[0001] This invention relates to a method and apparatus for correcting a widthwise bend
in an end portion of a hot-rolled elongate sheet-shaped metal product, the correction
being performed while the product is still hot from the hot-rolling or after reheating
of the product. The invention further relates to a hot strip mill including straightening
apparatus for correcting such a bend. The invention is particularly applicable to
hot-rolled products of steel and aluminium. The products may be intermediate products
or final products.
[0002] In the hot-rolling of steel or aluminium products, typically a hot ingot is first
passed several times through a roughing mill which forms it into a so-called bar,
which is an elongate sheet-shaped product. Typically this bar has a width of 900 to
1500mm, a thickness of 20 to 80mm and a length of for example, 50m. This bar, when
intended for further rolling into a strip, is fed into a finishing mill comprising
a number of roll sets and is coiled as a strip having a thickness of, for example,
2 to 6mm, while still hot. Alternatively, the product from the roughing mill may take
the finished form of a so-called sheet or plate.
[0003] All of these products from the roughing mill may suffer from the defect of a lateral
bend in their head end portion or their tail end portion. The bend in the head end
portion is usually larger, and causes greater difficulties, particularly if the product
is a bar which is subjected to finishing rolling as described above. The bent head
end causes problems during threading into the finishing train, which can lead to non-uniform
thickness of the rolling in the finishing train and also a problem of folding of the
leading end, as well as possible difficulties in coiling.
[0004] One solution to the problem is to cut off the bent portion, but since this may be
4m long, it amounts to perhaps 8% of the product, which is wasteful.
[0005] One proposal in the prior art has been to correct the bend during the roughing rolling,
using edger rollers which engage the edges of the bar during a rolling pass through
the roughing mill. These edger rollers have vertical axes which are adjustable laterally
of the bar and remain fixed during a rolling operation. A problem particularly caused
here is that the edger roller presses with high force against the bar, causing thickening
of the bar at that side, with consequent further problems during rolling.
[0006] An alternative possibility, not disclosed in the prior art, is to adjust the rollers
of the roughing mill during a rolling pass, so that they roll the bar non-uniformly,
in a manner which corrects the bend. This method however is thought to be not practical,
on account of the high investment cost in designing the mill to perform this action.
[0007] In a hot-rolling mill, fixed side guides are disposed at several locations on the
conveyor table for the hot-rolled bar, e.g. as illustrated in the Japanese-language
Iron & Steel Handbook, page 416, for example. These side guides are fixed during rolling,
but may effect some straightening of a bar having a widthwise bend simply by pressing
upon the bar. However, the amount of straightening is small, because such guides are
designed with a clearance between them and the edges of the bar. Typically this clearance
is about 50mm and is necessary because the edge of the strip is not straight. Accordingly,
such a side guide cannot effect correction of a bend except perhaps over a very long
length of the bar.
[0008] The object of the present invention is to provide a method and apparatus for correcting
a bend in a hot-rolled product, in order to avoid at least partly the problems discussed
above.
[0009] According to the invention in one aspect there is provided a method of correcting
a widthwise bend of an end portion adjacent an end of a hot-rolled elongate sheet-shaped
metal product while it is hot, comprising the steps of simultaneously:
(i) holding the two edges of the product at at least two positions longitudinally
spaced along said product thereby to hold, at least laterally, a portion of said product
spaced from said end, and
(ii) pushing said end portion laterally by means of a laterally moving member so as
at least partly to correct said bend.
[0010] The present invention is based on the realization that it is possible successfully
to remove, at least partly, a widthwise bend in a hot-rolled product, while it is
hot, by pushing the end portion laterally relative to an adjacent portion which is
maintained along an axis so as to resist the pushing force. This can be done at a
location spaced from any roll set. A laterally moving member is required to provide
the lateral movement of the end portion. Fixed guides are not sufficient. In order
to achieve the removal of the bend, at least partially, it is necessary to effect
plastic deformation. It has now been found that this can be done without loss of planarity
of the sheet-shaped product, i.e. buckling, and without deformation of the edge of
the product by the forces applied to it. The material of the product must be sufficiently
plastically deformable; practical limits are discussed below, and depend on at least
temperature, thickness and width of the product.
