JPH04231143A - Achieving device for low pressure multistage casting, its mold and its device - Google Patents

Abstract

PURPOSE: To prevent the degradation in quality and to simultaneously pack molten metal into respective stages in low-pressure casting using multi-stage type sand molds. CONSTITUTION: At the time of supplying the molten metal into the cavities of the respective stages of castings 4, the molten metal is pushed up by pressure through passages 30A, 30B from inlets 28, further via ingates 32A, 32B into the cavities 31 existing on the right and left of the inlets. In such a case, the total of the cross-sectional areas at the inlets of intermediate passages is made much smaller than the total of the cross-sectional areas of the inlets and the flow rate of the molten metal is throttled in the inlets of the intermediate passages by each of the respective stages. As a result, the pressure of the molten metal is relieved, the erosion and occlusion of air bubbles of the casting molds by turbulence are prevented and the improvement in quality is obtd.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the low-pressure casting of metals in multi-stage sand molds that are open on one side. The invention primarily relates to a method for supplying molten metal under low pressure into the cavity of a multi-stage sand mold that is open on one side. This supply is carried out via a casting spout, at least one intermediate passage extending from said spout for each stage, and a weir connecting this passage to each cavity.

Low-pressure casting (for example, French patent applications FR-A-2 295 808, 2 367 of the applicant)
566 and 2 556 996) is particularly advantageous in the production of metal products with thin walls and/or complex shapes and/or large dimensions compared to gravity casting. In fact, the pressure exerted on the metal as a result of the injection of gas into the gas-tight casting pot containing the liquid metal can be controlled at will to cause the metal to flow throughout the cavity.

0003

BACKGROUND OF THE INVENTION In conventional methods, for each stage of a mold, a single intermediate passage with a large cross-sectional area or two intermediate passages with a large cross-sectional area extending in opposite directions connect the casting opening to a series of weirs in the corresponding stage. It is designed to connect to.

Such structures have the following problems due to the large cross-sectional area of the one or more intermediate passages.

(1) Significant turbulence occurs in the metal flow, which promotes sand erosion and bubble occlusion, resulting in defects in the formed product.

(2) It is not possible to raise the metal to the top of the casting spout at high speed, and filling is performed step by step, making it impossible to take advantage of all the advantages of low-pressure casting.

(3) If the pressure is relieved after the weir has solidified and started to perform the blocking function (FR-A-2 mentioned above)
295 808), the metal in the intermediate passage, ie a relatively large amount of metal which has been significantly cooled, is returned to the casting pot. During the next pour, this cooled metal first rises through the pour spout, resulting in some quality loss of the cast product. For the same reason, excessive metal transfer is required for each pour.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to solve these problems.

[0009]

To this end, the method of the invention is characterized in that the flow rate of the liquid metal is throttled at each stage at the entrance of the intermediate channel.

The method of the present invention also has the following features.

- ensuring that the pressure on the liquid metal is relieved after it has entered the intermediate channel, especially when it enters the weir;

- Feed the liquid metal into the inlet tube at a flow rate suitable to raise it above all intermediate passages.

- Maintaining the supply pressure of the mold until all intermediate passages have solidified and then releasing this pressure.

The invention also relates to a sand mold, open on one side, for carrying out this method. The mold includes a spout and at least two stages, each stage having at least one cavity, the supply of which is connected to the spout by at least one intermediate passage. It is characterized in that the sum of the cross-sectional areas of the entrances of the intermediate passages of each stage is much smaller than the cross-sectional area of the pouring opening.

[0015] The mold of the present invention also has the following features.

- the sum of the cross-sectional areas of the weirs fed via the same passage is at least equal to the cross-sectional area of the entrance to the passage;

- The supply of each cavity takes place via at least two intermediate channels extending on either side of the pouring spout.

- The sum of the cross-sectional areas of the inlets of the intermediate passages of each stage is less than 10% of the cross-sectional area of the casting spout.

The invention also relates to an apparatus for low-pressure casting of metals in a multi-stage sand mold that is open on one side. The apparatus includes a casting pot, an inlet pipe extending upwardly from the casting pot and having an upward opening, and a pressurized gas source connected to the casting pot.
In addition to the casting spout with a downward opening, the casting spout comprises at least two stages, each stage being provided with at least one cavity, and connected to the casting spout by at least one intermediate passage. of the type comprising at least one side-open sand mold adapted for supplying the cavity, and means for bringing the bottom of the casting spout into contact with the opening of the introduction tube, the mold being of the aforementioned type; It is characterized by following the definition.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will now be explained in more detail by way of non-limiting examples with reference to the accompanying drawings.

