JP2010014314A - Heating furnace and its control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heating furnace capable of reducing the amount of decarbonization of a workpiece, and its control method. <P>SOLUTION: The heating furnace has a hearth 3, a furnace body 2 in which an opening 2b closed by the hearth 3 is formed at a lower part, and a hollow part 2a is formed in communication with the opening 2b, and a lifting means for lifting the hearth. A control means is provided for heating the hollow part 2a to 900°C or higher and controlling the lifting means so that an aspect ratio x of the hollow part 2a satisfies 0.5≤x≤3.0, and the opening/closing speed v(mm/s) of the opening 2b with the hearth 3 satisfies 5≤v≤50. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a heating furnace for heating a workpiece, and a control method when the workpiece is taken in and out of the furnace body.

Conventionally, in an open air heating furnace that heats a workpiece such as steel, a large amount of decarburization has occurred in the workpiece at a heating temperature of 1100 ° C. or higher. Examples of a heating furnace that suppresses decarburization when the workpiece is heated include an atmosphere furnace and a vacuum furnace.
However, since the atmosphere furnace requires an auxiliary equipment such as an inert gas supply device and a vacuum pump, the cost required for the device and maintenance is high, and there is a risk in handling the gas. On the other hand, in a vacuum furnace, since the apparatus itself is expensive and gas is used for return pressure, the workpiece may be cooled during removal. In addition, since the atmosphere contains a large amount of O ₂ and H ₂ O, which are gases that promote decarburization, the occurrence of decarburization is significant when the workpiece is heated at a high temperature in the atmospheric air.

  3 and 4 are side views showing the configuration of a conventional horizontal heating furnace. The horizontal heating furnace is a heating furnace in which doors for taking a workpiece into and out of the furnace body are installed in the lateral direction (side surface direction of the furnace body). As shown in FIGS. 3 and 4, the heating furnace 1 includes a furnace body 2 in which a hollow portion 2 a is formed and communicated with the hollow portion 2 a, and an opening 2 b that is open to the side is formed. And a door 20 that closes the portion 2b. The inner peripheral end surface of the door 20 contacts the outer edge end 2c of the opening 2b. A heater 5 is installed in the hollow portion 2a. The heater 5 heats the inside of the hollow portion 2a and the accommodated workpiece 50. A workpiece 50 is placed on the upper surface of the hollow portion 2a.

  In the horizontal heating furnace 1 having such a configuration, the atmosphere is easily stirred in the opening 2b when the door 20 is opened and closed, and there is a problem that a large amount of gas that promotes decarburization is supplied to the interior 2a of the furnace body 2. . In order to solve this problem, as shown in FIG. 4, a spacer 6 made of a material such as ceramic and having a function as a sealing material is installed at the outer edge 2 c where the furnace body 2 and the door 20 abut. A horizontal heating furnace has also been proposed. However, even in this horizontal heating furnace, the hermeticity is poor, and even when the door 20 is closed, a large amount of outside air is circulated inside the furnace body 2 during heating.

Therefore, a vertical heating furnace in which the hearth moves up and down is disclosed as a heating furnace that realizes high sealing performance (see Patent Document 1).
In the heating furnace described in Patent Document 1, since the door that opens and closes in order to put in and out the workpiece is an opening that opens downward, the property that the heated air rises is used to improve the sealing performance. Can be increased.
Japanese Patent Laid-Open No. 3-17492

However, the heating furnace shown in Patent Document 1 has a configuration that does not impose a mechanical burden on the lifting device while maintaining the hermeticity inside the furnace. It was difficult to reduce the amount of decarburization.
Therefore, the present invention has been made paying attention to the above problems, and an object thereof is to provide a heating furnace with a reduced decarburization amount and a control method thereof.

