JP6631080B2 - Method for producing sintered body and heating furnace - Google Patents

Description

The present invention relates to a manufacturing how you and furnace of the sintered body.

  The powder metallurgy method of firing a compact containing a metal powder to produce a sintered body is widely used in many industrial fields because it is possible to produce a metal product having a desired shape.

  Several methods are known for the production of a molded article. One of the methods is to mix and knead a metal powder and an organic binder, and to perform injection molding using the kneaded product. There is a metal injection molding (MIM) method. The molded body manufactured by the MIM method is subjected to a degreasing treatment (a binder removal treatment) to remove an organic binder, and then subjected to firing. In firing, the target metal product (sintered body) is obtained by bonding the particles of the metal particles to each other and leading to sintering.

  For example, Patent Document 1 discloses a method of manufacturing a sintered magnetic material in which a metal powder and an organic binder are kneaded, then subjected to an injection molding process, a degreasing process, and a two-stage sintering process under different conditions. ing. As an example of a two-stage sintering process, performing sintering at a relatively low temperature and sintering at a relatively high temperature is disclosed.

JP-A-2-138443

  However, in the sintering process, a large amount of gas is unintentionally generated from the object to be processed, and the processing conditions may change during the process. When the processing conditions are changed in this way, it affects the progress of the sintering phenomenon of the object to be processed, and good sintering may not be performed.

An object of the present invention relates to a method for producing a middle even processing environment changes can produce high quality sintered compact sintered body of the firing process, it and the middle in the processing environment as firing engineering is changed Another object of the present invention is to provide a heating furnace capable of performing a sufficient process on an object to be processed.

Such an object is achieved by the present invention described below.
The method for producing a sintered body of the present invention is a method for producing a sintered body by firing a molded body containing a metal powder and an organic binder,
A first step of placing the compact in a firing furnace, and in a reducing atmosphere, starting heating in the firing furnace based on a first heating program;
A second step of measuring the dew point of the firing furnace in the middle of the heating,
When the measured value or the arithmetic processing value thereof dew point measured in the second step does not satisfy the predetermined condition, performs a heating based on another second heating program from the first Atsushi Nobori program, when the measured value or the arithmetic processing value thereof dew point measured in the second step satisfies a predetermined condition, and a third step of performing heating based on the first Atsushi Nobori program,
It is characterized by having.

  Thus, a high-quality sintered body can be manufactured even if the processing environment changes during the firing process.

  In the method for manufacturing a sintered body according to the present invention, it is preferable that the second temperature raising program is a program in which the temperature raising rate is increased among the elements constituting the first temperature raising program.

  Thereby, the reduction in the reaction rate of the reduction reaction of the metal oxide caused by the degree of vacuum or the dew point not satisfying the predetermined condition can be compensated for by the promotion of the reduction reaction by increasing the rate of temperature rise. As a result, it is possible to prevent a state in which the reaction rate of the reduction reaction is reduced from continuing for a long time, and to suppress occurrence of sintering failure.

In the method for manufacturing a sintered body of the present invention, after the third step, a fifth step which is the same as the second step,
When the measured value of the dew point measured in the fifth step or the processing value thereof does not satisfy a predetermined condition, the temperature is raised based on the second temperature raising program, and the dew point measured in the fifth step is measured. A sixth step of raising the temperature based on the first temperature raising program when the value or the processing value thereof satisfies a predetermined condition;
It is preferable to have

  Thereby, it can be verified whether or not the application of the second temperature raising program has exerted an effect. That is, in the third step after the second step to be performed again, it is determined again whether or not the degree of vacuum or the dew point satisfies the predetermined condition. A heating program can be selected. This makes it possible to minimize the variation in the quality of the sintered body, and to maximize the effect of the second temperature raising program.

In the production method of the sintered body of the present invention, in the second step, it calculates the time integral of the dew point of the firing furnace,
Wherein the predetermined condition in the third step is preferably a condition relating to the time integral of the previous SL dew point.

  Thereby, the determination as to whether or not the predetermined condition is satisfied in the third step is performed based on the relatively strict predetermined condition, as compared with the case where the condition relating to the measured value of the degree of vacuum or the dew point is used as the predetermined condition as it is. be able to. For this reason, a change in the degree of vacuum or dew point can be dealt with earlier, and a state in which the reaction speed of the reduction reaction is reduced can be prevented from continuing for a long time.

