PROCESS FOR MARKING A REFRACTORY CERAMIC PART

Abstract

A process for marking a surface of a refractory ceramic part, known as the “surface to be marked.” The part has a microstructure of grains including more than 50% by mass of ZrO.sub.2, bound by a silicate binder phase, and a total porosity of less than 5% by volume. The process involves irradiation of the surface with a laser beam. The beam is emitted by a laser device set to comply with relationship: a.V.sup.2+b.F.sup.2+c.VF+d.V+e.F+f<0, in which: a=10.sup.4.D+2×10.sup.6, b=0.5×10.sup.6.D−150×10.sup.6, c=0.5×10.sup.6.D−300×10.sup.6, d=5×10.sup.3.D−2.5×10.sup.6, e=−5×10.sup.3.D+2.0×10.sup.6, and f=−5×10.sup.9.D+1.8×10.sup.12. V is expressed in mm/second, D is expressed in mm and F is expressed in kHz.

Claims

1. A process for marking a surface of a refractory ceramic part, known as the “surface to be marked”, said part having a microstructure comprising grains each including more than 50% by mass of ZrO.sub.2, bound by a silicate binder phase, a total porosity of less than 5% by volume, said process involving irradiation of said surface with a laser beam, the beam being emitted by a laser device set to comply with relationship below:
a.V.sup.2+b.F.sup.2+c.VF+d.V+e.F+f<0, in which: a=10.sup.4.D+2×10.sup.6 b=0.5×10.sup.6.D−150×10.sup.6 c=0.5×10.sup.6.D−300×10.sup.6 d=5×10.sup.3.D−2.5×10.sup.6 e=−5×10.sup.3.D+2.0×10.sup.6 f=−5×10.sup.9.D+1.8×10.sup.12 V being expressed in mm/second, D being expressed in mm and F being expressed in kHz.

2. The process as claimed in claim 1, in which the frequency F is less than 300 kHz and/or the speed V is less than 5000 mm/sec.

3. The process as claimed in claim 2, in which the frequency F is less than 100 kHz and/or the speed V is less than 3000 mm/sec.

4. The process as claimed in claim 1, in which, to make the mark erasable, F/V<D/800.

5. The process as claimed in claim 1, in which the exposure energy is adapted to remove the binder phase over a depth of between 5 and 100 μm and/or to remove the binder phase over a depth of greater than 10% and less than 50% of the mean size of the grains of the surface to be marked.

6. The process as claimed in claim 1, in which, before irradiation, the surface to be marked has a roughness Ra, measured according to the standard ISO 4287/1997, of less than 20 μm and/or the refractory ceramic part has a percentage of moisture of less than or equal to 1%.

7. The process as claimed in claim 1, in which the grains include more than 95% of ZrO.sub.2, as a mass percentage on the basis of the oxides.

8. The process as claimed in claim 1, in which the refractory ceramic part is made of a fused material.

9. The process as claimed in claim 1, in which the refractory ceramic part is made of a material consisting, for more than 90% of its mass, of one or more oxides chosen from the group consisting of ZrO.sub.2, Al.sub.2O.sub.3, SiO.sub.2, Cr.sub.2O.sub.3, Y.sub.2O.sub.3 and CeO.sub.2.

10. The process as claimed in claim 1, in which the equivalent diameter of the cross section of the beam when it meets the surface to be marked is greater than 30 μm and less than 100 μm.

11. A refractory ceramic part having a microstructure consisting of grains including more than 50% by mass of ZrO.sub.2, bound by a silicate binder phase, a total porosity of less than 5% by volume, said refractory ceramic part including a mark, preferably inscribed by means of a marking process according to the invention, the mark defining a cavity with a depth of between 5 μm and 100 μm, and/or from the bottom of which the grains project, on average, by more than 5% and less than 50% of their mean size.

12. The refractory ceramic part as claimed in claim 11, in which the mark includes a plurality of dots, the dot density being between 100 and 1000 dots per mm.sup.2.

