EP2133165A1 - Method for casting copper and alloys containing copper - Google Patents

Abstract

Process for casting copper and copper alloys, comprises: providing a mold; applying a coating on the inner wall of the mold, where the coating comprises at least one inorganic oxide and a binder; solidifying the coating; filling a melt of copper or copper alloy into the mold, where the mold is heated to 60-200[deg] C before the filling process; and extracting the resulting cast from the mold. Independent claims are included for: (1) reusable molds hydrophobic coating, produced from a coating comprising at least one inorganic oxide, at least 1 wt.% of polysiloxane and a binder; and (2) a mold with extended stable time comprising a hydrophobic coating, where the mold is temperature controlled at 60-200[deg] C.

Description

FIELD OF THE INVENTION

The present invention relates to a method for potting copper and copper-containing alloys and semi-permanent mold coatings suitable for this method.

BACKGROUND OF THE INVENTION

In so-called mold casting usually metal permanent molds are used, in which the liquid casting metal under the action of gravity (gravity casting) or in the low pressure process by applying a negative pressure are poured. With the die casting process can be accurately tailored castings with good surface finish and excellent produce mechanical properties. Quality defects are much less common in chill casting than, for example, in sand casting or die casting.

Chill casting processes are also used in brass casting. With the help of brass casting, for example, fittings for the sanitary sector, such as faucets are made.

However, die casting is more expensive than other casting methods. This is mainly due to the costs for the molds, which must be amortized over the entire expected service life. Moreover, due to intermediate steps required by conventional methods, such as cleaning steps, only a relatively small number of castings per unit time can be produced, resulting in low productivity.

A significant influence on the durability of a mold and the quality of the castings has the sizing, which is usually applied as a protective layer on the inside of the mold. The sizing is intended to protect the mold from premature wear, to prevent adherence of the castings to the mold wall and to facilitate demoulding. In addition, the sizing influences the heat dissipation and also the quality of the casting. For example, graphite and water can evaporate or decompose and lead to errors in the casting pattern.

Usually, the mold walls are first cleaned by sandblasting with molten slag, broken glass, glass beads or corundum and then painted or sprayed on the optionally heated surfaces, the size. The melt is subsequently introduced into the coated molds.

There are commercially available inorganic sizes based on the compounds graphite (C), molybdenum disulfide (MoS ₂ ) and / or boron nitride (BN) and containing these in proportions of up to 70 wt .-% solids. Such sizes are usually slurries without further additives, which are intended for single use, so must be renewed after each casting. Usually, when casting copper and copper-containing alloys, graphite suspensions are used as size. Although these materials have good demolding and heat-conducting properties, but are not very resistant to abrasion and very often lead to damage to the mold by welding or alloying of the casting metal with the mold material. As a result, such sizings wear out very quickly and are generally not suitable for repeated use. Renewing the sizings after each casting operation results in a significant reduction in productivity. In addition, the use of graphite-containing sizings, despite good release effect, leads to considerable reject rates due to surface defects on the casting (such as blowholes, turbulences or cracks) as well as considerable repair costs for machines and equipment. When casting brass, there is the particular problem that high levels of zinc are discharged from the brass, which also leads to an increase in the reject rate.

The use of graphite-containing sizing also creates an extreme fine dust pollution for man and machine and causes a high degree of contamination of the workplace. This can lead to health problems of workers and poses further safety risks in the workplace, such as a high risk of slipping in the work area due to the lubricating properties of graphite dust. Furthermore, it may due to the electrical conductivity of the graphite to disturbances in the electrical system, and so to impair the plant technology of the foundry, such as hydraulics, come. In addition, high costs must be incurred for the disposal or recycling of the spent graphite sizing. Graphite-free sizing compositions have already been described in the field of casting. An abrasion resistant, graphite free composition for Preparation of a size is for example in the German patent application DE 10 2005 045 666 the applicant described.

In addition to the composition of the mold sizing used and the type of application of the sizing coating, the temperature control of the mold also plays an essential role for mold casting. During the casting process it is crucial that a balance is established between the heat input through the melt and the heat loss by cooling the mold. Since the heat loss and supply of the mold also depends on the type and thickness of the applied size, the sizing material used in the temperature control must also be taken into account. Severe variations in heat balance from casting cycle to casting cycle can result in increased rejects. In addition, excessively high casting temperatures lead to breakage of the casting, while too low temperatures result in incomplete spills, cold running or gas pockets. In addition, in processes for casting brass, an undesirable discharge of zinc is frequently observed, with the result that the cast part and the mold are welded together by the zinc droplets. This leads to surface defects and cracks on the cast part as well as poor demoulding and defective ejection of the part from the mold. This problem occurs in particular in semipermanent or permanent mold coatings, since, unlike disposable sizes, the discharged zinc is not removed between the casting operations.

Thus, there is a need for an improved method for potting copper and copper-containing alloys, as well as corresponding improved sizes.

SUMMARY OF THE INVENTION

The object of the present invention is to at least partially avoid the abovementioned disadvantages. In particular, it is an object of the present invention to provide a method for potting copper or copper-containing alloys which increases the number of potting operations until the size is renewed. Another object of the present invention is to provide a mold having a prolonged life.

It is also desirable to provide a method for potting copper and copper-containing alloys which has the lowest possible reject rate, results in castings having very good surface properties, and reduces production and maintenance costs of casting equipment. It would also be desirable to improve the productivity of the casting process through lower scrap, better process control and increased product output per time.

Furthermore, it is desirable to reduce the zinc discharge from the molten brass when casting brass and to reduce environmental pollution such as particulate matter in the casting plant.

In addition, it is desirable to provide a mold coating which has good thermal shock resistance, good thermal properties, good release properties and good adhesion to the mold.

The aforementioned objects are achieved by the method with the features of claim 1 and coating with the features of claim 12. Preferred embodiments are described in the dependent claims.

