JPS6255050B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to improvements in infrared burners used for household heating, cooking, etc., and particularly aims to improve material corrosion in the combustion parts of these burners and infrared radiation efficiency. Conventional burners for cooking grilled foods include pipe burners, ceramic plate burners, and wire mesh burners made of braided heat-resistant wire. The above-mentioned pipe burner has poor energy efficiency, requires a large amount of combustion, and has many problems in practical use due to corrosion of the pipe. Furthermore, although the ceramic method is more efficient than a pipe burner, it has a slow start-up time, has poor fuel combustion characteristics, and generates unburned gases such as CO and HC, making it dangerous from a safety standpoint. In addition, the thermal expansion of the metal frame for installing the burner and the ceramics is significantly different, which causes cracks in the bonded area when the burner gets hot, which can cause gas leaks and the plate to fall.
Although corrosion resistance is excellent, fuel efficiency, start-up characteristics,
This is not practically preferable from the viewpoint of the difficulty of precision processing of incomplete combustion of unburned gas. Regarding wire mesh burners made of braided heat-resistant wires, currently available ones mainly comply with JIS standards in terms of materials.
FCH-2W, which is mainly made of iron-chromium-aluminum, is used and is extremely excellent in the initial stage of use from the viewpoint of infrared ray rise characteristics, complete combustion of fuel, and efficiency, but it has poor heat resistance and corrosion resistance. This is a problem from a practical point of view as the lifespan is short. As a method for improving wire mesh burners made of braided heat-resistant wires, a method has been proposed in which SiO ₂ or Al ₂ O ₃ is deposited on the heat-resistant wires to a thickness of about 1 μm using a vacuum evaporation method to improve the characteristics. However, from an industrial standpoint, it is difficult to put this vacuum deposition method into practical use due to cost, workability, continuous productivity, time required for deposition, adhesion strength between the heat-resistant wire and the inorganic substance, and so on. In addition, vapor-deposited inorganic substances have little adhesion strength against water or water vapor, making it difficult to put them into practical use.Also, vapor-deposited substances adhere uniformly to about 1 μm on heat-resistant wires, resulting in a small surface area, which is difficult to use from a catalytic point of view. This is a problem, and normally SiO ₂ and Al ₂ O ₃ are not catalytic materials but carrier materials for supporting catalysts. Further, when used in the normal high temperature range (700 to 800°C), corrosion resistance cannot be expected with a thickness of about 1 μm, and with a vapor deposition method, expecting a thickness of 1 μm or more will result in extremely high costs. The present invention solves these conventional drawbacks, and embodiments thereof will be described below with reference to the drawings. In FIGS. 1 to 3, 1 is a lower mold having an open stepped mixing chamber a, which is connected by a guide portion b. c.
is a half-shaped mixing tube that is perpendicular to the guide section b, and the mixing chamber a, the guide section b, and the mixing chamber c are all integrally pressed. 2 is an upper mold, an open port d facing the lower mold stepped mixing chamber a, and a half-split upper mixing pipe facing the lower mold mixing pipe c.
It has C′. 3 is a wire mesh 2 made by braiding heat-resistant wires
It is a laminated combustion body in which one or more pieces are piled up and welded locally in dots or lines around the periphery. However, if the laminated combustion body 3 is placed in the stepped mixing chamber a provided in the lower mold 1, and the upper mold 2 is placed thereon, the periphery of the lower mold is folded and the periphery of the upper mold 2 is sandwiched. The combustion body 3 has a lower mold stepped mixing chamber a and an upper mold 2.
The upper and lower surfaces are held down by the open opening d. Next, the operation will be explained. Gas is ejected from a fuel nozzle (not shown) into the mixing tubes C and C'.
