JPH07228917A - Tempering furnace - Google Patents

Abstract

PURPOSE:To reduce the unevenness of temp., to reduce the running cost, to secure the uniform temp. distribution in a furnace and to widen the width of a soaking zone. CONSTITUTION:Radiant tube burner 2 is arranged in the carrying direction of a material to execute heat treatment above a mesh belt 3 for carrying the treating material and used to a heat source so as to continuously and uniformly heat the treating material carried in the furnace 12 during carrying with the radiation heat. Further, a blowing means 5 blowing combustion exhaust gas exhausted from the radiant tube burner 2, is the mesh belt 3 at the front of a carrying inlet 11 for the treating material in a tempering furnace.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to tempering furnaces. More specifically, the present invention relates to a small tempering furnace for tempering an object to be heat-treated on a mesh belt and continuously carrying it.

[0002]

2. Description of the Related Art Conventionally, a small continuous tempering furnace, for example, a small tempering furnace having a furnace length of about 1 m, which is mainly used for adjusting hardness of a spring, uses an electric heater with a sheath tube as a heat source. The soaking furnace zone at a predetermined temperature is formed in the furnace. For example, FIGS.
As shown in FIG. 3, in order to make the heat distribution in the furnace as uniform as possible in the longitudinal direction (transport direction of the heat-treated object), a plurality of sheathed heaters 102 are provided above and below the mesh belt 103, respectively. A mesh belt 1 which is arranged so as to traverse and penetrates the furnace body 101 in the longitudinal direction.
The object to be heat-treated conveyed in 03 is heated to a predetermined temperature. Since the sheathed heater 102 mainly heats the work by convection heat transfer rather than radiant heating, fans 104, 104 for causing forced convection in the furnace 112 are installed between the sheathed heaters 102. Has been done.

On the other hand, the periphery of the mesh belt 103 protruding to the outside of the furnace body 101 is surrounded on three sides by refractory covers 105 and 106 except for the surface where the object to be heat-treated is put in or taken out. It is designed to be isolated from and not cooled.
The mesh belt 103 is stretched around the drums 108 and 109 and the idle drum 110. The furnace body 101 is movably supported by a pedestal 107 equipped with casters.

In the tempering furnace having a large number of sheathed heaters 102 as heat sources, on-off control of the sheathed heaters 102 or proportional control by an inverter or the like is used to maintain the inside 112 of the furnace at a predetermined temperature so that the soaking zone is maintained inside the furnace 112. I am trying to form.

[0005]

However, the conventional tempering furnace using this sheathed heater as a heat source has the drawback that the width of the soaking zone is narrow and the temperature unevenness is large.

That is, in order to make the heat distribution in the furnace as uniform as possible in the longitudinal direction, a large number of sheathed heaters 1 are used.
Even if No. 02 is arranged, temperature unevenness occurs unless the stirring of the atmosphere in the furnace is uniform because the heating is mainly performed by convection heat transfer. Further, since the sheathed heaters 102 are collectively arranged so as to avoid the agitating fans 104, 104, temperature unevenness is promoted and radiation heat due to concentration of heat sources is affected. Furthermore, since the inside 112 of the furnace is controlled to a predetermined temperature by controlling the on / off of the sheath heater 102, the temperature difference between the time of heat generation and the time of non-heat generation becomes large, which promotes temperature unevenness. Further, even when proportional control is performed by an inverter or the like, temperature unevenness in the furnace length direction occurs. Therefore, the tempering process may be non-uniform. For example, when adjusting the hardness of the spring, there is a possibility that the hardness may vary.

Moreover, the entrance 10 of the furnace body 101 is covered.
Even if it is surrounded by 5,106, the entrance and exit, especially the entrance 111
Since cold air outside the furnace enters the inside of the furnace 112 from the inside, the temperature of the inside of the furnace 112 decreases near the carry-in port 111, and the soaking zone reaching the set temperature inside the furnace is narrow (about 40% of the furnace length: Fig. Three
However, there is a problem that the processing speed becomes slow and the furnace length is required to be long to take up space.

Furthermore, since the electric heater, which has a high energy cost, is used as the heat source, there is a problem that the running cost of the heat treatment becomes high.

It is an object of the present invention to provide a tempering furnace which has a low temperature unevenness and a low running cost.
Another object of the present invention is to provide a tempering furnace which can secure a uniform temperature distribution in the furnace and has a wide soaking zone.

