LU86694A1 - METHOD OF MARKING THE SURFACE OF A CYLINDER USING A LASER BEAM - Google Patents

Description

*. c 2374 2.5413

! · 'TW ^ RAND-DUCHY OF LUXEMBOURG

December 1, 1986 (ŒwW) Minister of the Economy and the Middle Classes

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

'~~ 7 ~ Zl LUXEMBOURG

Patent Application L Request. The ...... GLH.T.EE ..... DE .... BLCHEE.QHE.S „ÆE.I: ALLUEGI.QUE.S-.QLMïRIM .... VQQE ..„ RE .SEARCH__, (1).

IN DE METALLURGIE.association non-profit-verenlglng zonder winstoogmerk, 47, rue Montoyer, 1040 Bruxelles.Belgique, represented by Me Alain RUKAVINA, attorney-attorney, acting as agent, files (nt) this. „.. first. ..... December ..... 1900 ..... q.ua.tr-e -. vi.ng.t ^ si.x -------- (3) to .. 1.5 .... Q.0 ...... hours, at the Ministry of Economy and the Middle Classes, in Luxembourg: 1. this request for obtaining a patent for invention concerning: .. .................................................. .................................................. .............................................., _____________________________________________ (4 ). ". Process ..... of .... tide ..... of ..... the ... on ... surface ..... dinn ..... cylinder .. ... to .... li.aide- ~ -d -! - a— beam ..... laser .. "................... .................................................. .................................................. ...........................................

2. the delegation of power, dated______Brussels_____________________ie 27 November Ï9jB6 3. the description in French .............................. of the invention in two copies; 4 ..... UU6___________ drawing boards, in two copies; 5. the receipt of the taxes paid to the Luxembourg Registration Office, on .......... December 1, 1986 ___________________________ * _____________________________ declares, assuming responsibility for this declaration, which inventor (s) ) is are) :

Mo.nsi.eur ..... Guy - .. M0NEQ.RT.r-X1.7.;, .-- r.ue .-. Neu-v: -ice- <43-2Q - MGn- begne-e ··; - --- (5)

Mon.sie.ur ..... J.ea, n ..... CRAHAY -, ...... S.te.F -. ^ Q.7-y - ^ 8-7- 8 --- gr-an.GO-rphafflP-s -; --—------

Mp.n.si.e.ui: .... Ad.o.lpli.e .... BARGARD ^ —Chemin.-des — Qpi4; es-t — 4ö§OLEsssö3e ~ - · - tms ... ... les ..... tr, Q.is ...... en .... Belgi.q.ue _______________________________________....-------------- claim ) for the above patent application the priority of one (s) request (s) from (6) _________________ LL ._________________________________________ filed (s) in (7) ______________ /. / ___________________________— on ________________ U ..._________________________________________________________________________________________________________ (8) at name of ___________ / .. L_____________________________________________________________ (9) elect (elect) for him (die) and, if appointed, for his proxy, in Luxembourg____ IDA., boulevard de la..Eo.irô ---------- --------------------------- (10) seeks (s) the issue of a patent for the invention for the object described and represented in the abovementioned appendices, —j with postponement of this issue to _________ dix — k-Uît- · 1— ™ ois. (11)

Le .......... mandaéiaifce..L.i ...... ", t * a λ ιηπ ..... LU 4A't '\ / j' Γ G V L u- L \ U Π. Deposit Minutes

The aforementioned patent application has been filed with the Ministry of the Economy and the Middle Classes, Intellectual Property Service in Luxembourg, on: 1 pr riérLpn ^ h-rP 1 QRP,

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Lrf A ^ Pt. Le faste wv ** 'at 15.0.0 hours U of Economy ^^^ Middle Classes,! v 2.5413

DESCRIPTIVE MEMORY

filed in support of an INVENTION PATENT application

in the Grand Duchy of LUXEMBOURG

on behalf of: METALLURGICAL RESEARCH CENTER

for: "Method of marking the surface of a cylinder using a laser beam" * i> C 2374 / 861Z.

METALLURGICAL RESEARCH CENTER -CENTRUM VOQR RESEARCH IN DE METALLURGIE,

Non-profit association -Vereniging zonder winstoogmerk in BRUXELLES, (Belgium).

Method of marking the surface of a cylinder using a laser beam.

The present invention relates to a method of marking the surface of a cylinder using a focused laser beam. It more particularly aims at creating a roughness on the surface of a cold rolling cylinder of steel strips.

Such a method of marking the surface of a cylinder is already known in particular from patent BE-A-880.996.

