GB2315034A

GB2315034A - A method for casting aluminium; release agents

Info

Publication number: GB2315034A
Application number: GB9614380A
Authority: GB
Inventors: Lothar Thoni
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-07-09
Filing date: 1996-07-09
Publication date: 1998-01-21
Anticipated expiration: 2016-07-09
Also published as: GB9614380D0; GB2315034B

Abstract

A steel mould of a desired configuration associated with a particular product is prepared by the use of selection quantities of graphite, a micro-colloid, waterglass and water which are combined to form an aqueous release agent composition. A coating of this release agent composition is sprayed onto internal surfaces of the mould. The mould is closed. Molten aluminium is prepared in a furnace and poured into the mould. After cooling the aluminium in the mould to form the desired product the mould is opened and the product is ejected from the mould.

Description

"A method for casting aluminium" This invention relates to a method for casting aluminium products.

The invention is particularly concerned with casting aluminium products in steel moulds. It is known to coat internal surfaces of the mould with a release agent to facilitate removal of a casting from the mould. However, many of the known release agents are very isolating and therefore inhibit cooling of the molten aluminium in the mould resulting in relatively long cooling times and therefore limiting production. Further, with many existing release agents it is only possible to make relatively rough castings which have to be subsequently machined to meet the desired tolerances. Such machining is relatively expensive and greatly increases the product price.

The present invention is directed towards overcoming these problems.

According to the invention, there is provided a method for casting aluminium in a steel mould comprising: preparing a steel mould of a desired configuration, preparing an aqueous release agent composition comprising graphite, a micro-colloid, waterglass and water, coating internal surfaces of the mould with the release agent composition, closing the mould, preparing molten aluminium in a furnace and pouring the molten aluminium into the mould, cooling and solidifying the molten aluminium in the mould to form a desired cast aluminium product, and opening the mould and removing the cast aluminium product from the mould.

In one embodiment of the invention the method includes the step of preparing the aqueous release agent composition by mixing the graphite, micro-colloid, waterglass and water in the ratio 4 - 8 parts graphite with 3 - 6 parts microcolloid, 0.5 - 2 parts waterglass and 4 - 6 parts water, all parts being by volume.

In a preferred embodiment of the invention, the method includes the step of preparing the aqueous release agent composition by mixing the graphite, micro-colloid, waterglass and water in the ratio 8:4:1:5 parts respectively by volume.

In another embodiment the method includes the step of preparing the aqueous release agent composition by mixing the graphite, micro-colloid, waterglass and water in the ratio 5:5:1:5 parts respectively by volume.

In another embodiment, the graphite is prepared by combining a mixture of carbon, silicon dioxide and aluminium oxide.

Preferably the method includes the step of preparing the graphite by mixing the carbon, silicon dioxide and aluminium oxide in the ratio 40 - 50% carbon with 25 - 35% silicon dioxide and 10 - 20% aluminium oxide with the balance water.

Preferably, the carbon, silicon dioxide and aluminium oxide are combined in the ratio 45% : 30% : 16% with the balance water.

In a further embodiment, the micro-colloid is a 20% colloidal graphite solution in water.

In another embodiment, the waterglass is a water solution containing about 8% sodium oxide and about 28% silicon dioxide.

In another embodiment the method includes the step of preparing a two-part mould having an upper part and a lower part, the upper part having a downwardly opening sand core, the lower part comprising a steel plate, an upper surface of the steel plate being coated with the aqueous release agent composition prior to closing mould.

In another aspect the invention provides an aqueous release agent composition for use in casting aluminium products in steel moulds, the aqueous release agent composition comprising graphite, a micro-colloid, waterglass and water.

Preferably the composition comprises 4 - 8 parts graphite with 3 - 6 parts micro-colloid, 0.5 - 2 parts waterglass and 4 - 6 parts water, all parts being by volume.

Preferably the composition comprises graphite, a microcolloid, waterglass and water in the ratio 8:4:1:5 parts by volume.

In another embodiment the composition comprises graphite, a micro-colloid, waterglass and water in the ratio 5:5:1:5 parts respectively by volume.

In another embodiment the graphite comprises a mixture of carbon, silicon dioxide and aluminium oxide. Preferably the graphite comprises 40 - 50% carbon with 25 - 35% silicon dioxide and 10 - 20 % aluminium oxide with the balance water.

Most preferably the carbon, silicon dioxide and aluminium oxide are combined in the ratio 45%:30%:16% with the balance water.

In another embodiment the micro-colloid is a 20% colloidal graphite solution in water.

In a further embodiment the waterglass is a water solution containing about 8% sodium oxide and about 28% silicon dioxide.

The invention will be more clearly understood by the following description of some embodiments thereof, given by way of example only, with reference to the accompanying drawing which is a schematic flow chart illustrating an aluminium casting method according to the invention.

A steel mould 10 of a desired configuration associated with a particular product is prepared. A water-based release agent composition is delivered from a reservoir 12 to a spray head 13 for spraying internal surfaces of the mould when the mould is in an open position.