The heating furnace of the present invention, a furnace body,
Heating means for heating the inside of the furnace body,
Output adjusting means for adjusting the output of the heating means,
Measuring means for measuring the dew point of the furnace body,
Control means including a function of controlling the operation of the output adjusting means based on the temperature raising program, and a function of rewriting the temperature raising program based on the measurement result of the measuring means,
It is characterized by having.

  Thus, when this heating furnace is used as a firing furnace, a high-quality sintered body can be manufactured even if factors of the processing environment change during the firing step.

It is a sectional view showing a baking furnace to which a first embodiment of a heating furnace of the present invention is applied. FIG. 2 is a sectional view taken along line AA of FIG. 1. It is sectional drawing which shows the degreasing furnace which applied the 2nd Embodiment of the heating furnace of this invention. It is a flowchart for explaining embodiment of the manufacturing method of the sintered compact of the present invention. It is each example of the temperature profile which shows a 1st temperature rise program, the temperature profile which shows a 2nd temperature rise program, and the graph which shows transition of the measured value of the degree of vacuum. It is a flowchart for explaining embodiment of the manufacturing method of the degreased body of the present invention.

  Hereinafter, a method for manufacturing a sintered body, a method for manufacturing a degreased body, and a heating furnace according to the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

<Heating furnace>
<< 1st Embodiment >>
First, a baking furnace to which the first embodiment of the heating furnace of the present invention is applied will be described. The firing furnace is a heating furnace for sintering by heating a molded body containing a metal powder and an organic binder.

  FIG. 1 is a sectional view showing a firing furnace to which a first embodiment of the heating furnace according to the present invention is applied, and FIG. 2 is a sectional view taken along line AA of FIG. In the following description, the upper part of FIGS. 1 and 2 will be described as “upper” and the lower part will be described as “lower” for convenience of description.

  A firing furnace 1 shown in FIG. 1 is provided along a cylindrical furnace main body 2 having a long axis in a horizontal direction, a cylindrical partition wall 4 provided in the furnace main body 2, and provided along an inner wall of the partition wall 4. A heater 5, a gas introduction system 6 for introducing gas into the furnace body 2, and a gas exhaust system 7 for exhausting gas. Hereinafter, each part of the firing furnace 1 will be described in detail.

  The furnace body 2 shown in FIG. 1 has a cylindrical shape having an axis in the horizontal direction, and one end (the right end in FIG. 1) in the extending direction of the axis is closed, while the other end (the left end in FIG. 1). ) Can be opened and closed. Then, an object to be processed can be put in or taken out from the other end side of the furnace main body 2.

  The furnace main body 2 is made of, for example, an iron-based alloy such as heat-resistant steel. The inner wall surface of the furnace main body 2 may have a polygonal shape such as a square, a hexagon, or an octagon in a cross section perpendicular to the axis of the furnace main body 2, but may have a perfect circle shape as shown in FIG. In addition, it is preferable to form a circle such as an ellipse and an ellipse. This makes it easier to make the temperature distribution inside the furnace body 2 more uniform.

  The partition wall 4 is provided inside the furnace main body 2 and has a cylindrical shape having an axis parallel to the axis of the furnace main body 2. Further, the shape of the inner wall surface of the partition wall 4 has a quadrangular shape in a cross section perpendicular to the axis of the partition wall 4.

  Such a partition wall 4 is made of, for example, a metal material such as stainless steel or heat-resistant steel, or a carbon material such as carbon.

  The flat stage 3 is provided inside the partition wall 4. The stage 3 is fixed to the inner wall surface of the furnace main body 2 via a leg 31 penetrating the partition wall 4. The stage 3 is capable of mounting a workpiece W to be subjected to a baking process in the baking furnace 1.

  A gas introduction system 6 for introducing a firing gas is connected to the furnace body 2. The gas introduction system 6 shown in FIG. 1 includes a pipe 61 through which gas can flow, and a gas generation source (not shown). One end of the pipe 61 is connected to the furnace main body 2, and the other end of the pipe 61 is connected to a gas generation source. Thereby, a firing gas can be introduced into the furnace main body 2 through the pipe 61.

  Further, a gas exhaust system 7 for exhausting gas is connected to the furnace main body 2. The gas exhaust system 7 shown in FIG. 1 includes a pipe 71 through which gas can flow, and an exhaust pump 72. One end of the pipe 71 is connected to the furnace main body 2, and the other end of the pipe 71 is connected to the exhaust pump 72. Thereby, the inside of the furnace main body 2 can be exhausted by the exhaust pump 72 via the pipe 71.

