LU86705A1 - PROCESS FOR FORMING MICROPERFORATIONS ON THE SURFACE OF A ROLLER CYLINDER - Google Patents

Abstract

Process for forming microperforations with the aid of a pulsed laser beam, in which the duration of a laser pulse of the beam is adjusted so that the value of the ratio of the pulse duration (Ti) to the duration (Tc) of a complete cycle is between approximately 0.03 and approximately 0.60. At least a part of the available energy in the laser source is stored, but not transmitted in the form of a beam during a rest period (Tr) and this stored energy is added to the energy of the laser pulse emitted by the source during the subsequent pulse duration (Ti), in order to increase the power of this subsequent laser pulse. <IMAGE>

Description

C 2.5419 f | ~ j "

- t - '....... ^ J U 0 GRAND-DUCHY OF LUXEMBOURG

i of December 8, 19S6 · Minister j gôëri of the Economy and the Middle Classes

Title issued: ..................................... Intellectual Property Service

! \ "LÜXEMBOUEG

SX.28 • his Patent Application

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I. Request

THE CENTER ..... OF METALLURGICAL RESEARCH-CENTRÜM VOOR "RESEARCH (¾ IN DE, METALLURGY, as socla.t.ion ..... without ..... but ..... lucr.ati £ - v.eEenlgi.ag-s © ïid © -i * winstoogmerk, 47, rue Montoyer, 1040 Bruxelles ....... Belglque, reprisent #) by Me Alain RUKAVINA, lawyer-attorney. acting in ..... quality of mandateaii deposit (s) this ... eight ...... December 1900 four-vi: ng.t.-r: six _________________...... (3) to ... 1.5.00 .. .... hours, at the Ministry of the Economy and the Middle Classes, in Luxembourg: 1. this request for obtaining a patent of invention concerning: ............ .................................................. .................................................. .................................................. ................................................— ( 4) "Process ..... for ..... fQrm.e..r ...... des .... mic.r.Qp.e.rf..Qr.ati.oiis. ... to .... la ... sur £ ac.e ..... dL. un ...-...-.-.......

rolling mill cylinder "2. the delegation of power, dated ... Brussels ............................. on.,. 5 „„. December December — .ISS © 3. description in French ............ language .................. ..of the invention in two copies; 4 .......... LL .............. drawing boards, in two copies; 5. the receipt of taxes paid to the Registration Office in Luxembourg on ..... 8 December ..... 19.8.6 .___________________________________________________________________________________________________________________________________________ decïare (nt) assuming responsibility for this declaration, that the inventor (s) is are) :

Monsieur ·.-J-ean ..... CRAHA-Y -, - 30-7 ··· $ —Sl-er ..... 48'7B '~ "frânc © rchainp'S''j' — Belgium' .......

claim) for the above patent application the priority of one (s) application (s) of (6) .......................... .LL ___________________________________________ filed in (7) ________ /. / ------------------------------------- ----- on ___________________________ 11 ________________________________________________________________________________________________________________ 1 —_______________ (3) in the name of _____________________________________________________________________________________________________________________________________________________— (S) elect (elect) for him / her and, if appointed, for his / her representative, in Luxembourg. „.......... ..........

lûA ^ - .. boul- & vapd ..- 4th · —la- F © -ire ------------------------------ ---------------------- · ——— · -------------- · (-) requests (s) the issuance of a patent for the subject described and represented in the abovementioned appendices, - with postponement of this grant to ____ dix-htrrt ------ m ° is- PI)

The __________________________ .

jf * 'S jj Deposit minutes / The above-mentioned patent application djinvention was filed with the Ministry of Economy and the Middle Classes, Service de la Propriété Intejleefcseôe ^ in Luxembourg, on: • 8 I l - ij Pr. the 1st minister at 15; 00 hours 1 | ide the Economy and ^ [Middle Classes, S / A G8O07 ‘’ l / __ 2.5419 't

DESCRIPTIVE MEMORY

filed in support of an INVENTION PATENT application

in the Grand Duchy of LUXEMBOURG

on behalf of: METALLURGICAL RESEARCH CENTER

for: "Process for forming microperforations on the surface of a rolling mill cylinder" 'i C 2385/8612.

