Device for the continuous casting of thin metal products between two cooled rotating rolls
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to the continuous casting of thin metal products, particularly in steel. More particularly, it relates to installations referred to as being for casting between two rolls. 
     2. Description of the Prior Art 
     It will be understand that these installations comprise two rolls with substantially horizontal, parallel and coplanar axes, rotating about their respective axes in opposite directions and having cooled lateral cylindrical surfaces forming the walls of the ingot mould against which the cast molten metal solidifies. The casting space is limited laterally by closure plates, referred to as side dams, applied against the lateral faces of the rolls. The portions of the side dams in contact with the molten metal are generally made from a refractory material with good insulating properties. The side of the side dams turned towards the rolls can be entirely flat, but it may also have a projection, or &#34;insert&#34;, penetrating inside the inter-roll space, as in French Patent 2,636,259 in the name of the Applicant. In French Patent No. 2,636,259, the contacts between the rolls and the side dams are in the form of a wedge and it is the front face of the insert which laterally limits the casting space. The depth of penetration of this insert into the inter-roll space may be uniform over its entire height or may diminish as it descends towards the gap at the center of the rolls. The insert is then said to be recessed. 
     The presence of this insert is advantageous, since it permits better control of the solidification of the product in the ingot mould relative to the side dams. However, control of the play provided between each roll and the protuberant part of the insert poses a problem. In fact, it is necessary to minimise the friction between the insert and the rolls so as not to disturb the operation of the machine and, at the same time, to prevent infiltrations of molten metal between the insert and the rolls, which may occur when the play exceeds 0.1 mm. The dimensions of the insert are fixed so that the play is sufficiently small when the machine is operating under hot conditions. That is to say when the rolls which have expanded through contact with the molten steel, the rolls have reached their final radius which is increased on the order of a half millimetre relative to their size at ambient temperature. However, this expansion is not immediate: it may be spread over approximately 10 seconds from filling of the casting space. During this period of time, the play between the roll and the insert retains values which may be too large to guarantee the leaktightness of the casting space. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to remedy this drawback of the side dams with an insert by permanently guaranteeing satisfactory leaktightness of the casting space with respect to the molten metal. 
     Another object of the invention is to provide a device for casting thin metallurgical products by means of solidification of the molten metal on the cooled lateral surfaces of two parallel horizontal rolls rotating in opposite directions about their respective axes and separated from one another so as to define a casting space which is closed laterally by side dams which each comprise an insert penetrating into the inter-roll space, comprising providing films of a consumable or deformable material to ensure an operational joint between the lateral faces of the inserts and the ends of the opposite rolls as the rolls heat up and thereafter. 
     Prior to casting, these films may be placed either on the lateral faces of the inserts or on the lateral surface of the rolls. 
     As will understood, the device according to the present invention makes it possible to achieve the leaktightness of the casting space, firstly when cold, and then throughout the duration of the expansion of the rolls, without said expansion being affected, since the leaktightness material is consumable or deformable and the thickness of the films does not diminish as the rolls expand. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood when reading the following description which refers to the appended figures: 
     FIG. 1 is a front perspective view of a side dam with an insert equipped with a consumable or deformable film according to the invention; 
     FIG. 2 is a section through II--II in FIG. 1, and also partially shows the rolls of the continuous casting machine; 
     FIG. 3 shows an alternative embodiment of the device according to the invention under the same conditions as in FIG. 2. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows in isolation a possible configuration for a side dam 1 equipped with a projection, or insert, 2 intended to penetrate inside the inter-roll space. This insert is built into the side dam or is attached to its front face 3 which is fitted against the front surfaces of the rolls when the side dam is installed on the machine. The outlines 4, 4&#39; of the front surfaces of the rolls are shown in broken lines in FIG. 1. The insert has two curved cutouts 5, 5&#39; matching the form of the rolls. According to the invention, in the configuration shown, the surfaces of these cutouts 5, 5&#39; are each coated with a film 6, 6&#39; intended to ensure the leaktightness of the contact between the rolls and the surfaces of the cutouts 5, 5&#39;. The film 6, 6&#39; must satisfy various criteria. 
     Firstly, its initial thickness is such that, at the very start of casting, when the rolls are cold, the play between the film and the roll opposite the film does not exceed 0.1 mm in order to prevent infiltrations of molten metal between the roll and the cutout. Moreover, as the roll expands and frictionally contacts the film, the thickness of the film diminishes through wear and/or through compression. This reduction naturally follows the and generally matches expansion of the casing of the roll, since the variation in thickness of the film is linked to the pressure exerted by expansion. When the roll has reached its maximum expansion, which it will retain throughout the remainder of casting if the operating conditions remain stable, the film must be entirely consumed or have a stable residual thickness, so that the play between the roll and the cutout still does not exceed 0.1 mm. 
     In a known manner, the cutout of the insert may itself be coated with a metal foil (not shown) intended to reduce the wear of the insert in contact with the rolls. The leaktightness film 6, 6&#39; is then deposited on this metal foil. 
     FIG. 2 shows the side dam 1, which has just been described, mounted in a continuous casting machine, of which a portion of the rolls 7, 7&#39; is shown. In particular, the lateral surfaces 8, 8&#39; of the rolls, are in frictional contact against the films 6, 6&#39; may be seen from FIG. 2. 
     In an alternative embodiment, the film 6, 6&#39; may be deposited not on the cutouts of the insert of the side dams, but on the rolls themselves prior to casting, as shown in FIG. 3. Each film thus forms a circular band surrounding one end of a roll. It is then recommended to hollow out grooves 9, 9&#39; on the lateral surfaces 8, 8&#39; of the rolls, in each of which grooves a protuberance 10, 10&#39; is made on the inner face of the film 6, 6&#39;. This arrangement makes it possible to ensure the lateral retention of the films 6, 6&#39; during rotation of the rolls when the films are in frictional contact against the lateral surfaces 5, 5&#39; of the insert 2. The groove or the surface of the rolls may also comprise means, such as milling or rough patches, which serve to prevent or limit the sliding of the film on the roll. 
     The film may be made from a material which is consumable through wear, such as carbon or cellulose fibres. The reduction in thickness of the film may also principally be the result of the compressive force exerted on the film by the roll and the insert. The use of a metal softer than copper, such as aluminium or lead, is then perfectly suitable. 
     Of course, the invention is not restricted to the example which has just been described and shown. Various other configurations of the insert and of the side dam as a whole can be envisaged, the essential point being the presence of the leaktightness films with a thickness which decreases over time between the rolls and the lateral surfaces of the inserts as the casting rolls commence operation under hot conditions.