JPH06292962A - Differential pressure casting apparatus - Google Patents

Abstract

PURPOSE:To carry out production of a cast product without using a block-state mold. CONSTITUTION:The inner part of an apparatus body 1 is partitioned into a melting chamber 2 at the upper part and a mold chamber 3 at the lower part with a crucible table 4 having a pouring hole 5, and to the crucible table 4 at the mold chamber 3 side, a porous mold is air-tightly fitted so as to plug the pouring hole 5. This mold chamber 3 is sucked and also, while supplying inert gas into the melting chamber 2, an ingot 6 in the melting chamber 2 is melted and poured into the mold through the pouring hole 5 to execute the casting. Then, as the mold, a ceramic shell mold 15 formed to thin thickness is used, and also a flange 17 is arranged the upper part of this ceramic shell mold 15. A mold fitting mechanism 19 for air-tightly fitting the flange 17 in this ceramic shell mold 15 to the crucible table 4, is arranged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a differential pressure casting apparatus for casting using a ceramic shell mold manufactured by the lost wax method.

[0002]

2. Description of the Related Art Relatively small castings such as teeth and arts and crafts made of precious metals, titanium, and other materials are generally thin and have delicate patterns, and are liable to cause defective spinning during casting. Therefore, in order to improve this, the temperature of the molten metal during casting is suppressed by raising the mold temperature and the casting temperature. However, when titanium or titanium alloy is used as the material, it is very difficult to raise the casting temperature by heating the molten metal in the actual work. Further, due to the reactivity specific to titanium, the reaction between titanium and the mold becomes more intense as the mold temperature rises, resulting in deeper contamination of the cast product.

As another method for suppressing the poor bathing,
Centrifugal casting method to improve the flow of molten metal by centrifugal force, reversal casting method, reversal pressure casting method, suction casting method to pour molten metal while sucking and depressurizing the cavity of the mold, casting machine with a mold chamber and melting chamber isolated There is a method using a mechanical auxiliary means such as a differential pressure casting method (suction / pressurizing casting method) in which the melting chamber is pressurized by argon gas while the chamber is sucked and depressurized.

Each of these methods has advantages and disadvantages and is properly used depending on the material, shape, size, etc. of the cast product, but the differential pressure casting method, which provides good bathing, is often used.

The differential pressure casting method is carried out as follows by a differential pressure casting apparatus as shown in FIG. 5, for example.

(1) First, the block-shaped porous mold 25 manufactured by the burying method is placed on the ring base 26, and the crucible base 4 and the mold 25 are put through the packing 27 to the jack 1
Mechanically tighten at 2, and seal between the crucible base 4 and the mold 25.

(2) The mold chamber 3 and the melting chamber 2 are sucked and evacuated, and the air in each chamber 3, 2 is discharged.

(3) Thereafter, while sucking the mold chamber 3, an argon gas (Ar gas) is introduced into the melting chamber 2 to provide a differential pressure (for example, a pressure difference of 10 to 20 cmHg). As a result, the inside of the porous mold 25 is sucked.

(4) Then, an arc is generated between the ingot 6 in the crucible 7 and the electrode 8 to melt the ingot 6.

(5) The ingot 6 melts into the crucible 7
It is naturally dropped from its bottom hole by its own weight and poured into the mold 25, and its upper surface is pressurized with argon gas.

Since the material of the casting mold 25 is poured while the inside of the porous casting mold 25 is sucked in this way, there is a feature that it is possible to improve the molten metal and gas defects of the cast product.

[0012]

By the way, in the above-mentioned differential pressure casting, it is most important that the contact surface between the mold and the crucible base can maintain sufficient airtightness. In particular, the mold is easy to install and will not break even if it is tightened with a jack. No strength is needed.

Therefore, the mold is usually limited to a block-shaped and porous mold having a relatively high mechanical strength produced by the burying method or the ceramic molding method. As described above, the mold is limited to the block-shaped one.
Generally about 6-7 in the same casting compared to shell mold
Double the amount of mold material is required, and the wall thickness of the mold becomes thicker, which also affects the air permeability during casting. Further, a thick mold has a poor thermal conductivity and is vulnerable to thermal shock, and there is a problem that the mold is easily cracked during the heat treatment process or casting.

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a differential pressure casting apparatus capable of producing a cast product without using a block-shaped mold.