In order to solve the above-mentioned problems, the present inventors have conducted extensive studies, and as a result, there is a close relationship between the heating temperature inside the furnace body, the opening / closing speed of the opening, and the aspect ratio of the furnace body. I found out.
This invention is based on the said knowledge by the present inventors, The heating furnace which concerns on invention of Claim 1 for solving the said subject has an opening part in a lower surface, and is connected to this opening part A furnace body in which a hollow portion is formed, a heater installed in the hollow portion, a work piece installed on an upper surface so as to be accommodated in the hollow portion, and a hearth for opening and closing the opening, and the furnace A heating furnace having a raising and lowering means for raising and lowering the floor, wherein the hollow portion is heated to 900 ° C. or more by the heater, and the aspect ratio x of the hollow portion satisfies 0.5 ≦ x ≦ 3.0 The control means is provided for controlling the elevating means so that an opening / closing speed v (mm / s) for opening and closing the opening by the hearth satisfies 5 ≦ v ≦ 50. However, the aspect ratio x is (height in the hollow portion) / (area of the opening) ^1/2 .

A heating furnace according to the invention described in claim 2 is characterized in that, in the heating furnace described in claim 1, an elastic spacer is installed between the furnace body and the hearth.
According to a third aspect of the present invention, there is provided a method for controlling a heating furnace, comprising: a furnace body having an opening on a lower surface and having a hollow portion communicating with the opening; a heater installed in the hollow portion; The workpiece is installed on the upper surface so as to be accommodated in the hollow portion, and includes a hearth that opens and closes the opening, and lifting means that lifts and lowers the hearth, and the aspect ratio x of the hollow portion is When the workpiece is accommodated or removed from the furnace body before and after the hollow portion is heated to 1100 ° C. or higher by the heater, the opening is formed by the hearth. The opening / closing speed v (mm / s) for opening and closing the lens satisfies 5 ≦ v ≦ 50. However, the aspect ratio x is (height in the hollow portion) / (area of the opening) ^1/2 .
According to a fourth aspect of the present invention, there is provided a method for controlling a heating furnace according to the third aspect, wherein an elastic material is installed between the furnace body and the hearth. It is said.

According to the heating furnace according to claim 1 of the present invention, since the workpiece is taken in and out at the opening portion opened in the lower surface of the furnace body so that the circulation of the atmosphere is difficult to occur, the conditions are defined. A heating furnace with a reduced amount can be provided.
Moreover, according to the heating furnace according to claim 2 of the present invention, since the elastic intermediate material is installed between the furnace body and the hearth support means, the hermeticity of the hollow part during heating is further increased. Therefore, the atmosphere is shut off and the amount of decarburization is reduced.

Moreover, according to the control method of the heating furnace which concerns on Claim 3 among this invention, the control method of the heating furnace with which the decarburization amount was reduced can be provided.
Further, according to the control method for a heating furnace according to claim 4 of the present invention, since an elastic material is installed between the furnace body and the hearth support means, the sealing property of the hollow part during heating is set. Becomes higher, the atmosphere is shut off and the amount of decarburization is reduced.

  Hereinafter, an embodiment of a heating furnace according to the present invention will be described with reference to the drawings. FIG. 1 is a side view of an embodiment of a heating furnace according to the present invention. As shown in FIG. 1, the heating furnace 1 of the present invention includes a furnace body 2 in which a hollow portion 2a is formed, communicated with the hollow portion 2a, and has an opening 2b opened on the lower side. And a hearth 3 that closes the portion 2b. The hearth 3 is accommodated in the hollow portion 2a, and includes a workpiece support portion 3a that places the workpiece 50 on the upper surface, and a flange portion 3b that abuts on the outer edge 2c of the opening 2b. Elevating means 4 for elevating the hearth 3 in the vertical direction is installed below the flange portion 3b. A heater 5 and a temperature sensor 7 are installed in the hollow portion 2a. The heater 5 heats the inside of the hollow portion 2a and the accommodated workpiece 50. The temperature sensor 7 detects the temperature T in the hollow portion 2a. The lifting / lowering means 4 is communicably connected to a control means 8 that controls the lifting / lowering direction and the lifting / lowering speed. Moreover, the control means 8 is connected to the temperature sensor 7 so that the temperature information detected by the temperature sensor 7 can be received.