1. (a) Bereitstellen einer Kokille,
2. (b) Applikation einer Schlichte auf die Innenwand der Kokille zur Herstellung einer Beschichtung, wobei die Schlichte mindestens ein anorganisches Oxid und ein Bindemittel umfasst,
3. (c) Verfestigen der Schlichte zu einer Beschichtung,
4. (d) Einfüllen einer Schmelze von Kupfer oder kupferhaltigen Legierungen in die Kokille, wobei die Kokille vor dem Einfüllen auf 60°C bis 200°C temperiert wird, und
5. (e) Herauslösen des entstandenen Gussteils aus der Kokille.

In a first aspect of the invention there is provided a method of potting copper and copper-containing alloys comprising the steps of:

1. (a) providing a mold,
2. (b) applying a size to the inner wall of the mold to produce a coating, the size comprising at least one inorganic oxide and a binder,
3. (c) solidifying the size into a coating,
4. (D) filling a melt of copper or copper-containing alloys in the mold, wherein the mold is heated to 60 ° C to 200 ° C before filling, and
5. (e) removing the resulting casting from the mold.

According to a preferred embodiment of the present invention, the application of the size is carried out as a suspension or dispersion.

According to a further preferred embodiment of the present invention, the application of the size is carried out at a mold temperature of 90 to 200 ° C, preferably between 100 and 150 ° C.

In a preferred embodiment of the present invention, the solidification of the coating takes place at a mold temperature of 250 to 400 ° C, preferably between 280 and 350 ° C, preferably over a period of 1 to 3 h.

According to one embodiment of the present invention, the solidification of the coating takes place by filling the melt of copper or copper-containing alloys in the mold.

According to a further embodiment of the present invention, the mold is tempered to 80 to 150 ° C, preferably to 100 to 130 ° C, more preferably to 110 to 125 ° C and particularly preferably to about 120 ° C before filling the melt.

According to a further embodiment, the temperature of the mold during the entire casting process remains largely constant and deviates from the initial temperature only by a maximum of 10 ° C.

According to the present invention, the tempering of the mold preferably takes place via an actively controllable Peltier element and / or a water bath and / or an actively controllable water jet cooling and / or air.

According to a preferred embodiment of the process according to the invention, the size additionally contains at least 1% by weight of polysiloxane and / or at least 1% by weight of boron nitride, MoS ₂ and / or WS ₂ , in each case based on the total weight of the size. The boron nitride, MoS ₂ and / or WS ₂ preferably acts as a demolding lubricant.

According to a further aspect of the present invention, there is provided a reusable hydrophilic mold coating which can be prepared from a size comprising at least one inorganic oxide, at least 1% by weight of polysiloxane, based in each case on the total weight of the size, and a binder.

According to a preferred embodiment, the size from which the coating is produced additionally contains at least 1% by weight of polysiloxane and / or at least 1% by weight of boron nitride, MoS ₂ and / or WS ₂ , in each case based on the total weight of the size.

According to another embodiment of the present invention, the binder contains nanoscale particles.

In a preferred embodiment of the present invention, the coating obtained by application of the size has a thickness of from 1 μm to 250 μm, preferably from 10 to 150 μm, more preferably from 10 to 90 μm and particularly preferably from 30 to 60 μm.

According to a further aspect of the present invention, a mold comprising a hydrophobic mold coating with a prolonged service life is provided, wherein the mold is selectively temperature controllable in the range of 60 to 200 ° C.

In a further aspect of the present invention, the size according to the invention or the resulting mold coating is used to extend the service life of a mold.

DETAILED DESCRIPTION OF THE INVENTION

1. (a) Bereitstellen einer Kokille,
2. (b) Applikation einer Schlichte auf die Innenwand der Kokille zur Herstellung einer Beschichtung, wobei die Schlichte mindestens ein anorganisches Oxid und ein Bindemittel umfasst,
3. (c) Verfestigen der Schlichte zu einer Beschichtung,
4. (d) Einfüllen einer Schmelze von Kupfer oder kupferhaltigen Legierungen in die Kokille, wobei die Kokille vor dem Einfüllen auf 60°C bis 200°C temperiert wird, und
5. (e) Herauslösen des entstandenen Gussteils aus der Kokille.

According to the present invention, there is provided a method of potting copper and copper-containing alloys comprising the steps of:

1. (a) providing a mold,
2. (b) applying a size to the inner wall of the mold to produce a coating, the size comprising at least one inorganic oxide and a binder,
3. (c) solidifying the size into a coating,
4. (D) filling a melt of copper or copper-containing alloys in the mold, wherein the mold is heated to 60 ° C to 200 ° C before filling, and
5. (e) removing the resulting casting from the mold.

Steps (d) and (e) may be repeated several times before sizing is applied and solidified again (steps (b) and (c)). Preferably, steps (d) and (e) are repeated at least 10 times, more preferably at least 50 times, and most preferably at least 100 times before steps (b) through (c) are again carried out. In the case of small-area damage to the mold coating, a premature complete reapplication of a mold coating can be avoided by aftertreating or subsequently misting the defective site (s) with the size according to the invention. The aftertreatment can take place during the ongoing casting process.

Moreover, the present invention relates to a reusable hydrophilic mold coating, which can be prepared from a sizing comprising at least one inorganic oxide and at least 1 wt .-% polysiloxane, based on the total weight of the sizing, and a binder and a corresponding mold with extended life.

It has surprisingly been found that very good casting results can be obtained with the aid of the method according to the invention and the mold coating or mold according to the invention. In particular through the use of Sizing or coating according to the invention in combination with the temperature control of the mold, a process for casting copper and copper-containing alloys, and in particular brass, which is significantly improved over conventional methods can be provided. Significant advantages of the method according to the invention arise due to the extended life of the mold and significantly lower production losses and maintenance costs. By means of the method according to the invention, the coating obtained by solidification of the size can be used for several casting operations before it has to be renewed. The mold coating according to the invention is therefore semipermanent. In addition, with the aid of the process according to the invention and the mold coating according to the invention, it is possible to obtain castings having excellent surface properties and in particular having a uniform surface structure and low surface roughness. Furthermore, by avoiding, for example, graphite-based sizing the environmental impact such as the particulate matter pollution in the casting plant is reduced. Furthermore, the inventive method can be carried out with steel or gray cast iron molds instead of much more expensive molds made of copper or copper alloy.

