GB2460427A

GB2460427A - Investment casting flask

Info

Publication number: GB2460427A
Application number: GB0809749A
Authority: GB
Inventors: Patrick Shannon; Michael Shannon; Liam Shannon
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-05-29
Filing date: 2008-05-29
Publication date: 2009-12-02
Also published as: GB0809749D0

Abstract

An investment casting flask which comprises a cylindrical body 104 that is open at either end and has a plurality of substantially circular apertures 108 disposed in circumferential rows therein. A handle 110 formed from substantially flat cross-member bridges a first open end of the cylindrical body 104 and an annular platform 112 which projects orthogonally from the cylindrical body 104 is located adjacent the opposite end of the cylindrical body 104. A cylindrical flange 116 projects orthogonally from the annular platform 112 towards the handle 110. This flange 116 is co-axial with the cylindrical body 104 and is equidistant from the inside and outside edges of the annular platform 112. The flange 116 provides for increased stability of the flask during vacuum casting and further allows for a strong air-tight seal to be formed between the flask and the casting chamber during the casting process.

Description

"A FLASK"

INTRODUCTION

The present invention relates to an investment casting flask comprising a cylindrical body, a handle section and a collar section, the cylindrical body having a plurality of substantially circular apertures disposed in circumferential rows therein, the handle section comprising a substantially flat cross-member bridging a first open end of the cylindrical body; the collar section comprising an annular platform surrounding the flask and projecting substantially orthogonally from the cylindrical body at a location adjacent a second open end of the cylindrical body, the annular platform having an inside edge abutting against the cylindrical body and an outside edge. Such flasks are used to hold moulds in investment casting processes.

The process of lost wax or investment casting has been known for many hundreds of years and is known to be used for providing high quality, repeatable components in a wide variety of industries including the manufacture of automotive parts, medical devices and jewellery manufacture.

In the area of jewellery manufacture, it is common to form a single combined mould, referred to as a tree, comprising a number of smaller moulds each, for example, representing a single ring or the like, wherein the smaller moulds are fitted with sprues, which are in turn then connected to a riser fitted to a sprue base. A casting flask is then placed over the tree and secured to the sprue base, and the flask is inserted into the chamber of a casting furnace. Next, investment plaster is poured into the flask, forming a shell around the tree. The wax is then burned away and molten metal such as silver or gold is poured into the shell. The metal is supplied to the shell using a vacuum system and it is therefore very important for the quality of the casting that a strong seal is formed between the flask and the casting chamber. If the seal is insufficiently strong, the molten metal will not be distributed evenly throughout the tree resulting in sub-standard pieces which must be scrapped or else require significant re-working. The re-working is a costly and time consuming process and when combined with those pieces that must be melted down, the efficiency of the casting process is greatly reduced.

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It is an object therefore of the present invention to provide a flask that overcomes the problems discussed above.

STATEMENTS OF INVENTION

According to the invention there is provided investment casting flask comprising a cylindrical body, a handle section and a collar section, the cylindrical body having a plurality of substantially circular apertures disposed in circumferential rows therein, the handle section comprising a substantially flat cross-member bridging a first open end of the cylindrical body; the collar section comprising an annular platform surrounding the flask and projecting substantially orthogonally from the cylindrical body at a location adjacent a second open end of the cylindrical body, the annular platform having an inside edge abutting against the cylindrical body and an outside edge characterized in that the collar section further comprises a cylindrical flange projecting orthogonally from the annular platform, in the direction of the handle section; the flange being co-axial with the cylindrical body, equidistant from the inside edge and outside edge of the annular platform and having a thickness in the range of 20% to 36% of the width of annular platform.

In this way, an improved seal may be formed between the flange and the casting chamber, ensuring that a sufficiently strong vacuum is generated to ensure satisfactory distribution of molten metal throughout the plaster mould. The efficiency of the casting process is improved as the number of faulty pieces that must be melted down is reduced and the amount of re-working required on the cast pieces is also decreased. The positioning and dimension of the flange also ensure the stability of the flask within the casting chamber throughout the casting process and further ensure the structure and shape of the flask is not damaged by any expansion or contraction of the flask due to the extreme changes in temperature during the casting process.