13. The refractory ceramic part as claimed in claim 11, in which the mark is an alphanumeric character, a line or a dot matrix or a graphic representation.

14. A process for manufacturing a furnace, in particular a glass furnace or a metallurgical furnace, said process including the following steps: 1) manufacturing a plurality of refractory ceramic parts and inscription of a mark on each part in accordance with a marking process as claimed in claim 1, the mark inscribed on a part being dependent on an intended position for said part in the furnace; 2) assembling the refractory ceramic parts so that each part is in a position in accordance with the mark inscribed thereon.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0074] Other features and advantages of the invention will emerge more clearly on reading the following detailed description and on examining the appended drawing, in which:

[0075] FIG. 1 shows the cross section, on a cut plane perpendicular to the marked surface, of a part according to the invention, marked by laser irradiation;

[0076] FIG. 2 shows the transition between the marked surface of a refractory ceramic part obtained according to a process according to the invention and an unmarked surface, the marked zone on the left half of the photo having a vitreous appearance and the zone not irradiated with the laser on the right half of the photo revealing the texture of the base product;

[0077] FIG. 3 shows an example of a Datamatrix inscribed on a refractory part according to a process according to the invention, this square mark of about 30 mm by 30 mm consisting of a set of squares with a side length of about 1 mm.

DETAILED DESCRIPTION

[0078] The refractory ceramic part to be marked comprises or preferably consists of a sintered or, preferably, fused material. Its total porosity is preferably less than 5%, preferably less than 3% or preferably less than 1%.

[0079] The refractory ceramic part to be marked is preferably obtained by melting a feedstock composed of refractory particles, casting of the liquid bath thus obtained in a mold, and then cooling to solidify the liquid mass in the mold. Preferably, the refractory ceramic part to be marked is obtained by electrofusion, preferably using an arc furnace.

[0080] Preferably, the refractory ceramic part has a maximum thickness of greater than 50 mm, or 75 mm, and/or preferably less than 300 mm, less than 200 mm, or even less than 100 mm.

[0081] The refractory ceramic part to be marked may in particular be chosen from the group consisting of tank blocks, plate blocks, burner arches or other parts of the superstructure of a glass furnace, preferably tank blocks.

[0082] The surface to be marked may be on any face of the refractory ceramic part. Preferably, it is on the hot face or on a side face, or a cold face.

[0083] The ceramic part conventionally includes an intergranular binder phase, connecting the crystalline grains.

[0084] The crystalline grains include, preferably for more than 80%, more than 90%, more than 95%, or even substantially 100% by volume, ZrO.sub.2 grains and, optionally, corundum-zirconia eutectic mixtures.

[0085] Preferably, more than 80%, more than 90%, more than 95%, or even substantially 100% of the grains, as mass percentages, are ZrO.sub.2 grains.

[0086] The zirconia in the refractory ceramic part is present in the form of grains. These monocrystalline or polycrystalline grains comprise the element Zr, and preferably consist of ZrO.sub.2 for more than 95%, more than 98%, more than 99% or substantially 100% of their mass.

[0087] The mean grain size, in particular on the surface to be marked, is preferably greater than 10 μm, preferably greater than 20 μm, preferably greater than or equal to 30 μm and/or less than 200 μm, preferably less than 100 μm.

[0088] The refractory ceramic part preferably consists, for more than 90% of its mass, of one or more oxides chosen from the group consisting of ZrO.sub.2, Al.sub.2O.sub.3, SiO.sub.2, Cr.sub.2O.sub.3, Y.sub.2O.sub.3 and CeO.sub.2. Preferably, ZrO.sub.2, Al.sub.2O.sub.3 and SiO.sub.2 together represent more than 90% of the mass of the refractory ceramic part.

[0089] The refractory ceramic part preferably includes more than 15% of ZrO.sub.2, and more preferably includes between 26% and 95% of ZrO.sub.2.

