Heating – Heating apparatus element having protective cooling structure – Conveyor – chute or work agitator element
Reexamination Certificate
2001-09-13
2003-04-15
Wilson, Gregory (Department: 3749)
Heating
Heating apparatus element having protective cooling structure
Conveyor, chute or work agitator element
C492S046000
Reexamination Certificate
active
06547557
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a water-coolable furnace roller for transporting goods to be transported, in particular, continuous-cast strip material of a continuous casting plant, through a roller hearth heating furnace. The furnace roller comprises a shaft driven in rotation and supported external to the furnace. The shaft has cooling medium channels positioned, in particular, in the interior and comprises support rings for supporting the goods to be transported which are arranged on the shaft by means of receiving bores and form a conveying plane.
2. Description of the Related Art
Thin slabs are, for example, pre-heated to rolling temperature in roller hearth furnaces of continuous casting plants. Conveying the rolling stock or the slabs through the roller hearth furnaces is carried out by means of furnace rollers of different configurations. The roller hearth furnace is positioned conventionally in line between the casting device and the mill train and is characterized by its function as a heating, compensation, and buffering zone. As a result of the types of stress of furnace rollers during the furnace operation, the furnace roller types of the prior art have a service live of different lengths.
The dimensions of such furnaces and its devices for heat application, for example, burners, are designed such that at the exit of the furnace the thin slabs have the required rolling temperature. In this connection, a uniform temperature distribution in the slab over its length, width, and height at the furnace exit is a mandatory prerequisite for the subsequent rolling action. The furnace length allows several thin slabs to be received which, after casting at different casting speeds, are separated from the cast strand.
The transport of such thin slabs is carried out within the furnace by means of driven furnace rollers. They are arranged at a certain furnace height at a level—the transport level—at predetermined spacings relative to one another. Relatively speaking, the dimensions of the rollers are characterized in that the diameter of the support rings and of the shafts are small in comparison to the length of the rollers.
The transport rollers in the roller hearth furnaces can be provided with water cooling, but can also be without a cooling device, i.e., they are so-called dry rollers.
The conventional configuration of water-cooled rollers comprises several support rings arranged at an axial spacing to one another on the water-cooled shaft. The latter is insulated between the support rings with refractory material, wherein this insulating layer is almost as thick as the outer diameter of the support rings.
The shaft is supported external to the furnace and provided in this external area with connectors for the inner cooling of the shaft. This inner cooling is achieved by a tube with circular cross-section which is arranged concentrically in the shaft. Cooling water flows into the tube, then flows through the tube to the opposite side of the furnace, and flows at the other side into the annular gap between the tube and the shaft, flows therethrough, and finally exits the shaft at the inlet side. In the annular gap between the shaft and the inserted tube, insert members in the widest sense of the meaning of the word can be provided which have the objective to secure the tube in the radial position and to increase the flow velocity of the water in the annular gap.
The support rings mounted on the roller axle are comprised conventionally of cast material and are produced of high temperature-resistant nickel-based or cobalt-based alloys. The shaft is preferably manufactured of heat-resistant steels.
The water-cooled rollers are used primarily, but not exclusively, in the heating zone of a roller hearth furnace. In the transport direction, they are alternatingly provided with different numbers of support rings. Conventionally, the shafts are provided with four or five support rings, usually alternatingly. In this connection, in the transport direction from one roller provided with four support rings to a roller with five support rings, the support rings are located on different lines. The roller with four support rings has two of its support rings positioned on one half of the shaft, respectively, while on the roller with five support rings one roller is arranged at the center of the roller and the others are positioned so as to be laterally outwardly staggered relative to the support rings on the roller with four support rings.
In the prior art the support rings are secured on the shaft against axial movement usually by welding seams. The torque can be transmitted by known shaft/hub connections, for example, feather keys, but also by welding seams.
As a result of the thermal expansion of the support ring material during heating as well as in the operating state, the seat of the support rings on the shaft will loosen. Reverse bending fatigue stress of the furnace roller as well as the intended higher heat dissipation from the support ring surface to the cooling water at the inner side of the shaft cause, primarily during the heating phase, thermal stress in the welding seams which, over time, can lead to their destruction and to unusable furnace rollers.
An important reason for failure of a furnace roller is the damage or destruction of the insulation of the roller because, in particular, by this event, the welding seams are directly exposed to the high furnace temperatures.
By contact between the support ring and the water-cooled shaft, the heat is dissipated from the support ring surface, and the surface temperature of the support rings is thus significantly reduced. The more heat is dissipated, the cooler the support ring surface becomes. The cooler the support ring surface, the lower the tendency of scale deposition and pick-up thereon.
During the manufacture of, for example, thin slabs, hot steel comes into contact with oxygen in the atmosphere. Accordingly, the steel surface is oxidized with formation of scale. Such scale formation occurs basically everywhere where oxygen is available in the surrounding gas medium for reaction with the steel surface.
During the transport of a thin slab through the furnace, the scale falls off the billet surface and is removed through scale flaps in the lower part of the roller hearth furnace. On the other hand, during the contact of the thin slabs and the furnace roller in the roller hearth furnace scale can adhere to the support ring surface and can form deposits thereon, which can be pressed into the thin slab underside and, depending on the depth of the hot strip to be rolled therefrom, can appear as a surface flaw. Such flaws then cause rejects and thus represent a severe quality problem for the slab manufacturer.
The prior art document DE 40 22 768 describes a roller table with rollers for conveying and guiding a workpiece through a heating furnace. The rollers comprise shafts whose ends are rotatably supported in bearings. They form wheel-like support devices which, in the longitudinal direction of the shaft, are fastened at a spacing from one another on the outer shaft periphery. The surfaces of the wheel-like support devices which are positioned in the radial direction farthest outwardly are provided as supports for the workpiece while it is being guided through the heating furnace. The wheel-like support devices are comprised of a hub which are connected by ribs with a wheel rim-like continuous ring structure. The ribs are separated from one another by open spaces in order to reduce their cross-sectional surface area and to thus make the thermal flow from the annular structure to the hub more difficult. The hub is comprised of several core members arranged angularly at a spacing to one another and having a nose-like portion and a head portion. A welding seam connects exclusively the nose-like portions with the shaft so that the head portions can move relative to the shaft as a result of different expansion as well as during bending. Means for thermal insulation of the shaft are subst
Kueffner Friedrich
SMS Demag Aktiengesellschaft
Wilson Gregory
LandOfFree
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