JP2014016118A - Continuous sintering furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a continuous sintering furnace which sufficiently and uniformly cools an entire muffle, inhibits the deposition of salt components, and improves the cooling efficiency in a structure where the muffle is cooled by contact of a coolant.SOLUTION: A continuous sintering furnace passes a workpiece W through a dewaxing part 20, a sintered part 30, and a cooling part 40 using transfer means 50 to sinter the workpiece W. In the continuous sintering furnace, a spiral fin 43 is provided on an outer surface of a muffle 42 in the cooling part 40 formed by disposing a furnace shell 41 around the muffle 42 and thereby forms a cooling passage 44, which spirally extends along a periphery of the muffle 42 from the transfer upstream side toward the downstream side, between the muffle 42 and the furnace shell 41. A coolant is flowed in the cooling passage 44 to cool the muffle 42 and an atmosphere in the muffle 42.

Description

  The present invention relates to a continuous sintering furnace that performs a sintering process while continuously conveying 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, in order to give desired characteristics to the workpiece, in the dewaxing part and the sintering part, an appropriate atmosphere gas is supplied and heated, respectively. It cools below to the temperature which can maintain a non-decarburized state.

  FIG. 5 shows an example of the structure of the cooling section in the mesh belt type continuous sintering furnace. In this continuous sintering furnace, a muffle 42 is inserted into a furnace shell 41 to form the furnace body 10, and a cooling passage 49 through which cooling water flows is provided between the muffle 42 and the furnace shell 41 covering the muffle 42. It is formed as. Both the furnace shell 41 and the muffle 42 are made of metal, and as shown in FIG. 5 (c), the bottom of the in-furnace transport path in the muffle 42 is located downstream from the upstream side in the transport direction (FIG. 5 (a)). , (B), a plurality of skids 46 extending from the left side to the right side) are provided, and a conveying means (mesh belt) 50 on which the workpiece W is placed slides and moves on the skid 46. ing.

  Cooling water is supplied to a cooling passage 49 in the furnace body 10 from a water supply port 491 provided at an end portion on the upstream side of the conveyance. The cooling water flows downstream through the cooling passage 49, and an end portion on the downstream side of the conveyance portion It drains from the drainage port 492 provided in the. The temperature in the muffle 42 is cooled by the cooling water flowing through the cooling passage 49, and the workpiece W is cooled during conveyance by coming into contact with the cooled atmosphere in the muffle 42.

JP 2001-303105 A

  In the cooling section, if the cooling water in contact with the outer surface of the relatively high heat muffle 42 inside the furnace is continuously exchanged, that is, if it does not flow quickly, overheating occurs on the outer surface of the muffle 42 and cooling is performed. The water may partially boil. When the cooling water boils, a phenomenon in which salt components such as calcium and magnesium contained in the cooling water precipitate occurs on the outer surface of the muffle 42. Such a salt component has a lower thermal conductivity than cooling water, and the precipitation temperature is about 60 to 70 ° C., which is lower than the boiling point of water. Therefore, precipitation tends to accelerate and solidify and expand, and the outer surface of the muffle 42 The heat exchange efficiency (cooling efficiency) due to the cooling water decreases and the temperature distribution in the furnace is disturbed.

  In the conventional cooling section shown in FIG. 5, the cooling passage 49 is a simple space opened between the furnace shell 41 and the muffle 42. For this reason, the cooling water flows in a straight line from the water supply port 491 toward the drain port 492 as indicated by an arrow A in FIG. 5B, and the main flow path is limited to a portion with low resistance. Thus, for example, in a portion relatively far from the water supply port 491 and the drain port 492, it is difficult for the cooling water to flow, and the flow velocity tends to be low. In such a portion where the flow velocity is low, the temperature of the cooling water rises and the salt component tends to precipitate. The precipitation of the salt component on the outer surface of the muffle 42 causes the cooling efficiency to be lowered and the temperature distribution in the furnace to be disturbed as described above, and the muffle 42 is thermally deformed due to partial increase in the temperature of the cooling water. Problems also arise.

  The generation of the salt component in the cooling passage 49 includes measures such as performing ion exchange before supply to remove the salt component of the cooling water in advance, or performing flushing to wash the cooling passage 49, and There are other means such as collecting the high-temperature gas in the furnace, cooling it with a heat exchanger, and using the cooling gas, but all of this takes time, increases the complexity and cost of the structure. Further, when the cooling water flows linearly, for example, the cooling water flowing through the shortest flow path is drained without being sufficiently heated by the muffle 42, that is, without sufficiently exchanging heat, and this also decreases the cooling efficiency. Occurs.

  The present invention has been made in view of the above circumstances, and its main purpose is to suppress precipitation of salt components by cooling the entire muffle sufficiently and uniformly in a structure in which the muffle is cooled by contact with cooling water. As a result, it is to provide a continuous sintering furnace capable of improving the cooling efficiency of the workpiece by the cooling unit.