[0090] In various preferred embodiments, the composition of the base product is such that, for a total of more than 90%, more than 95%, or even more than 98%: [0091] ZrO.sub.2: 26 to 45%; [0092] Al.sub.2O.sub.3: 40 to 60%; [0093] SiO.sub.2: 5 to 35%;
or such that [0094] ZrO.sub.2: 50 to less than 80%; [0095] Al.sub.2O.sub.3: 15 to 30%; [0096] SiO.sub.2: 5 to 15%;
or such that [0097] ZrO.sub.2: 80 to 98%; [0098] Al.sub.2O.sub.3: 5 to 20%; [0099] SiO.sub.2: 1 to 12%;
or such that [0100] 10%<ZrO.sub.2≤25%; [0101] 50%<Al.sub.2O.sub.3<75%; [0102] 5%<SiO.sub.2<35%.

[0103] Preferably, in particular for all these embodiments, the mass content of Na.sub.2O and B.sub.2O.sub.3 is less than 2%, as a mass percentage on the basis of the oxides of the base product.

[0104] The binder phase includes, and preferably consists of, one or more vitreous or vitroceramic phases. It preferably represents between 5% and 50%, preferably between 10% and 40% by mass of the refractory ceramic part.

[0105] Preferably, the binder phase is a silicate phase, the mass proportion of Na.sub.2O of which is preferably less than 20%, preferably less than 10% and/or the mass proportion of Al.sub.2O.sub.3 of which is less than 30%.

[0106] To mark the surface of the refractory ceramic part, a predetermined amount of energy is concentrated on a small surface area, for a predetermined time.

[0107] Preparation

[0108] Before projecting the laser beam, the refractory ceramic part to be marked is prepared.

[0109] Preferably, the refractory ceramic part to be marked is ground down so that the surface to be marked is flat. Preferably, the planarity of this surface, or “camber”, measured using a micrometric feeler gauge, preferably on a representative length of at least 10 cm, is less than 100 μm, preferably less than 50 μm.

[0110] The roughness of the surface to be marked is preferably such that the roughness Ra, measured according to the standard ISO 4287/1997, is less than 20 μm, preferably less than 15 μm, more preferably less than 10 μm over a reference length of 100 microns. Thus, for example, on materials of AZS type, the variation of z (troughs and peaks) measured with the feeler gauge on a profile of 150 microns is +30/−30 micrometers, preferably +20/−20 micrometers.

[0111] Preferably, the part to be marked is dried so that its percentage of moisture is less than or equal to 1%, preferably less than 0.5%.

[0112] Irradiation

[0113] The device emitting the laser beam may be a conventional laser device, preferably of the CO.sub.2 type, preferably with a wavelength of 1065±5 nm, preferably with a mean laser beam power (or “mean output power”) of between 10 W and 100 watts, preferably between 20 W and 60 W.

[0114] This device may comprise a targeting device which aids in positioning the laser beam and/or a graphic interface for importing an image, for example in JPEG format, representing a symbol or a trademark or a two-dimensional code to be reproduced on the refractory ceramic part.

[0115] The device is set so as to irradiate the surface to be marked using a laser incident beam so as to transmit to this surface an exposure energy preferably greater than 5 J/mm.sup.3, preferably greater than 7 J/mm.sup.3, preferably greater than 10 J/mm.sup.3, preferably greater than 20 J/mm.sup.3, or even greater than 30 J/mm.sup.3 and/or less than 2000 J/mm.sup.3, preferably less than 1500 J/mm.sup.3, preferably less than 1000 J/mm.sup.3, preferably less than 500 J/mm.sup.3.

[0116] The exposure energy is the ratio between the power per unit area of the beam and the travel speed of the incident beam over the surface to be marked.

[0117] The power per unit area is the ratio of the power, in watts, of the incident beam divided by the surface area, in mm.sup.2, of the cross section of the incident beam when it meets the surface to be marked.

[0118] The cross section of the incident beam may be of varied shape, for example of circular cross section.

