EP0061539A1

EP0061539A1 - Control method for multi-strand rolling mill

Info

Publication number: EP0061539A1
Application number: EP19810301316
Authority: EP
Inventors: Koichi Ohba
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1981-03-26
Filing date: 1981-03-26
Publication date: 1982-10-06
Also published as: EP0061539B1; DE3168723D1

Abstract

When two workpiece strands (14,16) pass through a roll gap between two grooved working rolls (10, 12) on a roll stand to be rolled, the trailing end of one of them may leave the rolls to change the roll gap. At that time screw-down devices (20, 22) on each side of the roll stand are controlled to adjust the roll gap at least at the position of the remaining workpiece. Also in a multi-strand tandem rolling mill, rolling speeds on roll stands upstream of a roll stand from which one of the strands has departed are changed by a speed ratio of (1-b₂)/(1-b₁) where b, and b₂ designate the rates of backward slips in the presence of the two strands and in the absence of one of the strands on the last-mentioned roll stand. Alternatively roll speeds on roll stands downstream of that roll stand may be changed by a speed ratio of (1 + f₂)/(1 + f₁) where f₁ and f₂ designate the rates of forward slip which correspond to the b₁ and b₂ respectively.

Description

This invention relates to a control method for a multi-strand rolling mill, and more particularly to such a method responsive to at least one workpiece strand leaving or entering a roll stand serving to roll simultaneously a plurality of strands to remove the influence of the strand leaving or entering the stand on the remaining strands both in that roll stand and in the following roll stands.
In Figure 1 of the accompanying drawings, there is illustrated the essential portion of a roll stand for rolling a pair of workpiece strands simultaneously. The arrangement illustrated comprises a pair of upper and lower working rolls 10 and 12 arranged one above the other to form a roll gap therebetween. Each of the upper and lower rolls 10 and 12 includes a plurality of axially spaud forming grooves, in this case, two grooves extending circumferentially around the entire surface thereof opposite those on the other roll. Each of the opposed pair of grooves have a cross section substantially complementary to that of a workpiece strand to be rolled. In Figure 1 a pair of workpiece strands 14 and 16 are shown in cross section as being sandwiched between the opposite forming grooves on the upper and lower rolls 10 and 12 respectively with a small spacing therebetween. The lower roll 12 includes a pair of shafts protruding from both sides thereof and extending rotatably through the opposite lateral walls of a housing 18. The upper roll 10 includes a pair of similar shafts extending not only rotatably but also movable toward and away from the lower roll 12 under the control of screw-down devices 20 and 22 disposed in the upper portions of the opposite walls of the housing 18 on the working and driving sides respectively.
The screw-down devices may be of the electrically operated type or the oil pressure type but they are generally of the manually operated type with rolling mills rolling a plurality of strands simultaneously.
The roll gap between the upper and lower rolls 10 and 12 is variable in accordance with their loading as shown in Figure 2. Under no load i.e. in the basence of the workpieces, the upper and lower rolls 10 and 12 respectively are located at thier positions shown by the horizontal lines 26 and 24 in Figure 2 to maintain therebetween a roll separation S_o equal to a magnitude determined by the particular rolling schedule. In Figure 2 the lower roll 12 is fixed to its position shown by the lower horizontal line 24.
With a pair of workpiece strands 14 and 16 simultaneously sandwiched between the two rolls 12 and 14 as shown in Figure 1, the upper roll 12 is located at its position as shown by the horizontal line 28 in Figure 2. However with only the strand 16 on the driving side disposed between the two rolls 10 and 12, the upper roll 10 can be located at its position shown by the tilted line 30 in Figure 2.
Conventional rolling methods along with objections thereto will now be described with reference to both conventional roll stands such as shown in Figure 1 and the positions of the upper and lower working rolls as shown in Figure 2. It is assumed that such a roll stand rolls only two strands for purposes of illustration.
According to the conventinal rolling method, the rolling speed on each roll stand arranged in a tandem arrangement in a rolling mill has been preliminarily set to a magnitude determined by a rolling pass schedule and a pair of screw-down device on each side of each roll stand have been manually operated to set a roll gap between the mating upper and lower working rolls to the magnitude determined by that schedule.
The strands 14 and 16 as shown in Figure 1 are simultaneously rolled by a rolling mill scuh as described above so that those strands are successively rolled on the succeeding roll stands. During the rolling, each workpiece path along which the strands travel may include a gap between the trailing end of one strand and the leading end of the next.
As a result, the roll stand as whon in Figure 1 may change from its state in which both the strans 14 and 16 are being simultaneously rolled to the state in which only either one of these strands is being rolled.
With-the two workpieces disposed in the forming grooves on the working and driving sides, it is assumed that in Figure 2 F_W and F_D designate the rolling force for the strand 14 on the working side and that for the strand 16 on the driving side respectively. Under the assumed conditions screwing-down forces F_WSO and ^F _DSOare generated, as reactions to those rolling forces, at screw-down positions on the working and driving sides respectively and hold
Also assuming that M designates a mill constant of the roll stand, those forces F_W and F_D cause the roll gap S₀ between the upper and lower working rolls to increase by a magnitude S_DW expressed by
and the upper roll 10 adopts its position shown by the horizontal line 28 in Figure 2. In other words, when the roll stand as shown in Figure 1 performs the rolling operation with a pair of strand workpieces passing therethrough, the roll opening of (S_o + S_DW) is formed between the upper and lower rolls 10 and 12 respectively. Therefore the product has a dimension corresponding to that roll separation opening.
