METHOD OF DETERMINING THE OPTIMUM RATIO FOR THE NUMBER OF ROLL ROTATION IN A COLD ROLLING MILL, OPERATION METHOD AND COLD ROLLING MILL

Abstract: The present invention has an aim of providing a rolling mill and an operation method thereof for remarkably extending a roll life, optimizing a driving source and attaining maintenance free in the rolling mill, in which an optimum ratio for the number of driving rotations between each of driving roll stands can be obtained by arranging rolls of predetermined shapes in a plurality of roll stands and adjusting the rolling reduction so as to obtain a required shape, then gripping a material to be formed completed with formation by a clamping device, drawing the same for a required length without driving all the rolls and determining the number of rotation or the like of each of roll stands, and driving force between each of driving roll stands can be matched and optimized by driving each of the driving roll stands at the optimum ratio for the number of driving rotation, which can remarkably extend the roll life, optimize the driving source and attain the maintenance free in the rolling mill.

Description: DESCRIPTION METHOD OF DETERMINING THE OPTIMUM RATIO FOR THE NUMBER OF ROLL ROTATION IN A COLD ROLLING MILL, OPERATION METHOD AND COLD ROLLING MILL Technical Field The present invention concerns a method of determining the optimum ratio for the number of rotation of a plurality of forming rolls used in a cold rolling mill, a method of operating the roll mill based on the determined value and a cold rolling mill and it has a feature of attaining matching" between a plurality of forming rolls during driving 'in a cold rolling mill comprising a plurality of forming roll stands . Referring more specifically, the present invention comprises disposing- forming rolls of predetermined shapes in a plurality of forming roll stands and controlling the rolling reduction so as to obtain a required shape, then gripping a material to be formed after the completion of formation by a clamping device, drawing- it for a required length in an idle state without driving all rolls and determining the angle of rotation and the number of rota¬ tion of roll shafts in each of the forming roll stands in this state, thereby obtaining an optimum ratio for the number of rotation between each of driven forming roll •' • stands and between upper and lower roll shafts relative to a certain standard roll shaft. The present invention concerns a method of determining an optimum ratio for the number of roll rotation in a cold roll forming- machine, operation method and a cold rolling mill capable of matching driving- force in the entire rolling mill, remarkably extending- the life of rolls, optimizing a driving source such as saving electric power 10 consumption and using a smaller size motor, and attaining to save maintenance in the rolling mill. Background Art i Cold rolling mills (hereinafter referred to as rolling mills) are generally used for forming metal materials for • ^ industrial products into various shapes, and relevant facilities for supplying raw materials are connected to the upstream and subsequent step facilities such as for drilling, cutting and bending are connected to the downstream of a forming line in which a plurality of 20 forming roll stands (hereinafter referred to as roll stands) are disposed. Formation of a plurality of different shapes In such a forming line has been greatly time and labor consuming such as exchange for the number of roll stages and forming -*i c *"* rolls for exclusive use depending on the shapes and control for the rolling reduction force by adjusting the gap between the upper limit roll shaft. In view of the above, a so-called cassette type cold rolling mill has been put to practical use in which a plurality of roll stands are mounted on a sub-base consti¬ tuted detachably to a common place, exchange for the • forming rolls and the control described above are previously completed in off-line, they are exchanged on every sub- bases and connected with a driving source attached to the common base. Further, for attaining labor-saving, a plurality of such sub-bases are provided, forming rolls for exclusive use are disposed on every shape to be formed for exclusive use and the sub-bases are exchanged in accordance with a demand. On the other hand, in the forming by a rolling mill, the shape of the forming rolls and the positions for disposing them on the line are determined depending on the shape required, and the number of roll stands and the change and adjustment for the rolling reduction or the amendment and change of the roll shape has been conducted so that a required forming shape is obtained and the formability is stabilized while actually conducting the forming. if desired formability is obtained, for example, by the change and adjustment for such rolling reduction, an appropriate change and adjustment for the rolling reduc¬ tion can not always be attained. For instance, if the balance for the rolling reduction ratio between each of the roll stands in lost greatly, rather forced forming is conducted by the roll stand whose rolling reduction is increased or decreased or a roll stand in adjacent there¬ with, which results in abrasion of rolls and damages to a driving system and, further, a desired shape can no more be obtained as the roll is abraded and it again requires change and adjustment for the rolling reduction. One of the objects of the so-called cassette type rolling mill of exchanging the sub-bases is to save labor by previously completing the exchange of the forming rolls or adjustment in off-line. However, since there is no method for appropriately judging the adequacy for the change and the adjustment of the rolling reduction or the change of the roll shape and it generally relies on the experience of operation, if the balance of the rolling reduction between each of the roll stands is lost, for example, by the change and control for the rolling reduc¬ tion ratio, abrasion of the forming rolls and degradation of the shaping property are repeated, making it necessary to exchange the forming rolls in an early stage to bring about a problem that the merit inherent to this system can not be obtained. In view of the foregoing present situation, it is an object of the present invention to provide a means for appropriately judging the adequacy for the change and the adjustment of the rolling reduction and the change of the roll shape, as well as to provide a means capable of