JP2014006019A - Continuous sintering furnace and operating method of continuous sintering furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce gas consumption and power consumption rather than the prior arts, in a continuous sintering furnace, and to suppress a sintering defect by completing dewaxing in a dewaxing section.SOLUTION: In the continuous sintering furnace, a dewaxing section 20, a sintering section 30 and a cooling section 40 are provided continuously from a conveyance upstream side to a downstream side in a furnace body 10 penetrated with a furnace inside conveyance path 11 for a work W. The continuous sintering furnace comprises conveyance means 50 for conveying the work W along the furnace inside conveyance path 11. Within a connection passage 14 provided in a boundary portion between the dewaxing section 20 and the sintering section 30, shield air stream jetting means 60 is provided which includes a nozzle 61 for jetting out a shield air stream shielding and partitioning a space within the furnace into the dewaxing section 20 and the sintering section 30. A jetting direction and a flow velocity of the shield air stream are set appropriately to prevent harmful gas generated in the dewaxing section 20 from being infiltrated into the sintering section 30, and while reducing a sintering defect, the quantity of atmospheric gas to be supplied to the sintering section 30 and power consumption for heating the atmospheric gas are reduced.

Description

  The present invention relates to a continuous sintering furnace and a method of operating the continuous sintering furnace in powder metallurgy technology for sintering a green compact formed into a predetermined shape.

  The sintering process of the powder metallurgy product obtained by sintering the green compact obtained by compression molding the raw material powder into a predetermined shape is a dewaxing process as a preliminary process for removing the lubricant contained in the green compact, a predetermined temperature This requires a sintering process, which is the main process of heating in step 1, and a cooling process, which is a prognostic process for cooling the sintered body. As a furnace for carrying out these processes, a continuous sintering furnace in which a dewaxing section, a sintering section, and a cooling section for performing each process while conveying a work with a mesh belt are continuously used is used (Patent Literature). 1).

  In this type of continuous sintering furnace, it is required to optimize the furnace environment such as atmosphere and temperature in order to give the workpiece desired characteristics. In general, in the dewaxing section, hydrocarbon gas such as propane or butane is incompletely burned as a heat source to prevent oxidation of the work, and discharge secondary soot generated from the lubricant in the generated exhaust gas. ing. This soot is likely to occur when the temperature of the dewaxing portion is low, and the dewaxing is insufficient. Therefore, the soot is suppressed by increasing the temperature to lower the carbon potential and promoting decarburization. However, if harmful gas containing zinc oxide, which is a thermal decomposition component of the lubricant (for example, zinc stearate) used in compression molding due to decomposition of the heated combustion gas, enters the sintered part, In addition to excessive decarburization reaction, the desired strength and dimensions cannot be obtained, and the appearance is deteriorated to cause defects.

  Therefore, conventionally, an atmospheric gas composed of a reducing gas and a non-oxidizing gas such as nitrogen exceeding the amount of exhaust gas generated by the thermal decomposition of the lubricant is supplied into the furnace near the downstream end of the sintered part. By increasing the internal pressure, the invasion of harmful gases from the dewaxed part to the sintered part is suppressed. In addition, a ceiling that can be moved up and down is provided at the boundary between the dewaxed part and the sintered part, and the partition door is lowered to a height that does not hinder the passage of the work, and the space between the dewaxed part and the sintered part is lowered. Measures such as restricting the flow of free gas are also being implemented.

JP 2001-303105 A

  In the conventional continuous sintering furnace described above, the amount of combustion gas generated fluctuates when the amount of work input into the furnace changes, or the combustion amount is increased or decreased to maintain an appropriate temperature at the dewaxing section. Accordingly, it is required that the supply amount of the atmospheric gas from the downstream end portion of the sintering portion into the furnace is always higher than the gas amount in the dewaxing portion. Moreover, in order to maintain the predetermined furnace atmosphere, in order to prevent gas from entering from the cooling part to the sintering part, the consumption of the supplied atmosphere gas and the power consumption for heating the atmosphere gas are large. There is an economic disadvantage.