  A heater 5 (heating means) is provided inside the partition wall 4. By energizing the heater 5, the atmosphere inside the furnace main body 2, the partition 4, the stage 3 and the like are heated, and the workpiece W is heated accordingly.

  Further, an output adjusting unit 52 is connected to the heater 5 via a wiring 51. The output adjusting unit 52 changes the output of the heater 5 to change the temperature of the workpiece W.

  The furnace body 2 shown in FIG. 2 is provided with a total of four heaters 5 so as to surround the workpiece W, that is, one each above, below, and on both sides of the workpiece W. I have. Further, in FIG. 1, three sets of the four heaters 5 are arranged along the axis of the furnace main body 2. Therefore, in the furnace body 2 shown in FIGS. 1 and 2, a total of 12 heaters 5 are provided. Further, an output adjusting unit 52 is individually connected to each of these heaters 5. 1 and 2, illustration of some of the heaters 5 and the output adjustment unit 52 is omitted. Further, the number and arrangement of the heaters 5 are merely examples, and are not limited to the above.

  A thermocouple 8 (temperature measuring means) is provided inside the partition wall 4. The thermocouple 8 is connected to a temperature adjusting unit 82 (temperature adjusting means) via a wiring 81. Further, the temperature adjustment section 82 and the output adjustment section 52 are connected to each other via a wiring 83. The symbols X, Y, and Z shown in FIG. 1 indicate connection destinations of the wiring 83, respectively. That is, the wires 83 are laid so that the symbols X, the symbols Y, and the symbols Z shown in FIG. 1 are electrically connected to each other.

  The temperature inside the partition wall 4 is measured by the thermocouple 8, the wiring 81, the temperature adjusting unit 82, and the wiring 83, and an appropriate output value is instructed to the output adjusting unit 52 based on the measured temperature. The output adjusting unit 52 supplies electric power to the heater 5 according to the output value.

  Further, the firing furnace 1 according to the present embodiment includes a general control unit 85 (control means), and a wiring 86 for electrically connecting the general control unit 85 and each temperature adjusting unit 82. The general control unit 85 can control the operations of the plurality of temperature adjustment units 82 at the same time. Thus, even when a temperature difference occurs inside the furnace main body 2, control can be performed such that the entire inside of the furnace main body 2 has a target temperature.

  Further, the firing furnace 1 according to the present embodiment includes a vacuum gauge 91 (measuring means) for measuring the degree of vacuum inside the furnace body 2 and a dew point meter 92 (measuring means) for measuring the dew point inside the furnace body 2. , Is provided. The vacuum gauge 91 is electrically connected to the general control unit 85 via a wiring 911. Further, the dew point meter 92 is electrically connected to the general control unit 85 via a wiring 921.

  The general control unit 85 has a function of controlling the operations of the temperature adjustment unit 82 and the output adjustment unit 52 based on a preset first temperature increase program, and a second function based on the measurement result of the vacuum gauge 91 or the dew point meter 92. A function of rewriting the first temperature raising program into a second temperature raising program and controlling the operations of the temperature adjusting section 82 and the output adjusting section 52 based on the second temperature raising program.

<< 2nd Embodiment >>
Next, a degreasing furnace to which the second embodiment of the heating furnace of the present invention is applied will be described. The degreasing furnace is a heating furnace that obtains a degreased body by heating a molded body containing a metal powder and an organic binder to thermally decompose and remove at least a part of the organic binder.

FIG. 3 is a sectional view showing a degreasing furnace to which a second embodiment of the heating furnace of the present invention is applied.
Hereinafter, the second embodiment will be described, but in the following description, differences from the above-described first embodiment will be mainly described, and description of similar items will be omitted. In the drawings, the same reference numerals are given to the same items as those in the above-described embodiment.

  The degreasing furnace 10 shown in FIG. 3 has a vacuum gauge 91 for measuring the degree of vacuum inside the furnace main body 2 and a dew point meter 92 for measuring the dew point inside the furnace main body 2, and is provided with a pyrolysis gas of an organic binder. Except for having a gas concentration sensor 93 (measuring means) for measuring the concentration, it is the same as the firing furnace 1 according to the first embodiment.

  The gas concentration sensor 93 is electrically connected to the general control unit 85 via a wiring 931.

  The general control unit 85 has a function of controlling the operations of the temperature adjustment unit 82 and the output adjustment unit 52 based on a preset first temperature increase program, and a first temperature increase based on the measurement result of the gas concentration sensor 93. A function of rewriting the program into a second heating program and controlling the operations of the temperature adjustment unit 82 and the output adjustment unit 52 based on the second heating program.

