JPH04137480A - Infrared heater - Google Patents

Abstract

PURPOSE:To prevent such nonconformity as generation of dispersion of infrared radioactivity between respective heaters or a drop of infrared radioactivity, etc., while the heaters are in use by finishing the surface roughness of the external face of a hermetically sealed container made of insulation ceramic at 1.8mum or less. CONSTITUTION:The external surface of a hermetically sealed container 10 is surface-treated to be finished smoothly so that its average surface roughness is 1.8mum or less. In the case of the surface work of such a hermetically sealed container 10, as an almina tube constituting the container 10 has its property of being eroded when it is dipped into a solution of borate, it is possible, to get a desired surface roughness by controlling the temperature of this solution of borate and the dipping time of the tube in the solution. That is, as the surface roughness of the external face of the container 10 is set smooth at 1.8mum or less, it becomes difficult for foul or contaminant or dust to attach to the surface of the container 10. There is therefore, no chance to lower the penetrability of infrared and a chance to prevent such nonconformity as generation of dispersion of infrared radioactivity between respective heaters or a drop of infrared radioactivity while the heaters are in use.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an infrared heater in which a heating element is housed in a sealed container made of insulating ceramic.

(Prior Art) Infrared heaters are used, for example, to dry food, paint, and various other industrial parts.

Infrared heaters used in such fields have conventionally housed a heating element in a cylindrical sealed container made of insulating ceramic such as alumina. It is constructed by arranging heating lines made of a carbon-based conductive film such as graphite in a spiral or meandering shape on the surface of a cylindrical base made of an insulating ceramic such as.

In such an infrared heater, when electricity is applied to a heating line made of a spiral or meandering conductive film, the heating line generates heat. Therefore, the infrared rays emitted from this heating line pass through the sealed container and heat the object to be heated outside.

(Problem to be Solved by the Invention) In such an infrared heater, in order to prevent the heating element from oxidizing, the heating element is housed in a sealed container, and the inside of this sealed container is kept in a vacuum or an inert gas atmosphere. I keep it. Therefore, the sealed container must be made of a heat-resistant material that transmits infrared rays, and conventionally, it is made of an insulating ceramic such as alumina.

However, when forming a sealed container with insulating ceramic, a method is adopted in which alumina powder is pressure-molded into a predetermined mold and then baked at high temperature. The surface has fine irregularities as if it had been blasted, and the surface roughness (roughness) is 2.5□ or more.

In the case of a sealed container with such a satin-like surface, dirt, dust, and flakes tend to adhere to the outer surface of the sealed container during assembly and use, and once they have adhered, it is difficult to wipe them off as the surface becomes minutely uneven. It's difficult to take.

If dirt, dust, or debris adheres to the surface,
The above-mentioned dirt and dust are heated and the surface temperature of the sealed container becomes high, causing thermal stress that obstructs the transmission of infrared rays, causing variations in infrared radiation performance between heaters, and a significant decrease in infrared radiation power over time. Sealed containers may cause heat damage.

On the other hand, this type of infrared heater, which is used for drying food and paint, mainly uses wavelengths in the near-infrared region of 900 to 2,500 nm, and wavelengths in other regions are used as a source of light and other unnecessary heat. is consumed as.

However, recently there has been a demand for higher output power for infrared heaters, and for this purpose it is necessary to increase the irradiation efficiency in the wavelength range of 900 to 2500 no+, and the energy of wavelengths in other wavelength ranges that were wasted as mentioned above must be increased. Research is underway to effectively utilize this.

As one of these, the present inventors have been considering and researching the formation of a wavelength-selective reflective film that reflects wavelengths in the far infrared region of 280 On11 or more on the outer surface of an airtight container as an envelope. As the selective reflection film, an interference film is formed by alternately stacking a large number of thin films of silica SiO2 and titania TiO2.

Such a multilayer interference film has the effect of reflecting far-infrared energy in the wavelength range other than 900 to 250 OnIl emitted from the heating element and returning it to the heating element, and the heating element is heated by this returned energy. This has the advantage of increasing the radiation efficiency of the heating element relative to the input.

A wavelength selective reflection film made of such a multilayer interference film is obtained by applying a SiO2 solution and a TiO2 solution alternately to the outer surface of an airtight container by vapor deposition, sputtering, a dip method, or the like.

However, as mentioned above, the surface of the sealed container has a surface roughness of 2.5□ or more, as if it had been blasted, so the flow of the coating liquid during coating and forming of the wavelength-selective reflective film is prevented. Although the film is uniform, there are problems such as significant variations in film thickness and failure to achieve a desired wavelength selection effect.

