JPS6358201B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a continuous sintering furnace.

As a sintering facility for powder molded products, a dewaxing zone and a cooling zone are installed before and after the sintering zone, which has a built-in electric heater, etc., and the powder molded products are sequentially moved by a conveyor belt that circulates through these zones. A sintering furnace that performs sintering is used.

By the way, in such continuous sintering, in order to obtain a sintered product with good quality and properties, it is necessary to completely burn off the lubricant mixed in the powder molded product before it reaches the sintering zone. This is necessary, and if it is incomplete, the product may become rough or
This impedes higher density.

Therefore, the dewaxing zone in front of the sintering zone is an extremely important furnace structure. Conventionally, the dewaxing zone was constructed by passing the furnace core tube through the furnace body and passing a protective atmosphere through it. Because the furnace was configured to heat indirectly using an electric heater installed on the outside, it took a long time to burn off, which resulted in a long furnace length, and it required a large amount of protective atmosphere gas, among other problems.

Therefore, recently, as shown in FIGS. 1 and 2, a wide heating chamber 51 is formed in the dewaxing furnace body 50, and a plurality of direct-fired burners 52, 52 are arranged in this heating chamber 51 at predetermined intervals. A direct flame heating type dewaxing zone in which the workpiece is directly heated by the flames of these direct flame burners 52, 52 has been proposed and implemented.

However, in this type of direct flame heating type dewaxing method, the object to be processed is directly heated by the flame, so combustion becomes unstable due to the influence of the protective atmosphere flow, and the object to be processed tends to be locally overheated. To avoid this, each direct-fired burner must be adjusted to have a uniform and stable flame length, and a large number of burners must be arranged, which also has the disadvantage that the dewaxing zone becomes longer.

The present invention aims to eliminate all of the drawbacks of the conventional continuous sintering furnace as described above, and provides a continuous sintering furnace that can perform burn-off extremely efficiently with a compact structure using a single burner. This is what we are trying to provide.

In order to achieve this object, the present invention does not directly heat the object to be treated with a combustion flame, but instead uses combustion exhaust gas obtained by combusting a raw material gas with an air deficiency, that is, with less than the theoretical amount of air. The powder compact is effectively sprayed onto the compact, rapidly heated under non-oxidizing conditions, and a part of the H ₂ O produced by combustion is thermally decomposed to react with the lubricant in the liquid or vapor state. A dewaxing zone, a sintering zone, and a cooling zone are successively connected to each other in a tunnel furnace with a closed cross section, and a conveyor belt is passed through them to mix lubricant and press. While conveying the compacted powder compacted body by using a belt conveyor, the lubricant is burnt off using a burner, followed by heating and sintering.
In a sintering furnace that performs cooling, a cavity is provided above the passage of the processed material in the dewaxing zone, and a flame path is communicated from the outer periphery of the furnace body to the side of the cavity,
A burner is attached to the outside of this to burn the raw material gas in an air-deficient condition, and the non-oxidized combustion exhaust gas generated in the void is placed at the boundary of the passageway for the processed material at the bottom of the void. A mixed gas supply system including a partition wall having a plurality of ventilation holes penetrating through the burner in the thickness direction for ejecting the gas vertically toward the burner, and including a mixing controller for adjusting the ratio of raw material gas and air to the burner. is connected.

An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 3 shows a continuous sintering furnace according to the present invention, in which the dewaxing zone A is
, a sintering zone B, and a cooling zone C are successively installed, and a mesh conveyor belt D is passed through each zone.By circulating the conveyor belt D by a belt drive mechanism E, a powder molded product (workpiece ), the removal of lubricant contained in the process, heating and sintering, and cooling of the product are performed sequentially.

4 to 6 show details of the dewaxing zone A, which is a feature of the present invention. First, this dewaxing zone is made of a refractory furnace body continuous with the furnace body 1 of the sintering zone B. 2, and the outer periphery is made gas tight by an airtight steel plate 3. A workpiece passage 5 communicating with the tunnel-shaped heating chamber 4 of the sintering zone B is formed in the furnace body 2, and a charging section 6 having an exhaust pipe 61 is provided at the starting end of the workpiece passage 5. There is.

A cavity 8 surrounded by a refractory wall 7 is formed in the furnace body above the material passage 5, and this cavity 8 is separated from the material passage 5 as shown in FIG. It is also a space with a large volume in cross section. A flame path 9 is communicated from the outer periphery of the furnace body 2 to one side of the space 8, and natural gas, propane,
A burner 10 is attached to burn a mixed gas of a raw material gas such as butane and air in an air-deficient state.