[0015]

In order to achieve the above object, the present invention divides the inside of the apparatus main body into a crucible stand having a pouring hole in an upper melting chamber and a lower mold chamber, and the mold chamber is divided. To the crucible table on the side, a porous mold is attached with good airtightness so as to block the pouring hole, and the ingot in the melting chamber is melted while sucking the mold chamber and supplying an inert gas to the melting chamber, which is In a differential pressure casting apparatus for pouring and casting into a mold through a pouring hole, a thin ceramic shell mold is used as the mold, and a flange is provided on the ceramic shell mold.・
A mold attachment mechanism is provided for attaching the flange of the shell mold to the crucible base with good airtightness.

[0016]

[Function] Ceramic shell molds are relatively weak against bending stress and easily cracked, so they are not used for differential pressure casting. However, a flange is provided on the ceramic shell mold and this flange is attached to the mold. By attaching the crucible base to the crucible base with good airtightness by the mechanism, almost no bending stress is applied to the mold itself, and the mold is not broken. Further, since the mold is attached only by attaching the flange to the crucible base by the mold attaching mechanism, the mold can be easily attached. Therefore, it is possible to manufacture a cast product by differential pressure casting using a thin ceramic shell mold without using a block-shaped mold.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings.

In FIG. 1, reference numeral 1 denotes a main body of a differential pressure casting apparatus, and a crucible stand 4 for partitioning the inside into a melting chamber 2 and a mold chamber 3 is provided at the center of the main body 1. .

A pouring hole 5 is provided in the center of the crucible table 4, and an ingot 6 made of a material (such as a noble metal such as gold or platinum) that melts is directly above the pouring hole 5 on the crucible table 4. The crucible 7 is placed so as to be positioned at. Above the crucible 7, an electrode 8 made of tungsten or the like for generating an arc that melts the ingot 6 on the crucible 7 by applying a voltage.
Is provided. The melting chamber 2 is provided with a viewing window 9 capable of monitoring the state of the melting chamber 2 such as an arc or an ingot, and a gas port 10 for introducing or exhausting an inert gas such as Ar gas. Has been.

The mold chamber 3 has an exhaust port 11 for exhausting the interior of the chamber 3.
Is provided. Below the pouring hole 5 in the mold chamber 3,
Ring stand 1 that moves up and down in the chamber 3 by the jack 12
3 is provided, and the mold receiving base 14 is placed on the ring base 13. The mold cradle 14 is a porous ceramic shell mold 15 having a flange 17 at the upper end of the sprue cup 16 of the mold 15 which is folded outward by approximately 90 ° in the radial direction. It supports 15 in a suspended state, and for example, is formed in a cylindrical shape made of metal or refractory material divided in two in the diameter direction as shown in FIG. The mold stand 14 is placed on the ring stand 13 so that the sprue cup 16 of the supported mold 15 is located directly below the pouring hole 5.
3 is lifted by the jack 12 so that ceramic
The flange 17 of the shell mold 15 is pressed against the lower surface of the crucible base 4 via a packing 18 made of a refractory material,
The flange 17 is mechanically fastened to the crucible base 4 and the space between them is sealed. A mold mounting mechanism 19 is configured by the mold receiving base 14, the jack 12, the ring base 13, and the like, and the flange 17 of the ceramic shell mold 15 is airtightly mounted on the crucible base 4 by the mold mounting mechanism 19.

The ceramic shell mold 15 is manufactured by, for example, the lost wax method.

First, as shown in FIG. 2, a desired model with a flange is manufactured from wax or a material capable of being eliminated.
Specifically, the pouring hole 5 is provided through a runner forming portion 21 for forming a runner in a product portion 20 similar to a target product.
The gate cup forming portion 22 is provided so that the gate cup 16 having substantially the same diameter as the above is formed, and the flange forming portion 23 is provided on the upper end portion of the gate cup forming portion 22 to manufacture a model.
Next, a predetermined coating is applied to this by the lost wax method, and this is dewaxed and fired to manufacture a thin ceramic shell mold 15 with a flange 17 as shown in FIG.

Here, for the flange 17 of the mold, for example, only the flange 17 is separately manufactured by using a refractory material, and the ceramic shell mold without the flange 17 is joined, or the refractory flange is made into a wax shape. Built-in ceramic
Shell molds can also be made. However, such a method may cause cracks due to the difference in the coefficient of thermal expansion between the flange and the ceramic shell mold, and may be considerably expensive, so the flange should be manufactured at the same time as the ceramic shell mold. , It is best to have the same wall thickness.