[0010]

In order to achieve such an object, the present invention provides a tempering furnace that heats a material to be heat-treated with a mesh belt to a predetermined temperature to carry out a tempering treatment. A radiant tube burner is arranged in the upper direction in the conveying direction of the object to be heat treated, and this is used as a heat source.

Further, the tempering furnace of the present invention is provided with a blowing means for blowing the combustion exhaust gas discharged from the radiant tube burner to the mesh belt before the heat-treatment target carry-in port of the tempering furnace.

Here, the radiant tube constituting the radiant tube burner may be a single tube, but preferably, a portion excluding both ends is a double tube, and the inner tube is heated by the combustion gas. good.

Further, in the tempering furnace of the present invention, the secondary air is supplied into the radiant tube constituting the radiant tube burner.

[0014]

Therefore, in the case of the first aspect of the invention, the object to be heat-treated carried into the furnace body is continuously and uniformly heated by the radiant heat radiated from the radiant tube extending in the carrying direction on the mesh belt.

Further, in the case of the invention of claim 2, the combustion exhaust gas after being used for heating the inside of the furnace before the carry-in port is blown to the mesh belt, so that the mesh belt and the object to be heat-treated are preheated by the combustion exhaust gas. Since it is carried into the furnace after that, the temperature decrease in the furnace due to carrying the mesh belt and the object to be heat-treated is suppressed and the temperature rising time of the object to be heat-treated is shortened. Moreover, even if the air outside the furnace tries to enter the furnace from the carry-in port, a part of the combustion exhaust gas injected toward the mesh belt is also accompanied, so that the temperature decrease in the furnace is reduced. .

Furthermore, in the case of the third aspect of the invention, since the inner tube of the radiant tube is heated by the combustion gas, the outer tube is uniformly heated mainly by the solid radiant heat from the inner tube.

Further, in the case of the invention of claim 4, since the amount of the combustion gas is increased by the introduction of the secondary air, the radiant tube is heated more uniformly. In particular, when the radiant tube is a double tube, the outer tube is more uniformly heated by the convective transfer heat from the combustion gas whose volume is increased by the introduction of the secondary air and the solid radiant heat radiated from the inner tube, Radiates uniform radiant heat throughout the furnace.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of the present invention will be described in detail below with reference to the embodiments shown in the drawings.

1 and 2 show an embodiment of the tempering furnace of the present invention. This tempering furnace includes a furnace body 1 provided with an inlet 11 and an outlet 10 at both ends in the longitudinal direction so that an object to be heat-treated (not shown) can pass through it, a radiant tube burner 2 serving as a heat source, and a heat-treated object. It is mainly composed of a mesh belt 3 that conveys objects.

The furnace body 1 is not particularly limited in its structure and material, and is constituted by, for example, a steel casing lined with a refractory material, and is slightly wider than the mesh belt 3 in the radiant tube burner 2. And a furnace space (furnace) 12 having a height sufficient to install a fan 4 for stirring the atmosphere in the furnace, and a carry-in port 11 and a carry-out port having a minimum width necessary for carrying in and carrying out the heat-treated object. And 10 are provided. Longitudinal direction of the furnace body 1 (the carry-in port 11 and the carry-out port 1
A mesh belt 3 that conveys a heat-treated object is provided so as to penetrate therethrough, and a heat-treated object placed on the mesh belt 3 is provided so as to pass through the furnace 12 in the longitudinal direction. ing. The furnace body 1 is mounted on a pedestal 6 having casters so as to be movable.

The radiant tube burner 2 includes a tube 7 arranged in parallel with the mesh belt 3 in the longitudinal direction of the furnace body 1, that is, in the conveying direction of the heat treated object so as to penetrate through the furnace 12, and a burner installed outside the furnace. It is composed of 8 parts. The burner 8 is not particularly limited,
In the case of the present embodiment, a premix burner is used which burns a premix gas in which a fuel gas such as LNG or LPG and combustion air are premixed to have an appropriate air ratio. In addition, the radiant tube burner 2 is an outlet 10 for the furnace body 1.
The combustion gas is injected from the side and the combustion exhaust gas is exhausted from the carry-in port 11 side. The exhaust port side of the tube 7 is connected via an exhaust pipe 9 to a jetting means such as a nozzle 5 installed below the mesh belt 3. Therefore, the combustion gas of the radiant tube burner 2 is
After the tube 7 is heated, it is drawn out of the furnace through the exhaust pipe 9 and ejected from the nozzle 5 toward the mesh belt 3. Then, the mesh belt 3 moving on the nozzle 5
And used for preheating the heat-treated object placed thereon.

