JPH0130076B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an infrared drying device, and particularly to an infrared drying device used for drying ceramics and plaster molds thereof. The general drying method for ceramic products and plaster molds is hot air drying using conduction convection, but in recent years, methods such as microwave drying, vacuum drying, and infrared drying have been developed and are attracting attention. In normal hot air drying, the object to be heated is heated, and as a result, water vapor is dissipated from the surface and the object is dried. There are three elements to heat a substance: conduction, convection and radiation, and heating can be achieved by one or a combination of these elements. Hot air drying is heating drying using conduction convection, and uses air water vapor or the like as a medium, so there is a large energy loss due to heating of the inactive portion of the medium. Heating by radiation is efficient because it is directly absorbed by the object to be dried. For heating methods that use radiation, it is necessary to consider materials with good radiation efficiency. Generally, a quartz tube is used, but since the radiation efficiency is poor in a long wavelength region of 5 μm or more, that is, in a far-infrared wavelength region, it is desirable to select and use another suitable far-infrared radiation material. The shapes of conventional infrared heating elements and reflectors are straight sheathed tubes and round mirrors, and they were developed for full-surface heating for drying paint, etc.
It is difficult to uniformly irradiate round, round, deep objects such as ceramics, and for heating, and there is a drawback that they are easily cut, distorted, etc. Note that in order to increase drying efficiency, it may be desirable to use radiation and localized air blowing together, but this is rarely used for purposes other than general exhaust equipment. SUMMARY OF THE INVENTION An object of the present invention is to provide a far-infrared drying apparatus for ceramics, etc., using a radiating element that does not suffer from the above-mentioned drawbacks. The radiating element in the device of the present invention is molded from a thermal shock-resistant high-density material such as zircon-based, zircon-ferrite-based, cordierite-based, petalite-based, etc., and has a hollow cross section with a closed curve shape such as an annular shape, and a heating element is inserted into the hollow interior. . As a result of comparative measurements, the above-mentioned materials have better radiation characteristics in the far-infrared region than quartz glass tubes, but have significantly lower characteristics in the near-infrared region. It has been confirmed that ceramics and the like have good absorption characteristics in the far infrared region, and are therefore excellent as radiating elements for drying. Furthermore, by using a closed curve shape such as an annular shape, uneven heating will not occur, and the occurrence of defects will be significantly reduced. The drying device according to the present invention includes an aluminum reflector plate that is combined with the above-mentioned radiating element to perform unidirectional radiation, a blower tube in the center of the reflector plate, and a blower combined with the blower tube. Regarding the reflective properties of the reflector material, an aluminum plate is superior to a stainless steel plate, and commercially available aluminum foil is an inexpensive and effective reflective material. As a result of drying experiments, it was found that the combination of the radiation from the above-mentioned radiating element and a gentle breeze is the most effective in terms of energy. Embodiments and drawings illustrating the present invention will be described. First, the spectral radiation characteristics of various ceramic materials were tested. Zircon base material (ZrSiO ₄ 60%, 40% clay) as zircon type, 60% petalite, 40% frog's eye clay as petalite type, 50% cordierite siamotsu as cordierite type, 40% clay, 10% magnesite, As a zircon-ferrite system, 70% zircon base material and 30% ferrite are made into a tube shape with a diameter of 5 mm and a length of 25 mm. 1200
It was fired at ~1250°C and heated to 600-800°C, and its radiation properties were recorded and compared with those of a quartz tube and a glass tube. As a result, quartz tubes and glass tubes tend to have strong radiation characteristics in the near-infrared region with wavelengths of 5 μm or less. On the other hand, all of the samples have strong radiation characteristics in the far-infrared region of 5 μm or more, and weak radiation characteristics in the near-infrared region. Therefore, it has become clear that zircon-based, zircon-ferrite-based, petalite-based, and cordierite-based materials are more suitable for heating by far-infrared radiation than quartz tubes and glass tubes. . Furthermore, when a quartz glass tube is coated with the above-mentioned ceramic material, it has almost the same radiation characteristics in the far-infrared region of 5 μm or more, which is superior to that of the quartz glass tube, and it has better radiation characteristics in the near-infrared region. has stronger radiation characteristics than a tube made of a single material, and its value is between that of a tube made of a single material and a quartz glass tube. Therefore, if near-infrared radiation can also be used, a quartz glass tube whose outer surface is coated with a ceramic material can be effectively used. Second, the reflective properties of the mirror material were tested. In order to utilize radiation effectively, materials with high reflectance over the entire wavelength range are required. The materials tested were a standard aluminum-deposited mirror, commercially available aluminum foil for shoe wrapping, an aluminum plate, a stainless steel plate, an anodized aluminum plate, and an aluminum plate for building materials. Among the reflectance measurement samples, the aluminum foil for cushioning showed extremely good reflection characteristics in all wavelength ranges, almost the same as standard mirrors. Stainless steel sheets, which are commonly used, are particularly inferior to aluminum in the near-infrared region. Alumite processing and aluminum plates for building materials are extremely affected by the resin processing on their surfaces, and cannot be used as they are as reflectors. Third, the absorption and reflection properties of clay and gypsum were tested. The absorption properties were tested using the KBr tablet method, and the reflection properties were tested using the reflection method. The trends are similar for both materials, with long wavelengths of 5~
Absorption rate exists on the side of 6 μm or more. Therefore, long wavelength heating is effective. The reflection characteristics of both materials are approximately equal over all wavelengths, but gypsum has a prominent reflection peak around 9 μm. FIG. 1 shows an example of molding a flowerpot 2 in a plaster mold 1 as an example of a ceramic product to be dried. Usually, the flowerpot 2, which has been dried with hot air to shrink and solidify to some extent, is removed from the mold 1 and fired. As a result of a test to quantitatively understand this situation, it was found that dehydration from the pot itself followed a nearly linear process, with the plaster mold absorbing a significantly large amount of water at the beginning, and the mold absorbing water due to the formation of voids. I learned that it decreases. The demolding time could be determined from the water absorption characteristics of the plaster mold. FIGS. 2A and 2B show an annular far-infrared radiating element used in the apparatus of the present invention, and FIG. 3 shows a box-type dryer using this radiating element. The radiating element 3 shown in FIG. 2 has a shape in which a nichrome wire heating element 5 is housed in a cordierite toric body 4, and as shown in FIG. 3, it is covered with a reflecting plate 6.
A blower tube 7 is passed through the center of the reflector 6 so that air from a blower 8 can be sent to the item 10 to be dried. The air blower 8 can adjust the amount of circulating air, and the radiating element 3 can also be switched in strength. In the illustrated example, the drying chamber 11 is of a closed type and has a heat insulating wall 13 having a reflective plate 12 on its inner surface. The indoor exhaust gas is exhausted during the initial period when a large amount of water vapor is generated, and is connected to the blower 8 via the circulation path 14 as required. As a result of comparative experiments using a straight pipe and a torus as a radiating element, we found that the difference in temperature between the top and bottom of a straight pipe is significantly large, while that of a torus is relatively uniform. I learned that it gets heated. As for air blowing during drying, we learned that the combination of radiation and light wind produces the maximum amount of evaporated water and is the most advantageous in terms of energy. If the air volume is large, only the bottom part tends to dry prematurely, resulting in defective products. As mentioned above, since the amount of water absorbed by the plaster mold is extremely large in the early stage of drying, it is desirable to dry the plaster mold every time it is demolded. The dryer shown in FIG. 3 shows a case where the drying chamber 11 is supported by a support shaft (not shown) in a variable angle. The matters revealed by the present invention are as follows. Any radiating element in which a heating element is placed in a tube made of fired heat-resistant ceramic material has a higher specific energy intensity in the far infrared region than quartz glass, and is more advantageous than a quartz glass tube in terms of energy. The cordierite type had the best radiation characteristics in the normal usage range of surface temperature 600-800°C.
However, other ceramic materials can also be used. Aluminum is the best in terms of reflective properties, and commercially available aluminum foil is inexpensive and highly effective. For drying items with circular tops such as flower pots, toroidal radiating elements are significantly more effective than straight tubes in terms of uniform heating. The combination of radiation and air blowing is most effective in terms of energy. However, a light wind speed is good, and excessive wind speed will cause disadvantages. Radiant drying is superior when comparing hot air and radiant drying. With conventional hot air drying, 2 to 2 times a day for an 8-inch pot
Although the mold could only be demolded three times, the time required for demolding by radiation drying was about 30 minutes, and even if the mold drying time of about 10 minutes was added, extremely efficient drying could be achieved. In addition, in order to make the effects of the device of the present invention more clear, the experimental results regarding the water loss rate of clay due to hot air and infrared radiation drying using the device shown in Figure 3 are summarized in Table 1 and Figure 4 below. This will be illustrated in detail with a diagram. Regarding this experiment, in order to investigate how the drying speed differs when the product is dried using hot air and radiation using the same amount of energy, a confectionery pot with a diameter of 26 cm was molded using a mechanical potter's wheel. Immediately after demolding (moisture 24 to 25%), the mold was placed in the apparatus shown in Figure 3, and experiments were conducted with the various combinations shown in Table 1 using the same power of 300W for hot air and radiation, and the results are shown in Figure 4. This is shown in a diagram. As is clear from the above explanation, the apparatus of the present invention can effectively dry the material to be dried by radiation and air blowing, and can independently control radiation and air blowing. It is ideal for drying that requires complex and delicate control.

