Abstract:
A control assembly for controlling reciprocal motion of a stopper used with a tundish dish including a shaft movably guided within a guiding assembly and connected to the stopper and wherein a motor is movable between a first postion wherein output from the motor is disengaged from a motion converting device connected to the shaft and a second position wherein the motor is drivingly engaged with the motion converting device. A linking device is also provided to secure the motor relative to the motion converting device in the second position thereof.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an assembly for controlling a stopper belonging to a continuous casting installation, as well as to a continuous casting installation provided with such a control assembly. 
   2. Brief Description of the Related Art 
   The first step of a continuous casting operation conventionally consists in pouring molten metal into a basin, also called tundish, from a ladle. This tundish is, in addition, provided with a stopper. 
   When the molten metal has reached a given level in the tundish, it is then poured into a mould, under the effect of a movement of release of the stopper. This then initiates a phase of filling of the mould until a given reference level is reached. 
   According to a first variant, it is firstly known to start up this continuous casting manually. However, in addition to its relative lack of repetitivity, this solution requires the intervention of at least one operator. 
   In order to overcome these drawbacks, it has been proposed to effect the afore-mentioned start up automatically. In this spirit, the stopper is driven by means of a control assembly, also called actuator, in a stroke guaranteeing a satisfactory phase of filling of the mould. 
   Such an arrangement is known in particular from EP-A-0 734 801. The assembly for controlling the stopper, described in this document, comprises a drive shaft free to slide in a movement of translation with respect to a guiding assembly. 
   This drive shaft is fast with an intermediate arm directly supporting the stopper. A rotary servo-motor is also provided, as well as a device for converting the rotational movement, imparted by this motor, into a movement of translation of the shaft. 
   More precisely, this movement converting device is in the form of a screw jack. It should, moreover, be noted that the motor is offset laterally with respect to the drive shaft, with reference to the principal direction of the latter. 
   However, this known solution presents certain drawbacks. 
   For example, the assembly controlling the stopper presents relatively large dimensions. Furthermore, it is necessary to provide as many motors as guiding members, which is disadvantageous from the economic standpoint. 
   It is an object of the present invention to overcome the different drawbacks of the prior art set forth hereinabove. 
   SUMMARY OF THE INVENTION 
   The present invention relates to an assembly for controlling a stopper for a continuous casting installation, comprising a guiding assembly, a shaft for driving the stopper that is adapted to move in translation with respect to the guiding assembly, a motor having a rotary shaft, as well as means adapted to convert the rotational movement of the motor shaft into a movement of translation of the drive shaft, characterized in that means are provided, allowing the motor to be removably mounted on the movement converting means, with the result that the motor is selectively in a position of engagement with the movement converting means and a position spaced from the movement converting means, and in that, in the position of engagement, the rotary shaft of the motor extends substantially in a principal direction of the drive shaft. 
   According to other characteristics of the invention, the means to removably connect the motor are of the bayonet type. The bayonet-type fixation means comprises at least one stud, mounted on the guiding assembly, adapted to cooperate with at least one notch made in a linking piece secured to move in translation with the motor. In the position of engagement, the or each stud is received in a corresponding cavity of the notch, which cavity is bordered by an intermediate neck. 
   Return means are provided, particularly elastic, adapted to urge each stud axially towards the bottom of a corresponding cavity so as to prevent any untimely disconnection between the motor and the movement converting means. 
   The motor is received at least partly in a housing, particularly provided with handles for manually moving the motor. In the position of engagement, the housing lies approximately in line with the guiding assembly. In the position of engagement, the housing is arranged below the guiding assembly and the linking piece is mounted on said housing. 
   The linking piece is cylindrical and it is adapted to penetrate at least partially in a open area of the guiding assembly. The rotary shaft of the motor extends at least partially into an interior volume of said linking piece. 
   The movement converting means comprises a jack, particularly a screw jack, including a pin adapted to be driven in rotation by the rotary shaft of the motor, and means for temporarily drivingly engaging this pin and this shaft are provided. 
   The temporary means for drivingly engaging comprises two drive members adapted to mesh mutually and, in this respect, the members include intermeshing lands and grooves. Further, each member is mounted on either the pin or on the shaft. 
   One of the coupling members is secured to a flexible housing adapted to receive the other drive member, in the position of mutual mesh of these two members. 
   The invention also relates to a continuous casting installation comprising a tundish, which is adapted to receive molten metal and which is provided with an orifice ensuring flow of this molten metal, a mould disposed downstream of this orifice, so as to collect this molten metal, a stopper intended to selectively obturate this orifice, as well as an assembly for controlling this stopper, characterized in that this control assembly is as defined hereinabove. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described hereinafter with reference to the accompanying drawings, given solely by way of non-limiting example, in which: 
       FIG. 1  is a general view illustrating a continuous casting installation according to the invention. 
