Patent Publication Number: US-8113026-B2

Title: Apparatus and method for reducing the section and sizing of rolling mill products for wire rod

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention refers to an apparatus and method for reducing the section and sizing of rolling mill products for wire rod. 
     In a rolling plant or rolling mill for wire rods, according to well-established technology, one operates on a billet previously taken to a higher temperature than the re-crystallization temperature to then subject it to rolling so as to gradually reduce its section up to the desired section. 
     In the rolling mill, one of the critical operations therefore consists of the finishing carried out through a plurality of rolling stands. The plurality of rolling stands reduce the size of the billet that produces the wire rod that is sent to the sizing monoblock or that is sent directly to the laying head. 
     Currently, rolling mills for producing wire rod are constructed in different ways. 
     They can comprise a monoblock group with 6-8-10 rolling stands controlled by a single motor, with a succession of oval-round reductions followed a certain distance behind by a second group of monoblock stands that can be formed from a group of four stands with oval-round-round-round reduction sequence. 
     A rolling mill of this type forms the object of European patent no. 0 51 to Morgan. 
     Another type of known rolling mill foresees a monoblock group with 6-8-10 rolling stands as above followed by two groups of stands each formed from two stands with oval-round reduction sequence in the first group and oval-round in the second group. 
     Each group is controlled by a motor. 
     Since one problem of production is linked to the large number of formed products, i.e. of the required diameters, it is necessary to make the rolling mill flexible so as to be able to carry out quick changes in equipment and in rolling rings. 
     The reduction sequences, in the first and in the second monoblock, are carried out according to a prior art that allows the changes in the first monoblock to be minimised and the entire range of foreseen diameters, which normally range from a diameter of 5.5 mm to maximum diameters of 18-22 mm, to be finished in the second monoblock. 
     A particularly disadvantageous condition in plants of this type-consists of the fact that the synchronization between the output speed of the rolled product from the first monoblock and the input speed into the second group of stands (monoblock) is extremely difficult for which reason the speed of the second monoblock tends to be adjusted with a slightly greater speed than the output speed of the first monoblock so that the material between the two groups is always in slight pull. 
     The value of the speed difference must be such as to contain within its range all normal variations, even if small, in readjustment of speeds, which occur each time a load is taken relative to the succession of billets being rolled. 
     The consequence of what has been outlined above causes a substantial variation in the section of the rolled product between the first monoblock and the second monoblock. 
     The variation in section indicated above, which occurs along the entire billet, reaches its maximum at the start and end of the billet, where there is no pull. Moreover, already inside the first monoblock there are pulls between the stands such as to generate substantial variations in section already in output from it. 
     The aforementioned variations in section between the two monoblocks are the cause of substantial problems in the second monoblock since they greatly reduce the lifetime of the rolling guides, they produce large variations in filling of the oval groove and consequently large variations in roundness in the subsequent grooves if they have large recesses with extension beyond the edge if the grooves cover the full 360°. 
     The substantial variations in section in the initial portion of the rolled product, as stated above, determine an increase in the entry angle to the second monoblock both for the round section that enters into the oval, and for the subsequent section that enters the finishing round stock. Said large entry angles are the cause of frequent cobbles. 
     It is also known to men skilled in the art that a sections with errors in roundness is unstable since it tends to rotate and be arranged according to the minimum height to which the minimum rolling pressure corresponds. 
     BRIEF SUMMARY OF THE INVENTION 
     The general purpose of the present invention is, therefore, that of providing an apparatus and method suitable for allowing the solution of the problems outlined above with the aim at obtaining a rolled product with narrow tolerances and with greater reliability of operation. 
     In view of the aforementioned purposes, according to the present invention, it has been thought to make an apparatus and a method having the characteristics outlined in the subsequent claims. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       The morphological and functional characteristics of the present invention as well as its advantages compared to the prior art shall become clearer from an examination of the following description, referring to the attached FIGURE that schematically illustrates the sections of the product in the passage in each of the rolling stands of the apparatus. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     With reference to the FIGURE, the apparatus for reducing the section and sizing of rolling mill products for wire rod, object of the present invention, comprises: rolling of a first monoblock  10  consisting of a sequence of rolling stands in a variable number (G 1 -Gn) where the last stands Gm-Gn have the grooves with oval-round sequence with large recesses to minimize the risks of overfill beyond the edge of the initial and end part of the rolled round stock from each billet and to make the distribution of the spread more uniform. 
     A second monoblock  20 , arranged a suitable distance d from the first monoblock  10  such as to allow the cooling of the product coming out from said monoblock  10  at a predetermined temperature and sufficiently equalized in section, consisting of: 
     at least one first stand S 1  equipped with a suitable rolling guide with a round groove so as to reduce the variations in section arriving into the output section, and also making it easier to bite the rolled product as a consequence of the small grip angle. The stand S 1 , at the start of the second monoblock, has a round groove with suitable recesses to make it easier to bite the round stock with increased size at the end caused by the pulling of the rolled material inside the first monoblock  10 . 
     a second subsequent stand S 2  with an oval groove to generate an oval of constant width and thickness along the entire rod. 
     a third subsequent stand  83  with a round groove that produces a finished round stock on the height of the profile. 
     a fourth stand  84  follows the third stand  83  and has a rolling ring R 4  rotated by 90° with respect to the corresponding rolling ring R 3  of the third stand  83 . 
     Such rollers are equipped with the same groove as those of said third stand S 3 . 
     In the fourth stand S 4 , it is foreseen to eliminate the variation in width of the round stock coming out from the previous stand and to thus obtain a product with narrow tolerances. 
     The method for making a wire rod according to the present invention comprises the following steps:
         a) feeding the product to be rolled to a first finishing monoblock comprising a number of rolled stands (G 1 -Gn) selected according to the rolled diameter and having a number of last stands (Gm-Gn) with grooves with large recesses to minimize the risks of extension beyond the edge of the initial and end part of the round stock from each billet and to make the distribution of the spread more uniform;   b) feeding the product coming out from the first monoblock into a second monoblock  20 , arranged a suitable distance (d) from said first monoblock  10  so as to allow the rolling of the product in the second monoblock at a predetermined temperature, feeding the product into a sequence of round-oval-round-round stands, foreseen in said second monoblock  20 .