[0011] In applying the appropriate forces to the hot-rolled product, various factors must
be taken into consideration, depending on each case. Such factors are the temperature
of the product, and width and thickness of the product. If it is too thin or too wide,
there may be a risk of buckling or of deformation of the edges. Thus, the product
should have the appropriate deformability, based on its Young's modulus and yield
stress at the temperature in question.
[0012] While in principle the invention can be applied to a hot-rolled product which is
temporarily held stationary for the bending operation to take place, this is not preferred,
because the stopping of the hot product is liable to cause non-uniform cooling of
parts thereof, leading to problems during subsequent rolling. Therefore, the invention
is preferably performed upon a product which is moving continuously.
[0013] In the invention, the product is sufficiently held against lateral movement caused
by the pushing force, this restraint occurring over a holding portion having a predetermined
length adjacent the bend portion. It is sufficient to support the product at only
the opposite ends of this holding portion, and at least for reasons of simplicity
this is preferred in the invention. Alternatively, further supports may be provided
between the ends of this holding portion.
[0014] Preferably, the distance l₁ between the pushing member which effects the correction
of the bending and the nearer end of the holding portion is not larger than the length
l₂ of the holding portion, and more preferably l₂ is not less than 1.5 l
1.
[0015] It is particularly preferred in the invention that the distance of lateral pushing
effected by the pushing member is more than that required merely to straighten the
bend, that is to say an excess or overpush is performed. When the end portion is released
by retraction of the pushing member, it will spring back to a certain extent. If correctly
calculated, this springback will bring the end portion back to the straight position,
so that the bend is completely removed. Since, at least approximately, the amount
of springback is independent of the plastic deformation which has taken place, the
amount of the overpush required is independent of the amount of the initial bend.
Thus, it is possible to control the pushing member so that, for each of a series of
similar products which are subjected to straightening, it pushes the bent end portion
to the same position, giving a predetermined amount of overpush, regardless of the
initial pushing position. This predetermined amount of overpush is selected in accordance
with the dimensions, temperature and nature of the material of the product.
[0016] To summarize this aspect therefore, the invention lies in a method of correcting
a widthwise bend of an end portion of a hot-rolled elongate sheet-shaped metal product
while it is hot, comprising applying a lateral pushing force to said end portion by
means of a laterally moving member so as at least partly to eliminate the bend while
holding a longitudinally extending portion of the product adjacent the end portion
at both edges so as to resist the pushing force. Preferably the pushing force is sufficient
to cause non-elastic deformation, while maintaining planarity of said product and
substantially avoiding deformation of the edges of said product.
[0017] In a second aspect, the invention provides an apparatus for correcting a widthwise
bend of an end portion of a hot-rolled elongate sheet-shaped metal product while the
product is hot, comprising,
(a) an elongate zone to receive said product,
(b) means for engaging the edges of said product at at least two positions longitudinally
spaced along said zone, so as to hold said product at least laterally,
(c) pushing means including at least one pushing member spaced longitudinally along
said zone from said engaging means and drive means to cause said pushing member to
push said end portion laterally.
[0018] Preferably the edge engaging means comprise longitudinally spaced pairs of opposed
rollers and means for moving the rollers laterally into engagement with the edges
of the product. The means for moving the rollers may comprise a pair of side frames
positioned respectively at the two sides of the elongate zone and supporting the rollers
so that the roller axes on each side of the elongate zone are in a common plane, the
common planes being parallel. Means are provided for moving the side frames towards
and away from the elongate zone while maintaining the common planes parallel. The
pushing member of the pushing means may be mounted on one of the side frames.
[0019] Suitably, the apparatus has a pair of the pushing members, mounted on opposite sides
of the elongate zone, the drive means being arranged to cause the pushing member to
push the bent end portion laterally from one of the opposite sides, in dependence
on the direction of the bend.
