WO2012073153A1

WO2012073153A1 - Method of increasing a thermal conductivity, in particular laser-assisted crystallization in a glass-ceramic hotplate, and domestic appliance component

Info

Publication number: WO2012073153A1
Application number: PCT/IB2011/055236
Authority: WO
Inventors: Miguel Angel BUÑUEL MAGDALENA; Rafael Cases Andreu; Andres Escartin Barduzal; Francisco Javier Ester Sola; José Ignacio Peña Torre; Fernando Planas Layunta; Daniel SOLA MARTÍNEZ
Original assignee: BSH Bosch und Siemens Hausgeräte GmbH
Priority date: 2010-11-29
Filing date: 2011-11-22
Publication date: 2012-06-07
Also published as: ES2400636A2; ES2400636R1

Abstract

In order to provide a domestic appliance component having a selectively increased thermal conductivity in at least one region of the domestic appliance component, a method of increasing a thermal conductivity of a material (10), in particular a glass-ceramic, by means of a laser (12), in which a laser beam (14) having a power density of at least 100 kW/cm² is focused in the material (10), is proposed.

Description

METHOD OF INCREASING TEMPERATURE CONCRETE, ESPECIALLY LASER-BASED CRYSTALLIZATION IN A CERAMIC GLASS PLATE, AND HOUSEHOLD COMPONENT

From DE 20 2006 004 064 U1 a glass-ceramic disc is known, in which by means of a pulsed laser, which emits light having a wavelength of 532 nm or 1064 nm, characters and / or ornamentation are introduced. A focusing of the light inside the glass-ceramic pane results in the formation of reflection surfaces within the glass-ceramic pane, whereby the characters and / or the ornamentation become visible to a viewer.

The object of the invention is, in particular, to provide a domestic appliance component with a selectively increased thermal conductivity in at least one area of the household appliance component. The object is achieved by a method according to claim 1 and by a domestic appliance component according to claim 1 1. Advantageous embodiments and further developments of the invention can be taken from the subclaims.

It is proposed a method for increasing a thermal conductivity of a material, in particular a glass ceramic, by means of a laser, in which a laser beam is focused with a power density of at least 100 kW / cm ² in the material. A "thermal conductivity" of a material is to be understood in particular to mean a temperature-dependent material constant which serves to describe a temporal change in a spatial distribution of a temperature due to heat conduction as a consequence of a temperature gradient.

The thermal diffusivity is defined in particular as a quotient of a thermal conductivity of the material and the product of a density and a specific heat capacity of the material. By "increasing a thermal diffusivity" is meant, in particular, that the thermal diffusivity of a treated material at a temperature is greater than the thermal diffusivity of the same untreated material at the temperature In particular, a "laser" is to be understood as a radiation source which generates electromagnetic radiation by means of stimulated emission. <br/><br/> Preferably, the radiation emitted by the laser has a very narrow frequency spectrum, high parallelism and a long coherence length be understood by a laser emitted bundle of coherent electromagnetic radiation. Preferably, the laser beam has a cross-sectional area oriented perpendicular to a radiation direction, which in the absence of a laser optical unit is nearly identical for each point along the radiation direction. In particular, a deviation of less than 1%, in particular less than, should be considered as "almost identical"

