Process and unit for rolling metals to produce a round bar or wire rod from a round bar or wire rod having a larger diameter

Abstract: A process and unit for hot- and cold-rolling ferrous and non-ferrous metals in order to produce a round bar or wire rod from a round bar or wire rod having a larger diameter. The process consists in inserting a bar or wire rod (5), whose initial profile has a round cross-section, in a rolling unit (1) which is provided with rolling rolls (3,4) whose profiles (3b,4b) define a round passage whose diameter is smaller than the diameter of the input bar or wire rod. Upstream from the rolling unit (1), the larger-diameter bar or wire rod (5) is subjected to the action of free rollers (7,8) whose profiles (7b,8b) are suitable to deform the larger-diameter bar or wire rod according to a shape which produces, in output from the rolling unit (1), a bar or wire rod (5) whose cross-section is round and has a smaller diameter.

Description: The present invention relates to a process and a unit for the hot- and cold-rolling of ferrous and non-ferrous metals for the manufacture of a round bar or wire rod from a bar or round wire rod having a larger diameter. As is known, metal rolling generally uses rolling mills which comprise a plurality of stands or rolling units arranged in a line in order to progressively reduce the diameter of the bar in input. It is furthermore known that on a rolling stand it is practically impossible to obtain a bar with a round profile directly from a round-profile bar having a larger diameter. More precisely, if one feeds a round-profile bar to a rolling stand which has rolls shaped so as to provide a round profile, the output result is not a bar with a round profile but a lobed-profile bar which is not acceptable for the market. Due to this reason, in a rolling line with rolling units having rolls shaped so as to generate a round profile, one alternates rolling units having rolls shaped so as to generate a non-round intermediate profile which is studied so that during the subsequent passage through a rolling unit with round-profile rolls one actually obtains a round-profile bar which can be accepted by the market. Currently, in order to obtain rolled products with a round profile, rolling mills of two types are mainly used: rolling mills with two-roll stands and rolling mills with three-roll stands. In rolling mills with two-roll stands, stands with two rolls shaped so as to provide a round profile are generally alternated with stands with two rolls shaped so as to provide an oval profile. Figures 2 to 5 illustrate the sequence of the cross-sections of an initially round bar (figure 1) in output from the various rolling stands in rolling mills of this type. In rolling mills with three-roll stands, stands with three rolls which are arranged so that their axes define the sides of an equilateral triangle and are shaped so as to provide a round profile are alternated with stands with three rolls which are arranged in a similar manner and have a cylindrical skirt in order to define a profile having an almost triangular cross-section. Figures 7 to 10 illustrate the sequence of the cross-sections of an initially round bar (figure 6) in output from the various rolling stands in rolling mills of this type. A two-roll stand rolling mill is known from JP-A-61-150703, which teaches a method and device according to the pre-characterising parts of claims 1 and 3 for working metallic stock by roll die without causing the breakage of the stock even in a case of using a number of roll-die groups by using, as a unit, two sets of forced driving rolls arranged so that the axes of both sets are perpendicular to each other and making the distance between the roll axes of both sets smaller than the diameter of the roll. Known from FR-A-2403119 is a rolling mill having three-roll stands for rolling wires or bar products. The rolling units are arranged sequentially one after another and their axial spacing is equal to or less than the diameter of the rolls. This document discloses a method and device according to the pre-characterising parts of claims 2 and 6 In any kind of rolling mill, the rolls of the various rolling stands are actuated so that they rotate about their axes by means of one motor for each stand, or by means of a single motor which, by means of a speed reduction unit, actuates the rolls of the various stands so that the rotation rate of the rolls complies with the well-known laws of constant rates of metal flow in the various rolling stands which cooperate to deform the bar starting from its entry in the rolling stands up to its exit. The use of these rolling stands shows problems particularly when it is necessary to pass from the production of bars of a certain diameter to bars having a different diameter. In this case, in fact, with conventional rolling stands it is necessary to replace the sets of two or three rolls of the two final rolling units and of their guides and adapt the rotation rates of the rolls, for example by replacing some components of the reduction unit which is connected to the rolls or by means of electric adjustments. These operations entail relatively long rolling stand downtimes which make