JP2004293900A - Fluidized bed type heat treatment furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluidized bed type heat treatment furnace being more compact and capable of performing higher quality heat treatment when compared with a conventional fluidized bed furnace. <P>SOLUTION: This fluidized bed type heat treatment furnace 3 is constituted in such a way that the inside of a furnace body 39 is filled with a powder and granular material, which is heated by heated air blown into the inside of the furnace body 39 through a heated air pipe 14 and flows to form a fluidized bed 13, and a metal-made workpiece 11 is heat-treated in the fluidized bed 13. In this fluidized bed type heat treatment furnace 3, flow velocity of heated air for letting the powder and granular material flow is 0.05 to 0.2 m/sec, the powder and granular material has apparent specific gravity of 1.6 to 1.8, and substantially spherical bodies having diameter of 400 to 600 μmϕ occupy 60% or more. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluidized bed heat treatment furnace used for heat treatment of metals.
[0002]
2. Description of the Related Art It is generally known that mechanical properties can be improved by heat-treating a metal to change the composition structure inside the metal. For example, in an alloy (AC4A, AC4C, AC4CH, AC4D, etc.) obtained by adding a small amount of magnesium (Mg) to an aluminum (Al) -silicon (Si) -based alloy, a non-equilibrium phase crystallized during solidification by a solution treatment is heated to a high temperature. After forming a solid solution at room temperature, a uniform solid solution is obtained at room temperature by water cooling, and then maintained at a relatively low temperature by artificial aging treatment to cause precipitation hardening by an intermediate precipitation phase, thereby improving mechanical properties. I can plan.
Conventionally, for such a solution treatment and an aging treatment, an atmosphere furnace such as a tunnel furnace using air as a heat medium has been used. However, in an atmospheric furnace, the temperature rise rate to the solution temperature is slow and it takes time to raise the temperature.Moreover, the processing apparatus becomes large, and the operation operation is complicated and requires a lot of manpower. There is a problem that a large amount of heat energy is required to maintain the temperature. In order to solve the problems of the conventional atmosphere furnace, the present applicant has developed a new furnace in which a fluidized bed is formed and a workpiece is heat-treated therein, and disclosed in Patent Documents 1 and 2. did.
[0004]
[Patent Document 1]
JP 2002-54880 A [Patent Document 2]
JP, 2002-107064, A
The present invention is based on the technical idea relating to the heat treatment furnace disclosed in Patent Documents 1 and 2, and is a new advanced creation. The fluidized bed furnaces disclosed in Patent Literature 1 and Patent Literature 2 achieve a certain level of goals such as compactness, space saving, reduction of heat energy loss, and full automation of operation, respectively, with respect to the atmosphere furnace. However, the present invention has been made with the aim of further pursuing compactness and obtaining a fluidized bed furnace capable of performing higher quality heat treatment.
[0006]
That is, according to the present invention, a furnace is filled with particles, and the particles are heated by hot air blown into the furnace and flow to form a fluidized bed. A furnace in which a workpiece made of metal is heat-treated in a fluidized bed. Hot air has a flow velocity of 0.05 to 0.2 m / sec, and powder and granules have an apparent specific gravity of 1.6 to 1.8. And a substantially spherical body having a diameter of 400 to 600 μmφ occupies 60% or more.
[0007] In the present invention, it is preferable that the granular material contains silicon dioxide as a main component.
[0008] According to the fluidized bed heat treatment furnace of the present invention, the expansion rate of the fluidized bed can be reduced to 120% or less. Further, it is possible to make the height of the free board 2.5 times or less the filling height of the granular material.
The fluidized-bed heat treatment furnace of the present invention is suitably used when the workpiece is a vehicle wheel.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be specifically described. However, the present invention should not be construed as being limited to the following description, and unless departing from the scope of the present invention. Various changes, modifications, and improvements can be made based on the knowledge of those skilled in the art.
The fluidized bed heat treatment furnace of the present invention is used for heat treatment of a workpiece made of metal. The metal is preferably an Al alloy, but is not limited as long as a certain effect can be obtained by performing a heat treatment. Examples thereof include an Mg alloy, an iron alloy such as carbon steel and cast iron, and titanium (Ti). ) Alloys and others are also included.