  This invention is made | formed in view of the said situation, The main objective is to provide the operating method of the continuous sintering furnace and continuous sintering furnace which can reduce the gas amount and electric energy which are consumed. .

  The continuous sintering furnace of the present invention is provided with a dewaxing part, a sintering part, and a cooling part continuously from the upstream side to the downstream side of the furnace body through which the workpiece conveyance path passes, and In a continuous sintering furnace having a conveying means for conveying along an inner conveying path, shielding for separating the dewaxed part and the sintered part by shielding the furnace space at the boundary part between the dewaxed part and the sintered part It has the shielding airflow ejection means which ejects an airflow (Claim 1).

  According to the continuous sintering furnace of the present invention, harmful gas generated in the dewaxing portion can be prevented from entering the sintered portion by the shielded air current ejected to the boundary portion between the dewaxing portion and the sintered portion. . Thereby, the effect | action of preventing the penetration | invasion of harmful gas from a dewaxing part to a sintering part by the pressure of the atmospheric gas supplied to the sintering part becomes unnecessary. The temperature of the shielding airflow that shields the space in the furnace from the dewaxing part to the sintering part and partitions the dewaxing part and the sintering part may be about the heating temperature of the dewaxing part, and is lower than the temperature of the sintering part. For example, the temperature of the dewaxing part is about 600 to 750 ° C., and the temperature of the sintered part is about 1100 to 1200 ° C. Therefore, the supply amount of the atmospheric gas to the sintered part and the electric power for heating the atmospheric gas can be reduced. Further, dewaxing is easily completed at the dewaxed portion, and poor sintering is suppressed.

  In the continuous sintering furnace of the present invention, the shielded airflow ejecting means has a nozzle for ejecting a shielded airflow into the furnace space, and the direction of ejection of the shielded airflow from the nozzle is from above to below, A configuration in which it is inclined at an angle of 40 to 60 ° with respect to the horizontal direction toward the direction of the brazing part, and the flow velocity of the shielding airflow is preferably 5 to 30 m / s (Claim 2).

  Regarding the direction of jetting of the shielded airflow, it is harmful to the sintered part because the shielded airflow is opposed to the gas flow from the dewaxed part to the sintered part by ejecting from above to the direction of the dewaxed part. Gas becomes more difficult to enter. Further, when the jet angle is less than 40 °, the shield airflow hardly reaches the work, and the entire cross section of the in-furnace transport path becomes difficult to shield. On the other hand, when the ejection angle exceeds 60 °, a circulating flow is generated around the workpiece, and the gas in the dewaxing portion becomes a turbulent state and easily enters the sintered portion. From the above, it is preferable that the spray angle of the shield airflow jetted from the upper side to the lower side and toward the dewaxing portion is inclined at 40 to 60 °. In this angle range, 45 to 60 ° is more preferable. Thus, since the shielding airflow has directivity, an advantage that the shielding property is further improved is obtained.

  When the flow rate of the shield airflow is less than 5 m / s, the replacement with the dewaxing gas that has entered the lower part of the furnace does not proceed smoothly. On the other hand, when the flow rate exceeds 30 m / s, Will move within. Therefore, the flow rate of the shielding airflow is preferably 5 to 30 m / s, and in this range, 15 to 30 m / s is more preferable.

  Next, according to the operation method of the continuous sintering furnace of the present invention, when the workpiece is sintered using the continuous sintering furnace according to claim 1 or 2, the atmospheric gas supplied to the sintered part is shielded. The atmospheric gas is distributed to the airflow ejecting means and ejected from the shielded airflow ejecting means to the boundary portion as the shielded airflow.

  According to the operation method of the continuous sintering furnace of the present invention, a part of the atmospheric gas supplied to the sintered part is diverted to a shielded air current that is jetted to the boundary part between the dewaxed part and the sintered part, According to this, the supply amount of the atmospheric gas to the sintered part and the electric power for heating the atmospheric gas can be reduced as described above.