The mould is then closed (14). Molten aluminium is prepared in a furnace 15 and delivered to the mould 10 at a pouring station 16 at which the molten aluminium is poured into the mould.

After pouring the aluminium is allowed to cool in the mould at a cooling stage 17, solidifying the molten aluminium in the mould to form a desired cast aluminium product.

Subsequently the mould is opened (18) and the cast aluminium product is removed (19) from the mould which is again prepared for moulding another product.

The water-based release agent composition is prepared comprising a mixture of graphite, a micro-colloid, waterglass and water. The ratios of the constituents can be varied according to the particular product being produced. A typical general purpose release agent composition comprises 8 parts graphite, 4 parts microcolloid, 1 part waterglass and 5 parts water by volume.

However, other ratios are possible. For example, 5 parts graphite, 5 parts micro-colloid and 1 part water-glass with 5 parts water. This gives a very smooth spray with a good surface.

The graphite essentially comprises carbon (about 45%), silicone dioxide (about 30%) and aluminium oxide (about 16%) with the balance being water.

The micro-colloid comprises an approximately 20% colloidal graphite solution in water.

The waterglass is prepared by making a sodium oxide (approximately 8%) and silicone dioxide (approximately 28%) solution in water.

It will be appreciated that the release agent composition functions as a release agent and gives the necessary roughness to the mould surface to facilitate the diecasting process. Different sprays can be individually prepared depending on the finishing surface required on different moulds.

Advantageously the composition is not isolating thus allowing the molten aluminium to be cooled down by the steel mould as quickly as possible. Thus a relatively quick casting cycle can be achieved for improved productivity.

Further, the spray provides excellent lubrication which allows the manufacture of cast aluminium products with very little taper (necessary for ejecting the cast product from the mould). This facilitates the casting of aluminium to relatively accurate tolerances which do not have to be machined after moulding, such machining as previously stated being relatively expensive.

Conveniently the coating of the release agent on the mould can be stripped from the mould very easily by shotblasting as the waterglass adhesive is not very strong.

Advantageously in view of the excellent lubrication provided by the release agent composition there is relatively little wear on the dies, extending the life of the dies and reducing the requirement for die repair.

Also the good lubrication facilitates ejection of the cast product from the mould without difficulty.

It will be noted that the spray can also be used effectively in half die systems in which portion of the mould is steel. In this case a two-part mould is prepared having an upper part and a lower part, the upper part having a downwardly opening sand core, the lower part comprising a steel plate. An upper surface of the steel plate is coated with the aqueous release agent composition prior to closing the mould. Cooling of the aluminium within such a mould is quicker, due to the steel plate, than if a full sand core was used. There is faster solidification of the aluminium achieving a better structure in the aluminium with higher specification and quality. Further, it is easier and faster to make the mould as only the top part of the mould has to be formed.

The casting, after cooling down can be taken out of the mould easier.

The invention is not limited to the embodiments hereinbefore described which may be varied in both construction and detail.

Claims

1. A method for casting aluminium in a steel mould comprising: preparing a steel mould of a desired configuration, preparing an aqueous release agent composition comprising graphite, a micro-colloid, waterglass and water, coating internal surfaces of the mould with the release agent composition, closing the mould, preparing molten aluminium in a furnace and pouring the molten aluminium into the mould, cooling and solidifying the molten aluminium in the mould to form a desired cast aluminium product, and opening the mould and removing the cast aluminium product from the mould.

2. A method as claimed in claim one including the step of preparing the aqueous release agent composition by mixing the graphite, micro-colloid, waterglass and water in the ratio 4 - 8 parts graphite with 3 - 6 parts micro-colloid, 0.5 - 2 parts waterglass and 4 6 parts water, all parts being by volume.

3. A method as claimed in claim 1 or 2 including the step of preparing the aqueous release agent composition by mixing the graphite, micro-colloid, waterglass and water in the ratio 8:4:1:5 parts respectively by volume.

4. A method as claimed in any preceding claim which includes the step of preparing the aqueous release agent composition by mixing the graphite, micro colloid, waterglass and water in the ratio 5:5:1:5 parts respectively by volume.

5. A method as claimed in any preceding claim wherein the graphite is prepared by combining a mixture of carbon, silicon dioxide and aluminium oxide.

6. A method as claimed in claim 5 wherein the carbon, silicon dioxide and aluminium oxide are combined in the ratio 45% : 30% : 16% with the balance water.

7. A method as claimed in any preceding claim wherein the micro-colloid is a 20% colloidal graphite solution in water.

8. A method as claimed in any preceding claim wherein the waterglass is a water solution containing about 8% sodium oxide and about 28% silicon dioxide.

9. A method as claimed in any preceding claim including the step of preparing a two-part mould having an upper part and a lower part, the upper part having a downwardly opening sand core, the lower part comprising a steel plate, an upper surface of the steel plate being coated with the aqueous release agent composition prior to closing the mould.

10. A method for casting aluminium substantially as hereinbefore described with reference to the accompanying drawings.

il. Aluminium products whenever produced according to the method as claimed in any preceding claim.