Abstract:
An apparatus serves for the continuous surface cleaning of rotationally movable casting rolls ( 2, 3 ) of a strip-casting machine. A plurality of laser beam units ( 25 ) are arranged on the circumference of the respective casting roll ( 2, 3 ), which laser beam units ( 25 ) are arranged next to one another, are distributed over the casting-roll length and by means of which the casting-roll surface ( 2   a   , 3   a ) can be acted upon with one or more laser beams over the entire casting-roll length. Additional cleaning units ( 30, 31, 35, 45 ) for the mechanical cleaning of the casting-roll surface are advantageously connected ahead of and/or behind the laser beam units ( 25 ). This makes gap-free and regular surface cleaning of the casting rolls possible.

Description:
FIELD OF THE INVENTION 
     The invention concerns an apparatus for continuous surface cleaning of rotationally movable casting rolls of a strip-casting machine. 
     BACKGROUND OF THE INVENTION 
     In casting mills containing one or two casting rolls, it is known that liquid steel comes into contact with the cooled surface of the casting rolls, in order to consolidate thereon. Before the rotating casting roll comes into contact again with the liquid steel, it must be continuously cleaned, in order to prevent any accumulation of metal oxides, slag or other contaminants on the casting-roll surface. Mechanical cleaning devices are used for surface cleaning, such as scrapers, brushes or cleaning belts, with which it is difficult to guarantee consistent cleaning over the entire length of the casting roll. This uneven cleaning has a negative effect on the quality of the cast product. To improve cleaning, there is a known method of distributing a plurality of cleaning devices in sequence along the length of the casting roll, but this gives rise to the risk of gaps forming which impair the surface cleaning. The cleaning devices are also objects which may cause scratching or scraping on the casting-roll surface. These tend to form surface defects on the cast strip. In the casting region, gases and splashes escaping through the liquid steel may contaminate the casting roll surfaces during casting. 
     From U.S. Pat. No. 5,651,413 it is known that the casting-roll surface can be cleaned by means of a particle/sand blasting device. This involves using one or more spray nozzles distributed over the length of the casting roll. The volume of particles and the spray rate reduces towards the exterior of the spray cone, so that the cleaning is irregular. When several spray nozzles are arranged, areas of contact or overlap arise, which can also lead to irregular cleaning. The particle/sand blasting device which, in addition to the nozzle or nozzles, comprises a receiving container for the sand particles, a return for same, a collecting container, a power supply and a pressurised distributor to send the sand particles back to the nozzle, takes up space. There is also additional dust produced by the atomisation of the particles. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     The present invention is based on the problem of creating an apparatus of the aforementioned type which enables consistent surface cleaning over the entire casting roll length, and in which the risk of damage or of degradation of the casting roll surface is largely eliminated. 
     This problem is solved according to the invention by an apparatus for the continuous surface cleaning of rotationally movable casting rolls of a strip-casting machine in which a laser beam unit or a plurality of laser beam units is/are arranged on a circumference of the respective casting roll, and is/are distributed over the casting-roll length by means of which the casting-roll surface is acted upon with one or more laser beams over the entire casting-roll length. 
     Further preferred embodiments of the apparatus according to the invention form the subject matter of dependent claims. 