In one embodiment of the invention there is provided a flask in which the thickness of the flange is 25% to 31% of the width of platform.

In another embodiment of the invention there is provided a flask in which the thickness of the flange is in the range of 27% to 29% of the width of platform. This is a particularly efficient thickness for providing stability and structural integrity of the flask. Furthermore, a flange in this range of thickness provides a strong seal between the flask and casting chamber.

In another embodiment of the invention there is provided a flask in which the length of the flange is in the range 8 mm to 12 mm. Again this is a particularly efficient embodiment of the flange for providing stability in use.

According to the invention there is provided a method of manufacturing jewellery by investment casting using the flask of the invention. In this way, a method of manufacturing jewellery having increased efficiency in provided.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be more clearly understood from the following description of an embodiment thereof given by way of example only with reference to the accompanying drawings in which:-Fig. I is a perspective view of the flask according to the invention; Fig. 2 is a side view of the flask according to the invention; Fig. 3 is a top view of the flask according to the invention; Fig. 4 is a perspective view of a sprue base for use with the flask of the invention; Fig. 5 is a perspective view of a sprued mould; Fig. 6 is a perspective view of the sprue base and a riser fitted with the sprued mould; Fig. 7 is a perspective view of a tree formed on the sprue base; Fig. 8 is a top view of the flask of the invention fitted to the sprue base; and Fig. 9 is a cross-section view of the flask positioned in the casting chamber.

Referring to the drawings, and initially to Figs. I to 3 thereof, there is shown an investment casting flask indicated generally by the reference numeral 100, comprising a handle section 102, a cylindrical body 104 and a collar section 106. The cylindrical body 104 has a first open end adjacent the handle section 102 and a second open end adjacent the collar section 106. The cylindrical body 104 has a thickness a of approximately 2 mm to 3 mm and an external diameter b of 100 mm. A plurality of substantially circular apertures 108 are formed in the cylindrical body 102 and are disposed in circumferential rows thereon. The apertures are approximately 15 mm in diameter. The handle section 102 of the flask 100 comprises a substantially flat bar 110 which bridges the first open end of the cylindrical body 104. The collar section 106 of the flask 100 comprises an annular platform 112 which is welded to the cylindrical body at a location approximately 10% or 15% along the cylindrical body 104 from the second open end of the cylindrical body 104. The annular platform 112 projects orthogonally from the cylindrical body 104. The annular platform 112 has an inner edge which abuts against the outside of the cylindrical body 104 and an outer edge 115, the distance c between the two being approximately 12.5 mm, such that the external diameter d of the annulus forming the platform is approximately 125 mm. Depending from the annular platform 112 is a cylindrical flange 116, which surrounds the cylindrical body 104 of the flask 100.

The flange 116 is positioned on the annular platform 112 midway between the inner and outer edge 115 thereof and is welded thereto in an airtight manner. The flange 116 has a height f of approximately 10mm and a thickness g of approximately 3.5 mm. All components of the flask are manufactured from stainless steel.

Referring now to Fig. 4, in which like parts have been given the same reference numerals as before, there is shown a sprue base indicated generally by the reference numeral 400 comprising a flat circular metal base section 402 which is surrounded by a cylindrical rubber wall 404. A hollow frusto-conical riser support 406 is located centrally on the base section 402 projecting upwardly therefrom. A riser-receiving aperture 408 is formed at the upper edge of the riser support 406.

Referring now to Fig. 5, in which like parts have been given the same reference numerals as before, there is shown a sprued mould, indicated generally by the reference numeral 500, for making a ring. The sprued mould 500 comprises a ring section 502, a narrow cylindrical section joined to the ring section and terminating in a riser engaging section 506 having a splayed end. In Fig. 6, the sprued mould 500 of Fig. 5 is shown affixed to a riser 600 comprising a wax rod which projects upwardly from the sprue base 400. The base of the riser 600 is inserted into the riser-receiving aperture 408 of the riser support 406.

Referring now to Fig. 7, in which like parts have been given the same reference numerals as before, there is shown a completed tree 700 of moulds comprising a plurality of sprued moulds 500 affixed to the riser mounted in the sprue base. The sprued moulds are arranged symmetrically around the riser.