it economically unprofitable to perform small-scale production of profiles whose diameter differs from the "standard" diameters which can be obtained in output from the rolling stands usually used. The aim of the present invention is to solve the problem described above by providing a rolling process which allows to obtain greater flexibility for rolling facilities, allowing production changes which can be performed in reduced times. Within the scope of this aim, an object of the invention is to provide a rolling process which makes it economically profitable to produce even small series of round-profile bars whose diameters differ from the "standard" ones, so as to meet practically all the demands of the market. Another object of the invention is to provide a rolling unit which is simple to manufacture for carrying out the process according to the invention. This aim, these objects and others which will become apparent hereinafter are achieved by a process for rolling metals to produce a round bar or wire rod from a round bar or wire rod having a larger diameter as defined in the appended claims. In order to perform the process according to the invention it is possible to advantageously use a rolling unit as defined in the appended claims. Further characteristics and advantages of the process and unit according to the present invention will become apparent from the description of a preferred but not exclusive embodiment of the process according to the invention and of the rolling unit for performing it, which are illustrated only by way of non-limitative example in the accompanying drawings, wherein: figures 1 to 5 and 6 to 10 show, as mentioned, the rolling sequences in a known rolling mill with two-roll stands and in a rolling mill with three-roll stands; figure 11 is a schematic view of a rolling unit suitable for performing the process according to the invention; figure 12 is a partially sectional top plan view of the free rollers; figures 13 and 14 are partially sectional front views of the free rollers in two operating positions; figure 15 is a view of the shape of the bar in output from the rolling unit according to an embodiment of the present invention during the startup of said unit; figure 16 is a view of the shape of the bar in output from the free rollers; and figure 17 is a view of the shape of the bar in output from the rolling unit in the steady-state condition. With reference to figures 11 to 17, a preferred rolling unit for performing the process according to the invention, generally designated by the reference numeral 1, comprises, in the illustrated embodiment, a pair of rolling rolls 3 and 4 which can be actuated so as to rotate about their axes 3a and 4a, which are mutually parallel, in order to roll a bar 5 and make it advance along an advancement direction 6. The rolling rolls 3 and 4 have, on their skirt, a circumferential concavity 3b and 4b which is shaped so as to obtain, in output, a bar whose profile has a round cross-section. The rolling rolls 3 and 4 can be actuated in a known manner by means of an independent gearmotor or by means of a reduction unit with interchangeable gears which is connected to a motor which also actuates other conventional rolling units. According to the invention, free rollers 7 and 8 are provided upstream from the rolling rolls 3 and 4 along the advancement direction 6, can engage the bar 5 in sequence with respect to the rolls 3 and 4 and have such a shape as to pre-deform the bar 5 from an initial profile with a round cross-section to an intermediate profile with a non-round cross-section. In the illustrated embodiment, which relates to a two-roll rolling unit, the free rollers are constituted by a pair of rollers 7 and 8 which are arranged mutually opposite and so that their axes 7a and 8a are mutually parallel but angularly offset substantially by 90° about the axis 5a of the bar 5 with respect to the axes 3a and 4a of the motorized rollers 3 and 4. The free rollers 7 and 8 have, on their skirt, a circumferential concavity 7b and 8b which is shaped so as to obtain, at the output from said rollers, a bar which has an intermediate profile with an oval cross-section, as shown in figure 16. Conveniently, actuation and control means, generally designated by the reference numeral 9 in figures 13 and 14, are provided in order to move the free rollers 7 and 8 closer to, or further away from, the axis 5a of the bar 5. More particularly, the free rollers 7 and 8 are mounted in a fixed structure 10 which is associated with the supporting structure 11 of the rollers 3 and 4. The actuation means comprise a gearwheel 12 which is supported by the fixed structure 10 so that it can rotate about its axis 12a arranged parallel to the axis 5a of the bar 5, and can be actuated so as to rotate about its axis by means of an actuation handwheel 13. The gearwheel 12 meshes, in two diametrically opposite regions, respectively with a first rack 14, which is rigidly associated with a first frame 15 which supports the roller 7 so that it can rotate about its axis 7a, and with a second rack 16, which is rigidly associated with a second frame 17 which supports the roller 8 in a similar manner. The frames 15 and 17 can slide, with