Patent Publication Number: US-11020795-B2

Title: Method and device for producing foundry ingots from metal

Description:
STATE OF THE ART 
     The invention relates to a method for producing ingots from metal, in particular from steel, having a cross-sectional area of more than 0.1 m 2  according to the preamble of claim  1 . Furthermore, the invention relates to a device for performing the method according to the invention. 
     From WO 2015/079071 A2, a generic method is known, which is characterized in that the cast ingot is rotated about its longitudinal axis in the area of a tertiary cooling section only after complete withdrawal from an ingot mold, i.e. after completion of the casting process. 
     From the applicant&#39;s WO 2015/101553 A2, another method for producing ingots from metal having the features of the preamble of claim  1  is known. Small quantities of ingots having a diameter of 300 mm and more and block lengths of more than 5 m can be efficiently produced by means of the known method, liquid metal continuing to be fed to the ingot mold circulation after the end of the regular casting process in such an amount that at least the shrinkage of the metal or steel melt occurring during the solidification is compensated. 
     Additionally, there is a call for a high-quality ingot regardless of the diameter or the length of the ingot. This relates in particular to a good solidification structure, in particular with respect to the segregation and the porosity of the center, so that such ingots can make full use of their (quality) properties. The method known from the aforementioned disclosure does not indicate any measures to ensure or to obtain an optimal casting quality because the disclosure deals primarily with maximum efficiency. 
    
    
     DISCLOSURE OF THE INVENTION 
     Starting from the aforementioned state of the art, the object of the invention is to improve a method for producing ingots from metal, in particular from steel, having a cross-sectional area of more than 0.1 m 2  according to the preamble of claim  1  in such a manner that the produced ingots have a particularly high quality. This means, in particular, that the cross section of such an ingot can be realized so as to be as homogenous and as free of segregation as possible and comprising pores and cavities which are as few or small as possible. 
     Concerning a method for producing ingots from metal, said object is attained by the features of claim  1  by at least temporarily rotating the ingot about its longitudinal axis, at least during the casting process, the rotation of the ingot being preferably realized via a pedestal element or a withdrawing tool on which the ingot stands with its facing side. 
     Such an at least temporary rotation of the ingot about its longitudinal axis during the casting process while the liquid metal of the ingot has not completely solidified yet acts like an electromagnetic stirrer over the entire ingot length, the solidified ingot thus having a greatly reduced porosity and segregation of the center. Furthermore, it has been found that the solidification time can be reduced by the constant movement of the still liquid metal melt in the ingot and, therefore, a particularly high performance per time unit in the generation or production of ingots can be achieved. 
     Advantageous embodiments of the method according to the invention for producing ingots from metal are disclosed in the dependent claims. All combinations of at least two features disclosed in the description, the claims and/or the FIGURES constitute part of the scope of the invention. 
     As explained above, the principle of the invention consists in an at least temporary rotation of the ingot about its longitudinal axis while the metal of the ingot is not completely solidified yet, the rotation already taking place during the actual casting process, i.e. within the area of the ingot mold. The time for the start and the end of the rotation of the ingot, the type of rotation and the direction of rotation depend on different factors and are to be adjusted to the specific application, if required. A first version of the method, which is particularly simple to realize in terms of the device, provides that the ingot is continuously rotated in a (single) direction about the longitudinal axis. 
     Alternatively, the ingot may be rotated in an oscillating manner about the longitudinal axis, for example, about a rotation angle of ±45° with respect to a mean position. 
     An additional possibility for influencing the quality or the solidification properties of the ingot provides that the rotational angular velocity of the ingot about the longitudinal axis is varied during the rotation of the ingot. For example, a constant increase or reduction of the rotational angular velocity or a sudden stopping and a subsequent rotating with high acceleration can be provided. 