Referring now to Fig. 8, in which like parts have been given the same reference numerals as before, there is shown a top view of the tree 700 which has been placed within the investment casting flask 100 of the invention such that the collar section 106 engages the sprue base 400 in an air-tight manner.

Referring now to Fig. 9, in which like parts have been given the same reference numerals as before, there is shown a cross-section view of the investment casting flask 100, including the sprue base 400 and the tree 700 of moulds located, in the casting chamber indicated generally by the reference numeral 800. The casting chamber 800 comprises a cylindrical chamber 802 having a closed base and annular top plate 804 which partially covers the opposite end of the cylindrical chamber 802, providing a circular flask-receiving aperture therein. The flask-receiving aperture is surrounded by a flat annular rubber seal 806. The flask 100 is positioned in the casting chamber with the handle section 102 disposed downwardly into the casting chamber. In this way, the flange 116 will rest on the rubber seal 906, thereby providing an airtight seal between the flask and the chamber. The casting chamber further comprises a lid 808 which covers the top end of the cylindrical chamber 802 and the projecting end of the flask 100.

In use, a tree 700 of sprued moulds 500 is formed by mounting a riser 600 in the riser-receiving aperture 408 of the riser support 406 of the sprue base 400, and subsequently affixing a plurality of the sprued moulds 500 to the riser 600. It will be understood the person skilled in the art that the manner of constructing a correctly sprued tree is well known and will not be elaborated on here.

The flask 100 is then secured to the sprue base 400 such that the flask 100 surrounds the tree 700. The collar section 106 of the flask is inserted into the sprue base such that the cylindrical rubber wall 404 abuts against the outside of the portion of the cylindrical body 104 of the flask 100 between the annular platform 112 and the second open end of the cylindrical body 104. The respective dimensions of the cylindrical body 104 and the sprue base 400 and the rubber surface of the cylindrical rubber wall 404 ensure that an air-tight seal is formed between the flask 100 and the sprue base 400. The flask 100 is then placed in the casting chamber 800 with the handle section 102 of the flask 100 being inserted through the circular flask-receiving aperture in the annular top plate 804 of the casting chamber 800. The flange 116 will then rest on the rubber seal 906.

The lid 808 of the casting chamber 800 is then closed over and the vacuum casting process begins. When a vacuum is applied, the flask 100 will be pulled downwards into the casting chamber 800, causing the flange 116 of the flask 100 to press firmly against the rubber seal 906. This causes a strong air-tight seal to be formed between the flange 116 of the flask 100 and the casting chamber 800, ensuring that a vacuum is maintained around the tree 700 within the flask 100. The remaining steps of the casting process are well known in the art and will not be discussed further here.

In the specification the terms comprise, comprises, comprised and comprising or any variation thereof and the terms include, includes, included or including or any variation thereof are considered to be totally interchangeable and they should all be afforded the widest possible interpretation.

The invention is not limited to the embodiment herein described, but may be varied in both construction and detail within the terms of the claims.

Claims

CLAIMS1. An investment casting flask comprising a cylindrical body, a handle section and a collar section, the cylindrical body having a plurality of substantially circular apertures disposed in circumferential rows therein, the handle section comprising a substantially flat cross-member bridging a first open end of the cylindrical body; the collar section comprising an annular platform surrounding the flask and projecting substantially orthogonally from the cylindrical body at a location adjacent a second open end of the cylindrical body, the annular platform having an inside edge abutting against the cylindrical body and an outside edge characterized in that the collar section further comprises a cylindrical flange projecting orthogonally from the annular platform, in the direction of the handle section; the flange being co-axial with the cylindrical body, equidistant from the inside edge and outside edge of the annular platform and having a thickness in the range of 20% to 36% of the width of annular platform.
2. A flask as claimed in claim I in which the thickness of the flange is 25% to 31% of the width of platform.
3. A flask as claimed in claim I or 2 in which the thickness of the flange is in the range of 27% to 29% of the width of platform.
4. A flask as claimed in any preceding claim in which the height of the flange is in the range 8 mm to 12 mm.
5. A flask as hereinbefore described with reference to the accompanying drawings.
6. A method of manufacturing jewellery by investment casting using the flask of any preceding claim.