     The apparatus according to the invention, in which a laser beam unit or a plurality of laser beam units are arranged next to one another on the circumference of the respective casting roll, distributed over the casting-roll length, by means of which the casting-roll surface can be acted upon with one or more laser beams over the entire casting-roll length, enables gap-free and regular surface cleaning of the casting rolls, since the laser beams have very clear borders and can be harmonised with each other in such a way that no gaps or overlaps arise. No scratches or scrapes on the casting-roll surface arise. The apparatus can be used throughout the entire casting operation in the maintenance positions or in an external workshop. It is compact and low-maintenance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will next be explained in more detail with the aid of the drawings, which show in purely schematic form: 
         FIG. 1  part of a strip-casting machine  1  with two casting rolls, each with an apparatus according to the invention for the surface cleaning of the casting rolls; 
         FIG. 2  the strip-casting machine part according to  FIG. 1  in perspectival view. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 and 2  show a part of a strip-casting machine  1  with two casting rolls  2 ,  3  rotatable about horizontal axes, whose directions of rotation have been given the references D 2  and D 3  and of which at least one casting roll can be movably adjusted in order to modify the casting gap. To produce a metal strip  4 , the liquid metal is poured between the two casting rolls  2 ,  3  and two lateral sealing elements  5  arranged in the front end area of the casting rolls  2 ,  3  (cf.  FIG. 2 , which shows one of the two lateral sealing elements  5 ) via a pouring device  6  out of a vessel  7  and forms a molten bath  8 . The metal strip  4  produced is carried away through a through-gap  9  between the two cooled casting rolls  2 ,  3  in the direction of arrow A according to  FIG. 1 . 
     Above the molten bath  8 , a chamber  10  for a protective gas, e.g. argon, is formed. The upper housing part  11  encircling this chamber  10  is equipped with a sealing system  12 ,  13 , co-operating with the respective casting roll  2 ,  3  and the respective lateral sealing elements  5 , and said sealing system separates the chamber  10  from the rest of the interior of the housing of the strip-casting machine  1 . 
     As can be seen in particular from  FIG. 1 , an apparatus  20  for surface cleaning according to the invention is assigned to each of the two casting rolls  2 ,  3 , by means of which the casting-roll surface  2   a  or  3   a  respectively, effecting the solidification of the liquid metal, cooled and rotating, is continuously cleared of metal oxides, slag or other contaminants, before coming into renewed contact with the liquid metal. 
     According to the invention, surface cleaning is conducted by means of a laser unit  25  arranged on the circumference of the respective casting roll  2 ,  3  (with one or more laser beams striking the respective casting roll  2 ,  3  over its entire length) or by means of several laser beam units  25 . In the latter variant with several laser beam units  25  these—as  FIG. 2  shows—are arranged side by side in one or more rows and distributed over the entire length of the respective casting roll  2 ,  3 . At the same time, care is taken that the laser beams strike the casting-roll surface  2   a ,  3   a  completely and consistently over the entire length. The laser beam units  25  can be arranged fixedly at a distance from the casting roll or movably in the axial direction of the casting rolls  2 ,  3 . 
     The laser beams can be harmonised with each other in such a way that no gaps or overlaps occur. They work extremely rapidly and generate extremely high local temperatures, so that the contaminants vaporise or are blasted away. No scratches or scrapes arise on the casting-roll surface  2   a ,  3   a , because the extremely brief and locally-limited effect of the radiation has a very protective action. As the roll surface  2   a ,  3   a  does not absorb the laser beam, unlike the top layer, but reflects it, the cleaning process stops. 
     Thus there is no interference with the conditions between the casting-roll surfaces  2   a ,  3   a  and the metal melt during the entire casting period due to the cleaning apparatus and so the quality of the cast strip is not affected. The lifetimes of the casting-roll surfaces and the casting rolls cover are extended. 
     A suction and filter device  26  is provided for the contaminants detached by the laser beam unit and the laser beam units  25  respectively. In order to protect the casting-roll surfaces from contamination by the gases and smoke escaping from the liquid steel, these are carried away together with added inert gas from the chamber  10 . To keep splashes away from the casting roll, especially when casting-on, a splash protector  44  is provided. 
     The laser beam cleaning and/or the removal of oxides can in some circumstances be automatically interrupted: if there are no longer any oxides on the casting-roll surface, the laser beam is reflected and thus the effect on the casting-roll surface is stopped, so that this suffers no damage. 
     The apparatus  20  according to the invention for surface cleaning of the respective casting roll  2 ,  3  can, in addition to the laser beam unit or laser beam units  25 , also have at least one additional cleaning unit for the mechanical, chemical, galvanic and/or thermal cleaning of the casting-roll surface  2   a ,  3   a , which can be connected upstream or downstream of the laser beam unit or the laser beam units  25  in the direction of rotation D 2 , D 3  of the casting roll. 
