JPH0217385A - Sintering furnace equipped with wax removing device - Google Patents

Abstract

PURPOSE:To prevent the deterioration of a heat conductive coefficient due to adhered wax and reduce exhaust resistance by providing a forcibly removing means, removing the wax adhered to a discharging passage for discharging gas including the vapor of wax to the outside of a furnace. CONSTITUTION:A heater element 5 in a processing chamber 1 is conducted to discharge gas, produced by evaporating wax included in a work 6 to be processed, to the outside of a furnace through a gas introducing pipe 15. In this case, wax 16, adhered to a discharging passage 7 at the center of a lower lid 3, is scraped down by the ascending and descending of pistons 12a, 12b. The wax 16 is guided to an outlet port while one part of the wax is evaporated and flows into the introducing pipe 15. A means, forcibly removing the wax adhered to the discharging passage 7, removes the wax perfectly before the trapping of a next process which is performed in usual manner whereby the deterioration of heat conductive coefficient due to the adhered wax may be prevented and exhaust resistance may be reduced.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a dewaxing sintering furnace, and more specifically, the present invention relates to a dewaxing and sintering furnace for continuously dewaxing and sintering powder compacts of cemented carbide, ceramics, etc. in one furnace. The present invention relates to a furnace for performing vacuum sintering and pressure sintering.

(Prior art) Sintering of powder compacts of cemented carbide, ceramics, etc. is carried out by adding an appropriate medium such as wax to the raw material powder, forming it, and then sintering it at high temperature. Some of the above-mentioned waxes have a negative effect on the properties of the sintered crystals, so they must be completely removed as a pre-sintering treatment.

Therefore, conventionally, the molded body is set in a sintering furnace maintained at a temperature considerably lower than the sintering temperature, and the wax is evaporated from the molded body into the atmosphere, and the wax inside the furnace is removed using a vacuum pump. Atmospheric gases containing steam are being exhausted, and in furnaces used for such processing, it has recently been proposed to interpose a wax trap element in the flow path of the gas containing wax vapor. .

(Refer to Japanese Utility Model Application No. 60-113333) Figure 6 shows an example of the device according to the above proposal, in which a gas inlet pipe (21) connected to the exhaust pipe of the sintering furnace is connected. First wax trap element (23a) arranged in an inclined manner
, a liquefaction tank (24) installed horizontally on the foundation (25) adjacent to this, a second wax trap element (23b) installed vertically on this tank, and a second wax trap element (23b) facing this element. A third wax trap element (23c) is installed vertically in such a manner and connected to a third wax trap element (23c) connected to a gas exhaust pipe (22) connected to an exhaust pipe line on the vacuum pump side near the lower end of the first side thereof. Among the exhaust gas sucked from the sintering furnace, vapor of high melting point wax is first captured by condensation on the surface of the trap piece in the first wax trap element (23a), and this is eventually trapped. It grows and is stored in the liquefaction tank (24).

The exhaust gas then diffuses in the liquefaction tank (24) before being introduced into the second wax trap element (23b) where the medium melting point wax vapor is trapped and
This forms droplets and drips into the liquefaction tank (24).

Note that the wax stored in the liquefaction tank (24) does not solidify.
In addition, the temperature is adjusted to a predetermined value to prevent re-evaporation.

Furthermore, the exhaust gas is introduced via the flow duct into the third wax trap element (23c), where it is connected to the first wax trap element (23c).
All the low melting point wax vapor that was not removed by the second trap element is trapped, and this low melting point wax drips into the tank section (26) at the bottom and is stored, while the exhaust gas except the wax vapor is Gas exhaust pipe (2
2) and is sucked into a vacuum pump (not shown) for dewaxing.

(Problem to be Solved by the Invention) However, in the dewaxing process using a furnace as described above, wax having a high melting point in the core part is likely to be trapped in the gas introduction pipe (21) due to the structure of the gas introduction pipe part.
It often occurred that wax adhered to the inner wall of the tube before the first wax trap element (23a).

This is because even though it is possible to create a temperature difference between the wax trap element (23a) and the gas introduction pipe (21) (in this case, the wax trap element is made relatively low), the pipe itself is a heat conductor. This is due to the fact that it could not be said to be sufficient and could not avoid being incomplete.

Further, when wax adheres to the inner wall of the tube as described above, the thermal conductivity with respect to heating from the outer surface of the tube deteriorates, and the heat exchange efficiency when the wax trap element is viewed as a heat exchanger decreases.

Furthermore, the exhaust resistance increases, resulting in an increase in the cycle time required for dewaxing treatment.

The present invention deals with the above-mentioned actual situation and solves the above problems by finding a means to remove wax adhering to the inner wall of the pipe, prevents a decrease in thermal conductivity, reduces exhaust resistance, and improves the cycle time of the dewaxing process. The purpose is to shorten and improve the efficiency of the process.

(Means for Solving the Problems) That is, a feature of the present invention that satisfies the above-mentioned object is that the gas introduction pipe section connected to the wax trap device of the sintering furnace, in other words, the gas introduction pipe section made of cemented carbide, ceramics, etc. A dewaxing sintering furnace used for sintering the powder compacts of The object of the present invention is to provide a means for forcibly removing wax adhering to a discharge path of a gas containing wax vapor from a sintering furnace for sintering a molded body to the outside of the furnace.

Here, the forced removal means is usually to mechanically scrape off the wax adhering to the discharge passage, and this is accomplished by arranging a reciprocating or rotating piston in the discharge passage.

