Metal deforming – By use of roller or roller-like tool-element – With carrier for roller-couple or tool-couple
Reexamination Certificate
2000-06-23
2002-03-12
Tolan, Ed (Department: 3725)
Metal deforming
By use of roller or roller-like tool-element
With carrier for roller-couple or tool-couple
C072S010100, C072S010400, C072S014400, C072S245000
Reexamination Certificate
active
06354128
ABSTRACT:
FIELD OF THE INVENTION
This invention concerns a method to eliminate the play between chocks and the relative support blocks in four-high rolling stands, and the relative device, as set forth in the respective main claims.
The invention is employed to minimize and even eliminate the value of the play and gaps between the chocks and the uprights of the housings, or between the chocks and the supporting bearing elements, or gibs, during the cross-over movement of the rolls (pair crossing).
BACKGROUND OF THE INVENTION
The state of the art includes the rolling technique of pair crossing, wherein the working rolls, and possibly the relative back-up rolls, are crossed over so as to obtain a wide field of adjustment of the crown of the rolls, a better control of the profile of the rolled stock during the processing step and therefore a better quality final product.
During the crossover of the rolls, and because of it, a moment of flection is generated on the chocks of the back-up rolls; this moment of flection is determined by the misalignment of the vertical thrust forces which the rolled stock impresses on the rolls with respect to the load exerted by the hydraulic pressure means acting on the chocks of the said back-up rolls.
In other words, according to the angle of crossing of the rolls, the position of the horizontal resultant of the force of the hydraulic pressure means and the force transmitted by the rolled stock to the relative working roll, and from this to the back-up roll, may even be positioned outside the supporting planes between the chocks of the back-up rolls and the relative support blocks-gibs.
When this happens, the chock is no longer correctly supported and a flection torque is generated.
This flection torque generates an increase, on one side, in the forces which are exerted between the support element or gib and the relative chock.
This fact, with the same coefficient of friction between the sliding elements included between the chock and the supporting element, leads to an increase in the forces of friction.
Moreover, this turnover component generated by the flection torque tends to make the chock rotate on the vertical plane with respect to its longitudinal axis and, should there be an excessive gap, or a gap which has not been pre-set, between the chock and the housing, or between the chock and the support block, it can cause the edges of the chock itself to tip up against the relative bearing element.
This unplanned space or play between the chock and the bearing element can be caused by various factors, including the absence of compensation means or an imperfect functioning of such compensation means as are present.
This space or play in any case must always be guaranteed during the design step, even if only at a minimum value, due to the contraction of the space of the housing stressed by the rolling force.
This contraction of the space is due to the deformation under load of the structure of the housing which leads to the deformation of the uprights which bend, to values in the order of one or two millimetres, and curve inwards at the centre because of the extremely high rolling loads, causing zones of maximum proximity of the chock and the relative gib.
This play must therefore be planned in such a way that, when the rolling forces which deform the housing of the stand are at their highest values, there is no jamming of the chocks and the relative gibs. The greater the horizontal contraction of the uprights of the housing is, the greater the play must be.
An incorrect value of the play can lead to a risk of blows and impacts during the crossover displacement of the chock and relative gib or bearing block.
All this leads to incorrect functioning, risks of jams and damage, inaccurate control of the thickness and profile of the rolled stock, and therefore the final products are not of optimum quality and the sliding surfaces between the chocks and the gibs are subject to premature wear.
Moreover, the very presence of play between the chocks of the working rolls and the relative support blocks can lead to an inaccurate control of the angle of crossing of the rolls.
This leads to errors and imperfections in the technological control of the rolling process, with negative consequences on the adjustment of the profile and the thickness of the strip.
Furthermore, the presence of unplanned play can cause vibrations to start, caused by the horizontal movement of the working rolls in the direction of rolling.
The interaction of possible horizontal vibrations of the working rolls with the rolling process itself can generate self-excited linear vibrations, caused by the fact that the coefficient of rolling friction is a function of the relative speed of the rolls and the material being rolled.
Document JP-A-05-293518 describes a method to adjust the crossing angle between the working rolls in a four-high rolling stand according to the rolling load.
It provides to continuously monitor the value of the rolling load by means of a measuring device provided for this purpose, and to send the relative signal to a processor which adjusts in feedback the drive of the hydraulic jacks which act on the chocks of the working rolls.
This document does not teach to minimize the play between the chocks and the relative support blocks as the rolling load varies.
Documents JP-A-56-074310, JP-A-56-074311 and JP-A-56-074312 refer to devices to control on-line the thickness of the strip based on the control of the deformation of the stand under working conditions and with a crossing angle which is not zero.
In practice, these devices provide to calculate the actual deformation of the stand by continuously measuring the actual rolling force and the crossing angle, and taking into account the working parameters such as width and thickness of the strip.
According to these calculations, the pressure means on the stand are consequently adjusted so as to maintain the thickness of the strip at the values established by the working specifications.
The evolution described in JP'311 provides to control the actual position of the chocks, rather than the crossing angle, in such a way as to compensate any difference between the center of the crossing angle of the rolls and the vertical median plane of the stand.
These documents, like JP'518, do not provide to compensate the play between the chock and support blocks according to the rolling load.
Document JP-A-08-294713 shows a method to annul the play between the chocks of the working rolls and the back-up rolls and the relative support blocks in a four-high rolling stand, wherein hydraulic compensation cylinders are provided, on the inlet side of the stand, associated with position transducers.
The position transducers monitor the actual position of the chocks and supply this value to the relative hydraulic cylinders, which are thus able to take the chocks, at the outlet side of the stand, into contact with the relative support blocks.
This solution, although it is efficacious in itself, does not take into account the variation of the rolling load, and is simply directed to compensate wear on the sliding parts, which increases with time.
Document JP-A-59-087914 describes an embodiment which is substantially the same as the previous one.
The present applicants have designed, tested and embodied this invention to overcome this serious disadvantage which businessmen in the field have long complained of, and also to obtain further advantages.
SUMMARY OF THE INVENTION
The invention is set forth and characterized in the respective main claims, while the dependent claims describe other characteristics of the main embodiment.
The purpose of the invention is to provide a play compensation method, and a device connected thereto, suitable to obviate those problems which derive from the partial rotation of the chock of the back-up rolls with respect to the housing, or the support element, due to the turnover component caused by the eccentricity between the rolling thrust and the thrust of the hydraulic pressure system.
In other words, the invention
Dal Pan Giacinto
Donini Estore
Danieli & C. Officine Meccaniche SpA
Stevens Davis Miller & Mosher LLP
Tolan Ed
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