When using the method according to the invention in brass casting also the unwanted zinc discharge can be significantly reduced.

• "Nanopartikel" im Sinne der vorliegenden Erfindung sind Partikel mit einem mittleren Partikeldurchmesser (auch als mittlere Partikelgröße bezeichnet) von nicht mehr als 100 nm oder aber re-dispergierbare Agglomerate solcher Partikel.

In the following section, terms used in the present application are explained in more detail:

• "Nanoparticles" in the sense of the present invention are particles having an average particle diameter (also referred to as average particle size) of not more than 100 nm or else re-dispersible agglomerates of such particles.

The term "average particle diameter" or "mean particle size" is understood here to mean, unless stated otherwise, the particle diameter based on the volume average (D ₉₀ value). The D ₉₀ value is determined by dynamic light scattering, for example with a UPA (Ultrafine Particle Analyzer). The principle of dynamic light scattering is also known by the terms "photon correlation spectroscopy" (PCS) or "quasi-elastic light scattering" (QELS). For particularly small particles, quantitative electron microscopic methods (in particular TEM) can also be used. In addition, X-ray diffraction (XRD) can also be used to determine primary particle size.

For the purposes of the present invention, the term "sizing" describes a composition with demolding properties which is applied to the inside of the mold, e.g. in the form of a suspension or dispersion. The amounts in wt .-% as used in the present application in connection with the components of the size, relate (unless stated otherwise) on the finished size comprising components and suspension and / or solvent. The respective components of the size can be used, for example, in the form of a solid, a suspension, a dispersion or a solution or added to the size. After solidifying the applied size, e.g. by drying or baking, a coating is formed on the inside of the mold, which is largely free of any suspending or solvents used.

A "copper-containing alloy" in the sense of the present invention is any alloy containing copper. Examples of copper-containing alloys are bronze, gunmetal or brass. The term "brass" in the context of the present invention describes any copper-zinc alloys. In addition, the copper-containing alloys may contain other ingredients such as Ni, Zn, Sn, Pb, Al or Sb.

The mold used in the method according to the invention can be made of any material that withstands the temperatures of the casting process. Examples of suitable materials are aluminum, titanium, iron, steel, copper, chromium, cast iron, cast steel, boiler steel or gray cast iron and alloys of the aforementioned materials. Molds made of copper or copper alloys are particularly suitable for brass casting.

The size according to the invention contains at least one inorganic oxide and preferably at least 1% by weight of hexagonal boron nitride, WS ₂ and / or MoS ₂ , based on the total weight of the size, and a binder.

The inorganic oxide may be selected from the group consisting of aluminum oxide, zirconium oxide, aluminum titanate, iron oxide, wollastonite, xonotlite, zirconium silicate, calcium silicate, bone ash, as well as so-called "red mud" and titanium dioxide. Preferably, the inorganic oxide is alumina or aluminum titanate or a mixture thereof. The inorganic oxide particles may have an average particle size between 200 nm and 1 μm, preferably between 100 nm and 1 μm. However, larger average particle sizes, for example around 10 μm, may also be suitable. The inorganic oxide may preferably be present in the size according to the invention in an amount of from 1 to 80% by weight, in particular from 10 to 70% by weight, preferably from 20 to 60% by weight and more preferably from 30 to 50% by weight on the total weight of the sizing, be included.

In a preferred embodiment, the size according to the invention contains at least 1% by weight of boron nitride, WS ₂ and / or MoS ₂ , based on the total weight of the size. The inventors have found that in the method according to the invention a proportion of boron nitride has a positive effect on the flexibility, in particular the susceptibility to cracking and the elasticity of the sizing agent produced coating can affect. The proportion of boron nitride may preferably be 1-50 wt.% Or 5-40 wt.% Or 10-30 wt.% Or about 20 wt.%, Based on the total weight of the size. Preferably, the proportion of boron nitride about 5 wt .-%, based on the total weight of the size.

The binder used according to the invention may be an organic or inorganic binder. It may contain nanoscale particles according to a particularly preferred embodiment.

Examples of organic binders are organic natural products, e.g. Natural resins, organic modified natural products, e.g. Cellulose derivatives or modified natural resins, or organic synthetic compounds such as e.g. Polyacrylic and polymethacrylic compounds, vinyl polymers, polyesters, epoxy resins, phenolic resins, polyamines and polyamides. Suitable inorganic binders may include polysilicic acids, glass frits, clay minerals, bentonites, phosphates or inorganic oxides. Particular preference is given to using inorganic nanoparticles, glass frits and phosphates as binders. The binder may be contained in the size in an amount of 1 to 40% by weight, 3 to 20% by weight, preferably 5 to 15% by weight, based on the total weight of the size.

Binders with nanoscale particles which can be used in the process of the present invention are described, for example, in US Pat WO 03/093195 described in detail. "Nanoscale particles" in the sense of the present invention are particles having an average particle diameter (also referred to as average particle size) of not more than 100 nm in the non-agglomerated state. Preferably, the nanoscale particles have an average particle size of less than about 50 nm.

Examples of suitable nanoscale particles are aluminum oxide, zirconium oxide, boehmite or titanium dioxide or else mixtures or precursors of these compounds. The nanoparticles used in the binder may have very large specific surfaces, which are preferably coated with reactive hydroxyl groups which are able to crosslink at room temperature with the surface groups of the (usually coarser) particles to be bound. Particular preference is given to using Al ₂ O ₃ , TiO ₂ , boehmite or ZrO ₂ in the form of nanoscale particles.

According to another particularly preferred embodiment of the present invention, the size additionally comprises at least 1% by weight of polysiloxane, based on the total weight of the size. The polysiloxane may be selected from the group consisting of polyalkylsiloxane, polyalkylphenylsiloxane, alkylsilicone resin and phenylsilicone resin. Particularly preferred is polymethylphenylsiloxane. The proportion of the polysiloxane may be 1-50 wt.% Or 5-40 wt.% Or 10-30 wt.% Or about 20 wt.%, Based on the total weight of the size. Preferably, the proportion of the polysiloxane is 20 to 25 wt .-%, and preferably about 23 wt .-%, based on the total weight of the size.

