ES2400636A2 - Method of increasing a thermal conductivity, in particular laser-assisted crystallization in a glass-ceramic hotplate, and domestic appliance component - Google Patents

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

TEMPERATURE CONDUCTIVITY, AND DOMESTIC APPLIANCE COMPONENT

TECHNICAL FIELD OF THE INVENTION

The invention relates to a process for increasing a temperature conductivity of a glass ceramic material by means of a laser, especially a glass ceramic plate for a cooking field.

BACKGROUND OF THE INVENTION

From DE 20 2006 004 064 U1, a glass ceramic plate is known, in which, by means of a pulsed laser that emits light with a wavelength of 532 nm or 1,064 nm, characters and / or ornamentation are introduced. A focus of the light inside the glass ceramic plate leads to the formation of reflection surfaces within the glass ceramic plate, through which, for an observer, the characters and / or ornamentation become visible.

DESCRIPTION OF THE INVENTION

The invention poses the technical problem, inter alia, of providing a household appliance component with a selectively increased temperature conductivity in at least one area of the household appliance component. This technical problem is solved according to the invention by a method according to claim 1, and by means of a household appliance component according to claim 11. Advantageous embodiments and improvements of the invention can be extracted from the secondary claims.

A procedure is proposed for increasing a temperature conductivity of a material, especially a glass, a ceramic glass or a glass ceramic, by means of a laser, in which a laser beam is focused on the material with a power density of at least 100 kW / cm2. The term "temperature conductivity" of a material includes the concept of a constant of the temperature-dependent material, which serves for a description of a temporary modification of a spatial distribution of a temperature by thermal conduction as a consequence of a temperature gradient The conductivity of the temperature is defined, in particular, density and a specific thermal capacity of the material. The term "increase in temperature conductivity" should be understood, in particular, that the temperature conductivity of a material treated at a temperature is greater than the temperature conductivity of the same material not treated at temperature. The term "laser" includes the concept of a radiation source that produces electromagnetic radiation through stimulated emission. Preferably, the radiation emitted by the laser has a very narrow frequency spectrum, a high parallel, and a long coherence length. The term "laser beam" includes the concept of a beam of coherent electromagnetic radiation, emitted by a laser. Preferably, the laser beam has a cross-sectional surface oriented perpendicularly to a radiation direction, which, in the absence of an optical laser unit, is virtually identical for each point along the radiation direction. The term "practically identical" includes the concept of a deviation of less than 1%, preferably, less than 0.5% and, more preferably, less than 0.1% per meter along the radiation direction. . The term "laser optical unit" includes the concept of a unit that is intended to, preferably by means of lenses, modify the cross-sectional surface along the radiation direction, preferably, at least 1%, preferably, at least 5% and, more preferably, at least 10% per meter along the radiation direction. The term "intended" includes the concept of configured and / or provided and / or programmed specifically. The term "cross-sectional surface" of the laser beam includes the concept of a surface perpendicular to a direction of propagation of the laser beam, through which at least 68.3% is transported, preferably at least , 95.5% and, more preferably, at least 99.7% of a radiation power. Preferably, the cross-sectional surface is a circle. By the fact that the laser beam "is focused on the material", it should be understood, in particular, that a minimum of the cross-sectional surface is present in the material, preferably the entire cross-sectional surface is present in the material . Preferably, the processed material is at least partially permeable for at least one wavelength of radiation emitted by the laser. By the fact of the wavelength of radiation emitted by the laser ”, it should be understood, in particular, that there is at least a fraction of radiation that has the radiation wavelength, and whose intensity is weakened in the material , at most, 98%, preferably, at, at most, 95% and, more preferably, at, at most, 90% per centimeter. Preferably, the intensity of the radiation fraction is weakened in the material by at least 50%, preferably, at least 60%, more preferably, at least 70% and, more preferably, at least 80% per centimeter. The term "power density"; It includes the concept of an amount of energy radiated by the laser per unit of time and surface. If the laser is pulsed, the power density is given, in particular, through the amount of energy radiated per pulse divided by a pulse duration product and an irradiation surface. By the fact that the laser "is pulsed", it is especially understood that the laser is activated in a mode of operation in which at least a large part of the radiation power is emitted in consecutive pulses temporarily and, preferably, temporarily separated from each other. The term "at least a large part" includes the concept of at least 85%, preferably, at least 90% and, more preferably, at least 95%. The term "pulse duration" includes the concept of a temporary duration of a pulse. Preferably, the laser beam is focused on the material with a power density of at least 150 kW / cm2, preferably of at least 175 kW / cm2 and, more preferably, of at least 200 kW / cm2. Preferably, the laser beam is focused on the material with a power density of a maximum of 300 GW / cm2, preferably of a maximum of 275 GW / cm2, more preferably of a maximum of 250 GW / cm2 and, more preferably, of at most 225 GW / cm2. By such a procedure, in at least one area of the material, the conductivity of the temperature can be selectively increased, in particular, by a photochemical reaction in the material and / or, especially advantageously, by an induced growth of crystals in the material.

