JP5622150B2 - Open firing furnace and dewaxing method in the firing furnace - Google Patents

Description

  The present invention relates to an open-type firing furnace and a dewaxing method in the firing furnace. More specifically, the present invention relates to an open-type firing furnace for producing a sintered part by firing a metal powder compact including a mold lubricant and a dewaxing method in the firing furnace.

  Various parts for automobiles are usually manufactured using a molded body obtained by press-molding metal powder filled in a recess of a die.

  When metal powder is pressed, mold lubricants such as wax are used to reduce the friction generated between the inner wall of the die and the metal powder and to produce a high-quality molded body without seizure. Yes.

  Such a mold lubricant is removed by being vaporized by combustion gas in a preheating zone or a preheating chamber in a firing furnace for firing the molded body. Conventionally, as a firing furnace, an open-type firing furnace in which the inside of the furnace is open to the outside air and a closed firing furnace in which the inside of the furnace can be shut off from the outside by a shutter or the like are used.

  Among them, the open-type firing furnace has an advantage that the structure of the furnace is simplified because it does not require a shutter for shutting off from the outside air and a mechanism for operating the shutter, but has entered the preheating chamber. Parts may be oxidized by the oxidizing atmosphere gas, and a decarburization phenomenon may occur in the oxidized portion in the subsequent heating process. When the decarburization phenomenon occurs, a predetermined strength (hardness) cannot be obtained, resulting in a product defect.

  On the other hand, in a closed type firing furnace as described in Patent Document 1, for example, an oxidizing atmosphere gas can be prevented from entering the preheating chamber, so that a decarburization phenomenon does not occur. Therefore, a sintered part having a predetermined strength can be obtained.

Japanese Patent Publication No. 60-27912

  However, in the closed firing furnace, the preheating chamber is not opened to the outside air, so that the mold lubricant vaporized by the combustion gas accumulates in the preheating chamber as “soot”. When the accumulated “soot” adheres to the powder compact, and this powder compact is heated in the subsequent heating process, the adhering “soot” becomes a nest, resulting in poor appearance. In order to prevent this, it is necessary to frequently clean the preheating chamber, which reduces productivity.

  The present invention has been made in view of such circumstances, and provides an open-type firing furnace capable of suppressing the decarburization phenomenon that was unavoidable in the conventional open-type firing furnace, and a dewaxing method in the firing furnace. It is intended to provide.

(1) In the open-type firing furnace of the present invention, a preheating chamber, a heating chamber, a slow cooling chamber, and a cooling chamber are provided in this order, and a powder molded body obtained by press-molding a metal powder containing a mold lubricant is sintered. An open-type firing furnace,
A combustion gas supply unit for supplying combustion gas to the upper space of the preheating chamber;
The preheating chamber and the lower of Oite said combustion gas supply unit to being disposed above the conveyed powder compact to the preheating chamber, the combustion gas supplied from said combustion gas supply unit, the powder compact and the dispersion plate and supplying the dispersion towards the,
A shielding portion provided on the dispersion plate to adjust the amount of combustion gas that hits the powder compact ,
A pair of combustion gas supply parts are provided along the traveling direction of the powder compact in the preheating chamber,
The shielding portion is disposed corresponding to the combustion gas supply portion on the downstream side in the traveling direction of the pair of combustion gas supply portions.
It is said.

In the open-type firing furnace of the present invention, the combustion gas supplied into the preheating chamber can be dispersed by the dispersion plate disposed in the preheating chamber, and the combustion gas can be supplied uniformly to the powder compact. Thereby, the oxidation of the powder compact and the decarburization phenomenon caused by excessive combustion gas can be prevented.
Moreover, the further includes a shielding portion provided in the dispersion plate in order to adjust the amount of combustion gas which corresponds powder compact, it is possible to shut off the flow of combustion gases through the shielding part, by the dispersion plate However, even if there is a place where a large amount of combustion gas flows locally, the shielding portion can be adjusted so that the amount of combustion gas corresponding to the powder compact is more uniform.
Further, since the combustion gas supply unit on the downstream side is supplied with combustion gas having a temperature higher than that on the upstream side, the influence of oxidation of the powder compact due to excessive combustion gas is great. Since the shielding portion is provided corresponding to the above, oxidation of the powder molded body can be prevented with the minimum necessary equipment (shielding portion).