METALLURGICAL RESEARCH CENTER -CENTRUM VOOR RESEARCH IN DE METALLURGIE Non-profit association -Vereniging zonder winstoogmerk in BRUXELLES, (Belgium).

Method for forming microperforations on the surface of a rolling mill cylinder.

The present invention relates to a method for forming microperforations on the surface of a rolling mill cylinder.

It is known that the surface roughness of a rolled steel product is, to a large extent, imparted to it by the cylinders fitted to the last rolling stand of this product. The phenomenon of roughness transmission is of particular interest in the case of cold-rolled thin sheets, for which roughness largely conditions several properties such as the ability to stamp and the adhesion of the paint.

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There is already known, in particular from patent BE-A-880.996, a method of the aforementioned type, in which the microperforations, also called microcraters, are carried out by means of a continuous laser beam made intermittent by an open-ended rotating disc, called a dividing disc or chopper. The cylinder is rotated about its axis, and the laser beam moves along it, so that the point of impact of the beam describes a helix along which the microperforations are distributed.

It may be recalled that, in this process, each pulse of the intermittent laser beam yields its energy at its point of impact on the surface of the cylinder. This sudden addition of a relatively large amount of energy causes the metal to heat up in an area surrounding the point of impact, the fusion of part of this metal and even the vaporization of a portion of the molten metal. Above the molten metal, a plasma is formed consisting of ions of the vaporized metal, as well as surrounding gases. This plasma exerts on the molten metal a certain pressure which causes its repression. This repression effect can be further accentuated by the action of a jet of oxygen blown into the impact zone to improve the melting of the metal. The discharge of the molten metal beyond the periphery of the molten zone reveals a microcrater in the surface; moreover, the molten metal thus repelled reaches a less hot zone surrounding the aforementioned microcrater and it solidifies in a bead surrounding this microcrater.

The roughness referred to in the present application, namely the arithmetic mean roughness Ra whose definition is standardized, is determined by the dimensions of the microcraters and the beads mentioned above.

This prior process generally gives satisfactory results in terms of microcrater formation. It is however handicapped by the fact that it requires the use of a dividing disc to make the beam intermittent. This results on the one hand in a complication of the installation and on the other hand a substantial loss, usually of the order of 50%, of the energy of the laser beam. Furthermore, in a given divider disk, the dimensions of the windows as well as the distances which separate them are fixed and do not allow any adjustment of the duration of a pulse relative to the total duration of a cycle.

It had been suggested, in particular in patent BE-A-870,609, to use a pulsed laser beam with high frequency and high power, to carry out the desired microperforations. Such use was however not possible in practice, since there were then no sources of pulsed laser beam sufficiently stable for the needs of the treatment.

For some time now, sources of pulsed laser beam have appeared with a frequency which can vary from 5C00 Hz to 200,000 Hz approximately and exhibiting, over time, a stability such that the fluctuations of the frequency do not exceed 2%.

The present invention is based on the use of a pulsed laser beam of the aforementioned type. It relates to a process which makes it possible to adjust to a large extent and in a simple manner, the size and the shape of the microcraters.

In the course of its experimental work, the Applicant has indeed observed that not only the shape, but also the size of a micro-crater were directly influenced not by the absolute duration of the laser cycle, but by the relative duration of the pulse. relative to the duration of the cycle that contains it. A pulse cycle, which in fact corresponds to the period of the pulsed laser beam, has a duration Te which is the sum of the pulse time Ti proper and the rest time Tr which separates the end of a pulse c) u start of the next one. It appeared that the important factor for the shape and size of a microcrater was not the duration Te of the pulse cycle, but the Ti / Tc ratio. In this regard, it should be specified that, within the meaning of the present application, the time Ti ensures the transmission of the total quantity of energy of a pulse. Under given operating conditions, the amount of energy is identical for each pulse and the power of a pulse is therefore higher the shorter the duration Ti.

