Metal founding – Process – Shaping liquid metal against a forming surface
Patent
1993-06-24
1995-06-13
Batten, Jr., J. Reed
Metal founding
Process
Shaping liquid metal against a forming surface
164119, 164120, 164254, 164306, B22D 1712, B22D 1802, B22D 1806
Patent
active
054233690
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method of casting molten metal sucked from a molten metal reservoir into a cavity held under a reduced pressure by opening a gate having been blocking the communication between the molten metal reservoir and the cavity (hereinafter referred to as method of vacuum casting) and an apparatus for carrying out this method.
BACKGROUND ART
The vacuum casting can suppress the trapping of air in molten metal and this permits obtaining high quality casting with less casting defects such as cavity blanks, blowholes and microporocity. An example of the apparatus to this end is disclosed in Japanese Laid-Open Utility Model Publication No. 3-31058. FIG. 18 shows the apparatus disclosed in the publication.
This apparatus comprises a cavity 2 formed in a casting die 1 and a vacuum pump 4 for reducing the pressure in the cavity 2. The cavity 2 can communicate with a molten metal tank 8, in which molten metal 6 is stored, via a molten metal passage 10. At a sprue 2a of the cavity 2, a gate mechanism 12 is provided for on-off switching the communication between the molten metal passage 10 and the cavity 2. The gate mechanism 12 has an internal axial passage 12b communicated with a pressure reducing pump 20. The passage 12b has an end communicating with the molten metal passage 10 via a vent 12a at a position closer to the molten metal tank 8 than the gate mechanism 12 is.
A molten metal reservoir 14 having a predetermined volume is provided in an intermediate portion of the molten metal passage 10 located to be closer to the molten metal tank 8 than the gate mechanism 12 does.
In this casting apparatus, molten metal is introduced into the cavity 2 in the following way.
First, in a state with the sprue 2a held closed by the gate mechanism 12, the pressure in the cavity 2 is reduced by operating the vacuum pump 4. At this time, the pressure reducing pump 20 is also operated to produce a negative pressure in the molten metal reservoir 14 and molten metal passage 10, thus causing molten metal 6 stored in the molten metal tank 8 to be sucked up to the position of the end of the gate mechanism 12. That is, the molten metal 6 is tentatively stored in the molten metal reservoir 14 and molten metal passage 10.
In this state, the gate mechanism 12 is opened, causing the molten metal 6 stored in the molten metal reservoir 14 and molten metal passage 10 to be sucked and fill the cavity 2.
SUMMARY OF THE INVENTION
In the above prior art casting apparatus, however, the level (or height) of the top of the molten metal reservoir 14 is lower than the level of the opening/closing position of the gate mechanism 12. Therefore, as the molten metal 6 having been stored in the molten metal reservoir 14 and molten metal passage 10 is sucked quickly into the cavity 2, gas and foreign matter which have been floating in an upper portion of the molten metal reservoir 14 are carried along with the molten metal 6 into the cavity 2. Gas which is once sucked into the cavity 2 can not be removed even by bringing about a high vacuum state of the cavity 2 and thus causes defective product.
The present invention is predicated in the development of a technique of preventing gas and foreign matter floating in the molten metal reservoir from being sucked into the cavity when molten metal is sucked thereinto.
In the casting apparatus according to the invention, an accommodation space is provided, which can accommodate gas and foreign matter floating atop molten metal stored in the molten metal reservoir. This accommodation space is located at a position from which any matter accommodated in the accommodation space is unable to enter the cavity. The provision of this accommodation space has an effect of effectively suppressing the suction of gas or foreign matter into the cavity.
In a first mode of the invention, the molten metal reservoir is formed in the molten metal passage by making the volume of a portion of the molten metal passage located above the height (or level) of a position at which the cavity is opene
Arakawa Yasuyuki
Onishi Hirokazu
Ota Atsushi
Tamura Shigeki
Uozumi Minoru
Batten, Jr. J. Reed
Toyota Jidosha & Kabushiki Kaisha
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