     During the production of the ingot, liquid metal constantly enters the area of the ingot mold, the at least partially solidified block being withdrawn by means of the withdrawing tool at the same time, so that liquid metal can continue to be supplied. In general, such a withdrawing movement of the ingot takes place continuously, i.e. at a constant withdrawing speed, at least until the time of the end of the casting, at which point the withdrawing speed is reduced, for example. 
     An additional version of the above-described method according to the invention provides that the ingot mold (in addition to the ingot) is rotated about the longitudinal axis. Such a rotation of the ingot mold about the longitudinal axis can be realized either by means of an additional, separate drive or by the fact that the ingot mold is disposed so as to be rotatable about its longitudinal axis and that a rotation of the ingot mold is caused by the friction with the metal of the ingot. 
     Furthermore, the ingot may continue to be rotated about its longitudinal axis for a certain duration of time after the end of casting in order to obtain the highest quality possible. The rotation of the ingot about its longitudinal axis is to be performed, in particular, until it is ensured that the cross section of the ingot has completely solidified over its entire length. 
     An additional optimization of the quality of the ingot can be obtained if the liquid metal of the ingot is moved by means of an electromagnetic stirring coil. Such a stirring coil can be disposed so as to either be fixed in the area of the ingot or to be longitudinally displaceable in the direction of the longitudinal axis of the ingot about the ingot. It is also possible to provide a combination of a fixed and a displaceable electromagnetic stirring coil. 
     Furthermore, the invention comprises a device for performing the above-described method according to the invention, the device having a casting ladle and a tundish, if required, for introducing liquid metal melt into an ingot mold open at the bottom. Additionally, a withdrawing tool which is vertically moveable is provided for at least indirectly disposing the ingot on a pedestal surface facing the ingot mold. The device according to the invention is characterized by means for rotating the ingot about its longitudinal axis. 
     According to a version for rotating the ingot about the longitudinal axis which can easily be realized in terms of the equipment needed, the means are formed by the withdrawing tool itself or by a pedestal element on which the ingot stands, the withdrawing tool or the pedestal element being rotatable about its longitudinal axis by means of a drive. With means for string rotation of such a design, mechanical loads of the circumferential surface of the ingot are avoided, in particular. 
     Alternatively or additionally, the means may be formed by driving means, in particular in the form of rotatable rolls or rollers, acting on the outer circumference of the ingot. Such rolls or rollers are in contact, at least frictionally, with the outer circumference of the ingot and cause the desired rotation of the ingot, in which case the withdrawing tool needs to be disposed so as to also be rotatable (merely) about the longitudinal axis but does not need a separate drive. 
     Furthermore, the ingot mold may be disposed so as to be rotatable about the longitudinal axis and/or at least one electromagnetic stirring coil may be provided for the ingot. 
     Further advantages, features and details of the invention can be derived from the following description of preferred exemplary embodiments and from the drawing. 
     In the only FIGURE, it shows a highly simplified longitudinal section of a device for producing an ingot. 
     Device  10  shown in the FIGURE is used for the discontinuous production of an ingot  1  from metal  2 , in particular from steel, having a cross-sectional area of preferably more than 0.1 m 2  and a length of, for example, up to 15 m. The cross-sectional area of ingot  1  is preferably circular, but it can also be in the form of a rectangle or a square or in any other desired form. 
     Device  10  comprises a casting ladle  11  from which liquid metal  2 , via a provided tundish  12 , if required, can be withdrawn into an ingot mold  15  open at the bottom. Above ingot mold  15 , a lining  16  which is radially surrounded by a heating device in the form of an induction coil  17  can optionally be provided at the side which faces tundish  12 . The unit of lining  16  and heating device or induction coil  17  is also known as a “feeder”. The feeder is used for the heating of the liquid metal, in particular at the end of casting. 
     It is additionally mentioned that another form and disposition of a heating device can be provided, for example, in the form of heating rods, electrodes etc. disposed above lining  16 . 
