Patent Application
20050115295
The invention relates to a process and unit for producing a cold rolled strip of aluminium or an aluminium alloy with a textured surface comprising passing a cold rolled strip immediately after cold rolling through a roll gap of two textured rolls bearing a roughness pattern, wherein the roughness pattern is transferred to the surface of the strip as a result of the force of the textured rolls acting on the strip, and, thereafter, coiling the textured strip.
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 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 is achieved by providing a process comprising passing a cold rolled strip immediately after cold rolling through a roll gap of two textured rolls bearing a roughness pattern, wherein the roughness pattern is transferred to the surface of the strip as a result of the force of the textured rolls acting on the strip, and, thereafter, coiling the textured strip.
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.
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
A unit for producing an aluminium strip with a textured surface according to
Likewise installed in the stand 26 is a texturing roll stand 28 which is smaller than the cold rolling mill 17.
As shown in
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 02405193.0 | Mar 2002 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP03/02094 | 2/28/2003 | WO |