According to another embodiment of the present invention, the sizing additionally comprises a vitreous constituent which usually functions as a binder or constituent of the binder. The glassy constituent may be a low-melting glass frit, ie a glassy system in which water-soluble salts such as soda or borax and other substances are silicate bound and thus largely converted into a water-insoluble form. In addition, the glass frits should largely contain no lead or other heavy metals. Preferably, the softening point of the glass frit is less than 500 ° C. In a further preferred embodiment, the Glass frit at least 50 wt .-% SiO ₂ , at least 5 wt .-% boron oxide (B ₂ O ₃ ) and / or Al ₂ O ₃ and preferably has a high alkali content.

According to a preferred embodiment, the binder used according to the invention comprises at least one of the previously described vitreous constituents or a binder with nanoscale particles (nanobinders) or a combination of vitreous constituents and nanoscale particles.

According to another preferred embodiment of the present invention, the size additionally comprises fillers. Examples of suitable fillers are oxides or nitrides of Al, Si, Zr, Ti, Fe, B, Wo or Mo and silicates of Al, Zr, Ti, B, Wo or Mo.

According to another embodiment of the present invention, the sizing additionally comprises a suspending agent. For example, polar suspending agents can be used. Suitable examples are water or alcohols such as isopropanol. In many cases, however, it is desirable to dispense with organic components in the suspending agent. Thus, in the presence of organic solvents due to their low vapor pressure always the risk of fire (including deflagration and explosion). Accordingly, in a preferred embodiment, the sizing agent comprises a suspending agent that is substantially free of nonaqueous liquid components. In addition, the size may contain at least one surfactant, eg a polyacrylate. The addition of a surfactant may be particularly advantageous in those cases where the suspending agent is free of nonaqueous liquid components. Preferably, water is used as the suspending agent.

According to another embodiment of the present invention, the sizing additionally comprises a thickening agent. Suitable thickening agents are, for example, inorganic thickeners, e.g. Polysilicic acids, clay minerals or zeolites, organic natural products, e.g. Gum arabic, pectins, starch or dextrins, organic modified natural products, e.g. Carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose or cellulose ethers, or organic fully synthetic thickeners, e.g. Poly (meth) acrylic compounds, vinyl polymers, polycarboxylic acids, polyethers, polyamines or polyamides. Preferably, an anionic heteropolysaccharide is used.

According to another embodiment of the present invention, the size additionally comprises a corrosion inhibitor. Examples of suitable corrosion inhibitors are Korantin MAT ^® (BASF, Ludwigshafen), 2-amino-2-methyl-1-propanol (AMP), mixtures of inorganic phosphates such as Zinkphoshate or alkali / alkaline earth metal phosphates and phosphoric acid.

The sizing agent may contain a solids content of between 10 and 80% by weight, between 20 and 60% by weight, and preferably about 40% by weight, based on the total weight of the sizing.

In a particularly preferred embodiment of the present invention, the size comprises:
From 30% to 40% by weight of a 50% by weight aqueous aluminum oxide suspension;
3 to 6 wt .-% boron nitride;
15 to 20 wt .-% of a 34 wt% aqueous nanoscale particle-containing binder;
20 to 25% by weight of phenylmethylpolysiloxane; possibly together with one or more of the following components:
2 to 4% by weight of a 50% by weight aqueous glass frit suspension;
3 to 8% by weight of additional water;
1 to 3% by weight AMP;
0.1 to 1.5 wt .-% Korantin MAT ^®;
1 to 5% by weight of aluminum titanate;
1 to 5% by weight of wollastonite;
1 to 5% by weight of xonotlite; and or
0.5 to 3% by weight of a 2% strength by weight aqueous deuteron XG solution,
wherein the ranges in wt .-% each relate to the total weight of the size.

The sizing can be applied by means of conventional application methods such as doctoring, dipping, spinning, flooding, brushing, brushing, brushing or spraying. The application of the size to the mold inside can be done when the mold is installed in the casting device. Alternatively, the size can also be applied to the inside of a dismantled mold.

In a preferred embodiment of the method according to the invention, the size is applied by spraying. The layer properties, the roughness and the surface morphology of the coating, which is produced by the application of the size, in this case of the spray parameters, such as the spray pressure, the type of spray gun used and spray nozzle, the spray distance between mold and nozzle, the temperature of the mold and / or size depending on the order and the concentration of the size, and can be controlled by varying these parameters targeted. Suitable spray pressure ranges are for example 1 to 6 bar, preferably 1.5 to 3 bar. The spraying distance between nozzle and mold surface may be, for example, 15 to 40 cm and preferably 20 to 30 cm. A suitable nozzle diameter is preferably in the range between 1.0 and 2.0 mm.

The application of the size can be carried out at room temperature or at higher mold temperature. Preferably, the sizing may be applied at a temperature of about 60 ° C to about 200 ° C. Particularly preferably, the application of the size takes place at a mold temperature of about 90 ° C to about 150 ° C. The application of the size can be carried out as a suspension, dispersion or paste. Optionally, the solids content of the size can be directly dispersed as freeze-dried material immediately before application in a solvent. Preferably, the size is applied as a suspension or dispersion.

In a further preferred embodiment of the present invention, the inside of the mold is pretreated prior to application of the size. A common pretreatment is the cleaning by blasting, for example with CO ₂ , sand, glass beads, glass breakage, melt-chamber slag, corundum, steel shot or metal balls, brushing or grinding. Other pretreatments include, for example, a structure specification by blasting or milling and the use of laser technology if the coating is to be carried out by means of PVD or CVD or when using thin sol-gel layers.

The coating obtained according to the invention by application of the size to the inside of the mold and subsequent solidification has a thickness of 0.5 μm to 200 μm, from 1 μm to 150 μm, 20 μm to 120 μm or approximately 80 μm. The thickness of the coating obtained is preferably 20 to 60 μm. The insulating effect of the coating produced can be controlled by the composition of the size and the layer thickness targeted.

