[0001] The present invention relates to a roll for strip rolling mill stands, in particular
but not exclusively for a backing roll in a four-high or six-high stand and possibly
also as an intermediate roll in six-high stands. Such a roll is of the type pointed
out in the pre-characterising part of the claim.
[0002] In strip rolling mills it is frequently necessary to roll sheet metal strips of different
widths. The rolling mills presently used for producing strips are of the so-called
four-high stand type (or four-high rolling mills) in which the rolling mill stands
include four rolls, two working rolls in contact with the strip to be rolled and two
backing rolls which bear on the working cylinders transmitting their rolling forces.
[0003] Generally a rolling mill of the said type is designed to produce good results when
working strips of a predetermined width ; when used to roll strips of different widths
the resultant product is of notably inferior quality.
[0004] Indeed, as is well known, reaction forces are applied to the necks of the backing
rolls to withstand and counter the pressure which the strip of sheet metal exerts
on the rolls during rolling. The backing rolls are thus forced to bend, their fibres
being compressed by the strip, with resulting curving. The working rolls follow the
deformation of the backing rolls and, as a result, the rolled strip has a transverse
section which, instead of being rectangular, tends to take on a form substantially
like a biconvex lens, that is, with a greater thickness in the middle.
[0005] There thus exists a problem of devising a rolling mill which allows strips of different
widths to be rolled while always producing strips with a flat rectangular cross-section.
[0006] The most obvious solution - that is, the use of rolls appropriate for the width of
the strip to be rolled - cannot be adopted in practice due to the very high costs
both of the apparatus (the need to have a store of rolls with different dimensions)
and particularly of operation (extremely long setting up times for the rolling mill).
[0007] One attempt to resolve this problem has been to apply to the working rolls corrective
loads tending to force the facing ends of the two working rolls apart and induce a
bending force in the opposite sense to that caused by the rolling force. In this respect
GB-A-2 094 687 teaches the use of a backing roll in which the effective profile is
adjusted by means of bearing means, e. g. hydrostatic bearings. The effectiveness
of this solution is not however sufficient and the precision obtained is again often
poor.
[0008] In order to solve the said problem it has also been proposed to interpose axially-movable
intermediate rolls between the working rolls and the backing rolls. During the rolling
of strips of a maximum width, these intermediate rolls are located symmetrically relative
to the rolling axis. When it is necessary to roll narrower strips, the intermediate
rolls are moved along their axes in opposite directions by a distance substantially
equal to the difference between the half-width of the strip to be rolled and that
of the widest strip rollable. In this manner the intermediate rolls cause the action
of the backing rolls to be distributed only over a central part of the working rolls
that is as wide as the strip ; the working rolls are thus subject to smaller forces
and curve less.
[0009] The solution described immediately above, even though satisfactory from a technical
point of view is unsatisfactory from a economic viewpoint. Indeed, not only does it
involve the use of a six-high stand which has a more complicated structure than the
conventional four-high stands, but it is also heavier and more bulky as well as being
further complicated structurally and functionally by the fact the intermediate rolls
must be axially movable in a registerable manner.
[0010] A further disadvantage is that, taking account of the relatively long lifetime of
the rolls, which is of the order of several tens of years, there is often a problem
of refurbishing existing installations in which the introduction of the new technology
would involve, at a very high cost, the replacement of complete stands by the above-said
special six-high stands.
[0011] Consequently, and more precisely, the technical problem underlying this invention
is that of making it possible to roll sheet metal strips of different widths accurately
without the need to replace existing structures of rolling plants. In other words,
the conventional four-high stands already operating in the plant under consideration
must, above all else, still be usable.
[0012] According to the present invention this problem is resolved by a roll characterised
in the following claim.
[0013] Further characteristics and advantages of the invention will become more apparent
from one embodiment of a roll for strip rolling mill stands, described below with
reference to the appended drawings, given purely by way of non-limiting example in
which :
Figure 1 is a schematic view of a four-high stand including a roll according to the
invention;
Figure 2 is a partially sectioned view of a detail of the roll according to the invention
in an operative condition,
Figure 3 is a partial schematic view in section of the same detail of the roll of
Figure 2 in a different operative condition of the roll.
[0014] With reference to the drawings, a four-high stand is schematically shown at 2 the
uprights 6 and 7 whereof support a stiffening cross-beam 2a. The stand 2 includes
two backing rolls, 1, 3 and two working rolls 4 and 5 each rotatably supported by
the uprights 6, 7 of the stand 2 in a conventional manner not shown in detail.
[0015] The backing roll 1 includes a cylindrical core 8 constituted by a larger-diameter
central portion 9 and two identical portions 10, 11 of smaller diameter than the central
portion 9 and extending symmetrically relative thereto. The central portion 9 is encased
by a cylindrical shell 8a rigid with the core 8.
[0016] In contrast, portions 10, 11 of the core 8 coaxially mount a plurality of expansion
rings each indicated 12 (in the example illustrated there are three rings 12 on each
of the portions 10, 11). According to a preferred but non-limiting embodiment, the
rings 12 are all identical and similarly arranged on their respective portions 10,
11 of the core 8. In particular, the rings 12 touch each other and the shall 8a and
are retained in this disposition by annular shoulders 15. Between each of the expansion
rings 12 and the corresponding portion 10, 11 of the core 8 is an annular chamber
into which pressurised fluid (in particular, oil) can be passed. As will become clearer
from the following description, upon an increase in fluid pressure, each expansion
ring 12 is isotropically deformed from a contracted (inoperative) condition in which
its outer diameter is less than the outer diameter of the shell 8a, to an expanded
(operative) condition in which its outer diameter is the same as the outer diameter
of the shell 8a.