( 2 ) In the open-type firing furnace according to ( 1 ), the combustion gas supply unit is provided on one of the wall portions on the left and right walls in the traveling direction of the powder compact in the preheating chamber,
The shielding part is made of a strip-shaped member,
It is preferable that the side edge of the longitudinal direction of this strip-shaped member is arrange | positioned along the inner surface of the other wall part. When the combustion gas is supplied from one wall side of the preheating chamber to the preheating chamber, a large amount of combustion gas is supplied to the other wall side opposite to the one wall portion, It is conceivable that the combustion gas hits the arranged powder compact. Even in this case, the shielding portion made of a strip-shaped member is disposed so that the side edge in the longitudinal direction is along the inner surface of the other wall portion, so that the combustion gas along the inner surface of the other wall portion is reduced. The flow can be cut off. Accordingly, it is possible to prevent the combustion gas from hitting the powder molded body disposed on the other wall side, and to prevent the powder molded body from being oxidized by too much combustion gas.

( 3 ) In the open-type firing furnace of (1) to ( 2 ), the flow path is changed to change the flow direction of the combustion gas blown into the preheating chamber in front of the gas blowing port of the combustion gas supply unit. A plate is preferably provided. In this case, the combustion gas can be effectively diffused in the upper space of the preheating chamber by changing the flow direction of the combustion gas upward by the flow path changing plate and applying it to the ceiling of the preheating chamber.

( 4 ) In the open-type firing furnace of ( 1 ) to ( 3 ), it is preferable that the shielding portion is formed integrally with the dispersion plate. In this case, since the shielding part is formed integrally with the dispersion plate, the number of parts can be reduced.

( 5 ) In the open-type firing furnace of (1) to ( 4 ), the dispersion plate may be made of a ceramic plate having a plurality of openings. In this case, the dispersibility of the combustion gas can be adjusted to some extent by appropriately adjusting the size, position, number, etc. of the openings formed of round holes.

( 6 ) The dewaxing method in the open-type firing furnace according to the first aspect of the present invention includes a preheating chamber, a heating chamber, a slow cooling chamber, and a cooling chamber provided in this order in the preheating chamber in the open-type firing furnace, A dewaxing method for removing a mold lubricant contained in a powder compact obtained by pressure-molding metal powder,
The temperature of the combustion gas supplied toward the powder compact and preheating the powder compact is set in the range of 590 to 610 ° C., and the composition ratio of the combustion gas is butane: air = 1: 21 to 25 It is characterized by being set within the range.

In the dewaxing method in the open-type firing furnace according to the first aspect of the present invention, the temperature of the combustion gas for preheating the powder molded body is set in the range of 590 to 610 ° C., so that the powder molded body is configured. It is possible to effectively vaporize the mold lubricant contained in the powder compact while suppressing oxidation of the metal powder. Further, the composition ratio of the combustion gas is set within a range of butane: air (air) = 1: 21 to 25, and the butane is completely burned (the composition ratio at this time is butane: air = 1: 31). Since the proportion of butane is increased, the hardness of the product can be increased by utilizing the carburizability of butane while suppressing the generation of “soot” due to butane.
In the present invention, the type of mold lubricant is not limited to wax (wax), but since wax is generally used frequently, the mold lubricant is vaporized and removed in the preheating step. This method is referred to as a “dewaxing method”.

