IES20040507A2

IES20040507A2 - A method for die casting a component of metal with minimised surface contaminants, and a die cast component

Info

Publication number: IES20040507A2
Authority: IE
Inventors: Hans-Friedrich Wiegand; Sean Francis Lyons; John Anthony Lyons; Ken Anthony Hall; Denise Fitzgerald; Mary Nolan; Carstern Wiegand; Philip Lyons; John Derrick Tuite
Original assignee: Sternford Ltd
Priority date: 2004-07-27
Filing date: 2004-07-27
Publication date: 2005-07-13

Abstract

A method for die casting a component of aluminium with minimised surface contaminants comprises initially spraying an oil-in-water emulsion comprising a lubricant and deionised water on the surfaces of the dies which form the die cavity prior to injection of the molten aluminium into the die cavity for facilitating release of cast component from the dies. The preparation of the oil-in-water emulsion with deionised water has been found to substantially eliminate the presence of contaminants such as magnesium, calcium, phosphate, sodium, ammonia and chloride in the oxide layer formed on the surface of the cast component on release of the cast component from the dies. With the oxide layer substantially free of such contaminants, the oxide layer forms a boehmite layer which permits adhesion to the cast component, and in particular, permits adhesion of mastic sealants to the cast component, as well as permitting anodising of the cast component. Deionising the water which forms the oil-in-water emulsion containing the lubricant removes contaminants such as magnesium, calcium, sodium, phosphate, ammonia and chloride from the water prior to the preparation of the oil-in-water emulsion, which otherwise form a deposit on the surfaces which form the die cavity and are in turn fused onto the cast component during casting.

Description

“A method for die casting a component of metal with minimised surface contaminants, and a die cast component” The present invention relates to a method for die casting a component of metal, and in particular, though not limited to a method for die casting a component of aluminium with minimised surface contaminants, and the invention also relates to a component formed by die casting according to the method.

In the die casting of components of metal, for example, aluminium, a lubricant in a water carrier is applied to surfaces of the die which form the die cavity in which the component is to be cast for facilitating subsequent release of the cast component from the dies. The mixture of lubricant and water carrier, typically, is an oil-in-water emulsion, and is applied to the surfaces which form the die cavity by spraying.

When the cast components are released from the die, the components immediately oxidise, thereby an oxide layer is formed over the entire surface of each component. However, in known casting methods, it has been found that the oxide layer formed on such components contains a significant level of contaminants, in particular, magnesium, calcium, sodium, phosphate, ammonia and chloride. These contaminants, in particular magnesium and calcium, tend to be at relatively high levels, and it has been found that the presence of such contaminants inhibits adhesion to the surface of the cast components. In particular, adhesion of mastic sealants is inhibited, and it has also been found that such components cannot be adequately anodised, as the contaminants in the oxide layer prevent uniform anodising of the surface and cause breaks in the anodised layer, thus leading to subsequent corrosion of the cast component. The high level of such contaminants in the oxide layer also inhibits painting and the application of other surface coatings such as protective coatings to the cast components.

It has been found that the contamination in the oxide layer which is initially formed when the component is released from the dies results from the application of the oilin-water emulsion which is applied to the surfaces of the dies which form the die cavity. It has been found that the oil-in-water emulsion contains contaminants such I--------— OPES TO PUBLIC IfilSPECTIOfll ™ER SECTIOH 28 AMD RULE 23 IE 0 4 0 5 0 7 as magnesium, calcium, sodium, phosphate, ammonia and chloride, and when the oil-in-water emulsion is applied to the surfaces of the dies which form the die cavity, the surfaces being hot from the previous cast shot cause the water from the oil-inwater emulsion to evaporate, thus leaving the lubricant lining the surfaces which form the die cavity. However, in addition to the lubricant, the surfaces of the die cavity are also lined with the contaminants from the water which remain after the water has been evaporated. When the hot molten metal comes in contact with the contaminants, the contaminants are fused by heat onto the surface of the component as it is being cast in the die cavity. Release of the cast component from the dies causes the oxide layer to be formed over the entire surface of the component. However, as well as the oxide layer comprising aluminium oxide, the oxides of the contaminants, namely, magnesium, calcium, phosphate, sodium, chloride and ammonia are also formed in the oxide layer. The oxides of the contaminant it has been found inhibit adhesion to the cast component.

