US3861188A

US3861188A - Rolling process and rolling stand of steel plate

Info

Publication number: US3861188A
Application number: US420565A
Authority: US
Inventors: Norimasa Kamit; Ryozi Terakado
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 1972-11-30
Filing date: 1973-11-30
Publication date: 1975-01-21
Anticipated expiration: 1992-01-21
Also published as: DE2359201A1; JPS5147421B2; JPS5234022B2; DE2359201C2; JPS4977865A; JPS49122867A; BR7309448D0

Abstract

A process and a rolling mill for rolling thin plate by means of a tandem rolling mill characterized in that the diameter of either of the upper or the lower working rolls in optional rolling stands situated in the rear step of the tandem rolling mill for thin plate consisting of a plurality of rolling stands is chosen smaller than that of other corresponding working rolls and that the rolling work is carried out by driving only the working rolls with larger diameter.

Description

United States Patent Kamit et al.

[451 Jan. 21, 1975 [54] ROLLING PROCESS AND ROLLING STAND OF STEEL PLATE [75] Inventors: Norimasa Kamit; Ryozi Terakado,

both of Hokkaido, Japan [73] Assignee: Nippon Steel Corporation, Tokyo,

Japan [22] Filed: Nov. 30, 1973 [21] Appl. No.: 420,565

[30] Foreign Application Priority Data Nov. 30, 1972 Japan 47-120057 Mar. 28, 1973 Japan 48-35398 [52] U.S. Cl. 72/234 [51] Int. Cl B2lb 1/24 [58] Field of Search 72/234, 226, 205, 366, 72/249 [56] References Cited UNITED STATES PATENTS 1,810,167 6/1931 George 72/234 X No.| No.2 No.3

2,139,872 12/1938 Worthington ..72/203 Primary Exam iner- Milton S. Mehr Attorney, Agent, or Firm-Torch, McGeady and Stanger [57] ABSTRACT A process and a rolling mill for rolling thin plate by means of a tandem rolling mill characterized in that the diameter of either of the upper or the lower working rolls in optional rolling stands situated in the rear step of the tandem rolling mill for thin plate consisting of a plurality of rolling stands is chosen smaller than that of other corresponding working rolls and that the rolling work is carried out by driving only the working rolls with larger diameter.

9 Claims, 8 Drawing Figures No.4 No.5 No.6

PATENTED 21 1915 SHEET 1 OF 4 FIG! TI MAX TIMAX Tl MAX No.2 No.3 No.4 No.5 No.6 No.7

ROLLING MILL STANDS FIGZ ROLLING MILL STANDS PATENTEU JAN 2 1 I975 SHEET 2 [IF 4 FIG.3

FIG.4

PATENTEU 3,861. 188

SHEET 30F 4 ROLLING PROCESS AND ROLLING STAND OF STEEL PLATE SUMMARY or THE INVENTION The present invention relates to a rolling process to reduce the rolling load and thus enable the rolling of a thinner plate by means of a tandem rolling mill consisting of a plurality of rolling stands, and the rolling stand to carry out the process.

Further the present invention relates to a rolling process to roll checkered plates such as for flooring which present on the one surface checker patterns consisting of discontinuous unevenness or lengthwise checkered plates which present on the one surface lengthwise checker patterns consisting of continuous unevenness.

Until now the tandem rolling mills for thin plates have been developed in such a manner that the production speed has been increased continually. Accordingly the capacity of the motor for driving a rolling mill has increased continually while the diameter of rolling rolls has also increased. The above can be said to be reasonable measures in order to meet the increase of the driving moment, to maintain the strength of roll necks as well as of components such as spindles, pinion gears andd so on composing the driving system.

However the increase of the diameter of the rolls of a rolling mill means the decrease of the ratio of the plate thickness to the roll diameter. In other words, according to the theory of the rolling technique the average rolling pressure is greatly influenced by the ratio of the plate thickness to the roll diameter so that the average rolling pressure increases as the ratio decreases. Further the contact length under the same rolling reduction is proportional to the square root of the roll diameter so that the rolling load is all the more increased. This will result in the increase of the power to be used for the same rolling, of the pressure working upon the rolls, of the torque and so on in such a manner that the smaller the thickness of the plates to be rolled, the more difficult the rolling work becomes. Namely according to the theory of the rolling technique it is desirable to reduce the diameter of the working rolls as much as possible within the allowance of the design. However, the increase of the rolling speed and the decrease of the roll diameters means the increase of the rotational speed of the rolls, which as a result means the significant increase of rotational speed of the driving system of rolls. This further means the increase of the rotational speed of motors, which has many problems in the practical design bringing about an increase of the installation cost. Further in case of a thicker plate, the decrease of the roll diameter is not as important.