  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, the cooling section covers the muffle as a furnace body, and a metal muffle formed inside the furnace conveying path. A cooling passage extending spirally along the periphery of the muffle from the upstream side to the downstream side is formed between the muffle and the furnace shell. Cooling water is circulated through the passage.

  According to the continuous sintering furnace of the present invention, the cooling water spirally flows along the cooling passage formed around the muffle, thereby cooling the muffle. Since the cooling passage is defined in a spiral shape, the flow rate of the cooling water becomes substantially uniform. By forming the cooling passage in the most part of the periphery of the muffle, the entire muffle can be cooled sufficiently and uniformly. . As a result, it is possible to suppress the precipitation of the salt component accompanying the boiling of the cooling water, thus eliminating the conventional problems such as a decrease in the cooling efficiency due to the precipitation of the salt component, and improving the cooling efficiency.

  In this invention, the said cooling channel | path includes the form comprised with the fin provided in at least one of the outer surface of the said muffle, or the inner surface of the said furnace shell.

  In the present invention, a skid extending in a transport direction is provided at a bottom portion of the muffle so that the transport unit slidably supports the transport unit during a transport operation, and the transport unit and the skid are connected to each other. Including forms composed of the same kind of metal. If the skid and the transport means are made of the same type of metal, the heat of the transport means that has moved to the cooling section due to high heat is transferred to the skid, causing so-called "displacement" close to adhesion, which may result in poor transport. There is. However, in the present invention, since the conveying means can be sufficiently cooled, deviation hardly occurs and stable conveyance is achieved.

  According to the present invention, in the structure in which the muffle is cooled by contact with cooling water, the precipitation of the salt component can be suppressed by sufficiently and uniformly cooling the entire muffle, and as a result, the workpiece is cooled by the cooling unit. There is an effect that a continuous sintering furnace capable of improving the efficiency is provided.

It is a sectional side view showing typically a continuous sintering furnace concerning one embodiment of the present invention. It is a three-plane figure which shows the structure of the cooling part of one Embodiment, (a) Top surface sectional view, (b) Side sectional view, (c) Transverse sectional view. It is the (a) sectional side view of the furnace shell which comprises the furnace body of the cooling unit of one Embodiment, (b) It is a cross-sectional view. It is the (a) sectional side view of the muffle which comprises the furnace body of the cooling unit of one Embodiment, (b) It is a cross-sectional view. It is a three-plane figure which shows an example of the cooling part structure of the conventional continuous sintering furnace, (a) Top sectional drawing, (b) Side sectional view, (c) Transverse sectional drawing.

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.

  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. Moreover, the penetration of harmful gas from the dewaxing part 20 into the sintered part 30 and the entry of outside air from the discharge port 13 into the cooling part 40 are suppressed by the pressure of the atmospheric gas supplied to the sintered part 30.

  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. And by passing the cooling part 40, it cools to the temperature below the temperature (for example, 200 degrees C or less) in which the state of a non-oxidation and a non-decarburization is ensured.

  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 structure of the cooling unit 40 according to the present invention will be described.

(2) Structure of cooling unit

  As shown in FIG. 2, the cooling unit 40 includes a furnace body 10 in which a muffle 42 is inserted into a furnace shell 41. 3 and 4 show a furnace shell 41 and a muffle 42, respectively. Each of the furnace shell 41 and the muffle 42 is a cylindrical body having a rectangular cross section, and is formed of an iron material such as SS (rolled steel for general structure).

  A space in the muffle 42 serves as the in-furnace conveyance path 11, and a plurality of skids 46 extending along the conveyance direction are spaced apart in the width direction at the bottom of the muffle 42 as shown in FIG. 2 (c). Laid in state. The mesh belt as the conveying means 50 slides on the skid 46 and moves. In this case, the conveying means 50 and the skid 46 are made of the same kind of metal, and for example, SUS (various stainless steel) is used.

  As shown in FIG. 4, on the outer surface of the muffle 42, fins 43 are formed spirally along the outer surface from the upstream side to the downstream side. The fins 43 stand at right angles to the outer surface of the muffle 42 and are provided over the substantially entire length of the muffle 42 at an appropriate pitch. The fins 43 can be provided continuously by means of integral molding with the muffle 42 or by fixing the material of the fins 43 to the outer surface of the muffle 42 by welding.

  As shown in FIG. 2, a spiral space partitioned by fins 43 between the furnace shell 41 and the muffle 42 in a state where the muffle 42 is inserted into the furnace shell 41 and the furnace body 10 is configured. 44 is formed. The fins 43 are formed in a rectangular shape along the outer surface of the muffle 42, and the tips of the fins 43 are in contact with the inner surface of the furnace shell 41, or a slight gap is left between the inner surface of the furnace shell 41. .