[0119] The equivalent diameter of the cross section of the incident beam, when it meets the surface to be marked, or “radiation width”, is preferably greater than 10 μm, preferably greater than 30 μm, preferably greater than 35 μm, and/or less than 100 μm, preferably less than 55 μm. Such an equivalent diameter is particularly suitable for marking a refractory ceramic part which has ceramic grains bound by a vitreous or vitroceramic phase.

[0120] Preferably, the beam width is adapted as a function of the mean size of the ZrO.sub.2 grains present at the surface of the base product. Preferably, the larger the mean grain size, the larger the beam width. Preferably, the beam width is between 0.5 and 2 times the mean size of the ZrO.sub.2 grains.

[0121] The power per unit area of the incident beam is greater than 1000 W/mm.sup.2, preferably greater than 5000 W/mm.sup.2, preferably greater than 7000 W/mm.sup.2, preferably greater than 10 000 W/mm.sup.2, and/or preferably less than 100 000 W/mm.sup.2, preferably less than 50 000 W/mm.sup.2, preferably less than 30 000 W/mm.sup.2.

[0122] The energy supplied to the surface to be marked must be supplied so as to limit the depth to which the binder phase is removed.

[0123] The device used is a pulsed laser, the pulse frequency “F” preferably being greater than 10 kHz, preferably greater than 20 kHz, and/or less than 300 kHz, preferably less than 200 kHz, preferably less than 100 kHz.

[0124] The combination of the pulsing and of the travel of the beam advantageously makes it possible to create a mark consisting of a plurality of dots, each dot resulting from the action of a pulse on the surface to be marked.

[0125] Preferably, the dot density is between 100 and 1000 dots/mm.sup.2.

[0126] A mark is a visual indication which has a meaning for a person or a machine, for example an alphanumeric character, or a two-dimensional code, for example a dot matrix (for example a Datamatrix or a QR code) or a graphic representation, for example a symbol or a drawing.

[0127] Preferably, the mark is a code that is readable by a Datalogic matrix 210 Datamatrix reader sold by the company Trumpf or by an in-sight 7210 camera sold by the company 7tech, equipped with a sensor having a resolution of 600×800 pixels.

[0128] Preferably, the mark consists of one or more groups of said dots. Preferably, a mark, notably when it represents an alphanumeric character or a code, has a largest dimension of between 1 and 5 cm.

[0129] The surface area of all of the marks on the refractory ceramic part, or “marking field”, for example the surface area over which a plurality of alphanumeric characters extends, is preferably greater than 100 cm.sup.2 and/or less than 1000 cm.sup.2, preferably less than or equal to 200 cm.sup.2. The marking field may be, for example, a square with a side length of 30 cm.

[0130] The marking field may comprise a set of alphanumeric characters, for example a sequence of 5 to 15 figures, each preferably having a height of from 1 to 5 cm. These characters are preferably obtained by a sequence of dots, with a density of from 100 to 1000 dots/mm.sup.2.

[0131] The linear travel speed “V” of the incident beam on the surface of the refractory ceramic part, in mm/s, is preferably greater than 30 mm/s, greater than 40 mm/s, preferably greater than 50 mm/s, and/or less than 3000 mm/s, preferably less than 2000 mm/s, preferably less than 1500 mm/s, preferably less than 1000 mm/s.

[0132] An incident beam is conventionally obtained by focusing a primary beam.

[0133] The shorter the focal distance “D”, the higher the power per unit area.

[0134] The focal distance D is preferably between 50 and 500 mm, preferably between 100 and 450 mm, preferably between 150 and 400 mm. Such a focal distance is advantageously compatible with the equivalent diameters described above, and in particular with an equivalent diameter of between 10 and 100 μm.

[0135] The inventors have discovered that it is particularly advantageous for the setting of the laser device to comply with the following relationship (1): a.V.sup.2+b.F.sup.2+c.VF+d.V+e. F+f<0, in which: [0136] a=10.sup.4.D+2×10.sup.6 [0137] b=0.5×10.sup.6.D−150×10.sup.6 [0138] c=0.5×10.sup.6.D−300×10.sup.6 [0139] d=5×10.sup.3.D−2.5×10.sup.6 [0140] e=−5×10.sup.3.D+2.0×10.sup.6 [0141] f=−5×10.sup.9.D+1.8×10.sup.12
V being expressed in mm/second, D being expressed in mm and F being expressed in kHz.