0.5% and more preferably less than 0.1% per meter along the direction of radiation. A "laser optics unit" is to be understood in particular as meaning a unit which is intended, preferably by means of lenses, to change the cross-sectional area along the radiation direction, preferably by at least 1%, in particular by at least 5% and particularly advantageously by at least 10% per Meter along the direction of radiation. "Provided" is to be understood in particular to be specially designed and / or equipped and / or programmed. A "cross-sectional area" of the laser beam is to be understood as meaning, in particular, a surface perpendicular to a propagation direction of the laser beam through which at least 68.3%, in particular at least 95.5% and preferably at least 99.7% of a radiation power are transported The cross-sectional area is a circle, in which it should be understood, in particular, that the cross-sectional area in the material has a minimum, that the laser beam is "focused in the material". Preferably, the machined material is at least partially transmissive to at least one radiation wavelength emitted by the laser. By the fact that the material should be "at least partially transmissive for at least one radiation wavelength emitted by the laser", it should be understood in particular that at least one radiation component exists which has the radiation wavelength and whose intensity in the material is at most 98%, in particular at most 95% and preferably at most 90% per centimeter is attenuated Material attenuated by at least 50%, in particular by at least 60%, preferably by at least 70% and particularly advantageously by at least 80% per centimeter. A "power density" is to be understood as meaning, in particular, an amount of energy radiated by the laser per unit time and area.When the laser is pulsed, the power density is given in particular by the amount of energy irradiated per pulse divided by a product of a pulse length and an irradiation area in that the laser is operated "pulsed" should be understood in particular that the laser is operated in an operating mode in which at least a majority of the radiation power is emitted in temporally successive and preferably temporally separate pulses. At least 85%, preferably at least 90% and particularly advantageously at least 95% are to be understood as "at least a large part." A "pulse length" is to be understood as meaning, in particular, a time duration of a pulse. Preferably, the laser beam is focused with a power density of at least 150 kW / cm ² , in particular of at least 175 kW / cm ² and particularly advantageously of at least 200 kW / cm ² in the material. Preferably, the laser beam is focused with a power density of at most 300 GW / cm ² , in particular of at most 275 GW / cm ² , advantageously of at most 250 GW / cm ² and particularly advantageously of not more than 225 GW / cm ² in the material. By means of such a method, the thermal diffusivity can be selectively increased in at least one region of the material, in particular by a photochemical reaction in the material and / or particularly advantageously by induced crystal growth in the material.

Advantageously, a material having at least one crystalline phase and one amorphous phase is used. A "phase" is to be understood as meaning, in particular, a spatial region of the material in which certain order parameters and a chemical composition are homogeneous A "crystalline phase" is to be understood in particular as a spatial region in which atomic and / or molecular constituents of the material in an at least substantially regular, periodic crystal structure are arranged. The fact that the constituents are arranged in an "at least essentially regular, periodic crystal structure" should in particular mean that a structure deviating from the regular, periodic crystal structure is due only to lattice defects, in particular by vacancies and / or interstitial atoms and and / or substitution atoms and / or dislocations and / or grain boundaries and / or pores and / or inclusions, and preferably occurs only locally.An "amorphous phase" is to be understood in particular as a spatial region of the material in which the molecular constituents of the material are free of an ordered structure. In particular, there is a phase interface between the crystalline phase and the amorphous phase. As a result, crystal growth in the amorphous phase can be induced, whereby the thermal conductivity can be advantageously increased. Furthermore, crystal growth enables creation of an optical waveguide.

In a preferred embodiment of the invention, it is proposed that the laser is operated pulsed. As a result, a higher power density can be achieved. In a particularly preferred embodiment of the invention, it is proposed that the laser is operated with a pulse length of at most 40 ns. Preferably, the laser is operated with a pulse length of at most 35 ns, in particular of at most 30 ns and particularly advantageously of a maximum of 25 ns. In this way, it can be achieved that an energy deposition and, concomitantly, a local heating of the material takes place in a very short time interval. As a result, an unfavorable cooling of the material by heat conduction can be largely prevented.

It is also proposed that the laser be operated with a pulse repetition frequency of at most 20 kHz. A "pulse repetition frequency" is to be understood as meaning, in particular, a reciprocal value of a time duration between start times of two successive pulses Pulse repetition frequency of a maximum of 15 kHz, in particular at most 10 kHz and particularly advantageously operated by a maximum of 5 kHz. As a result, a sufficiently high power density can be achieved with an advantageously short pulse length.

In a further embodiment of the invention, it is proposed that a focal point of a laser optical unit is moved relative to the material at a speed of at least 100 mm / s. A "focal point" of the laser optical unit should in particular be understood as a spatial area onto which a laser beam is focused after passing through the laser optical unit.

Preferably, the focal point is a minimum cross-sectional area along the laser beam. Preferably, the focal point is moved relative to the material at a speed of at least 150 mm / s, more preferably at least 200 mm / s and most preferably at least 250 mm / s. In this way it can be achieved that a distance between two laser processing points is at least 50 μηη, whereby damage to the material can be avoided. A "laser processing point" is to be understood as meaning, in particular, a spatial area within the material in which a structural change was induced by laser irradiation.Preferably, the laser processing point has a diameter of less than 1 mm, in particular less than 0.5 mm, and preferably of The focal point is preferably moved relative to the material at a speed of at most 600 mm / s, in particular of at most 500 mm / s, preferably of at most 400 mm / s and particularly advantageously of not more than 300 mm / s In this way it can be achieved that the distance between two laser processing points remains advantageously small, thus ensuring that the local increase in the thermal conductivity of the laser processing points can be measured macroscopically Advantageously, a distance of at least 50 μm is maintained between two adjacent laser processing points between the Laserb an interval of at least 75 μηη and especially Partially adhered to at least 100 μηη. As a result, cracking in the material can be effectively avoided.

