JP2011110576A - Lost foam pattern casting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lost foam pattern casting method capable of minimizing a head pressure and of keeping a sprue height as low as possible in a structure for discharging a combustion gas by a cavity arranged in a mold. <P>SOLUTION: In the lost foam pattern casting method, a melt is poured into a mold formed by embedding a pattern comprising a resin foaming body in casting sand and a product is cast while losing the pattern by the melt. A cavity for degassing with an upper end set at a position lower than the uppermost part of the pattern is formed at a position other than the final filling part of the melt to the pattern in the casting sand, and a filter is arranged at the upper end of the cavity. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a disappearance model casting method, and more particularly to a technique for smoothly discharging combustion gas generated in a mold out of the mold.

  In the disappearance model casting method, the model in the mold is burned at the initial stage of pouring to generate a large amount of combustion gas, and this combustion gas is discharged out of the mold through the mold. Here, when the pressure in the mold (internal pressure), which is increased by the generation of combustion gas, exceeds the head pressure of the molten metal, it is called a residual defect in which the molten metal is blown out from the gate and the model remains burnt due to prolonged pouring time. Casting defects may occur. For this reason, smooth discharge of the combustion gas out of the mold is required. As a measure for this, a technique is known in which a discharge passage communicating from the model to the atmosphere is provided to improve the exhaustability of the combustion gas (Patent Document 1).

  However, when casting a casting of about 2 to 10 tons with a large modulus (volume / surface area) of a product, that is, a model, combustion gas is generated explosively at the initial stage of pouring, so that the one described in Patent Document 1 is used. Then, there is a possibility that the molten metal may be ejected through the filter provided in the discharge passage. Therefore, it is considered that the combustion gas can be discharged without ejecting the molten metal by providing a cavity in which the combustion gas is discharged in a state of being confined in the mold (see Patent Document 2 and the like).

JP 2003-001377 A JP 2009-166105 A

  However, the cavity described in Patent Document 2 (in the same document, the internal space of the cylindrical member 10) has an upper end that is higher than the upper surface, which is the uppermost part of the model. In such a mold structure, in order to accurately discharge the combustion gas into the cavity, it is necessary to raise the gate and set the head pressure appropriately high. Increasing the gate height increases the overall height of the mold, increasing the amount of casting sand used and increasing the cost. Therefore, there is a demand for keeping the gate height as low as possible.

  Therefore, an object of the present invention is to provide a vanishing model casting method capable of suppressing the height of the gate as low as possible with the minimum head pressure in a structure in which combustion gas is discharged by a cavity provided in a mold.

  The vanishing model casting method of the present invention is a vanishing model casting method in which a molten metal is poured into a mold in which a model made of a resinous foam is embedded in foundry sand, and the product is cast while the model is lost by the molten metal. And forming a degassing cavity whose upper end is set at a position below the uppermost part of the model at a position other than the final filling portion of the molten metal with respect to the model in the foundry sand, A filter is provided.

  According to the present invention, since the upper end of the cavity for exhausting the combustion gas provided in the mold is set to a height below the uppermost part of the model, it is not necessary to increase the head pressure by increasing the height of the gate. It can be cast with minimum head pressure. As a result, the gate height can be kept as low as possible, and the cost of mold production can be suppressed.

It is sectional drawing of the casting_mold | template which showed the vanishing model casting method of this invention notionally.

Embodiments according to the present invention will be described below with reference to the drawings.
FIG. 1 shows a cross section of a mold 1 conceptually showing a vanishing model casting method according to an embodiment. The mold 1 is configured by burying a model 3 in foundry sand 2 filled in a casting frame (not shown).

  The model 3 is a cylindrical member having a hat-shaped cross section in which a collar portion 3b is formed below the trapezoidal peak portion 3a. In the foundry sand 2, a gate 4 connected to the flange 3 b of the model 3 and a runner 5 connected to the gate 4 are formed. In this case, the runner 5 has a lower runner 5a that communicates between the gates 4 below the model 3 and a vertical runner that extends vertically from one (right side in FIG. 1) gate 4 and opens to the upper surface of the mold 1. The opening of the vertical runway 5b is provided as a gate 6.

  A plurality of combustion gas discharge cavities 7 are formed in the foundry sand 2 in a state of being confined in the foundry sand 2. These cavities 7 extend in the vertical direction. In this case, the cavity 7 extends upward from the flange portion 3b of the model 3, and the cavity 4 extends upward from the other gate 4 (left side in FIG. 1) not connected to the vertical runner 5b. There is. The upper ends of the cavities 7 are positioned at a height that coincides with the upper end surface of the peak 3 a that is the uppermost portion of the model 3. At the upper end of the cavity, a filter 8 is disposed that releases only the combustion gas generated during casting to the atmosphere outside the mold 1 through the foundry sand 2.

  The mold 1 is manufactured according to the following procedure. First, a mold-forming agent having graphite as a main component and having excellent fire resistance is applied to the surface of the model 3 and sufficiently dried. On the other hand, the runner 5, the gate 4, and the cavity 7 are formed in the casting frame by a method such as assembling a paper tube, and the model 3 is arranged and supported at a substantially central portion in the casting frame. At this stage, the filter 8 is also disposed in the cavity 7. Thereafter, the casting sand 2 is filled in the casting frame, the model 3 is buried, and the gate 6 is provided.