  The gas concentration sensor 93 may be any sensor as long as it can measure the concentration of the pyrolysis gas of the organic binder. Examples of the type of the pyrolysis gas of the organic binder include hydrocarbon-based gases such as methane, ethylene, ethane, propylene, propane, butane, pentane, hexane, and formaldehyde, and derivatives thereof.

  Among these, for example, a thermal catalyst system, an infrared absorption spectroscopy system, a thermal conductivity detection system, and the like are known as a detection system of a sensor for detecting the concentration of methane. In the present invention, any of these detection-type sensors can be used.

<Sintered body manufacturing method>
Next, an embodiment of a method for manufacturing a sintered body according to the present invention will be described. In the following description, a method using the above-described firing furnace 1 will be described.
FIG. 4 is a process chart for explaining an embodiment of the method for manufacturing a sintered body according to the present invention.

  The method for manufacturing a sintered body shown in FIG. 4 includes: [1] a first step of putting a formed body (object to be processed) into the firing furnace 1 and starting a temperature rise based on a first temperature rise program; 2] The second step of measuring the degree of vacuum or dew point in the firing furnace 1 during the temperature rise, and [3] applying the second temperature rise program when the measured degree of vacuum or dew point does not satisfy the predetermined condition. When the measured degree of vacuum or dew point satisfies a predetermined condition, a third step of raising the temperature by applying a first temperature raising program, and [4] a first temperature raising in the third step If the program is selected and the end condition of the first temperature raising program is satisfied at that time, the first temperature raising program is ended and the end condition of the first temperature raising program is satisfied at that time. If not, a fourth step of returning to the second step. Hereinafter, each step will be sequentially described.

  [1] First, a formed body is put into the firing furnace 1 as the workpiece W. This compact contains a metal powder and an organic binder. Specifically, this molded body is formed by using a mixture of a metal powder and an organic binder, and various moldings such as a powder compaction (compression molding) method, a metal powder injection molding (MIM: Metal Injection Molding) method, and an extrusion molding method. It is manufactured using a method. The molded body thus obtained is in a state where the organic binder is uniformly distributed in the gaps between the particles of the metal powder.

  Further, the molded body placed in the firing furnace 1 may be subjected to a degreasing treatment as necessary. That is, a degreased body may be placed in the firing furnace 1 as an object to be processed. Examples of the degreasing treatment include a method of heating the molded body, a method of exposing the molded body to a gas that decomposes the organic binder, and the like.

  Note that the above-described heating furnace of the present invention can also be used for the degreasing treatment. The degreasing treatment will be described later in detail.

  Next, the gas in the furnace main body 2 of the firing furnace 1 is exhausted with the molded body placed in the firing furnace 1. Thereby, the inside of the furnace main body 2 is depressurized and brought into a vacuum state.

Although the degree of vacuum in the furnace main body 2 is not particularly limited, it is preferably from 10 ⁻⁵ Pa to 10 ³ Pa, more preferably from 10 ⁻⁴ Pa to 10 ² Pa. By setting the degree of vacuum in the furnace main body 2 within the above range, the concentration of oxygen, nitrogen, water, etc. in the furnace main body 2 is sufficiently reduced, so that oxidation, nitridation, etc. of the metal powder in the compact is suppressed. The molded body can be fired while performing.

  Further, by setting the degree of vacuum in the furnace main body 2 within the above range, it is possible to induce a reaction between carbon contained in the compact and oxygen contained in the metal powder. This corresponds to a reduction reaction of a metal oxide with carbon. Further, when a gas is generated from the compact during the firing process, the gas can be quickly discharged out of the firing furnace 1. Thereby, it is possible to suppress a reduction in the degree of vacuum due to the generated gas, a reduction in the reaction rate of the reduction reaction, and a stop of the reduction reaction.

The furnace body 2 may be in a vacuum state, but may be in a reducing atmosphere instead.
As the reducing atmosphere, for example, a reducing gas (firing gas) such as hydrogen or carbon monoxide, or an atmosphere containing these reducing gases can be mentioned. These atmospheres allow the compact to be fired while suppressing oxidation, nitridation, and the like of the metal powder in the compact.

  Further, by setting the inside of the furnace main body 2 to a reducing atmosphere, a reaction between the reducing gas and oxygen contained in the metal powder can be induced. This corresponds to a reduction reaction of a metal oxide with a reducing gas such as hydrogen.

