Investment molding flask assembly

Abstract

An investment molding flask assembly having a base with a central positioning boss protruded from a center thereof and at least one positioning annular groove defined therein around the central positioning boss, and a conical sleeve formed with a small opening end to be securely positioned on the base without any displacement in horizontal directions by means of the central positioning boss or the positioning annular groove. Whereby, the conical sleeve can be readily removable from a solidified semi-finished investment mold, and then the solidified semi-finished investment mold is sent into an oven independently for heating. Therefore the sleeve can be used repeatedly, and the investment mold can be manufactured rapidly and readily.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an improved molding flask assembly used in investment casting, particularly to an investment molding flask assembly, which can be used repeatedly to manufacture investment molds rapidly and readily.

[0003] 2. Description of Related Art

[0004] Lost wax investment casting is used in the making of 3 dimensioned articles such as a dental molds, metal ornaments, sculptures etc. In a lost wax investment casting, a molding flask assembly is normally used to form an investment mold, which is utilized to cooperate with a spin casting apparatus to manufacture a desired article.

[0005] As shown in FIG. 8, a conventional investment molding flask assembly comprises a base (50) having a spherical central positioning boss (51) protruded from a center thereof, and a cylindrical sleeve (60) having a lower opening end seated on a top of the base (50) and enclosing around the central positioning boss (51). A preliminary wax pattern (70) is securely fixed on a top end of the positioning boss (51) by means of melted wax drops (52). An investment material (80) is charged into an internal space of the cylindrical sleeve (60) up to an upper opening end of the cylindrical sleeve (60) so as to completely embed the wax pattern (70) in the cylindrical sleeve (60). After a semi-finished investment mold is solidified, the semi-finished investment mold with the cylindrical sleeve (60) enclosed therearound is sent into an oven to be heated together. Whereby the wax pattern (70) is melted and dispersed from the investment mold with the desired molding cavities defined therein. Casting material is then directed into the mold cavity by means of centrifugal techniques utilizing the spin casting apparatus, and then the casting material hardens to form a desired article.

[0006] However, because the cylindrical sleeve (60) seated on the top of the base (50) is not retained at a fixed position, when the investment material is poured into the cylindrical sleeve (60), the cylindrical sleeve (60) may be moved sideways, and in this case the wax pattern (70) may not be embedded properly in the center of the investment mold.

[0007] The aforesaid conventional investment molding flask assembly still has another important disadvantage. Because the sleeve (60) is formed as a cylindrical shape, it is not easy to remove the sleeve (60) from the semi-finished investment mold when the investment mold is solidified, and the cylindrical sleeve (60) enclosing the investment mold has to be sent into the oven together with the investment mold. However, because the sleeve (60) and the investment material normally have different thermal expansion rates, after the investment mold and the sleeve (60) are heated together, the sleeve (60) may be deformed or even damaged by the overexpansion of the investment mold, or the investment mold may be deformed, therefore the sleeve (60) can not be used repeatedly, and the rate of finished product is low.

[0008] Therefore, it is an objective of the invention to provide an improved investment molding flask assembly to mitigate and/or obviate the aforementioned problems.

SUMMARY OF THE INVENTION

[0009] A first object of the present invention is to provide an improved investment molding flask assembly, which comprises a base having a central positioning boss protruded from a center thereof and at least one positioning annular groove defined therein around the center thereof, and a conical sleeve having a small opening end thereof being securely positioned on the base by means of the central positioning boss or a corresponding one of the at least one positioning annular grooves without any displacement in horizontal directions.

[0010] A second object of the present invention is to provide an improved investment molding flask assembly, wherein the sleeve is particularly formed as a cone having a small opening end to be positioned on the base and a large opening end, such that when a solidified semi-finished investment mold in the sleeve is inverted and placed on a flat board, the sleeve is readily removable from the solidified semi-finished investment mold. Thus, the sleeve can be used repeatedly.

[0011] Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is an exploded perspective view of a first embodiment of an investment molding flask assembly in accordance with the invention;

[0013] FIG. 2 is a cross sectional view of the first embodiment of the investment molding flask assembly in accordance with the invention;

[0014] FIG. 3 is a cross sectional view of a second embodiment of the investment molding flask assembly in accordance with the invention;

[0015] FIG. 4 is a cross sectional view of a third embodiment of the investment molding flask assembly in accordance with the invention;

[0016] FIG. 5 is a cross sectional view of a fourth embodiment of the investment molding flask assembly in accordance with the invention;

[0017] FIG. 6 is a cross sectional view of a fifth embodiment of the investment molding flask assembly in accordance with the invention;

[0018] FIG. 7 is a cross sectional view of a sixth embodiment of the investment molding flask assembly in accordance with the invention; and

[0019] FIG. 8 is a cross sectional view of a conventional investment molding flask assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0020] As shown in FIG. 1, in a first embodiment of the present invention, an investment molding flask assembly comprises a base (10) and a sleeve (20) detachably positioned on a top surface of the base (10).

[0021] The base (10) is formed as a circular plate having a central positioning boss (11) protruded from a center thereof and two positioning annular grooves (12) defined therein around the center thereof. Wherein the central positioning boss (11) has a lower portion thereof formed as a cylinder and an upper portion thereof formed as a cone. An upper end of the upper portion of the central positioning boss (11) is defined with a positioning recess (111) in a center thereof.

[0022] The sleeve (20) is formed as a hollow cone having a small opening end particularly dimensioned with an inner diameter slightly larger than an outer diameter of the lower portion of the central positioning boss (11), and a large opening end with a diameter larger than that of the small opening end. The sleeve (20) is further defined with a maximum volume mark (21) optionally labeled on an inner or outer surface near the large opening end thereof.