[0020] In one embodiment, the edge engaging means has, at a first one of the two longitudinally
spaced positions which is closer to the pushing member, roller means for contacting
an edge of said product, said roller means comprising a plurality of rollers rotatable
about vertical axes which, as seen in plan view, lie on a curve, so that the spacing
of the axes from the elongate zone increases with decrease of the distance of the
axes from the pushing member.
[0021] Preferably the two longitudinally spaced positions at which the edge engaging means
engages said edges of said product are spaced apart longitudinally by a distance greater
than the longitudinal distance along said zone between the pushing member and the
closer of the two longitudinally spaced positions thereto.
[0022] The present invention is particularly useful when applied in a hot strip mill.
[0023] In another aspect the invention provides a hot strip mill comprising,
(a) a roughing mill;
(b) a finishing mill;
(c) conveying means for conveying elongate roughed bar product from said roughing
mill to said finishing mill, and
(d) a straightener for correcting an end bend of said roughed bar product while on
said conveying means, the straightener comprising at least one laterally movable member
for pushing sideways on the bent end while lateral movement of a portion of the bar
adjacent the bent end is restrained.
[0024] To give some non-limitative examples of dimensions and other factors which typically
arise in present hot strip mill practice, and to which the invention is particularly
applicable, the length of the bent end portion at the leading end of a so-called bar
product emerging from the roughing mill is about 4m. Thus, the distance l₁ mentioned
above is preferably in the range 3.5 to 5.5m, and the length l₂ mentioned above is
correspondingly at least equal to this distance or larger. The thickness of such a
product is typically in the range 20 to 80mm and its width in the range 900 to 1500mm,
although narrower products, e.g. down to 600mm or wider products, e.g. up to 2m, may
also be suitable in the invention. More particularly, when the width is in the range
900 to 1200mm, the thickness is preferably in the range 20 to 40mm, in order for the
invention to apply satisfactorily, and when the width is in the range 900 to 1500mm,
the thickness may be in the range 40 to 80mm.
[0025] In the case of steel, the products in question are normally mild steel, silicon steel
or stainless steel, and the temperature of the product during the straightening operation
in a hot strip mill is generally over 700°C, preferably at least 900°C. Such a product
is typically moving at a speed of about 2 m/s on the roller table, so that pushing
means must operate in preferably a time of 1 s or even less.
[0026] For aluminium, the relevant temperature is lower, for example in the region of 400
to 500°C.
[0027] Although the invention is in principle applicable to both the head end and the tail
end, it is more effective when applied to the head end.
[0028] Embodiments of the inventions will now be described by way of non-limitative example
with reference to the accompanying drawings, in which:-
Fig. 1 is a top plan view showing apparatus for correcting the bend of the leading
end of a hot-rolled sheet according to one embodiment of the present invention;
Fig. 2 is a section taken along lines II-II of Fig. 1;
Figs. 3(a) to 3(d) are diagrams explaining the process for correcting the bend of
the leading end;
Fig. 4 is a diagram plotting the experimental results for the depth of push;
Fig. 5 is a top plan view showing bend correcting apparatus according to another embodiment
of the present invention;
Fig. 6 is an enlarged plan view of part of Fig. 5 showing the portion including the
pushing rolls;
Fig. 7 is an end view taken along line VII-VII of Fig. 6;
Fig. 8 is an enlarged diagrammatic view showing an element of correcting apparatus
according to still another embodiment of the present invention; and
Fig. 9 is a diagrammatic view of a hot strip mill embodying the invention.
