JP3060758B2 - Differential pressure casting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for immersing a tip of a sprue pipe connected to a sprue of a mold into a molten metal in a hot water storage tank located below the mold, and reducing a pressure in a cavity of the mold. The present invention relates to a differential pressure casting method in which the molten metal in the hot water storage tank is led to the cavity through the gate pipe by making the pressure lower than the pressure in the tank.

[0002]

2. Description of the Related Art A casting method related to this is disclosed in Japanese Utility Model Laid-Open Publication No.
No. 3361. In this casting method (suction casting method), the pressure in the cavity of the mold is reduced, and the molten metal in the hot water storage tank is sucked into the cavity through a cylindrical sprue pipe. It is suitable for producing castings of excellent quality with little entrainment of air or the like at the time. Here, the gate pipe for guiding the molten metal from the hot water storage tank to the mold is generally made of a metal similar to the molten metal in order to minimize contamination of the molten metal. For this reason, if the gate pipe is immersed in the molten metal for a long time, the dipped part of the gate pipe is melted and airtightness cannot be maintained. Therefore,
In the above suction casting method, the thickness of the immersion part of the gate pipe is increased in order to make the time until the gate pipe melts longer than the casting time.

[0003]

However, in the method of increasing the thickness of the sprue tube, the heat capacity of the sprue tube increases, so that when the sprue tube is immersed in the molten metal, the heat of the molten metal flows into the sprue tube. The molten metal near the sprue pipe is temporarily cooled. In addition, the molten metal passing through the gate pipe is also cooled. For this reason, the temperature of the molten metal in the early stage of casting decreases, which hinders the operation of the molten metal. In order to prevent this, a method in which casting is performed by increasing the temperature of the molten metal is conceivable, but the higher the temperature of the molten metal, the more the melting loss of the sprue tube is promoted. In order to solve the above problem, a method of using a ceramics gate pipe is conceivable, but there is a problem that the reliability of airtightness is poor because the ceramics gate pipe is weak to thermal shock. Moreover, since ceramics is expensive, production costs are increased.

[0004] The technical problem of the present invention is to make it possible to immerse the sprue pipe deeper into the molten metal before the tip of the sprue pipe immersed in the molten metal is melted and airtightness cannot be maintained. By doing so, casting is possible even with a metal gate gate having a small thickness (small heat capacity), and the casting quality is improved.

[0005]

The above-mentioned object is achieved by a differential pressure casting method having the following steps. That is,
In the differential pressure casting method according to the present invention, the tip of a sprue pipe connected to a sprue of a mold is immersed in molten metal in a hot water tank located below the mold, and the pressure in the cavity of the mold is adjusted to the hot water tank. In the differential pressure casting method in which the molten metal in the hot water storage tank is guided to the cavity via the gate pipe by lowering the pressure inside the molten metal, the tip of the gate pipe immersed in the molten metal is melted and airtight. Before the holding becomes impossible, the sprue tube and the mold are relatively moved with respect to the hot water storage tank, and the sprue tube is immersed further in the molten metal.

[0006]

According to the present invention, the sprue tube is immersed further in the molten metal before the part (first immersion part) immersed in the molten metal is melted and airtightness cannot be maintained. For this reason, even if the first immersion portion is melted, the airtightness of the gate pipe is maintained and casting can be continued until the portion newly immersed in the molten metal (the second immersion portion) melts. Similarly,
Before the second immersion part is melted and the airtightness cannot be maintained, if the gate pipe is immersed further deeper in the melt again, the part newly immersed in the melt (third immersion part) is melted and damaged. The airtightness of the gate pipe is maintained. In this way, even a thin gate pipe that is eroded in a short time can be used for long-time casting by repeatedly performing the above operation. Here, since the thinner gate pipe has a small heat capacity, even if the gate pipe is immersed in the molten metal, the amount of heat taken from the nearby molten metal or the molten metal passing through the gate pipe is small. Therefore, poor running of the melt due to a decrease in the temperature of the molten metal in the early stage of casting hardly occurs, and the casting quality is improved.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a vertical sectional view of a main part of a suction casting apparatus 10 used in the present embodiment, and FIG. 2 is a graph showing a dipping pattern of a gate pipe in a casting method according to the present embodiment. As shown in FIG. 1, the suction casting apparatus 10 includes a mold plate 12 and a surface plate 16 on which an airtight chamber 14 covering the mold 12 is placed. The platen 16 is a flat iron plate formed in a flat rectangular shape, and also serves as a bottom plate of the airtight chamber 14, and has a through hole 16k formed at a predetermined position. Then, a cylindrical gate 20 is inserted into the through hole 16k. Here, the sprue pipe 20 is made of a material similar to the molten metal material (0.08% C, balance Fe).
It has an outer diameter of 60mm, a length of 400mm, and a thickness of 1.6mm. The space between the through hole 16k and the sprue tube 20 is sealed by a sealing material (not shown).