[0017] Solely for the purpose of simplification, the following description relates to only
one of the expansion rings 12 and is given with reference to Figure 2 in which the
structural details of the other rings are identified by the same reference numerals.
[0018] Each expansion ring 12 has an outer cylindrical wall and an internal, conical wall
with a taper that extends towards the shell 8a of the backing roll under consideration.
[0019] A support ring 14 is coaxially mounted on the corresponding portion 10, 11 of the
core 8 and is movable axially within the chamber 13 formed between the ring 12 and
the core 8. The support ring 14 has an outer conical wall with the same taper and
taper direction as that of the inner wall of the expansion ring 12.
[0020] An annular chamber 18 is formed between the support ring 14, the corresponding portion
10, 11 of the core 8, and two annular seals 16,17 spaced axially on the portion 10,
11. Similarly, an annular chamber 21 is formed between the support ring 14, the expansion
ring 12 and two annular seals 19, 20 concentric with the annular seals 16, 17 mentioned
above.
[0021] The chambers 18 and 21 are in fluid communication through a passage 22 extending
radially through the support ring 14.
[0022] The support ring 14 has an axial length less than the axial length of the corresponding
expansion ring 12 and hence of the chamber 13 in which it is axially movable.
[0023] Consequently, respective annular chambers 23, 24 and 25 are defined between adjacent
support rings 14, between one end support ring 14 and the portion 9, and between the
other end ring and the annular shoulder 15. The sealing of these annular chambers
against pressurised fluid is ensured by seals each schematically indicated 26.
[0024] A plurality of ducts generally indicated 27 extend axially through the core 8 of
the backing roll under consideration and communicate at one end with a hydraulic control
unit, not shown, and at the opposite end with each of the chambers 18-21, 23, 24 and
25.
[0025] The operation of the backing roll 1 embodying the invention will now be described
starting from an initial situation in which all the support rings 14 have been moved
as far towards the annular shoulder 15 as possible. Under these initial conditions,
the rings 12 are in their contracted states and their outer cylindrical walls have
a smaller diameter than the diameter of the skirt 8a.
[0026] In this situation the backing roll 1 is adapted for rolling a strip of a minimum
width, and behaves as a backing roll of a width equal to the width of the shell 8a
only. The underlying working roll 4 is thus subject to thrust from the backing roll
1 over only its central part just as the opposing forces produced by the strip being
rolled act only on this central part. The working roll 4 thus only takes on the deformation
of the central portion or shell of the backing roll 1, a deformation which is substantially
zero.
[0027] When it is necessary to roll strips of a greater width than that considered above,
it it necessary to increase the operative width of the backing roll 1 and this is
achieved by bringing into operation one or more pairs of expansion rings 12 by transforming
them from their contracted condition considered previously to an expanded condition.
Under these conditions, the outer diameter of the cylindrical walls of the expansion
rings is the same as the diameter of the shell 8a.
[0028] In order to expand, for example, the first expansion ring (that is, the ring 12 adjacent
the cylindrical shell 8a), pressurised oil is delivered into the corresponding annular
chambers 18 and 21 to expand the ring 12, and into the chamber 23 adjacent thereto
to move the support ring 14 towards the shell 8a as the ring 12 expands.
[0029] Once the expanded condition is reached, the oil pressure is removed and the ring
12 remains locked in the expanded condition due to the action of the support ring
14 which thus behaves as a wedge. The operations of expanding the remaining rings
12 are entirely similar.
[0030] In order to return, for example, the first ring 12 to its contracted condition, it
is necessary to deliver pressurised oil into the corresponding chambers 18 and 21
and into the chamber 24 to move the support ring 14 into a position opposite to that
previously considered, that is towards the annular shoulder 15. After this displacement,
the oil pressure is removed and the ring 12 takes up its initial contracted condition
again. The same support ring 14 keeps the expansion ring 12 in this position.
[0031] A roll according to the invention thus allows the rolling of strips of different
widths, with the resultant rolled strips having flat rectangular cross sections.
[0032] Furthermore such a backing roll may be used either in an existing four-high stand,
or in a conventional six-high stand as an intermediate roll.
[0033] Depending on operational requirements, either a single backing roll may be used as
described above, acting on only one working roll, or a pair of backing rolls embodying
the invention may be used each acting on a respective working roll in this case, naturally
the effectiveness of the invention will be increased.
[0034] A backing roll according to the invention may be used together with conventional
corrective loads further increasing the working precision. It will thus be clear that
a backing roll according to the invention solves the technical problem previously
explained, ensuring rolling results which are technically consistent, with reasonable
production, installation and operating costs.
Cylindre (1) pour une cage de laminoir à feuillard comprenant un noyau cylindrique
(8), un corps cylindrique (8a), monté autour de la partie centrale (9) dudit noyau
(8), au moins une paire d'anneaux extensibles (12), montés autour du noyau (8) au
niveau des extrémités opposées du corps (8a), lesdits anneaux (12) définissant avec
les parties respectives (10, 11) du noyau (8) des chambres annulaires correspondantes
(18, 21), des moyens (27) assurant le passage d'un fluide sous pression dans lesdites
chambres (18, 21), de manière à provoquer une extension isotrope des anneaux correspondants
(12), d'une position contractée à une position dilatée, caractérisé en ce que chacun
des anneaux extensibles (12) présente une surface interne conique, et, en ce qu'un
support conique d'anneau (14) est monté coaxiallement avec le noyau (8), afin d'effectuer
un mouvement axial dans chacune des chambres (18, 21), le support d'anneau (14) jouant
le rôle de câle de blocage pour l'anneau extensible correspondant (12), à la fois
lors des positions contractée et dilatée.