The apparatus shown in FIG. 1 includes a vessel 1 constituting a pot or reservoir containing liquid metal 2, a mold support frame 3, and a sand mold 4. This equipment can be used to cast cast iron (gray cast iron or spheroidal graphite cast iron), steel or superalloy into a mold 4.
used for low pressure casting. Except for the internal structure of the mold, this device is similar to the above-mentioned FR-A-2 295 80.
It is the same as the device described in No. 8.

The stationary casting pot 1 includes an upper lid 5 which is hermetically fixed to the side wall and locked by suitable means (not shown). This lid 5 is provided with a hole 7, into which a casting nozzle 6 is inserted. This nozzle 6 is
a tubular lower part 8 having an outer diameter corresponding to the diameter of the bore 7;
A generally frustoconical upper part 9 rests in a gas-tight manner on the periphery of the bore via a larger planar base 10. The bottom 10 of this nozzle is provided with a groove in which a sealing packing 11 made of asbestos string is arranged. An introduction pipe 12 made of a heat-resistant material passes through the nozzle 6 and extends to near the bottom of the casting pot 1. The upper portion of the introduction tube 12 communicates with the center of the planar upper surface of the nozzle 6 .

The casting pot 1 is connected via a pipe 14 to a pressurized gas source 13, and the communication between the casting pot 1 and the pressure source 13 or the atmosphere is effected via suitable means 15 external to the casting pot. . The pressure inside the casting pot during casting is observed by a manometer 16.

The frame 3 includes a side post 17 with a roller 18 at the bottom running on two rails 19.

The side columns 17 are connected to each other at their upper ends via a ceiling portion 20. A jack 21 extending downward is attached to this ceiling portion, and an abutment plate 23 is pivotally attached to the lower end of the piston rod 22 of the jack.

Each side post 17 also has a collar 24 against which a coil spring 25 rests. Horizontal support plate 26
can slide vertically along the part of the side post 17 above the collar 24. This plate 26 is always in contact with the upper end of the spring 25 and is subjected to upward stress by this spring. When no downward pressure is applied to plate 26, it is above the upper surface of nozzle 6. The plate 26 is provided with a circular hole 27 having a diameter large enough to allow the nozzle 6 to pass through.

The mold 4 is, as shown in FIG. 2, a multi-stage solid mold with only one side open, including, for example, three stages. The mold has a vertical pour spout 28 with a circular cross-section of approximately the same diameter as the inlet tube 12. The casting port is open at the bottom, and has a accommodating portion 29 in the shape of a widening truncated cone that matches the shape of the nozzle 6. The spout extends some distance from the top of the mold.

All three stages are the same and have a structure as shown in FIG. In this structure, from the casting port 28 to 2
The two passages 30A and 30B extend horizontally with the casting port 28 in between, forming extensions of each other. Each stage further includes two cavities 31 of identical elongated shape. These cavities exist on either side of the spout 28 and receive liquid metal via three weirs. In this embodiment, each cavity is provided with one weir 32A or 32B on one side of the casting opening and two weirs 32B or 32A on the opposite side. Three weirs 32A connect the cavity to passage 30A, and three weirs 32B connect the cavity to passage 30B. Each passage 30A or 30B is therefore used to connect the spout 28 to all weirs located on the same side of the spout 28, and to feed the two cavities of that stage.

Passages 30A and 30B have relatively small cross-sectional areas. More precisely, the sum of the cross-sectional areas of the intermediate passages 30A and 30B of one stage is much smaller than the cross-sectional area of the casting spout 28, for example less than 10% thereof. If the cross-sectional area of these passages varies, the cross-sectional area of the entrance to these passages should meet this condition.

Furthermore, the total cross-sectional area of the plurality of weirs that receive supply through the same passage is at least equal to the cross-sectional area of the entrance of the passage.

The apparatus operates as follows. With the frame 3 separated from the casting pot 1, apply a suitable heat-resistant seal 3.
3 is applied to the bottom of the housing 29 of the mold 4. A mold 4 with a core (not shown) in each cavity is placed on the plate 26 and centered with respect to the central hole 27 of the plate. The frame 3 is then slid on the rails 19 and moved above the liquid cast iron ladle 1 so that the nozzle 6 and the mold housing 29 face each other. By extending the jack 21 in this state, the mold 4 and the support 26 are lowered via the plate 23 while resisting the force of the spring 25. As a result of this operation, the seal 33 is tightened between the bottom of the accommodating portion 29 and the nozzle 6, and the casting port and the introduction pipe are connected in an airtight manner.

