JPS62230932A - Method for cooling metallic body - Google Patents

Abstract

PURPOSE:To increase the rate of cooling of a hot metallic body when the metallic body is rapidly cooled in a fluidized bed, by specifying the particle size of solid particles and expansion ratio. CONSTITUTION:Solid particles 5 are charged into a vessel 6 and a fluidizing gas 7 is introduced into the vessel 6 through an introduction pipe 1, a wind box 2, and a dispersion plate 3 to fluidize the particles 5. A hot metallic body 4 is put in the resulting fluidized bed and cooled. In this cooling method, the average particle size of the particles 5 is regulated to <=100mum and expansion ratio calculated by dividing the height of the fluidized bed by the height of a fixed bed is regulated to >=1.5. The height of the fluidized bed is the height of a layer of the particles 5 fluidized with the gas 7, and the height of the fixed bed is the height of a layer of the particles 5 not fluidized with the gas 7.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] This invention relates to a method of rapidly cooling a high-temperature metal lump, etc., among heat treatments for improving the properties of metal. The present invention relates to a method for cleanly cooling a high-temperature metal lump or the like at a high cooling rate by immersing it in a fluidized bed of granular material that is undulated by air.

[Conventional technology]

As a method for rapidly cooling a lump of metal (hereinafter referred to as a metal body), a method of immersing it in molten salt is known and widely used. However, this method requires work to remove the molten salt that adheres to the surface of the metal body after cooling [-1], which contaminates the air, resulting in a poor working environment and a sanitary problem. As a method to eliminate the above-mentioned drawbacks of the molten salt quenching method, a method has been proposed in which a high-temperature metal body is immersed in a fluidized bed of powder and granular material fluidized by means such as inflow of fluid and a stirrer. That is, Japanese Patent Application No. 58-22690 (Japanese Unexamined Patent Publication No. 59-
150013) is a method in which a metal body heated to a predetermined temperature is immersed in powder or granular material having good thermal conductivity.

[The gap that the invention attempts to solve]

The quenching method using a bath melting chamber has poor workability, poses problems in terms of Nfuneral hygiene, and requires equipment for melting the salt, which requires a large amount of cost.On the other hand, the well-known quenching method using a water bath or a moving bed Since the method does not specify the particle size of the powder, the cooling effect on the high-temperature metal body is not very large. High temperature metal bodies are
Both the fluidizing gas and the fluidized powder and granules receive a cooling effect, but the latter is generally the case because the thermal conductivity due to contact between the solid surface and solid particles is significantly higher than the heat transfer coefficient between the solid surface and the gas. This is the rate-limiting step in cooling high-temperature metal bodies.

Thermal conductivity between the solid wall surface and the solid particles increases as the contact area increases, but in known fluidized beds, the particle size of the powder is not specified, so the cooling rate is not sufficient.

The reason why the quenching method using a fluidized bed has not been widely used in the underground market even though it is far superior in terms of workability and environmental hygiene is as follows.
This is because the cooling rate is lower than that of the molten salt cooling method.

[Means to resolve the gap]

In order to solve the above-mentioned problem, in the present invention, the homogeneous particles 5 are placed in the main container 6, and a dispersion plate 3 is placed in the lower part of the main container 6.
- A wind box 2 is provided, and the introduction pipe 1 is installed in the wind box 2. In order to increase the contact area between the solid particles and the wall surface of the high-temperature metal body, the solid particles have a particle diameter of 12 μm or less, specifically 100 μm or less (7 μm).

[Effect]

The above technical means works as follows.

Solid particles 5 having a particle diameter of 100 μm or less are placed in the main container 6, and a fluidizing gas 7 such as air is introduced through the introduction pipe 1. The fluidizing gas 7 enters the wind box 2, is uniformly dispersed by the dispersion plate 3, and rises inside the solid particles 5 in the form of bubbles. The rising force of the bubbles generated at this time forms a so-called fluidized bed.In the fluidized bed, intense stirring and mixing action takes place.As a result, the metal body 4 comes into violent contact with the same particles 5 flowing in the main container 6. The solid particles 5 are cooled by coming into contact with the fluidizing gas.

〔Example〕

1, 3, 4, and 5 show an embodiment of the present invention.

As shown in FIG.
Solid iron particles 5 of 0 μm and 125-350 μm are introduced. As shown in FIG. 2, the layer height when the solid particles 5 are placed in the main container 6 and the fluidizing gas is flowed is called the solid T layer height. As shown in Fig. 1, the height of the bed when solid particles 5 are placed in the main container 6 and the fluidizing gas 7 is flowed is called the fluidized bed height. It becomes a certain joist. That is, it becomes a state of intense fluidity.

4a shown in the cylinder 5 figure is a metal body placed in the main container 6 and cooled. 8 is a sheathed thermocouple made of 70 Meru alumel, which is used to measure the temperature at the center of the metal body 4a. Reference numeral 9 denotes a hanging metal fitting, which is used to hang the metal body 4a.