( 7 ) Further, the dewaxing method in the open-type firing furnace according to the second aspect of the present invention is a method for forming a powder compact obtained by pressure-molding metal powder in the preheating chamber in the open-type firing furnace of (1). A dewaxing method for removing the contained mold lubricant,
The temperature of the combustion gas for preheating the powder compact is set in a range of 590 to 610 ° C., and the composition ratio of the combustion gas is set in a range of butane: air = 1: 21 to 25. Yes.

  Also in the dewaxing method in the open-type firing furnace according to the second aspect of the present invention, the temperature of the combustion gas for preheating the powder compact is set as in the dewaxing method in the open-type firing furnace according to the first aspect. Since it is set within the range of 590 to 610 ° C., it is possible to effectively vaporize the mold lubricant contained in the powder molded body while suppressing oxidation of the metal powder constituting the powder molded body. it can. In addition, the composition ratio of the combustion gas is set within the range of butane: air = 1: 21 to 25, and the proportion of butane is larger than when butane burns completely. While suppressing, the hardness of the product can be increased by utilizing the carburizing property of butane.

  Furthermore, in the dewaxing method in the open-type firing furnace according to the second aspect of the present invention, since the open-type firing furnace of (1) is used, the dispersion plate disposed in the preheat chamber allows the preheat chamber to enter the preheat chamber. The supplied combustion gas can be dispersed, and the combustion gas can be supplied uniformly to the powder compact. Thereby, the oxidation of the powder compact and the decarburization phenomenon caused by excessive combustion gas can be prevented.

( 8 ) In the dewaxing method in the open firing furnace of ( 6 ) or ( 7 ), it is preferable that the temperature of the combustion gas is set to about 600 ° C. In this case, it is possible to effectively vaporize the mold lubricant contained in the powder molded body while more effectively suppressing the metal powder constituting the powder molded body from being oxidized.

( 9 ) In the dewaxing method in the open-type firing furnace of ( 6 ) to ( 8 ), it is preferable that the composition ratio of the combustion gas is set to approximately 22 with respect to butane 1. In this case, the hardness of the product can be increased by utilizing the carburizing property of butane while suppressing the generation of “soot” due to butane more effectively.

  According to the open-type firing furnace and the dewaxing method in the firing furnace of the present invention, the decarburization phenomenon that is unavoidable in the conventional open-type firing furnace can be suppressed.

It is a schematic explanatory drawing of an open type pusher baking furnace. It is plane explanatory drawing of the preheating chamber in the open type pusher baking furnace which concerns on one embodiment of this invention. It is a cross-sectional explanatory drawing of the preheating chamber shown by FIG. It is a figure which shows the relationship between the temperature of combustion gas, and process capability. It is a figure which shows the relationship between the composition ratio of butane and air which comprises combustion gas, and process capability. It is a figure which shows the presence or absence of decarburization. It is a figure which shows the other example of a dispersion plate.

Hereinafter, embodiments of an open-type firing furnace and a dewaxing method in the firing furnace according to the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic explanatory view of an open type pusher firing furnace in which a workpiece is moved by a pusher, and FIG. 2 is a plan view of a preheating chamber 1 in an open type pusher firing furnace F according to an embodiment of the present invention. FIG. 3 is a cross-sectional explanatory view of the preheating chamber 1 shown in FIG.

  The open-type pusher firing furnace F is a tunnel-like structure constructed of a refractory and a heat insulating material, and a preheating chamber 1, a heating chamber 2, a slow cooling chamber 3, and a cooling chamber 4 are connected in order from the entrance side. Yes. A skid rail 5 is laid on the floor surface of each chamber, and a laminated body 19 of works (powder compacts) placed on the tray 6 along the skid rail 5 is transferred from the preheating chamber 2 to the cooling chamber 5. Moving. Loading of the tray 6 into the furnace and movement within the furnace are performed by a pusher 7 disposed outside the furnace.

