EP0090761B1 - Spout for molten metal - Google Patents

Description

The present invention relates to a pouring channel intended to receive liquid metals from a furnace and in particular from the cast iron of a blast furnace.

Drains are known comprising a wear refractory layer, in contact with the liquid metal, enveloped by a permanent coating which is housed directly in the reinforced concrete slab of the pouring floor.

As soon as the tap hole opens, the channel fills with cast iron and slag which floats. A baffle system allows density separation of the pig iron and the slag. At the end of the casting, the channel is emptied and it is necessary to carry out work of restoration. The accessibility of the hot channel as well as the duration of these works prevent a rapid re-use of the channel, which is incompatible with the rate of casting of modern blast furnaces. Rehabilitation involves a large volume of strenuous work. We have therefore changed the technique of using the channel to permanently store in it a liquid iron bath covered with a more or less significant layer of slag. Between two flows, the temperature of the cast iron can drop from around 1500 ° C to around 1300 ° C. The permanent presence of liquid iron in the channel results in a continuous thermal flow towards the reinforced concrete of the slab of the pouring floor which heats up in its mass, which causes stresses of expansion, bursts and cracks.

To overcome this drawback, we used channels whose refractory lining is housed in a sheet metal construction which itself is supported by structural elements of the pouring floor. Depending on the support, the sheet can be cooled, either by natural convection of the ambient air, or by forced ventilation. This inefficient cooling mode does not allow any preferential cooling of a determined zone of the channel. Normally the sheet reaches a temperature which is 150 to 300 ° C depending on the wear of the refractory. The rate of cooling of the cast iron in this channel, although higher than for a massive channel, is still low enough for the cast iron to remain in its liquid state, even if the interval between 2 successive flows is of the order of 5 to 8 hours. Under the effect of temperatures, the support sheet and the refractory lining undergo differential expansion, which does not fail to cause stresses and cracks in the refractory lining, especially when the thermal regime to which the channel is subjected is variable p .ex. in case of occasional emptying of the channel during a shutdown of the blast furnace. These cracks allow the cast iron to infiltrate the refractory lining and this results in breakthroughs in the channel. A channel, the air flow rate of which can be adjusted individually in different conduits surrounding the permanent refractory is described in the prior patent application EP-A-60 239.

According to the document Patents Abstracts of Japan, vol.5, no. 156 (C-74) (828), October 6, 1981, a channel for liquid metals is known, in which a wall with high thermal conductivity is disposed on each lateral side of the channel. Each of the walls is traversed longitudinally by a slot-shaped duct. This duct can guide air, steam or water as a coolant.

The object of the present invention is to propose a channel which does not have the defects described above and which is capable of being installed directly in the reinforced concrete structures of the pouring floor.

This object is achieved by a channel as characterized in the independent claims. Preferential embodiments are described in the dependent claims.

The advantages of the channel are due to the presence of a layer of material maintained at low temperature and practically isothermal, which limits the heating of the support structures of the channel and which by its great capacity of distribution and evacuation of calories. allows all liquid metal infiltration to be frozen in the permanent refractory lining of the channel. As the distribution of temperatures in the refractory lining can be calculated, well-defined expansion joints can be provided without danger, which reduces the mechanical stresses, due to thermal expansion, experienced by the assembly and transmitted to the supporting structures of the channel . In addition, by using refractories in the permanent layer before different thermal conductivities, it is possible either to thermally isolate different zones of the channel to limit the heat losses of the cast iron, or on the contrary to cool more intensively zones which are highly stressed. The overall cooling rate is always quite low, so that the cast iron remains liquid even if the interval between two successive castings is 5 to 8 hours.

The invention will be better understood with the aid of the drawing, where a possible embodiment is shown in a nonlimiting manner in FIG. 1. The drawing shows a partial section through a channel according to the invention.

