Abrading – Precision device or process - or with condition responsive... – Computer controlled
Reexamination Certificate
1999-01-26
2001-10-23
Rose, Robert A. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
Computer controlled
Reexamination Certificate
active
06306007
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a rolling mill equipped with an on-line roll grinding system, and more particularly to an on-line roll grinding system for effectively grinding mill rolls on-line without undergoing influences of vibration of work rolls.
Generally, when slabs are rolled by work rolls of a strip rolling mill, there occurs a periphery difference between the rolling zone and the unrolling zone because only the former is abraded or worn away. This imposes such restrictions upon the rolling operation as necessity of rolling slabs in order of wide ones to narrow ones. To solve that problem, there have been proposed various techniques and control methods in relation to on-line roll grinders.
For example, “Development of On-Line Roll Grinders”, Mitsubishi Giho, Vol. 25, No. 4, 1988, discloses a technique that a plurality of cup grinding stones are arranged along one work roll and mounted to a one-piece frame, the frame being always moved in its entirety over a certain range, and the cup grinding stones are not positively driven to rotate but passively driven with the aid of torque of the work roll, thereby grinding the entire surface of the work roll (hereinafter referred to as first prior art).
Also, JP, U, 58-28705 discloses a technique that one roll grinding unit is disposed for one work roll, contact rolls serving as position sensors are held in contact with neck portions at both ends of the work roll on the side thereof opposite to the roll grinding unit, the position sensors detecting an offset of the work roll, and a shifting device is controlled to move a grinding wheel following the detected offset (hereinafter referred to as second prior art).
Further, “On-Line Constant Pressure Grinding for Work Rolls”, Proceedings of 1992 Spring Lecture Meeting of Precision Engineering Society of Japan, reports an experimental result of forming an abrasive layer of a cup grinding stone using abrasives of cubic boron nitride (CBN), arranging a spindle of the grinding stone perpendicularly to the axis of a work roll, and grinding the work roll (hereinafter referred to as third prior art).
In addition, JP, U, 58-28706 and JP, U, 62-95867 disclose a technique that a cup grinding stone arranged substantially perpendicular to a work roll is mounted to a spindle slidably in its axial direction, and the grinding stone is axially supported at its backside by an elastic body directly or via a boss, thereby absorbing vibration of the work roll (hereinafter referred to as fourth prior art).
Meanwhile, in strip rolling machines, it has been conventionally proposed to measure the profile of a work roll and control the crown and shape of a strip by utilizing the measured profile. As a technique for measuring the profile of the work roll, an on-line roll profile meter has been developed which employs a ultrasonic profile meter. The system configuration of this profile meter is described in “Development of On-Line Roll Grinding System with Profile Meter”, Mitsubishi Giho, Vol. 29, No. 1, 1992. In this system, a column of water is produced between a probe with a ultrasonic profile meter built therein and a work roll, and the spacing from the probe to the work roll is determined based on the time required for pulsatory ultrasonic waves emitted from the probe to reciprocate between the probe and the surface of the work roll (hereinafter referred to as fifth prior art).
SUMMARY OF THE INVENTION
Work rolls of a rolling mill are each held by bearings assembled in metal chocks and rotated at a high speed. The metal chocks each have gaps in its inner and outer circumferences for facilitating replacement of the work roll and the bearing. During rotation, therefore, the work roll is rotated while moving back and forth in the gaps. In addition, since a cylindrical portion of the work roll undergoes an offset with respect to the bearings, the work roll is vertically moved by a screwdown device during strip rolling. As a result of those movements combined with each other, the work roll is rotated while vibrating at all times.
Generally, when grinding cylindrical works, the work to be ground is supported by a tail stock rotating with high precision to carry out the grinding under a condition that vibration of the work is suppressed to be as small as practicable. In an attempt to grind the work roll while rolling a strip in the rolling mill, however, it is impossible to carry out the grinding under a condition of very small vibration like works in the above ordinary case. During the rolling, the work roll is rotated while vibrating usually with an amplitude of 20 &mgr;m to 60 &mgr;m and an acceleration of
1
G to
2
G. An on-line roll grinding system must precisely grind the work roll under such a condition.
With the above first to third prior arts, when they are applied to the grinding of such a vibrating work roll, there produce irregularities on the surface of the work roll due to chattering marks. Also, the grinding stone or wheel is remarkably worn away with the impact force caused by chattering, and its service life is so shortened as to require more frequent replacement. Further, it is difficult to control the contact force in the case of grinding the work roll into a predetermined profile.
The above fourth prior art is designed to absorb the vibration of the work roll by the elastic body. With this prior art, however, since the entire grinding stone including a stone base is supported by the elastic body and moved back and forth, there accompanies a problem that the movable mass of the grinding stone, i.e., the weight of a portion which is forced to move following the vibration, is great. Even in the case of using, as the abrasive layer of the grinding stone, abrasives of cubic boron nitride (CBN) which has a high grinding ratio, the movable mass of the grinding stone supported by the elastic body and moving back and forth is at least more than 5 Kg, including the stone itself of which diameter is assumed to be 250 mm, slide bearings and sealing parts. Supposing that an allowable value of change in the contact force between the work roll and the grinding stone is 4 Kgf and the amplitude of vibration of the work roll is 30 &mgr;m, the spring constant of the elastic body must be set to 130 Kgf/mm. Under the above conditions, the natural frequency of the movable portion including the elastic body is calculated to be 80 c/s. The movable portion including the elastic body, which has such a low natural frequency, is caused to resonate with the vibration of the work roll, thereby producing chattering marks on the roll surface and accelerating abrasion of the grinding stone. If the stone size is reduced to make the movable mass smaller, the grinding ability would be lowered to a large extent.
The cup grinding stone is slidable in the axial direction of the spindle and supported at its backside by the elastic body. During the roll grinding, however, a coolant, grinding dust and the like are scattered around the grinding stone, and these foreign matters may enter clearances between the grinding stone and the spindle to impede smooth movement of the grinding stone. It is therefore difficult for the elastic body to stably develop its function for a long period of time.
The above first and second prior arts also have the following problem. The unrolling zone of the work roll is not subjected to abrasion by the strip and hence should be ground to a larger extent than the rolling zone. With the above first embodiment, however, because the circumferential speed of the cup grinding stone is limited by the rotational speed of the work roll, the grinding rate can be controlled only by changing the contact force in the case of grinding the unrolling zone to a larger extent. This imposes a limitation upon the grinding rate, making it difficult to keep a constant roll profile for a long period of time.
With the above second embodiment, since the spindle is arranged perpendicularly to the work roll, the abrasive layer of the grinding wheel contacts the work roll at two right and left points
Imagawa Yasuharu
Kondoh Shigetoshi
Mori Shigeru
Nishino Tadashi
Shiraiwa Hiroyuki
Crowell & Moring LLP
Hitachi , Ltd.
Rose Robert A.
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