(Function) In a dewaxing sintering furnace with the above configuration, when a gas containing wax vapor is introduced into the gas introduction pipe connected to the subsequent wax trap device, as the process progresses, the gas discharge passage of the furnace is When a certain thickness of wax has been deposited, a forced displacement means is activated to remove the deposited wax, some of which is vaporized and flows to a subsequent wax trap, while the other is collected in a wax sump. As a result, the reduction in thermal conductivity caused by wax adhesion is prevented, and the exhaust resistance is also reduced.

(Example) Hereinafter, the present invention will be described in detail based on the accompanying drawings.

1 to 4 show an example of the sintering furnace according to the present invention in order of operation. In FIG. 1, (11 is a pressure vessel constituting the furnace body, (2) and (3) are the vessels (These are the upper and lower lids that seal the upper and lower openings of the pressure vessel (11).
A processing chamber is defined by 1), an upper lid (2), and a lower lid (3), and a heat insulating layer (4) is placed on the outside of the inside, and a heater element (5) is placed inside, respectively, to form a furnace. However, it is the same as in known sintering furnaces that the processed material (6) such as a molded body is housed inside and sintering or other processing is performed.

In the above configuration, the lower cover (3) has a gas exhaust passageway (7) that communicates with the gas inlet pipe α of the wax trap device (not shown) which is connected to the vacuum suction mechanism (not shown) outside the furnace. is provided in the center, and in the illustrated example, this passage extends to the vicinity of the bottom of the object to be processed (6) to suck and discharge gas containing wax vapor that has evaporated into the processing chamber. .

(12a) and (12b) are the gas discharge passages (7)
A feature of the present invention is that the pistons (12a) and (12b) are connected by a cylinder mechanism 00, and the pistons (12a) and (12b) are moved by the operation of the actuator αυ. It is arranged to move up and down within the gas exhaust passage (7).

In addition, in the figure, (9) is a guide, (8) is a tape heater,
04) is Patsukin.

In addition, in Figure 1 above, the discharge passage (7) is provided directly below the processing chamber, but it may be sloped or right sideways, and can be designed as appropriate depending on the situation. be.

Next, the operation of the furnace having the above configuration will be explained with reference to FIGS. The gas containing steam is discharged as a gas stream to the outside of the furnace as indicated by the gas inlet pipe aω. In Figure 2, Q10 is the discharge passageway (7) in the center of the lower M (3).
This is wax that adheres to the inner wall of the wafer, and gradually increases in thickness as the process progresses. Therefore, it is necessary to remove this attached wax.

FIG. 3 shows this wax removal process, in which the pistons (12a) and (12
b) rises, scrapes off the wax adhering to the discharge passage (7), and collects it in the wax reservoir αη. and,
As shown in FIG. 4, there are further pistons (12a), (1
The wax α scraped off with the descent of 2b) is guided to the outlet, where a portion is vaporized and communicated with the subsequent wax trap device through the gas introduction pipe a! 19.

At this time, the remainder can be recovered as wax.

The gas containing some wax vapor flowing into the wax trap device is dewaxed in a subsequent wax trap device according to a conventional dewaxing method.

Although a reciprocating piston has been shown above as a means for removing wax from the inner wall of the gas discharge passage, this means is not limited to the above means and may be replaced by other means.

In FIG. 5, a piston with a spiral groove is used in place of the piston (12b), which also performs rotational movement, thereby making wax removal more efficient. In this case, of course, the rotational movement mechanism 01 is also provided.

In addition, in any of the above cases, the piston (12a)
, (12b) It is desirable to heat the rod αj, piston 0, etc. with a built-in heater so that wax vapor does not adhere to these parts.

In this way, the efficiency of the dewaxing process can be improved and the cycle time required for the dewaxing process can be shortened.

(Effects of the Invention) As described above, the present invention is provided with a means for forcibly removing the wax adhering to the inner wall of the pipe inside the gas exhaust passage containing wax vapor of the sintering furnace, and the following steps are normally performed. By completely removing adhering wax before reaching the wax trap in the process, it is possible to prevent a decrease in thermal conductivity due to adhering wax and reduce exhaust resistance, reducing the cycle time required for the dewasox process. This is expected to have the remarkable effect of further promoting the sintering of the powder compact, making it possible to recover the wax without reheating, and simplifying the dewaxing process.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional schematic diagram showing one example of a dewaxing sintering furnace according to the present invention, and FIGS. FIG. 5 is a schematic sectional view showing a modified embodiment of the dewaxing and sintering furnace of the present invention, and FIG. 6 is a schematic side view, partially in section, showing an example of a Wankstranop apparatus following the dewaxing and sintering furnace of the present invention. (1)...Pressure vessel, (2)...Top lid, (3)
... Lower lid, (6) ... Processing material, (7) ... Gas discharge passage, (12a) (12b) - Piston, α
Sequence: Gas inlet pipe, αω: Adhesive wax, θ Odor
・Piston with spiral groove. Figure Figure Figure Figure

Claims (2)

[Claims] 1. In a dewaxing sintering furnace, a molded body made by adding wax to powder of cemented carbide, ceramics, etc. is stored, and the wax is evaporated from the molded body and the molded body is sintered. A dewaxing sintering furnace characterized in that a forced removal means for removing adhered wax is provided in a discharge passage for discharging the wax to the outside of the furnace. 2. 2. The dewaxing sintering furnace according to claim 1, wherein a reciprocating or rotating piston is used as means for forcibly removing the deposited wax.