Furthermore, even if such a wavelength-selective reflective film is applied, the smoothness of the outer surface cannot be improved, and dirt, dust, and flakes are likely to accumulate thereon.

Therefore, the problem of the present invention is that because the surface of the sealed container is rough, dirt, dust, and debris easily adhere to the surface, which obstructs the transmission of infrared rays and causes variations in infrared radiation performance between heaters. The infrared radiation performance deteriorates during use.

Another problem is that when forming a wavelength-selective reflective film on the surface, not only does the wavelength-selective reflective film not adhere firmly due to the rough surface of the sealed container, but also differences in film thickness occur, making it difficult to achieve the desired wavelength-selective reflection. The point is that the function cannot be obtained.

The present invention was developed based on these circumstances, and its first purpose is to make it difficult for dirt, dust, and debris to adhere to the surface of a sealed container, and to maintain a high level of infrared transmission performance. However, it is an object of the present invention to provide an infrared heater that can prevent problems such as variations in infrared radiation performance between heaters and a decrease in infrared radiation performance during use.

A second object of the present invention is that when a wavelength selective reflective film is formed on the surface, the wavelength selective reflective film is firmly attached to the surface.
The present invention aims to provide an infrared heater that can prevent film thickness differences and provide a predetermined wavelength selective reflection function.

[Structure of the Invention] (Means for Solving the Problems) The first aspect of the present invention is that the outer surface of the sealed container made of insulating ceramic is finished to a surface roughness of 1.8 or less.

The second aspect of the present invention is a sealed container made of insulating ceramic, in which a wavelength-selective reflective film is formed on the outer surface of the container, characterized in that the outer surface of the sealed container has a surface roughness of 1.8 μm or less.

(Function) According to the first aspect of the present invention, the surface condition of the outer surface of the sealed container becomes smooth, making it difficult for dirt, dust, and debris to adhere to this surface, and maintaining a high level of infrared transmission performance. This makes it possible to prevent problems such as variations in infrared radiation performance between heaters and deterioration of infrared radiation performance during use.

Further, according to the second aspect of the present invention, the outer surface of the sealed container is smooth, so when a wavelength selective reflective film is formed on this surface, the wavelength selective reflective film will firmly adhere to this surface, preventing the occurrence of a difference in film thickness. As a result, a predetermined wavelength selective reflection function can be obtained.

(Example) The present invention will be described below based on an example shown in FIGS. 1 to 3.

In the figure, reference numeral 10 denotes a sealed container, which is made of cylindrical ceramic that transmits infrared rays.

In this embodiment, the sealed container 10 has an outer diameter of 26 mm and an inner diameter of 24 mm.
It is made of a translucent alumina tube with a tube length of 220 mm.

Both ends of this cylindrical sealed container 10 are capped with caps 11 and 11.
It is hermetically sealed. These caps 11.1
1 is also made of translucent alumina, and is hermetically bonded to the end of the cylindrical sealed container 10 with solder glass containing alumina, calcia, magnesia, etc. as a main component.

A sealing tube 1 is provided in the center of these caps 11 and 11.
2.12 are hermetically joined, and these sealing tubes 12.12 are made of a heat resistant conductive metal such as niobium.

The inside of such a sealed container 10 is, for example, 1° Torr.
It is maintained in a moderately high vacuum or in an atmosphere of an inert gas such as argon, xenon, or krypton.

A heating element 2o is housed inside this sealed container 10. The heating element 2o includes, for example, an insulating cylindrical base 21, a heating line 22 made of a conductive film formed on the outer surface of the insulating base 21, and a holder attached to the end of the insulating base 21. It is composed of power receiving terminals 24 and 24.

The insulating base 21 is made of an insulating ceramic such as boron nitride, and has an inner diameter of, for example, 12a+11. Outer diameter 14av, wall thickness 1ff1Ins
It has a true cylindrical shape with a length of 20o+m. The insulating substrate 21 made of boron nitride is formed by vapor phase growth.

A band-shaped heating line 22 made of a conductive film is formed on the inner surface of such an insulating substrate 21 .

The heating line 22 made of a conductive film is made of a carbon-based material such as graphite and is formed on the outer surface of the insulating substrate 21 by vapor phase growth. The heating line 22 is formed in a spiral or meandering pattern on the outer surface of the insulating substrate 21, and the thickness of the conductive film is 80M, the band width W is 6cm, and the interval g between adjacent bands is 1
．． It is formed to have a thickness of 0 mm and an electrical resistance of 10 ohms.

Note that the heating line 22 made of such a conductive film can also be formed by a vapor phase growth method.

Power receiving terminals 24 and 24, which also serve as holders, are connected to both ends of the cylindrical insulating base 21.