[0029] With reference to Figs. 1 to 4, the correcting apparatus of the present embodiment
is equipped with a pinch roller 2 for feeding forward a hot-rolled sheet 1 having
a bend A at its leading end. This pinch roller 2 is driven by a drive motor 5 through
a bearing 3 and a reduction gear mechanism 4. Downstream of the pinch roller 2, there
are arranged at the two sides of the path of the hot-rolled sheet 1 a pair of side
guide frames 6, which are driven to open or close by a drive motor 11 through racks
7 and 8, pinions 9 and a reduction gear machanism 10, as also shown in Fig. 2. At
two longitudinally spaced portions of the side guide frames 6, there are attached
two pairs of opposed vertical rollers, i.e. first rollers 12 and second rollers 13,
which are moved away from or towards each other by opening or closing the side guide
frames 6. Downstream of these first and second rollers 12 and 13, there are arranged
another opposed pair of vertical pushing rollers, i.e. third rollers 14. These rollers
14 are attached to movable frames 15, which in turn are hinged by means of vertical
pins 16 to the front end portions of the side guide frames 6. When the movable frames
14 are driven by means of cylinders 17, the third rollers 14 are pushed widthwise
of the hot-rolled sheet 1.
[0030] In operation of the structure thus far described, when and after the leading end
of the hot-rolled sheet 1, which is still in hot condition, passes the first and second
rollers 12 and 13, the hot-rolled sheet 1 has its leading end given a sufficient counter
bend and corrected by holding the hot-rolled sheet 1 centrally of its path line by
means of the first and second rollers 12 and 13 and by pushing the third rollers 14
widthwise. At this time, the feeding force necessary for moving the bar during correcting
of the bend of the leading end is given the pinch roller 2.
[0031] The process for correcting the bend of the leading end will be described in more
detail with reference to Fig. 3.
[0032] The first, second and third rollers 12, 13, and 14 are held on standby while in the
open state, as shown at (a) in Fig. 3, until the leading end of the hot-rolled sheet
1 having the bend A passes the second rollers 13. When the leading end comes near
to the position of the third rollers 14, the first and second rollers 12 and 13 are
moved widthwise, as shown at (b) in Fig. 3, to hold or restrain the hot-rolled sheet
1 centrally of the path line. At this time, the third rollers 14 are not yet in contact
with the sides of the hot-rolled sheet 1.
[0033] As the leading end of the hot-rolled sheet 1 passes the third rollers 14, one of
these rollers 14 gradually starts to push. This lateral push of the third rollers
14 is performed by forcing widthwise the roller 14 located in the bend direction of
the leading end, i.e., the lower roller in the case as shown. The remaining opposite
or upper roller, as shown is either caused to follow the lower one or held in its
open position. Moreover, the push of the third roller 14 is performed to a position
over the sheet width beyond the position corresponding to the straight sheet, i.e.
there is an over-push. This is because a relatively large bend is left after the push
unless the push is excessive, since the hot-rolled sheet is elastic and springs back
when released.
[0034] Fig. 4 plots the experimental results concerning the relation of necessary depths
of over-push Δ (equal to the amount of the spring back) to the width B of the hot-rolled
sheet 1 for different values of the parameter of span l₁ between the second and third
rollers 13 and 14 and for material of Young's modulus 1.2 x 10⁴kg/mm²and yield stress
of 6 kg/mm². It is understood from the graph that the necessary depth of push Δ becomes
more for the smaller sheet width B and for the longer span l₁.
[0035] Thus, by performing the over-push estimating the extent of the springback after release,
the residual bend is reduced to one quarter or less of the initial bend of the leading
end. The bend of the leading end of the hot-rolled sheet 1 is usually 30 to 40mm or
less. In this case the residual bend after the correction is 10mm or less. A residual
bend of this order will raise no substantial problem in the passage through the subsequent
finish rolling machine (or the reduction due to an unbalanced push), in the offset
of the take-up machine (coiler), and in the production yield.
[0036] After the push is complete, the first to third rolls 12, 13 and 14 are rapidly opened,
as shown at (d) in Fig. 3, to end the correction.
[0037] According to the present embodiment, therefore, the bend of the leading end of the
hot-rolled sheet can be positively corrected to improve the passage through the finish
rolling machine thereby to prevent reduction and offset at the take-up machine and
to improve the production yield.