Preferable examples of the heat treatment include a solution treatment and an aging treatment, but the treatment is not limited as long as the treatment can produce a certain effect on the metal.
Specific examples of the metal product as the work piece include a vehicle wheel. However, the metal product is not limited as long as a certain effect such as improvement of mechanical properties is expected by heat treatment. Other parts include vehicle suspension parts, body chassis parts, transmission mechanical parts such as gears and cams, aerospace industry structural parts, and others. Particularly, the vehicle wheel is significant in that the effect of substantially improving the mechanical properties can be reduced to a reduced thickness by heat treatment. By heat treatment, even if the thickness becomes thinner, the same mechanical properties as when no heat treatment is performed, for example, tensile strength, elongation, etc. can be maintained, so that in addition to the use of light alloy materials, further weight reduction is achieved. . A lightweight vehicle wheel is a product that is desired by automobile manufacturers or consumers who are required to improve fuel efficiency in order to reduce environmental load.
The fluidized bed type heat treatment furnace of the present invention is a heat treatment furnace in which powder is filled in a furnace, and the powder is heated by hot air blown into the furnace and flows to form a fluidized bed. . The fluidized bed is formed by uniformly mixing powders and granules, and has better heat transfer efficiency to an atmosphere furnace using air as a heat medium. In addition, since it has the features described below, it is more compact than a conventional fluidized bed type heat treatment furnace, and the fluidized state of the fluidized bed can be substantially uniform, so that the quality of the heat treatment can be improved. .
[0015] The compact heat treatment furnace referred to in this specification refers to a furnace having a low overall height. Fluidized bed heat treatment furnace of the present invention, compared with the conventional heat treatment furnace, the required height plus the filling space of the granular material and the free board is about half, the overall height of the furnace is also significantly lower I have. Therefore, the installation place of the conventional heat treatment furnace is limited to a factory having an outdoor space or a stairwell, whereas the fluidized bed heat treatment furnace of the present invention can be installed in a factory having a normal floor height and can be carried in. Because of its simplicity, restrictions on the installation location are greatly reduced.
The term "heat treatment quality" as used herein refers to the quality of the heat treatment itself which can be evaluated based on the improvement in the mechanical properties and the like of the workpiece. The high-quality heat treatment refers to, for example, a heat treatment that can impart higher mechanical properties to a work piece with more energy saving, safer and more reliable while realizing higher productivity. Since the solid solution and other desired phenomena in the heat treatment depend on the temperature, a high-quality heat treatment requires a heat treatment furnace having a fluidized bed with a uniform temperature distribution. In order to obtain a fluidized bed having a uniform temperature distribution, a fluidized bed having a substantially uniform fluidized state over the entire area is desired. Since the fluidized bed is blown by hot air and the granular material flows, if the fluidized state of the fluidized bed is disturbed, it will be difficult to maintain the balance of heat for each part of the fluidized bed, leading to disturbance of the temperature distribution. is there.
The fluidized bed heat treatment furnace of the present invention has essential features for the flow rate of hot air for heating and fluidizing and fluidizing the powder and the powder constituting the fluidized bed. In the present invention, the flow velocity of the hot air is set to 0.05 to 0.2 m / sec. More preferably, it is approximately 0.1 m / sec. The powdery granule has an apparent specific gravity of 1.6 to 1.8, and a substantially spherical body having a diameter of 400 to 600 μmφ occupies 60% or more. A more preferred powdery granule has an apparent specific gravity of about 1.7, a diameter of about 400 to 600 μmφ of about 70% or more, and a diameter of about 100 to 800 μmφ of about 95% or more. Occupy.
In order to make the fluidized bed furnace compact, the expansion rate of the fluidized bed is reduced, and the height of the free board on the fixed bed (the bed of the granular material before flowing) of the granular material to be filled is set. Need to be lowered. Then, in order to reduce the expansion rate of the fluidized bed, it is considered that the floating speed of the fluid having a certain weight should be suppressed by reducing the flow velocity of the fluid for fluidization. However, simply reducing the flow velocity of the hot air may cause a new problem, making it difficult to achieve the object.