At this time, 100% of the primary air required for combustion is sucked and mixed, introduced into the mixing chamber a through the guide part b, and then ejected uniformly from the back surface of the stacked combustion body 3. When this mixed gas is ignited, a thin carpet-like flame is formed on the surface of the combustion body 3. Therefore, the surface of the combustion body 3 becomes red hot and emits infrared rays. Unlike a ceramic combustion body, such a combustion body 3 is a wire gauze with a small heat capacity, so that it has a quick red-hot rise time and a high red-hot degree. Therefore, it becomes possible to shorten the cooking time in practical terms. As detailed above, the wire mesh combustion body has extremely excellent characteristics at the initial stage of use, but when actually used for cooking, () the wire mesh combustion body is subjected to high-temperature heat cycles of 350 to 850°C and suffers oxidative corrosion. ,()
During cooking, the burning part of the wire gauze is covered with carbonaceous residue due to the scattering of the cooked food, resulting in accelerated carburization corrosion. The decomposition of the SH groups in the fuel and the sulfur corrosion caused by the sulfur content in the fuel are accelerated. Even if iron-chromium steel is used as a material, it is difficult to avoid significant intergranular corrosion due to factors such as the promotion of steam oxidation due to the generation of water during combustion. Despite having these characteristics, there are many problems from the viewpoint of lifespan. In order to avoid such grain boundary corrosion, nickel-
Chromium steel, iron-chromium steel, iron-nickel-chromium-silica-manganese steel, iron-chromium-aluminum steel, iron-nickel-chromium-silica-manganese-titanium steel, etc. in terms of oxidation resistance, heat resistance, and corrosion resistance. However, it was difficult to solve the essential problem of intergranular corrosion, and improving the corrosion resistance from the viewpoint of the material caused problems in wire drawing. Processing and processing of wire mesh made by braiding thin wires becomes difficult, making it impossible to put it to practical use. In order to solve the various problems mentioned above and provide a stable infrared burner with a long lifespan, the present inventors used an alloy material with heat resistance, corrosion resistance, and catalytic ability in the main part of the combustion part, and a heat-resistant inorganic material. It is characterized in that it is constructed using a composite material consisting of a compound (ceramics) coated by thermal spray coating on the surface of a base material and a welded coating of these substances. The present invention will be described in detail below. (A) Wire mesh base material that constitutes the combustion body. The wire mesh base material constituting the combustion body of the present invention is selected from ordinary steel, enamel, etc. by taking into consideration the combustion temperature, atmosphere, usage conditions, etc. during use, and judging from the shape, expansion coefficient, heat resistance, economic efficiency, etc. of the base material. Suitable materials include stainless steel, nickel-chrome steel, nickel-chrome-aluminum steel, and stainless steel. (B) Shape of the substrate. Taking into consideration the material of the base material, it is also possible to use a lath wire mesh shape, a punched metal shape, or a shape obtained by rolling a lath wire mesh. (C) Surface treatment of base material. Once the desired base material and shape have been determined, surface enlarging treatment and surface activation treatment are performed by sandblasting, chemical treatment, etc. as pretreatment before welding. (D) Welding method. Welding methods include arc spraying, flame spraying, etc., but plasma spraying is preferred in order to achieve the purpose of the present invention, because the bonding layer between the base material and the sprayed powder is metallurgically bonded, and there is no intermetallic bonding. If the bonding layer is not such that a compound can be obtained, the bonding strength will be weak in methods other than plasma spraying because the thermal cycle usage conditions and usage environment conditions are severe. In addition, the plasma conditions during plasma spraying are argon gas-hydrogen,
Or argon gas-helium system is preferable,
Particularly good results were obtained with the argon gas-helium gas system, and the preferable thermal spraying conditions are secondary output conditions of 30 V or more DC and 600 A or more. This condition is judged especially from the viewpoint of lifespan, and although plasma spraying is possible at 30V and 600A or less, below these conditions the lifespan of the sprayed part will be shortened under the cooking environment conditions of thermal cycle use. (E) Type of thermal spray powder. An effective thermal spray powder for achieving the purpose of the present invention is one consisting mainly of Al ₂ O ₃ and particles of Ti or oxides of Ti and Cr. Examples of these powders will be described in detail later, but the most effective powders include Cr ₂ O ₃ , MoO ₂ and TiO ₂ . Note that alloys are included in metals. These thermal spray powders are selected based on the composition of the base material, the shape of the base material, the environmental conditions of use, etc., and in particular the type of powder from the viewpoint of the coefficient of thermal expansion between the base