  The spiral space 44 is formed so as to extend spirally along the periphery of the muffle 42 from the transport upstream side to the downstream side, and this space 44 serves as a cooling passage through which cooling water flows. That is, the furnace body 10 in the cooling unit 40 has a cooling passage 44 that spirally extends from the transport upstream side to the downstream side. A water supply port 441 for introducing cooling water into the cooling passage 44 is provided at the upstream end of the furnace shell 41, and a drain outlet 442 of the cooling passage 44 is provided at the downstream end of the furnace shell 41. .

  A cooling water introduction pipe (not shown) is connected to the water supply port 441, and a cooling water drain pipe (not shown) is connected to the drain port 442. At both ends of the cooling unit 40, an annular closing plate 45 that closes the opening between the furnace shell 41 and the muffle 42 is fixed, and the cooling passage 44 is a space closed between the furnace shell 41 and the muffle 42. It has become.

(3) Action of Cooling Section and Effects Accompanied With it In the cooling section 40 of the continuous sintering furnace according to the above-described embodiment, the cooling water introduced into the cooling passage 44 from the water supply port 441 is cooled in FIG. As indicated by the arrow in the passage 44, it flows spirally from the upstream side to the downstream side along the cooling passage 44 formed around the muffle 42, and is drained from the drain port 442. In this way, the cooling water flowing through the furnace body 10 contacts the outer surface of the muffle 42, whereby the muffle 42 is cooled. As the muffle 424 is cooled, the atmosphere in the muffle 42 is cooled, and the workpiece W conveyed by the conveying means 50 is cooled by coming into contact with the cooled atmosphere in the muffle 42.

  The cooling passage 44 partitioned by the inner surface of the furnace shell 41, the outer surface of the muffle 42 and the fins 43 is spirally defined by the fins 43, whereby the cooling water flow velocity becomes substantially uniform, and the cooling water around the muffle 42 is cooled. Is less likely to stay partially. Further, the cooling passage 44 is formed on almost the entire outer surface of the muffle 42. Therefore, the entire muffle 42 is sufficiently and uniformly cooled by the cooling water flowing through the cooling passage 44. As a result, the problem that the salt component precipitates due to boiling or high heat of the cooling water contacting the muffle 42 is suppressed. Therefore, the conventional problem such as a decrease in cooling efficiency due to precipitation of the salt component is solved, and the cooling efficiency is improved.

  Moreover, in this embodiment, the skid 46 provided in the bottom part in the muffle 42 and the conveyance means 50 (mesh belt) are comprised with the same kind of metal. Thus, when the skid 46 and the conveyance means 50 are comprised with the same kind of metal, even if the heat | fever of the conveyance means 50 which moved to the cooling part 40 with high heat is transmitted to the skid 46, it will generate | occur | produce and will become conveyance defect. As described above, there is a fear. However, in this embodiment, the cooling efficiency of the cooling unit 40 is high, and the conveying unit 50 can be sufficiently cooled. Therefore, the skid 46 and the transport means 50 are not easily displaced, and stable transport is achieved.

  The present invention is based on the fact that a spiral cooling passage 44 is formed around the muffle 42 of the cooling unit 40, and the conveying means of the continuous sintering furnace is not limited to the mesh belt, but a roller hearth furnace. Any sintering furnace having continuous conveying means such as a pusher furnace or a walking beam furnace can be applied.

  Further, the spiral fins 43 that form the spiral cooling passage 44 may be provided on the inner surface of the furnace shell 41 instead of being provided on the outer surface of the muffle 42 as in the above-described embodiment. The spiral cooling passage 44 can be formed by providing both on the outer surface of 42 and the inner surface of the furnace shell 41.

DESCRIPTION OF SYMBOLS 10 ... Furnace body 11 ... In-furnace conveyance path 20 ... Dewaxing part 30 ... Sintering part 40 ... Cooling part 41 ... Furnace shell 42 ... Muffle 43 ... Fin 44 ... Cooling passage 46 ... Skid 50 ... Conveying means W ... Workpiece

Claims (3)

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,
The cooling part is
As the furnace body, it has a metal muffle formed inside the furnace conveyance path, and a furnace shell disposed to cover the muffle,
Furthermore, a cooling passage extending spirally along the periphery of the muffle is formed between the muffle and the furnace shell from the upstream side to the downstream side, and cooling water is circulated through the cooling passage. A continuous sintering furnace.   The continuous sintering furnace according to claim 1, wherein the cooling passage is configured by fins provided on at least one of an outer surface of the muffle and an inner surface of the furnace shell. A skid extending in the transport direction is provided at the bottom of the muffle so as to support the transport means in a slidable manner during the transport operation.
The continuous sintering furnace according to claim 1 or 2, wherein the conveying means and the skid are made of the same kind of metal.

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