Advantageously, a material with at least one crystalline phase and an amorphous phase is used. The term "phase" includes the concept of a spatial area of the material, in which certain order parameters and a chemical composition are homogeneous. The term "crystalline phase" includes the concept of a spatial area, in which atomic and / or molecular constituents of the material are arranged in a periodic, at least essentially regular, crystalline structure. By the fact that the constituents are arranged in a "periodic crystalline structure, at least essentially regular", it should be understood, in particular, that a structure that differs from the periodic, regular crystalline structure is only caused by network defects , especially, by empty spaces and / or interstitial atoms and / or substitution atoms and / or dislocations and / or boundaries of the grains and / or pores and / or inclusions and, preferably, occur only locally. The term "amorphous phase" includes the concept of a spatial area of the material, in which the molecular constituents of the material are exempt from an ordered structure. Between the crystalline phase and the amorphous phase, there is, in particular, an interface. Through this, crystal growth in the amorphous phase can be induced, through which the temperature conductivity can be advantageously increased. Also, through the growth of crystals, it is possible to create an optical waveguide.

In a preferred embodiment of the invention, it is proposed that the laser be operated pulsed. In this way, a higher power density can be achieved.

In an especially preferred embodiment of the invention, it is proposed that the laser be operated with a pulse duration of at most 40 ns. Preferably, the laser is operated with a pulse duration of at most 35 ns, preferably at most 30 ns and, more preferably, at most 25 ns. In this way, it can be achieved that, in a very short time interval, an energy deposition takes place, and local heating of the material that is attached to it. Through this, disadvantageous cooling of the material through thermal conduction can be largely avoided.

It is also proposed that the laser be operated with a pulse repetition frequency of a maximum of 20 kHz. The term "pulse repetition frequency" includes the concept of an inverse value of a time duration between start times of two consecutive pulses. Preferably, the laser is operated with a pulse repetition frequency of at most 15 kHz, preferably at most 10 kHz and, more preferably, at most 5 kHz. In this way, a sufficiently high power density can be achieved with an advantageously short pulse duration.

In another embodiment of the invention, it is proposed that a focus of an optical laser unit be moved relative to the material with a speed of at least 100 mm / sec. The term "focus" of the laser optical unit includes a spatial area on which a laser beam is focused after a passage through the laser optical unit. Preferably, the focus constitutes a minimum cross-sectional area along the laser beam. Preferably, the focus is moved relative to the material with a speed of at least 150 mm / sec, preferably of at least 200 mm / sec and, more preferably, of at least 250 mm / sec. In this way, a distance of two laser processing points can be achieved at least 50

�m, through which a deterioration of the material can be avoided. The term "laser processing point" includes the concept of a spatial area within the material, in which a structural modification was induced by laser irradiation. Preferably, the laser processing point has a diameter of less than 1 mm, preferably less than 0.5 mm. and, more preferably, less than 0.1 mm. Preferably, the focus is moved relative to the material with a speed of at most 600 mm / sec, preferably of at most 500 mm / sec, more preferably of at most 400 mm / sec. and, more preferably, of, at most, 300 mm / sec. Through this, it can be achieved that the distance of two laser processing points remains advantageously small. Thus, it can be ensured that the local increase in the temperature conductivity of the laser processing points is macroscopically measurable.

Advantageously, between two adjacent laser processing points, a distance of at least 50 μm is respected. Preferably, between the laser processing points, a distance of at least 75 µm, and preferably at least 100 µm, is respected. In this way, a crack formation in the material can be effectively avoided.