[0142] In one embodiment, F/V is greater than D/800. The mark is then very heat-resistant, and in particular is still legible after the refractory ceramic part has undergone a heat treatment at 800° C. in air for 24 hours.

[0143] In one embodiment, F/V is less than D/800. The vitreous phase is then removed by the laser beam over a depth typically less than 20% of the mean size of the grains of the refractory ceramic part. The mark remains legible and sufficiently contrasted but does not affect the abrasion resistance of the refractory ceramic part. However, it is erasable after a heat treatment at 800° C. in air for 24 hours.

[0144] Preferably, the leaktightness of the radiation is conventionally ensured by a dome isolating the surface to be marked, a positive pressure of air being maintained in the dome.

[0145] The marking process increases the roughness of the surface of the refractory ceramic part, by creating cavities between the ZrO.sub.2 grains. The depth of these cavities is, however, less than the mean size of these grains. In the case of material of AZS type, for example, the roughness of the marked surface is such that the Ra measured according to the standard is typically between 5 and 50 μm. The variation of z measured with a feeler gauge on a profile 800 microns in length is on average about +5/−20 micrometers, troughs of from 10 to 100 μm being formed over a length of about a hundred micrometers. Such a surface profile appears to constitute a signature of a process according to the invention.

EXAMPLES

[0146] The examples that follow are provided for illustrative purposes and do not limit the invention.

[0147] Dry blocks, with dimensions of 500 mm×600 mm×75 mm, made of a fused product ER1681, sold by the company Zefpro (32% ZrO.sub.2, 51% Al.sub.2O.sub.3, 15% SiO.sub.2) were marked in air, using an ytterbium-doped YAG source class IV LASER Solution F-30 fiber laser, with a wavelength of 1064 nm, a mean output power of 30 W, and the beam of which, of circular cross section, has a diameter of about 50 microns. Two focal distances of 160 mm and 330 mm were used. The functioning of the laser was managed by a control unit directly connected to the fiber laser.

[0148] The total porosity of the fused product ER1681 is 2.5%.

[0149] The fused product ER1681 has a conventional microstructure of AZS fused products, i.e. ZrO.sub.2 grains bound by a silicate binder phase.

[0150] For the marking, each block is placed on a face with dimensions of 500 mm×600 mm, and the laser beam is moved along the opposite face. The block is then observed.

[0151] To observe whether a mark is erasable, the marked part is subjected to firing in air at 800° C. for 24 hours, and it is observed whether the mark has been erased.

[0152] Table 1 shows the results of these observations.

[0153] The fused product ER1681 has a conventional microstructure of AZS fused products, i.e. ZrO.sub.2 grains bound by a silicate binder phase.