remarkably extending the life of rolls, reducing the electric power consumption and attaining to save maintenance for the rolling mill, a rolling mill and an operation method therefor. Disclosure of the Invention For taking the advantage of the cassette type and aiming at a rolling mill with less abrasion of rolls and less frequency of maintenance such as change and adjust- ment of rolling reduction, the present inventor has made various studies and has accomplished the present invention based on the following knowledge. Since the roll shafts in each of roll stands of a rolling mill are generally driven rotationally by a common motor, each of the shafts is driven at a certain ratio or at an identical number of rotation and, considering the state of contact between a forming roll and a raw material, all the surfaces in contacts do not agree with the forming speed of the raw material. A product feed radial position of a roll that agrees with the forming speed of the raw material is assumed in the design so that ideal forming is applied as much as possible, but It is considered that this differs between each of the roll stands depending, for example, on a given reduction state. That is, assuming that the speed of the raw material to be formed is constant relative to each of the stands and each of the rolls and that the rotational speed of each of the roll shafts is constant, the product feed radial position of the roll (pass line) at which the speed of the raw material to be formed agrees with the rotational speed of the roll shaft often differs between each other depending on the adjusted or changed rolling reduction in each of the stands and the roll shape. Accordingly, if the roll shaft Is driven at a constant rotational speed, it is considered that the set number of rotation Is not always optimum but it can be considered that a roll not rotating at an optimum speed accelerates or decelerates the raw material to be formed due to excess •friction in addition to forming. By the way, it is imagined that an idle roll does not uniformly contact a raw material to be formed so that the non-uniform contact causes the roll to accelerate or decelerate the raw material to be formed. However, assuming that the number of rolling rotation is determined at a certain position, the number of rotation of the idle roll is a number of rotation with least resistance in the state of rolling reduction, and most effective driving can be attained by giving a number of rotation at an identical ' speed with the number of rotation of the idle roll. In view of the above, the optimum ratio for the number of rotation between each of roll stands and between upper and lower rolls in each of the roll stands, or the optimum ratio for the driving number of rotation to an arbitrary standard roll can be obtained by disposing rolls of predetermined shapes to a plurality of roll stands and adjustiog the rolling reduction thereof so as to obtain a required shape, confirming that a predetermined forming shape is obtained, then gripping a material to be formed that Isϊarves the final roll stand and is completed with the forming by a clamping device, drawing it for a required length in a free state without driving all of the rolls and determining, for example, the rotational angle and the number of rotation of the roll shafts for upper and lower rolls In each of the roll stands. The determining method according to the present inven¬ tion cam determine the optimuas number of roll rotation for indiviftaal rolls and, further, the optimum ratio for the number of roll rotation for each of upper and lower rolls among a plurality of roll stands in a rolling mill capable of obtaining a required forming shape, that is, under the conditions that the present roll shape and the rolling reduction used in a plurality of roll stands are not varied. In a rolling mill designed and controlled so as to obtain a desired forming shape, the roll shape and the rolling reduction set to each of the roll stands are not always set to best conditions. However, an operation method according to the present invention of measuring the ratio for the optimum number of roll rotation and applying the result to the control for the number of rotations between upper and lower rolls in each of the roll stands and/or between upper and lower rolls in adjacent roll stands or a rolling mill according to the present invention in which various speed changing means or 1 driving source control means are disposed for applying such control can drive under an optimum rotational number of roll shaft in each of the roll stands at least under the present conditions and, accordingly, it can provide such function and effect as free from the occurrence of problems, for example, acceleration or deceleration to a material to be formed due to excess frictional force as in the prior art, capable of reducing the electric power consumption and remarkably reducing the occurrence of surface flaws due to slip or biting or abrasion of rolls. Accordingly, the rolling mill applied with the opera¬ tion method according to the present invention can attain the matching for the driving system under a constant load since driving is conducted at an optimum ratio for the number of roll rotation in each of driving roll stands, can extend the life of rolls, makes the adjustment of rolling reduction ratio unnecessary for a long period of time and can attain the long working life with saving of maintenance. Further, in a rolling mill having a plurality of roll stands, by making roll shafts of roll stands on the sub- base unit or at an optional number of units free without driving and drawing the material to be formed by using a clamping device or applying roll forming under driving of other roll stands, the optimum ratio for the number of roll rotation between upper and lower roll shafts of the roll stand set free can be determined and further, the optimum ratio for the number of roll rotation roll stands set free can be determined. Accordingly, in a rolling mill comprising a multi¬ stage constitution, by dividing the plurality of roll stands with sub-base units or optional units and successively applying the determining method according to the present invention while making them free without driving on every unit, it is possible to determine the optimum ratio for the number of roll rotation between the roll stands for the entire number of stages and the optimum ratio for the number of roll rotation between upper and lower roll shafts in the roll stands at each