Once the contaminants are fused onto the surface of the cast component, it is virtually impossible to remove them by any conventional means, such as washing, scrubbing, shot blasting and the like.

German Patent Specification No. 43 03 339 of Ritter Aluminium Giesserei GmbH discloses a method for overcoming the problem of adhesion to die cast components of aluminium with high levels of contaminants in the oxide layer. In the method disclosed in the German specification, after the oxide layer has been formed with the high level of contaminants the component is immersed in deionised water where a further oxide layer is formed which forms a boehmite layer, and the level of contaminants in the boehmite layer is significantly reduced. It is suggested in the German specification that the deionised water leaches many of the contaminants from the already formed oxide layer which forms after release from the dies, so that the boehmite layer can be formed substantially contaminant free. However, while this method does provide a boehmite layer which facilitates adhesion to the cast component, it requires an extra step in the processing of the cast component, which increases the time cycle for producing a cast component, and also adds to the cost of production of the cast component.

There is therefore a need for a method which permits die casting of a component on which the presence of surface contaminants is minimised.

The present invention is directed towards providing such a method, and the invention is also directed towards providing a component die cast according to the method.

According to the invention there is provided a method for die casting a component of metal on which the presence of surface contaminants on the surface thereof is minimised, the method comprising the steps of applying a lubricant mixed in a water carrier to surfaces of dies which form a die cavity in which the component is to be cast prior to injecting molten metal into the die cavity for facilitating release of the cast component from the dies, wherein the water carrier is deionised water.

In one embodiment of the invention the water carrier is deionised prior to mixing with the lubricant.

Preferably, the lubricant is mixed with the water carrier to form an oil-in-water emulsion.

In one embodiment of the invention the lubricant is in concentrated form, and the lubricant is mixed with the water carrier in the ratio range of one part volume of lubricant to 100 parts volume of water carrier, to one part volume of lubricant to 250 parts volume of water carrier. Preferably, the lubricant is mixed with the water carrier in the ratio range of one part volume of lubricant to 130 parts volume of water carrier, to one part volume of lubricant to 200 parts volume of water carrier. Advantageously, the lubricant is mixed with the water carrier in the ratio range of one part volume of lubricant to 150 parts volume of water carrier, to one part volume of lubricant to 180 parts volume of water carrier.

IE 0 4 0 5 0 7 In another embodiment of the invention a lubricating amount of the mixture of lubricant and water carrier is applied to the surfaces of the dies which form the die cavity for preventing adhesion of the cast component to the surfaces which form the die cavity.

In a further embodiment of the invention a temperature reducing amount of the mixture of lubricant and water carrier is applied to the surfaces which form the die cavity, the temperature reducing amount of the mixture of lubricant and water carrier being sufficient for reducing the temperature of the surfaces which form the die cavity by a temperature in the range of 50°C to 150°C. Preferably, the temperature reducing amount of the mixture of lubricant and water carrier which is applied to the surfaces which form the die cavity is sufficient for reducing the temperature of the surfaces which form the die cavity by approximately 100°C.

In one embodiment of the invention the mixture of lubricant and water carrier is applied to the surfaces which form the die cavity in an amount such that substantially all the water carrier is evaporated from the surfaces which form the die cavity prior to injection of the molten metal into the die cavity. Preferably, the mixture of lubricant and water carrier is applied to the surfaces which form the die cavity by spraying. Advantageously, the mixture of lubricant and water carrier is applied to the surfaces which form the die cavity in an atomised spray form.

In one embodiment of the invention the water carrier is deionised to an extent that the contaminating effect on the surface of the cast component of one or more of the following contaminants: magnesium, calcium, sodium, phosphate, ammonia, and chloride is reduced to a level which permits adhesion to the surface of the cast component.