The power receiving terminals 24.24 are made of conductive metal such as stainless steel, and are bonded to both ends of the cylindrical insulating base 21 via a conductive adhesive.
are electrically connected to both ends of the heat generating line 22.

Each of these power receiving terminals 24.24 has a conductive support 25.
．． 25 are connected, and these supports 25.25 are connected to the sealing tube 12.1 provided at the end of the sealed container 10.
It is joined to 2. In this example, conductive support 2
5.25 hermetically passes through the sealing tube 12.12 and is led out to the outside.

Therefore, the heating element 20 is housed concentrically within the airtight container 10.

The outer surface 10a of the airtight container 10 configured as described above has been surface-treated to have a smooth finish.

That is, if the outer surface of the airtight container 10 made of a translucent alumina tube is left as it is, the average surface roughness will be 2.5μ, as shown by the imaginary line in the enlarged cross section shown in FIG.
It is about m. In contrast, in this embodiment, as shown by the solid line in FIG. 3, the outer surface 10a of the airtight container 10 is surface-processed to have an average surface roughness of 1.8. □This is below.

The surface of the airtight container 10 has the property of being eroded when the alumina tube constituting the container is immersed in a borate solution, so the desired surface can be achieved by controlling the temperature and immersion time of the borate solution. Can you get the roughness?

The operation of the infrared heater having such a configuration will be explained.

When the conductive support 25.25 is connected to a power source, the heat generating line 22 of the insulating substrate 2 is connected via the power receiving terminal 24.24.
A current flows through the line 22, and this heating line 22 generates heat.

Therefore, since the heating line 22 emits infrared rays,
This infrared rays pass through the sealed container 10 and are emitted to the outside.

In such embodiments, the outer surface 10 of the sealed container 10
The surface roughness of a is 1.8#. I smoothed it as below, so
It becomes difficult for dirt, dust, and dust to adhere to the surface of the sealed container 10. Therefore, there is no reduction in infrared transmission performance, and it is possible to prevent problems such as variations in infrared radiation performance between heaters and a decrease in infrared radiation performance during use.

The results of experiments regarding this kind of effect will be explained.

Regarding the rated output 2KW type infrared heater having the size of the above example, the surface roughness of the sealed container 10 is 0.7□, 1.0-
Three pieces each of 11.5-11, 8-12.0□ and 2.2 μm@ were manufactured. These infrared heaters were used at 10% higher than the rated value, and a repeated energization test of 3 hours ON and 1 hour OFF was carried out at a temperature of 1150°C, and the tests were carried out in a sealed container at 0 hours, 100 hours, 300 hours, 500 hours, and 1000 hours. 10, whether the radiation power in the wavelength range of 780 to 2000 nm decreased to an unusable level, and the radiation variation among the heaters were investigated.

The results are shown in the table below.

From the above experiments, the surface roughness of the sealed container 10 is 1.8M,
It is confirmed that good characteristics can be obtained if the following regulations are followed.

Next, a second embodiment of the present invention will be described based on FIGS. 4 to 7.

In this embodiment, a wavelength selective reflective film 3 is provided on the outer surface of the sealed container 10.
The difference from the first embodiment is that 0 is formed.

Incidentally, the same members as those in the first embodiment are given the same numbers and their explanations will be omitted.

The surface roughness of the sealed container 1° made of a translucent alumina tube is 1.8μ or less, and this smooth surface 1
A wavelength selective reflection film 3o is formed on 0a. This wavelength selective reflection film 30 transmits a wavelength range of 900 to 250 On11 and reflects wavelengths other than this range, and is made of a metal oxide film with a high refractive index such as 8102, for example.
It is obtained by alternately stacking low refractive index metal oxide films such as TiO2 to form a multilayer film with a total of 12 to 24 layers.

In addition, when forming such a multilayer film 30, as described above, the alumina tube constituting the airtight container 1o is treated to have a surface roughness of 1.8□ or less by immersing it in a borate solution. After that, this alumina tube is housed in a vacuum evaporation apparatus, and SiO2 and TiO2 are alternately heated and evaporated from below onto this alumina tube in a vacuum atmosphere to form a SiO2 film and a TiO2 film, which are then fired. It will be done.

In addition, by alternately immersing the alumina tube in a SiO2 solution and a TiO2 solution, a multilayer film similar to the above 3
0 can also be formed.

In the case of the configuration of the second embodiment, the sealed container 10
Since the wavelength selective reflective film 30 is formed on the outer surface 10a of the heating element 20, the wavelength range of 900 to 2500 nm, that is, near infrared rays, emitted from the heating element 20 is transmitted to the outside, and energy in other wavelength ranges is transmitted through the wavelength selective reflective film. 30 and returned to the heating element 20. Therefore, since the heating element 20 is reheated by this feedback energy, the amount of heat generated relative to the input increases, and the radiation efficiency improves. As a result, the radiation output in the wavelength range of 900 to 2500 nm, that is, near infrared rays, is improved compared to a heater not provided with the wavelength selective reflection film 30, despite the same amount of human effort.