of the stages. Further, in the determining method according to the present invention when the ratio for the number of roll rotation is determined by dividing a plurality of roll stands by optional units while making them free without driving on every unit, it is necessary to amend the ratio for the number of roll rotation of the divided unit and another divided unit adjacent to the first-mentioned divided unit. In such case the optimum ratio for the number of roll rotation throughout the entire number of stages can be determined in such a manner that the divided position is shifted to measure again the ratio for the number of roll rotation so that the thus measured ratio is amended together with the previously measured ratio for the number of roll rotation. Furthermore, in the rolling mill having a plurality of roll stands, the raw material to be formed is lotted in a plurality of lumps, each having a desired length, and each of thus lotted raw material passes through each divided unit of roll stands, thereby measuring easily the ratio for the number of roll rotation. In this case, thus measured ratio for the number of roll rotation is obtained in the state wherein the adjacent roll stands are made free, and, therefore, as above mentioned, the divided position is shifted to measure again the ratio for the number of roll rotation of the shifted unit of roll stands so as to amend the measured ratio for the number of roll rotation of the shifted roll stands together with the previously measured ratio for the number of roll rotation, thereby determining the optimum ratio for the number of roll rotation throughout the entire number of stages . For the optimum ratio of the number of roll rotation between the roll stands according to the present invention, which setting the roll stands for the entire number of stages free without driving, drawing and measuring the material to be formed by using a clamp device the exten¬ sion of the formed material per se has to be taken into consideration and it is preferable to conduct the drawing in such that an average longitudinal tension stress is applied to the entire sectional area of the material to be formed within a range of elastic deformation of the material Further, the optimum ratio for the number of roll. rotation between the free roll stands which is measured by selecting the roll stands on the sub-base unit and setting them free while driving others, the elongation of the formed material per se and the difference of the forming speed between adjacent sub-base units have to be taken into consideration. That is, a more optimized ratio for the number of roll rotation can be determined by amending the measured optimum ratio for the number of roll rotation with an amendment coefficient considering the elongation of the formed material per se, the entire forming speed and the difference .of. the forming speed on every measuring units. In the determining method according to the present invention, it is desirable to amend the resultant ratio for the number of rotation depending on various conditions upon measurement such as the entire number of stages for the roll stands, number of stages for measured units and the kind of the material to be formed. As an effective means for obtaining such an amendment coefficient, there can be mentioned an electric power required for forming shown in examples, for example, a current value of a motor. The formability and the forming amount in each of the roll stands can be evaluated by measuring the current value throughout the entire number of stages and the current value of the motor required for formation in each of the roll stands, and magnitude or ratio of the current value can be utilized for the amend¬ ment coefficient. Further, as an effective means for obtaining other amendment coefficient, there can be mentioned a ratio for the difference of the shaping speed of the formed material between each of the roll stands, which can be used toge¬ ther with the elongation of the formed material per se and the current value described above. Clamping Device The method of determining the optimum ratio for the number of roll rotation according to the present invention has a feature a drawing formed material which leaves the final roll stand and is completely formed ' for a required length while setting the rolls free without driving thern in a rolling mill of disposing forming rolls so as to obtain a required shape by a known method, for example, as has been conducted so far, adjusting rolling reduction thereof, and confirming that a required formability is obtained, for which a clamping device for gripping the formed material completed with formation is necessary. The clamping device can utilize such a constitution, for example, in a case where the formed material is a pipe, as gripping the pipe with a cylindrical or tubular cylindrical member which is bisected and expansible in the diametrical direction at the inside and the outside of the pip, or a constitution of utilizing a known mandrel mill. Further, in a case of a formed material having a usual open profile, it is possible to properly utilize a device having a split tubular member forming a required cross sectional shape such as a circular or rectangular shape by using an internal core mating the shape of the open cross sectional shape when it is inserted therein and enabling to grip the entire cross sectional shape for clamping- the formed material. Measuring Means In the present invention, as the measuring means for determining the number of rotation and the rotational angle of upper and lower rolls in each of roll stands upon drawing a formed material for a required length or upon driving formation, known mechanical, optical or magnetic type rotational meter or arious kinds of encoders can be selected properly and, urther, a rotational speed meter using, for example, optical rotary encoder or magnetic sensor can also be used. For instance, the measured number of rotation may be calculated as the ratio for the number of rotation between upper and lower rolls in each of roll stands or between each of the roll stands .of the rolling mill. Further, as the most simple method for obtaining the ratio for the number of rotation, a rotational angle for. each of the roll shafts upon drawing by a required length may be measured which can be calculated easily as a ratio for the number of rotation relative to an arbitrary standard roll shaft. Operation Method and Rolling Mill The operation method according to the present