  The operation method of the continuous sintering furnace according to the present invention is the same gas as the dewaxing gas supplied to the dewaxing part when the workpiece is sintered using the continuous sintering furnace according to claim 1 or 2. Is introduced into the shielding airflow ejection means, and the dewaxing gas is ejected from the shielding airflow ejection means to the boundary portion as the shielding airflow. According to this method, the dewaxing gas is a gas containing moisture suitable for dewaxing, and is preliminarily jetted in the direction of the dewaxing part by being heated to the temperature of the dewaxing part in advance. However, the atmosphere in the dewaxing portion is not disturbed, and it is not necessary to heat the gas separately, which is economical.

  According to the present invention, there is an effect that a continuous sintering furnace and an operation method of the continuous sintering furnace that can reduce the amount of gas and electric power consumed are provided.

It is a sectional side view showing typically a continuous sintering furnace concerning one embodiment of the present invention. It is a figure which shows the II-II cross section of FIG. It is a sectional side view which shows the shielding airflow ejection means of one Embodiment. It is a sectional side view which shows typically the continuous sintering furnace which concerns on other embodiment of this invention.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
(1) Basic Configuration of Continuous Sintering Furnace FIG. 1 shows a continuous sintering furnace according to an embodiment. This continuous sintering furnace includes a furnace body 10 in which a tunnel-shaped in-furnace conveyance path 11 for conveying a workpiece W in a horizontal direction is linearly formed inside, and an upstream of the in-furnace conveyance path 11. Conveying means 50 for conveying along the downstream side (from the left side to the right side in FIG. 1) is provided.

  An inlet 12 is provided at the upstream end of the furnace body 10, and a discharge port 13 is provided at the downstream end. In this case, the conveying means 50 is composed of an endless mesh belt. The mesh belt includes a transport unit 51 horizontally installed along the in-furnace transport path 11 extending from the charging port 12 to the discharge port 13, and a return unit that returns from the discharge port 13 to the charging port 12 through the lower side of the furnace body 10. 52, and the transport unit 51 is driven to move from the loading port 1 toward the discharge port 13 at a predetermined speed and rotate as a whole.

  Although the continuous sintering furnace of the present embodiment uses a mesh belt as the conveying means, the conveying means of the present invention is not limited to the mesh belt, and continuous conveying means such as a roller hearth furnace, a pusher furnace, a walking beam furnace, etc. If it is a sintering furnace which has this, it is applicable.

  The furnace body 10 has a configuration in which a dewaxing portion 20, a sintering portion 30, and a cooling portion 40 are continuously and integrally provided from the upstream side to the downstream side of the workpiece W. The dewaxing part 20, the sintering part 30, and the cooling part 40 are passed through the conveying means 50 in this order and sintered.

  The workpiece W is placed on the conveying means 50 from the loading port 12 of the furnace body 10 and is first introduced into the dewaxing section 20. The workpiece W placed on the conveying means 50 from the loading port 12 is a green compact obtained by compression-molding raw material powder into a predetermined shape, and the workpiece W is brought to a predetermined temperature (for example, about 600 to 750 ° C.) in the dewaxing portion 20. Heated. The workpiece W is heated by a heating means (not shown) corresponding to the dewaxing temperature disposed in the dewaxing section 20. Examples of the heating means for the dewaxing section 20 include a cup burner, an open flame gas burner, an electric heater, a radiant tube burner, and the like.

  A dewaxing gas is introduced into the dewaxing unit 20 from a dewaxing gas generation unit 21. The dewaxing gas is obtained by incomplete combustion of a hydrocarbon gas such as propane or butane as a heat source, and is generated by the dewaxing gas generation unit 21. The dewaxing gas generated in the dewaxing gas generation unit 21 passes through a pipe 22 communicating with a connection passage 14 provided at a boundary portion between the dewaxing unit 20 and the sintering unit 30, and the dewaxing unit 20. Supplied in.