For example, in a fluidized bed furnace of a conventional indirect heating system using a radiant tube (see FIG. 5 (b) of Patent Document 2), if the flow velocity of a fluid (air (cold air) in this example) is reduced, Although the state is weakened, it is possible to reduce the expansion rate of the fluidized bed, but since the radiant tube is statically present in the fluidized bed, the particles on the upper surface of the radiant tube do not directly hit the fluid blown from below. The bodies accumulate and lose a uniform fluidized state, and the temperature of the powder particles in contact with the radiant tubes increases, resulting in a fluidized bed having a significantly uneven temperature distribution. In such a fluidized bed furnace, it is difficult to perform a solution treatment at a higher temperature, and the quality of the heat treatment cannot be improved.
Also, in the case where fluidization is realized by using a gas (hot air, cold air, or the like) as a fluid to flow solid particles, the difference in density between the gas and the solid is large, Since the viscosity is small, it is considered that it is difficult to uniformly disperse the powder. Therefore, even if the flow rate is changed for a granular material having a constant weight to reduce the expansion rate of the fluidized bed, at the same time, a uniform fluidized state of the fluidized state can be obtained over the entire area where high quality heat treatment can be realized. It is not easy, and in fact, no public proposal has been made in the past.
According to the present invention, the influence of the variation in the diameter of the granular material on the flow state, and even if the weight is the same, the resistance to the fluid (hot air) can be substantially changed depending on the shape and size to change the flow state. The research and experiment were repeated based on the idea of this. The present invention provides a fluidized bed in which a powder having a predetermined apparent specific gravity, shape and diameter is heated while flowing at a predetermined hot air flow rate, while maintaining a uniform flow state, at the beginning of the flow. A near fluid state is realized.
In the present invention, the heat transfer efficiency is further increased because the density of the powdery medium as the heat medium in the fluidized bed can be increased. On the other hand, since fluidization has occurred, the degree of freedom of the granular material is secured, and the workpiece can move freely in the fluidized bed. Due to the high density of the granules, the probability that the granules collide with each other is high, but due to the fact that they are approximately spherical and that they are in a weak flow state and the momentum of the granules is small, dust Occurrence is small, and it is difficult for powders to flow out even if the free board is lowered.
The apparent specific gravity of the granular material is a specific gravity including voids in a fixed layer state, in other words, in a stationary state of the granular material. That is, it is equal to the true specific gravity of the granular material × the packing ratio. Further, the diameter of the roughly spherical powder means the average value of the short axis and the long axis of the spherical body.
In the present invention, the components of the granules are not limited. In general, artificial granules of silicon dioxide, alumina, zirconia, magnesia, etc., which are the main components of natural sand, or other components may be used. Good. Preferably, it is a powder containing silicon dioxide as a main component. This is because it is safer, easily available, and inexpensive without dust explosion. Specifically, as the granules, those obtained by separating Camlan Silica sand from Vietnam, Flatary sand from Australia, etc. by separating them for each particle size distribution can be used.
Conventionally, for example, in a fluidized bed furnace of an indirect heating system using a radiant tube disclosed in Patent Document 2, the expansion rate of the fluidized bed has been required to be 150% or more. In addition, the spreading rate of the fluidized bed can be set to 120% or less. More preferably, the expansion rate is 110% or less, and the furnace body can be made more compact. The expansion rate refers to the ratio of the height of the dynamic powder after the flow (the height of the fluidized bed) to the filling height of the static powder before the flow (the height of the fixed bed).
In the above-mentioned conventional fluidized bed furnace, the freeboard height is required to be at least 5 times the filling height of the granular material, but in the fluidized bed heat treatment furnace of the present invention, it is 2.5 times. It is possible to: More preferably, the freeboard height relative to the filling height of the granular material is twice or less. The free board refers to the free space up to the ceiling surface in the furnace inside the fluidized bed of the granular material to be filled, and the free board height refers to the free space above the fixed layer when the granular material is stationary. Height.
According to the present invention, a powder having a predetermined apparent specific gravity, a shape and a diameter is caused to flow while being heated at the predetermined hot air flow rate, so that a uniform flow rate can be obtained even with a small expansion rate as described above. The state can be maintained. In addition, the characteristics of the present invention, and the small expansion rate derived therefrom, due to the uniform flow state, even at a low freeboard height as described above, it is difficult for powders and dust to flow out. . In addition, it is possible to perform high-quality heat treatment on the work piece while using a compact heat treatment furnace.