[0038] Since, moreover, the push of the hot-rolled sheet is accomplished by means of the
rollers 12, 13 and 14, the correction of the bend of the leading end can be accomplished
while the hot-rolled sheet is being continuously fed. With this correction during
the movement of the hot-rolled sheet 1, it is possible to prevent the temperature
of the hot-rolled sheet 1 from dropping and the sheet from being cooled down at the
feed rollers.
[0039] In order to effect the correction during the movement of the hot-rolled sheet 1,
the first to third rollers 12, 13 and 14 have to be opened or closed at high speeds.
Preferably the actual pushing is accomplished in 1 s or less. On the other hand, the
first and second rollers 12 and 13 and the third rollers 14 have to be operated at
predetermined timings. These timings can be realized, for example, by arranging a
sensor upstream of the pinch roller 2 to detect the passage of the leading end of
the hot-rolled sheet, and by driving the motor 11 and by driving the cylinders 16
at predetermined times after detection.
[0040] The bend of the leading end of the hot-rolled sheet 1 is usually 30 to 40mm or less
and is frequently located at a distance of about 5m from the leading end. Hence, the
distance between the second rollers 13 and the third rollers 14 is desirably 5m or
less, e.g. about 4m.
[0041] It will be appreciated that the direction of pushing of the bent end depends upon
the direction of the bend being corrected. Since, as explained above, the end position
to which the pushing member pushes the bent end can be chosen independently of the
initial amount of bend, the control of the apparatus in dependence upon the particular
product can be limited to control of the direction of pushing. This can be done manually,
following inspection of the next product to be treated. Alternatively, a sensor may
be arranged to detect the direction of the bend and control the direction of pushing
accordingly.
[0042] Another embodiment of the present invention will be described with reference to Figs.
5 to 7. Parts corresponding to those of Fig. 1 are not fully described again. In the
present embodiment, the pushing third rollers 14 are separated from the side guide
frames.
[0043] In Fig. 5, the side guide frames 20 are constructed to carry the first and second
rollers 12 and 13 only and are opened or closed by means of the mechanism of the racks
7 and 8 and the pinions 9. On the other hand, the third rollers 14 are carried by
chocks 21 which can be reciprocated in a stand 22. Thus, the third rollers 14 are
opened or closed by driving push means 23, which are connected to the chocks 21, by
means of motors 25 through gear mechanisms (not shown) which are built in the stand
22 and reduction gear mechanisms 24.
[0044] In the present embodiment, too, similar effects can be attained by correcting the
bend of the leading end of the hot-rolled sheet 1 in the same way as with the foregoing
embodiment.
[0045] Still another embodiment of the present invention will be described with reference
to Fig. 8 which differs only at the second rollers. In this case, the second rollers
are not constructed as a single pair of rollers but are each composed of a number
of vertical small-diameter basket rollers 30 having a large virtual roller diameter.
As Fig. 8 shows, the axes of these rollers 30 lie on a curve, so that they are increasingly
spaced from the centre line of the path of the moving hot-rolled sheet in the downstream
direction. This structure is made to avoid the local deformation of the hot-rolled
sheet. Specifically, what is given most intense force for the correction in the foregoing
embodiments is the second rollers 13. Depending upon the specification of the hot-rolled
sheet, it is necessary to avoid any significant reduction in the width due to the
local pushing by the second rollers 13. According to the present embodiment, however,
the load can be dispersed by using the numerous basket rollers 30 having a large virtual
roller diameter so that the tendency to width reduction can be decreased.
[0046] Fig. 9 shows diagrammatically a hot strip mill to which the invention is applied.
A hot ingot 40, e.g. from a soaking furnace passes through a scale breaker 42 to a
roughing mill 44 where it is rolled in many passes into a bar of sheet shape. Then
it is straightened by straightening apparatus 46 of the invention as illustrated above
before being rolled in a single pass through finishing train roll stands 48 and being
coiled at coiler 50.
[0047] One non-limitative example of the method of the invention will now be given.
