a heating furnace in which an object of treatment is conveyed by means of a conveyer means within a hot temperature atmosphere present inside the furnace.
2. DESCRIPTION OF THE RELATED ART
A conventional heating furnace of the above type having the conveyer means for conveying the object within the hot temperature atmosphere inside the furnace, for use in e.g. a hot rolling process of steel production is shown in FIG. 7. With this furnace, objects W such as steel pieces are pushed into the furnace 100 one after another by means of a pusher 110 provided adjacent the charging side of the furnace 100. As the objects W are pushed by the pusher, the objects W come into slide contact with each other and are conveyed in this condition on a water-cooling slider pipe 120 to the extracting side of the furnace.
In recent years, a new type of furnace has been developed. This new furnace, as shown in FIG. 8, has a plurality of movable beams arranged along the object conveying direction inside the furnace 100 and these beams repeated effect a series of motions along a rectangular path in a direction of arrow Z consisting of an upward movement, a forward movement, a downward movement and a rearward movement. With the upward movement, the beam lifts up the object on a fixed beam. Next, with the forward movement, the beam forwardly moves the object W. And, with the subsequent downward movement of the beam, the object W is placed onto a further fixed beam disposed more downstream than the aforesaid fixed beam. After completion of this operation, the beam moves rearward to become ready for a next operation. This type of furnace is commonly referred to as a walking beam type furnace and has already been put into practice in some applications such as a heating furnace used in a hot rolling process of steel production and a heating furnace used for other types of processes such as production of a seamless steel pipe and a copper alloy treatment process.
However, with the first-described pusher type furnace, during the conveying operation effected inside the furnace under the severe condition of high temperature atmosphere (e.g. as high as 1,300 degrees in Celsius in the case of hot rolling of steel pieces), there often occurs abrasive damage on the objects W through their sliding contact with the water cooling slider pipe 120. This results in deterioration in the product quality and yields.
Further, in e.g. steel manufacturing process, the objects often weight over several hundreds of tons. Then, in order to forcibly push such enormous mass into the furnace against large friction between the objects W and the slider pipe 120, the pusher 110 must exert an extremely large pushing force. Accordingly, the system suffers high running costs for its conveyer unit and the application of such large pushing force tends to aggravate the abrasive damage on the objects.
Moreover, in case the furnace has a significant length, the length of the object group increases accordingly. Then, the greater this length of object group is, the greater pushing force the pusher must exert. Further, when the objects having such significant length are pushed in the forcible manner, there often occur the trouble that the pushing force raises some of the objects of the group relative to the rest or that the force causes overlapping of the objects. In either case, the entire conveying operation can be disabled. In this respect, the scale or the length of the furnace is restricted.
For instance, in the case of the pusher type furnace, in order to avoid the above-described troubles, the following practice is usually observed: EQU thickness of steel piece.times.(200 through 250)&gt;the maximum length of the objects (i.e. steel pieces) feedable by the pusher
Accordingly, when the steel piece has a thickness of 100 mm, it is unfeasible to extend the length of the furnace beyond 25 m.
On the other hand, in the case of the walking beam type furnace, while this construction decreases the occurrence of the abrasive damage on the objects W in comparison with the above-described pusher type, the construction suffers the problem of complexity and high installment and running costs. Specifically, the plurality of movable beams which effect the rather complicated rectangular movement (along the arrow Z in the drawing) must be installed inside the furnace. Further, in order to endure the high temperature atmosphere inside the furnace often exceeding 1,000 degrees in Celsius, each of the fixed beams and the movable beams must be equipped with its cooling means. Thus, the system becomes complicated and such complicated system inevitably suffers high installment and running-maintenance costs.
Also, in order to lift up and then to forwardly move the object W, the movable beam must be supplied with a large power. This fact further adds to the increase of the running costs.
The primary object of the present invention is to solve the above-described problems of the convention through improvement of the conveyer means of the furnace, which improvement effectively overcomes the problems of the conventional pusher type and walking beam type furnaces while maintaining good heat-resistance against the high temperature atmosphere inside the furnace.