On the tray 6, a plurality of workpieces 9 are placed with the fireproof plate 8 interposed therebetween. A plurality of workpieces 9 and a plurality of refractory plates 8 constitute a workpiece laminate 19. The tray 6 is pushed by the succeeding tray 6 and sequentially moves to the outlet side.
The preheating chamber 1 is provided with a radiant burner 10 that is a combustion gas supply unit for supplying combustion gas into the preheating chamber 1, and a heater 11 is provided inside the heating chamber 2. A cooling water jacket 12 is disposed on the outer periphery of the cooling chamber 4.

  In the work 9 carried into the preheating chamber 1, the mold lubricant contained in the work 9 is vaporized and removed by the combustion heat of the combustion gas supplied by the radiant burner 10. In the subsequent heating chamber 2, the workpiece 9 from which the mold lubricant has been removed is heated to a predetermined temperature (for example, 1250 ° C.) and sintered. The sintered workpiece 9 is gradually cooled in the subsequent slow cooling chamber 3 and cooling chamber 4 and is carried out of the furnace.

  In the present embodiment, as shown in FIG. 2, a pair of radiant burners 10a and 10b are arranged along the traveling direction of the workpiece 9 (the direction indicated by the arrow A in FIG. 2). One radiant burner 10a is arranged at the upper part of the left wall portion facing the traveling direction of the workpiece 9, and the other radiant burner 10b is downstream of the radiant burner 10a and the workpiece 9 proceeds. It is disposed in the upper part of the right wall part facing the direction. In the radiant burners 10a and 10b, a mixed gas of butane and air is combusted, and this combustion gas is supplied to the upper space of the preheating chamber 1 from the gas outlets 16a and 16b of the radiant burners 10a and 10b. In FIG. 2, 13 is a supply pipe for a mixed gas of butane and air.

  Dispersion plates 20 a and 20 b that disperse and supply the combustion gas supplied from the radiant burners 10 a and 10 b toward the workpiece 9 are disposed in the preheating chamber 1. The dispersion plate 20a is disposed corresponding to the radiant burner 10a, and the dispersion plate 20b is disposed corresponding to the radiant burner 10b. Dispersion plates 20 a and 20 b are placed on stepped portion 17 at the upper wall of preheating chamber 1.

  The dispersion plates 20a and 20b have a rectangular shape in plan view, and the side surfaces thereof have a mountain shape bent at the center as shown in FIG. The dispersion plates 20a and 20b are made of a ceramic plate having a thickness of about 50 to 90 mm, and a plurality of round holes (openings) 21 are formed in a staggered pattern. The diameter and pitch of the round holes 21 can be appropriately selected in consideration of the dispersibility of the combustion gas. For example, the diameter and the pitch can be set to 25 mm and 50 mm. Further, the aperture ratio can be appropriately selected in consideration of the dispersibility of the combustion gas, and can be set to 15%, for example.

  A flow path changing plate 25 is disposed in front of the gas outlet 16b of the radiant burner 10b (forward in the outlet direction) to change the flow direction of the combustion gas blown into the preheating chamber 1 upward. The flow path changing plate 25 is inclined and arranged in front of the gas outlet 16b so as to be positioned higher as it is away from the gas outlet 16b. As a result, the combustion gas blown out from the gas outlet 16b hits the surface 25a of the flow path changing plate 25, changes the flow direction upward as indicated by the arrow in FIG. 3, and further, the ceiling 1c of the preheating chamber 1 In this case, the flow direction is changed downward or diagonally downward. Thereby, in the upper space of the preheating chamber 1, combustion gas can be disperse | distributed effectively.

  The flow path changing plate 25 can be made of alumina, for example, and the thickness thereof can be about 50 to 70 mm. The flow path changing plate 25 is supported by a pair of support portions 26 fixed to the dispersion plate 20b.