It is also proposed that a solid state laser pumped by diode be used. The term "solid state laser" includes the concept of a laser whose amplifying active medium is composed of a solid body, which is provided with active laser ions in a given concentration. The term "solid state laser pumped by diode" includes the concept of a solid state laser in which at least one laser diode is provided for the excitation of electrons at a higher energy level by electromagnetic radiation. Preferably, an Nd: YAG laser is used. The term "Nd: YAG laser" includes the concept of a solid-state laser whose active medium is composed of a neodymium yttrium aluminum grenade crystal. In this way, constructive space can be saved, and greater reliability in operation can be achieved. Likewise, an optical pumping efficiency and a radiation quality can be advantageously increased.

In a preferred embodiment of the invention, it is proposed that the laser beam be focused on the material over a diameter of less than 30 µm. By the fact that the laser beam "is focused on the material on a diameter smaller than x", it should be understood, in particular, that the focus has an extension that is less than x. Preferably, the laser beam is focused on the material on a diameter of less than 25 µm, preferably, less than 20 µm and, more preferably, on a diameter of less than 15 µm. In this way, an especially high energy density can be achieved in the material.

In an especially preferred embodiment of the invention, it is proposed that the laser beam be generated with a wavelength of at least 355 nm and a maximum of 3,000 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 determined wavelength. Preferably, the laser beam is generated with a wavelength in the near infrared wavelength range, especially with a wavelength of at least 780 nm and preferably with a wavelength of at most 3,000 nm and, more preferably, at most 1,400 nm. Preferably, the laser beam is generated with a wavelength of

1,064 nm. In this way, an advantageous interaction between the electromagnetic radiation and the material can be achieved.

a component of a domestic ceramic hob apparatus, which has at least one laser processing point in an interior area, which is processed by the method according to the invention. The term "interior area" of the household appliance component includes the concept of a partial area of the household appliance component, which is completely disposed within the household appliance component and, preferably, is completely filled with a material that forms the household appliance component.

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

In a preferred embodiment of the invention, it is proposed that an average number of crystallites per volume at the laser processing point be increased with respect to an environment of the laser processing point. The term "crystallite" includes the concept of a spatial area that has a crystalline phase, and that preferably has an extension of at most 1 µm, more preferably, of at most 500 nm, more preferably, of at most 100 nm and, more preferably, at most 50 nm. Preferably, the crystallite is embedded in an amorphous phase. By the fact that "an average number of crystallites per volume at the laser processing point is increased with respect to an environment of the laser processing point", it should be understood, in particular, that, in a volume within the point of laser processing, more crystallites are present than in a volume of the same size outside of any laser processing point. In this way, a household appliance component can be made available, whose temperature conductivity in at least one area is increased by a larger number of crystallites.

In an especially preferred embodiment of the invention, it is proposed that the crystallites at the laser processing point are, on average, identical to the crystallites in an environment of the laser processing point. By the fact that "the crystallites at the laser processing point are, on average, identical to the crystallites around the laser processing point", it should be understood, in particular, that a composition and / or a phase and / or a crystal size are identical. Through this, a household appliance component whose temperature conductivity is increased by at least one area can be provided, with virtually unmodified mechanical properties, especially a degree of hardness, and a flexural strength.

Likewise, it is proposed that a distance between two laser processing points be at least 50 μm. Preferably, the distance between the laser processing points is at least 75 µm and, preferably, at least 100 µm. In this way, a household appliance component can be made available whose temperature conductivity is increased in at least one area, and which is free from deterioration, especially of a crack formation, inside. Also, an impression of a large surface decoration can be achieved, with an advantageously low processing cost.

Likewise, a domestic appliance, in particular a cooking appliance, with a household appliance component according to the invention is proposed. Preferably, the component is a cooking field plate, especially of a cooking field with resistance heating bodies. Through this, in particular, in the area of resistance heating bodies, an increased temperature conductivity of the cooking field plate can be achieved.

BRIEF DESCROPTION OF DRAWINGS

Other advantages are drawn from the following descriptions of the drawings. An embodiment of the invention is represented in the drawings. The drawings, descriptions and claims contain numerous features in combination. The person skilled in the art will consider the characteristics advantageously also separately, and will gather them in other reasonable combinations.