According to a further preferred embodiment of the present invention, at least one further coating is applied to the first mold coating, wherein the composition of the at least one further coating Coating may be different or identical in composition of the first coating.

The solidification of the mold coating obtained by application of the size can be effected by drying and optionally further thermal compression. The drying of the coating can be carried out at room temperature or at elevated temperature, e.g. at temperatures of 80 to 100 ° C. By further temperature treatment, the coating can be further compressed. In an exemplary embodiment, the solidification of the coating takes place at a mold temperature of 250 to 350 ° C over a period of 1 to 3 h. In a preferred embodiment of the method according to the invention, the sizing is solidified at a mold temperature of 90 to 140 ° C and then at 280 to 320 ° C, preferably about 300 ° C for 1.5 h. In another exemplary embodiment, the solidification of the coating takes place by filling the melt of copper or copper-containing alloys in the mold. Another possibility of solidification is the burning and solidification by means of direct or indirect gas flame.

When the mold is installed in the casting apparatus, solidification of the size into a coating may preferably be carried out by performing a brass casting operation (pouring brass into the mold) or by direct heat (e.g., gas firing). If the mold is removed from the casting plant, the solidification can also be solidified by introducing the Kokillenhälften in an oven.

According to one embodiment, the coating which is produced according to the invention by application of the size to the inside of the mold, is a ceramic coating. The ceramic coating may have, for example, a pore or foam structure, a dense structure, a smooth-compact structure or a sharp-edged surface structure. The roughness R _{z of} the ceramic Coating may preferably be between 20 μm and 250 μm. The roughness is particularly preferably 50-150 μm. The roughness of the coating can also be controlled by the particle size of the inorganic oxide particles contained in the size. The roughness R _z can be determined by means of the surface roughness tester Mitutoyo SJ 201 (Mitutoyo Messgeräte GmbH, Neuss) using the differential inductive method.

According to a particularly preferred embodiment, the mold coating according to the invention has a surface structure which shows a "foamy" appearance. This "foam structure" has proved to be particularly advantageous for the inventive method for casting copper and copper-containing alloys. In particular, very good demoulding, insulating and zinkaustragsreduzierende properties are obtained.

The thermal shock resistance of the ceramic coating provided according to the invention can be increased by using platelet-shaped particles and / or a binder according to the invention having elastic properties. Suitable platelet-shaped particles consist for example of BN, WS ₂ , MoS ₂ or phyllosilicates. An example of a binder for improving elastic properties is boron nitride.

According to a preferred embodiment, the coating produced according to the invention by application of the size to the inside of the mold has a hydrophobic surface. Without being bound by any particular theory, it is believed that the addition of at least 1% by weight of polysiloxane increases the hydrophobicity of the surface of the coating made from the size. The hydrophobicity of the resulting coating can be increased or improved by so-called burn-in, ie solidification of the coating at elevated or appropriate temperature. A higher hydrophobicity of the Kokillenbeschichtung leads to a poorer wettability by the Melting of copper or copper-containing alloys, and thus to an improved demolding of the casting. In addition, due to the increased hydrophobicity of the coating prevents water can penetrate into the coating. For the penetration of water, it may, for example, during the cooling process of the mold come by immersion in a water bath or spraying with water. This leads to a sudden evaporation of the water in the pores in the coating (so-called micro-explosions) during the casting process, which causes defects in the casting surface and thus a high rejection. For example, microbursts are commonly observed in graphite-based single-size siftings because the water molecules can attach between the graphite agglomerates.

According to the invention, the mold is heated to about 60 ° C to about 200 ° C before filling the melt of copper or copper-containing alloys in the mold. Preferably, a tempering of the mold is carried out at 80 to 150 ° C, preferably at 90 to 130 ° C, more preferably at 110 to 125 ° C and more preferably at about 120 ° C prior to filling the melt of copper or copper-containing alloys in the mold , The temperature control has proved to be particularly important for the inventive method and in particular with regard to the reusability of Kokillenbeschichtung and the control of Zinkaustrags.

According to a further preferred embodiment, the temperature of the mold is adapted before filling the melt of copper or copper-containing alloys in the mold to the properties of the mold coating obtained by application of the size.

The inventors have also found that when casting brass, the zinc discharge from the melt can be reduced or avoided if the mold temperature before filling the melt in a range of 60 ° C to 200 ° C and preferably 90 ° C to 130 ° C is maintained. Precisely coordinated cooling of the mold allows both its service life to be significantly extended and rejects during casting to be significantly reduced. In addition, the zinc discharge can be further reduced by additives in the cooling water bath, for example acids or complexing agents, which dissolve zinc or keep it in solution. Another additional measure to reduce the zinc discharge in brass casting may be to provide the knife edge of the mold with a riser. The zinc deposits then arise preferably in the riser channel and do not affect the quality of the surface structure of the brass casting, such as a fitting.

Furthermore, it was found that the structure of the brass can be set closer due to the low mold temperature. Without wishing to be bound by any particular theory, the inventors speculate that the larger bulk density is caused by the faster cooling of the charged melt, since the shorter cooling time produces smaller crystallites. Thus, by means of the method of the present invention, the structure density of castings can be selectively controlled or optimized.

A further advantage of the method according to the invention is that the low mold temperature makes it possible to cast more complex and / or by casting methods difficult or hitherto impossible realizable geometries.