  The concentration of the reducing gas in the furnace main body 2 is not particularly limited, but is preferably 10% by volume or more, and more preferably 50% by volume or more. By setting the concentration of the reducing gas within the above range, the reaction rate of the reduction reaction of the metal oxide by the reducing gas becomes sufficiently high, and the occurrence of poor sintering can be suppressed.

  And although the dew point in the furnace main body 2 is not specifically limited, It is preferable that it is -30 degreeC or less, and it is more preferable that it is -40 degreeC or less. By setting the dew point in the furnace body 2 within the above range, the concentration of water vapor in the furnace body 2 is sufficiently reduced, so that the oxidation of the metal powder in the compact is suppressed and the metal oxidation by the reducing gas is performed. It is possible to suppress a reduction in the reaction speed of the reduction reaction of the substance and a stop of the reduction reaction.

  Next, while maintaining the inside of the firing furnace 1 in a vacuum state or a reducing atmosphere, a first temperature raising program preset in the general control unit 85 is started. Thereby, the temperature adjustment unit 82 and the output adjustment unit 52 are operated based on the first temperature increase program, and the temperature increase in the firing furnace 1 is started (first step).

  Here, the first temperature raising program defines the relationship between the elapsed time and the set temperature. By defining the elapsed time in fine steps, the rate of temperature rise for each elapsed time can be more finely defined.

  The general control unit 85 operates the temperature adjustment unit 82 and the output adjustment unit 52 based on such a relationship between the elapsed time and the set temperature. That is, since the relationship between a certain set temperature and the output required by the heater 5 to achieve the set temperature differs depending on the structure of the firing furnace 1 and the like, such a relationship is grasped in advance. By maintaining such a relationship in the general control unit 85, it is possible to instruct a necessary output of the heater 5 based on the set temperature defined by the first temperature raising program.

  FIG. 5 is an example of a temperature profile showing the first temperature raising program. The horizontal axis in FIG. 5 indicates the elapsed time and the vertical axis indicates the set temperature, and the temperature profile indicating the first temperature raising program is indicated by a broken line.

  The first heating program shown in FIG. 5 includes a step 1 (S1) of raising the temperature from room temperature to 700 ° C., a step 2 (S2) of maintaining the temperature at 700 ° C., and a step 3 (S1) of raising the temperature from 700 ° C. to 1000 ° C. S3), Step 4 (S4) maintaining at 1000 ° C., Step 5 (S5) increasing the temperature from 1000 ° C. to 1250 ° C., Step 6 (S6) maintaining at 1250, and cooling down from 1250 ° C. to room temperature Step 7 (S7).

  [2] Next, the degree of vacuum or dew point in the firing furnace 1 is measured during the temperature rise (second step). The measured value is transmitted to the general control unit 85.

  For example, when the inside of the furnace main body 2 is in a vacuum state, the degree of vacuum is measured. When the inside of the furnace main body 2 is in a reducing atmosphere, the dew point is measured.

  Note that the degree of vacuum and the dew point may be constantly monitored, and the measured value may be transmitted to the general control unit 85 as needed.

  [3] Next, the general control unit 85 determines whether the measured vacuum degree or dew point satisfies a predetermined condition. Such predetermined conditions are appropriately set in consideration of the degree of vacuum and dew point which affect the reaction rate of the reduction reaction of the metal oxide. That is, the upper limit of the degree of vacuum or dew point is set so that the reaction rate does not decrease to the extent that poor sintering occurs, and if the measured value or its calculated value is included in a range lower than the upper limit, Satisfies predetermined conditions. "

  Then, when it is determined that the measured vacuum degree or dew point does not satisfy the predetermined condition, that is, when the measured value of the vacuum degree exceeds the upper limit, or when the measured value of the dew point exceeds the upper limit, In the general control unit 85, the first temperature raising program is rewritten to the second temperature raising program. Thus, thereafter, the general control unit 85 operates the temperature adjustment unit 82 and the output adjustment unit 52 based on the second temperature increase program, and the temperature inside the firing furnace 1 is increased (third step).

  Here, the second temperature raising program defines the relationship between the elapsed time and the set temperature similarly to the first temperature raising program, but this relationship is different from the first temperature raising program. Specifically, the second heating program may have a lower heating rate than the first heating program, but preferably has a higher heating rate. As a result, the reduction in the reaction rate of the reduction reaction can be compensated for by promoting the reduction reaction by increasing the rate of temperature rise. In other words, the decrease in the reaction rate of the reduction reaction is indirectly detected from the measured value of the degree of vacuum or the dew point and reflected in the temperature raising program (feedback), thereby promptly compensating for the reduction in the reduction reaction. Can be. Thereby, the state in which the reaction rate of the reduction reaction is reduced can be prevented from continuing for a long time, and occurrence of poor sintering can be suppressed.