Furthermore, a partition wall 11 made of refractory is provided at the boundary between the cavity 8 and the object passage 5 to be treated, so that the partition wall 11 is supported on both sides in the width direction by the lower surfaces 81, 81 of the cavity 8. The partition wall 11 has a mountain-shaped or arch-shaped cross section, and is provided with a large number of ventilation holes 12 extending through its entire surface in the thickness direction. Since the partition wall 11 has a mountain-like or arch-like shape, the vent hole 12 has a centripetal center with respect to the width direction of the object passageway 5, as shown in FIG. 5a. The strength of the bulkhead is high,
Further, gas can be sprayed intensively onto the objects to be processed placed on the conveyor belt in the passage.

Here, the burner 10 includes a flame path 9 of the furnace body 2.
Refractory layer 1 having flame forming recesses 14 concentric with
3 and a water-cooled mantle part 15 surrounding this refractory layer 13, which fits into the flame channel 9 through a protrusion 16 formed at the center of the tip of the refractory layer 13, and a flange part 17 on the outer periphery. It is detachably attached to the furnace body 2. A nozzle hole 18 for a mixed gas of fuel gas and air is connected to the flame forming concave hole 14 from the rear end of the burner 10, and a pilot burner 19 for igniting and burning the mixed gas is inserted. As shown in FIG.
The supply system tied with 0 is connected.

The main pipe 20 is provided with a blower 23, which sucks air from the atmosphere through a filter 24 and a flow meter 25, and feeds the raw material gas through a check valve 2.
6. A mixture of air and raw material gas is continuously supplied through a flow meter 27, a solenoid valve 28, a mixing controller 29, and a speed regulating valve 30, and is sent into the main pipe 20 by a blower 23. The main pipe 20 is provided with a motor control valve 31 and a flame backflow safety device 32 at the tip of the blower 23, and a thermoelectric resistor 33 inserted into the workpiece passage 5 and a temperature An automatic control system equipped with a controller 34 is connected, and the temperature controller 34 and motor control valve 31 automatically control the amount of mixed gas supplied to the burner 10 to keep the temperature of the dewaxing zone always between 700 and 900. It is maintained at a temperature of around 30°F to prevent it from getting too hot.

In addition, in order to heat the material to be treated without oxidation, it is necessary to keep the ratio of fuel gas and air within a certain range (for example, about 1:17 for propane and about 1:6 for natural gas). In the present invention, the fuel gas pressure is controlled to a predetermined value by the mixture controller 29, and this pressure value controls the front of the orifice in the air piping, opens the orifice, and opens the regulating valve 30. As a result, the ratio of fuel gas and air can be arbitrarily set, and the mixing ratio can be increased or decreased by setting the regulating valve 30 to a predetermined opening degree and adjusting the throttle valve 36 of the air pipe 21. In addition, when the flame of the burner 10 goes out, the piping is automatically closed by the solenoid valve 28 of the raw material gas piping 20, and when the flame flows backward, the thermostat (not shown) of the flame backflow safety device 32 is closed. ) automatically stops the burner ignition and sounds an alarm.

In addition, the charging section 5 is provided with an ignition burner 37, which burns the combustion exhaust gas jetted from the cavity 8 into the material passage 5 to smoothly guide the burn-off gum out of the furnace. I have to.

The belt drive mechanism E may be a conventional drive drum type, but in this embodiment, the conveyor belt D on the return side is sandwiched between upper and lower pairs of roll groups 38, and this roll group 38 is rotated. I'm trying to send the belt with this. This method has the advantage of improving belt life because the belt does not bend, making the structure more compact since it does not require a large diameter drum, and reducing meandering and slipping because the belt's pressing force is dispersed. There are advantages in this point.
The cooling zone C has a circulating air cooling system in which the protective gas in the passage is sucked in by a blower 40, cooled through a cooler 41, and then sent into the passage again.