       FIG. 2  is a front view illustrating a control assembly belonging to the continuous casting installation of FIG.  1 . 
       FIG. 3  is a side view in section illustrating the control assembly of FIG.  2 . 
       FIG. 4  is a view on a larger scale illustrating a part of this control assembly, and 
       FIG. 5  is a view in longitudinal section illustrating a linking piece belonging to the control assembly of  FIGS. 2  to  4 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to the drawings, the continuous casting installation illustrated in  FIG. 1  comprises a tundish  2  which is filled with molten metal  4 , for example steel. The latter has been poured into the tundish from a ladle (not shown). 
   The bottom of this tundish is closed, in known manner, by a stopper  6  or plug, which defines a lower orifice for passage of the metal, also called a nozzle  8 . This stopper may be driven along its principal axis, namely vertically in  FIG. 1 , via a control assembly  10 , or actuator, which will be described more precisely hereinafter. 
   The control assembly  10  comprises in particular a drive shaft  12  which may be displaced in translation in the direction of arrow F, in the present case vertically. This movement of the shaft  12  then induces a displacement of the stopper  6 , shown by vertical arrow F′, via an intermediate arm  14 . 
   The walls of the nozzle  8  are, furthermore, provided with a tube  16 , made of a refractory material, which opens out in a mould  18 . The latter receives a dummy bar (not shown), intended to be progressively withdrawn in order to ensure in known manner the extraction of a bar of solidified metal, likewise not shown. 
     FIGS. 2  to  5  illustrate the control assembly  10  in greater detail. They show the shaft  12 , of which the principal axis, vertical, in the present case, is given reference A, as well as the intermediate arm  14 , illustrated partially. The control assembly also comprises a fixed guiding assembly, of conventional type, which is generally designated by reference  20 . 
   This assembly  20  has a cylindrical body  22  on which are added flanges  24  allowing the assembly to be mounted on a plate  26  secured to the tundish  2 . This cylindrical body  22  contains, in manner known per Se, two ball-bearing bushes  28  as well as a device  30  conventionally preventing rotation of the shaft  12  about its vertical axis A. 
   The cylindrical body  22  is screwed, at its lower end, on a base  32 , which is itself extended, opposite the cylindrical body, by an annular skirt  34 . The latter thus defines, with the opposite walls of the base  32 , an open area  36  placed in communication with a central opening  38  made axially in the base  32 . 
   Furthermore, the walls of the skirt  34  bear studs  40  extending radially towards the inside. The function of these studs  40 , which are provided to be three in number in the present case, will be explained hereinbelow. 
   In addition, the control assembly  10  comprises a motor  42  of conventional type, provided with a vertically extending rotary drive shaft  44 . This motor is received partially in a housing  46 , equipped with handles  48 , as well as with a current supply  50 . 
   This housing  46  is closed, in its upper part facing the cylindrical body  22 , with a cover  52  in which is a central orifice for passage of the motor drive shaft  44 . The latter is secured, via a key  54 , with a first drive coupling member  56  received in a flexible housing  58 , which will both be described in greater detail hereinafter. 
   This housing  58  is disposed in the interior volume of a linking piece or mounting collar  60 , of cylindrical shape, which is secured on the motor  42  by any appropriate means. As will be shown more particularly in  FIG. 5 , the wall of this linking piece  60  has different notches  62  therein, which are provided in a number corresponding to that of the studs  40 . 
   More precisely, each notch  62 , which is substantially in the form of an L, opens at the end of the linking piece  60  opposite the cover. This notch extends in a arcuate groove  64  which defines an end cavity  66 , bordered by an intermediate neck  68 . 
   The control assembly also comprises means for converting the rotational movement of the motor drive shaft  44  into a movement of translation of the shaft  12 . 
   More precisely, these means comprise a screw jack  70 , known per se, which is housed principally in the cylindrical body  22  of the guiding assembly  20 . A pin  72  of this jack  70 , which traverses the base  32 , is secured, via a key  74 , with a second drive coupling member  76 . This pin  72  which may be driven by the shaft  44  of the motor  42 , is adapted to cooperate, in conventional manner, with a nut  78  secured to the drive shaft  12 . 
   The two coupling members  56  and  76  include intermeshing lands and gooves. In service, the lands of one of the two members conventionally penetrate in the gooves or recesses of the other, with the result that there is a temporary coupling, with disengagement being possible, between these two members  56  and  76 . 
   It should be noted that member  56  is permanently housed in the flexible housing  58 , while member  76  is adapted to extend into this housing temporarily. Finally, an elastic element  80  is provided, in the present case a spring lock washer, to urge or return the coupling member  76  downwardly. 
