第17页辽宁科技大学本科生毕业设计Method of operating a mixer type hot metal car for the transport of molten iron and a device for carrying out the methodAbstractA hot metal car is used for the transport of molten pig iron from a blast furnace to a steel making plant, the car having an opening through which it is filled and emptied. To restrict heat loss from the car, the opening is closed during at least one of (a) the journey from the blast furnace station to the steel making plant and (b) the journey from the steel making plant back to the blast furnace by a disposable cover which is at least partly lost into the molten iron during the course of the emptying or filling of the car at the end of the journey concerned. Inventors:Baas, Willem (Heemskerk, NL) Hof, Tette (Heemskerk, NL) Comes, Heinrich (Borken, DE) Jaunich, Helmut (Raesfeld, DE) Krampe, Hubert (Reken, DE) BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a method of operating a mixer type hot metal car for the transport of molten iron, particularly in conveying pig iron from a blast furnace to a steel making plant, and to a device for carrying out this method. 2. Description of the Prior Art In the steel industry, pig iron manufactured in a blast furnace is usually conveyed in the liquid state to a steel making plant by means of transport vessel known as a mixer type hot metal car. Another name used for this vehicle is a torpedo car. This hot metal car is a rail vehicle having a torpedo-shaped transfer vessel which is lined on its inside with refractory bricks and is supported on a bogie at each end. The transfer vessel is provided with an opening, known as the pouring mouth, which during filling with pig iron and while the transfer vessel is being conveyed is located at the top of the transfer vessel. The transfer vessel is rotated about its longitudinal axis to empty the vessel, so that the pig iron is discharged through the opening into a receiver. An example of such a car is given in Netherlands patent application No. 68.14343 (U.S. Pat. No. 3,661,374). In practice, the transfer vessel is filled at a blast furnace with molten pig iron at about 1500 C., and is then conveyed to a steel making plant. The pig iron is transferred from the vessel into a receiver in the steel making plant and the empty vessel is returned to a blast furnace to be refilled with pig iron. Sometimes an intermediate stop is made on the outward journey with the full vessel, during which the pig iron in the vessel subjected to treatment, typically being desulphurised. For this purpose a lance is inserted into the vessel through the opening. In a steel works a number of such cars are simultaneously in operation. The cycle time of a car is an average of 15 hours, comprising 3 hours for filling, 6 hours for the outward journey and 6 hours for return of the empty vessel. In practice these average times regularly show considerable variations because stops are made for various reasons during the outward and return journey. An example of a stop made on the return journey is when a car is temporarily put out of operation. One problem with the known method is that heat loss occurs whilst the car is in operation. Some of this heat loss is the result of radiation and convection from the outside surface of the vessel; more heat loss is due mainly to heat radiation through the opening from the inside of the vessel to the atmosphere. Heat loss during the outward journey means that the pig iron is supplied to the steel making plant at a lower temperature than that at which it is filled into the vessel. If there is and extremely long stop, this may mean that the pig iron can no longer be processed in the steel making plant. Because of heat loss during the return journey, the refractory brick in the empty vessel cools down. This also leads to a lower temperature of the pig iron when supplied to the steel making plant, since the pig iron, when charged into the vessel at the blast furnace, loses heat to the brick. Also, if the brick cools down considerably as a result of a long return journey, cracks may then occur in the brick thereby reducing the life of the brick. SUMMARY OF THE INVENTION The object of the invention is to provide a method of operating a mixer type hot metal car for molten iron in which the heat loss through the opening of the transfer vessel is reduced. A further object of the invention is to provide low cost, simple and safe device for reducing the heat loss through the opening of the transfer vessel for molten iron. According to the invention, a disposable cover is fitted to seal the opening of the vessel, after it is filled and/or after discharge of the iron from the vessel in order to reduce the heat loss from the vessel through the opening, and the cover is allowed to be carried away with the iron at the end of the subsequent journey when the pig iron is discharged from the vessel or the vessel is filled w