The tempering of the mold can be carried out by means known in the art, for example by a heat-dissipating medium such as air, water or thermal oil. For example, the use of a Peltier element for cooling allows the targeted adjustment of temperature gradients and temperature distributions, and thus a control of the solidification of the melt and the interception of temperature peaks. A tempering of the mold can also by heat pipes or an actively controlled Wasserbad- or water jet cooling be achieved. Air cooling of the mold can be done by blowing air or dry ice. There is also the option to dimension the mold accordingly, so to choose the Kokillenmasse-cast body ratio so that the heat dissipation is optimal. According to one embodiment, the tempering of the mold takes place via an actively controllable Peltier element and / or water bath and / or an actively controllable water jet cooling. According to another exemplary embodiment of the present invention, after the actual casting process, the mold is transferred to a water bath for cooling and left therein for a certain time. The cooling time is to be selected according to the invention such that the mold is cooled to the temperature range according to the invention before the next casting operation. Alternatively, suitable molds between the inside and outside of the mold may have cooling channels for cooling, through which a coolant is passed during the casting process. Corresponding embodiments of coolable or heatable molds are for example made US 4,875,518 or DE 103 59 066 are known and used in particular for aluminum casting.

The filling of the melt of copper or copper-containing alloys can be carried out by low-pressure casting or by gravity casting.

• i) Formfüllung (Dauer: 2-10 Sek.)
• ii) Abkühlen und Erstarren (Dauer: 15-60 Sek.)
• iii) Kokille öffnen (5-10 Sek.)
• iv) Kokille kühlen, beispielsweise durch Wasserbad (Dauer: 5-10 Sek.)
• v) ggf. Kokille sprühen bzw. Nachnebeln (Dauer: 10-20 Sek.)
• vi) Kern einlegen, Ausblasen und Kokille schließen (Dauer: 15-30 Sek.)

The actual casting can be done according to the present invention in the so-called hand casting or by conventional casting machines (for example, two-, four- and six-carousel). A typical casting process in machine casting may include the following steps:

• i) mold filling (duration: 2-10 sec.)
• ii) cooling and solidification (duration: 15-60 sec.)
• iii) Open mold (5-10 sec.)
• iv) cool mold, for example by water bath (duration: 5-10 sec.)
• v) If necessary, spray mold or misting (duration: 10-20 sec.)
• vi) insert core, blow out and close mold (duration: 15-30 sec.)

A typical period for a total casting process is about 50 and 120 seconds, and typically about 70 seconds, depending on the casting.

The dissolution of the resulting casting can be done in any manner known in the art.

EXAMPLES Example 1 - Preparation of size A

For the preparation of size A, the components listed in the table below are used in the stated% by weight, which relate to the total weight of the size. substance Wt .-% Alumina suspension (50% by weight in water) 45.9 lead free frit mixture (50 wt .-% in water) (The frit mixture containing min. 50 wt .-% Al ₂ O _3, based on the solids content of the frit, at least 5 wt. .-%, based on the solids content of the frit, B ₂ O ₃ , Al ₂ O ₃ , high alkali content, softening point: <500 ° C) 5.2 Basic zirconia nanobinder (34 wt% in water); Manufacturer ItN Nanovation AG 22.5 Korantin MAT 0.85 2-amino-2-methyl-1-propanol (AMP) 2.06 Deuterone XG (2 wt% in water) 6.95 Phenylmethylsilicone resin emulsion (Silres MP42 E) 3.62 Aluminum titanate, 0-10 μm mean particle size 2.36

To prepare the size, the aluminum oxide suspension and the frit mixture are placed in a stirred vessel and stirred for 10 minutes at 100 U / min. Then Korantin MAT and AMP are stirred. The nanobinder is added at an increased speed of 130 rpm. At 170 rpm, the aluminum titanate is stirred in within 10 minutes, followed by Silres MP42E and the deuteron XG (2% solution). The mixture is then stirred again for 30 minutes.

Example 2 - Preparation of size B

For the preparation of size B, the components listed in the table below are used in the stated% by weight, which relate to the total weight of the size. substance Wt .-% Alumina suspension (50% by weight in water) 35.03 lead-free frit mixture (50% by weight in water) (The frit mixture contains at least 50% by weight Al ₂ O ₃ , based on the solids content of the frit, at least 5% by weight, based on the solids content of the frit, Al ₂ O ₃ , high alkali content, softening point: <500 ° C) 2.88 water 5.53 2-amino-2-methyl-1-propanol (AMP) 1.67 Korantin MAT 0.72 Basic nanobinder based on n ZrO ₂ - (34 wt% in water); Manufacturer ItN Nanovation AG 17.59 Aluminum titanate, ≤10 μm mean particle size 2.36 boron nitride 4.56 Phenylmethylsilicone resin emulsion (Silres MP42 E) 22.53 wollastonite 2.60 xonotlite 2.60 Deuterone XG (2 wt% in water) 1.92

To prepare the size, the aluminum oxide suspension, the frit mixture and the water are placed in a stirred vessel and stirred for 10 min at 85 rev / min. After 10 minutes, the AMP is added with stirring and then the Korantin MAT is stirred. The speed is then increased to 130 rpm and the nanobinder added with stirring. The aluminum titanate and the boron nitride Hebofill 110 are first stirred in at 170 rpm, and then the phenylmethylsilicone resin emulsion, the wollastonite MM80 and the xonotlite Promaxon D successively in each case within 5 min. Subsequently, deuteron XG is stirred in at 170 rpm and more Stirred for 30 min. The solids content of the resulting size was 41.8%.

Example 3 - Coating of a mold with size A to produce a foam structure

The copper mold is first pretreated by blasting with glass granules (150-300 microns). Before application, the size A was stirred for about 15 minutes and then at a mold temperature of 130 ° C with the spray gun SATA-jet HVLP (SATA GmbH & Co. KG) with a WSB 1.2 -1.4 mm nozzle with a spray pressure of 2 bar sprayed onto the inside of the mold with a moderate flat jet. The distance to the mold surface was about 30 cm and the spraying was done in the double cloister to produce a layer thickness of about 30 microns. As the illustration 1 shows, the mold coating thus prepared on a pronounced Schaumstrukur.

Example 4 Potting Brass Using Sizing A Without Temperature Control or Cooling of Molds (Comparative Example)

Several copper molds were removed from the casting machine and blasted with glass beads (100 μm to 350 μm). Then the molds were heated to temperatures between 100 to 125 ° C by means of a gas burner directed to the outside and then coated with the size A by means of SATA-jet HVLP 3000 WSB (spray pressure: 1.5 bar). After sizing, the molds were installed in the caster and cooled to 50 ° C until the first casting. The layer thicknesses were about 20 to 70 microns because of the order. Subsequently, the brass melt was filled.