TABLE-US-00001 TABLE 1 Example 1a 1a* 1b 1c 1d 2a 2a* Focal distance D, in mm 160 160 160 160 160 330 330 Laser pulse frequency F, 70 30 70 30 70 30 30 in kHz Travel speed V, in mm/sec 50 50 300 300 1000 60 1 Beam power per unit area P, 15 000 15 000 15 000 15 000 15 000 15 000 15 000 in W/mm.sup.2 Exposure energy (P/V) 300 300 50 50 15 250 15 000 a   3.6E+06   3.6E+06   3.6E+06   3.6E+06   3.6E+06   5.3E+06   5.3E+06 b −7.0E+07 −7.0E+07 −7.0E+07 −7.0E+07 −7.0E+07   1.5E+07   1.5E+07 c −2.2E+08 −2.2E+08 −2.2E+08 −2.2E+08 −2.2E+08   4.4E+08   4.4E+08 d −1.7E+06 −1.7E+06 −1.7E+06 −1.7E+06 −1.7E+06 −8.5E+05 −8.5E+05 e   1.2E+06   1.2E+06   1.2E+06   1.2E+06   1.2E+06   3.5E+05   3.5E+05 f   1.0E+12   1.0E+12   1.0E+12   1.0E+12   1.0E+12   1.5E+11   1.5E+11 (1) a .Math. V.sup.2 + b .Math. F.sup.2 + c .Math. VF +   4.0E+11   6.2E+11 −3.6E+12 −7.2E+11   4.1E+13 −6.0E+10   1.6E+11 d .Math. V + e .Math. F + f= Relationship complied with yes no yes yes yes yes no if (1) < 0 800*F./(V*D)= 7.0 1.2 0.5 0.4 1.2 72.7 Mean roughness (μm) R 50 90 30 20 10 50 90 Mean roughness (μm) R max Legibility of the mark High Low High High High High Low Erasable mark? no no no yes yes no no Superficial destruction of the no yes no no no no yes material Example 2b* 2c 2d 3 4 Focal distance D, in mm 330 330 330 330 160 Laser pulse frequency F, 70 70 30 70 50 in kHz Travel speed V, in mm/sec 60 3000 300 300 100 Beam power per unit area P, 15 000 15 000 15 000 15 000 15 000 in W/mm.sup.2 Exposure energy (P/V) 250 5 50 50 150 a   5.3E+06   5.3E+06   5.3E+06   5.3E+06   3.6E+06 b   1.5E+07   1.5E+07   1.5E+07   1.5E+07 −7.0E+07 c   4.4E+08   4.4E+08   4.4E+08   4.4E+08 −2.2E+08 d −8.5E+05 −8.5E+05 −8.5E+05 −8.5E+05 −1.7E+06 e   3.5E+05   3.5E+05   3.5E+05   3.5E+05   1.2E+06 f   1.5E+11   1.5E+11   1.5E+11   1.5E+11   1.0E+12 (1) a .Math. V.sup.2 + b .Math. F.sup.2 + c .Math. VF + −3.2E+11   2.0E+13 −5.7E+11 −2.1E+12 −2.4E+11 d .Math. V + e .Math. F + f= Relationship complied with yes no yes yes yes if (1) < 0 800*F./(V*D)= 2.8 0.1 0.2 0.6 2.5 Mean roughness (μm) R 30 1 10 8 Mean roughness (μm) R max 75 Legibility of the mark High Low High High High Erasable mark? no no yes yes no Superficial destruction of the no no no no no material *outside the invention

[0154] The examples according to the invention show that if the variables F and V are chosen so that the relationship (1) is complied with, the mark has a uniform color, with no gradation, and a contrast which ensures very good legibility.

[0155] Comparative example 1a*, performed with a lower pulse frequency than that of example 1a according to the invention, has an indelible but poorly legible contrasted marking. The mean roughness of the marked surface is higher.

[0156] The travel speed of comparative examples 2a* and 2b* was significantly modified relative to examples 2a and 2b according to the invention, respectively. The legibility of the mark is thereby considerably degraded.

[0157] Comparison of examples 1c and 1 b shows that the reduction of the pulse frequency F enables the mark to be made erasable after heat treatment at 800° C. for 24 hours.

[0158] Examples 3 and 4 according to the invention show that, at a constant frequency, the mark can become erasable (for a product according to the invention) by changing the travel speed of the laser beam along the surface of the refractory block to be marked.

[0159] The satisfactory behavior with respect to blistering of the parts marked according to the invention was observed in a conventional blistering test with soda-lime glass at 1100° C. for 30 hours. The parts marked according to a marking process according to the invention are thus suitable for use in a lining of a glass smelting furnace.

[0160] As is now clearly apparent, the invention provides a marking process that is easy to perform, which does not modify the properties of the refractory ceramic part, and which makes it possible to obtain a mark that is suitable for the refractory ceramic parts of metallurgical or glass furnaces.

[0161] Needless to say, the invention is not limited to the embodiments described, which are provided as nonlimiting illustrations.