Metal deforming – With use of control means energized in response to activator... – Metal deforming by use of roller or roller-like tool element
Reexamination Certificate
1997-10-22
2001-08-07
Tolan, Ed (Department: 3725)
Metal deforming
With use of control means energized in response to activator...
Metal deforming by use of roller or roller-like tool element
C072S009100, C072S011400, C072S205000
Reexamination Certificate
active
06269668
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a tandem cold rolling method and a tandem cold rolling mill thereof, the number of cold rolling stands of which is not less than 4, by which the occurrence of heat scratches is prevented and the productivity is enhanced so that the production cost can be decreased.
BACKGROUND ART
When the work roll speed is increased or the ratio of reduction is increased in a tandem cold rolling mill, heat scratches are caused on the surface of a cold-rolled sheet. A heat scratch is defined as a defect of seizing caused by metallic contact of a work roll with a sheet to be rolled when the temperature of an interface between the work roll and the sheet to be rolled is raised in a rolling bite and an oil film is broken.
When heat scratches occur on the surface of a product, the product becomes defective, and the product yield is lowered. Further, the work rolls of a cold rolling stand in which the heat scratches occur must be changed. Accordingly, the productivity of the cold rolling mill is remarkably deteriorated, which is a serious problem.
Accordingly, concerning the prevention of heat scratches, the following methods have been disclosed. For example, Japanese Unexamined Patent Publication No. 5-98283 discloses a method in which a rolling lubricant having a high anti-seizing property is used. Japanese Unexamined Patent Publication No. 56-111505 discloses a method in which a quantity of coolant is controlled so as to lower the temperatures of cold-rolled sheets and work rolls. Japanese Unexamined Patent Publication No. 6-63624 discloses a method in which the work roll speed is lowered. All of the methods relate to a technique for preventing an increase in the temperature of the interface between the work roll and the sheet to be rolled in the work roll bite and also relates to a technique for preventing a break in an oil film even when the temperature of the interface in the work roll bite is raised. However, even if the above methods are adopted the following problems may be encountered. When a rolling lubricant, the anti-seizing property of which is high, is used, there is a possibility that the production cost is raised. When the temperatures of cold-rolled sheets and work rolls are controlled by controlling a quantity of coolant, it is possible to provide an effect, however, the responding property is not so high, and further the productivity of cold rolling is deteriorated since the work roll speed is decreased.
Japanese Unexamined Patent Publication No. 60-49802 discloses a method to change a reduction schedule and tension, by which the occurrence of heat scratches can be prevented without deteriorating the productivity and increasing the production cost. However, an amount of control to be conducted by the above method is limited by the restriction placed on the apparatus of the cold rolling mill.
Fluctuation in the width of a cold-rolled sheet in the process of cold rolling is smaller than that of a hot-rolled sheet in the process of hot rolling. Therefore, conventionally, sheet width control is seldom conducted in the process of cold rolling unlike the process of hot rolling in which width gauges are arranged on the entry and the delivery side of the hot rolling mill and tension is controlled in accordance with the results of measurement of the width of a sheet measured by the width gauges.
CONSTRUCTION OF THE INVENTION
As described above, the effect provided by the conventional tandem cold rolling method is limited. The reasons are described as follows. According to the method by which the occurrence of scratches is prevented without deteriorating the productivity and raising the production cost, there is a possibility that the accuracy of sheet thickness is temporarily deteriorated in the case of changing the reduction schedule. According to the method by which the tension given to the sheet is changed, since the rolling pressure is decreased and the generation of heat caused by friction is decreased by increasing the tension, it is possible to prevent the occurrence of heat scratches. However, when the tension is increased in order to enhance the effect of prevention of heat scratches, the sheet to be rolled tends to break. According to the tandem cold rolling mill of the prior art, heat scratches tend to occur in the cold rolling stands in the latter stage, and further it is impossible to increase a tension between the rolling stands for the reasons of the restriction placed on the apparatus. Accordingly, in a rolling stand in the latter stage, an intensity of tension given to the sheet on the entry side tends to be higher than an intensity of tension on the delivery side. Therefore, slipping between the sheet to be rolled and the work roll, and chattering, tend to occur in the rolling stand in the latter stage, which causes another problem. According to a method by which tension is controlled in accordance with the sheet temperature that has been detected on the delivery side of the rolling stand, control is conducted when the temperature has risen to a value at which heat scratches occur. For this reason, there is a possibility that heat scratches occur temporarily.
Further, when the intensity of tension given to the sheet is increased, the fluctuation of sheet width is increased, which deteriorates the accuracy of sheet width. Therefore, according to the conventional method, the prevention of heat scratches is incompatible with the enhancement of economy and productivity.
The present invention has been achieved to solve the above problems of the conventional method. The summary of the present invention will be described as follows:
(1) A tandem cold rolling method of cold-rolling a sheet by a tandem cold rolling mill, the number of rolling stands of which is not less than 4, comprising the step of conducting rolling at least in the final rolling stand while a rolling tension, the intensity of which is not less than 30% of the deformation resistance of the sheet to be rolled, is given to the sheet.
(2) A tandem cold rolling method of cold-rolling a sheet by a tandem cold rolling mill, the number of rolling stands of which is not less than 4, having a coiler on the delivery side, or a coiler and a bridle roller, or a coiler and a pinch roller, comprising the step of conducting rolling at least in the final rolling stand while a rolling tension, the intensity of which is not less than 30% of the deformation resistance of the sheet to be rolled, is given to the sheet, while an average thickness ({overscore (h)}) of a cold-rolled sheet to be produced by the tandem cold rolling mill, an output of the main motor of the coiler arranged on the delivery side, and/or an output of the main motor of the bridle roller, and/or an output of the main motor of the pinch roller, and an output of the main motor of the final rolling stand of the tandem cold rolling mill, are adjusted.
(3) A tandem cold rolling mill comprising: cold rolling stands, the number of which is not less than 4; and a coiler, or a coiler and a bridle roller, or a coiler and a pinch roller arranged on the delivery side of the tandem cold rolling mill, wherein the inequality of J
C
≧(0.375{overscore (h)}+0.275)J
M
is satisfied, wherein the average thickness of a product to be produced by the tandem cold rolling mill is {overscore (h)}, and an output of the main motor of one coiler arranged on the delivery side of the tandem cold rolling mill, or a sum of an output of the main motor of one coiler on the delivery side and an output of the main motor of the bridle roller on the delivery side, or a sum of an output of the main motor of one coiler on the delivery side and an output of the main motor of the pinch roller, is J
C
, and an output of the main motor of the final rolling stand of the tandem cold rolling mill is J
M
.
(4) A rolling method of rolling a cold-rolled sheet by a tandem cold rolling mill, in the rolling stand of which heat scratches tend to occur, comprising the steps of: detecting or calculating a sheet temperature on the delivery side of the rolling
Hamauzu Shyuichi
Ishii Atsushi
Ogawa Shigeru
Shiraishi Toshiyuki
Kenyon & Kenyon
Nippon Steel Corporation
Tolan Ed
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