Next, the casting pot 1 is connected to the pressure source 13 by operating the device 15 . As a result, the pressure acting on the free surface of the cast iron causes the cast iron to rise within the tube 12 and fill the spout 28, passages 30A and 30B and cavity 31 of the mold. The pressure is maintained for a predetermined period of time determined depending on the size and shape of the product to be manufactured. Meanwhile, the pour spout 28 serves as a reservoir or sprue that supplies supplemental liquid cast iron into the cavity to compensate for shrinkage.
). Next, when the weir and the intermediate passage are solidified, the gas pressure in the casting pot 1 is returned to atmospheric pressure by operating the device 15, and the liquid cast iron in the pouring port 28 and the pipe 12 is flowed out from these two pipes to form the casting pot. Return to within 1.

The action of the jack 21 is then removed, the mold-support plate assembly 26 is moved away from the nozzle 6 by the action of the spring 25, and the entire frame 3 is moved onto the rail 19.
It is moved horizontally from the casting pot 1 by sliding on the top.

Since the passages 30A and 30B have the aforementioned dimensions and a suitable flow rate of gas is introduced through the pipe 14, the liquid metal rises at high speed in the casting spout 28 and flows into the passages at each stage. Pressure metallo
statique) is established and the two cavities of each stage are supplied with liquid metal via a pair of corresponding passages 30A and 30B. In such a structure, all cavities are filled simultaneously, regardless of their shape. Additionally, the narrow intermediate passages limit the flow rate of metal flowing through them, thus allowing filling to occur more quietly and reproducibly in each cavity of each stage and with better control during each casting operation. Metal migration is minimized. This is further facilitated by the pressure relief on the liquid metal at the inlet of these weirs due to the dimensions of the weirs as described above. This also leads to improved quality of cast products.

As a variation, the pressure relief effect of metal is
This may be facilitated by gradually increasing the cross-sectional area of the intermediate passageway from upstream to downstream.

Furthermore, since the intermediate passage is used as a closing means, the return of extremely cooled metal into the casting pot is avoided without reducing the metal yield. This is extremely advantageous for the reproducibility of casting conditions. Also, the slightly cooled metal in the pouring spout will be distributed among all cavities of the mold during the next pouring operation.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view simply showing a casting apparatus of the present invention.

FIG. 2 shows the mold used in the apparatus of FIG. 1 along line II-- of FIG.
FIG. 2 is an explanatory diagram shown in a longitudinal cross-sectional view along II.

3 is a cross-sectional view along the line III-III of FIG. 2; FIG.

[Explanation of symbols]

4 Mold (sand mold) 28 Casting port 30A, 30B Middle passage 31 Cavity 32A, 32B Weir

Claims (10)

[Claims] 1. A method for supplying liquid metal under low pressure into a cavity of a multi-stage sand mold open on one side, the supply being connected to a casting spout and at least one intermediate passage extending from the spout for each stage. and a weir connecting this passage to each cavity, the flow rate of the liquid metal being throttled at each stage at the entrance of the intermediate passage. 2. A method as claimed in claim 1, characterized in that the pressure on the liquid metal is relieved after it enters the intermediate passage. 3. A method according to claim 2, characterized in that the pressure on the liquid metal is relieved as it enters the weir. 4. A method as claimed in claim 1, characterized in that the liquid metal is fed into the inlet pipe at a flow rate suitable to rise above all intermediate passages. 5. A method according to claim 1, characterized in that the mold supply pressure is maintained until all intermediate passages have solidified, and then this pressure is relieved. 6. A sand mold with only one side open for carrying out the method according to any one of claims 1 to 5, comprising:
a spout and at least two stages, each stage having at least one cavity, the supply of which is via a plurality of weirs connected to the spout by at least one intermediate passage; A sand mold with only one side open, characterized in that the sum of the cross-sectional areas of the entrances of the intermediate passages of each stage is much smaller than the cross-sectional area of the pouring port. 7. Sand mold according to claim 6, characterized in that the sum of the cross-sectional areas of a plurality of weirs fed through the same passage is at least equal to the cross-sectional area of the entrance of the passage. 8. A sand mold according to claim 6, wherein each cavity is supplied via at least two intermediate passages extending on either side of the casting spout. 9. The sand mold according to claim 6, wherein the total cross-sectional area of the entrances of the intermediate passages in each stage is 10% or less of the cross-sectional area of the pouring port. 10. An apparatus for low-pressure casting of metal in a multistage sand mold with only one side open, comprising: a casting pot; an introduction pipe extending upward from the casting pot and having an upward opening; a source of pressurized gas connected to the pan, and a spout having a downwardly directed opening, including at least two stages, each stage being provided with at least one cavity, and at least one intermediate passage connecting said spout. a sand mold with at least one side open, the sand mold being adapted to be supplied to the cavity via a plurality of weirs connected to the mold, and means for bringing the bottom of the casting spout into contact with the opening of the introduction pipe. 10. An apparatus characterized in that the sand mold is a sand mold according to any one of claims 6 to 9.