Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
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1. Field of the Invention
The present invention relates to a method for producing
a predetermined yield strength and surface roughness during
skin pass rolling of pretreated metal strip. The invention
also relates to an arrangement for carrying out the method.
2. Description of the Related Art
For the treatment of metal strip and particularly strip
of steel alloys, strip treatment plants are known in which
one or more treatment units are followed by a skln pass
rolling stand in the form of a two-high stand, four-high
stand or cluster roll stand. The treatment units are
arrangements for the chemical treatment, for cleaning and
degreasing, for annealing and thermal treatment, for coating
with metal coatings such as tin, zinc, aluminum or the like,
for applying paints, varnishes or photo-chemical layers on
metal strips. Such skin pass rolling stands are frequently
also called temper pass rolling stands.
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The skin pass rolling stand has the purpose of adjusting
the strip materia} to a predetermined yield strength by
performing a specific strain hardening treatment.
Simultaneously, a defined roughness is to be imparted by the
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rolls onto the s~rip surface. In this connection, it is a
problem that metal strips of different steel qualities are
rolled to an increasing extent in the same line. For
example, the steel may be relatively soft, e.g., extra deep-
drawing quality steel with yield points of approximately 140
to 180 N/mm2 and higher strength steels with yield points of ~-
approximately 300 to 600 N/mm2. In the case of conventional
strip thicknesses of about 0.4 to 0.8 mm and strip widths of
up to 2000 mm, only four-high rolling mill stands can be used
for the desired strain-hardening treatment. In dependence
upon the respective metal strips, these four-high rolling
mill stands are operated with rolling forces of about 600 t
in the case of strip thicknesses of more than 1.0 mm and with
rolling forces of up to about 1500 t in the case of strip
thicknesses of less than 1.0 mm, i.e., in the case of thin
metal strips. However, the soft qualitiest particularly the
extra deep-drawing qualities, may only be subjected to a low
strain hardening treatment, particularly since they have a
deep cold work hardening or strain-hardening characteristic.
For example, a four-high rolling mill stand may be operated
for such metal strips only with a rolling force of 50 to 100
t and only specially roughened rolls may be used for
obtaining the desired roughness. However, these rolls lose
their roughness due to the contact with the back-up rolls
and, therefore, must be frequently exchanged. As a result,
particularly in continuously operating plants, large strip
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storage units are required on the entry side and on the exit ;~
side for bridging the exchange periods.
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Another problem resides in the fact that a large control
range is required for the four-high rolling mill stand for
hydraulically adjusting the rolling force. For example, in ;~
the case of metal strips to be rolled hard, hydraulic
pressures of 250 bar at a rolling force of 1500 t are
required, while hydraulic pressures of only 8 to 16 bar may ~ -~
be used in the case of soft metal strip, such as, extra deep-
drawing strip. Control pressure variations of approximately
~/- 1 bar in power-assisted valves result in one situation in
a folding force control deviation of +/- 0.4 %, while in the
other case they mean a control deviation of ~/- 12.5% or
+/- 6.25% and the attendant different cold work hardening and
roughness degrees in the same metal strip.
~ For thcse reasons, it is not possible to obtain a well `~
defined yield strength and simultaneously a well defined, ~;
uniform surface roughness in metal strip of different
qualities.
It is a primary object of the present disclosure to
provide a method and an arrangement for producing a well
defined yield strength and simultaneously a
producing a wcll de~incd yield strength and sirultaneously a
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well defined surface roughness during skin pass rolling of
pretreated metal strip of different qualities.
As here described, the method for
producing a predetermin~d yield strength and surface
roughness during skin pass rolling of preheated metal strips
includes rolling the metal strip under predetermined tension
in a hardening pass and/or subsequently rolling the roughness
onto the strip with continuous strip travel.
Within the scope of this disclosure, roughness means a
certain surface conditioning.
The desired yield strength and surface roughness can be
obtained in two treatment steps which are independent of each
other but subseguent to each other while the metal strip
travels continuously. In fact, it is now possible to adjust
and control the rolling force in an optimum manner for soft
metal strip as well as for hard metals strip. In the case of
deep-drawing qualities, the hardening pass can be omitted and
the surface conditioning with roughened rolls can be carried
out at low rolling pressures.
We have found that the adjustable
tensions have a significant influence on the rolling degree
and, thus, also on the strain hardening and roughness of the
strip material. This is cf particular significance when the
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hardening pass is omitted in the case of extra deep-drawing
qualities.
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The arrangement for carrying out the method ~ -
includes at least one set of tension
rolls on the entry side and a set of tension rolls on the
exit side for continuously traveling metal strip and a
cluster roll stand, particularly a four-high roll stand, for
rolling a hardening pass, the cluster roll pass being
arranged between the two sets of tension rolls. The
improvement resides in a two-high roll stand for rolling the
roughness arranged between the cluster roll stand and the set
of tension rolls on the exit side.
Thus, the skin pass rolling stand of conventional strip
treatment plants is divided into a cluster roll stand for the
hardening pass and a two-high roll stand for carrying out
surface conditioning.