  The shielding part 30 is provided along the inner surface of the wall part 1b which opposes the wall part 1a in which the radiant burner 10b was provided among the wall parts 1a and 1b on the left and right in the traveling direction of the work 9 in the preheating chamber 1. This shielding part 30 consists of a strip-shaped member, and the side edge of the longitudinal direction is arrange | positioned along the inner surface of the wall part 1b. In the present embodiment, the dimension in the longitudinal direction (left and right direction in FIG. 2) of the dispersion plate 20b and the dimension in the longitudinal direction of the shielding part 30 are the same. Although the width | variety (dimension of a transversal direction) of the shielding part 30 is not specifically limited in this invention, For example, it can be about 100-130 mm. The shielding unit 30 can be made of alumina, for example.

  When combustion gas is supplied into the preheating chamber from one wall portion side of the preheating chamber 1, a large amount of combustion gas is supplied to the other wall portion side facing the one wall portion, and the other wall portion side. It is conceivable that the combustion gas hits the workpiece 9 disposed in However, when the shielding portion 30 made of a strip-like member is disposed so that the side edge in the longitudinal direction is along the inner surface of the other wall portion, as in the present embodiment, the inner surface of the other wall portion. The flow of the combustion gas along can be cut off. Therefore, it is possible to prevent the combustion gas from hitting the work 9 arranged on the other wall side, and to prevent the work 9 from being oxidized by too much combustion gas.

  In the present embodiment, among the pair of radiant burners 10a and 10b, the flow path changing plate 25 and the shielding portion 30 are provided corresponding to only the radiant burner 10b on the downstream side in the traveling direction of the work 9, and the upstream side The radiant burner 10a is not provided with the flow path changing plate 25 and the shielding part 30. Since the downstream radiant burner 10b is supplied with combustion gas having a temperature higher than that of the upstream side, the influence of the oxidation of the work 9 due to excessive combustion gas is great. In other words, since the temperature of the combustion gas blown out from the upstream radiant burner 10a is relatively low, the work 9 is hardly oxidized by the combustion gas. Therefore, by providing the flow path changing plate 25 and the shielding portion 30 corresponding to the downstream radiant burner 10b having a large influence, the oxidation of the workpiece 9 can be prevented with the minimum necessary equipment.

  In the present invention, in the preheating chamber 1, the temperature of the combustion gas for preheating the workpiece 9 is set in the range of 590 to 610 ° C., and the composition ratio of the combustion gas is in the range of butane: air = 1: 21 to 25. Is set in. The temperature of the combustion gas is preferably lower because the oxidation of the workpiece 9 progresses as the temperature becomes higher. However, when the temperature is too low, the vaporization of the mold lubricant is suppressed, and the setting of 550 ° C. or lower is, for example, as a facility. Since it is difficult, it is set within the range of 590 to 610 ° C. By setting within this range, the mold lubricant contained in the workpiece 9 can be effectively vaporized while suppressing the metal powder constituting the workpiece 9 from being oxidized.

  Further, in the present invention, the ratio of butane is set higher than when butane completely burns (the composition ratio at this time is butane: air = 1: 31). That is, butane is actively left in the combustion gas. Butane has a carburizing property, and by applying this butane to the work 9, the hardness of the work 9 can be increased. On the other hand, since butane easily generates soot, Adhesion causes poor appearance. Therefore, by setting the composition ratio of the combustion gas within the range of butane: air = 1: 21 to 25, the hardness of the product using the carburizing property of butane while suppressing the occurrence of “soot” due to butane. Can be increased.

Of the temperature range, the temperature of the combustion gas is preferably set to approximately 600 ° C. In this case, the mold lubricant contained in the work 9 can be effectively vaporized while suppressing the oxidation of the metal powder constituting the work 9 more effectively.
Further, in the composition range, it is preferable that the composition ratio of the combustion gas is set to approximately 22 with respect to butane 1. In this case, the hardness of the product can be increased by utilizing the carburizing property of butane while suppressing the generation of “soot” due to butane more effectively.