  While the workpiece W passes through the dewaxing portion 20, the wax-like lubricant components such as zinc stearate and metal soap used during compression molding of the green compact are thermally decomposed and removed, that is, dewaxed. . Exhaust gas generated from the workpiece W by dewaxing is discharged to the outside from an exhaust tube 23 provided in the dewaxing portion 20. This exhaust gas contains soot in addition to surplus moisture accompanying the temperature rise of the workpiece W and zinc oxide which is a thermal decomposition component of the lubricant. When the exhaust gas enters the sintered portion 30, the decarburization reaction of the workpiece W is performed. Is a harmful gas that cannot obtain the desired strength due to its excessive amount or changes its appearance.

  The workpiece W that has passed through the in-furnace conveyance path 11 of the dewaxing section 20 by the movement of the conveyance means 50 is introduced into the sintering section 30 through the connection path 14, and a predetermined sintering temperature (for example, 1100 to 1100) in the sintering section 30. About 1200 ° C.). Although heating means in the sintered part 30 is not shown, a heating element (for example, nichrome, cantal, silicon carbide, etc.) corresponding to the heating temperature is selected and an appropriate density is set in the furnace body 10 of the sintered part 30. Arranged.

  An atmosphere gas is introduced into the sintering portion 30 from a sintering gas source 31 through a sintering gas introduction pipe 32 connected to the downstream end of the sintering portion 30, and the atmosphere gas is used for sintering. The inside of the connection part 30 is maintained at a predetermined pressure.

  The atmosphere gas to be introduced into the sintered part 30 is nitrogen gas, hydrogen gas, ammonia decomposition gas, exothermic gas (hydrocarbon modified gas obtained by exothermic reaction of hydrocarbon gas such as propane, butane, methane, etc.) and endothermic. Reducing gas or non-oxidizing gas such as gas (same raw gas as exothermic gas, gas decomposed by reducing the air / gas ratio) or non-oxidizing gas is selected and dehydrated at room temperature to reduce moisture In this state, the gas is introduced from the sintering gas introduction tube 32 into the sintered portion 30. The atmospheric gas introduced into the sintering part 30 is heated to the sintering temperature by the heating means 33 in the sintering part 30. For this reason, the temperature drop in the sintered part 30 does not occur.

  The workpiece W is heated in the atmospheric gas while being conveyed through the in-furnace conveyance path 11 in the sintering unit 30, and the heat treatment necessary for sintering is completed at the final stage of the sintering unit 30, and then the workpiece W is cooled by the cooling unit 40. To be introduced. The cooling unit 40 is provided with a cooling means (not shown) (for example, a water jacket provided in the furnace body 10), and the workpiece W passes through the cooling unit 40, thereby ensuring a non-oxidized and non-decarburized state. It is cooled to a temperature or lower (eg, 200 ° C. or lower).

  The workpiece W that has passed through the cooling unit 40 and has been finally subjected to the sintering process is discharged from the discharge port 13 to the outside of the furnace body 10. The discharged work W is collected and moved to the next step.

  The above is the basic configuration and operation of the continuous sintering furnace of one embodiment. Next, the shielding airflow ejecting means provided at the boundary portion between the dewaxing portion 20 and the sintered portion 30 according to the present invention will be described.

(2) Shielding Airflow Ejecting Means As shown in FIG. 1, the dewaxing portion 20 and the sintered portion 30 are shielded at the boundary portion between the dewaxing portion 20 and the sintered portion 30 by shielding the space in the furnace at the boundary portion. Shielding airflow ejecting means 60 for ejecting a shielding airflow that divides the airflow is provided.