【table】

【table】 [Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a molded flowerpot as an example of an item to be dried, FIG. 2A is a plan view of a toric radiating element used in the apparatus of the present invention, and FIG.
FIG. 3 is an enlarged sectional view taken along line B, FIG. 3 is a sectional view of the drying apparatus of the present invention, and FIG. 4 is a diagram showing a comparison of water reduction rates due to radiation and hot air. 1... Gypsum mold, 2... Flower pot, 3... Radiating element, 4... Toric body, 5... Heat generating element, 6... Reflection plate, 7... Blower tube, 8... Blower, 10... Object to be dried, 11...Drying chamber, 12...Reflector, 13...
…Insulation walls.

Claims (1)

[Claims] 1 A drying chamber 11 consisting of a heat insulating wall 13, a blower 8 equipped with a blower tube 7 inserted into the drying chamber 11, and a zircon system attached to the outside of the blower tube 7 of the blower 8. , an annular far-infrared radiating element 3 in which a heating element 5 is accommodated in a toric body 4 with a hollow cross section and made of a thermal shock-resistant material such as zircon-ferrite, cordierite, or petalite, and a blower tube of the blower 8. A far-infrared drying device for ceramics, plaster molds, etc., which comprises a reflector 6 attached to a mirror 7 and a circulation path 14 communicating the blower 8 and a drying chamber 11.