Further, in order to roll the checkered plates, a roll presenting grooves corresponding to the patterns of the checkered plates as final products has been used as one of the final working rolls of the finishing rolling mill consisting of a plurality of the rolling stands such as for example hot strip mills and a flat roll as the other one. In the present case the formation of the checker pattern has to be carried out in only one rolling stand, which means that a comparatively large rolling reduction is necessary to from unevenness with sufficient height i.e., sufficiently projecting parts. Therefore the grooved roll is exposed to a large rolling load so that the edges of the grooves are often broken or crushed. In case further steel plates such as those for flooring presenting discontinuous check patterns not parallel to the rolling direction are rolled, the rolling work is carried out in a discontinuous state in such a manner that the roll starts to vibrate, giving off a loud noise. Therefore, the correspondingly large strength works between the check patterns to be formed and the grooves of the roll so that check patterns are often inclined along the rolling direction or often becomes narrow. This causes inferior products.

The purpose of the present invention is to solve the above mentioned disadvantages of the conventional technics.

BRIEF DESCRIPTION OF THE DRAWING Below the present invention will be explained in detail according to the attached drawings.

FIG. 1 shows a diagram showing the maximum and the minimum nominal driving torque of the seven conventional hot strip mill stands (tandem rolling mill for thin plates);

FIG. 2 shows a diagram showing the speed cones of the seven rolling stands;

FIG. 3 shows a diagram showing the actual distances between rolls of the tandem rolling mill consisting of six rolling stands;

FIGS. 4, 5, 6 and 7 show an embodiment of the present invention whereby;

FIG. 4 shows a side view of the whole of the embodiment of a tandem rolling stand;

FIG. 5 shows a front view of the fourth rolling stand of FIG. 4; and

FIG. 6 shows an enlarged side view of the important part.

FIG. 7 shows another embodiment of the present invention, and FIG. 8 shows a diagram for the explanation of the effect of the above embodiment.

FIG. I shows a diagram showing the maximum and the minimum nominal driving torques of the finishing rolling stand of the hot strip mill, in the present example of the tandem rolling mill consisting of seven rolling stands. The maximum torque naturally takes place in the first rolling stand and the torque in the third rolling stand is already half of that of the first rolling stand. Further the torque in the fifth rolling stand is nearly one fifth as low. The same thing can at the same time be said of the minimum torques of the high rotation speed side of the rolling stand.

Namely, T in the drawing shows the driving torques of the rolling stands, whereby T, max. shows the maximum torque of the first rolling stand while T min. shows the minimum torque of the first rolling stand. Along the ordinate of the diagram in FIG. 1 are shown the ratios of. the maximum and the minimum torque of other rolling stands to the maximum torqueof the first rolling stand, whereby the magnitude is shown in the line a. T max. shows the maximum torque of the second rolling stand, while T min. shows the minimum torque of the second rolling stand. The torques of the third to seventh rolling stand are indicated in the same way.

FIG. 2 shows a diagram showing the speed cones of the seven rolling stands, whereby it is shown that the increase of the speed in the rolling stands in the rear step is remarkable. The mark X in the drawing showsthe maximum rotation speed of the motor, whereby a speed step up means is built in the seventh rolling stand to increase the roll speed. The economy of adoption of the high power motor lies in this respect so that the decrease of the roll diameter presents many disadvantages.

FIG. 3 shows the actual value of the distance t between the upper and the lower working rolls in case thin plates with 1.2 mm thickness and 1.6 mm thickness are rolled in a continuous hot rolling. The present case relates to an example of a tandem rolling mill consisting of six rolling stands. The roll intervals in the diagram shows that the upper and the lower rolls in the third and the following rolling stands are nearly in the contacting states, whereby in the fourth rolling stand the upper and the lower rolls are completely in contact with each other in such a manner that a remarkable load already exists between the rolls before the plate material is put therebetwee. This means that only by means of the one working roll the other working roll can be driven in rotation. Namely it is possible to drive reinforcing rolls or other working rolls into rotation only by driving one working roll, whereby it is not always necessary to take the roll balance in a case like the present.