Moreover, in the case of this embodiment, the surface roughness of the outer surface 10a of the sealed container 10 made of insulating ceramic is finished to 1.8□ or less, so it is flat in advance, and a thin film formed on this surface is formed. The wavelength selective reflection film 30 can be evenly and reliably attached to the outer surface 10a of the sealed container 10 without causing a difference in film thickness. This prevents variations in the wavelength selective reflection function.

Regarding the second example, experimental results will be explained.

A conventional infrared heater without a wavelength-selective reflective film and a surface roughness of the outer surface 10a of the sealed container 10 of 1 as in this embodiment.
．． 8M. When the relative spectral output with an infrared heater having the wavelength-selective reflective film 30 provided on the surface 10a was investigated, the results shown in FIG. 7 were obtained.

As can be seen from FIG. 7, the infrared heater of this embodiment shown by the solid line has improved output in the wavelength range of 900 to 250 OnIg, that is, near infrared rays, and is approximately 2800 to 420 OnIg compared to this.
0 nm output has decreased. This means 2800
It can be interpreted that far infrared rays of nm or more are returned to the heating element 20 by the wavelength selective reflection film 30 and converted into near infrared rays of 900 to 2500 rv.

In addition, the surface roughness of the outer surface 10a of the sealed container 10 is set to 1.8μ.
Since the finishing was as follows, there was no difference in the thickness of the wavelength-selective reflective film 30 anywhere on the heater, and the wavelength-selective reflective film 30 did not peel off even after 1000 hours of use.

In addition, in the present invention, the configuration of the heating element 20 is not limited to the above-mentioned embodiment, and in short, it may be a nichrome wire heater, a coil heater, etc. as long as it is an electric heating element.

Therefore, the insulating base 21 is not limited to a cylindrical shape, but may also be a flat plate shape.

Further, the insulating substrate 21 is not limited to being made of boron nitrate, but may be made of insulating ceramic such as alumina or other heat-resistant material.

The heating line 22 formed on the insulating base 21 is not limited to being formed of a conductive film [Effects of the Invention] As explained above, according to the first aspect of the present invention, the heating line 22 is formed of an insulating ceramic. The surface roughness of the outer surface of the sealed container is 1.8.
Since it is finished to less than ffi, the outer surface of the sealed container is smooth, making it difficult for dirt, dust, and flakes to adhere to the surface, and maintaining a high level of infrared transmission performance. Further, it is possible to prevent problems such as variations in infrared radiation performance between heaters and a decrease in infrared radiation performance during use.

Further, according to the second aspect of the present invention, the surface roughness of the outer surface of the sealed container made of insulating ceramic is finished to 1.81 or less, and the wavelength selective reflective film is formed on this smooth surface. It is possible to firmly adhere to the film, prevent a difference in film thickness from occurring, and obtain a predetermined wavelength selective reflection function.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of an infrared heater showing a first embodiment of the present invention, Fig. 2 is a cross-sectional view taken along the line ■-■ in Fig. 1, and Fig. 3 is an enlarged cross-section of the m section in Fig. 1. 4 is a cross-sectional view of an infrared heater showing a second embodiment of the present invention, FIG. 5 is a cross-sectional view taken along line V-■ in FIG. 4, and FIG. 6 is an enlarged view of part ■ in FIG. The cross-sectional view shown in FIG. 7 is a characteristic diagram of the spectral distribution. DESCRIPTION OF SYMBOLS 10... Sealed container, 10g... Surface, 11... Cap, 12... Sealing tube, 20... Heating element, 21... Insulating base, 22...
Heat generation line, 24... Power receiving terminal, 30... Wavelength selective reflection film. Applicant's agent Patent attorney Takehiko Suzue

Claims (3)

[Claims] (1) An infrared heater in which a heating element is housed in a sealed container made of insulating ceramic, characterized in that the outer surface of the sealed container has a surface roughness of 1.8 μm or less. (2) In an infrared heater in which a heating element is housed in a sealed container made of insulating ceramic, and a wavelength-selective reflective film is formed on the outer surface of the sealed container to reflect a predetermined wavelength, the surface roughness of the outer surface of the sealed container is as follows: An infrared heater characterized in that the infrared heater is finished to a thickness of 1.8 μm or less. (3) The wavelength selective reflective film is composed of SiO_2 and TiO_2.
The infrared heater according to claim 2, characterized in that it is formed by laminating a large number of thin films alternately.