"- 2 -"

Briefly recalled, this process consists in sending on the surface of a rotating cylinder, and perpendicular to this surface, a focused intermittent laser beam which melts the material of the cylinder at the successive points of impact and forms in the. surface a series of microcraters distributed along a helical trajectory. The formation of these microcraters and of the beads which surround them is facilitated by the insufflation of oxygen under pressure in the impact zone of the laser beam.

This known method generally gives very satisfactory results for conventional roughness. It will be indicated here that, within the meaning of the present application, the roughness is the value Ra, mean arithmetic roughness, the definition of which is normalized.

In certain cases, however, it is necessary to form a significant roughness, for example of the order of 8 to 10 qjm. or more.

The logical solution based on the aforementioned method would consist either in increasing the flow, and consequently the pressure, of the oxygen jet, in order to dig the microcraters further, or in increasing the power of the laser beam.

From a certain level of roughness (approximately 8 to 10 μm), this solution however has two significant drawbacks.

First, to get a deeper crater, you have to melt a larger amount of metal. This is, under the effect of the increased oxygen pressure, discharged onto a cold portion of the surface of the cylinder, that is to say beyond the zone heated by the laser beam. This metal, intended to constitute the bead, badly adheres to the surface of the cylinder to which it is not welded, but simply glued. Such a bead is very quickly damaged or torn off during the rolling of the steel strips, and it therefore does not achieve the desired roughness.

s «- 3 -

Furthermore, the increased pressure of the oxygen jet causes a deformation of the microcrater and of the bead, which elongate in the direction of this oxygen jet. The roughness thus obtained is not regular.

The present invention provides a method which makes it possible to form in the surface of a cylinder microcraters of regular shape surrounded by well-adhered beads, which ensure that the desired high roughness is obtained.

The process which is the subject of the present invention is based on an unexpected observation that the applicant has made during his research with a view to improving the above-mentioned process.

It has indeed appeared that the marking of a cylinder by the aforementioned method gave rise to the formation of a plasma located above the portion of the surface of the cylinder heated by the focused laser beam; most of this plasma is located immediately above the melted part of the surface in the impact zone of the laser beam. This plasma consists of ionized gas originating in particular from the surrounding atmosphere, but also of metal of the cylinder brought to very high temperature and vaporized by the energy of the laser beam. It is also known that in this process, the plasma exerts a low pressure on the molten metal and thus causes a slight random deformation of this molten metal in the form of a shallow depression surrounded by a thin irregular bead.

The present invention is based on the exploitation of the particular electrical properties of the plasma so as to control the pressure exerted by the plasma on the molten metal, with as a consequence a regular roughness and a symmetrical shape of the microcraters and the beads obtained.

To this end, the process which is the subject of the present invention is essentially characterized in that one acts on said plasma so as to control the pressure of the latter on the surface of said molten metal; in that a controlled quantity of molten metal is thus forced out of the microcrater so as to form around it a regular bead leading to the desired roughness.

According to a first implementation of the method of the invention, said plasma is subjected to the action of a magnetic field oriented transversely to the axis of the focused laser beam, so that it exerts on the plasma a force parallel to the axis of the focused laser beam and oriented towards the surface of said molten metal.

The intensity of this magnetic field can be constant or present a variation in a direction parallel to the axis of the focused laser beam.

This variation in intensity advantageously results in a decreasing magnetic field gradient in the direction of the molten metal.

According to another implementation of the method of the invention, said plasma is subjected to the action of an electric field oriented parallel to the axis of the focused laser beam, in the direction of the molten metal, so that it exerts on the plasma a force directed towards the surface of said molten metal.

In the context of the present invention, it may also be advantageous to inject, in the zone of impact of the laser beam on the surface of the cylinder, a jet of an oxidizing gas, in particular oxygen, under a pressure sufficient to favor the fusion of the metal, but insufficient to disturb the plasma and / or the bead.

According to another advantageous characteristic of the process of the invention, the intensity of the magnetic field, respectively of the electric field, can be adjusted, so as to vary the pressure exerted by the plasma on the molten metal and thus to have a range for adjusting the roughness of the cylinder.

t - 5 - “” By way of simple illustration, a description will now be given in more detail of the process of the invention, with reference to the appended drawing, in which FIG. 1 shows, in elevation and in plan, a deformed microcrater. by too strong a jet of oxygen; FIG. 2 illustrates, in elevation and in plan, a microcrater of regular shape obtained by the method of the invention.

For the sake of clarity of the drawing, each time there has been shown schematically only one microcrater. It goes without saying, however, that the surface of the cylinder is provided with an extremely large number of such microcraters; in practice, this number can reach 100,000 micro-craters per square centimeter, the dimension of a microcrater in the plane of the surface generally being between 30 μm and 250 μm approximately. In the two figures, the corresponding elements are designated by the same reference numerals, and we have omitted to represent all the elements which are not essential for understanding the invention.