     At the side facing away from tundish  12 , ingot mold  15 , which can optionally be radially surrounded by an electromagnetic stirrer  19 , is adjacent to ingot  15 . Meniscus  3  of the metal melt is exemplary located in the area of ingot mold  15 ; meniscus  3  may be covered by a powder (not shown) for lubrication and/or for (thermal) insulation. Furthermore, it is to be mentioned that the inner cross section of ingot mold  15  is adjusted or equivalent to the cross section of ingot  1  to be formed. 
     If required, a cooling device  21  which is disposed in operative connection with ingot  1  is located underneath ingot  15  at the side facing away from tundish  12 . An additional electromagnetic stirrer  22  which can be disposed so as to be movable along longitudinal axis  5  of ingot  1  in the direction of double arrow  23  can optionally be provided underneath ingot mold  15 . 
     Furthermore, it is mentioned that ingot mold  15  may be disposed so as to be rotatable about longitudinal axis  5  of ingot  1  and ingot mold  15  by means of bearing devices (not shown). 
     Underneath ingot  1 , a pedestal element  25  which is cooled, if applicable, and which forms a pedestal surface  26  for ingot  1  at the side facing ingot  1  is provided. Pedestal element  25  is connected to a withdrawing tool  28  which is connected to a longitudinal column  30  via a cross member  29 . Cross member  29  or withdrawing tool  28  can be raised and lowered in the direction of longitudinal axis  5  by means of a drive (not shown). Furthermore, pedestal element  25  may also be mounted so as to be rotatable about longitudinal axis  5  and an active rotation of ingot  1  about longitudinal axis  5  during the casting process of ingot  1  can be generated by means of a drive  32 . 
     It is exemplarily shown that pedestal element  25  and ingot  1  and ingot mold  15  rotate clockwise according to arrows  33 ,  34 . Preferably, drive  32  is configured in such a manner that, depending on the specific application, it can move ingot  1  or pedestal element  25  also in an oscillating manner, for example, by 45° about a mean position of ingot  1 , as well as at different rotational angular velocities according to a provided velocity profile. 
     If no pedestal element  25  rotatable about longitudinal axis  5  by means of a drive  32  is provided, rolls  35  which can rotate about an axis  36  and which are driven by means of a drive  37  and which act on circumference  6  of ingot  1  above pedestal element  25  can serve as an alternative, for example. In general, several of these rolls  35  are provided, preferably in equal angular distances about longitudinal axis  5 . 
     During the production of ingot  1 , ingot  1  is withdrawn from ingot mold  15  downward in the direction of longitudinal axis  5  by means of withdrawing tool  28 . The withdrawing speed of ingot  1  can be constant or discontinuous. Furthermore, an at least temporary rotation of ingot  1  about longitudinal axis  5  takes place during the withdrawal of ingot  1  from ingot mold  15 , i.e. during the casting process and after the end of the withdrawing process, if required. 
     Liquid metal  2  solidifies inside ingot  1  from outer circumference  6  of ingot  1  to longitudinal axis  5 . After the regular end of the casting process, liquid metal may continue to be fed into ingot mold  15  according to the disclosure of WO 2015101553 A2 in order to made up for the shrinkage of the metal melt. 
     Above-described device  10  and the described method can be altered or modified in many ways without deviating from the idea of the invention. 
     REFERENCE SIGNS 
     
         
           1  ingot 
           2  metal 
           3  meniscus 
           5  longitudinal axis 
           6  outer circumference 
           10  device 
           11  casting ladle 
           12  tundish 
           15  ingot mold 
           16  lining 
           17  induction coil 
           19  stirrer 
           21  cooling device 
           22  electromagnetic stirrer 
           23  double arrow 
           25  pedestal element 
           26  pedestal surface 
           28  withdrawing tool 
           29  cross member 
           30  longitudinal column 
           32  drive 
           33  arrow 
           34  arrow 
           35  roll 
           36  axis 
           37  drive