Since the present invention has the above-described configuration, when a mixture of fuel gas and air is fed into the burner 10 through the supply system and ignited by the pilot burner 19, the mixture gas flows into the flame forming concave as shown in FIG. The flame passes through the hole 14 and the flame path 9 and burns as a flame whose tip reaches into the cavity. At this time, since the space 8 and the workpiece passage 5 are partitioned by the partition wall 11, the flame is concentrated in this closed space and becomes a safe and uniform flame without being affected by the protective gas flow. , CO, CO ₂ , H ₂ , H ₂ O and N ₂ , and no free carbon, a high quality non-oxidizing exhaust gas is produced. Moreover, the space 8
Its cross section is larger than that of the lower processing material passage 5, and its volume is large, and the processing material passage 5 is partitioned by a partition wall 11 and is appropriately stored, so that the previous combustion The exhaust gas has a uniform pressure throughout the space and is at a considerably high pressure, and in this state, it is jetted vertically toward the object passage 5 from all the ventilation holes 12 provided in the partition wall 11. Therefore, the workpiece being moved on the conveyor belt D is exposed to a shower of hot and uniform combustion exhaust gas jets when it reaches the bottom of the cavity 8, and as a result, the entire object is uniformly and rapidly heated, and at the same time The jet gas is uniformly blown, causing intense gas conversion on the surface of the workpiece, and since the jet gas is reducing, the lubricant is removed continuously and rapidly.

Since the lubricant thus removed flows out to the inlet by the suction action of the charging section 6, there is no adverse effect on the sintering zone, and the workpiece from which the lubricant has been removed is sintered in a predetermined manner in the sintering zone. It is heated and sintered to a temperature (1120 to 1150° C. for iron-based materials), then rapidly cooled by a direct forced convection cooling mechanism in cooling zone C, and taken out of the furnace.

According to the present invention described above, a cavity 8 is recessed above the workpiece passage 5 in the dewaxing zone, and a flame path 9 is communicated with the side of the cavity 8 from the outer periphery of the furnace body, A burner 10 for burning the raw material gas in an air-deficient state is attached to the
On the lower side of the space 8, at the boundary of the object passage 5,
A large number of vent holes 12 for vertically ejecting the non-oxidized combustion exhaust gas generated in the cavity 8 toward the object to be treated.
A partition wall 11 is provided extending through the wall in the thickness direction, and a mixed gas supply system including a mixing controller for adjusting the ratio of raw material gas and air is connected to the burner 10. burn-off can be performed quickly and completely with a compact structure.

That is, since the mixed gas in an appropriately controlled ratio in the supply system is combusted from the side of the space 8 above the object passage 5 to be combusted, the flame is stable and high-temperature non-oxidized combustion exhaust gas is generated. In addition, the pressure can be made uniform in the large-volume space 8 and sprayed as a laminar shower from the ventilation hole 12 of the partition wall 11 onto the workpiece passing below. At the same time, the lubricant in the object to be treated can be rapidly reacted and gasified by the laminar flow shower of non-oxidized combustion exhaust gas, and only one burner is required. Since the non-oxidized combustion exhaust gas is also blown out in the height direction of the object passage,
The passage structure is simple, the furnace can be made compact, and the burner can be maintained easily, making it a highly effective idea in practical terms.

[Brief explanation of the drawing]

Fig. 1 is a partially cutaway side view showing a conventional continuous sintering furnace, Fig. 2 is a sectional view taken along the line shown in Fig. 1, and Fig. 3 is an example of a continuous sintering furnace according to the present invention. 4 is a vertical sectional side view showing details of the dewaxing zone in the present invention, FIG. 5 is a sectional view taken along the line of FIG. 4, and FIG. 5a is a partially enlarged view of FIG. 5. FIG. 6 is also a partial cross-sectional view of FIG. 5. A... Dewaxing zone, 5... Processing material passage, 7... Fireproof wall, 8... Vacant space, 9... Flame path,
10... Burner, 11... Partition wall, 12... Ventilation hole.

Claims (1)

[Claims] 1 A dewaxing zone, a sintering zone, and a cooling zone are sequentially connected using a tunnel furnace with a closed section.
A conveyor belt is passed through them, and the compacted powder is mixed with lubricant and molded using a press, etc. While the conveyor conveys the lubricant, the lubricant is burnt off using a burner, followed by heating, sintering, and cooling. In the sintering furnace in which the sintering process is carried out, a cavity 8 is recessed above the workpiece passage 5 in the dewaxing zone, and a flame path 9 is communicated from the outer periphery of the furnace body to the side of the cavity 8. A burner 10 is installed to burn the raw material gas in an air-deficient state, and below the cavity 8,
A partition wall 11 is provided at the boundary of the passage 5 for the object to be treated, in which a large number of ventilation holes 12 are provided in the thickness direction for vertically ejecting the non-oxidized combustion exhaust gas generated in the cavity 8 toward the object to be treated. A continuous sintering furnace characterized in that the burner 10 is connected to a mixed gas supply system including a mixing controller for adjusting the ratio of raw material gas and air.