IE 0 4 0 5 0 7 In another embodiment of the invention the water carrier is deionised to the extent that the presence of magnesium on the surface of the cast component does not exceed 1 pgm per cm2 surface area of the cast component. Preferably, the water carrier is deionised to the extent that the presence of magnesium on the surface of the cast does not exceed 0.5pgms per cm2 surface area of the cast component. Advantageously, the water carrier is deionised to the extent that the presence of magnesium on the surface of the cast component does not exceed 0.2pgms per cm2 surface area of the cast component.

In one embodiment of the invention the water carrier is deionised to the extent that the presence of calcium on the surface of the cast component does not exceed 1 pgm per cm2 surface area of the cast component. Preferably, the water carrier is deionised to the extent that the presence of calcium on the surface of the cast component does not exceed 0.7pgms per cm2 surface area of the cast component. Advantageously, the water carrier is deionised to the extent that the presence of calcium on the surface of the cast component does not exceed 0.5pgms per cm2 surface area of the cast component.

In another embodiment of the invention the water carrier is deionised to the extent that the presence of chloride on the surface of the cast component does not exceed 0.25pgms per cm2 surface area of the cast component. Preferably, the water carrier is deionised to the extent that the presence of chloride on the surface of the cast component does not exceed 0.2pgms per cm2 surface area of the cast component.

In a further embodiment of the invention the water carrier is deionised to the extent that the presence of phosphate on the surface of the cast component does not exceed 0.1 pgms per cm2 surface area of the cast component. Preferably, the water carrier is deionised to the extent that the presence of phosphate on the surface of the cast component does not exceed 0.07pgms per cm2 surface area of the cast component. Advantageously, the water carrier is deionised to the extent that the presence of phosphate on the surface of the cast component does not exceed IE 0 4 0 5 0 7 O.O5pgms per cm2 surface area of the cast component.

In another embodiment of the invention the water carrier is deionised to the extent that the presence of ammonia on the surface of the cast component does not exceed 0.1 pgms per cm2 surface area of the cast component. Preferably, the water carrier is deionised to the extent that the presence of ammonia on the surface of the cast component does not exceed 0.07pgms per cm2 surface area of the cast component Advantageously, the water carrier is deionised to the extent that the presence of ammonia on the surface of the cast component does not exceed 0.05pgms per cm2 surface area of the cast component.

In another embodiment of the invention the water carrier is deionised to the extent that the presence of sodium on the surface of the cast component does not exceed 0.7pgms per cm2 surface area of the cast component. Preferably, the water carrier is deionised to the extent that the presence of sodium on the surface of the cast component does not exceed 0.5pgms per cm2 surface area of the cast component. Advantageously, the water carrier is deionised to the extent that the presence of sodium on the surface of the cast component does not exceed 0.2pgms per cm2 surface area of the cast component.

In one embodiment of the invention the cast component is of aluminium.

In another embodiment of the invention the cast component is allowed to oxidise on being released from the dies to form a boehmite layer on the surface thereof.

In a further embodiment of the invention the boehmite layer is substantially free of contaminants.

In one embodiment of the invention the water carrier is deionised to an extent that the total level of contaminants in the boehmite layer constituted by the following contaminants does not exceed 5pgms per cm2 surface area of the boehmite layer: magnesium, IE 0 4 0 5 Ί calcium, sodium, phosphate, ammonia, and chloride.

Preferably, the total level of contaminants in the boehmite layer constituted by the following contaminants does not exceed 3pgms per cm2 surface area of the boehmite layer: magnesium, calcium, sodium, phosphate, ammonia, and chloride.

Advantageously, the total level of contaminants in the boehmite layer constituted by the following contaminants does not exceed 1 pgm per cm2 surface area of the boehmite layer: magnesium, calcium, sodium, phosphate, ammonia, and chloride.

The invention also provides a component die cast by the method according to the invention.

In one embodiment of the invention the component is of aluminium having a boehmite layer formed on the surface thereof.