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In accordance with another feature, a
tension measuring device each is provided in ~ront of the
cluster roll stand, the subsequent two-high roll stand and
the set of tension~rolls on the exit side and the drives
of the ~cluster roll stand, the two-high roll stand and the
set of tension rolls on the exit side are guided by the
respective tension measuring devices. This makes it
possible, on the one hand, to compensate the elongation of
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the respective metal strip in the individual por~ions which
elongation cannot be exactly measured; on the other hand,
the strip tensions can be adjusted in front of an behind the
rolling mill stands within wide limitsl so that it is
possible in this manner to influence tlle rolling deyree and,
thus, the strain hardening and roughness of the strip
material.
In accordance with an advantageous feature, the set of ; -~
tension rolls on the entry side is the guiding drive or speed
master.
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It is also possible to arrange a roll leveling machine
each following the cluster roll stand and the two-high roll
stand. For example, when the operation is for
extra deep-drawing propertiesthrough the tension measuring
with low back tension and low forward tension with the
cluster roll stand being open, then the set of tension rolls
on the exit side operates the corresponding leveling machine
in a pulling action and applies the bending 109ses thereof.
In accordance with a first aspect of the invention there is
provided in a method for producing a predetermined yield
strength and surface roughness during skin pass rolling of
pretreated metal strip, the improvement comprising subjecting ~
the metal strip under predetermined strip tension to a ~ -
hardening pass and/or subsequently rolling the roughness.
In accordance with a second aspect of the invention there is
provided in an arrangement for producing a predetermined
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yield strength and surface roughness of pretreated metal
strip, the arrangement including at least one set of tension
rolls on an entry side and a set of tension rolls on an exit
side for continuously traveling metal strip and a cluster
roll stand ~or rolling a hardening pass arranged between the
two sets of tension rolls, the improvement comprising a two
high roll stand for rolling the roughness arranged between
the cluster roll stand and the sets of tension rolls on the
exit side.
Embodiments o~ the invention will now be described with
reference to the accompanying drawings wherein:
Fig. 1 is a schematic side view of the arrangement
embodying the present invention; and
Fig. 2 is a schematic side view of the arrangement of
Fig. 1 including leveling machines.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The figures of the drawing show an arrangement for
producing a predetermined yield strength and surface
roughness during the skin pass rolling of pretreated metal
strip 1. The arrangement includes essentially at least one
set of tension rolls 2 on the entry side and a set of tension
rolls 5 on the exit side for the continuously traveling metal
strip 1 and a cluster roll stand 3, particularly a four-high
roll stand, for rolling a hardening pass. The cluster roll
stand 3 is arranged betwesn the two sets of tension rolls 2,
5. A two-high roll stand 4 for rolling the roughness is
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~` arranged between the cluster roll stand 3 and the ~et of
tension rolls 5 on the exit side. Tension measuring devices
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Tl, T2, T3 are arranged in front of the cluster roll stand 3,
the subsequent two-high roll stand 4 and the set of tension :~
rolls 5 on the exit side, respectively. The drives of ~;-
cluster roll stand 3, two-high roll stand 4 and set of
tension rolls 5 on the exit side are driven or guided by the ~ :
respective tension measuring devic~s Tl, T2, T3. The sets of
tension rolls 2 on the entry side operate as speed master.
The cluster roll stand 3 and the two-high roll stand 4 are
each followed by a roll leveling machine 6, 7.
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The operation for hard metal strip is as follows:
a) adjusting back tension through tension measuring
device T1,
b) rolling hardening pass by means of cluster roll
stand 3, ;
c) adjusting back tension for the two-high roll stand
4 through tension measuring device T2, ~:-
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d) adjusting forward tension for the two high rolling
stand 4 to tension measuring device T3, and
e) rolling roughness by means of two-high roll stand
4.
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In addition to the power re~uired for rolling and the :~
bearing losses, the drive of the roll stands 3, 4 also absorbs
the difference between forward tension and bac~ tension. The
tension distribution may be, for example:
back tension to cluster roll stand 312 t
forward tension to cluster roll stand 3 4 t `
back tension to two-high roll stand 44 t
forward tension to two-high roll stand 4 2 t
For soft metal strip, for example, extra deep-drawing
properties, the operation may be as follows:
.. a) cluster roll~stand 3 is open,
b) back tension for two~high stand 4 from tension
measuring device T2,
c) forward tension for two-high roll stand 4 from
tension measuring device T3, wherein
tension adjustment, for example, back tension to two
high roll stand 4: 3 t
forward tension to two-high roll stand 4: 1.5 t
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When the above arrangement and manner of operation are
used, the yield point of the extra deep-drawing material is
only slightly increased, so that the deformability is
maintained. In the case of large roll diameters of the two-
high roll stand 4 and low strip tensions and low rolling
forces of, for example, 70 to 100 t, the cold deformation is
approximately 0.3 to 0.5 %. The roughness of the rolls is
imparted well to the metal strip 1.
In the case of higher strength metal strips 1, rolling.
forces of about 250 to 300 t are required in the two-high
roll stand 4 for applying the roughness. With a maximum
pressure of 250 bar, the control deviation is `~
in soft metal strips 1, rolling force 70 t at -
84 bar ~/-1.1 %, .
in hard metal strip 1, rolling force 300 t at
250 bar ~/- 0.4%
Thus, the rolling force can be well adjusted and
controlled even in the case of soft metal strip 1.
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While a speciflc embodiment of the invention has been
shown and described in detail to illustrate the application
of the inventive principle, it will be understood that the
invention may be embodied otherwise without departing from
such principle~. .