  FIG. 5 shows an example of a temperature profile showing the second temperature raising program and an example of a graph showing transition of a measured value of the degree of vacuum. The temperature profile indicating the second heating program is indicated by a solid broken line, and the transition of the measured value of the degree of vacuum is indicated by an alternate long and short dash line.

  As shown in FIG. 5, in the temperature profile indicating the second temperature raising program, when the degree of vacuum increases, the temperature rising rate is correspondingly larger than the temperature profile indicating the first temperature raising program. In the temperature profile indicating the second temperature raising program shown in FIG. 5, the temperature raising rate increases in the middle of step 1 (S1). That is, assuming that this temperature change portion is step 8 (S8), the heating rate in step 8 is higher than the heating rate in step 1.

  It is preferable that the heating rate in Step 8, that is, the heating rate in the second heating program that is higher than that in the first heating program is 101% or more and 200% or less of the heating rate in Step 1, More preferably, it is 110% or more and 180% or less. Thereby, the shortage of the reduction reaction can be compensated in a short time while suppressing oversintering.

  In the example shown in FIG. 5, in step 8, the temperature is raised beyond the set temperature in step 2, but the second temperature raising program is not limited to such a setting. For example, similarly to the first temperature raising program, the temperature may be raised to the set temperature in step 2.

  FIG. 5 shows an example in which the heating rate is increased in step 8, but the setting in step 8 is not limited to this. For example, the setting may be such that the temperature exceeds the temperature in step 2 without changing the heating rate. The temperature may be set to increase.

  Further, although the setting in step 8 shown in FIG. 5 is set to decrease the temperature after the temperature is increased, the set temperature in step 2 may be changed to a higher temperature without decreasing the temperature.

  If the rewriting to the second temperature raising program is not performed in spite of the fact that the degree of vacuum and the dew point have risen, for example, instead of rewriting to the second temperature raising program, the first temperature raising program If measures are taken to temporarily stop the progress, the state in which the reaction rate of the reduction reaction is reduced will continue for a long time. In this case, a metal oxide that cannot be finally reduced is likely to remain, which may cause poor sintering.

  On the other hand, by rewriting the program to the second temperature raising program, it is possible to finally suppress the occurrence of sintering failure. As a result, a high-quality sintered body can be efficiently manufactured.

  On the other hand, when it is determined that the measured vacuum degree or dew point satisfies the predetermined condition, that is, when the measured value of the vacuum degree is below the upper limit, or when the measured value of the dew point is below the upper limit value In the general controller 85, the temperature in the firing furnace 1 is continuously raised based on the first temperature raising program (third step).

  By the way, after the rewriting to the second temperature raising program is performed in this step, in the present embodiment, as shown in FIG. 4, the process is returned to the second step again. That is, in the present embodiment, the second step is repeated a plurality of times. Thereby, it can be verified whether or not the rewriting to the second temperature raising program has exerted an effect.

  Then, when the rewriting to the second temperature raising program is effective, in this step (third step), it is determined that the degree of vacuum or the dew point satisfies the predetermined condition. In this case, the general control unit 85 rewrites the second temperature raising program back to the first temperature raising program. Thus, thereafter, the general control unit 85 raises the temperature inside the firing furnace 1 again based on the original first temperature raising program. In this way, when the increased vacuum degree or dew point decreases, the temperature can be immediately returned to the temperature increase based on the first temperature increase program. This allows the sintering process to proceed almost as designed, thereby minimizing variations in the quality of the sintered body.

  If the effect has not been sufficiently exhibited even though the program has been rewritten to the second temperature raising program, it is determined that the degree of vacuum and the dew point do not satisfy the predetermined conditions. In this case, the second temperature raising program is continuously applied, and the second step and the third step are repeated until the second temperature raising program exerts its effect to satisfy the predetermined condition. As a result, the increased degree of vacuum and dew point can be rapidly reduced, and a reduction in the reaction rate of the reduction reaction can be minimized. In other words, since the temperature increase by the second temperature raising program is continued until the effect by the rewriting to the second temperature raising program appears, the effect by the second temperature raising program is maximized.

  When the second step and the third step are repeated a plurality of times, the contents of the second temperature raising program may be updated each time. For example, by updating to a second heating program in which the heating rate is further increased, it is possible to further promote the reduction of the degree of vacuum and the dew point.