IE 0 4 0 5 Ο 7 In another embodiment of the invention the total level of contaminants in the boehmite layer constituted by the following contaminants does not exceed 5pgms per cm2 surface area of the boehmite layer: magnesium, calcium, sodium, phosphate, ammonia, and chloride.

Advantageously, the total level of contaminants in the boehmite layer constituted by the following contaminants does not exceed 1 pgm per cm2 surface area of the boehmite layer: magnesium, calcium, sodium, phosphate, ammonia, and chloride. in one embodiment of the invention the contaminants in the boehmite layer are at a sufficiently low level to permit adhesion to the boehmite layer. Preferably, the E 0 4 0 5 0 Ί contaminants in the boehmite layer are at a sufficiently low level to permit adhesion of a mastic sealant to the boehmite layer.

In another embodiment of the invention the contaminants in the boehmite layer are at a sufficiently low level to permit anodising of the component on the boehmite layer. Preferably, the level of contaminants in the boehmite layer is at a sufficiently low level to permit uniform anodising of the component on the boehmite layer.

The invention will be more clearly understood from the following description of a preferred embodiment thereof, which is given by way of example only, with reference to the accompanying drawing, which illustrates a flow chart of a die casting method according to the invention.

Referring to the drawing, the method according to the invention for die casting a component of aluminium in which surface contaminants are minimised will now be described. The method comprises preparing an oil-in-water emulsion by mixing a lubricant with a deionised water carrier, for applying to surfaces of dies which form a die cavity in which the component is to be cast, for facilitating subsequent release of the cast component from the dies. The water prior to being mixed with the lubricant to form the oil-in-water emulsion is deionised to the extent that ionic contaminants in the water are substantially removed, and are removed to the extent that they have little or no effect on the oxide formed on the surface of the cast component on the component being released from the dies as will be described below. The deionising of the water is represented by block 1 of the drawing. Block 2 represents the lubricant, and block 3 represents the preparation of the oil-in-water emulsion. The oil-in-water emulsion is applied to the surfaces of the dies which form the die cavity when the dies are open and hot, typically, from the previous casting shot, see block 4. In this embodiment of the invention the oil-in-water emulsion is applied to the surfaces which form the die cavity as an atomised spray. The oil-in-water emulsion is prepared from a lubricant in concentrated form, in this embodiment of the invention the lubricant is a lubricant sold under the trade name GRACO CP-506HM by Acheson, a company within the ICE Group, which is mixed with the deionised IE 0 4 05 (,7 water in the mixing ratio of approximately one part volume lubricant to 150 parts volume deionised water.

The volume of the oil-in-water emulsion sprayed onto the surfaces which form the die cavity depends on the shape and size of the die cavity, however, the oil-in-water emulsion is applied to the surfaces forming the die cavity in an amount sufficient to facilitate easy release of the cast component from the dies. The oil-in-water emulsion is also applied in an amount sufficient for reducing the temperature of the dies from a temperature typically of the order of 250°C resulting from the previous casting shot to a temperature of approximately 150°C. Furthermore, the volume of the oil-in-water emulsion is applied in an amount not greater than that which facilitates substantially complete evaporation of the water of the oil-in-water emulsion. Air under pressure is applied to the surfaces of the dies which form the die cavity for dispersing the oil of the oil-in-water emulsion evenly over the surfaces which form the die cavity.

Once the lubricant has been evenly spread over the surfaces which form the die cavity, and the water of the oil-in-water emulsion has evaporated from the surfaces which form the die cavity, the dies are closed, see block 5, to form the die cavity. A shot of the molten aluminium is then injected into the die cavity, see block 6. The aluminium is allowed to solidify in the die cavity and the dies are then opened and the solidified cast component is released from the dies, see block 7. The casting cycle then recommences, and the surfaces of the dies which form the die cavity are sprayed with the oil-in-water emulsion to prepare the die cavity for the next shot of molten aluminium.