material and the thermal spray powder, heat resistance, corrosion resistance, and catalytic ability. Determine particle size. (F) Particle size of thermal spray powder. In the present invention, the powder is thermally sprayed onto the surface of the wire mesh or the surface of punched metal, but since the mesh of the wire mesh and the holes of the punching are small, thermal spray powder of normal particle size cannot be used, and particles of about 1 to 65 μm are preferable. . For example, if the particle size of the powder is too large, the openings of the wire mesh will become uneven, resulting in uneven combustion balance and a large amount of unburned gas being generated. I have to use something more detailed. However, if the thickness is less than 1 μm, the spray powder will not enter the plasma torch during thermal spraying, resulting in a marked decrease in thermal spraying efficiency, resulting in uneconomical results. Therefore, if the particle size is about 1 to 65 μm, such inconvenience will not occur. (G) Wire diameter of wire mesh. The wire diameter and mesh of the wire mesh 3 shown in the figure greatly affect the processability and combustion characteristics of thermal spraying of the heat-resistant thermal spraying material. Figure 4 is a plot of the mesh size and wire diameter of the wire mesh 3 of the infrared burner in Figures 1 to 3, and the time it takes for the wire mesh 3 to be heated to 50% red color after the infrared burner is ignited. Room temperature 26℃
It was measured with As a comparison, we plotted a ceramic infrared heater, and plotted the time for the ceramic heater to become red hot for about 30% of the total. Ceramic heaters took even longer to reach 50% red heat. In Fig. 4, A is drawn from iron-chromium-aluminum steel (JIS FCH-WZ) and braided into mesh with each wire diameter. B in Fig. 4
After sandblasting these wire meshes using 60 mesh alumina grid, as will be described in detail later, first thermal spray powder of Ni-Cr was sprayed on the surface of the wire meshes to an extent of 8 to 10 μm, and then Al 2 O ₃ 97% Al ₂ O 3 was applied. ,
A powder consisting of 3% TiO ₂ is thermally sprayed to the extent of 5 to 10μ,
A thermal spray coating of thermal spray material was applied to the surface of the wire mesh. From this experimental result, in order to achieve the purpose of the present invention, the wire diameter is preferably 0.2 to 0.5 mmφ and 40 to 15 meshes, and wire diameters of 0.2 mmφ or less may cause deformation of the wire mesh when using a burner during sandblasting or thermal spraying. Clogging occurs during thermal spraying, and the wire diameter is 0.5mmφ.
In the above case, the thickness of the wire mesh body increases, the heat capacity of the wire mesh body increases, and the time until it becomes red hot increases, and the combustion characteristics of the fuel gas worsen, resulting in the production of hydrocarbons (HC), carbon monoxide (CO), etc. This is not preferable because it involves the generation of unburned gas such as. It can be seen from FIG. 4 that the infrared burner of the present invention has significantly better start-up characteristics than the currently commercially available ceramic infrared burners, and when ceramics are sprayed on heat-resistant iron-chromium steel, the infrared start-up characteristics are as good as those of wire mesh. At the same time, the service life is improved by about 20 to 30 times compared to iron-chromium steel, as will be explained in detail later. The reason why the rise characteristics of the thermally sprayed ceramics shown in the figure are better than that of wire mesh only is that the sandblasting surface treatment activates and grinds the surface, reducing the wire diameter and heat capacity of the wire mesh as a whole. In addition to improved brightness, the entire wire mesh is coated with Ni-Cr and
This is because the thermal spray coating of Al ₂ O ₃ -TiO ₂ increased the surface area of the entire wire mesh by about 10 times (as measured by the BET method) and promoted the catalytic combustion effect in the wire mesh section. (H) How to configure wire mesh 3. An enlarged configuration diagram of the wire mesh 3 is shown in FIG. 5, but the wire mesh of the present invention usually consists of two or three layers, and it is preferable to overlap three wire meshes of different sizes rather than overlapping wire meshes of the same size. has the best combustion effect. Wire mesh a and wire mesh c in Fig. 5 have the same wire diameter and the same mesh, but wire mesh b is different from wire mesh a,
Combustion characteristics are improved by using a wire with a slightly larger diameter and mesh than c. The reason for this is that it has a buffering effect against linear expansion during heat cycle use and rapid heating and cooling of the wire mesh section, which reduces deformation of the combustion body and expands the combustion area to achieve more complete combustion. that it might be done. It is also effective in making the combustion temperature uniform and increasing the lifespan of the combustion part. In addition, the wire mesh c located in the combustion gas area in Fig. 5 is severely corroded by sulfur and water vapor, and the composition of the combustion part of Fe-Cr-Al and Fe-Mn stainless steel is not preferable. Al ₂ O ₃ thermal spraying, which is resistant to the atmosphere of
Al ₂ O ₃ serves as a hydrocarbon decomposition catalyst in thermal spray material
Adding small amounts of Cr ₂ O ₃ and TiO ₂ has a significant effect.