  [4] When the first temperature raising program is continuously used in the third step, it is determined whether or not the end condition of the first temperature raising program is satisfied as shown in FIG. When the termination condition is satisfied, the first temperature raising program is terminated, and the temperature rise in the firing furnace 1 is terminated. Thereby, the sintered body is cooled to room temperature by natural cooling or forced cooling.

  On the other hand, if the termination condition is not satisfied, in the present embodiment, the process returns to the second step again as shown in FIG. Thereby, the temperature increase by the first temperature increase program is continued (fourth step).

  The termination condition of the first temperature raising program may be, for example, an elapsed time from start-up, an elapsed time from a specific step, a measured value of the degree of vacuum or dew point in the firing furnace 1 or The calculated value may be used. It can be said that such termination conditions are conditions under which the compact can be sufficiently sintered.

  Note that the measured value of the degree of vacuum or dew point in the above-described second step may be transmitted to the general control unit 85 and then subjected to an arithmetic process as needed. That is, the integrated control unit 85 (in the third step) may apply the measurement values of the degree of vacuum and the dew point to this arithmetic processing to determine whether or not the obtained processing value satisfies a predetermined condition.

  Examples of the arithmetic processing include time differentiation processing, time integration processing, and the like. Among them, the time change of the degree of vacuum and the dew point can be integrated by being subjected to the time integration process. Then, the general control unit 85 determines whether the time integration of the degree of vacuum and the dew point satisfies predetermined conditions. As a result, it becomes easier to catch changes in the degree of vacuum and dew point at an earlier stage than monitoring the measured value itself. That is, when monitoring the measured value itself and making a determination in the third step, the determination condition must be set to some extent loosely in consideration of the fluctuation of the measured value. On the other hand, by using the time integral value, the sensitivity to fluctuation of the measured value is reduced. As a result, the conditions for the determination can be set relatively strictly, and changes in the degree of vacuum or dew point can be dealt with earlier. As a result, it is possible to prevent the degree of vacuum and the dew point from excessively deteriorating, and to prevent a state in which the reaction rate of the reduction reaction is reduced from continuing for a long time.

  The factors of the processing environment such as the degree of vacuum and the dew point are physical quantities that increase with the progress of the reduction reaction, the thermal decomposition of the organic binder, and the desorption of the components attached to the inner wall surface of the firing furnace 1, respectively. As described above, the reduction reaction of the metal oxide is easily affected by the increase in the degree of vacuum and the dew point directly and in a short time. For this reason, by performing the determination in the third step based on such a physical quantity, it is possible to prevent a state in which the reaction rate of the reduction reaction is reduced from continuing for a long time. In addition, since the degree of vacuum and the dew point have a small time lag when measured by the measuring means, that is, the change is a physical quantity that can be detected in a short time, it is useful as a physical quantity to be used in the determination in the third step. It is.

<Method for producing degreased body>
Next, an embodiment of the method for producing a degreased body of the present invention will be described. In the following description, a method using the above-described degreasing furnace 10 will be described.

FIG. 6 is a process chart for explaining an embodiment of the method for producing a degreased body of the present invention.
Hereinafter, an embodiment of a method for manufacturing a degreased body will be described. In the following description, differences from the embodiment of the method for manufacturing a sintered body described above will be mainly described, and a description of the same items will be omitted. I do.

  The manufacturing method of the degreased body shown in FIG. 6 uses a degreasing furnace 10 instead of the firing furnace 1, measures the concentration of the pyrolysis gas of the organic binder in the second step, and measures the pyrolysis gas measured in the third step. It is the same as the method for manufacturing a sintered body shown in FIG. 4 except that it is determined whether or not the concentration of the sintered body satisfies a predetermined condition.

  That is, the method of manufacturing a degreased body shown in FIG. 6 includes: [1] a first step of putting a formed body (object to be processed) into a degreasing furnace 10 and starting a temperature increase based on a first temperature increase program; [2] a second step of measuring the concentration of the pyrolysis gas of the organic binder in the degreasing furnace 10 during the temperature rise, and [3] a second step when the measured concentration of the pyrolysis gas does not satisfy the predetermined condition. A third step of raising the temperature by applying the first temperature raising program and raising the temperature by applying the first temperature raising program when the measured concentration of the pyrolysis gas satisfies a predetermined condition; In the case where the first temperature raising program is selected in the step, if the end condition of the first temperature raising program is satisfied at that time, the first temperature raising program is ended, and the first temperature raising program is performed at that time. If the termination condition of the temperature program is not satisfied, the second A fourth step of returning to the step.