Example
[0048] In straightening apparatus as shown in Fig. 1 a mild steel bar of dimensions 40mm
thick, 1000mm wide and 60m long at 1000°C (Young's modulus 1.1 x 10⁴ kg/mm², yield
stress 6.0 kg/mm²) is moved at 1.2 m/s. It had an initial bend of 40mm at its leading
end. The span l₁ (see Fig. 4) between second rollers 13 and the pushing rollers 14
is 4500mm, and the span l₂ between the first and second rollers is 6750mm. Straightening
of the bend to a residual bend of less than 10mm was achieved in the manner described
above. The maximum bending force at the second roller 13 was 23000 kg.
1. A method of correcting a widthwise bend of an end portion adjacent an end of a hot-rolled
elongate sheet-shaped metal product (1) while it is hot, comprising the steps of simultaneously:
(i) holding the edges of said product (1) at at least two positions (12,13) longitudinally
spaced along said product thereby to hold, at least laterally, a portion of said product
spaced from said end, and
(ii)pushing said end portion laterally by means of a laterally moving member (14)
so as at least partly to correct said bend.
2. A method according to claim 1 wherein said steps (i) and (ii) are performed while
said product is continuously moving along a path.
3. A method according to claim 2 wherein said steps (i) and (ii) are performed by rollers
rotatable about vertical axes.
4. A method according to claim 3 wherein said step (i) is performed by at least two longitudinally
spaced pairs of rollers (12,13), each pair comprising opposed rollers which respectively
engage opposite edges of said product, said axes of said rollers lying in two parallel
planes on opposite sides of said product, and said rollers being moved into engagement
with said edges of said product while said planes are maintained parallel.
5. A method according to any one of claims 1 to 4 wherein said step (ii) comprises pushing
said end portion laterally by an amount more than the amount of said bend, and permitting
said end portion to spring back after said pushing.
6. Apparatus for correcting a widthwise bend of an end portion of a hot-rolled elongate
sheet-shaped metal product (1) while said product is hot, comprising,
(a)an elongate zone to receive said product (1),
(b) means (12,13) for engaging the edges of said product at at least two positions
longitudinally spaced along said zone, so as to hold said product at least laterally,
(c)pushing means including at least one pushing member (14) spaced longitudinally
along said zone from said engaging means, to contact said end portion and drive means
(17) to cause said pushing member to push said end portion laterally.
7. Apparatus according to claim 6 wherein said edge engaging means comprises longitudinally
spaced pairs of opposed rollers (12,13) and means (6-11) for moving said rollers laterally
into engagement with said edges of said product.
8. Apparatus according to claim 7 wherein said means for moving said rollers comprises
(a) a pair of side frames (6) at the two sides of said elongate zone supporting said
rollers (12,13) so that the roller axes are in parallel planes at the two sides and
(b) means (7-11) for moving said side frames (6) towards and away from said elongate
zone while maintaining said planes parallel.
9. Apparatus according to any one of claims 6 to 8 wherein said engaging means (12,13)
has, at its end closer to said pushing member (14), roller means for contacting an
edge of said product, said roller means comprising a plurality of rollers (30) rotatable
about vertical axes which, as seen in plan view, lie on a curve in a manner such that
the spacing of said axes from said elongate zone increases with decrease of the distance
of said axes from said pushing member (14).
10. An apparatus according to any one of claims 6 to 9 wherein said two longitudinally
spaced positions at which said engaging means (12,13) engage said edges of said product
are spaced apart longitudinally by a distance greater than the longitudinal distance
along said zone between said pushing member (14) and the closer one (13) of said two
longitudinally spaced positions thereto.
11. A hot strip mill comprising,
(a)a roughing mill (44);
(b)a finishing mill (48);
(c)conveying means for conveying elongate roughed bar product from said roughing mill
to said finishing mill, and
(d)a straightener (46) for correcting an end bend of said roughed bar product while
on said conveying means, the straightener comprising at least one laterally movable
member (14) for pushing sideways on the bent end while lateral movement of a portion
of the bar adjacent the bent end is restrained.