A cast iron bath 1, carrying a layer of slag 2, is in contact with a wear layer 3, the section of which is U-shaped. This wear layer 3, consisting of an unshaped material, is produced on a permanent covering 4, which in the present case consists of two layers of overlapping bricks. The outer layer of bricks rests against graphite blocks 7 and cooling elements 10. These elements 10 arranged both in the side walls and in the bottom of the channel are formed by sealed longitudinal conduits 5, in which water circulates, sandwiched between flat graphite bricks 6 and 8. The bricks 8 are in contact with the permanent coating 4. The space 9 between the conduits 5, the bricks 6 and 8 as well as the graphite blocks 7, is filled with an unshaped material, good conductor of heat, ensuring good thermal contact with the cooling tubes. The unshaped material also allows expansion of the conduits caused by small temperature variations. The channel is housed in a reinforced concrete slab 12. An equalizing layer 11 eliminates the roughness of the concrete.

The upper graphite blocks and the adjacent bricks of the permanent coating are protected by sheet metal segments 14. On this sheet as well as on the wear layer 3 is a concrete layer 17, which protects the sheet during accidental overflows of laugh. Bars 16 fix the sheet 15, integral with the sheet 14, to the reinforcements of the concrete. Between the horizontal sheet 14 and the graphite blocks, as well as the bricks of the permanent covering, is an expansion joint 13.

The graphite blocks 6, 7, 8, excellent heat conductors, create a practically uniform temperature zone around the permanent coating 4. This temperature is mainly controlled by means of the flow rate and the temperature of the cooling water. The assembly is adjusted so as to make the temperature at the reinforced concrete - cooling layer interface prevail below 100 ° C and preferably around 60 ° C.

The permanent coating 4 made of bricks capable of withstanding the direct action of cast iron constitutes a thermal barrier which prevents the cooling system from drawing too much heat from the liquid cast iron. The material of the bricks resp. the number of brick layers to be superimposed is chosen in accordance with the desired degree of thermal insulation. Preferential cooling of certain highly stressed areas can be achieved by a judicious choice of the quality of the bricks of the refractory lining of the permanent layer. To drastically reduce the erosion of the wear layer, at the points where it is particularly stressed, one can replace some of the bricks of the coating 4 by bricks with high thermal conductivity 4a, which are preferably made of semi-graphite .

Temperatures between 100 and 1100 ° C prevail at the interface of the wear layer and the permanent coating, depending on the local thermal conductivity of the permanent coating and the degree of erosion of the wear layer 3.

In the event of infiltration of liquid iron into possible cracks in the wear layer 3 and in the permanent coating 4, the metal will solidify immediately on contact with the graphite blocks 7 and 8, kept at low temperature and not will have no harmful effect.

100 W/m ° K) en tout ou en partie par un autre matériau comme p.ex. un produit à base de carbure de silicium (À ≃ 18), de semi-graphite (λ ≃ 35) etc., dont les propriétés de conductibilité thermique sont élevées. On ne sort pas du cadre de l'invention en utilisant des matériaux métalliques, p. ex. des plaques de fonte (λ ≈ 100), d'acier (λ ≈ 35) ou de cuivre (λ ≈ 350) pour réaliser la zone de basse température. Il faut évidemment choisir les plaques métalliques assez épaisses (p. ex. 5 à 20 centimètres) pourqu'elles aient des capacités suffisantes d'absorption, de distribution et d' évacuation des calories. Ces plaques, dont l'épaisseur est choisie en fonction de leur conductibilité thermique, éviteront tout perçage lors d'infiltrations de métal liquide dans le revêtement réfractaire permanent.We can replace graphite (coefficient of thermal conductivity

100 W / m ° K) in whole or in part by another material such as a product based on silicon carbide (≃ ≃ 18), semi-graphite (λ ≃ 35) etc., the properties of which of thermal conductivity are high. It is not going beyond the scope of the invention to use metallic materials, p. ex. cast iron (λ ≈ 100), steel (λ ≈ 35) or copper (λ ≈ 350) plates to create the low temperature zone. Obviously, the metal plates that are thick enough (eg 5 to 20 cm) must be chosen so that they have sufficient capacity for absorbing, distributing and dissipating calories. These plates, the thickness of which is chosen according to their thermal conductivity, will prevent any drilling during infiltration of liquid metal into the permanent refractory lining.