  As shown in FIGS. 1 and 2, the shield airflow ejection means 60 includes a nozzle 61 installed in the ceiling portion 141 of the connection passage 14 at the boundary portion between the dewaxing portion 20 and the sintered portion 30, and the nozzle 61 as described above. A nozzle pipe 62 communicating with the dewaxing gas generation unit 21 is provided. In this case, a part of the dewaxing gas is used as the shielding airflow, and the dewaxing gas is ejected from the nozzle 61 as the shielding airflow.

  During the operation of the continuous sintering furnace to sinter the workpiece W as described above, a shielding airflow is ejected from the nozzle 61 to shield the furnace space of the connection passage 14 with the shielding airflow. And the state which partitioned off the dewaxing part 20 and the sintered part 30 in the connection channel | path 14 is maintained. As shown in FIG. 3, the shielding airflow gas is ejected downward from a nozzle 61 fixed to the ceiling portion 141 of the connection passage 14.

  2 and 3, the nozzle 61 has a rectangular tube-like outer shape extending in the width direction of the in-furnace transport path 11, and is slit-shaped along the longitudinal direction, that is, the width direction of the in-furnace transport path 11. , And a shield airflow (reference A in FIGS. 2 and 3) is ejected in the form of a film from the outlet 611. The nozzle 61 is not limited to such a form, and any form may be adopted as long as it is possible to spray a shielding airflow in a film shape downward and shield the furnace space. Can do.

  As shown in FIG. 3, the ejection direction of the film-like shielding air current from the nozzle 61 is 40 to the horizontal direction from the upper side to the lower side and toward the upstream side of the work W conveyance, that is, toward the dewaxing portion 20. It is configured to be inclined at an angle θ of 60 °. Moreover, the flow velocity of the shield airflow ejected from the nozzle 61 is set to about 5 to 30 m / s.

(3) Operational effect of shielded airflow ejecting means According to the continuous sintering furnace of the one embodiment, the harmful gas generated from the workpiece W heated in the dewaxing section 20 by including the shielded airflow ejecting means 60. Can be effectively prevented from entering the sintered portion 30 by the shield airflow ejected from the nozzle 61. Conventionally, intrusion of harmful gas from the dewaxing portion 20 to the sintered portion 30 is prevented by the pressure of the atmospheric gas supplied to the sintered portion 30, but this need is eliminated in this embodiment. Since the shielding airflow has directivity, the shielding property is high. For this reason, the supply amount of the atmospheric gas to the sintering part 30 can be reduced, and the heating means of the sintering part 30 for heating the atmospheric gas. The power consumed in 33 can also be reduced. Moreover, since it becomes easy to complete dewaxing in the dewaxing part 20, the sintering defect of the workpiece | work W is suppressed.

  Moreover, in this embodiment, the dewaxing gas produced | generated by the dewaxing gas production | generation part 21 and supplied to the dewaxing part 20 is introduce | transduced into the shielding airflow ejection means 60, and is ejected as shielding airflow. The dewaxing gas is a gas containing moisture suitable for dewaxing, and is preliminarily heated to the temperature of the dewaxing part 20, so that the dewaxing gas is jetted obliquely toward the dewaxing part 20. Since the atmosphere in the dewaxing portion 20 is not disturbed, and it is not necessary to prepare a gas for shielding airflow and heat the gas separately, it is possible to operate economically.

  Further, since the jet direction of the shield airflow is from above to below and toward the dewaxing portion 20 on the upstream side of the work W conveyance, the gas flow from the dewaxing portion 20 toward the sintering portion 30 is shielded. The airflow faces each other, and the harmful gas is less likely to enter the sintered portion 30. Further, regarding the angle θ in the jet direction of the shield airflow, the shield airflow hardly reaches the workpiece W at the jet angle less than 40 °, and the entire cross section of the in-furnace transport path 11 becomes difficult to shield. On the other hand, when the ejection angle exceeds 60 °, a circulating flow is generated around the workpiece W, and the gas in the dewaxing portion 20 becomes turbulent and easily enters the sintered portion 30. Therefore, the jetting angle θ of the shielding airflow is preferably inclined at 40 to 60 °, and in the range of this angle, 45 to 60 ° is more preferable.