A workpiece 50 is placed on the upper surface of the hearth 3. Examples of the shape of the workpiece 50 include a cylindrical shape. As a material of the workpiece 50, for example,
Examples include bearing steel.
In the heating process of the workpiece 50, the temperature T in the hollow portion 2a is preferably applied to a process at 900 ° C. or higher, which increases the amount of stirring with the outside air, and is applied to a process at 1100 ° C. or higher. More preferred.

The aspect ratio x of the hollow portion 2a preferably satisfies 0.5 ≦ x ≦ 3.0, and more preferably satisfies 0.8 ≦ x ≦ 3.0. Here, the aspect ratio x is calculated from (height in the hollow portion 2a) / (area of the opening 2b) ^1/2 . If the aspect ratio x is less than 0.5, there may be a problem that decarburization is easy. If the aspect ratio x exceeds 3.0, there may be a problem that it takes a long time or a large space is required when a workpiece is carried in or out.
Here, the aspect ratio x is obtained by (height in the hollow portion 2a) / (opening area of the opening 2b) ^1/2 . As shown in FIG. 1, the “height h in the hollow portion 2a” is a dimension from the opening surface of the furnace body 2 to the inner wall surface 2d facing the opening portion 2b.

  When the opening / closing speed v (mm / s) of the opening 2b by the hearth 3 is less than 5 mm / s, the contact time between the heated air in the hollow part 2a and the atmosphere increases, and the amount of decarburization increases. Since it may arise, 5 mm / s or more is preferable and 10 mm / s or more is more preferable. When the opening / closing speed v (mm / s) of the opening 2b exceeds 50 mm / s, the opening / closing operation of the hearth 3 with respect to the opening 2b increases the agitation amount of the heated air and the outside air in the hollow portion 2a, and is removed. Since the problem that the amount of charcoal increases may occur, it is preferably 50 mm / s or less, and more preferably 30 mm / s or less.

Here, the opening / closing speed v (mm / s) is defined by (moving distance (mm) / time (s)) of the hearth during opening and closing.
In the present invention, when the temperature T acquired from the temperature sensor 7 provided in the hollow portion 2a satisfies the above condition, and the aspect ratio x of the furnace body 2 input in advance satisfies the above condition, the switching speed v in the above range. Then, the control means 8 controls the raising / lowering means 4 so as to raise and lower the hearth 3.

An elastic spacer 6 may be provided at a contact portion between the furnace body 2 and the hearth 3 when the hearth 3 closes the opening 2 b by the elevating means 4. The interstitial material 6 may be provided at the outer edge 2 c of the opening 2 b in the furnace body 2 or may be provided at the flange 3 a in the hearth 3.
As the material of the interstitial material 6, in particular, as long as it is elastic, has airtightness as a sealing material interposed between the furnace body 2 and the hearth 3, and is not easily denatured by the heat of the heating furnace. There is no restriction, and it can be selected according to the purpose. For example, ceramic is preferable. The form of the interstitial 6 is preferably a fiber form and is preferably processed into a rope shape or a blanket shape.

(Example)
Hereinafter, examples of the heating furnace and the control method thereof according to the present invention will be described.
First, as the workpiece 50, a steel material processed into a cylindrical shape was heated and cooled under the heating conditions (test Nos. 1 to 21) shown in Table 1. All heating times are 30 minutes.
In addition, the aspect and aspect ratio of each experimental furnace in Table 1 are as follows. In the following experimental furnaces Nos. 1 to 3, an interstitial material 6 made of ceramic fibers was installed between the furnace body 2 and the hearth 3.
Experimental furnace No. 1: Vertical heating furnace, aspect ratio x = 0.5
Experimental furnace No. 2: Vertical heating furnace, aspect ratio x = 0.8
Experimental furnace No. 3: vertical heating furnace, aspect ratio x = 3.0
Experimental furnace No. 4: Horizontal heating furnace, aspect ratio x = 0.6
Experimental furnace No. 5: Horizontal heating furnace, aspect ratio x = 0.9
In addition, when the workpiece 50 is taken in and out of the furnace body 2 before and after the heating of the workpiece 50, control is performed based on the temperature T and the aspect ratio x in the hollow portion 2a shown in Table 1. The hearth 4 was moved up and down by means 8 at the opening / closing speed v shown in Table 1.