It is also proposed that a diode-pumped solid-state laser is used. A "solid-state laser" is to be understood in particular as meaning a laser whose amplifying active medium consists of a solid doped with laser-active ions in a specific concentration is provided for exciting electrons in a higher energy level by electromagnetic radiation. Preferably, a Nd: YAG laser is used. A "Nd: YAG laser" is to be understood as meaning, in particular, a solid-state laser whose active medium consists of a neodymium-doped yttrium-aluminum garnet crystal, whereby space can be saved and higher operational reliability can be achieved optical pumping efficiency and beam quality can be increased advantageously.

In a preferred embodiment of the invention, it is proposed that the laser beam is focused in the material to a diameter smaller than 30 μm. The fact that the laser beam is "focused in the material to a diameter smaller than x" is to be understood in particular to mean that the focal point has an extension that is smaller than x. Preferably, the laser beam in the material is reduced to a diameter smaller than 25 μm. in particular less than 20 μm and particularly advantageously focused to a diameter of less than 15 μm, whereby an advantageously high energy density in the material can be achieved.

In a particularly preferred embodiment of the invention, it is proposed that the laser beam is generated with a wavelength of at least 355 nm and at most 3000 nm. By the fact that the laser beam is "generated" with a certain wavelength, it should be understood in particular that the laser emits electromagnetic radiation of the particular wavelength. Preferably, the laser beam is generated with a wavelength in the near-infrared wavelength range, in particular with a wavelength of at least 780 nm and advantageously with a wavelength of at most 3000 nm and more preferably of at most 1400 nm. Preferably, the laser beam is generated with a wavelength of 1064 nm. As a result, an advantageous interaction between the electromagnetic radiation and the material can be achieved.

Furthermore, a domestic appliance component, in particular a glass-ceramic domestic appliance component, is proposed, which has at least one laser processing point in an inner area, which is processed by the method according to the invention. An "inner region" of the domestic appliance component is to be understood in particular to be a partial region of the domestic appliance component which is arranged completely within the domestic appliance component and is preferably completely filled up with a material forming the domestic appliance component.

Advantageously, a thermal conductivity of the laser processing point is increased in relation to an environment of the laser processing point. Preferably, the thermal conductivity of the laser processing point is increased by at least 1%, in particular by at least 2%, and preferably by at least 3%, relative to an environment of the laser processing point. In this way, a household appliance component can be provided whose thermal diffusivity is increased in at least one area.

In a preferred embodiment of the invention, it is proposed that an average number of crystallites per volume in the laser processing point is increased compared to an environment of the laser processing point. A "crystallite" is to be understood as meaning, in particular, a spatial region which has a crystalline phase and which preferably has an extension of not more than 1 μm, in particular not more than 500 nm, preferably not more than 100 nm and particularly preferably not more than 50 nm the crystallite is embedded in an amorphous phase. In particular, it should be understood that more crystallites are present in a volume within the laser processing point than in a volume of equal size outside each laser processing point. In this way, a household appliance component can be provided whose thermal diffusivity is increased in at least one area by a larger number of crystallites.

In a particularly preferred embodiment of the invention, it is proposed that the crystallites in the laser processing point are identical on average

Crystallites in an environment of the laser processing point. By saying that "the crystallites in the laser processing point are on average identical to crystallites in the vicinity of the laser processing point, it should be understood in particular that a composition and / or a phase and / or a size of the crystallites are identical. In this way, a household appliance component can be provided whose thermal diffusivity is increased in at least one region with virtually unchanged mechanical properties, in particular a degree of hardness and a flexural strength. It is also proposed that a distance between two adjacent laser processing points is at least 50 μm. Preferably, the distance between the laser processing points at least 75 μηη and particularly advantageously at least 100 μηη. In this way, a household appliance component can be provided whose thermal diffusivity is increased in at least one area and which is free from damage, in particular cracking in the area

Inside, is. Furthermore, an impression of a large-scale decoration can be achieved with an advantageously low processing cost.