invention has a feature of applying the ratio for the number of rotation between upper and lower rolls in each of roll stands or between each of roll stands obtained by the measurement as described above upon operation of the rolling means, and a means for giving the ratio for the number of rotation to each of the driven roll stands for controlled driving during driving is properly selected depending on the constitution of the rolling mill and the driving method. Various constitutions are adopted for the driving method of a rolling mill and, in a case of constitution having a driving motor on every roll stands, for instance, voltage and current may be controlled depending on the type of the motor and the it may be controlled so as to provide a required number of rotation respectively. Further, in a case of driving the entire stages by a common motor or in a case of driving every several stages by one motor, adjustment or modification can be applied to each of speed retarders interposed between the motor and the roll shaft, so as to change the gear ratio for obtaining a required number of rotation. Further, in a case of placing roll stands for several stages to a sub-base and exchanging sub-bases depending on the shape of the formed material, adjustment after the ' exchange of the sub-bases is no more required by disposing a speed changing means giving a previously measured optimum ratio for the number of rotation between upper and lower rolls in each of the roll stands and between each of the roll stands on the side of each driving roll stands. For example, there can be adopted such a means as disengageably disposed an intermediate gear between a driving gear and a driven gear so as to be adjustable to provide a required ratio for the number of rotation depending on the number of teeth of a driven gear or intermediate gear. The rolling mill according to the present invention " has a feature of embodying the operation method described above to a rolling mill in which the speed changing means or the driving source control means may be adopted properly In accordance with the constitution of the rolling mill. Further, the optimum ratio for the number of roll rotation is previously measured so that each of the roll stands in the rolling mill may be driven at an optimum ratio for the number of roll rotation, the measurement can, of course, be conducted in the rolling mill, as well as it can be measured by other testing machines of a fundamentally identical structure having a structure that facilitates the change or adjustment of roll exchange adjustment for, inter-shaft distance or adjustment or- rolling reduction thereby easily recognizing the amount of change, capable of measuring the number of roll shaft rotation and rolling reduction for each of roll stands and having a calculator capable of directly calculating the obtained measured value as an optimum ratio for the number of rotation between each of the roll stands, and the results for the measurement of the number of rotation and the conditions such as for rolling reduction can be applied to the rolling mill. Further, the inventor has already proposed a roll forming method and a pipe mill capable of manufacturing pipes of a plurality of different open diameters with no exchange for rolls (Japanese Patent Publication Hei 3- 12975-7 , US P 4,770,019), which has a feature of changing the abutting direction of a forming roll including a predeter¬ mined involute curve in a cross sectional shape to a material upon changing the diameter to be formed, to change the shape of the face of contact, thereby elimina- ting the requirement of roll exchange and improving the formability. When the present invention is applied to such a pipe mill, the driving system can be optimized, and improvement for the formability and increased life for the forming roll can be attained by controlling a driving motor on every roll stands so as to provide a required number of rotation upon changing the diameter. Brief Description of Drawings Fig. 1 is an explanatory top plan view showing the constitution of an arrangement for a sub-base exchanging type rolling mill according to the present invention. Fig. 2 is an explanatory side elevational view showing a driving force transmission mechanism between a • speed retarder and a roll shaft in the rolling mill of Fig. l. Fig. 3 is an explanatory block diagram showing a driving force transmission mechanism between a speed retarder and a roll shaft so as to compare the method of the present invention with the conventional one. Fig. 4 - Fig. 9 are explanatory views showing a relationship between upper and lower rolls and a material to be formed in each of roll stands, which illustrates the forming step of an open profile material according to the present invention. Fig. 10 is an explanatory upper plan view illustra- ting the constitution of an arrangement of a test bench for production of pipes according to the present invention. Best Mode for Carrying Out the Invention Example 1 In a rolling mill showing in Fig. 1, five stages of roll stands 11 are placed in each of three sub-bases 10 and the number of the sub-bases 10 is selected to consti¬ tute into a required number of stages, in which warm gear- type speed retarders 2 are arranged by the number of roll stands in the direction of the forming line on the side of a common base and unified ' by. bonding by way of counter shafts, and connected with an electric motor 4 as a power source at the upstream end. The sub-base 10 is mounted on the side of the eciitmon i base 1 and a driving shaft for each of the speed retarders 2 and the roll shaft of the roll stand 11 are usuall connected by way of a coupling, and it is so ada ted here that a driving shaft gear 5 of a speed retarder 2 ajad a roll shaft gear 12 are engaged by means of an intermediate gear 13 to transmit the driving force as shown in Fig:. 