GB2362348A - Casting method utilising an engraved biscuit die - Google Patents

Abstract

A method of casting a unique product comprising steps of; engraving a preformed biscuit die 1 with a pattern 8 that imparts a unique character to the product to be cast, inserting the engraved biscuit die 1 into a solid support 9; and pouring a molten material into the die, allowing the substance to solidify therein and opening the die 1, 6 to remove the cast product. The biscuit die 1 is preferably of a hardness of between 2 and 4 on the Mohs scale. The molten material may be a metal or metal alloy. The method may be used to cast metal signs and the like.

Description

2362348 1 CASTING METHOD The present invention relates to a method of

casting a unique product and also to apparatus suitable for use in such methods.

Various methods of casting have been developed. These methods may be divided into two main groups. The first group is based upon techniques utilising expendable moulds (e.g. sand casting) and is mainly used for low volume or one-off casts. The second group utilises permanent moulds that may be reused (e.g. hard-die casting) and are therefore suited for high volume production where many pieces of the same precise shape may be required.

Casting in expendable moulds (e.g. sand casting) requires a pattern to be made in the moulding material. TWs moulding material is usually mineral based (e.g. sand, cement, fireclay, plaster etc) and is usually combined with a bonding agent (e.g. sulphite solution, synthetic resins, oil or even water). Bonding ot trie mouid may be achieved'by simply allowing the mould to dry or may involve some sort of chemical consolidation (curing). A pattern (corresponding to the shape of the product to be caste) is embedded in the moulding material to create the outer shape of the product. The pattern is removed to leave the hollow mould and molten metal is then poured into the cavity. Once the metal has solidified the moulds are often broken open to retrieve the product. The casting apparatus (e.g. a box mould employed in sandcasting) is usually fitted with a pouring gate, metal supply riser and exhaust system. These techniques are useful when casting a unique product. However it is ofien inconvenient, and time consuming, to make ftesh moulds - particularly when the next product to be caste has at least some common properties with that of a previous mould.

Many permanent mould casting techniques utilise hard-dies cast from iron or tool steel. A molten substance is poured into the dies and allowed to solidify to form the product. In contrast to sand casting techniques and the like, the hard-dies may be opened and the product removed with out destroying the mould, and the dies reused 2 repeatedly to cast flirther objects of the same pattern. However the Hard- die casting techniques have several disadvantages. For instance, new hard- dies are slow and expensive to manufacture. Furthermore, a hard-die can only produce the shape for which it is designed and even the slightest alteration requires more machining to the die itself making it impracticable for low volume or one-off pieces.

It will be appreciated from the above that it would be desirable to develop a casting technique that utilises moulds with advantageous features of both expendable and permanent moulds. Accordingly it is an object of the present invention is to provide a casting technique utilising moulds with:

(i) the advantages of hard dies (i.e. moulds which do not require male/ female pattern making and mould impression as required in sandcasting and related techniques); and also (11) the advantages of sand moulds (i.e. quick, cost-effective casting of t> t> unique products) According to the present invention there is provided a method of casting a unique product comprising:

(1) engraving a preformed biscuit die with a pattern that imparts a unique character to the product to be caste; (ii) inserted the engraved biscuit die into a solid support; and (Iii) pouring a molten substance into the die, allowing the substance to solidify therein and opening the die to remove the caste product.

The present invention combines the speed and economy advantages of known hard-die production in line with low volume or unique one-off individual castings previously produced by methods utilising expendable moulds (e.g. sand-casting methods).

By "biscuit die" we mean a die that is formed of a soft toolable substance (STB die) that may be inserted into a solid support. The die should be resistant to degradation by the molten substance poured into the die such that a cast may be 3 formed. The biscuit die is preferably configured such that it fits into the solid support as a changeable inner section.

The. biscuit die may be formed of a variety of materials provided that it is soft enough to be toolable and also have a higher melting temperature than the molten substance that is to be poured into it.

The biscuit die may be formed of press moulded high temperature resisting powders in a compound with suitable binders which when cured allow easy routing, engraving or carving.

It is preferred that the biscuit die is formed firom a mixture of a powder and a resin.

The powder may be ceramic flour or a hollow ceramic microsphere, For instance, the powder may be a glass microsphere, inert hollow siii-caie sphere comprised of shell A1203 (27-33%), S102 (55-65%) or Fe 203 (6% maximum). The internal space may comprise air or a mixture of gases (e.g. 70% carbon-dioxide, 30% nitrogen). A most preferred ceramic microsphere is available to the public under the trade name FELLITE (RTM).

The resin may be chosen from a number that are commonly used in the foundry industry. It is preferred that a resin is used which will harden (and thereby bind the powder) by chemical reaction with carbon dioxide. Carbon dioxide may be added by gas injection (e.g. from a C02 cylinder channelled through a filter and pressure reducer, to a needle tip which is probed into the mixed resin and powder).