In the case of the present embodiment, the tube 7 has a double tube except the both ends, the inner tube 7a is heated by the combustion gas, and the outer tube 7b around the inner tube 7a is heated by the inner tube 7.
It is provided so as to be heated by the solid radiant heat from a. In this case, since the outer pipe 7b is heated by the convection-transfer heat from the combustion gas and the solid radiant heat radiated from the inner pipe, it is uniformly heated and radiates uniform radiant heat throughout the furnace 12. Further, the radiant tube burner 2 of the present embodiment is provided so that the secondary air is supplied into the tube 7 by the ejector effect of the burner 8 or pushing by the fan. Since the amount of combustion gas is increased by the introduction of the secondary air in the tube 7, the outer tube 7b is heated more uniformly. If the secondary air is shut off, the burner 8 burns at an appropriate air ratio, so the heating of the radiant tube 7 becomes uneven, but the combustion temperature rises. Therefore, for example, when the tempering furnace is started up, the temperature of the combustion gas can be raised by shutting off the secondary air to shorten the start-up time. For example, the temperature inside the tempering furnace with a furnace length of about 1 m is 425 ° C.
If it is set to, it takes 120 minutes to start up in 90 minutes, enabling a reduction of about 25%.

The mesh belt 3 is wound around rollers 13 and 14 and an idle roller 15 installed outside the furnace and rotated by driving a motor 19. The mesh belt 3 is hung so that an upper portion of the mesh belt 3 between the rollers 13 and 14 is tightly passed through the inside 12 of the furnace and a lower portion thereof is outside the furnace. Each of the rollers 13 and 14 and the idle roller 15 includes support frames 17 and 18 protruding from the furnace body 1.
Supported by.

Furthermore, a fan 4 for stirring the furnace atmosphere is provided in the furnace 12. The fan 4 agitates the atmosphere in the furnace and assists in heating the object to be heat-treated by uniform convection heat transfer. The fan 4 is driven by a motor 16 installed outside the furnace.

According to the tempering furnace configured as described above, the heat treatment of the heat-treated object, for example, the tempering for adjusting the hardness of the spring can be performed as follows.

The object to be heat-treated is carried into the tempering furnace which has been set up at the set temperature by utilizing the mesh belt 3 protruding outside the carry-in port 11. The object to be heat treated is carried into the furnace 12 by the drive of the mesh belt 3 and moves at a constant speed. Here, on the front side of the carry-in port 11, the combustion belt discharged from the jet nozzle 5 preheats the mesh belt 3 and the object to be heat-treated placed thereon. At the portion of the inside 12 of the furnace near the carry-in port 11 side, there is a risk that the temperature inside the furnace will drop due to the entry of outside air from outside the furnace. Moreover, the temperature of the radiant tube 7 is lower on the carry-in port 11 side than on the carry-out port 10 side. However, after the object to be heat treated and the mesh belt 3 are preheated by the combustion exhaust gas injected from the nozzle 5 provided near the carry-in port 11, the inside of the furnace 12
The temperature of the temperature near the inlet 11 of the furnace 12 is increased because the flow of the combustion gas prevents the outside air from entering through the inlet 11, and even if it invades, a part of the combustion exhaust gas is accompanied. There is little decline.

The object to be heat-treated, which has been carried into the furnace 12 through the carry-in port 11, has radiant heat from the radiant tube 2 arranged vertically in the carrying direction along the mesh belt 3 and convective heat due to agitation of the fan 4. Heated by transmission. At this time, in the heat distribution in the furnace 12, as shown in FIG. 3, the temperature rises rapidly from the carry-in port 11, and approximately 80% of the furnace length constitutes a soaking zone. For example, in a tempering furnace with a furnace length of approximately 1 m, the temperature inside the furnace is 425 ° C.
When set to 1, 79% of the furnace length was able to achieve soaking. Even if the nozzle 5 for ejecting the combustion exhaust gas was not installed, uniform radiation heat of the radiant tube burner 2 was able to form a soaking zone in about 50% of the furnace length, as shown in FIG. Moreover, since the object to be heat treated has been preheated, the temperature rising time can be shortened significantly. After that, the object to be heat-treated on the mesh belt 3 is tempered to a predetermined temperature, then taken out from the carry-out port 10 and discharged. The furnace temperature is detected by the thermosensor 20 and adjusted by controlling the combustion amount of the radiant tube burner 2.