2. Further, as will be described later, the gear ratio between each of the driving shaft gears 5 and the interme¬ diate gear 13 is identical, and the number of teeth for each of the roll shaft gears 12 is made different so as to obtain a predetermined gear ratio respectively. The intermediate gear 13 is journaled to an extreme end of a piston rod 14 of 'a hydraulic cylinder 15 mounted on the common base 1. the intermediate gear 13 is made elevatable by telescopic motion of a hydraulic cylinder 15, so that it descends to release from engagement upon exchange of the sub-base 10, while it is engaged upon ascendant movement. Forming rolls are arranged in each of the roll stands 11 and roll forming is conducted while adjusting the rolling reduction so as to obtain a required shape and, after the material to be formed leaves the final roll stand 11 and is completed with formation into a preferred shaping property, the intermediate gear 13 in each of the roll stands 11 being driven so far is elevated to release, making the all roll stands free, the material to be formed which leaves the final roll stand and is formed completely is drawn by a required length, and the ratio for the number of rotation of the roll shafts in each of the roll stands is measured by a rotational angle meter for the roll shaft previously disposed. For drawing the material to be formed, a required cross sectional shape is formed by using an internal core " to be inserted into an open cross sectional shape and aligning with the shape and a clamping device comprising a split type cylindrical member capable of gripping the entire cross sectional shape was pulled at a predetermined constant speed by a winch. The predetermined ratio of the rotational number between the upper and lower rolls in each of the roll stands and between each of the roll stands measured were obtained, and the number of teeth of the roll shaft gears 12 described above is made different to predetermined gear ratio respectively so that a required driven roll stands are driven at that ratio. Further, another sub-space 10 was provided depending on the shape of the material to be formed, and arrangement for the forming rolls, control for the rolling reduction, determination of ' the optimum ratio for the number of rota¬ tion of the roll shafts and the change of the roll shaft gear 15 were conducted by the above-mentioned method with a constitution of the group for the roll stands 11. In this way, by providing separate sub-spaces 10 respectively in accordance with the required shapes of a plurality of materials to be formed, estimating the shaping property of the resultant materials to be formed respectively and optimizing the number of rotation of roll shafts In each of the driving roll stands, it is possible to conduct roll forming by mounting sub-bases 10 for obtaining a required shape directly to the forming line in accordance with a demand. By optimizing the number of driving rota¬ tion of the driving roll shafts, abrasion of the forming rolls is remarkably decreased, the formability was improved to reduce the occurrence of product flaws, maintenance such as control for the rolling reduction was no more required for a long period of time and products having constant shaping property could always be obtained stably by merely replacing a sub-space with a required one. Further, since the number of rotation of the roll shafts was optimized, the electric motor 4, the speed retarder 2 the driving system for each of the gears , there is no portion on which an overload is exerted and mainte¬ nance was no more ' required for a long period of time. Example 2 For obtaining an open profile product having a cross sectional shape with a central portion being angled, that is, a rail shaped product of a formed material 24 put between upper and lower forming rolls 22n and 23n as shown in Fig. 9, from a zinc-plated steel sheet of 3.2 mm thick¬ ness, a rolling mill for roll forming a strip steel by a 8-height roll stand, rolls of predetermined shapes were disposed in each of the roll stands, the rolling reduction or the like was controlled so as to obtain a required shape to confirm that the required forming shape was obtained, in which the operation conditions in the conven¬ tional operation methods, in particular current value for the electric motor, the number of rotation for each of the roll shafts and the forming speed in operation were measured. Further, the optimum ratio for the number of roll rotation in accordance with the present invention was de¬ termined and the operation method according to the present invention was conducted while changing the gear ratio of the speed retarder in each of the roll stands, in which the current value for the electric motor, the number of rotation for each of the roll shafts and the forming speed were measured. In practicing the operation method according to the present invention, the current value of the electric motor, the number of rotation for the each of the roll shafts and the forming speed were measured in a case of a comparative example in which the roll shaft in each of the roll stands was not driven. At first, rolls of predetermined shapes were arranged in each of the roll stands so as to obtain a predetermined forming shape. There are shown upper and lower forming rolls, i.e., for the first stage in Fig. 4, for the second stage In Fig. 5, for the fourth stage in Fig. 6, for the fifth stage in Fig. 7, for the sixth stage in Fig. 8 and for the eighth state in Fig. 9. The third state and seventh stages are not illustrated. Driving for each of the roll shafts has the same constitution as in Example 1 of transmitting a driving force by way of a speed retarder with a worm gear by an electric motor, in which a gear box is interposed between a speed retarder 20 and a roll stand gear 21 in each of the roll stands as shown in Fig. 3, so that the gear ratio can be changed. That is, it comprises a mechanism of transmitting a driving force from the speed retarder 20, from a gear A to a gear B meshing therewith, from a gear C coaxial with the gear B to a gear D meshing therewith, from a gear E (lower shaft) coaxial with the gear D to a gear F (upper shaft) meshing therewith. The specifications for the electric motor are 37 kW of power, 194.8 A of rated current, 850 rpm of rotational number and 1/31 of reduction ratio of the speed retarder. The gear ratio in the gear box by the conventional operation method is naturally at an equal speed ratio of 1:1 both for the upper and lower shafts between each of the roll stands as shown in Table 1, and the gear ratio is set in accordance, for example, with the outer diameter of rolls mounted between the upper and lower roll shafts in each of the roll stands. The results of measurement for the operation condi- tions by the conventional operation method are as shown in Tables 2, 3 and 4. In comparison with the present inven¬ tion in Table 2, comparison is made while converting the forming speed to 13.5 m/min which is the same as in the present invention. Table 1 : Gear setting ratio (conventional method) Table 2 Conventional Comparison with the method ' present invention 1 