The process which is the subject of the present invention for forming microperforations on the surface of a rolling mill cylinder using a pulsed laser beam is essentially characterized in that the duration of a pulse is regulated laser of said beam so that the value of the ratio of said pulse duration (Ti) to the duration (Te) of a complete cycle is between approximately 0.03 and approximately 0.60.

This condition controls the shape and size of the microcraters.

For an equal total energy, a short duration pulse has a high power. Because of its short duration, such an impulse gives rise to a rounder crater; on the other hand, the bead is not very marked because the high power of the pulse causes a more pronounced vaporization of the metal from the surface. It has been found that the value of Ti = 0.03 constitutes a lower limit under which a sufficient roughness is not obtained.

On the contrary, a long-lasting pulse has less power and gives rise to a more marked bead. Beyond a Ti / Tc ratio = 0.60, however, there is a clear ovalization of the microcrater and the almost systematic formation of an asymmetric bead. The resulting roughness is therefore not isotropic.

Under these conditions, the invention proposes to modify the texture formed on the surface of a cylinder by adjusting the value of the Ti / Tc ratio of the pulsed laser beam.

According to another embodiment of the method of the invention, an oxygen jet is injected into the impact zone of the pulsed laser beam in a direction parallel to the axis of said pulsed laser beam.

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This oxygen jet is advantageously coaxia !. said pulsed laser beam; it can also be pulsed.

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Such oxygen insufflation is possible due to the absence of a chopping disc which, in existing installations, was generally placed in the focusing cone of the laser beam, that is to say near the surface to be treated. .

According to yet another embodiment of the method of the invention, at least part of the power of said source not transmitted during time is added to the power emitted by the laser source during the pulse time (Ti) of rest (Tr).

A pulsed laser beam is generated by a laser emission source which is generally continuously supplied with electrical energy. This supply is therefore not interrupted during the rest times (Tr), but the energy supplied during these rest times is not used to generate a laser beam.

The present variant proposes to store this unused energy during a rest time (Tr) and to restore it, during the following pulse time (Ti), to the system generating the laser pulse. This energy can be stored in electrical form, in particular by charging a capacitor which then discharges during the next pulse time; it can also be accumulated in another form and be reused to accentuate the phenomenon giving rise to the laser beam.

The power gain of the pulses obtained by this method obviously varies as a function of the value of the Ti / Tc ratio. With a Ti / Tc ratio = 0.50, a power gain greater than 50% can be achieved.

Claims (5)

1. Method for forming microperforations on the surface of a rolling mill cylinder using a pulsed Paser beam, characterized in that the duration of a laser pulse of said beam is adjusted so that the value the ratio of said pulse duration (Ti) to the duration (Te) of a complete cycle is between approximately 0.03 and approximately 0.60. 2. Method according to claim 1, characterized in that a jet of oxygen is blown into the impact zone of the pulsed laser beam in a direction parallel to the axis of said pulsed laser beam. 3. Method according to claim 2, characterized in that said oxygen jet is coaxial with said pulsed laser beam. 4. Method according to either of claims 2 and 3, characterized in that said oxygen jet is oulsé. 5. Method according to one or the other of claims 1 to 4, characterized in that at least one part of the energy available in the laser source is stored, but not transmitted in the form of a beam for a time of rest (Tr) and in; e that this stored energy is added to the energy of the laser pulse emitted by said source during the following pulse time (Ti), in order to increase the power of said laser pulse next. Drawings: ......... ^ D ... JL plates .... pages of which ....... j ........ cover page _______ S ...... .description pages ....... A ....... claim paQss ..... A ........ fcbrégé descriptif Luxembourg, h -y DEC. 1988 The representative: Me Alain Rukavina