The expansion ratio defined as fluidized bed height ÷ fixed bed height is 1.3°1.
The high temperature metal body 4a is immersed in the solid iron particles 5 in the main container 6, and the change in the temperature at its center is recorded by changing the inflow amount of room temperature air 7 as a fluidizing gas so that the temperature becomes 1.7.
This is shown in Figures 3 and 4.

In FIG. 3, the expansion ratio is 1.5, and in FIG. 4, the solid particle diameter 5 is 40 to 100 μm. From Figure 3,
It can be seen that when the expansion ratio is the same, the smaller the solid particle diameter, the faster the cooling rate. From FIG. 4, it can be seen that when the solid iron particle diameter is the same, the larger the expansion ratio (ie, the more severe the 6it dynamic state), the higher the cooling rate.

When cast iron with an austenite structure is rapidly cooled at a high temperature, the austenite structure can be brought to a lower temperature, and if the temperature is kept warm and the transformation is completed, the entire structure can be changed to a uniform structure such as bainite. Generally known as υ, the separation of cooling treatment and constant temperature treatment is generally referred to as two-stage austempering treatment.

In this case, the rapid cooling requires a cooling rate that reduces the temperature from around 870°C to around 500°C or less within 100 seconds.

In Figure 6, when the expansion ratio is 1.5, the iron solid particle size is 4
Those with iron solid particle diameters of 0 to 100 μm satisfy the above cooling rate, but those with iron solid particle diameters of 125 to 350 μm do not satisfy the cooling rate.
Not yet.

In FIG. 4, when the iron particles have a diameter of 40 to 100 μm, those with expansion ratios of 1.5 and 1.7 satisfy the above cooling rate, but those with expansion ratios of 1.3 do not.

Note that the cooling rate obtained using copper solid particles was almost the same as that obtained using iron solid particles. That is, there is almost no difference depending on the material of the solid particles.

A high-temperature metal body is cooled by both the fluidizing gas and the flowing solid particles, but the thermal conductivity due to contact between the metal body surface and the solid particles is significantly higher than the heat transfer coefficient between the metal body surface and the scum. Therefore, the latter becomes the rate-determining step in cooling the high-temperature metal body.

Strictly speaking, the contact between the optical surface of the metal body and the solid particles is through a very thin film of fluidized scum, and the contact area through this film is the rate-limiting step in cooling. There is almost no difference in speed depending on the material of the solid particles.

The cooling rate of the contact area between the gold layer surface and the solid particles is proportional to the contact area per unit time. The contact area per unit time is proportional to the total surface area of the particles that come into contact with each other due to the flow and the number of times the particles come into contact with each other.

The smaller the particle diameter, the larger the total surface area of the particle group.

The number of times the particle group comes into contact with each other increases as the fluidized bed becomes more similar (ie, the expansion ratio defined by the height of the fluidized bed divided by the height of the fixed bed increases).

Therefore, the smaller the particle size and the larger the expansion ratio, the higher the cooling rate.

According to this invention, the solid particle diameter is 100 μm or less, and the expansion ratio is 1.
．． Cooling using a fluidized bed with a temperature of 5 or more allows a high temperature metal body at around 870° C. to be brought down to around 500° C. or less within about 100 seconds, making it sufficiently convenient for cooling treatment in so-called two-stage austempering.

Note that the constant temperature treatment may be performed in an electric tunnel furnace, a batch furnace, or any other type of furnace.

〔Effect of the invention〕

This invention has the following unique effects.

Since a fluidized bed of solid particles is used instead of molten salt to rapidly cool a high-temperature metal body, there are no hygiene issues and workability is good.

Because fluidized bed cooling is performed with solid particles of 100 μm or less and an expansion ratio of 1.5 μm or more, the cooling rate significantly exceeds the cooling rate that was not always sufficient with conventional general fluidized bed cooling, and is suitable for cooling in so-called two-stage austempering processing. It can be used as a treatment and can also be used for other cooling treatments.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing one practical example of the invention. FIG. 2 is an explanatory diagram of a state in which fluidizing gas is not introduced in FIG. 1. FIG. 5 is a diagram showing a metal body cooled using the apparatus shown in FIG. 6 and 4 are diagrams showing temperature drop curves when a high-temperature metal body is cooled using the apparatus shown in FIG. 1. 1: Inlet pipe 2: Wind box 3 Bidispersion plate 4: Metal body 4a:
Metal body 5: Solid particle 6: Main container 7: Fluidizing gas 8: Sheath type thermocouple 9: Hanging fitting VT1 Figure 2? Lacquer 3 Diagram 3 (Seconds) Diagram 4 Diagram 1 Lock (Seconds)

Claims (1)

[Claims] A dispersion plate is installed at the bottom of the main container, a wind box is installed at the bottom of the dispersion plate, and solid particles are filled into the main container.
In this method, solid particles in the main container are fluidized by introducing fluidizing gas through an inlet pipe connected to a wind box, and the solid particles are cooled to a temperature of 100 μm or less. A method for cooling a metal body, characterized in that cooling is performed with an expansion ratio defined as fluidized bed height divided by fixed bed height of 1.5 or more.