Forming speed 14.5 m/min Motor r.p.m 840 rpm Non-load current 22 A value Load current 118 A 122.1 value Current value 96 A 131.4 % required for forming Table 3 : Number of rotation and feed diameter (Conventional Device) No.l No.2 No.3 No.4 No.5 No.6 No.7 No.8 lower 22.20 22.20 22.20 22.20 22.20 22.20 not- 22.20 shaft driven rpm Product 208.0 108.0 208.0 208.0 208.0 208.0 - 208.0 feed diameter upper 38.85 38.85 38.85 38.85 38.85 38.85 not- 38.85 shaft driven rpm Product 118.8 118.8 118.8 118.8 118.8 118.8 - 118.8 feed diameter Table 4 : Current value (Conventional device) All -No.2 No.3 No.4 No.5 No.6 No.7 No Then, the rotational angle for the roll shafts in each of the forming roll stands was measured when all the roll shafts in the mill were set free with no driving, gripping the formed material completed with formation by a clamping device and it was drawn by a required length, in which the optimum ratio for the number of rotation of all shafts was measured with reference to the lower roll shaft at the first stage. A rolling mill for practicing the operation method according to the present invention was manufactured while changing to the setting gear ratio shown in Table 5 so as to attain the optimum ratio for the number of rotation of all roll shafts and the results of the measurement for the operation conditions, etc. when conducting the roll forming are as shown in Tables 6, 7 and 8. Table 6 Method of Comparison with the the invention Conventional method Forming speed 13.5 m/min Motor r.p.m 840 rpm Non-load current 22 A value Load current 90 A 81.9 % value Current value 68 A 11.7 % required for forming Table 7: Number of rotation and feed diameter (This invention) No.l No.2 No.3 No.4 No.5 No.6 No.7 No.8 lower 22.20 22.20 23.28 24.42 22.20 21.17 not- 26.87 shaft driven rpm Product 193.6 193 . 6 184 . 6 176 . 0 193 . 6 203 . 1 159.9 feed diameter upper 34.15 30.13 27.94 28.86 25.78 23.15 - 22.52 shaft driven rpm Product 125.8 142.7 153.8 151.6 166.7 185.7 - 190.9 feed diameter Table 8 : Current value (This invention) After practicing the present invention described above, the roll forming was conducted without driving the upper shaft roll In each of the roll stands for compari¬ son. The setting gear ratio is the same as that in the present invention except for not driving the upper shaft roll. The results of the measurement for the operation conditions, etc. by the comparison method are as shown in Tables 9, 10 and 11. Upon comparison with the present invention in Table 9, comparison is made while converting the forming speed to 13.3 m/min which is the same as that in the present invention. Table 9 Comparative Comparison with the method this invention Forming speed 11.7 m/min Motor r.p.m 840 rpm Non-load current 22 A value Load current 84 A 107.7 % value Current value 62 A 105.2 % required for forming Table 10: Number of rotation and feed diameter (Comparative Example) No.l No.2 No.3 No.4 No.5 No .6 No.7 No .8 lower 22.20 22.20 23.28 24.42 22.20 21.17 not- 26.87 shaft driven rpm Product 167.8 167.8 160.0 152.5 167.8 176.0 138.6 feed diameter Table 11: Current value (Comparative Example) As apparent from the results of measurement described above, in the operation method according to the present invention of determining the optimum ratio for the number of driving rotation between each of the driving roll stands and applying the same to driving control, the current value of the motor required for forming is remarkably reduced, energy can be utilized effectively with less loss for roll forming an identical shape and less burden is applied to the forming rolls. Further, referring to the product feed diameter (unit: mm) of upper and lower shafts in each of the roll stands, that is, the roll radius position as viewed from the roll shaft at which the ' velocity of each of upper and lower rolls is made equal with that of the material is opened greatly in the -conventional case, whereas, as shown in Figs. 4 to 9 wherein a position at which the speed of the material is equal to that of the upper rolls is shown by a broken line and a position at which the speed of the material is equal to that of the lower rolls is shown by solid line, the gap between both of them is relatively narrow in the present invention and it can be found that the formed material is fed smoothly. From Figs. 4 to 9 wherein a position at which the speed of the material is equal to that of the upper rolls which are idling is shown by a dot and dash line it can be seen that the roll radius position between the upper and lower rolls is greatly opened. Further, the comparative example is for a case where all of upper rolls in each of the driving stands are set idle In the operation conditions of the present invention, in which the forming speed is greatly reduced and the current value of the motor required for forming is increased as compared with the present invention. It is not appropriate to apply, to this example, the common knowledge of the skilled in the art that the speed of the upper roll tends to become equal with that of the material to provide good forming property, if all of the upper rolls set idle while driving only the lower shafts. The present inventor has found that it is indispensable for matching and optimizing driving to positively drive each of the upper and lower roll shafts at an optimum number of rotation. In the foregoing examples, the optimum ratio for the number of rotation obtained by the determining method according to the present Invention is applied without amendment and it can be seen that the formability is improved outstandingly as compared with that in the conventional example. Then, when the present inventor corrected and amended the optimum ratio for the number of driving rotation between each of the roll stands, based on the elongation of the formed material through all the stages of roll stands or on every stages, the forming speed and the speed difference through all the stages of roll stands or on every stages, or a current value through all the stages of roll stands or on every stages, an effect of reducing the current value required for forming by several percents as compared with that of the examples described above in any of the amendment either alone or in combination for each of the amendment terms of the elongation for the formed material, difference in the forming speed and the current value. When the roll forming was practiced after amending the roll shape and controlling the rolling reduction while assuming that there is a problem