     So it is advantageous for strippers  30 ,  33 ′ in  FIG. 1  and strippers  30 ,  30 ′ in  FIG. 2  for stripping off the larger contaminants in the direction of rotation D 2 , D 3  of the casting roll  2 ,  3  to be connected in series with the laser beam unit or the laser beam units  25 , said strippers extending over the entire length of the respective casting roll  2 ,  3  and over the area of the front end adjacent the cover area. These adjoin, on the side facing away from the strip  4 , a first brush  35  arranged out of contact with the roll surface  2   a  and additional brushes  35 ′, which are arranged on the front end, and a suction hood  34 ,  36  surrounding these, through which the dirt particles detached by the brushes  35 ,  35 ′ are sucked away. In addition, a sand blasting device  31  with a sand suction device and sand recycling device  32  (or a row of such devices  31 , cf.  FIG. 2 ) can be connected upstream of the laser beam unit or the laser beam units  25 . It would also be possible to use additional brushes or cleaning belts, not shown in the drawing, upstream of the laser beam unit or the laser beam units  25 . 
     A cleaning brush  45  extending over the entire length of the respective casting roll  2 ,  3  can advantageously be connected downstream of the laser beam unit or the laser beam units  25  in the direction of rotation D 2 , D 3  of the casting roll  2 ,  3 , with which any residues can be completely removed. The cleaning brush  45  is, according to  FIG. 1 , preferably accommodated in a housing  47 , from which the residual particles are removed by means of a suction device  46 . A cleaning brush  45  of this type can, however, be substantially softer than ordinary cleaning brushes, and is also used with less pressing force. Cleaning brushes of this type thus also have longer lifetimes and cause no damage to the casting-roll surfaces  2   a ,  3   a.    
     A common housing for brushes or cleaning belts and laser units would also be possible, which would simplify the removal and filtration of the detached contaminants. Also, the entire cleaning apparatus  20 , for example when changing a casting roll, could be easily e.g. tipped up as a unit. 
     The condition of the cleaned casting-roll surface  2   a ,  3   a , the position, the temperature and the profile of the casting roll are monitored, for which a measurement device  40  is provided, which preferably includes a number of sensors arranged side by side or offset and distributed over the length of the casting rolls (cf. in particular  FIG. 2 ). 
     The apparatus according to the invention for surface cleaning/renewal of casting rolls can be used during the casting operation or during the entire casting period, in maintenance positions or in an external workshop. It is compact and low-maintenance. 
     The particle blaster and/or laser beam unit or the laser beam units  25 , the final cleaning with suction, an inert gas supply and a splash protector form a complete system, which guarantees optimal cleaning of the roll surfaces. 
     Mechanical cleaning can also be carried out using scrapers or graters. If a particle blaster is used for cleaning, organic, ceramic, metallic particles, plastic particles or dry ice can be used. It is also possible to turn, mill or grind these surfaces. 
     A chemical or a chemical-mechanical cleaning can also be applied, for example in the form of etching, preferably using a specific acid, or in the form of removal by caustics. There is also cleaning using ultrasound with a liquid carrier medium. 
     Thermal cleaning is another option. This involves targeted heating of the roll surface to effect a melting or burning-off of surface accumulations, with the melted accumulations being dabbed off or otherwise removed. 
     The at least one laser beam unit  25  can also be used for renewing the casting-roll surface during or outside operation, for example to create pits (dimples or textures). Such textures could also be produced by other means, such as for example diamonds, needles, compressed air needle scalers or milling rollers. It is also possible to achieve this effect using the aforementioned particle blaster with ceramic particles, plastic particles, metal particles etc. 
     The cleaning apparatus for cleaning in-line rolling mill rolls can be used individually or as a system, especially where long sequences are involved.