On the other hand, taking into consideration that the torque in the third rolling stand of the tandem rolling mill consisting of seven rolling stands is lower than half of the torque in the first rolling stand, the rolling stand is strong enough even if it is driven by only one roll.

The above mentioned fact can commonly be said of the tandem rolling mill for thin plate consisting ofa plurality of rolling stands.

The present invention is based upon the above mentioned consideration, and relates to (1) a process to roll thin plates by means of a tandem rolling stand characterized in that the diameter of either of the upper or the lower working rolls in optional rolling stands situated in the rear steps of the tandem rolling mill for thin plates consisting of a plurality of rolling stands is chosen smaller than that of other corresponding working rolls and that the rolling work is carried out by driving only the working rolls with larger diameter, (2) a tandem rolling mill for thin plates comprising a plurality of rolling stands characterized in that the diameter either of the upper or the lower working roll at least in one rolling stand situated in the rear step of the tandem rolling mill is chosen smaller than that of the other corresponding working roll and that only the corresponding working roll with larger diameter is driven, and (3) a method for rolling checkered plates in which the above roll of smaller diameter is used as a grooved roll.

FIGS. 4 to 7 show an embodiment of the rolling stand according to the present invention, in which:

1 shows the upper working roll, 2 the lower working roll, 3 the reinforcing roll, 4 the spindle, 5 the pinion gear, and 6 a driving motor. The diameter of the upper working rolls 1' of the fourth and the fifth rolling stand in the six rolling stands shown in FIG. 4 are chosen smaller than that of the other corresponding working rolls, and as is shown in FIG. 5 only the lower working rolls are to be driven. In a rolling stand like this, as is shown in FIG. 6 a large rolling reduction can be obtained by the upper working roll 1' with small diameter. Further, the rolling power hereby is smaller because of the smaller diameter of the roll. By means of the lower working roll, as large a rolling reduction as has been obtained by means of a conventional one can be obtained, so that as a whole alarge rolling reduction can be obtained. Because in this case a rolling stand in the rear step is concerned, there should be no problem in the mechanical strength as is shown in FIG. 1, while as large a rolling speed as ever can be obtained.

FIG. 7 shows another embodiment of the present invention and more precisely a finishing rolling stand of a hot strip rolling mill consisting of six rolling stands used for rolling a checkered plate. Namely the fourth rolling stand is equipped with a working roll with smaller diameter than that of the rolls of other rolling stands, whereby it is characterized that the working roll with smaller diameter is constructed as a roll with grooves corresponding to the patterns of the checkered plate. The grooved roll 1" with small diameter is not directly driven into rotation but by means of the friction with the other flat working roll set corresponding to the grooved roll 1" with small diameter.

In case of the hot strip mill, the checkered plate is, generally speaking, in either of the rolling stands in the latter half of the finishing rolling stands, whereby either the upper or the lower roll is adopted as a grooved roll. In case the rolling stand in question is not the one in the last step in the finishing rolling stand, the roll interval of the rolling stands after the one equipped with the grooved roll is chosen so large as to allow the plate to pass through freely, whereby the same thing can be said of the rolling stand according to the present invention.

Thus one of the features of the present invention relates to the last rolling work of the product, and lies in that as a working roll a roll, with grooves corresponding to the pattern of the checkered plates to give the check pattern to the plates is adopted, and the diameter of the working roll is chosen smaller than that of the other working roll.

According to the present invention a smooth operation can be obtained, by making the roll with small diameter freely rotatable, and not driven directly. Nevertheless in case for example the thickness of the plates to be rolled is large, the upper and the lower rolls are brought out of contact with each other after the plate has passed through and do not rotate until the next plate reaches, so that there is a danger that some irregularities should take place when the next plate reaches. In such a case, in order to avoid the irregularities the roll balance is cut off immediately after the plate has passed through and the upper and the lower rolls are allowed to come into contact with each other by means of their own weight, to convey the driving power from the working roll, and the roll balance is inserted immediately before the arrival of the material plate in such a manner that the interval between the upper and the lower rolls is properly adjusted. By operating as mentioned above, the rolling work can be carried out as satisfactorily as in the case the upper and the lower rolls are both driven.