A small amount of such a metal oxide as a catalyst is mixed with Al ₂ O ₃ , but since the thermal spray adhesion efficiency during thermal spraying is higher than that of Al ₂ O ₃ , even a small amount added has a large effect. In addition, since the wire mesh a located in the red _- hot region becomes an oxidizing atmosphere, the life of stainless steel and _{NiCr- based} materials is short _. It has been found that the combustion characteristics are significantly improved when the content is several percent. The present inventors supported and coated the Al ₂ O ₃ spray coating part of the combustion body part a with 0.2 wt% of platinum catalyst based on the weight of Al ₂ O ₃ , but several % of platinum catalyst was added to the Al ₂ O ₃ powder. _{Cr2O3 _}
Even when Al ₂ O ₃ mixed with powder and TiO ₂ powder was thermally sprayed, good combustion exhaust gas characteristics were obtained that were almost the same as those on which platinum was supported. (I) Method of composing the sprayed layer during thermal spraying. FIG. 6 shows thermal spraying material powders 33 and 34 on an active surface 32 whose surface has been activated by sandblasting, and the pores in the surface layer of the thermally sprayed layer are sealed (35). The method of constructing each sprayed layer is shown in a, b, c, and d. FIG. 6a shows a method in which a thermal spraying material 33 is directly sprayed onto the active surface 32 of a base material 31. In FIG. In this case, it is judged from the expansion coefficient of the base material and the sprayed material, and if the temperature in the practical environment is relatively low, then
It is also possible to thermally spray Al ₂ O ₃ directly onto the active surface 32 of the base material, but if the operating temperature is in the high temperature range of 800 to 950°C, the expansion coefficient will first be close to that of the base material, as shown in Figure 6b. It is also possible to thermally spray Ni-Cr, which is a heat-resistant alloy, and the alloy thermal spray material 33, and then thermally spray the Al ₂ O ₃ 34, which has excellent heat resistance. Further, as shown in FIG. 6c, it is also possible to thoroughly mix alloy powder with a relatively large coefficient of expansion and Al ₂ O ₃ with a relatively low coefficient of expansion before thermal spraying, and then perform the mixed thermal spraying during thermal spraying. In addition, when the base material 31 is made of common steel, which has many problems from the viewpoint of corrosion resistance, for example, as shown in FIG. 6d,
Even if the sprayed layers 32 to 34 are included, these sprayed layers usually have 10 to 20% porosity.
Under corrosive environmental conditions such as salt and sulfur dioxide gas, corrosive substances infiltrate through these voids and corrode the base material. As a method for sealing the voids in this sprayed layer, post-treatment coatings such as 3-45wt% water glass, silica sol, enamel frit, glass powder alumina sol, silicone resin, etc. synthesized from acid-resistant and heat-resistant raw materials are effective. It was hot. This method involves spraying the above-mentioned sealant at a concentration of 3 to 45 wt% onto the sprayed area after the spraying is completed.