  As the foundry sand 2, new sand or old sand such as zircon sand, chromite sand, and synthetic ceramic sand is used in addition to quartz sand mainly composed of quartz. A binder and a curing agent are added to the foundry sand 2 as necessary.

  The runner 5, the gate 4 and the cavity 7 are formed of commercially available products having a diameter of 30 to 70 mm (for example, runner pipes for quaker casting manufactured by Kao Corporation: EG runners CF-30S, CF-50S, CF-70S, etc.) Is recycled pulp). The filter 8 is made of a porous material or the like formed by mixing an appropriate binder with sand equivalent to No. 2 silica sand and having a thickness of about 40 mm.

The model 3 is made by hand-molding a synthetic resin foam such as expanded polystyrene. As the coating agent, for example, Kao Quaker PC260 manufactured by Kao Corporation is used, and is applied to the surface of the model with a thickness of 1.5 to 3.5 mm and an air permeability of about 10 mm ² .

  Thus, the mold 1 is manufactured. According to this mold 1, when molten metal (molten metal material) is poured from the gate 6, the molten metal reaches the model 3 through the runner 5 and the gate 4, and the model 3 disappears by being melted with the molten metal. The molten space is filled in the disappearing space. That is, the model 3 is replaced with molten metal. A large amount of combustion gas is generated at the initial stage of pouring in which the model 3 burns. The combustion gas enters the cavity 7, passes through the filter 8 installed at the upper end of the cavity 7, and further passes through the foundry sand 2. To the atmosphere. A part of the combustion gas passes through a coating film formed by applying a coating agent to the surface of the model 3, and further passes through the foundry sand 2 and is discharged to the atmosphere. The arrows in the mold 1 in FIG. 1 indicate the flow of combustion gas discharged out of the mold 1 in this way.

  In the mold 1, the internal pressure rises due to the combustion gas generated when the model 3 burns and disappears. This internal pressure is caused by the combustion gas being introduced into the plurality of cavities 7 and the combustion gas passing through the filter 8. In this case, the head pressure is controlled so as not to be exceeded by passing the coating agent and discharging it to the foundry sand 2. The head pressure corresponds to the height H from the gate surface to the gate 6 corresponding to the uppermost part of the model 3 (the upper end surface of the mountain portion 3a). For example, when the height H is 700 mm, the head pressure is 0.044 MPa.

  The internal pressure can be controlled by the gas passage cross-sectional area of the filter 8 installed at the upper end of the cavity 7. In this case, the gas passage cross-sectional area of the filter 8 is at least when the cavity 7 is opened to the atmosphere. The cross-sectional area of the cavity 7 is set larger (for example, about 8 times).

  According to the above-described embodiment, the upper end of the combustion gas discharge cavity 7 provided in the mold 1 is set to a height that coincides with the upper end of the peak portion 3 a that is the uppermost portion of the model 3. Even if the head pressure is not increased by increasing the height, the combustion gas can be sufficiently introduced into the cavity 7. For this reason, casting can be performed with the minimum necessary head pressure while keeping the height of the gate 6 as low as possible. As a result, the height of the entire mold and the amount of foundry sand used can be reduced, and the cost can be reduced.

  In addition, since the combustion gas is introduced into the cavity 7 confined in the mold 1, there is no fear that the molten metal will pierce the filter 8 through the filter 8, and safe casting can be performed. Further, when casting is performed by placing a weight on the upper surface of the mold 1, since the cavity 7 is not opened on the upper surface, there is an advantage that the shape of the weight and the layout freedom for placing the weight are increased.

  In the above embodiment, the position of the upper end of the cavity is set to a height that coincides with the uppermost part of the model. However, in the present invention, the upper end of the cavity coincides with the uppermost part of the model or is lower than that. However, the present invention is not limited to the above embodiment.

Casting was actually performed using a mold having the same configuration as the mold shown in FIG. That is, a model having a bottom surface diameter of φ1090 mm, a top surface diameter of φ760 mm, a wall thickness of 150 mm, and a modulus (volume ÷ surface area) of 6 is formed from foamed polystyrene, and a coating agent is formed on the surface of the model. (60-65 Baume) was applied and dried, then a mold was formed and cast. A plurality of cavities were formed in the mold so as to be connected to the model, and the upper ends of these cavities were made to coincide with the top of the model. A filter having a total gas passage cross-sectional area of 62000 mm ² was installed at the upper end of each cavity.

  The casting material was FC300 (flaky graphite cast iron), the temperature of the molten metal during pouring (casting temperature) was 1380 ° C., the pouring time was 37 seconds, and the casting weight was 2.2 tons. When casting, no molten metal was ejected, and a casting with good quality could be obtained.

DESCRIPTION OF SYMBOLS 1 ... Mold, 2 ... Foundry sand, 3 ... Model, 4 ... Gate, 5 ... Runway, 6 ... Spout, 7 ... Cavity,
8: Filter.

Claims (1)

In the disappearance model casting method in which a molten metal is poured into a mold in which a model made of a resinous foam is embedded in foundry sand, and the product is cast while the model is lost by the molten metal,
A degassing cavity having an upper end set at a position below the uppermost part of the model is formed at a position other than the final filling portion of the molten metal with respect to the model in the foundry sand, and a filter is formed at the upper end of the cavity. A vanishing model casting method characterized by being arranged.

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