Further the finishing rolling stand of the ordinary hot strip mill is composed of quadruple rolls with a back-up roll 3, whereby the present invention presents no restriction in the composition of the rolls in the rolling stand and further the cutting-off and the insertion of the roll balance can be carried out so that the present invention can be applied to any kind of rolling stand without difficulty.

As mentioned above for rolling the ordinary and checkered plates the diameter of one working roll is chosen smaller than that of the other working roll so that a large rolling reduction can be obtained at the side of the roll with smaller diameter, thus in case the smaller diameter roll is a grooved roll, the sufficient height of the uneven pattern namely of the check pattern can be obtained, while in comparison with the rolling reduction the rolling load is small so that the power working upon the grooves of the roll is reduced, bringing about many advantages such as the decrease of the damage of the grooves.

Below the effect of the present invention will be explained according to the examples.

EXAMPLE 1 The diameter of the upper working roll of the fifth rolling stand in the tandem rolling stand for the 56" inch hot strip mill consisting of six rolling stands is converted into the one with smaller diameter not to be driven directly. The sizes of the rolls of the then rolling stand are as follows:

Working roll: 650 mm (1) (standard diameter) Reinforcing roll: 1245 mm Hereby the comparison is made between the two cases, i.e., the case A when only the diameter of the upper working roll of the fifth rolling stand is chosen as a smaller diameter of 360 mm and the case B when the diameter of both the upper and the lower working rolls is chosen 650 mm. The test piece was a slab (185 mm thick X 930 mm wide, 8.1 ton) of low carbon rimmed steel, ordinary very soft steel. The temperature at the take-in side of the tandem rolling stand was indicated as high as nearly 1,100C, the rolling condition of the upper and the lower working rolls of the first to the fourth were rolling stand adjusted same, only the upper working roll of the fifth rolling stand was exchanged for the roll with the aforementioned diameter, whereby the rolling load of the fifth rolling stand was adjusted by means of the reduction screw in such a manner that the rolling load of the two kinds of rolls indicated by the load cell became the same. The obtained data for rolling is shown in Table 1.

rolling stand of the tandem rolling mill consisting of seven rolling'stands as shown in FIG. 7. Namely the grooved roll was adopted as the upper working roll, whose diameter was a standard diameter of 360 mm. On the other hand the corresponding lower working roll was a flat roll, whose diameter was 640 mm as usual. The patterns of the grooved roll was checks parallel to the rolling direction, whereby the height (the depth) of the groove was 2.2 mm, the width of the crown 4 mm, the pitch 10 mm and the groove itself was formed trapezoidal. Only the lower flat roll was driven, whilethe upper grooved roll with small diameter was left freely rotatable, not to be driven directly. Further the roll intervals of the rolling stands after the fifth one were chosen sufficient enough to allow the plate to pass through freely. The diameters of the working roll were 597 665 mm, while the length of the cylinder was 1422 mm. Further the diameters of the back-up rolls were 1150 1245 mm, while the length of the cylinder was 1372 mm.

By such a rolling mill as mentioned above,the test piece of a slab of very soft rimmed steel (C: 0.08 percent, Mn: 0.36 percent, 16.5 mm thick x 1260 mm wide) was rolled, whereby the temperature at the taker-in side of the finishing rolling stand was 11 10C. By properly operating the rolling work of the finishing rolling stand several checkered steel plate with thickness (the thickness at deep part) 1.2 4.5 mm were obtained.

For the purpose of comparison rolling works were also carried out using a grooved roll with the same diameter as that of the lower flat roll. The result is shown The above mentioned result has proved that by converting the diameter of the upper working roll of the fifth rolling stand from 650 mm to 360 mmdr and adjusting the rolling load working on the fifth rolling stand the rolling reduction of 0.62 mm i.e., 1.80 mm down to 1.18 mm can be obtained according to the present invention while in the example for comparison the rolling reduction of only 0.40 mm i.e., 1.79 mm down to 1.39 mm can be obtained, whereby a remarkable difference between both rolling reduction can be observed. As a whole this means that the finished thickness under the same rolling load is reduced from 1.2 mm down to 1.0 mm, which further means that the very thin plate can be rolled with ease.