  In the second step, the concentration of the pyrolysis gas of the organic binder in the degreasing furnace 10 is measured during the heating. The measured value is transmitted to the general control unit 85.

  In the third step, the integrated control unit 85 determines whether the measured concentration of the pyrolysis gas satisfies a predetermined condition. Such predetermined conditions are appropriately set in consideration of factors such as the concentration of the pyrolysis gas, which affect the reaction rate of the thermal decomposition reaction of the organic binder, because factors of the processing environment influence the reaction rate. That is, when the concentration of the pyrolysis gas increases, the pyrolysis rate decreases, and there is a risk that defective degreasing may occur (insufficient degreasing). Therefore, the thermal decomposition rate does not decrease to such an extent that such degreasing failure occurs. As described above, when the upper limit value of the concentration of the pyrolysis gas is set, and the measured value or the calculated value is included in a range lower than the upper limit value, it is determined that “the predetermined condition is satisfied”.

  In addition, the second to fourth steps of the embodiment of the method for manufacturing a degreased body are the same as those in the embodiment of the method for manufacturing a sintered body except that the degree of vacuum and the dew point are replaced with the concentration of a pyrolysis gas. You.

  As described above, the method for manufacturing a sintered body, the method for manufacturing a degreased body, and the heating furnace according to the present invention have been described based on the illustrated embodiments, but the present invention is not limited thereto.

  For example, in the heating furnace of the present invention, the partition 4 may be omitted from the above embodiment, and the position of the heater 5 may be between the partition 4 and the furnace main body 2. In the above embodiment, a so-called batch type furnace is used, but the heating furnace of the present invention may be a continuous type furnace.

  Further, the method for producing a sintered body of the present invention and the method for producing a degreased body of the present invention may each be obtained by adding an optional step to the above embodiment.

DESCRIPTION OF SYMBOLS 1 ... Firing furnace, 2 ... Furnace main body, 3 ... Stage, 4 ... Partition wall, 5 ... Heater, 6 ... Gas introduction system, 7 ... Gas exhaust system, 8 ... Thermocouple, 10 ... Degreasing furnace, 31 ... Leg part, 51 ... wiring, 52 ... output adjustment unit, 61 ... piping, 71 ... piping, 72 ... exhaust pump, 81 ... wiring, 82 ... temperature adjustment unit, 83 ... wiring, 85 ... general control unit, 86 ... wiring, 91 ... vacuum gauge , 92: dew point meter, 93: gas concentration sensor, 911: wiring, 921: wiring, 931: wiring, W: workpiece

Claims (5)

A method of firing a molded body containing a metal powder and an organic binder to produce a sintered body,
A first step of placing the compact in a firing furnace, and in a reducing atmosphere, starting heating in the firing furnace based on a first heating program;
A second step of measuring the dew point of the firing furnace in the middle of the heating,
When the measured value or the arithmetic processing value thereof dew point measured in the second step does not satisfy the predetermined condition, performs a heating based on another second heating program from the first Atsushi Nobori program, when the measured value or the arithmetic processing value thereof dew point measured in the second step satisfies a predetermined condition, and a third step of performing heating based on the first Atsushi Nobori program,
A method for producing a sintered body, comprising:   2. The method of manufacturing a sintered body according to claim 1, wherein the second temperature raising program is a program in which a temperature raising rate is increased among the elements constituting the first temperature raising program. 3. After the third step, a fifth step which is the same as the second step,
When the measured value of the dew point measured in the fifth step or the processing value thereof does not satisfy a predetermined condition, the temperature is raised based on the second temperature raising program, and the dew point measured in the fifth step is measured. A sixth step of raising the temperature based on the first temperature raising program when the value or the processing value thereof satisfies a predetermined condition;
The method for producing a sintered body according to claim 2, comprising: In the second step, it calculates the time integral of the dew point of the firing furnace,
Wherein the predetermined condition in the third step, the manufacturing method of the sintered body before Symbol according to any one of claims 1 to 3 which is a condition relating to the time integral of the dew point. A furnace body,
Heating means for heating the inside of the furnace body,
Output adjusting means for adjusting the output of the heating means,
Measuring means for measuring the dew point of the furnace body,
Control means including a function of controlling the operation of the output adjusting means based on the temperature raising program, and a function of rewriting the temperature raising program based on the measurement result of the measuring means,
A heating furnace comprising:

Images