Next, the structure of the cross section of the cooled workpiece 50 was observed, the depth of the decarburized layer was measured, and the decarburization amount was determined. The measurement results are shown in Table 1 and FIG.
For the measurement of the depth of the decarburized layer, a method for measuring the total decarburized layer depth (DM-T) according to 4.1 (measurement method using a microscope) of JIS G 0558 was used. However, if the workpiece 50 is an alloy tool steel other than for hot molds and it is difficult to measure with a microscope, the practical decarburized layer depth according to 4.2 (measurement method by hardness test) of JIS G 0558 It is preferable to use the measurement method of (DH-P).

As shown in Table 1, in the examples of Test Nos. 1 to 13 in which the heating temperature T, the opening / closing speed v, and the aspect ratio x satisfy the above-described conditions, the depth of the decarburized layer of the workpiece 50 is It was 0.38 mm or less, and reduction of decarburization was realized in an open air furnace. On the other hand, the comparative examples of Test Nos. 14 to 16, 19, and 20 in which the heating temperature T, the opening and closing speed v, and the aspect ratio x do not satisfy any of the above-described conditions are the decarburized layers of the workpiece 50. The depth was 0.49 mm or more, and a large amount of decarburization peculiar to the open air furnace was confirmed. Moreover, the comparative example of test No. 17 and 18 differed in the kind of furnace, and the decarburization depth became deep deeply compared with the Example of test No. 10 and 11 with other conditions approximate.
Thus, in the vertical heating furnace 1 in which the opening 2b closed by the hearth 4 is formed below the furnace body 2, the heating temperature T, the opening / closing speed v, and the aspect ratio x are appropriately combined. Thereby, the amount of decarburization of the workpiece 50 can be reduced.

It is a front view which shows the structure in one Embodiment of the heating furnace which concerns on this invention. It is a graph which shows the relationship between the heating temperature or switching speed of the heating furnace which concerns on this invention, and the depth of a decarburization layer. It is a front view which shows the structure of the conventional heating furnace. It is a front view which shows the structure of the conventional heating furnace.

Explanation of symbols

1 Heating furnace 2 Furnace body 2a Hollow part (inside the furnace body)
2b Opening 2c Edge 3 Hearth 4 Elevating device 5 Heater 6 Interim material 8 Control means 20 Door 50 Workpiece

Claims (4)

A furnace body having an opening on the lower surface and having a hollow portion communicating with the opening;
A heater installed in the hollow portion;
A work piece is installed on the upper surface so as to be accommodated in the hollow portion, and a hearth that opens and closes the opening,
A heating furnace comprising elevating means for elevating and lowering the hearth,
With the heater, the hollow part is heated to 900 ° C. or higher,
The aspect ratio x of the hollow portion satisfies 0.5 ≦ x ≦ 3.0,
A heating furnace characterized in that a control means for controlling the elevating means is provided so that an opening / closing speed v (mm / s) for opening and closing the opening by the hearth satisfies 5 ≦ v ≦ 50.
However, the aspect ratio x is ^1/2 (height at the hollow portion) / (area of the ^opening).   The heating furnace according to claim 1, wherein an interstitial material having elasticity is installed between the furnace body and the hearth. A furnace body having an opening on the lower surface and having a hollow portion communicating with the opening;
A heater installed in the hollow portion;
A work piece is installed on the upper surface so as to be accommodated in the hollow portion, and a hearth that opens and closes the opening,
Elevating means for elevating and lowering the hearth,
The aspect ratio x of the hollow portion satisfies 0.5 ≦ x ≦ 3.0,
When the workpiece is accommodated in or taken out of the furnace body before and after the hollow portion is heated to 900 ° C. or more by the heater,
An opening / closing speed v (mm / s) for opening and closing the opening by the hearth satisfies 5 ≦ v ≦ 50.
However, the aspect ratio x is ^1/2 (height at the hollow portion) / (area of the ^opening).   The method for controlling a heating furnace according to claim 3, wherein an interstitial material having elasticity is installed between the furnace body and the hearth.

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