EXAMPLE 2 lnthe finishing rolling stand of the 1422 mm hot strip mill the present invention was applied to the fourth Sectional Reduction Ratio Section at taker-in side Average section of checkered plate Section at taker-in side Thickness Reduction Ratio Thickness at thickness at deep part taker-in side of checkered plate Thickness at taker-in side ratio while the part B shows that the section is not reduced due to the formation of checks, namely the ratio of the formed checks, while the same thing can be said of the part A and the part B of the curve (II), whereby it is confirmed that the formation of checks is remarkably superior in its ratio in case of the curve (II) relating to an embodiment of the present invention.

What is claimed is:

l. A process for rolling a thin steel plate by means of a tandem rolling mill having a plurality of rolling stands, each stand having an upper working roll and a lower working roll comprising, reducing the plate through a plurality of front stands having equaldiameter working rolls, reducing the plate through at least one rear stand having working rolls of different diameters, rotating the working rolls of the first stand of said plurality so as to have the largest torque, and rotating the largest of said working rolls of said at least one stand following said first stand so that the torque of said at least one stand is less than half of the torque of said first stand.

2. The process according to claim 1, wherein said step of reducing the plate through at least one stand comprises reducing the plate through two stands having an upper working roll of smaller diameter than the lower working roll.

3. The process according to claim 2, wherein said step of reducing the plate through at least onestand comprises forming grooves on one of said working rolls of said at least one stand corresponding to a pattern for a checkered plate.

4. A tandem rolling mill for rolling thin steel plates comprising, a plurality of front rolling stands having an upper working roll and a lower working roll of equal diameter, at least one rear rolling stand having an upper working roll and a lower working roll, one of said working rolls having a a smaller diameter than the other, means for driving only the large diameter working roll, the first rolling stand of said plurality having working rolls driven so as to have the largest torque of all the stands, and said means for driving said larger diameter working roll driving said roll at less than half the torque of said first rolling stand.

5. The tandem rolling mill according to claim 4, wherein one of said working rolls of said at least one rear rolling stand comprises a grooved roll.

6. The tandem rolling mill according to claim 5, wherein said smaller working roll comprises a grooved roll.

7. The tandem rolling mill according to claim 4, comprising two rear rolling stands.

8. The tandem rolling mill according to claim 7, comprising six rolling stands, said plurality of front rolling stands comprises the first three stands, said two rear rolling stands comprises the fourth and fifth rolling stands, and the sixth rolling stand comprises a rolling stand similar to that of the first rolling stand.

9. The tandem rolling mill according to claim 4, wherein the torque of each stand is progressively lower as the plate travels from the first stand to subsequent stands.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3361188 Dated January 21, 1975 Inventor(s) NORIMASA KAMII et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading of the patent, change:

"[75] Inventors: Norimasa Kamit; Ryozi Terakado,

both of Hokkaido, Japan" "[75] Inventors: Norimasa Kamii; Ryozi Terakado both of Hokkaido, Japan" Signed and sealed this 19th day of March 1975.

(SEAL) Atte t:

C. E-LARSHALL DANN RUTH C. E'IASON Commissioner of Patents Attesting Officer and Trademarks FORM PO-1050 (10-69) USCOMM-DC 60376-P69 1r u.s. sovlnuuiu'r PRINTING omc: nu o-au-Ju.

Claims

1. A process for rolling a thin steel plate by means of a tandem rolling mill having a plurality of rolling stands, each stand having an upper working roll and a lower working roll comprising, reducing the plate through a plurality of front stands having equal-diameter working rolls, reducing the plate through at least one rear stand having working rolls of different diameters, rotating the working rolls of the first stand of said plurality so as to have the largest torque, and rotating the largest of said working rolls of said at least one stand following said first stand so that the torque of said at least one stand is less than half of the torque of said first stand.

3. The process according to claim 2, wherein said step of reducing the plate through at least one stand comprises forming grooves on one of said working rolls of said at least one stand corresponding to a pattern for a checkered plate.