On being released from the dies the cast component immediately oxidises, and thus an aluminium oxide layer is formed over the entire surface of the cast component, see block 8. It has been found that the oxide layer so formed is substantially completely free of contaminants, and forms an ideal boehmite layer which permits adhesion to the cast component. In particular, it has been found that the boehmite layer so formed promotes adhesion of a mastic sealant, for example, a thixotropic IE 0 4 0 5 0 7 adhesive sold by Dow Corning under serial number 3-6265. Additionally, it has been found that the cast component can be readily anodised directly onto the surface of the boehmite layer so formed, and the anodised layer formed on the cast component is uniform and continuous over the entire surface of the cast component, without any breaks therein. Furthermore, it has been found that other protective coatings can be readily applied directly to the boehmite layer of the cast component, and the protective coatings so applied are continuous and uniform over the entire surface of the cast component without a break. Such protective coatings are, for example, chromating, copper, nickel and/or tin plating.

Tests have been carried out on two batches of cast components to establish the efficacy of the method according to the invention. One batch of cast components, namely, a control batch have been die cast using a conventional prior art die casting method whereby the lubricant is applied to the surfaces of the dies which form the die cavity by spraying an oil-in-water emulsion prepared by mixing the lubricant with untreated town’s water. The other batch of cast components, namely, a test batch have been die cast using the method according to the invention whereby the lubricant is applied to the surfaces of the dies which form the die cavity by spraying an oil-in-water emulsion of the lubricant and deionised water. The components of the test batch and the control batch are identical to each other, and both are of aluminium, and the conventional prior art method by which the components of the control batch were die cast is identical to the method according to the invention, with the exception that the oil-in-water emulsion used in the conventional prior art method was prepared with untreated town’s water, while the oil-in-water emulsion used in the die casting method according to the invention was prepared with the deionised water. Otherwise, the two die casting methods were identical.

The amounts of the contaminants, namely, chloride, phosphate, sodium, calcium, magnesium and ammonia in the oxide layers of the respective cast components were determined based on the weight of the respective contaminants in pgms per cm2 of the surface area of the oxide layer. The results of the tests are set out in Table 1, which shows the average amount of each of the contaminants, chloride, phosphate, sodium, calcium, magnesium and ammonia in pgms per cm2 of surface area of the oxide layers formed on the respective cast components after being released from the dies. The contaminants are set out in column 1 of Table 1, while column 2 of Table 1 sets out the average amounts of the contaminants in the oxide layers of the components of the control batch of the cast components. Column 3 of Table 1 sets out the average amounts of the contaminants in the oxide layers of the components of the test batch of the cast components. Column 4 of Table 1 sets out the factors by which the amounts of each of the contaminants have been reduced by using the method according to the invention as opposed to the prior art conventional casting method.

Column 1 Column 2 Column 3 Column 4 Contaminants pgms per cm2 pgms per cm2 Factor Chloride 0.32 <0.19 >1.68 Phosphate 0.32 <0.02 >16 Sodium 1.51 <0.16 >9.44 Calcium 110.55 <0.29 >381 Magnesium 8.482 <0.151 >56 Ammonia 0.492 <0.02 . >24 Total 121.674 <0.831 >146 Table 1 As can be seen, the level of magnesium in the oxide layers of the components has been reduced from 8.482pgms per cm2 of the surface area of the oxide layers of the components cast by the conventional prior art method to less than 0.151 pgms per cm2 of the surface area of the oxide layer of the components cast by the method according to the invention. Accordingly, the magnesium in the oxide layer is reduced by a factor of more than 56 by using the method according to the invention as opposed to the prior art conventional die casting method.

The level of calcium in the oxide layers of the components has been reduced from IE 0 4 QS 0 7 110.55pgms per cm2 of the surface area of the oxide layers of the components cast by the conventional prior art method to less than 0.29pgms per cm2 of the surface area of the oxide layers of the components cast by the method according to the invention. Accordingly, the calcium in the oxide layer is reduced by a factor of more than 381 by using the method according to the invention as opposed to the prior art conventional die casting method.