It is now assumed that the strand workpiece 14 has been rolled by the roll stand as shown in Figure 1 and left the latter while only the strand 16 is still being rolled. Under the assumed conditions the roll force F_W diappears. As a result, the upper roll 12 "adopts its position shown by the tilted line 30 and the opening S^DW decreases to a magnitude S_D at the position of the strand 16. It is further assumed that (S_D + S_o) designates the roll gap at the position of the strand 14, ℓ_r the distance between the central section of the working roll perpendicular to the longitudinal axis and the position of each of the strands 14 and 16 and ℓ_f designates the distance between that central section and each of the screw-down positions. Under the assumed conditions the following equations hold
and
Therefore
and
From the foregoing it is seen that in the arrangement of Figure 1 the roll gap at the position of the strand 16 changes between the magnitudes (S + S_DW) and (So + S_D) depending on whether or not the strand 14 is present between the rolls 10 and 12. This has resulted in the disadvantage that the rolled product cannot be of uniform dimensions.
In a known example of multi-strand rolling mill a plurality of roll stands are disposed in tandem i.e. one after the other to roll simultaneously, for example, a pair of strands and are followed by a pair of branched arrays of roll stands disposed in tandem one for each workpiece each to roll only the associated workpiece. Each of the roll stands for rolling simultaneously the pair of strand workpieces includes a pair of upper and lower working rolls as described above and each of the roll stands in the branched arrays includes a pair of upper and lower working rolls differeing from those described above only in that in the former stand a single forming groove is disposed on each working roll.
When the roll gap changes in one of the roll stands the double grooved working rolls for the reason described above, the remaining strands undergo a change in entry and delivery speeds on that roll stand. As a result, the multi-strand rolling mill has been unable to keep a constant mass flow of the strand which is kept in normal operation.
However when at least one strand has left or entered an associated roll stand during the simultaneous rolling of a plurality of strands so that the remaining strands change in entry and delivery speeds, conventional control methods for multi-strand rolling mills have not particularly compensated for the change in speed. Therefore each of the remaining strands being rolled on the roll stand has much changed in its loop disposed downstream thereof with the result that all the roll stands downstream thereof are adversely affected.
The present invention seeks to provide a method of controlling a multi-strand rolling mill so that the roll gap is always correctly maintained on any roll stand disposed in the rolling mill to roll simultaneously a plurality of strand workpieces regardless of whether or not at least one of the strands is present in that roll stand.
The present invention also seeks to provide a method of controlling a multi-strand rolling mill comprising a plurality of roll stands disposed in tandem so-that, when at least one of a plurality of strands leaves or enters any one of the roll stands rolling simultaneously the strands, constant mass flow of the strands is maintained throughout the rolling mills.
According to one aspect thereof, the present invention provides a method of controlling a multi-strand rolling mill for rolling simultaneously a plurality of workpiece strands, comprising the steps of tracing the positions of the tailing end and the leading end of each of a plurality of strands, and controlling the roll gap of a roll stand simultaneously with the trailing or leading end of at least one workpiece strand leaving or entering the roll stand.
According to another aspect thereof, the present invention provides a method of controlling a multi-strand rolling mill comprising a plurality of stands disposed in tandem to roll simultaneously a plurality of workpiece strands, comprising the stps of tracing the trailing end and the leading end of each of a plurality or strands and each time at least one strand passes through each of the roll stands, adjusting the rolling speeds of the roll stands upstream of roll stand through which the end of said at least one strand passes, the rolling speed of the last-mentioned roll stand and the rolling speed of the roll stands downstream of the latter roll stand to a speed ratio maintaining a constant mass flow of the strands throughout the multi-strand rolling mill.
In a preferred embodiment of the present invention, the control method may render the speed ratio equal to:
where b₁ and f₁ designate the rate of backward slip and the rate of forward slip on the roll stand through which the end of said at least one strand passes when all the strands are present in the last-mentioned roll stand and_b2 and _f2 designate the rate of backward slip and the rate of forward slip on the last-mentioned roll stand when the end of said at least one strand has passed through the last-mentioned roll stand.
The present-invention will now be described further, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a side elevational view of the essential portion of a roll stand for rolling simultaneously a pair of strands with parts illustrated in cross section:
Figure 2 is a diagram illustrating the roll gap between the upper and lower working rolls shown in Figure 1 and dependent on the number of strands being rolled.
Figure 3 is a cross sectional view of working rolls shown in Figure 1 illustrating one of the strand workpieces as shown in Figure 1 being rolled:
Figure 4 is a schematic plan view of a double- strand; rolling mill; and
Figure 5 is a diagram similar to Figure 2 but illustrating the control of a roll stand according to the present invention.
Figure 3 shows the manner in which the arrangement of Figure 1 rolls the strands 16. During the rolling of the two workpiece strands 14 and 16 the roll gap at the position of the strands 16 is determined by the upper and lower roll now designated by an upper and lower dotted circle 32 and 34 respectively. That roll opening corresponds to the roll opening (S_o + S_DW) shown in Figure 2. The workpieces 16 enters to an entry speed _VEI into that roll gap and rolled into a strand 36. Then the rolled strand 36 leaves with a delivery speed V_DI the roll opening.,