It should be noted that the above-mentioned embodiment is an example of the preferred embodiment of the present invention, but the present invention is not limited to this, and various modifications can be made without departing from the gist of the present invention. For example, in this embodiment, the jetting means / nozzle 5 for spraying the combustion exhaust gas onto the mesh belt 3 is installed under the mesh belt 3, but it is not particularly limited to this.
It may be arranged on the mesh belt 3 and sprayed downward. The tube 7 of the radiant tube burner 2 may be a single tube instead of a double tube, or may be a U-shaped tube. In this case, the drawing of the nozzle 5 by the exhaust pipe 9 becomes long.

[0029]

As is apparent from the above description, in the tempering furnace of the present invention as defined in claim 1, since the radiant tube burner is arranged above the mesh belt in the conveying direction and used as a heat source, the furnace is used. The object to be heat-treated is continuously heated uniformly by radiant heat from the radiant tube burner during transfer, so the soaking zone can be set to about twice that of a conventional tempering furnace using an electric heater as a heat source. Along with that, there is little temperature unevenness. Therefore, the tempering process becomes uniform, and when used for adjusting the hardness of the spring, for example, the spring hardness has less unevenness. Moreover, since heat is obtained from combustion as compared with an electric heater, energy saving of about 50% can be achieved.

Further, in the tempering furnace of the present invention according to claim 2, since the combustion exhaust gas discharged from the radiant tube burner is arranged with a spouting means for spraying the exhaust gas onto the mesh belt before the inlet of the heat-treated object, the mesh belt and The object to be heat treated can be loaded into the furnace after being heated with the combustion exhaust gas in advance, and the decrease in the temperature in the furnace due to the loading of the mesh belt and the object to be heat treated can be suppressed. Moreover, even if the flow of the combustion gas injected toward the mesh belt in front of the carry-in port prevents the outside air from entering from the carry-in port, even if the air outside the furnace tries to enter the furnace from the carry-in port. Since a part of the combustion exhaust gas is entrained, the temperature decrease in the furnace can be reduced. Therefore, the soaking zone is more easily formed, and it becomes possible to form the soaking zone over about 80% of the reactor length.

Further, in the case of the invention of claim 3, the radiant tube is made into a double tube and the inner tube is heated by the combustion gas, and the outer tube around it is made uniform by the solid radiant heat mainly from the inner tube. Since it is heated, the uneven temperature is reduced.

Further, in the case of the invention of claim 4, since the amount of the combustion gas is increased by introducing the secondary air, the radiant tube is heated more uniformly and the temperature unevenness can be further reduced. In particular, when the radiant tube is a double tube, the outer tube is more uniformly heated by the convective transfer heat from the combustion gas whose volume is increased by the introduction of secondary air and the solid radiant heat radiated from the inner tube. Radiates uniform radiant heat throughout the furnace,
The temperature unevenness can be extremely reduced.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of a tempering furnace of the present invention.

FIG. 2 is a sectional view taken along line II-II in FIG.

FIG. 3 is a graph comparing in-furnace temperature distributions of a tempering furnace of the present invention and a conventional tempering furnace using an electric heater as a heat source.

FIG. 4 is a longitudinal sectional view showing an example of a conventional tempering furnace.

5 is a sectional view taken along line VV of FIG.

[Explanation of symbols] 1 furnace body 2 radiant tube burner 3 mesh belt 5 jet nozzle 7 radiant tube 7a inner tube 7b outer tube 8 burner 9 exhaust pipe 11 carry-in port 12 inside the furnace

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location F27D 7/06 B 7727-4K

Claims (4)

[Claims] 1. A tempering furnace for heating and tempering an object to be heat-treated by a mesh belt in a tempering furnace, wherein a radiant tube burner is provided above the mesh belt in a conveying direction of the object to be heat-treated. A tempering furnace that is arranged and used as a heat source. 2. The grill according to claim 1, further comprising a jetting means for spraying the combustion exhaust gas discharged from the radiant tube burner to the mesh belt before a heat-treatment target inlet of the tempering furnace. Return furnace. 3. The tempering according to claim 1, wherein the radiant tube constituting the radiant tube burner has a double tube except for both ends, and the inner tube is heated by combustion gas. Furnace. 4. The tempering furnace according to claim 1, wherein secondary air is supplied into the radiant tube forming the radiant tube burner.