for the shape of the forming roll in a roll stand in which the forming roll shape or the current value required for forming is greater than the mean value in the roll stand to be applied with the amendment described above, there was an effect of reducing the current value required for forming further by several percents as compared with the case of conducting the amendment. That is, the optimum ratio for the number of driving rotation between each of the roll stands according to the present invention is not only applied to the operation method, but it can also provide an appropriate judgment for the distribution of the forming amount and the forming roll shape by repeating the measurement for the optimum ratio of the number of driving rotation and the amendment for the forming conditions as described above. Example 3 A rolling mill shown in Fig. 10 is a pipe-manufacturing test bench according to the present invention and it illustrates an example in which it is applied to a pipe mill capable of manufacturing pipes of diameters in a required range without exchanging rolls as previously proposed by the present inventor (in Japanese Patent Pub¬ l ication H ei 3-12795-7, USP 4,770,019). Welding facilities are not illustrated in the drawing. From the upper stream of the pipe mill, that is, right side of Fig. 3, a group of breakdown roll stands Bl, B2, B3 are arranged, a breakdown roll stand B4 is arranged by way of a cluster roll stands CLl, CL2, and fin pass roll stands FI and F2 are arranged further to the down stream of four cluster roll stands CL3, CL4, CL5 and CL6. Forming rolls depending on the forming stages are arranged in each of the roll stands respectively, in which various kinds of forming rolls such as breakdown rolls and the cluster rolls used have cross sectional curves comprising involute curves based on a predetermined polygonal shape so as to align the curves for required portions of a strip steel in each of roll flowers of steel pipes with various outer diameters in the forming region although not illus¬ trated, and movable bearing portions are provided so as to move and rotate the bearing portion to linear or arcuate direction of the blank by means of a hydraulic cylinder or a hydraulic motor equipped with a lock so that the abutting angle and the position of the forming rolls to the forming blank may be changed depending on various outer diameters. For controlling the abutting angle and the position of the forming rolls to the formed material as previously set, various kinds of the hydraulic actuators are controlled by a calculator based on signals from a positional sensor disposed to the bearing portion. Further, a load cell for measuring the rolling reduc¬ tion is disposed, in addition to the rotational meter for measuring the number of rotation of the roll shafts, to each of the roll stands, and the output therefrom is inputted to the memory device for the calculator. Further, driving motors are disposed individually to required roll stands such as a group of breakdown roll stands requiring driving, and a controller for adjusting the driving force by the control for the voltage or the current is incorporated into the calculator. In the pipe mill with such a constitution, roll forming was at first conducted while adjusting the rolling reduction by changing the abutting angle and the position of the forming roll in each of the roll stands to the forming material so as to obtain a pipe of a required diameter and, after the shaping property of the pipe leaving the final roll stand and completed with the forming is made satisfactory, power supply to the motor for each of the roll stands under driving is interrupted to make all the roll stands free, and the tube leaving the final rolling stands and completed with the formation was drawn by a draw bench DB at a required constant speed, to measure 1 the number of rotation for roll shafts in each of the roll stands. By previously programming such that each of driving motors is controlled for driving at an optimum ratio for the number of driving rotation based on the number of rotation for the roll shafts in each of the roll stands previously measured by the calculator, the number of rota- tion for the produced pipe and the roll shafts was measured on every required diameters and the date for the rolling reduction in each of the roll stands and the number of rotation for the roll shafts on every diameter were stored, by which the motor can afterward be driven under control at an optimum'ratio for the number of driving rotation between the driving roll stands automatically depending on the diameter. As a result, abrasion of the forming rolls was remar¬ kably reduced, the forming property was improved to reduce the occurrence of product flaws, etc., maintenance such as for the adjustment of the rolling reduction was no more required for a long period of time and the durability of the entire pipe mill was remarkably improved. Industrial Applicability In accordance with the present invention, rolls of predetermined shapes are arranged in a plurality of roll stands and rolling reduction thereof are adjusted so as to obtain a required shape, formed material completed with forming is gripped by a clamp device after obtaining a predetermined formability, the material is drawn by a required length without driving all the rolls and determining the number of rotations, etc. in each of the roll stands, by which the optimum ratio for the number of driving rotation can be obtained between each of the driving roll stands, the driving force between each of the driving roll stands can be matched and optimized by driving each of the driving roll stands at the optimum ratio for the number of driving rotations, which can attain the maintenance free of the rolling mill such as reduction of occurrence for the surface flaws due to slip or biting, remarkable elon- gation or extension of the roll life, reduction of aging change and elimination for the requirement of fine adjust¬ ment of the rolling reduction for a long period of time, which has been indispensable so far, as well as driving force can be optimized, for example, in that a smaller motor as compared with usual case can be used. Further, in accordance with the present invention, since the measurement for the optimum ratio for the number of driving operation is- easy and the results of the measu- rement therefor can easily be applied also to existent rolling mills, the driving force for all of the rolling mills can be matched and optimized.

