Bearing for rolling stands with crossing rolls

Details Bearing for rolling stands with crossing rolls Bearing for rolling stands with crossing rolls

2000-12-12

2003-07-15

Hannon, Thomas R. (Department: 3682)

Bearings

Rotary bearing

Antifriction bearing

C384S620000

Reexamination Certificate

active

06592265

ABSTRACT:

The present invention belongs to the field of rolling of flat products, such as plates, slabs, strips and the like, carried out using crossing rolls.
As is known, this particular type of rolling is carried out with rolling mills wherein the various stands forming them are provided with a pair of opposed working rolls, between which the material to be rolled advances and which act respectively on the upper and on the lower face of the material.
The axes of rotation of the working rolls are not parallel as in conventional rolling mills built have an arrangement which, in plan view, has a “X” configuration which is precisely the origin of the naming “with crossing rolls” which distinguishes that type of rolling and the associated rolling mills.
The technical reasons underlying the special arrangement of the rolls just mentioned, have been widely explained in several scientific publications and patents concerning this subject; reference should therefore be made to those documents for further clarification while it will merely be added here that, internationally, the crosswise arrangement of the rolls is indicated by the adjective “crossing” which will also be used in the course of this description.
It should also be pointed out that, in view of the substantial forces occurring during the rolling process (of the order of 2×10
3
-4×10
3
tonnes), in order to prevent the working rolls from bending, it is known to stiffen them structurally by purposely using backup rolls.
Usually there are two backup rolls, respectively coupled to the working rolls in such a manner as to roll on their outer surfaces along a contact generatrix which is located on the side opposite to that acting on the material to be rolled; such a layout of the rolls is also known by the expression “pair crossing”.
It should however be specified that it is not necessary for the backup rolls to be in contact with the working rolls along a common generatrix; likewise, it should also be pointed out that examples of rolling mills are known where two or more backup rolls are associated with the working rolls of each stand. As can be appreciated there are thus numerous variants resulting from the different combinations which can be constructed on the basis of the teaching of rolling with crossing rolls; reference will be made to them hereinafter and in the appended claims, although for the sake of simplicity and clarity, consideration will be given mainly to the pair crossing rolling.
Within the framework of the search for novel technical solutions in order to obtain rolling mills having ever higher performances, substantial importance is currently attached to the adjustment under load of the angular position of the working rolls, that is to say, of the inclination of their axes with respect to the direction of the of advance of the material being worked or to a direction transverse thereto, either horizontal or vertical.
The adjustment takes place during rolling (i.e. when the rolls are under load) and is particularly suitable for continuous rolling mills, also known as endless rolling mills, the demand for which is currently growing.
An example of rolling stand so designed that the inclination of the rolls can be adjusted, is known from U.S. Pat. No. 4,453,393 of 12/06/1984 in the name of Mitsubishi.
This document discloses a rolling stand of the pair crossing type, that is to say a stand having two working rolls each having a backup roll associated thereto; each pair of rolls is mounted in a suitable support housing which is accommodated in a load-bearing structure of the stand formed by two opposed frames, in such a manner as to be orientatable relative to a vertical axis.
The inclination of the rolls is adjusted by causing the associated housing to rotate about the above-mentioned vertical axis, with thrust members located on the uprights of the load-bearing structure of the stand. Such a rolling stand is not, however, suitable for effecting adjustment during rolling, that is to say when the rolls are under load. It should indeed be borne in mind that when the working rolls roll the material, they must be maintained at a predetermined distance; in other words, in addition to the inclination, it is also necessary during rolling to check the interaxial spacing of the working rolls (because the thickness of the material being worked depends on it).
The rolling stand described in the above-mentioned US patent is therefore provided with two actuators which are incorporated in the upper portion of the frames of the structure and act along two parallel vertical straight lines passing through the support chocks of the rolls.
However it should be noted that during rolling, because of the strong stresses which are transmitted from the bearings of the rolls to the actuators, the frictions between the actuators and the surfaces on which they act are highly relevant and therefore the rotation of the housings necessary for adjusting the inclination of the rolls is not easly made.
For this reason in recent times a special axial thrust bearing has been developed, which forms the subject-matter of another U.S. Pat. No. 5,320,434 of 14/06/1994, the proprietor thereof is the Japanese company NSK.
This bearing is of the rolling-contact type and is interposed between the above-mentioned actuators and the surfaces against which they act, that may be located in various positions depending on the different possible configurations of the rolling stands, as will be seen more clearly hereinafter.
In practice, the bearing in question is formed by a series of rolling bodies (cylindrical rolls or balls) arranged side by side along arcs of circles which are concentric with to the vertical axis about which the working rolls of the stand are caused to rotate, in order to adjust their angular position.
To be more precise, the rolling bodies are accommodated in respective compartments formed inside a kind of stand which is movable along a seat present in a base plate; furthermore, each stand is subject to the resilient force of some springs which return it to a neutral centred position with reference to the bearing.
As will be appreciated from this brief and incomplete explanation, the bearing known from the second US patent is certainly not the simple from the structural point of view and therefore also its industrial manufacturing must be seemingly difficult, since it is not a standard thrust bearing of the commercially available type.
It should also be borne in mind that the mounting of these bearings has to be very accurate because otherwise, if they are not positioned precisely, the arcs of circle along which the rolling bodies are arranged would no longer be concentric with the vertical axis about which the rotation of the crossing rolls takes place. It may be inferred that an incorrect distance between the bearings and the vertical axis would cause slipping between the rolling bodies and the surfaces in contact therewith, which would give rise to problematic functioning of the bearings.
This last aspect also involves the important drawback that variations in the length of the crossing rolls of the stand, render necessary to change the axial bearings in order to keep the centre of their arcs located correctly along the vertical axis about which the angular adjustment of the rolls takes place.
In other words, this fact means that only one rolling stand having predetermined dimensions (of the crossing rolls) corresponds to a specific type of bearing according to the NSK patent, so that, from the point of view of industrial costs, such a situation is certainly not the most advantageous since it is clear that the economies of scale obtainable with standard series of bearings are certainly not attainable.
In view of the above it will be appreciated that a need is felt for a bearing for rolling stands having crossing rolls, with structural and functional features such as to overcome the disadvantages associated with the prior art above and in particular with the thrust bearing of U.S. Pat. No. 5,320,434.
This object of the present invention

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