Several types of gas curing resin are known to the art. It is preferred that resins based on sodium silicate solutions are used (e.g. solosil 433 produced by Foseco A Ltd).

The biscuit die should be hard enough to possess the characteristics of a solid object whilst being soft enough to allow easy engraving/tooling, or routing as 4 achievable in materials such as soft wood or a dense plastic foam. This consistency allows the biscuit die to be manipulated quickly and easily and is in complete contrast to dies used in hard-die casting.

It is preferred that the biscuit die is of a hardness of 2-4 on the Mohs scale and most preferred that the biscuit die is of a hardness of about 3 on the Mohs scale.

The biscuit die can be mass produced to a common shape for casting products that have a standard shape but which can be further manipulated to give the product a unique character. Umnanipulated biscuit dies can be kept in stock until a unique casting is required. The soft toolable surface of the biscuit die is then engraved or routed and the casting made.

It is preferred that the biscuit die comprises two reciprocating halves that may be engraved on their inner surfaces.

The biscuit die may comprise a nser inlet for pouring a molten substance. The die may also be adapted such that inlet forms a reservoir from which the molten substance may flow into the mould. The biscuit die may also comprise an exhaust for venting gases during the casting process.

The biscuit die may be used to making a cast a product that has a unique character on one face. In this case, the biscuit die may have one concave side with all the design and detail engraved thereon. The other side may be flat or be a "back plate" to form a flat back of the product. Should the product require design and detail on both faces then both sides of the die can be concave and engraved to provide the product with unique character on each face.

The method of the invention may be used to cast products made from a variety of substances. Preferably the products are cast from metals such as iron, steel, bronze, brass or some other metal alloy. Alternatively resins or plastics may be used.

The method of the invention may be utilised to make products such as signs (e.g. house signs) or name plates. Biscuit dies may be manufactured to enable the casting of signs and name plates of a standard shape. Such bl 1 4 iscuit dies may then be engraved or routed to give a unique character prior to casting (e.g. by engraving a name, house number, or the like, onto the inner surface of the biscuit die). Accordingly it is preferred that the method of the invention is a method for making signs.

It is preferred that the solid support is a hard production die used in permanent mould casting techniques (see above). The hard production die may be specially machined to receive the biscuit die. The use of such hard production dies is advantageous because the biscuit die can then be used with pre-existing casting apparatus. For example, apart ftom fitting and removal of prepared biscuit dies, the hard-die can be operated (filled and emptied) using standard casting methods (Including known manual, mechanical or semi-mechanical techniques).

The solid support may be formed of two reciprocating halves adapted to receive a biscuit die.

The solid support may further comprise location dowels and clamp fixing holes for assembling the casting apparatus. It will be appreciated that any convenient means for clamping, shuttering, enscapsulating or confining, a prepared biscuit die may be used, providing the means is of sufficient strength and suitably temperature resistant when the molten substance is poured into the cast.

The method of the invention may involve a technician selecting a biscuit die of a standard shape or design from stock. This choice may be based upon a customer selecting a basic shape from a catalogue. The technician will then rout or engrave the inner surface of the biscuit die to provide the mould with the unique character required by the customer. This process may be carried out by hand or automated by use of computer controlled engravers. Once engraving is completed the biscuit die is inserted and clamped into a hard production die adapted to receive the biscuit die.

6 Typically the casting apparatus may be formed as illustrated in the figures and Example. The molten substance (e.g. a metal alloy) is then poured into the die to produce a casting according to conventional methods. Once the casting has solidified the hard die may be opened and the product removed. The biscuit.dic may be expendable and broken open, or later discarded, to release the product.

The method of the invention represents a fast method for changing the final character, design, or detail of a casting, whilst benefiting from the use of hard-die casting techniques.

t> The method represents an improvement over individual sand-casting for producing unique castings. The use of preformed biscuit dies obviates the requirement to produce: (1) a one-off pattern for each sand casting; and (ii) subsequent impressions with casting channels etc.

A further advantage of the method of the invention is that a unique i)iscuii die may be prepared in a workshop away ftom the foundry. Accordingly foundry works need not be involved in individual male and female die making processes and can simply and efficient prepare castes as and when tooled biscuit dies are provided to them.

The method of the invention is particularly useful for sign makers as it represents a fast and economic die-making process.

A specific embodiment of the invention is now described by way of example only with reference to the accompanying drawings, in which:

Figure 1 is a schematic drawing of two halves of a biscuit die which may be used as a solid support according to the invention; Figure 2 is a schematic drawing of apparatus compnsing a biscuit die and solid support which may be assembled to cast a product according to the method of the invention; and Figure 3 is a plan view of the apparatus of figure 2 7 EXAMPLE 1

AMethod according to the invention was used to form a one sided metal house sign formed by gravity die-casting in a steel alloy 1. 1 Formation of the Biscuit Die First a plug or model is made, or selected from preformed plugs or models, that corresponds to the common general shape of the house sl,-,,m to be caste (but without any of the unique character introduced). Such a plug/model is also known as a pattern in the founding industry. It will be appreciated that the pattern need not be plain and, optionally, decorative elements may be included. Such decorative elements would obviously be common to all signs cast from the biscuit die formed ftorn such a pattern.