When the material is impregnated or adhered and water is removed at a temperature of 120° C. or higher, the openings 35 of the base material are sealed with a sealing agent, thereby significantly improving corrosion resistance. (J) Thickness of sprayed layer. The thickness of the sprayed layer varies depending on the particle size and material of the powder used, but if it is usually less than 5μ, the surface coverage of the base material will be less than 90% and effective spraying cannot be expected. Therefore, the thickness is preferably 5μ or more and 200μ or less. Furthermore, the most economical and effective thickness of the sprayed layer is 30 to 80μ. If the spray thickness is 200 μm or more, the linear expansion of the combustion zone will change significantly, causing cracks to occur due to thermal cycles and the constituent materials of the weld layer to fall off. Furthermore, if it is deposited too thickly, not only will the cost of thermal spraying increase, but it will also clog the wire mesh and change the combustion balance. (K) Surface area of spray coated surface. The surface area of the wire mesh in the combustion section varies depending on the material, wire diameter mesh size, etc., but is usually 0.01 to 0.005 m ² /g.
That's about it. When a thermal spray material is coated with plasma spraying, the surface area becomes significantly large, approximately 0.01 to 0.5 m ² /g, depending on the thermal spray powder material and thermal spraying conditions, and the infrared radiation effect and catalytic effect during combustion are enhanced. Conceivable. Next, examples will be given and explained. Specific Examples A thermal spray coating having typical heat resistance, oxidation resistance, and catalytic ability is applied to the wire mesh used in the infrared combustion section 3 of the infrared burner explained in FIGS. 1 to 3, and various coatings are applied.
Evaluations were conducted from various viewpoints, and the results are shown in the table below.
Column A indicates the powder material forming the sprayed layer, and column B
The column shows the material of the base material, the C column shows the oxidation weight gain, the D column shows the durability of accelerated corrosion test, the E column shows the weight increase (mg) in 400 ppm gas, and the F column shows the catalyst performance. .

[Table] In the table, as the surface treatment for Examples 3 to 6, the wire mesh was sufficiently degreased with trichloride, and then the surface was sandblasted with a 60-mesh alumina grid to sufficiently enlarge the surface. treatment and surface activation treatment. After washing with water and drying, thermal spraying was performed. The spraying conditions were as follows: using an 80KW output plasma spraying device (Plasma Dyne 80KW), applying a voltage of 45 to 100V, which varies depending on the powder conditions, and applying a current of 45 to 100V.
Thermal spray coating was carried out under plasma conditions consisting of argon-helium gas by flowing 600 to 1200 A.
The combinations of thermal spraying materials in Examples 2 to 6 are determined by taking into consideration the characteristics of the base material and the thermal spraying powder, and particularly considering the overall coefficient of linear expansion, heat resistance, oxidation resistance, various corrosion resistances, catalytic ability, infrared burner efficiency, etc. From this point of view, we selected typical composition combinations. In addition, in column A
MgO, CaO, _SiO2 are not shown but are present in the powder as minor components. Also, K,
Na, Mn, Cu, C, etc. are also spectrally detected as trace components, but they are not shown because they do not particularly participate in the intended effect. The final thickness of the sprayed layer was 40 to 60μ. The configuration of the sprayed layer in Specific Example 2 has the configuration shown in FIG. 6a, and the specific example 7 has the configuration shown in FIG. 6c, and both specific examples 2 can be completed with one thermal spraying. In specific examples 3 to 5, the sprayed layer is composed of two layers as shown in FIG. 6b. The first layer is made of iron-based alloys with a relatively large expansion coefficient and with sufficient consideration given to the material and shape of the base material, in order to achieve a more complete interlayer bond between the metal of the base material and the ceramic layer forming the surface layer. Approximately 10 to 20μ of a metal oxide consisting of Ni-Cr alloy and MoO ₂ , which were optimal for forming an intermediate layer with ceramics, was sprayed onto the first layer. The second layer is made of a heat-resistant inorganic compound (ceramics) that is most effective in terms of properties such as heat resistance, oxidation resistance, corrosion resistance, and catalytic ability when used in high-temperature thermal cycles.
It was sprayed to a thickness of ~60μ. Specific example 6 uses the sample of specific example 5 in the table and sprays it with a 10% water glass solution synthesized from heat-resistant and acid-resistant glass powder (for example, borosilicate glass) to improve the corrosion resistance of the base material. The water was then dried and the sealing process was carried out. Next, we will explain the effect of the thermal spray coating layer.