Furthermore, a domestic appliance, in particular a cooking appliance, with a household appliance component according to the invention is proposed. Preferably, the component is a

Hobbed plate, in particular a hob with resistance heaters. Here- By especially in the field of resistance heaters an increased thermal conductivity of the hob plate can be achieved.

Further advantages can be found in the following drawing descriptions. In the drawings, an embodiment of the invention is shown. The drawings, the descriptions and the claims contain numerous features in combination. The person skilled in the art will expediently also consider the features individually and combine them into meaningful further combinations.

Show it:

1 is a schematic representation of an apparatus for carrying out a method according to the invention,

2 is a schematic and enlarged view of two laser processing points and their environment,

Fig. 3 shows a hob with a processed by the method according to the invention hob ceramic hob in a plan view and

Fig. 4 shows the hob in a sectional view along a line IV-IV

in Fig. 3.

1 shows a schematic representation, not to scale, of an apparatus for carrying out a method according to the invention. The method serves to increase a thermal conductivity of a material 10 by means of a laser 12. The material 10 is a glass ceramic available under the trade name "Cleartrans." An absorption coefficient for a radiation wavelength of 1064 nm is 3.24 cm ^-1 . Laser 12 is a commercially available E-Line 20 series laser from ROFIN-SINAR Technologies, Inc. Laser 12 is a diode-pumped solid-state laser 26. Laser 12 is a diode-pumped Nd: YAG laser. The laser 12 emits a radiation wavelength of 1064 nm. The laser 12 has a maximum average power of 1 1 W. The laser 12 is operated by means of a Q-switch operated pulsed. A Gaussian beam TEM ₀ o emitted by the laser 12 has a diffraction factor M ² <1, 3.

A laser beam 14 emitted by the laser 12 is focused in the material 10 with a power density of 120 GW / cm ² by means of a laser optics unit 18, which is shown in simplified form in FIG. 1 but is basically known to a person skilled in the art. For this purpose, the laser optical unit 18 comprises a lens at a fivefold widening of the laser beam 14 and a convex lens with a focal length of 100 mm, so that the laser beam 14 behind the laser optical unit 18 has a Ray- leighlänge of 95 μηη. Furthermore, the laser optical unit 18 comprises a

Deflection mirror, which is controlled by a galvanometer by a CAD software. A focal point 17 of the laser optical unit 18 can thereby be moved relative to the material 10 at a speed 20 of 300 mm / s. Alternatively or additionally, an entire laser optical unit can also be moved relative to a material. In a further embodiment, a laser optical unit may be stationary while a material is being moved. The laser beam 14 is focused in the material 10 to a diameter 28 of 13 μηη. The pulse repetition frequency of 2 kHz and the speed 20 of 300 mm / s results in a distance between two adjacent laser processing points 22, 24 of 150 μηη. The high power density in the laser processing point 22, 24 during a pulse leads to a structural change of the material 10 in the laser processing point 22, 24. A material in an environment 32 of the laser processing point 22, 24 remains substantially unaffected due to the significantly lower power density prevailing there.

FIG. 2 illustrates this fact in a schematic and enlarged representation of the material 10. The glass-ceramic material 10 consists of an amorphous phase 16 and a crystalline phase 15. The crystalline phase 15 is present in crystallites 34 which are embedded in the amorphous phase 16 , In Fig. 2, the crystallites 34 are shown simplified in the form of diamonds whose boundary lines each correspond to a phase interface 36 between the amorphous phase 16 and the crystalline phase 15. An average number of crystallites 34 per Volume is increased in the laser processing point 22, 24 with respect to the surroundings 32 of the laser processing point 22, 24. The crystallites 34 in the laser processing point 22, 24 are on average identical to crystallites 34 in the vicinity 32 of the laser processing point 22, 24. This could be detected by an X-ray structure analysis. It was found that the crystallites 34 consist of a magnesium-aluminum silicate, more precisely of MgAl ₂ Si ₄ 0i2. A crystallite size is approximately 34.21 nm. Due to the higher number of crystallites 34 per volume, the thermal conductivity of the laser processing point 22, 24 is increased compared to the environment 32 of the laser processing point 22, 24.