The biscuit die is made by first mixing powder (fillite (RTM), standard grade) with the resin (solosil 433 (RTIA)) at approximately 4 parts powder with 1 pan resin by weight until the mixture handles and looks like damp impressionable fudge. This mixture is then placed into a flat tray like container with sides about 1.5 cin (half an inch) deeper than the thickest part of the plug. The mixture is levelled off in the tray and an impression made with the plug face down into the mixture. Once the plug is removed a concave shape is revealed that forms the inner surface of the biscuit die.

Once the impression has been made carbon dioxide is in ected into the mixture j by means of a narrow metal hollow needle whilst avoiding causing distortion of the die shape. The carbon dioxide cures the mixture and thereby forms one half of a biscuit die.

Figure 1 illustrates one half of a biscuit die (1) with a cavity (2) defining the common general shape of the home sign to be caste. The biscuit die flirther comprises a riser inlet (3) for metal pour; a reservoir (4) and an exhaust (5).

8 A suitable back plate (6) may be used to form the complete biscuit die. The tray used in this process is ideally designed such that the biscuit dies formed therefrom will fit in the solid support used according to the invention.

It will be appreciated that multiple biscuit dies may be formed at any one time. Such dies may be stored (Indefinitely in dry conditions) until it is desired to make a unique sign.

1.2 Engraving of the Biscuit Die The biscuit die is released from the tray (if stored therein) and fixed to an engraver table (which may be manual or computerised). Letters (8) are engraved or routed to a depth equal to the height of the letters that are required to be engraved on the sign. When the engraving or routing is complete all the lettering should be in complete reverse, reading back- wards from right to left. Wire wool was used to remove any sharp -edges left by the router cutter.

The engraved die is then assembled with ready-made permanent fixtures to complete a casting. These fixtures include the back plate, die closures and clamps and may be used in conventional casting techniques. The main back plate may contain an aperture with inlet and exhaust lines that allow molten metal to run freely from a reservoir area without air lock (if this is not provided on the first biscuit half (1)).

The main back plate (6) is clamped to the hollow face of the preformed biscuit die (1) with the end of the inlet and exhaust lines slightly past the extreme edge of the concave part of the biscuit die to form a fixed free standing secure die. If necessary further plates and clamping methods may be used to secure the die.

Figure 2 illustrates two halves of a biscuit die (1, 6) with suitable unique character (8) inserted into two halves of a hard production die (9, 10) acting as a solid support according to the invention. The assembly is held together by means of location dowels (11) and/or clamped by means of clamp fixing holes (12).

9 Figure 3 is a plan view of the assembly illustrated in Figure 2 showing a screw (13) for fixing, the assembly together by insertion into the fix holes (12).

The die is then assembled and the cast poured using conventional casting techniques. A suitable cooling period is allowed commensurate with sign size and die thickness, with some experience the reservoir can be an indication of sufficient hardening, however care should be taken until experience is gained.

Remove the clamps and separate the biscuit from the main back plate to release the casting, once this is properly cooled the cast riser is removed from the sign, typically by a saw and grinder.

EXAMPLE 2

A method according to the invention was used to form a two sided metal n ( 11 1,z c..-, a IrA, -9 a1V 2.1 Formation of the Biscuit Die A first half of the biscuit die is formed as described in 2, I.The process is then repeated with the other side of the plug (or a separate one) to make an impression in mixture placed in a second tray.

After curing with carbon dioxide (see 1.1) the two parts are used to make up the two halves of a biscuit die and a sign cast according to the method of the invention.

Claims (9)

1 A method of casting a unique product comprising:

(1) engraving a preformed biscuit die with a pattern that imparts a unique character to the product to be cast; (H) inserting the engraved biscuit die into a solid support; and (111) pouring a molten substance into the die, allowing the substance to solidify therein and opening the die to remove the cast product.

t> The method according to claim 1 wherein the solid support is a hard production die adapted for insertion of the biscuit die.

3. The method according to claim 1 or 2 wherein the hardness of the biscuit di le is 2-4 on the Mohs scale.

4. The method according to claim 3 wherein the biscuit die is formed of press moulded ffigh temperature resisting powders and curable binders.

5. The method according to claim 4 wherein the biscuit die comprises two halves and at least one half has a pattern formed by impression with a plug or model.

6. The method according to any preceding claim wherein the substance is a metal or metal alloy.

7. The method according to any preceding claim wherein the method is a method of casting signs.

8. A method of casting a unique product essentially as herembefore described with reference to the Example and drawings.

9. An apparatus for casting a unique product essentially as hereinbefore described with reference to the Example and drawings.