In Figure 1, the elevational view shows a section along the plane I-I of the plan view, of a fragment 1 of the surface layer of a cylinder. The rotating cylinder is shown schematically by its axis of rotation 2. An intermittent laser beam 3, focused by a lens 4, perpendicularly strikes the surface of the cylinder 1 at a point 0. It causes the heating of an area 5 delimited by a broken line, and merging of a more restricted zone 6. An oxygen jet (0 ^) applied in the impact zone of the laser beam intensifies these two heating and fusion effects. The molten metal of zone 6 undergoes a slight deformation due in particular to the low radiation pressure applied by the laser beam. Most of the deformation of the molten metal is however due to the mechanical pressure of the oxygen jet (C ^); in practice, this expels all of the molten metal from zone 6. The greater part of this molten metal is expelled in the direction of the oxygen jet, and in the case of high roughness, up to beyond zone 5 heated by the laser beam. An asymmetrical bead - 6 - * 7 is thus formed, which adheres badly to the cylinder beyond zone 5 and which is torn off from the first rolling operations.

FIG. 1 also includes the representation of a plasma 8 which forms above the zone 6 under the effect of the laser beam. This plasma consists of gaseous ions from the surrounding atmosphere, in particular oxygen ions supplied by the jet, and metal ions supplied by the metal of zone 6 vaporized by the laser beam. This plasma plays only a secondary role here.

FIG. 2 schematically illustrates the principle of the method which is the subject of the invention. The mounting of the cylinder 1,2 and of the laser beam 3, 4 is identical to that of FIG. 1, and the laser beam heats, respectively bottom, a zone 5, respectively 6.

In the present implementation according to the invention, a magnetic field H, perpendicular to the axis of the laser beam, is established in the vicinity of the surface of the cylinder 1 in the region occupied by the plasma 8. Under the effect of this magnetic field, part of the plasma 8 undergoes a force F and consequently performs a movement towards the surface of the molten metal. It thus exerts a uniform pressure on the molten metal, which is then pushed back uniformly towards the periphery of the zone 6 where it forms the regular bead 7 which does not extend beyond the hot zone 5. On cooling, the bead 7 is welded securely to the surface of the cylinder to which this combination of peaks (beads) and valleys (microcraters) thus gives a controlled roughness. By varying the intensity of the magnetic field H, it is possible to modify the pressure exerted by the plasma on the molten metal and consequently to adjust the depth of the microcrater and the height of the bead according to the desired roughness.

The method of the invention therefore makes it possible to produce microcraters and peripheral beads of regular shape ensuring the isotropy of the roughness of the surface of the cylinder. The desired depth of roughness can be achieved by eliminating the auxiliary oxygen jet, or at least by reducing its flow and pressure so that it does not cause any deformation of the bead.

Claims (6)

1. Method for marking the surface of a cylinder using an intermittent laser beam, · in which the surface of said cylinder is locally melted by means of said laser beam focused on this surface, in order to form in said surface microcraters which give it a controlled roughness, said melting resulting in the formation of a plasma immediately above the portion of metal melted by the laser beam, characterized in that one acts on said plasma so as to control the pressure of the latter on the surface of said molten metal, and in that a controlled amount of said molten metal is thus forced out of the microcrater, so as to form a regular bead around said microcrater. 2. Method according to claim 1, characterized in that said plasma is subjected to the action of a magnetic field oriented transversely to the axis of the focused laser beam, so that it exerts on the plasma a force parallel to the axis of the focused laser beam and oriented towards the surface of said molten metal. 3. Method according to claim 2, characterized in that the intensity of said magic field has a decreasing gradient towards the molten metal. 4. Method according to claim 1, characterized in that said plasma is subjected to the action of an electric field oriented parallel to the axis of the focused laser beam, in the direction of the molten metal, so that it exerts on the plasma a force directed towards the surface of said molten metal. 5. Method according to either of the preceding claims, characterized in that one regulates the pressure exerted by said plasma on the molten metal and in that one thus adjusts the depth of the roughness imparted to the cylinder surface. * - at - 6. Method according to claim 5, characterized in that said pressure is adjusted by varying the intensity of the magnetic field, respectively of the electric field acting on said plasma. Drawings: y \ rlanc.-s ^ _____. YAfl.-.- pagas of which .......... cover page ......... ê ...... description pages ........- ¾ ..... claim pages ....... Λ ....... descriptive abstract Luxembourg 12 -1 DEC, 1986 The representative: Me Alain Rukavina