Note: Descriptions are shown in the official language in which they were submitted.
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Process and Unit for Producing an Aluminium Strip with Textured Surface
The invention relates to a process and unit for producing a cold rolled strip
of
aluminium or an aluminium alloy with a textured surface according to the
description in the independent claims 1 and 5.
In the automotive industry strips and sheets of aluminium alloys are employed
for
the manufacture of bodywork parts, whereby the sheets are shape-formed by deep
drawing or stretch drawing. Lubricants have to be employed to carry out this
deep
drawing and other shape-forming steps. By pre-coating the strips or sheets in
the
rolling mill not only is the forming procedure simplified, but also optimal
protection
during transportation achieved.
In a procedure commonly used today the strip manufacturer coats the cold
rolled
strip with an oil or a water-soluble dry lubricant and the prepared strip
supplied to
the sheet-forming company for the purposes of deep drawing.
In the case of an aluminium strip that has been produced in the normal manner
using work rolls with a roll finish corresponding to a mill-finish surface
texture, the
lubricants exhibit relatively poor adhesion and distribution.
The adhesion and distribution properties of dry lubricants on the strip
surface can
be markedly improved by providing the surface of the strip with a roughness
pattern. To that end the roughening of the strip surface is effected by
transferring
the roughness pattern on the work rolls to the surface of the strip during
cold rolling
of the strip.
Today, the roughness patterns provided on the surface of the aluminium strip
to
improve the adhesion and distribution of a dry lubricant there are produced by
work
rolls which are roughened e.g. by electrical discharge texturing (EDT), by
electron
beam texturing (EBT) or by the PRETEX method. All of these methods of roughen-
ing result in a surface texture with irregularly distributed, closed
"lubricant pockets".
The above mentioned roughness patterns are produced on the surface of the
strip
in an additional cold rolling pass using a roll pass involving a small
thickness
reduction approx. 0.05 to 15%. In practice this additional cold rolling pass
incurs
correspondingly greater production costs. In addition, in order to produce the
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roughness pattern, it is necessary to change the work rolls that have a conven-
tional roll-grind pattern for textured rolls.
A process and unit of the above mentioned kind is known from EP-A-O 945 198.
The object of the present invention is to provide a process and a unit of the
kind
described at the start, by means of which the production costs for
manufacturing
textured strips can be reduced. A further objective is to avoid the loss of
capacity
on a production unit caused by an additional texturing roll pass.
The object of the invention with respect to the process is achieved by way of
a
process and unit having the features described in the independent claims 1 and
5.
With this process it is possible to dispense with a separate texturing roll
pass and
consequently save one roll pass compared with the state of the art method.
On performing the process according to the invention the cold rolled strip is
drawn
through the roll gap and the texturing rolls turned by the tension on the
strip.
In order to adjust the thickness as uniformly as possible over the whole
breadth of
the strip, the texturing rolls are preferably set at a constant roll force.
To endow the strip surface with the above mentioned property whereby it acts
as
substrate for a dry lubricant, the texturing rolls are - to advantage -
roughened
using electrical discharge texturing (EDT).
It has been found that the process according to the invention is also suitable
for
smoothing cold rolled strips. To that end it can also be proved advantageous
to
provide the texturing rolls with the conventional, simple roll grind that
results in the
so called "mill finish" surface quality. The rolls are only ground over their
outer
surface direction, i.e. the roll grind comprises a plurality of parallel
grooves distrib-
uted over the outer surface of the rolls.
Preferred is an arrangement in which the texturing rolls in the texturing roll
stand
are supported by intermediate rolls, which are in turn supported by backing
rolls.
The backing rolls may be arranged in several sets of rolls across the width of
the
intermediate rolls.
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The backing rolls are preferably joined up in co-action to hydraulic pistons
set at a
constant force.
Further advantages, features and details of the invention are revealed in the
following description of preferred exemplified embodiments and with the aid of
the
drawing; this shows schematically in
Fig. 1: the end view of a unit for producing a strip with a textured surface;
Fig. 2: the front elevation of a texturing roll stand;
Fig. 3: the cross-section through the roll arrangement of a roll stand shown
in
figure 2.
A unit for producing an aluminium strip with a textured surface according to
Fig. 1
comprises a cold rolling mill 17 with two work rolls 18, 20 forming a roll gap
19 and
two backing rolls 22, 24 supporting the work rolls. The work rolls 18, 20 and
the
backing rolls 22, 24 are mounted in a mill stand 26 in a known manner.
Likewise installed in the stand 26 is a texturing roll stand 28 which is
smaller than
the cold rolling mill 17.
As shown in figures 2 and 3, the texturing roll stand 28 exhibits two
texturing rolls
38,40 which delimit a roll gap 39 and are supported by a pair of intermediate
rolls
42, 44. Each pair of intermediate rolls 42, 44 is supported by five sets of
three
backing rolls 46, 48. The backing rolls 46, 48 are mounted in beams 50, 52
which
extend over the width of the rolls. The upper beam 50 is supported by an upper
part 54 of the roll stand frame via hydraulic pressure type pistons 58, the
lower
beam 52 lies directly on a lower part 56 of the roll stand frame. Both parts
54, 56 of
the roll stand frame may be moved towards and away from each other by means of
hydraulic raising or lowering pistons 60, 62 i.e. the roll gap 39 can be
opened as
desired viz., when no texturing pass is required, or when the necessary
dimension
for a texturing pass is being adjusted. The roll force is adjusted via the
hydraulic
pistons 58 and thus the reduction in strip thickness during the texturing roll
pass.
The roll force is set by via the hydraulic compressive piston 58 and with that
the
reduction in thickness of the strip during the texturing pass.
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In order to produce the surface texture pattern, a cold rolled strip coiled
onto a
reserve roll 14 is passed over a deflection roll 16 then fed in the rolling
direction x to
the roll gap 19 of the cold rolling mill 17. After it emerges from the roll
gap 19, the
strip 12 enters the roll gap 39 of the texturing mill stand 28. On leaving the
texturing
mill stand 28 the strip 12 is deflected around two further deflection rolls
30, 32 and
coiled onto a spool 34. The thickness of the strip is checked by a thick-ness
measuring device 36 situated between the texturing mill stand 28 and the
second
deflection roll 30. At the same time, the second deflection roll 30 serves to
check
the flatness of the textured strip 12.
The work rolls 18, 20 of the cold rolling mill 17 are driven and the strip 12
is drawn
into the roll gap 19 by the rolls themselves. The texturing rolls 38, 40 are
not driven,
the strip 12 must be drawn through the texturing roll stand. This is done by
the
driven spool 34. The braking action of the texturing rolls 38, 40 results in a
stress-
regulating effect, which leads to better flatness in the textured strip 12.
The diameter of the texturing rolls 38, 40 is of course smaller than the
diameter of
the driven work rolls 18, 20 of the cold rolling mill 17. This produces a
better texture
in the strip surface with the result that a smaller reduction in thickness is
necessary.
The diameter of a texturing roll is e.g. around 350 mm.
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