Assuming that the strand 14 leaves the upper and lower rolls after having been rolled and only the strand 16 is being rolled. At that time the roll gap at the position of the strand 16 is determined by the roll gap between the upper and the lower roll designated by the upper and lower solid circle 38 and 40 respectively. That roll gap corresponds to the separation (S_o + S_D) shown in Figure 2. The strand 16 is entered at an entry speed V_E2 into that roll opening and rolled into a strand 42. Then the rolled strand 42 leaves the roll gap at a delivery speed V_D2.
In Figure 3, the upper and lower working rolls have a common speed of rotation remaining unchanged regardless of whether or not a workpiece 14 is present between the working rolls. However, the rolled strand 42 has a ratio of its delivery speed to the circumferential speed of the roll (which is called hereinafter the rate of forward slip) larger than that of the rolled strand 36 because the rolls have more screwed down the strand 42 than the strand 36. Therefore at the outgoing side of the rolls the strand 36 travels at a lower speed than the strand 42. That is, V_D1<V_D2 holds. Similarly it is well known that the entry speed V_E1 is higher than that V_E2 due to the change in rate of backward slip which implies a ratio of the entry speed of the strand to the circumferential speed of the working roll.
Figure 4 shows a multi-strand rolling mill. The arrangement illustrated comprises a pair of roll stands 44 and 46 disposed in tandem to roll a pair of workingpi_ece strand, A and B simultaneously and a pair of branched arrays each including two roll stands 48 and 50 or 49 and 51 disposed in tandem to roll only an associated one of the strands A or B. The workpiece A is being rolled on the roll stands 44, 46, 48 and 50 while it travel along loops 52 and 54 netween the roll stands 46 and 48 and between the roll stands 48 and 50 respectively. The workpiece A leaves the roll stand 50 as shown by the arrow 56 in Figure 4.
On the other hand, the strand B is shown in Figure 4 as having just left the roll stand 46 and forming similar loops 53 and 55 between the roll stands 46 and 49 and between the roll stands 49 and 51 respectively. Then the workpiece B leaves the roll stand 51 as shown at the arrow 56 in Figure 4.
It will readily be seen that the roll stand 46 shown in Figure 4 corresponds to that described above in conjunction with Figure 3 because the strands B is shown in Figure 4 as having just left the roll stand 46.
In the arrangement of Figure 4 the roll stands 44, 46, 48, 49, 50 and 51 have respectively rolling speeds or speeds of the rolls as determined so that each of the roll stands is equal in mass flow in unit time of the workpiece A or B to other roll stands. However the workpiece B has already left the roll stand 46 and therefore the delivery speed of the strand workpiece A increases to V_D2 from V_D1 while at the same time the entry speed thereof decreases to V_E2 from VE1 as described above in conjunction with Figure 3. As a result, the strand A has a mass flow which is not kept constant throughout the arrangement of Figure 4.
This is true in the case when a strand following the workpiece B enters the roll stand 46. However conventional control methods for the multi-strand rolling mill have not comprises the special step of controlling such changes in entry and delivery speeds of the strand workpiece under rolling. Therefore the latter strand workpiece has greatly changed the shape of the loop 52 located downstream of that roll stand from which the one workpiece has departed. This has adversely affected the rolling effected byall the roll stands disposed downstream of the loop 52, In addition, as the roll stand 46 has a smaller mass flow than the roll stand 44 disposed upstream thereof, a compressive force is generated therebetween. This has resulted in a large defect in view of the rolling.
According to one aspect thereof, the present invention contemplates to maintain a constant roll separation on any roll stand disposed in a multi-strand rolling mill to roll simultaneously a plurality of strand workpieces at-the position of each of the strand workpieces being rolled regardless of whether or not at least one strand workpiece leaves or enters that roll stand.
To this end, each of the manual screw-down devices 20 or 22 as shown in Figure 1 is replaced by a remotely actuatable, fast response screw-down device such as an electrically operated or an oil pressure screw-down device and there is provided tracing means for tracing the position of the leading and trailing end of each of the workpiece strands. Simultaneously with the sensing of the trailing or leading end of at least one of the strand workpieces leaving or entering a roll stand, a roll opening on that roll stand is controlled through the screw-down devices disposed on the latter.