The level of sodium in the oxide layers of the components has been reduced from 1.51 pgms per cm2 of the surface area of the oxide layers of the components cast by the conventional prior art method to less than 0.16pgms per cm2 of the surface area of the oxide layers of the components cast by the method according to the invention. Accordingly, the sodium in the oxide layer is reduced by a factor of more than 9.44 by using the method according to the invention as opposed to the prior art conventional die casting method.

The level of phosphate in the oxide layers of the components has been reduced from 0.32pgms per cm2 of the surface area of the oxide layers of the components cast by the conventional prior art method to less than 0.02pgms per cm2 of the surface area of the oxide layers of the components cast by the method according to the invention. Accordingly, the phosphate in the oxide layer is reduced by a factor of more than 16 by using the method according to the invention as opposed to the prior art conventional die casting method.

The level of chloride in the oxide layers of the components has been reduced from 0.32pgms per cm2 of the surface area of the oxide layers of the components cast by the conventional prior art method to less than 0.19pgms per cm2 of the surface area of the oxide layers of the components cast by the method according to the invention. Accordingly, the chloride in the oxide layer is reduced by a factor of more than 1.68 by using the method according to the invention as opposed to the prior art conventional die casting method.

The level of ammonia in the oxide layers of the components has been reduced from 0.492pgms per cm2 of the surface area of the oxide layers of the components cast by the conventional prior art method to less than 0.02pgms per cm2 of the surface area of the oxide layers of the components cast by the method according to the invention. Accordingly, the ammonia in the oxide layer is reduced by a factor of more than 24 by using the method according to the invention as opposed to the prior art conventional die casting method.

Accordingly, the total amount of inorganic contaminants, namely, the total amount of the contaminants magnesium, calcium, sodium, phosphate, ammonia and chloride in the oxide layers of the components cast using the prior art conventional method was 121,674pgms per cm2 of surface area of the oxide layers of the cast components, while the total amount of the contaminants magnesium, calcium, sodium, phosphate, ammonia and chloride in the oxide layer of the components cast using the method according to the invention was 0.831 pgms per cm2 of the surface area of the oxide layers of the cast components, in other words, the total amount of these contaminants in the oxide layers of the components cast using the method of the invention was less than 1pgm per cm2 of the surface area of the oxide layers of the cast components. Therefore, the total amount of these contaminants in the oxide layers of the cast components can be reduced by a factor of more than 146 by using the method according to the invention.

Accordingly, it can be seen that the method for die casting according to the invention provides a casting with an oxide layer which is formed immediately the cast component is released from the dies which is a boehmite layer which permits adhesion to the cast component. This is achieved without any additional steps in the processing of the cast component, but rather by the mere substitution of town’s water with deionised water as a water carrier for forming the oil-in-water emulsion containing the lubricant for applying to the surfaces of the dies which form the die cavity for facilitating release of the cast component from the die.

While the method has been described for die casting a component of aluminium, it is envisaged that the method according to the invention and the advantages derived IE 040507 therefrom could also be used in the die casting components of other non-ferrous metals, for example, zinc, magnesium, brass, and other non-ferrous metals.

Claims

1. A method for die casting a component of metal on which the presence of surface contaminants on the surface thereof is minimised, the method comprising the steps of applying a lubricant mixed in a water carrier to surfaces of dies which form a die cavity in which the component is to be cast prior to injecting molten metal into the die cavity for facilitating release of the cast component from the dies, wherein the water carrier is deionised water.

2. A method as claimed in Claim 1 in which the water carrier is deionised prior to mixing with the lubricant, and the lubricant and the water carrier are mixed to form an oil-in-water emulsion.

3. A method as claimed in Claim 1 or 2 in which the water carrier is deionised to an extent that the contaminating effect on the surface of the cast component of one or more of the following contaminants: magnesium, calcium, sodium, phosphate, ammonia, and chloride is reduced to a level which permits adhesion to the surface of the cast component.

4. A method for die casting a component of metal on which the presence of surface contaminants on the surface thereof is minimised, the method being substantially as described herein with reference to and as illustrated in the accompanying drawing.

5. A component die cast by the method as claimed in any preceding claim.