Claims: CLAIMS 1. A method of determining the optimum ratio- for ' the number of roll rotation in a rolling mill for forming a plate material into a required shape by using a plurality of roll stands, which comprises arranging forming rolls of predetermined shapes in each of roll stands and adjusting rolling reduction thereof so as to obtain a required shape, then applying roll forming and gripping a material to be formed that leaves final roll stand and is completed with formation by a clamping device, drawing it for a required length without driving all the roll stands but left them free, and determining the ratio for the number of rotation of roll shafts between each of roll stands and/or the ratio for the number of rotation between upper and lower roll shafts in each of the roll stands. 2. A method of determining the optimum ratio for the number of roll rotation in a rolling mill for forming a plate material into a required shape by using a plurality of roll stands, which comprises arranging forming rolls of predetermined shapes in each of roll stands and adjusting rolling reduction thereof so as to obtain a required shape, setting upper and lower roll shafts in a predeter¬ mined number of units or optional roll stands free without driving, applying roll forming by the driving of other roll stands or further combining drawing for the material to be formed by using a clamping device, thereby determining the ratio for the number of rotation of roll shafts between each of the roll stands set free and/or the ratio for the number of rotation between upper and lower roll shafts in each of the roll stands. 3. A method of determining the optimum ratio for the number of roll rotation in a rolling mill as defined in claim 1 or 2, wherein the resultant ratio for the number of rotation is amended due to elongation of a material to be formed through all the number of stages or on every stages of roll stands as a term for the amendment. 4. A method of determining the optimum ratio for the number of roll rotations in a rolling mill as defined in claim 1 or 2, wherein the resultant ratio for the number of rotation is amended due to a difference of electric power required for forming through all the number of stages or on every stages of roll stands as a term for the amendment. 5. A method of .determining the optimum ratio for the number of roll rotations in a rolling mill as defined in claim 1 or 2, wherein amendment for the resultant ratio for the number of rotation is applied based on the forming speed through all the number of stages of the roll stands and the difference of the forming speed on every measuring units as the term for the amendment. 6. A method of determining the optimum ratio for the number of roll rotations in a rolling mill as defined in claim 1 or 2, wherein the amendment is applied for the resultant ratio of the number of rotation for two or more of the elongation of the formed material, difference of electric power required for forming and difference of forming speed on every measuring units through all number of stages of roll stands or on every stages of roll stands as the term for the amendment. 7. A method of operating a rolling mill for forming a plate material into a required shape by rotationally driving a plurality of roll stands, which comprises arranging forming rolls of predetermined shapes to each of roll stands and adjusting rolling reduction thereof so as to obtain a required shape, then applying roll forming and clamping a material to be formed that leaves the final roll stand and is completed with formation by a clamping device, drawing it for a required length without driving but setting free all the roll stands, previously determi¬ ning the ratio for the number of rotation of the roll shafts between each of the roll stands and/or the ratio for the rotation between upper and lower roll shafts in each of the roll stands by a measuring means disposed previously to required roll stands and driving the roll shafts of the required roll stands at the resultant ratio for the number of rotation of roll shafts between each of the roll stands and/or ratio for the number of rotation between upper and lower roll shafts in each of the roll stands. 8. A method of operating a rolling mill as defined in claim 7, which comprises applying roll forming without driving but setting free upper and lower roll shafts in a predetermined number of units or an arbitrary roll stand but by the driving of other roll stands, or drawing the material to be formed by using the clamping device and, driving the roll shafts by applying the resultant approxi- l mate optimum ratio for the number of rotation between the roll stands set free. 9. A rolling mill for carrying out the method of oeration claimed in claim 7 or 8 , wherein a speed conversion means or a control means for a driving source is provided for setting the resultant ratio for the number of rotation of roll shafts between each of the roll stands and/or ratio for the number of rotation between the upper and lower roll shafts -in each of the -roll stands to a ratio for the number of rotation between each of driving roll stands during driving.

Inventors: KURAMOTO RYOSUKE, KURAMOTO, RYOSUKE
Applicants: NAKATA MFG, NAKATA MANUFACTURING CO., LTD.
Application year: 1992
Main classification: B21D5
IPC codes: B21D5