respect to the fixed structure 10, in a plane which is perpendicular to the axis 5a of the bar 5, so that the rotation of the gearwheel 12 causes the sliding of the frames 15 and 17 in opposite directions, with the consequent approach or spacing of the rollers 7 and 8 with respect to the axis 5a. The rolling unit for performing the process according to the invention is intended to constitute a finishing unit to be arranged at the output of conventional rolling stands so as to allow to produce bars having a profile with round cross-section whose diameter differs from the "standard" diameters, so as to fully meet the demands of the market. The operation of the rolling unit in the execution of the process according to the invention is as follows. Initially, the free rollers 7 and 8 are mutually spaced so as to allow the free passage of the initial portion of the bar 5 until it engages the rolling rolls 3 and 4. After the rolling rolls 3 and 4 have engaged the bar 5, causing its advancement and obtaining the profile of figure 15, the free rollers 7 and 8 are moved closer to the axis 5a of the bar until they reach the correct position, which is determined according to the practice and theory of rolling. When it exits from the free rollers 7 and 8, the bar 5 has a profile with an oval cross-section (figure 16) and, by passing through the rolling rolls 3 and 4, exits from the rolling unit with a profile having a round cross-section (figure 17) whose diameter is reduced with respect to the initial profile with round cross-section. The initial portion of the bar which has not undergone pre-deformation by the rollers 7 and 8 has the shape shown in figure 15 and is meant to be discarded. The remaining part of the bar has the required profile with round cross-section, since the free rollers 7 and 8 deform the bar so as to re-establish equal rates of flow, preventing the forming of lobes, and so as to allow to produce a round bar within the limits of commercial tolerances. If one wishes to vary the diameter of the bar in output from the rolling unit, it is sufficient to change the rolling rolls 3 and 4, the free rollers 7 and 8, and to adjust the rotation rate of the rolling rolls alone, with a reduced waste of time. In practice it has been observed that the process according to the invention fully achieves the intended aim, since it significantly improves production flexibility of rolling facilities, reducing downtimes required for changes in production diameters. For the sake of simplicity, the process and the rolling unit for its execution have been described with reference to a pair of free rollers and to a pair of rolling rolls; however, it is also possible to provide rolling units for carrying out the process according to the invention with three free rollers and three rolling rolls arranged so that their axes define the sides of an equilateral triangle. In this case, the free rollers can have a cylindrical skirt in order to obtain a bar with a substantially triangular intermediate profile and the rolling rolls have a skirt with a circumferential recess in order to equally obtain a bar with a final profile having a round cross-section. Also according to the concept underlying the present invention, it is possible to provide an even larger number of free rollers and rolling rolls, according to the requirements. The process and the rolling unit thus conceived are susceptible to numerous modifications and variations, within the scope of the invention, which is defined in the appended claims. In practice, the materials employed, as well as the dimensions, may be any according to the requirements and the state of the art. Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the scope of each element identified by way of example by such reference signs.

Claims: Process for hot- and cold-rolling ferrous and non-ferrous metals in order to produce a round bar or wire rod (5) from a round bar or wire rod (5) having a larger diameter, which consists in inserting a bar or wire rod (5) whose initial profile has a round cross-section in a rolling unit which is provided with at least one pair of opposite driven rolling rolls (3,4), said rolling rolls having axes (3a,3b) mutually parallel and said rolling rolls (3,4) having a circumferential concavity (3b,4b) on their skirt defining a round passage whose diameter is smaller than the diameter of the input bar or wire rod (5), said circumferential concavity (3b,4b) being suitable to obtain, in output, a bar or wire rod (5) with a final profile having a round-cross section, and at least one pair of further rolls (7,8) with mutually parallel axes (7a,8a) acting on said larger-diameter bar or wire rod (5), upstream from said rolling unit, said pair of further rolls (7,8) having a circumferential concavity (7b,8b) on their skirt which is suitable to obtain, in output from said pair of further rolls (7,8), a bar or wire rod (5) having an intermediate profile with oval cross-section, said axes (7a,8a) of said pair of further rolls (7, 8) being angularly offset, by an angle of 90°, about the axis (5a) of the bar or wire rod (5) with respect to the axes (3a,4a) of said rolling rolls (3,4) characterised in that said further rolls are