After the first casting cycle, the mold temperatures were between 60 and 110 ° C. The castings were easy to remove and the visual inspection showed a flawless surface. The mold coatings had a uniform brown-black color. Strongly gray zinc deposits could not be observed.

After the third casting cycle, the mold temperatures rose sharply. The castings were difficult to remove and the visual inspection showed numerous surface defects. The mold coatings had turned from brown-black to gray, indicating a strong zinc discharge.

Example 5 - Casting brass using size A and cooling the molds

The pretreatment of the molds, the application of the size and the filling of the molten brass were carried out as described in Example 4.

The first casting cycle was carried out without cooling the molds, while in the subsequent casting cycles, the molds were cooled by means of a water jet cooling. After the first casting cycle, the mold temperatures were between 60 and 110 ° C. The mold temperature before filling the melt was kept at between 110 and 150 ° C in the subsequent casting cycles. In total, 22 casting cycles were carried out.

The castings were easily demolded after each casting cycle and the visual inspection showed a flawless surface. The mold coatings had a uniform brown-black color. Gray zinc deposits could not be observed.

Example 6 - Casting Brass Using Sizing B

Several molds made of copper, which were installed in the caster, were cleaned with a compressed air-operated stainless steel brush. Then the molds were heated by means of a directed to the outside gas burner to temperatures between 90 to 95 ° C and then coated by means of SATA-jet HVLP (spray pressure: 2 bar) with the size B. The layer thicknesses were between 30 and 55 microns. Subsequently, the brass melt was filled.

The first and second casting cycle was carried out without cooling the molds, while in the subsequent casting cycles, the molds were cooled by means of a water jet system. The mold temperature before filling the melt was maintained at between 130 and 150 ° C in the subsequent casting cycles. A total of 8 casting cycles were carried out.

The castings were easily demolded after each casting cycle and the visual inspection showed a flawless surface. The mold coatings showed a uniform brown-black color on. Gray zinc deposits could not be observed.

Example 7 - Casting Brass Using Sizing B

Several copper molds were removed and cleaned with glass bead blasting media (300-600 μm). Then the molds were heated to 130 ° C by means of a gas burner directed to the outside and then the size B applied by means of SATA-jet HVLP (spray pressure: 2 bar) at a distance of 20 cm on the inner sides of the molds. To solidify the coating, the mold was heated in the oven for 1.5 h, kept for 30 min at 300 ° C and then cooled in the oven. The layer thickness was between 60 and 70 microns. Subsequently, the brass melt was filled, the molten brass had a temperature of 1024 ° C.

The first casting cycle was carried out without cooling the molds, while in subsequent casting cycles the molds were cooled by water by means of an immersion bath. The mold temperature before filling the melt was maintained at between 130 and 150 ° C in the subsequent casting cycles. A total of 11 casting cycles were carried out.

The castings were easily demolded after each casting cycle and the visual inspection showed a flawless surface. The mold coatings had a uniform brown-black color. Gray zinc deposits could not be observed.

1. 1. Verfahren zum Vergießen von Kupfer und kupferhaltigen Legierungen, umfassend die folgenden Schritte:
   1. a. Bereitstellen einer Kokille,
   2. b. Applikation einer Schlichte auf die Innenwand der Kokille zur Herstellung einer Beschichtung, wobei die Schlichte mindestens ein anorganisches Oxid, und ein Bindemittel umfasst,
   3. c. Verfestigen der Schlichte zu einer Beschichtung,
   4. d. Einfüllen einer Schmelze von Kupfer oder kupferhaltigen Legierungen in die Kokille, wobei die Kokille vor dem Einfüllen auf 60°C bis 200°C temperiert wird, und
   5. e. Herauslösen des entstandenen Gussteils aus der Kokille.
2. 2. Verfahren gemäß Aspekt 1, wobei die Schlichte zusätzlich mindestens 1 Gew.-% Polysiloxan, bezogen auf das Gesamtgewicht der Schlichte, umfasst.
3. 3. Verfahren gemäß Aspekt 1 oder 2, wobei die Schlichte zusätzlich mindestens 1 Gew.-%, bezogen auf das Gesamtgewicht der Schlichte, von Bornitrid, MoS₂ und/oder WS₂ enthält.
4. 4. Verfahren gemäß der vorherigen Aspekte, wobei das Bindemittel nanoskalige Teilchen enthält.
5. 5. Verfahren gemäß den vorherigen Aspekten, wobei die Applikation der Schlichte als Suspension oder Dispersion erfolgt.
6. 6. Verfahren gemäß den vorherigen Aspekten, wobei die Applikation der Schlichte bei einer Kokillentemperatur von 90 bis 200°C erfolgt.
7. 7. Verfahren gemäß den vorherigen Aspekten, wobei das Verfestigen der Beschichtung bei einer Kokillentemperatur von 250 bis 400°C über einen Zeitraum von 1 bis 3 h erfolgt.
8. 8. Verfahren gemäß den vorherigen Aspekten, wobei das Verfestigen der Beschichtung durch das Einfüllen der Schmelze von Kupfer oder kupferhaltigen Legierungen in die Kokille erfolgt.
9. 9. Verfahren gemäß den vorherigen Aspekten, wobei die Kokille vor dem Einfüllen der Schmelze auf 80 bis 150°C, vorzugsweise auf etwa 120°C temperiert wird.
10. 10. Verfahren gemäß den vorherigen Aspekten, wobei die erhaltene Beschichtung eine Dicke von 1 µm bis 150 µm, vorzugsweise von 20 bis 90 µm aufweist.
11. 11. Verfahren gemäß den vorherigen Aspekten, wobei die erhaltene Beschichtung eine hydrophobe Oberfläche aufweist.
12. 12. Verfahren gemäß den vorherigen Aspekten, wobei die Temperierung der Kokille über ein aktiv steuerbares Peltiér-Element und/oder Luftkühlung und/oder Wasserbad und/oder eine aktiv steuerbare Wasserstrahl-Kühlung erfolgt.
13. 13. Mehrfach verwendbare hydrophobe Kokillenbeschichtung, herstellbar aus einer Schlichte umfassend mindestens ein anorganisches Oxid, mindestens 1 Gew.-% Polysiloxan, bezogen auf das Gesamtgewicht der Schlichte, und ein Bindemittel.
14. 14. Beschichtung gemäß Aspekt 13, wobei die Schlichte zusätzlich mindestens 1 Gew.-%, bezogen auf das Gesamtgewicht der Schlichte, Bornitrid, MoS₂ und/oder WS₂ enthält.
15. 15. Beschichtung gemäß Aspekt 13 oder 14, wobei das Polysiloxan ausgewählt ist aus der Gruppe umfassend Polyalkylsiloxan, Polyalkylphenylsiloxan, Alkylsiliconharz und Phenylsiliconharz.
16. 16. Beschichtung gemäß Aspekt 13, 14 oder 15, wobei das mindestens eine anorganische Oxid ausgewählt ist aus der Gruppe umfassend Aluminiumoxid, Zirkonoxid, Aluminiumtitanat, Wollastonit, Xonotlite, Zirkonsilikat, Eisenoxid und Titandioxid.
17. 17. Beschichtung gemäß Aspekt 13, 14, 15 oder 16, wobei die Beschichtung an der Oberfläche eine Schaumstruktur aufweist.
18. 18. Kokille mit verlängerter Standzeit umfassend eine hydrophobe Kokillenbeschichtung gemäß den Aspekten 13 bis 16, wobei die Kokille im Bereich von 60 bis 200°C gezielt temperaturgesteuert ist.
19. 19. Verwendung einer hydrophoben Beschichtung gemäß den Aspekten 13 bis 17 zur Verlängerung der Standzeit einer Kokille.
20. 20. Verwendung des Verfahrens gemäß einem der Aspekte 1 bis 12 zur Verminderung des Zinkaustrags beim Vergießen von Messing.