The mold 12 is composed of an upper mold 12a and a lower mold 12b. When the molds 12a and 12b are combined, a cavity 12k is formed inside the mold 12.
Is formed. A gate 12y is formed in the lower mold 12b, and the mold 12 is positioned on the surface plate 16 such that the gate 12y is connected to an upper end of the gate pipe 20. The mold 12 positioned on the surface plate 16 is covered with an airtight chamber 14. The hermetic chamber 14 is manufactured in a box shape, and a decompression port 14p connected to a vacuum pump (not shown) is formed on an upper surface thereof. Further, a sealing material (not shown) is attached to the lower end of the side wall of the airtight chamber 14, and the inside of the airtight chamber 14 is maintained in an airtight state while the airtight chamber 14 is mounted on the surface plate 16. Is done.

Here, the platen 16 is supported by a lifting device (not shown). When the lifting device is driven, the platen 16 moves up and down a predetermined range with the mold 12, the airtight chamber 14 and the gate 20 placed thereon. Further, a melting furnace 18 functioning as a hot water storage tank for storing the molten metal is provided directly below the surface plate 16. For this reason, the lifting device is driven to rotate the surface plate 1.
6 and the like descend by a predetermined distance, the mold 1
The tip of the sprue tube 20 connected to 2 is immersed in the molten metal in the melting furnace 18. Here, the molten metal is heat-resistant cast steel SCH21 (0.3%
C, 20% Ni, 25% Cr, residual Fe)
It is kept at a temperature of 1500 ° C.

Next, the suction casting method according to the present embodiment will be described by taking as an example a case where a machine part having a minimum thickness of 2.3 mm and a weight of 20 kg is cast. In the casting of this mechanical part, the pressure reduction rate in the hermetic chamber 14 is set to 100 mmHg / sec, and the final pressure in the hermetic chamber 14 is set to -600 mmHg. Under these conditions, the required coagulation time is 50 seconds, and
The immersion time is 60 seconds. Here, the graph of FIG.
When the tip of the sprue tube 20 is immersed in the molten metal at 00 ° C., the time (second) at which the tip of the sprue tube 20 melts and the time of the sprue tube 2
It shows the relationship with 0 thickness (mm). As can be seen from this graph, the sluice tube 20 having a thickness of 1.6 mm according to the present embodiment melts in about 20 seconds. Therefore, in order to secure a immersion time of 60 seconds using the gate pipe 20, in the present embodiment, as shown in FIG.
The method of increasing the immersion depth is adopted. In FIG. 2, the horizontal axis represents time (t), and the vertical axis represents the length (L) of the sprue pipe 20 located above the reference level and the level (H) in the melting furnace 18. ing.

First, as described above, when the gate 20, the mold 12, and the airtight chamber 14 are set on the surface plate 16, the elevating device is driven to lower the surface plate 16 and the like, and the leading end of the gate tube 20 is moved. Is immersed in the molten metal stored in the melting furnace 18 by 50 mm. From this timing (immersion start timing t = 0), the inside of the airtight chamber 14 is depressurized by a vacuum pump (decompression speed 100 mmHg / se).
c) The casting is started. Since the overall length of the sprue tube 20 is 400 mm, the length (L) of the sprue tube 20 located above the level (reference level) at the start of immersion.
Is 400-50 = 350 mm. When the pressure in the hermetic chamber 14 is reduced, the cavity 12k of the mold 12 housed in the hermetic chamber 14 is indirectly reduced in pressure, and the molten metal in the melting furnace 18 is transferred to the cavity 12k via the sprue pipe 20. It is sucked. Here, the molten metal is filled in the cavity 12k in about 5 seconds, but after the molten metal is filled, the pressure in the hermetic chamber 14 is continuously reduced in order to have a hot-water effect. The molten metal in the melting furnace 18 is sucked into the cavity 12k, so that the molten metal level is lowered by about 25 mm from the reference molten metal level.

From the immersion start timing (t = 0), 15
After a lapse of seconds, the lifting device is driven to lower the gate 20 by 50 mm integrally with the surface plate 16 and the like. That is, the length L of the gate pipe 20 above the reference molten metal level is L = 300 mm. As a result, the sprue tube 20 is newly immersed in the 50 mm molten metal, and even if the first immersed part (first immersion part) is melted and airtightness cannot be maintained, the immersed part (second immersion) The airtightness of the sprue tube 20 is maintained until the (part) is melted. Further, after 28 seconds from the immersion start timing (t = 0), the sprue pipe 20 is lowered by 50 mm integrally with the surface plate 16 and the like (the sprue pipe length L above the reference metal level L = 250 mm). As a result, the sprue pipe 20 is newly immersed in the 50 mm molten metal, and even if the previously immersed part (second immersion part) is eroded, the sluice pipe 20 is immersed until the currently immersed part (third immersion part) is melted. 2
The airtightness of 0 is maintained.