Next, experimental results obtained by changing the temperature or gas composition of the combustion gas in various ways will be described.
Table 1 and FIG. 4 show that the product hardness when the composition ratio of the combustion gas is constant (butane: air = 1: 31) and the temperature of the combustion gas is changed to 580 ° C., 600 ° C., 650 ° C., and 700 ° C. The result of examining the thickness (Rockwell hardness) and the process capability is shown. In the upper space of the preheating chamber, a flow path changing plate, a dispersion plate, and a shielding portion shown in FIGS. The specifications of the dispersion plate and the shielding part were as follows.
Channel change plate material: Alumina Thickness: 60mm
Length: 345mm
Width: 345mm
Dispersion plate material: Ceramics Thickness: 70mm
Hole pitch: 50mm
Hole diameter: 25mm
Opening ratio: 15%
Shielding material quality: Alumina Thickness: 60mm
Length: 690mm
Width: 115mm

  From Table 1 and FIG. 4, it can be seen that the process capability is maximized around 600 ° C.

  Table 2 and FIG. 5 show that the combustion gas temperature is constant (700 ° C.), and the combustion gas composition ratio (butane: air) is 1:18, 1:20, 1:22, 1:25, 1:27, The result of examining the hardness (Rockwell hardness) and the process capability of the product when changing to 1:31 is shown. In the upper space of the preheating chamber, a flow path changing plate, a dispersion plate, and a shielding portion shown in FIGS. The specifications of the dispersion plate and the shielding part were as described above (same as the experimental conditions in Table 1).

  From Table 2 and FIG. 5, it can be seen that the generation of soot is observed when the proportion of butane in the combustion gas increases, and that the process capability falls below the standard value of 1.33 when the proportion decreases.

  Table 3 summarizes the above results. In the comparative example, the workpiece was preheated at a combustion gas temperature of 700 ° C. and a combustion gas composition ratio of 1:31 using a conventional open-type firing furnace. In Examples 1 to 4, the work was preheated by changing the ceiling structure, temperature, and gas composition ratio as shown in Table 3.

  In the case of the comparative example, the hardness defect rate was 2.8%, and the process capability was 0.63. The hardness failure in the comparative example is due to the decarburization phenomenon caused by the oxidation of the workpiece as described above. 6A is an electron micrograph of the material structure of the product according to Comparative Example 1. FIG. It can be seen that the white structure (ferrite containing no carbon) increases due to the decarburization phenomenon.

  On the other hand, in all the examples, the hardness defect rate was 0%. In particular, in Example 4 in which the flow path changing plate, the dispersion plate, and the shielding portion described above are employed, the combustion gas temperature is 600 ° C., and the combustion gas composition ratio is air 22 with respect to butane 1, the hardness of the product And the best in process capability. FIG. 6B is an electron micrograph of the material structure of the product according to Example 4. It can be seen that this is a mixed structure of white and black (many bentonites containing carbon) and is a normal structure without decarburization.

[Other variations]
The present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the claims.
For example, in the above-described embodiment, the dispersion plate and the shielding portion are separate, but they can be integrally formed as shown in FIG. 7, for example. In the example shown in FIG. 7, the hole 121 is not formed in a predetermined range inward from the side edge 120 a disposed on the side far from the blowout port of the radiant burner in the dispersion plate 120. And the strip | belt-shaped area | region 130 in which this hole 121 is not formed is made into the shielding part. Even in this case, the region 130 can block the flow of the combustion gas along the inner surface of the wall portion far from the outlet of the radiant burner.
In the embodiment described above, the size of the round hole, which is the opening of the dispersion plate, is the same, but the size of the opening can be changed depending on the location. For example, by reducing the opening on the side far from the blowout port of the radiant burner, the flow of the combustion gas along the inner surface of the wall portion on the side far from the blowout port of the radiant burner can be suppressed or substantially blocked. In this case, even if a shielding part is not employed, the amount of combustion gas that hits the powder compact can be made uniform by the dispersion plate.