Referring back to Figure 1, it is assumed that the roll stand illustrated changes from its state in which the two strands 14 and 16 are simultaneously rolled to its state in which the strand 14 has left the working side. Under the assumed conditions, the position as shown at line 28 in Figure 2 of the upper roll 10 changes to its position as shown at line 30 in Figure 2 to change the roll opening at the rolling position on the driving side from its magnitude (S_DW + S_o) to (S_D + S_o) as described above in conjuction with Figure 2. Therefore the leading and trailing ends of the strand 14 on the working side are always traced and simultaneously with the trailing end of that strand leaving the roll stand, the two screw-down devices on the working and driving sides are equally controlled so that the upper roll 10 occupies a position as shown at tilted dotted line 58 in Figure 5 which is similar to Figure 2 expecting that the Figure 5 dotted line 58 is additional shown to be spaced from parallel line 30 by magnitude S . This results in a roll gap (S_DW + S_o) at the rolling position on the driving side.
From the foregoing it is seen that the two screw- down devices control the roll gap by a magnitude S_c expressed by
As F_n = F_W generally holds,
results. This means that the roll opening increases by a magnitude corresponding to S_W defined by the expression (4).
From the foregoing it will readily be understood that, when the leading end of the workpiece strands on the working side enters the roll stand, the roll gap at the rolling position on the driving side is simultaneously decreased by the magnitude S_w.
In this way the roll gap can be maintained constant at the rolling position of the strand workpiece on the driving side regardless of the presence or absence of the workpieces on the working side.
While the present invention has been described in conjuntion with the presence or absence of the strand workpiece on the working side it is to be understood that the same is equally applicable to whether or not the stand exists on the driving side. In the latter case, the leading and trailing ends of the strand workpiece on the driving side are traced and the roll opening at the rolling position of the strand on the working side increases or decreases by the magnitude S_s defined by the expression (3) simultaneously with the trailing or leading end of the strand on the driving roll leaving or entering the roll stand respectively.
It is also to be understood that, by controlling the screw-down devices on the working and driving sides to different screw-down magnitudes, the upper roll may occupy its position as shown at line 28 in Figure 5 with a satisfactory result. In summary it is essential to maintain a roll operation at the rolling position on the side of that strand workpieces continuously rolled, at a constant magnitude (^S _DW ⁺ So).
In the foregoing, the roll opening has increased or decreased simultaneously with the strand leaving or entering the roll stand, but this entering or leaving consumes some time interval. Therefore the increase or decrease in roll gap is preferably equal in time interval to the entering or leaving of the strand.
While the present invention has been described in conjunction with the simultaneously rolling of two strand workpieces it is to be understood that the same is equally applicable to the simultaneous rolling of more than two strand workpieces. In the latter case the roll opening on the roll stand is controlled in manner similar to that described above so that, when at least one strand leaves or enter the roll stand, the resulting influence of that roll opening on the remaining strand workpieces is minimized.
Also the present invention has been described by using the expressions formulated by way of example, with the positions of the strand workpieces under rolling bilaterally symmetric about a central control section of an associated working roll perpendicular to the longitudinal axis thereof but it is to be understood that the present invention is equally applicable to those positions bilaterally asymmetric about that central section. In the latter case the fundamental point of view is similar to that described about in conjunction with the symmetric positions of the strands under rolling excepting that controlled magnitudes are different from those described above.
According to another aspect thereof, the present invention, contemplates to maintain a constant mass flow throughout a multi-strand rolling mill comprising a plurality of roll stands disposed in tandem to roll simultaneously a plurality of strand workpiece even then at least one of the strand workpieces leaves or enters one of the roll stands.
In Figure 3 it is assumed that each of the upper and lower rolls is rotated at a constant circumferential speed or a constant rolling speed V_R and each of the plurality of strands has an entry speed V_E1 and a delivery speed V_D1 with the large roll gap or in the presence of all the strand workpieces on the rolls as well as an entry speed V_E2 and a delivery speed V_D2 with the small roll gap or in the absence of at least one strand workpieces on the rolls as described above. It is further assumed that, with the roll gap large, r_l, f₁ and b₁ designate a screw-down rate, a rate of forward slip and a rate of backward slip respectively while, with the roll opening small, r₂, f₂ and b₂ designate a screw-down rate, a rate of forward slip and a rate of backward slip respectively. Under the assumed conditions, there are held.