Next, the ceramic shell mold 15 having a predetermined temperature is attached to the mold holder 14 by the flange 1 as shown in FIG.
The mold 15 is supported so that it can be hung at the seven parts. At this time, the diameter of the flange 17 can be reduced by dividing the mold cradle 14 in two, and the operation is easy,
Even hot ceramic shell molds 15 can be set quickly.

Then, the ceramic shell mold 15 placed on the mold holder 14 is inserted into the mold chamber 3 of the differential pressure casting apparatus as shown in FIG. Flange 17 with the mold 15 suspended
The crucible base 4 and the crucible base 4 are mechanically fastened with the jack 12 via the fireproof packing 18.

As a result, the ceramic shell mold 15 manufactured by the lost wax method, which is the most widely used precision casting mold, can be easily fastened to the differential pressure casting apparatus with good sealing property and without breaking.

That is, the ceramic shell mold 15
Is relatively weak against bending stress and easily cracks, and is easily broken even when the entire mold 15 is tightened. For example, when the ceramic shell mold 15 is placed on the ring base 13 and is fastened with the jack 12 without using the mold receiving base 14, the ceramic shell mold 15 is easily broken. However, the ceramic shell mold 15 has a property of being able to withstand a local compressive stress considerably, and in order to utilize this, a flange 17 is provided at the upper end of the sprue cup 16, and only the flange 17 is provided with the packing 18. It is pressed against the crucible base 4 through. As a result, the mold 15 is subjected to the compressive stress only in the part of the flange 17 in contact with the packing 18 of the flange 17, so that the flange 17 is fastened by fastening.
Moreover, the ceramic shell mold 15 is hardly broken, and the airtightness of the fastening portion is practically sufficient.

Further, the ceramic shell mold 15 is supported by the mold cradle 14 in a suspended state, and the molten metal is poured in this condition. However, except for the ceramic shell mold 15 which has particularly weak strength, The ceramic shell mold 15 having the proper strength is hardly broken by the pouring. A ceramic shell mold that can withstand normal pouring is a ceramic shell that can be used with such equipment.
Since the size of the shell mold is relatively small, there is no particular problem even if the product is cast by hanging in the middle.

Next, a case where a cast product is concretely produced by using the above-mentioned differential pressure casting apparatus will be described.

[Specific Example 1] First, a wax pattern (12 g) as shown in FIG. 2 was produced by the lost wax method, and 12 wax patterns were assembled into one tree. This was coated with titanium castings by the method for producing precision casting molds disclosed in Japanese Patent Laid-Open No. 64-11049, and the wax was dewaxed to decompose the tree into 12 molds. The ceramic shell mold shown in FIG. 3 was manufactured by firing for a time.

The manufactured ceramic shell mold is heated to 800 ° C.
Preheat for 1 hour and support it on the mold cradle 14.
This was placed on the ring base 13, and the crucible base 4 and the mold (flange) were mechanically tightened with the jack 12 via the packing 18.

Next, the mold chamber 3 and the melting chamber 2 are sucked and decompressed by a vacuum pump to discharge the air in the chambers 3 and 2, and thereafter,
Argon gas with an original pressure of 1 kg / cm ² was introduced into the melting chamber 2 at the gas port 10.
Introduced from. At this time, the pressure in the mold chamber 3 is -10 to -20.
cmHg, while the pressure in the dissolution chamber 2 was 0.6-0.8 Kg / cm ² . That is, the pressure difference (differential pressure) between the mold chamber 3 and the melting chamber 2
Therefore, it was confirmed that the airtightness of the contact portion between the flange of the ceramic shell mold and the packing 18 was sufficiently maintained.

Next, the electrode 8 of the melting chamber 2 and 70 g of Ti-6Al
An arc was blown between the -4V ingots 6 to melt the ingots 6 and casting was performed. In this case, the pressure difference between the mold chamber 3 and the melting chamber 2 hardly changed during the melting and pouring of the ingot 6.

No cracks or other damage were found on the ceramic shell molds and flanges after casting. When the ceramic shell mold was destroyed and the cast product was visually inspected, the thin-walled area was completely covered, there were no pinholes or other gas defects on the surface of the cast product, and there was no burring due to cracks in the ceramic shell mold. A non-defective product was obtained.