[0023] With reference to FIG. 2, a preliminary wax pattern (30) is securely fixed on the upper end of the positioning boss (11) by means of melted wax (14) filled in the positioning recess (111). Then the small opening end of the sleeve (20) is placed on the top surface of the base (10) and mounted around the central positioning boss (11). Because the inner diameter of the small end of the sleeve (20) is slightly larger than the outer diameter of the lower portion of the central positioning boss (11), the small end of the sleeve (20) is retained at a fixed position on the base (10) without any horizontal displacement. Next an investment material (40) is charged into an internal space of the sleeve (20) till its upper level is flush with the maximum volume mark (21) so as to embed the wax pattern (30) in the sleeve (20). After the investment material (40) is solidified, the whole investment mold together with the investment molding flask assembly can be inverted together and placed on a flat board. Because the sleeve (20) is specially designed as a cone, the solidified semi-finished investment mold is readily separated from the flat board by gravity and a small impact force acted upon a bottom of the base (10), whereby the sleeve (20) is rapidly removed from the semi-finished investment mold. Finally the semi-finished investment mold is sent into an oven to be heated therein to obtain a finished investment mold.

[0024] In a second practicable embodiment as shown in FIG. 3, a sleeve (20a) is formed as a two-stepped cone having a small opening end mounted around the central positioning boss (11), so that the sleeve (20a) is retained at a fixed position without any horizontal displacement.

[0025] In a third embodiment as shown in FIG. 4, a sleeve (20b) is formed as a two-stepped cone having a small opening end thereof being properly inserted into an inner one of the annular groove (12), so that the sleeve (20b) is retained at a fixed position without any horizontal displacement.

[0026] In a fourth embodiment as shown in FIG. 5, a sleeve (20c) is formed as a cone having a small end thereof being properly inserted into the inner one of the annular grooves (12), so that the sleeve (20c) is retained at a fixed position without any displacement.

[0027] When a large article is to be molded in the investment molding flask assembly, a large sleeve is necessary to permit a large wax pattern to be received in the center of the sleeve. As shown in FIG. 6, in a fifth embodiment a conical sleeve (20d) having a small opening end thereof is properly inserted into an outer one of the annular grooves (12). A gasket ring (13) is further provided on the top surface of the base (10) between the sleeve (20d) and the central positioning boss (11) to prohibit the investment material (14) from going into the inner one of the two positioning annular rings (12). An inner edge of the gasket ring (13) is therearound formed with a flange having an upper conical surface extending flush with an outer surface of the cone-shaped upper portion of the central positioning boss (11). Whereby a pouring pit of the investment mold is formed with an upper opening larger than the outer diameter of the positioning boss so as to meet a volume requirement of a large molding cavity formed in the investment mold.

[0028] A sixth embodiment as shown in FIG. 7 is basically same as the fifth embodiment except for a sleeve (20e), which is formed as a two-stepped cone.

[0029] The investment molding flask assembly of the invention has an advantage that the sleeve is securely positioned on the base (10) by means of the positioning boss (11) or the positioning annular grooves (12), therefore it is retained in a fixed position without any horizontal displacement when the investment material (14) is charged into the internal space of the sleeve.

[0030] Another important advantage of the invention is that the sleeve can be used repeatedly and the investment mold can be made readily and rapidly, so that the production efficiency of the present invention is high and the production cost of the invention is low.

[0031] It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.

Claims

1. An investment molding flask assembly comprising:

a base formed as a circular plate having a central positioning boss protruded from a center of a top surface thereof, and at least one positioning annular groove defined in the top surface around the center thereof, wherein the central positioning boss is formed with a cylindrical-shaped lower portion and a cone-shaped upper portion;

a sleeve formed as a cone having a small opening end thereof to be securely positioned on the base without any horizontal displacement;

whereby after a wax pattern is fixed on a top end of the central positioning boss, an investment material is charged into an internal space of the sleeve to embed the wax pattern in the sleeve so as to form a solidified semi-finished investment mold, and then the solidified semi-finished investment mold is allowed to be removed from the sleeve to be heated in an oven independently, therefore a finished investment mold is rapidly obtained, and the investment molding flask assembly can be used repeatedly.

2. The investment molding flask assembly as claimed in claim 1, wherein the base is defined with two positioning annular grooves in the top surface around the center thereof.

3. The investment molding flask assembly as claimed in claim 1, wherein the sleeve has a small opening end defined with a diameter slightly larger than an outer diameter of the cylindrical-shaped lower portion of the central positioning boss.

4. The investment molding flask assembly as claimed in claim 1, wherein the sleeve has a small opening end defined with a diameter to be properly inserted into the at least one positioning annular groove.

5. The investment molding flask assembly as claimed in claim 1, wherein a positioning recess is defined in an upper end of the cone-shaped upper portion of the central positioning boss.

6. The investment molding flask assembly as claimed in claim 1, wherein the sleeve is formed as a cone.

7. The investment molding flask assembly as claimed in claim 1, wherein the sleeve is formed as a multi-stepped cone.

8. The investment molding flask assembly as claimed in claim 1, wherein the sleeve is defined with a maximum volume mark at an inner surface near the large opening end thereof.

9. The investment molding flask assembly as claimed in claim 1, wherein the sleeve is defined with a maximum volume mark at an outer surface near the large opening end thereof.

10. The investment molding flask assembly as claimed in claim 1, wherein a gasket ring is provided on the top surface of the base between the sleeve and the central positioning boss, an inner edge of the gasket ring is formed therearound with a flange having an inner cone surface extending in flush with an outer surface of the cone-shaped upper portion of the central positioning boss.