In the above-described embodiment, a round hole is adopted as the opening of the dispersion plate, but an opening having another shape such as a long hole or a rectangular opening may be used.
In the above-described embodiment, the flow path changing plate 25 is supported by the support portion 26. However, a structure in which the flow path changing plate 25 is suspended from the ceiling 1c of the preheating chamber 1 may be employed.

  In the embodiment described above, a pair of radiant burners is used. However, the number of radiant burners may be one, or may be three or more.

1 Preheating chamber 2 Heating chamber 3 Slow cooling chamber 4 Cooling chamber 9 Workpiece (powder compact)
10a Radiant burner (combustion gas supply unit)
10b Radiant burner (combustion gas supply unit)
16a Gas outlet 16b Gas outlet 20a Dispersion plate 20b Dispersion plate 21 Hole (opening)
25 flow path change plate 26 support part 30 shielding part F open type pusher firing furnace

Claims (9)

A preheating chamber, a heating chamber, a slow cooling chamber, and a cooling chamber are provided in this order, and is an open-type firing furnace that sinters a powder molded body obtained by pressure-molding a metal powder containing a mold lubricant,
A combustion gas supply unit for supplying combustion gas to the upper space of the preheating chamber;
The preheating chamber and the lower of Oite said combustion gas supply unit to being disposed above the conveyed powder compact to the preheating chamber, the combustion gas supplied from said combustion gas supply unit, the powder compact and the dispersion plate and supplying the dispersion towards the,
A shielding portion provided on the dispersion plate to adjust the amount of combustion gas that hits the powder compact ,
A pair of combustion gas supply parts are provided along the traveling direction of the powder compact in the preheating chamber,
The said shielding part is arrange | positioned corresponding to the combustion gas supply part of the advancing direction downstream among a pair of combustion gas supply parts, The open type baking furnace characterized by the above-mentioned. The combustion gas supply part is provided on one wall part side of the wall parts on the left and right in the traveling direction of the powder compact in the preheating chamber,
The shielding part is made of a strip-shaped member,
2. The open-type firing furnace according to claim 1 , wherein the strip-shaped member has a side edge in a longitudinal direction thereof disposed along an inner surface of the other wall portion. The opening according to claim 1 or 2 , wherein a flow path changing plate that changes the flow direction of the combustion gas blown into the preheating chamber is disposed in front of the gas outlet of the combustion gas supply unit. Mold firing furnace. The shield portion is open firing furnace according to any one of claims 1 to 3 which is formed integrally with the distribution plate. The dispersion plate, open firing furnace according to any one of claims 1 to 4 comprising a ceramic plate having a plurality of openings. Dewaxing to remove mold lubricant contained in a powder compact obtained by pressure-molding metal powder in the preheating chamber in an open-type firing furnace in which a preheating chamber, a heating chamber, a slow cooling chamber, and a cooling chamber are provided in this order. A method,
The temperature of the combustion gas supplied toward the powder compact and preheating the powder compact is set in the range of 590 to 610 ° C., and the composition ratio of the combustion gas is butane: air = 1: 21 to 25 A dewaxing method in an open-type firing furnace, characterized by being set within a range of A dewaxing method for removing mold lubricant contained in a powder molded body obtained by press-molding metal powder in the preheating chamber in the open-type firing furnace according to claim 1,
The temperature of the combustion gas for preheating the powder compact is set in a range of 590 to 610 ° C., and the composition ratio of the combustion gas is set in a range of butane: air = 1: 21 to 25. A dewaxing method in an open firing furnace. The dewaxing method in an open-type firing furnace according to claim 6 or 7 , wherein the temperature of the combustion gas is set to approximately 600 ° C. Dewaxing method in open firing furnace according to any one of claims 6-8 to set the air in a substantially 22 the composition ratio of the combustion gas to butane 1.