[Specific Example 2] Casting was performed in the same manner as in Specific Example 1 except that the other ceramic shell mold produced in Specific Example 1 was preheated at 100 ° C. for 1 hour.

No cracks or other damage were found in the ceramic shell molds and flanges after casting. When the ceramic shell mold was destroyed and the cast product was visually inspected, the thin-walled part was completely covered with molten metal, there were no pinholes or other gas defects on the surface of the cast product, and there were burrs due to cracks in the ceramic shell mold. A non-defective product was obtained.

Generally, the hot strength of ceramic shell molds is weak at 800 ° C. and 100 ° C., but the result is 100
It was confirmed that a ceramic shell mold at ℃ could be sufficiently used. The advantage of this is that, especially for cast products of titanium and titanium alloys, the lower the mold temperature, the shallower the contamination on the surface of the cast product.

[Example 3] A ceramic shell mold was produced by the method for producing a precision casting mold disclosed in Japanese Patent Application No. 4-82407, and this ceramic shell mold was produced at 100 ° C for 1 hour.
Casting was performed in the same manner as in Example 1 except that preheating was performed for a time.

No cracks or other damage were found on the ceramic shell molds and flanges after casting. When the ceramic shell mold was destroyed and the cast product was visually inspected, the thin-walled area was completely covered, there were no pinholes or other gas defects on the surface of the cast product, and there was no burring due to cracks in the ceramic shell mold. A non-defective product was obtained.

Comparative Example 1 Another ceramic shell mold produced in Example 1 was preheated at 200 ° C. for 1 hour and placed directly on the ring stand 13 shown in FIG. 1 without using the mold holder. The chamber 3 and the dissolution chamber 2 were decompressed by suction and air was discharged.
Then, argon gas was introduced in the original pressure 1Kg / cm ² in the melting chamber 2. In this case, since the mold chamber 3 and the melting chamber 2 were communicated with each other, there was no pressure difference, and the pressure in the chamber was 0 to 0.2 Kg / cm ² .
70 g of Ti-6Al-4V ingot in this state was melted and cast.

No cracks or other damage were found in the ceramic shell mold after casting, and there was no particular problem.
When the casting product was broken and the casting product was visually inspected, defective melt flow was observed in the thin portion, and gas defects such as pinholes were present, and a satisfactory casting product could not be obtained.

Therefore, by performing casting using the differential pressure casting apparatus according to the present invention, a good cast product having no pinholes or other gas defects on the surface and no defects such as burrs can be obtained. In particular, the differential pressure casting apparatus according to the present invention can obtain a precision casting product that is thin and has almost no gas defects even when precision casting a metal having a poor molten metal flow such as titanium or a titanium alloy. It is suitable for precision casting of titanium alloys and other castings that are liable to cause defective melt flow, and pinholes and other castings that are apt to generate gas defects.

[0043]

As is apparent from the above description, according to the present invention, it is possible to produce a cast product by using a thin ceramic shell mold without using a block mold.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a differential pressure casting apparatus of the present invention.

FIG. 2 is a sectional view showing an example of a wax mold for producing the ceramic shell mold of the present invention.

FIG. 3 is a sectional view showing an example of a ceramic shell mold of the present invention.

FIG. 4 is a view showing a state in which the ceramic shell mold of the present invention is supported on a mold cradle, in which (a) is a sectional view,
(B) is a top view.

FIG. 5 is a sectional view showing an example of a conventional differential pressure casting apparatus.

[Explanation of symbols]

 1 Equipment Main Body 2 Melting Chamber 3 Mold Chamber 4 Crucible Table 5 Pouring Hole 6 Ingot 15 Ceramic Shell Mold 17 Flange 19 Mold Mounting Mechanism

Claims (1)

[Claims] 1. The apparatus main body is partitioned by a crucible table having a pouring hole in an upper melting chamber and a lower mold chamber, and a crucible table on the mold chamber side is made of a porous mold so as to close the pouring hole. Is attached airtightly, the mold chamber is sucked and the ingot in the melting chamber is melted while supplying the inert gas to the melting chamber, and this is poured into the mold through the pouring hole to perform casting. In a pressure casting apparatus, a thin ceramic shell mold is used as the mold, a flange is provided on the ceramic shell mold, and the flange of the ceramic shell mold is attached to the crucible base with good airtightness. A differential pressure casting device characterized by being provided with.