Therefore
and
result.
From the above expressions it is seen that, when the strands B has left the roll stand 46 as shown in Figure 4, the entry speed of ths strand workpiece A changes from its magnitude V_E1 to V_E2 as long as the rolling speed V_Ron the roll stand 46 remains unchanged. In order to prevent this change in entry speed from affecting the strand workpiece A, each of all the roll stands disposed upstream of the roll stand 46 is required only to change the rolling speed thereon by a ratio of V_E2 to V_El expressed by
Similarly the rolling speed on each of the roll stands disposed downstream of the roll stand 46 for the strand workpiece A is required to change by a ratio of ^V _D2 to V_D1 expressed by
While the measures described above have resulted from a point of view that the speed V_R on the roll stand 46 remains unchanged, other measures may be adopted. More specifically, one of those measures is to change the speeds on all the roll stands disposed upstream of the roll stand 46 and including the latter alone and another measure is to change the speeds on all the roll stands disposed downstream of the roll stand 46 and including the latter' alone.
The measure to change the rolling speed on each of all the upstream roll stands alone is arranged to maintain the speeds on all the downstream roll stands constant although those speeds should actually change by a factor as defined by the expression (12). From this it will readily be understood that it is required only to multiply the speeds on all the upstream roll stands including the roll stand 46 by the reciprocal of.the factor defined by the expression (12). Thus it is concluded that it is sufficient to multiply the speed on the roll stand 46 by a factor (1 + f_l)/(1 + f₂) while at the same time multiplying the speeds on the roll stands disposed upstream of the roll stand 46 by a factor expressed by
Similarly the measure to change the delivery speeds of the strand on the downstream roll stands alone results in the multiplication of the speed on the roll stand 46 by a factor of (1 - b_l)/(l - b₂) and of the speeds on the roll stands disposed downstream thereof by a factor expressed by
In the foregoing it is to be understood that, since the rates of forward slip f₁ and f₂ approximate unity (1), it is possible to change the roll speeds on all the roll stands upstream or downstream of the roll stand 46 by multiplying by the same factor respectively with the satisfactory result.
From the foregoing it is seen that, in order to prevent one strand workpiece leaving or entering one of roll stands from changing a roll separation on that roll stand to affect the other strand workpieces adversely, the present invention has been illustrated and described in conjunction with a control method comprising steps of tracing the trailing and leading end of each of the strands, sensing the trailing or leading end of either one thereof leaving or entering one of roll stands and changing the speed ratios of the roll stands disposed upstream or downstream of that roll stand or all the roll stands simultaneously with the sensing of the associated workpiece, it is to be understood that it is essential to change the rolling entry, delivery speeds on the roll stands upstream of that roll stand changed in number of strand workpieces being roll, and last-mentioned roll stand and those downstream thereof following a speed ratio
By changing the speeds on all the roll stands as described above, a mass flow thereof is maintained constant throughout the multi-strand tandem rolling.
While the present invention has been illustrated and described in conjunction with a two-strand tandem rolling mill as shown in Figures 3 and 4, it is to be understood that numerous changes and modification may be resorted to without departing from the scope of the present invention as set out in the claims. For example, it is to be understood that the present invention is equally applicable to any multi-strand rolling mill including a plurality of roll stands disposed in tandem to roll simultaneously more than two strand workpiece. Also the present invention has been described in conjunction with ratios with which the rolling speeds are changed on the respective roll stands, but it is noted that at least one of the strands does not leave or enter the roll stand instantaneously but that it leaves or enters the roll stand within a constant time interval as determined by the speeds thereof, the diameter of the working rolls and screwdown rate on that roll stand. As a result, it has been found that the more satisfactory result is given by making substantially equal the time interval over which the speeds are changed to the constant time interval as described above.