The material 10 can be used as a household appliance component. FIG. 3 shows a hob 38 with a domestic appliance component embodied as a hob plate 40 in a plan view which is not to scale. The cooktop panel 40 is made of a glass ceramic. The glass ceramic is available under the trade name "Cleartrans." Heating zones 42, 44, 46, 48 are marked in a known manner on an upper side 41 of the hob plate 40 by means of an imprint 50. Each of the heating zones 42, 44, 46, 48 is, as shown by way of example in a not to scale section in Fig. 4 for the heating zone 48, a heating element 52. The heating element 52 is located just below the heating zone 48. The heating element 52 has the same cross-sectional area as the heating zone 48. In the heating element

52 is a resistance heating element, which connects directly to a bottom 54 of the hob plate 40 and this heated in an operating condition from below. The hob plate 40 is processed in the area of the heating zone 48 by means of the method described above. In an inner region 30 of the hob plate 40 are located in the heating zone 48 laser processing points 22, 24 with a mutual distance of 150 μηη. The laser processing points 22, 24 are arranged both side by side in a plane parallel to a main extension plane of the hob plate 40 and also one above the other in a direction perpendicular to the main extension plane. The laser processing points 22, 24 arranged one above the other extend from the

Top 41 of the hob plate 40 to the bottom 54. This is the thermal conductivity in the region of the heating zone 48 against an environment of heating increased zone 48. The temperature of the heated by the heating element 52 bottom 54 is preferably directed toward the top 41. In this way, a heating of the hob plate 40 can be counteracted in the vicinity of the heating zone 48. Furthermore, an advantageously shorter reaction time when heating the heating zone 48 can be achieved. Investigations showed that the temperature conductivity in the machined area is increased by about 3% at a temperature of 500 ° C. Furthermore, it could be shown that a change of a degree of hardness of the hob plate 40 is less than 5%. Further, it has been proved that a change of a flexural strength of the cooktop panel 40 is smaller than 10%.

reference numeral

10 material

12 lasers

14 vice beam

15 crystalline phase

16 amorphous phase

17 focus

18 Laser Optics Unit 20 Speed

22 laser processing point

24 laser processing point

26 solid-state lasers

28 diameter

30 indoor area

32 environment

34 crystallite

36 phase interface

38 hob

40 hob plate

41 top

42 heating zone

44 heating zone

46 heating zone

48 heating zone

50 printing

52 heating element

54 bottom

Claims

claims

1 . Method for increasing a thermal conductivity of a material (10), in particular a glass ceramic, by means of a laser (12), in which a laser beam (14) with a power density of at least 100 kW / cm ² in the material (10) is focused.

2. The method according to claim 1, characterized in that a material (10) having at least one crystalline phase (15) and an amorphous phase (16) is used.

3. The method according to claim 1 or 2, characterized in that the laser (12) is operated pulsed.

4. The method according to claim 3, characterized in that the laser (12) is operated with a pulse length of at most 40 ns.

5. The method according to any one of claims 3 or 4, characterized in that the laser (12) is operated at a pulse repetition frequency of at most 10 kHz.

6. The method according to any one of the preceding claims, characterized in that a focal point (17) of a laser optical unit (18) relative to the material (10) at a speed (20) of at least 100 mm / s is moved.

7. The method according to any one of the preceding claims, characterized in that between two adjacent laser processing points (22, 24) a distance of at least 50 μηη is maintained.

8. The method according to any one of the preceding claims, characterized in that a diode-pumped solid-state laser (26) is used.

9. The method according to any one of the preceding claims, characterized in that the laser beam (14) in the material (10) to a diameter (28) is less than 30 μηη focused.

10. The method according to any one of the preceding claims, characterized in that the laser beam (14) having a wavelength of at least 355 nm and at most 3000 nm is generated.

1 1. Household appliance component, in particular glass ceramic house appliance component, which in an interior region (30) at least one laser processing point (22, 24), which is processed by a method according to one of the preceding claims.

12. domestic appliance component according to claim 1 1, characterized in that a thermal conductivity of the laser processing point (22, 24) relative to an environment (32) of the laser processing point (22, 24) is increased.

13. domestic appliance component according to claim 1 1 or 12, characterized in that an average number of crystallites (34) per volume in the laser processing point (22, 24) relative to an environment (32) of the laser processing point (22, 24) is increased.

14. Domestic appliance component according to claim 13, characterized in that the crystal sides (34) in the laser processing point (22, 24) are on average identical to crystallites (34) in an environment (32) of the laser processing point (22, 24).

15. Domestic appliance component according to one of claims 1 1 to 14, characterized in that a distance between two adjacent laser processing points (22, 24) is at least 50 μηη.

16. Domestic appliance, in particular cooking appliance, with a domestic appliance component according to one of claims 1 1 to 15.