Next, the fluidized bed heat treatment furnace of the present invention will be described more specifically with reference to the drawings. FIG. 1 is a schematic sectional view showing one embodiment of the fluidized bed heat treatment furnace of the present invention. The fluidized bed heat treatment furnace 3 has a fluidized bed 13 in a furnace body 39, a hot air tube 14 is immersed in the fluidized bed 13, and the workpiece 11 is heat-treated in the fluidized bed 13 above the hot air tube 14. It is a furnace with a closed structure.
The fluidized bed 13 is composed of substantially spherical powder and granular material made of Cam Lang Silica sand produced in Vietnam. The granules were selected such that those having an apparent specific gravity of 1.7 and a diameter of 100 to 800 μmφ accounted for 95% or more, and those of 400 to 600 μmφ accounted for 70% or more. The powder is flowed and heated by hot air blown from the hot air tube 14 at a flow rate of 0.1 m / sec, and is uniformly mixed.
The hot-air producing apparatus 5 warms the air sent from a blower (not shown) by a flame. The hot air is temperature-controlled, and at the above-mentioned flow rate, passes through a hot-air tube 14 comprising a header tube and a dispersion tube. It is blown into the body 39 to form the fluidized bed 13. The blown hot air is discharged out of the furnace body 39 as exhaust gas, and the pressure in the furnace body 39 is kept constant.
In the fluidized bed heat treatment furnace 3, the height Hs of the fixed bed, which is the filling height of the granular material, is 800 mm, and the height Ha of the fluidized bed into which the granular material is fluidized is 850 mm. Therefore, these ratios, that is, the expansion ratio Ha / Hs, is 1.0625 (about 107%). In addition, the free board height Hf, which is the height from the upper surface of the fixed layer of the granular material to be filled to the ceiling surface in the furnace, is 1700 mm. Therefore, Hf / Hs is approximately 2.125 (about 2.2 times). The lower surface serving as a reference for the heights Ha and Hs is a horizontal plane passing through the distribution pipe nozzle of the hot air tube 14.
[0032]
As described above, the fluidized bed heat treatment furnace of the present invention regulates the apparent specific gravity, shape, and diameter of the granular material forming the fluidized bed, and the flow rate of hot air for forming the fluidized bed. As a result, the furnace becomes more compact, easier to carry in, and has no restrictions on the installation location.Furthermore, the fluidized state of the fluidized bed is uniform, and the outflow of powder and granules is suppressed. This furnace can perform high quality heat treatment. As an application of the fluidized bed heat treatment furnace of the present invention, for example, there can be mentioned a heat treatment of a vehicle wheel capable of improving fuel efficiency by realizing an effect of improving mechanical properties to reduce the thickness and reducing the weight.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view showing one embodiment of a fluidized bed heat treatment furnace of the present invention.
[Explanation of symbols]
Reference numeral 3 denotes a fluidized bed heat treatment furnace, 5 denotes a hot air production apparatus, 11 denotes a work piece, 13 denotes a fluidized bed, 14 denotes a hot air tube, and 39 denotes a furnace body.

Claims (5)

The furnace is filled with granules, the granules are heated by hot air blown into the furnace and flow to form a fluidized bed, and a workpiece made of metal is heat-treated in the fluidized bed. hand,
The hot air has a flow velocity of 0.05 to 0.2 m / sec,
The fluidized bed heat treatment furnace is characterized in that the granular material has an apparent specific gravity of 1.6 to 1.8 and a substantially spherical body having a diameter of 400 to 600 μmφ accounts for 60% or more. The fluidized bed heat treatment furnace according to claim 1, wherein the granular material contains silicon dioxide as a main component. The fluidized bed heat treatment furnace according to claim 1 or 2, wherein the expansion rate of the fluidized bed is 120% or less. The fluidized bed heat treatment furnace according to any one of claims 1 to 3, wherein a freeboard height is 2.5 times or less the filling height of the powder and granules. The fluidized bed heat treatment furnace according to claim 1, wherein the workpiece is a vehicle wheel.

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