Claims

1. A method of controlling a multi-strand rolling mill for rolling simultaneously a plurality of workpiece strands, comprising the steps of tracing the trailing end and the leading end of each of a plurality of strands and controlling the roll gap of the roll stand simultaneously with the trailing or leading end of at least one of workpiece strand leaving or entering the roll stand.

2. A method of controlling a multi-strand rolling mill comprising a plurality of roll stands disposed in tandem to roll simultaneously a plurality of strands, comprising the steps of tracing the trailing end and the leading end of each of a plurality of strands, and each time at least one strand passes through each of the roll stands adjusting at least two of three rolling speeds, namely the rolling speed of the roll stands upstream of roll stand through which the end of said at least one strand passes, the rolling speed of the last-mentioned roll stand and the rolling speed of the roll stands downstream of the latter roll stand to a speed ratio maintaining constant mass flow of the strands throughout the multi-strand rolling mill.

3. A control method as claimed in claim 2 wherein the ratios of the said three rolling speeds are given by:

(1 - b₂)/(1 - b_l)^: 1 :(1 ⁺ f₂)/(1 ^{+ f} _l) wherein b₁ and f₁ designate the rate backward slip and the rate of forward slip on the roll stand through which the end of said at least one strand passes when all the strands are present in the last-mentioned roll stand, and _b2 and f₂ designate the rate of backward slip and the rate of forward slip on the last-mentioned roll stand when the end of said at least one strand has passed through the last-mentioned roll stand.

4. A control method as claimed in claim 2 wherein the first and second rolling speeds have a speed ratio expressed by

while the third rolling speeds remain unchanged, wherein r₁ designates the screw-down rate on the roll stand through which the end of said at least one strand has passed when all the strands are present in the last-mentioned roll stand and r₂ designates the screw-down rate on the last-mentioned roll stand when the end of the said at least one strand has passed through the last-mentioned roll stand.

5. A control method as claimed in claim 2 wherein the second and third rolling speeds have a speed ratio expressed by

while the first rolling speeds remain unchanged wherein r₁ designates the screw-down rate on the roll stand through which the end of said at least one strand has passed when all the strands are present in the last-mentioned roll stand and r₂ designates the screw-down rate on the last-mentioned roll stand when the end of said. at least one strand has passed through the last-mentioned roll stand.