The use of an unshaped material suitable for making 1, all or part of the low temperature zone makes it possible to drown the cooling conduits therein. It is also possible to envisage placing the conduits in a layer of material of low thermal conductivity (eg λ ≈ 2) surrounding the low temperature zone and in direct contact with it. In this case, however, care must be taken to have sufficient heat dissipation so that the isothermal zone does not exceed around 100 ° C. This can for example be ensured by choosing a high number of conduits arranged very close to the low temperature zone.

When using metal plates it may be advantageous to fix the conduits guiding the cooling fluid to the outside thereon, eg by welding.

Since it is easy to maintain a temperature below 80 ° C in the isothermal zone, the channel is particularly suitable for being housed directly in the reinforced concrete structure of the pouring floor. When on the other hand prefers the use of a sheet metal construction to support it, the conduits guiding the cooling fluid may be placed outside the construction p. ex. by welding U irons along the sheet. The heat flow between the low temperature zone and the cooling system in this case passes through the support sheets without significant heating (temperature below 100 ° C).

The spacing, shape and arrangement of the conduits must be chosen as a function of the thermal conductivity and the thickness of the layer constituting the low temperature zone as well as the desired temperature profile in the refractory lining.

To increase the operational safety of the channel, it is possible to provide, instead of water, another cooling fluid, such as for example oil.

The conduits can be supplied in parallel or in series. To optimize the operation of the channel, the temperature of the coolant can be monitored and the flow rate can be varied depending on the temperature.

Claims (11)

1. A spout for receiving molten metal and, in particular, cast iron from a blast furnace, comprising a first layer (3) of a wearing refractory material, of U-shaped cross-section, defining two lateral walls which are joined by a base, and guiding the molten metal, the first layer (3) being housed in a second layer (4) of permanent refractory material also having a U-shaped cross-section and making thermal contact with the first layer, as well as conduits (5) which guide a coolant in thermal contact with the second layer (4), characterised in that the second layer (4) is housed in and makes thermal contact with an isothermal third layer (7) of which the lateral sides and the base are produced substantially from a product based on or made of graphite, semi-graphite, or silicon carbide, of which the thermal conductivity is higher than 12 W/m ° K and in that the conduits (5) which make thermal contact with the lateral sides and the base of the third layer (7) guide a cooling liquid.

2. A spout according to Claim 1, characterised in that the third layer (7) has a coefficient of thermal conductivity higher than 30 W/m ⁰ K.

3. A spout according to Claims 1 or 2, characterised in that the conduits (5) in which a cooling liquid circulates are integrated in the third layer (7).

4. A spout according to Claims 1 or 2, characterised in that the conduits (5) in which a cooling liquid circulates are integrated in or fixed on a layer of substance which makes thermal contact with the third layer (7).

5. A spout according to Claim 1, characterised in that the third layer (7) is constituted by materials which are different from one another.

6. A spout according to Claim 1, characterised in that the third layer (7) is of variable thickness.

7. A spout according to Claims 1, 5 or 6, characterised in that the arrangement, number and shape of the conduits (5) in which the cooling liquid circulates is a function of the desired temperature profile of the first layer (3).

8. A spout according to Claim 1, characterised in that the second layer (4) is constituted in part by a material (4a) having thermal conductivity higher than 12 W/m ⁰ K.

9. A spout for receiving molten metal and, in particular, cast iron from a blast furnace comprising a first layer of wearing refractory material (3), of U-shaped cross-section, defining two lateral walls which are joined by a base, making contact with the molten metal, the first layer (3) being housed in a second layer (4) of permanent refractory material also having a U-shaped cross-section and making thermal contact with the first layer, the second layer (4) being housed in and making thermal contact with a third layer (7) having lateral sides and a base produced substantially with metal elements, as well as conduits (5) guiding a coolant in thermal contact with the third layer, characterised in that the minimum thickness of the third layer is 5 cm while having thermal conductivity greater than 12 W/m oK and in that the conduits (5) which make thermal contact with the lateral sides and the base of the third layer (7) guide a cooling liquid.

10. A spout according to claim 9, characterised in that the conduits (5) are fixed to the exterior of the third layer, preferably by welding.

11. A spout according to one of claims 1 or 9, characterised in that the cooling liquid is water or oil.

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