opposite free rolls (7,8) and that said free rolls (7,8) are made to act on said bar or wire rod (5) immediately after engagement of said bar or wire rod (5) with said pair of rolling rolls (3,4). Process for hot- and cold-rolling ferrous and non-ferrous metals in order to produce a round bar or wire rod (5) from a round bar or wire rod having a larger diameter (5), which consists in inserting a bar or wire rod (5) whose initial profile has a round cross-section in a rolling unit which is provided with at least three mutually identical driven rolling rolls whereby said rolling rolls are arranged so that their axes define the sides of an equilateral triangle, said three rolling rolls having, on their skirt, a circumferential concavity in order to obtain, in output, a bar or wire rod (5) with a final profile having a round cross-section, and at least three mutually identical further rolls, which are arranged so that their axes define the sides of an equilateral triangle, acting on said larger diameter bar or wire rod (5), upstream from said rolling unit, said mutually identical further rolls having, on their skirt, a circumferential concavity in order to obtain, in output, a bar or wire rod (5) with an intermediate profile having a substantially triangular shape, said axes of said further rolls being angularly offset about the axis of the bar or wire rod (5) with respect to the axes of said rolling rolls characterised in that said further rolls are free rolls (7,8) and that said free rolls (7,8) are made to act on said bar or wire rod (5) immediately after engagement of said bar or wire rod (5) with said pair of rolling rolls. Unit for hot- and cold-rolling ferrous and non ferrous metals, comprising at least one pair of opposite rolling rolls (3,4) which can be actuated so that they rotate about their axes (3a,4a) and can engage a bar (5) to roll it and make it advance along an advancement direction (6), said rolls having a shape (3b, 4b) which is suitable to provide, at the output, a bar whose final profile has a round cross-section, wherein said pair of rolling rolls (3,4) have mutually parallel axes (3a, 4a), said shape (3b,4b) is a circumferential concavity arranged on the skirt of said rolling rolls, and in that said unit comprises, upstream from said pair of rolling rolls (3,4) along the bar advancement direction (6), a pair of opposite further rolls (7,8) which can engage said bar (5), said further rolls having mutually parallel axes (7a,8a) which are angularly offset, by an angle of 90°, about the axis (5a) of the bar with respect to the axes (3a,4a) of said rolling rolls (3,4), said further rolls (7,8) having a circumferential concavity (7b,8b) on their skirt which is suitable to provide, at the output, a bar whose intermediate profile has an oval cross-section, characterised in that said further rolls are free rolls (7,8). Rolling unit according to claim 3, characterized in that it comprises actuation and control means (9) which act on said free rolls (7,8) in order to move them toward or away from said bar (5). Rolling unit according to claim 4, characterized in that said actuation means (9) comprise a gearwheel (12) which meshes, in diametrically opposite regions, with two racks (14,16): a first rack (14), which is fixed to a first movable frame (15) which supports a free roller (7) of said pair of free rollers, and a second rack (16), which can be fixed to a second movable frame (17) which supports the other free roller (8) of said pair of free rollers, said first frame (15) and said second frame (17) being associated, so that they can slide along a direction which is substantially perpendicular to the axis of said bar, with a fixed structure (10) which rotatably supports said gearwheel (12), said gearwheel having its axis (12a) parallel to said advancement direction (6). Unit for hot- and cold-rolling ferrous and non ferrous metals, comprising at least three opposite rolling rolls which can be actuated so that they rotate about their axes and can engage a bar (5) to roll it and make it advance along an advancement direction (6), said rolling rolls having a shape which is suitable to provide, at the output, a bar whose final profile has a round cross-section, wherein said at least three rolling rolls have axes arranged so as to define the sides of an equilateral triangular, said shape is a circumferential concavity arranged on the skirt of said rolling rolls, and in that said unit comprises, upstream from said three rolling rolls along the bar advancement direction (6), at least three mutually identical further rolls which can engage said bar (5), said further rolls being arranged so that their axes define the sides of an equilateral triangle, said further rolls being offset with respect to the axes of said rolling rolls by an angle of 60°, said three further rolls having a circumferential concavity on their skirt which is suitable to provide, at the output, a bar whose intermediate profile has an oval cross-section, characterised in that said further rolls are free rolls.

Inventors: PROPERZI GIULIO, PROPERZI, GIULIO
Applicants: PROPERZI GIULIO, PROPERZI, GIULIO
Application year: 1992
Main classification: B21B1
IPC codes: B21B13, B21B31, B21B1