  Furthermore, if the flow velocity of the shield airflow is less than 5 m / s, the replacement with the dewaxing gas that has entered the lower part of the furnace does not proceed smoothly, whereas if it exceeds 30 m / s, the workpiece W is light. The workpiece W moves in the furnace. Therefore, the flow rate of the shielding airflow is preferably 5 to 30 m / s, and more preferably 15 to 30 m / s in this range.

(4) Other Embodiments In the above embodiment, the dewaxing gas is diverted to the shielding airflow that partitions the dewaxing portion 20 and the sintering portion 30, but the gas used for the shielding airflow is non-nitrogen or the like. An oxidizing gas may be used. However, for example, nitrogen is not preferable because it cannot be heated. Therefore, as shown in FIG. 4, the nozzle tube 62 of the shield airflow jetting means 60 is extended and connected to the sintering gas source 31, and the atmospheric gas supplied to the sintering section 30 is distributed to the shielded airflow jetting means 60. Then, it is ejected from the nozzle 61 as a shield airflow.

  In such an operation mode, a part of the atmospheric gas supplied to the sintered part 30 is diverted as a shielded air current that is jetted to the boundary part between the dewaxing part 20 and the sintered part 30. Similarly, the effect that the supply amount of the atmospheric gas to the sintered part 30 and the electric power for heating the atmospheric gas can be reduced can be obtained similarly. However, in this case, since the ambient gas supplied to the shield airflow ejecting means 60 is room temperature, it is possible to stabilize the operation of the dewaxing portion 20 by raising the temperature of the ambient gas ejected from the nozzle 61 to about the temperature of the dewaxing portion 20. Is preferred for.

  Unlike the gas supplied to the sintered part 30, the atmospheric gas supplied to the shield air current jetting means 60 is not dehydrated and can be used as it is containing moisture. For this reason, there exists an advantage that the power consumption for dehydrating the atmospheric gas of the side supplied to the sintering part 30 can be reduced conventionally.

DESCRIPTION OF SYMBOLS 10 ... Furnace body 11 ... In-furnace conveyance path 20 ... Dewaxing part 30 ... Sintering part 40 ... Cooling part 50 ... Conveyance means 60 ... Shielding airflow ejection means 61 ... Nozzle W ... Workpiece

Claims (4)

A dewaxing section, sintering section, and cooling section are continuously provided from the upstream side to the downstream side of the furnace body through which the work path in the furnace passes, and the work is transported along the furnace path. In a continuous sintering furnace having means,
Continuous sintering characterized by comprising shielded airflow jetting means for jetting a shielded airflow that shields the space in the furnace at the boundary portion between the dewaxed portion and the sintered portion and partitions the dewaxed portion and the sintered portion. Furnace.   The shielded airflow ejecting means has a nozzle for ejecting a shielded airflow into the furnace space, and the direction in which the shielded airflow is ejected from the nozzle is from the top to the bottom and horizontally toward the dewaxing portion. The continuous sintering furnace according to claim 1, wherein the continuous sintering furnace is inclined at an angle of 40 to 60 ° with respect to the flow rate, and the flow velocity of the shielding airflow is 5 to 30 m / s. In sintering a workpiece using the continuous sintering furnace according to claim 1 or 2,
An operation of a continuous sintering furnace characterized in that the atmospheric gas supplied to the sintered portion is distributed to the shielded airflow ejecting means and the atmospheric gas is ejected from the shielded airflow ejecting means to the boundary portion as the shielded airflow. Method. In sintering a workpiece using the continuous sintering furnace according to claim 1 or 2,
The same gas as the dewaxing gas supplied to the dewaxing part is introduced into the shielded airflow ejecting means, and the dewaxing gas is ejected from the shielded airflow ejecting means to the boundary portion as the shielded airflow. The operation method of the continuous sintering furnace.

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