Fig. 1

a schematic representation of a team for execution

of a method according to the invention,

Fig 2

a schematic and augmented representation of two points of

laser processing and its environment,

Fig. 3

a cooking field with a cooking field plate of

ceramic hob, processed

through he procedure according the

invention, in a top view, and

Fig. 4

the cooking field in a section representation along

of an IVIV line of Figure 3.

DESCRIPTION OF AN EMBODIMENT

Figure 1 shows a non-scale schematic representation of a device for executing a method according to the invention. The procedure serves to increase a temperature conductivity of a material 10 by means of a laser 12. The material 10 is a ceramic hob, which is available under the trade name "Cleartrans". An absorption coefficient for a radiation wavelength of 1,064 nm is 3.24 cm1. As laser 12, a commercially available laser of the "ELine 20" series from ROFINSINAR Technologies, Inc. is used. In laser 12, it is a solid state laser 26 pumped by diode. Laser 12 is an Nd: YAG laser pumped by diode. The laser 12 emits a radiation wavelength of

1,064 nm. The laser 12 has a maximum average power of 11 W. The laser 12 is operated in a pulsed manner by means of a Q switch. A Gaussian beam TEM00 emitted by the laser 12 has a diffraction index M2 lt; 1’3.

A laser beam 14 emitted by the laser 12 is focused on the material 10 with a power density of 120 GW / cm2 by means of a laser optical unit 18 shown in Figure 1 in a simplified manner, but basically known to a person skilled in the art . For this, the optical laser unit 18 comprises a lens for a fivefold divergence of the laser beam 14, and a convex lens with a focal length of 100 mm., So that the laser beam 14 presents behind the optical laser unit 18 a Rayleigh length of 95 �m. Likewise, the laser optical unit 18 comprises a deflector mirror, which is directed by a galvanometer through a CAD software. A focus 17 of the laser optical unit 18 can be moved thereon relative to the material 10, with a speed 20 of 300 mm / sec. Alternatively or additionally, an entire optical laser unit can also be moved relative to a material. In another embodiment, an optical laser unit can be stationary, while moving a material. The laser beam 14 is focused on the material 10 on a diameter 28 of 13 m. By means of the pulse repetition frequency of 2 kHz, and the speed 20 of 300 mm / sec, a distance between two adjacent laser processing points 22, 24 of 150 μm results. The high power density at the laser processing point 22, 24 during a pulse leads to a structural modification of the material 10 at the laser processing point 22, 24. Due to the markedly lower power density therein, a material in an environment 32 of the laser processing point 22, 24 it remains essentially uninfluenced.

Figure 2 illustrates this situation in a schematic and enlarged representation of the material 10. The glass-ceramic material 10 is composed of an amorphous phase 16 and a crystalline phase 15. The crystalline phase 15 is present in crystallites 34, which are embedded in the phase amorphous 16. In Figure 2, the crystallites 34 are represented in a simplified manner, in the form of rhombuses, whose boundary lines each correspond to an interface 36 between the amorphous phase 16 and the crystalline phase 15. An average amount of crystallites 34 by volume it is increased at the laser processing point 22, 24 relative to the environment 32 of the laser processing point 22, 24. The crystallites 34 at the laser processing point 22, 24 are, on average, identical to the crystallites 34 in the environment 32 of the laser processing point 22, 24. This could be verified by an X-ray structural analysis. The crystallites 34 were shown to be n composed of a silicate magnesioaluminio, more precisely, by MgAl2Si412. A crystallite size is approximately 34'21 nm. Through the greater number of crystallites 34 per volume, the temperature conductivity of the laser processing point 22, 24 is increased with respect to the environment 32 of the laser processing point 22, 24.