Similarly, when 40 seconds have elapsed from the immersion start timing (t = 0), the gate pipe 20 is integrated with the surface plate 16 and the like.
mm down (gate length L = 200mm above the reference level).
As a result, the sprue tube 20 is newly immersed in the 50 mm molten metal,
Even if the previously immersed part (third immersion part) is eroded, the airtightness of the gate pipe 20 is maintained until the part immersed this time (fourth immersion part) is eroded. Further, when 51 seconds have elapsed from the immersion start timing (t = 0), the sprue tube 20 is lowered by 50 mm integrally with the surface plate 16 (the length of the sprue tube above the reference molten metal surface L = 150 mm). As a result, the sprue pipe 20 is newly immersed in the 50 mm molten metal, and even if the previously immersed part (fourth immersion part) is eroded, the sluice pipe is immersed until the currently immersed part (fifth immersion part) is melted. The airtightness of 20 is maintained. In this way, a dipping time of 60 seconds is ensured while maintaining the airtightness of the gate pipe 20.

From the immersion start timing (t = 0)
When the molten metal in the mold 12 solidifies after 60 seconds, the inside of the airtight chamber 14 is opened to the atmosphere, and the gate 12y and the gate pipe 2 are opened.
The unsolidified molten metal within 0 is returned to the melting furnace 18, and the casting is completed. Here, if the immersion time of the sprue tube is to be secured for 60 seconds by the conventional casting method, the thickness of the sprue tube must be 4 mm or more, as shown in FIG. On the other hand, in the casting method according to the present embodiment, it is possible to perform casting using the thin gate pipe 20 having a small thickness (1.6 mm) as described above. For this reason, the calorie | heat amount which the gate pipe 20 takes away from a molten metal becomes small, and the fall of a molten metal temperature is suppressed. As a result, poor run-off is less likely to occur and casting quality is improved. Further, since the sprue tube 20 can be reduced in weight, productivity is improved and cost can be reduced. Further, it is not necessary to raise the casting temperature more than necessary, and energy can be saved.

FIG. 3 is a graph showing the immersion pattern of the gate pipe in the suction casting method according to the second embodiment of the present invention. In the first embodiment, the gate 20 is set at a predetermined timing (t
= 0, 15, 28, 40, and 51 seconds), and the immersion time of 60 seconds was secured by lowering by 50 mm at a time, but in this embodiment, the casting ends (t = 0) from the immersion start timing (t = 0). Until the spout tube
By lowering continuously at a speed of 4 mm / sec
An immersion time of 60 seconds is secured. Thereby, the first
Almost the same effects as in the embodiment can be obtained.

[0016]

According to the present invention, casting can be performed using a thinner gate pipe. For this reason, the amount of heat taken by the sprue pipe from the molten metal is reduced, and a decrease in the molten metal temperature is suppressed. As a result, poor run-off is less likely to occur and casting quality is improved. Further, since the weight of the gate pipe can be reduced, productivity can be improved and cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a main part of a suction casting apparatus used in a first embodiment of the present invention.

FIG. 2 is a graph showing an immersion pattern of a gate pipe in the suction casting method according to the first embodiment of the present invention.

FIG. 3 is a graph showing an immersion pattern of a gate pipe in a suction casting method according to a second embodiment of the present invention.

FIG. 4 is a graph showing the relationship between the time (seconds) at which the immersion part is melted and the wall thickness (mm) of the gate pipe when the gate pipe is immersed in a molten metal at 1500 ° C.

[Explanation of symbols]

 12 mold 14 chamber 16 surface plate 20 sluice pipe 18 melting furnace (hot water tank)

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-84757 (JP, A) JP-A-62-33051 (JP, A) JP-A-4-319906 (JP, A) 81752 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 18/06 B22D 18/04

Claims (1)

(57) [Claims] 1. A tip of a sprue pipe connected to a sprue of a mold is immersed in a molten metal in a hot water tank located below the mold, and a pressure in a cavity of the mold is set to be lower than a pressure in the hot water tank. In the differential pressure casting method in which the molten metal in the hot water storage tank is guided to the cavity through the gate pipe by reducing the temperature, the tip of the gate pipe immersed in the molten metal is melted and airtightness cannot be maintained. The differential pressure casting method further comprising: moving the sprue tube and the mold relative to the hot water storage tank, and immersing the sprue tube further deeply in the molten metal.