The oxidation weight gain in column C of the table is determined by first heating a test wire mesh with a size of 30 x 20 mm at 1200°C for 3 hours, and then measuring the weight after allowing it to cool to room temperature. Based on the weight at the first heat cycle, A cycle of heating at 1200°C for 3 hours and cooling to room temperature was repeated 15 times, and the weight increase at the 15th cycle was compared, and the result was as shown in column C. The durability test of the accelerated corrosion test in Column D was carried out by attaching a mixture of coal tar and common salt to the test wire mesh at 850°C.
The graph shows the weight increase due to oxidation corrosion, intergranular corrosion, etc. that occur during heating for 30 minutes.
The display method in column D is for current products (Fe-Cr-Al steel = JIS
The durability of FCH-W ₂ ) was calculated by proportional calculation based on the weight increase, assuming that the corrosion of FCH-W 2 ) was 1. That is, assuming that the corrosion durability of the specific example is 1, specific example 6 has 32 times the durability. For the weight increase test in SO ₂ gas in column E of the table, the same test wire used in column C was filled into a JARI (Japan Automobile Research Institute) type catalytic performance tester, and 400 ppm SO ₂ was added to the air using Chiaria gas. were mixed and flowed at 850°C for 3 hours at an SV value (space flow velocity) of 5000H ^-1 to examine the weight increase before and after the test. In addition, the catalytic performance in column F of the table was not required for this type of infrared burner in the past, but with the spread of aluminum sash, the housing environment has changed, the airtightness of the residence has been significantly improved, and the natural Ventilation frequency was significantly reduced. For this reason, the problem of CO and HC generated during cooking is greater than ever before, and in particular, conventional ceramic burners not only have poor infrared efficiency but also lack the ability to oxidize CH ₄ and CO, so their lifespan as a burner is long. is dangerous from a safety perspective. In the present invention, special consideration has been given to improving the infrared efficiency of the infrared burner and at the same time improving the generation of unburned gas such as CH ₄ and CO gas. However, if the wire mesh part has too much catalytic effect, such as a platinum catalyst, catalytic oxidation will proceed at low temperatures and the efficiency of the infrared burner will decrease. It was designed so that unburned gas could be purified while simultaneously emitting infrared rays. The test method for catalytic ability was to fill the tester of the JARI method described above with each of the wire meshes of Examples 1 to 6,
HC uses methane gas at 100ppm, CO uses CO gas
The temperature at which each gas is 100% catalytically purified at a space flow rate of 5000 H ^-1 when mixed in 100 ppm air is shown. In Example 1, even at 840°C, it was not possible to completely purify 100% of both CO and CH ₄ . As described in detail above, the infrared burner has the combustion section 3 and the main bodies 11 and 12, which are made of a composite material made of a thermal spray coating of an alloy material having heat resistance, corrosion resistance, and catalytic ability, and a heat-resistant inorganic compound (ceramics). Compared to conventional infrared burners made only of metal or burners made only of ceramics, significant improvements have been observed in terms of infrared efficiency, exhaust gas characteristics, corrosion life, etc. It is possible to use cheaper base materials than before, and it is also possible to further reduce the thickness of the base material and the wire diameter, so even if thermal spray coating is performed, the total cost will not be that high. It was found that there was no problem, and a great effect of industrial value was observed.

[Brief explanation of the drawing]

Fig. 1 is a bottom view of the infrared burner, Fig. 2 is a sectional view taken along line A-A' in Fig. 1, Fig. 3 is an exploded plan view, Fig. 4 is a characteristic diagram of rising to a red-hot state, and Fig. 5 is a wire mesh. FIGS. 6a to 6d are schematic sectional views showing the relationship between the base material and the sprayed layer in the embodiment of the present invention. 3... Combustion body.

Claims (1)

[Claims] 1. An infrared burner characterized in that a welding layer containing Al ₂ O ₃ as a main component and TiO ₂ as an additional component is formed on the surface of a metal base material. 2. The infrared burner according to claim 1, characterized in that the welding layer is formed mainly of Al ₂ O ₃ and TiO ₂ and Cr ₂ O ₃ are added thereto. 3. The infrared burner according to claim 1 or 2, characterized in that a Ni-Cr alloy or MoO ₂ layer is formed between the metal base material and the welding layer.