The material 10 can be used as a household appliance component. Figure 3 shows a cooking field 38 with a household appliance component, made as a cooking field plate 40, in a non-scale top view. The cooking field plate 40 is composed of a ceramic hob. The ceramic hob is available under the trade name "Cleartrans". On a top side 41 of the cooking field plate 40, heating zones 42, 44, 46, 48 are marked in a known manner by means of a print 50. As shown by way of example for the heating zone 48, in a non-scale sectional representation of Figure 4, a heating element 52 is assigned to each of the heating zones 42, 44, 46, 48. The heating element 52 is located exactly 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, it is a resistance heating element, which joins directly to a lower side 54 of the cooking field plate 40 and, in an operating state, heats it from below. The cooking field plate 40 is processed in the area of the heating zone 48 by the procedure described above. In an interior area 30 of the cooking field plate 40, in the area of the heating zone 48 there are laser processing points 22, 24 with a mutual distance of 150 μm. The laser processing points 22, 24 are arranged both side by side in a plane parallel to a main extension plane of the cooking field plate 40, and 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 upper side 41 of the cooking field plate 40 towards the lower side 54. Thus, the temperature conductivity in the area of the area of heating 48 is increased with respect to an environment of the heating zone 48. The temperature of the lower side 54 heated by the heating element 52 is thus preferably conducted in the direction of the upper side 41. In this way, heating of the cooking field plate 40 in the environment of the heating zone 48 can be counteracted. Also, during a heating of the heating zone 48, an advantageously shorter reaction time can be achieved. The investigations showed that, at a temperature of 500º C, the conductivity of the temperature in the processed area is increased by approximately 3%. In addition, it could be demonstrated that a modification of a degree of hardness of the cooking field plate 40 is below 5%. Likewise, it was verified that a modification of a flexural strength of the cooking field plate 40 is less than 10%.

Material

12

To be

14

Laser beam

fifteen

Crystalline phase

16

Amorphous phase

17

Focus

18

Optical laser unit

Speed

22

Laser processing point

24

Laser processing point

26

Solid state laser

28

Diameter

Interior area

32

Environment

3. 4

Crystallite

36

Interface

38

Cooking field

Cooking Field Plate

41

Top side

42

Heating zone

44

Heating zone

46

Heating zone

48

Heating zone

Print

52

Heating element

54

Lower side

Claims (18)

 Claims

one.

Method for increasing a temperature conductivity of a glass ceramic material (10) by means of a laser (12), which comprises focusing a laser beam (14) on the material (10) with a power density of at least 100 kW / cm2.

2.

Method according to claim 1, characterized in that the material (10) has at least one crystalline phase (15), and an amorphous phase (16).

3.

Method according to claim 1 or 2, characterized in that the laser (12) is pulsed.

Four.

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

5.

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

6.

Method according to one of the preceding claims, characterized in that a focus (17) of an optical laser unit (18) is moved relative to the material (10) with a speed (20) of at least 100 mm / sec. .

7.

Method according to one of the preceding claims, characterized in that, between two adjacent laser processing points (22, 24), a distance of at least 50 μm is respected.

8.

Method according to one of the preceding claims, characterized in that a solid state laser is used

(26) pumped by diode.

9.

Method according to one of the preceding claims, characterized in that the laser beam (14) is focused on the material (10) on a diameter (28) of less than 30 μm.

10.

Method according to one of the preceding claims, characterized in that the laser beam (14) is generated with a wavelength of at least 355 nm and, at most, 3,000 nm.

eleven.

Home appliance component, of a glass ceramic material (10), characterized in that it comprises an interior area (30) in which the material (10) is processed by a method according to one of the claims set forth above at a laser processing point (22, 24).

12.

Home appliance component according to claim 11, characterized in that the material has an increased temperature conductivity at the laser processing point (22, 24) with respect to an environment (32) of the laser processing point (22, 24 ).

13.

Home appliance component according to claim 11 or 12, characterized in that an average number of crystallites (34) per volume at the laser processing point (22, 24) is increased with respect to an environment (32) of the processing point by laser (22, 24).

14.

Home appliance component according to claim 13, characterized in that the crystallites (34) at the processing point

by laser (22, 24) they are, on average, identical to crystallites (34) in an environment (32) of the laser processing point (22, 24).

fifteen.

Home appliance component according to one of the claims

5 11 to 14, characterized in that a distance between two adjacent laser processing points (22, 24) is at least 50 μm. 16. Domestic appliance component according to one of the claims 11 to 15, characterized in that the household appliance component is a cooking field plate. 17. Domestic appliance, comprising a component of a material (10) of ceramic hob, characterized in that the component is a household appliance component according to one of claims 11 to 16. 18. Domestic appliance according to the preceding claim, characterized in that the domestic appliance is a cooking field.