Heating – Processes of heating or heater operation – Including repairing – converting or assembling apparatus
Patent
1990-07-19
1993-02-23
Yuen, Henry C.
Heating
Processes of heating or heater operation
Including repairing, converting or assembling apparatus
432 75, 432246, F27D 116
Patent
active
051885271
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method and a device for cleaning the surface of the furnace rollers of a roller hearth furnace.
It was hitherto necessary to shut down the roller hearth furnace and to cool it down to ambient temperature when it became necessary to clean the surface of the furnace rollers. This practice caused especially in the case of long roller hearth furnaces which have a length of 100 m to 150 m, considerable shutdown times of an order of 8 to 10 days. The loss of production was correspondingly high.
It is the object of the present invention to substantially shorten the shutdown times of the roller hearth furnace necessary for cleaning the furnace rollers.
To achieve this objective, the method referred to hereinabove is characterized by the removal of at least one of a multiplicity of furnace sections detachably assembled to form the roller hearth furnace from the furnace assembly in a direction which is transverse to the direction of travel through the roller hearth furnace, the integration in the furnace assembly of a replacement furnace section preheated to operating temperature to replace the furnace section so removed and the cool-down of the furnace section so removed to a temperature allowing its furnace rollers to be cleaned and their cleaning being carried out.
The roller hearth furnace must hence be shut down only until one of its furnace sections has been replaced by a preheated replacement furnace section. It is of essential importance that no cool-down or heating-up times are required. The time of such a shutdown may be reduced to approximately 20 to 30 minutes.
The method proposed by the present invention is particularly important in the case of high-temperature methods in which the temperature is above approximately 700.degree. C. The forward or reverse travel of plates or slabs then causes, through scale carried into or formed inside such a furnace, the build-up of lamination-type deposits on the surface of the furnace rollers commonly referred to as pickups or scale pickups. They damage the charge to be processed and must hence be removed. The build-up of pickups is a function of time. A complete cleaning operation is normally required at intervals of one to two months.
Using the method proposed by the present invention, such cleaning operations may be carried out in cycles. If a roller hearth furnace comprises, for example, twelve furnace sections of a length of 10 m each, then on average two furnace sections must be replaced and cleaned each week.
A typical application is provided by a continuous furnace for reheating thin slabs. The slabs are cast, passed through the roller hearth furnace and are thereafter rolled. Since the travel of the slabs must be accelerated inside the furnace, the alternative use of a walking-beam furnace where scale pickup problems are not encountered, is not possible. The plant operates continuously around the clock. It is only sometimes shut down when an empty ladle is replaced by a full ladle. The shutdown times take approximately 30 minutes. The method proposed by the present invention is in such cases the only method of avoiding longer shutdown times.
Preferably, the furnace section removed is preheated to operating temperature after its furnace rollers have been cleaned and is kept ready as a replacement furnace section. It is hence only necessary to have a single additional furnace section to apply the method proposed by the present invention.
It is also advantageous for the furnace section to be preheated to operating temperature to be connected with services for water, electricity, fuel, exhaust etc. and preferably with those of the roller hearth furnace. Heat-up is hence by the equipment such as burners etc. forming anyway part of the furnace section.
To minimize heat loss and to prevent a cool-down of the furnace rollers located close to the face sides, the present invention proposes that the face side of each of the two furnace sections adjacent to the furnace section removed from the furnace assembly and exposed by the removal and the
REFERENCES:
patent: 4249888 (1981-02-01), Werych
patent: 4764108 (1988-08-01), Carthew et al.
patent: 5088921 (1992-02-01), Csehi et al.
Ruhrgas Aktiengesellschaft
Yuen Henry C.
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