   Functioning of the control assembly  10  described hereinabove will now be explained. 
   When the motor  42  is disconnected from the drive shaft  12 , the operator has available, on the one hand, the afore-mentioned motor, which is housed in its housing  46  provided with the handles  48  for manual manipulation, the intermeshing drive coupling member  56  being accessible. On the other hand, the other intermeshing drive coupling member  76 , at the lower end of the pin of the jack  70 , is also accessible. 
   The housing  46  is then manipulated, thanks to the handles  48 , in a substantially upwardly directed movement of translation, so as firstly to engage the linking piece  60  in the open area  36 . 
   During this translation, it may become necessary to give a slight rotation to the motor housing, close to some degrees, to ensure the alignment of the two intermeshing drive coupling members  56  and  76 . Consequently, the member  76  is then received in the interior of the supple housing  58 , itself secured to the first drive coupling member  56 . 
   Then, the upward translation of the housing  46  continuing, the studs  40  are received in the vicinity of the openings of the different notches  62 , provided in the linking piece  60 . Rotation of the housing  46  allows the studs  40  to be moved relative to the notches, in the direction of arrow f 1  shown in FIG.  5 . 
   When the studs come into axial abutment against the walls of the notches  62 , the housing  46  is pivoted. This induces an advance of the studs  40  along the grooves  64 , in the direction of arrow f 2  shown in FIG.  5 . 
   At the end of this movement of pivoting, each stud  40  is received in a corresponding cavity  66 , after having passed relative to an intermediate neck  68 . It should be noted that the spring washer  80  provides a force to urge each stud  40  to the bottom of the cavity  66 , in the direction of arrow f 3  of this same FIG.  5 . This thus prevents any untimely emergence of the studs  40  from the cavities  66 . 
   In this way, the motor  42  may be removably connected to the pin  72  of the screw jack  70 . Consequently, the motor has two positions, namely a position of engagement, in which the two drive coupling members  56  and  76  are intermeshed, and a disconnected position, in which the afore-mentioned drive coupling members are spaced from each other. 
   Furthermore, in the example described and shown, the means for mounting the motor  42  on this jack  70  are of a bayonet type. In effect, it requires a movement of translation with the motor housing being moved upwardly, combined with a movement of rotation of the motor housing with respect to this jack to seat the studs  40  within the cavities of the notches. 
   In service, in the position of engagement set forth hereinabove, the drive shaft  44  of the motor  42  drives the shaft  12 , via the movement converting means, which comprise the two drive coupling members  56  and  76 , as well as the screw jack  70 . In this position of engagement, the rotary shaft  44  of the motor  42  extends substantially along the principal axis A of the drive shaft  12 . 
   Furthermore, the housing  46 , in which the motor  42  is received, is located below the cylindrical body  22 , substantially in line therewith. This is advantageous, in terms of compactness of the assembly  10  controlling the stopper  6 . 
   Finally, it should be noted that this control assembly  10  is provided with a lever (not shown), conventionally intended for moving the drive shaft  12  by hand. This is to be compared with the teaching of EP-A-0 734 801, in which the device for manually driving the stopper is constituted by a wheel coupled to a spindle. 
   Such a system cannot be used in casting, as the speed of displacement of the stopper is very limited. It is thus impossible to effect a manual start up of a casting with such a device, being given that the initial opening of the stopper, of the order of 15 to 20 mm, during start up, must be effected in less than a second. 
   This invention makes it possible to attain the objects set forth hereinabove. 
   In effect, as has been seen hereinabove, the compactness of the control assembly according to the invention is noteworthy in service. This is to be compared with the prior art in which the motor is offset laterally with respect to the guiding assembly. 
   Furthermore, the means for removably mounting or connecting the motor on the screw jack permits the latter to be rapidly disconnected. 
   Consequently, it is not necessary to have available as many motors as guiding assemblies, the motor being reserved solely for the step of casting. In other words, the guiding assemblies which are located at other stations of the continuous casting, such as assembly, dismantling, preheating or cooling, do not need to be provided with a corresponding motor. 
   The latter measure thus appears particularly advantageous, from the economic standpoint. 
   Finally, in the arrangement of the invention, emergency closure of the stopper is effected by gravity, upon simple deactivation of the motor. The weight of the mobile system, comprising the shaft, the arm and the stopper, thus suffices to cause the stopper to descend so as to allow such an emergency closure. 
   This is to be compared with EP-A-0 734 801 in which an electric resource by accumulation is employed, which operates the whole motorized chain, namely the electronic control device, the cables, the motor and the spindle. 
   Breakdown of one of these members, such as the tearing of a cable or a motor breakdown, thus renders any emergency closure impossible.