Further aspects of the present application relate to:

1. A method of potting copper and copper-containing alloys, comprising the following steps:
   1. a. Providing a mold,
   2. b. Applying a size to the inner wall of the mold for the production of a coating, wherein the size comprises at least one inorganic oxide, and a binder,
   3. c. Solidifying the size to a coating,
   4. d. Filling a melt of copper or copper-containing alloys in the mold, wherein the mold is heated to 60 ° C to 200 ° C before filling, and
   5. e. Removal of the resulting casting from the mold.
2. 2. The method according to aspect 1, wherein the sizing additionally comprises at least 1 wt .-% polysiloxane, based on the total weight of the sizing comprises.
3. 3. The method according to aspect 1 or 2, wherein the sizing additionally contains at least 1 wt .-%, based on the total weight of the sizing, of boron nitride, MoS ₂ and / or WS ₂ .
4. 4. Method according to the previous aspects, wherein the binder contains nanoscale particles.
5. 5. Method according to the previous aspects, wherein the application of the size is carried out as a suspension or dispersion.
6. 6. Method according to the previous aspects, wherein the application of the size takes place at a mold temperature of 90 to 200 ° C.
7. 7. Method according to the previous aspects, wherein the solidification of the coating takes place at a mold temperature of 250 to 400 ° C over a period of 1 to 3 hours.
8. 8. Method according to the previous aspects, wherein the solidification of the coating takes place by filling the melt of copper or copper-containing alloys into the mold.
9. 9. Method according to the previous aspects, wherein the mold is heated to 80 to 150 ° C, preferably to about 120 ° C before filling the melt.
10. 10. The method according to the previous aspects, wherein the coating obtained has a thickness of 1 .mu.m to 150 .mu.m, preferably from 20 to 90 .mu.m.
11. 11. Method according to the previous aspects, wherein the resulting coating has a hydrophobic surface.
12. 12. The method according to the previous aspects, wherein the tempering of the mold via an actively controllable Peltier element and / or air cooling and / or water bath and / or an actively controllable water jet cooling takes place.
13. 13. Reusable hydrophobic mold coating, producible from a sizing comprising at least one inorganic oxide, at least 1% by weight of polysiloxane, based on the total weight of the size, and a binder.
14. 14. Coating according to aspect 13, wherein the sizing additionally contains at least 1 wt .-%, based on the total weight of the sizing, boron nitride, MoS ₂ and / or WS ₂ .
15. A coating according to aspect 13 or 14, wherein the polysiloxane is selected from the group consisting of polyalkyl siloxane, polyalkylphenyl siloxane, alkyl silicone resin and phenyl silicone resin.
16. 16. A coating according to aspect 13, 14 or 15, wherein the at least one inorganic oxide is selected from the group consisting of alumina, zirconia, aluminum titanate, wollastonite, xonotlite, zirconium silicate, iron oxide and titanium dioxide.
17. 17. A coating according to aspect 13, 14, 15 or 16, wherein the coating has a foam structure on the surface.
18. 18. Mold with extended service life comprising a hydrophobic mold coating according to the aspects 13 to 16, wherein the mold is specifically temperature controlled in the range of 60 to 200 ° C.
19. 19. Use of a hydrophobic coating according to aspects 13 to 17 for extending the service life of a mold.
20. 20. Use of the method according to any one of aspects 1 to 12 for reducing the zinc discharge in the casting of brass.

Claims (16)

A method of potting copper and copper-containing alloys, comprising the following steps: a. Providing a mold, b. Applying a size to the inner wall of the mold for the production of a coating, wherein the size comprises at least one inorganic oxide, and a binder, c. Solidifying the size to a coating, d. Filling a melt of copper or copper-containing alloys in the mold, wherein the mold is heated to 60 ° C to 200 ° C before filling, and e. Removal of the resulting casting from the mold. The method of claim 1, wherein the sizing additionally comprises at least 1% by weight of polysiloxane, based on the total weight of the sizing. A method according to claim 1 or 2, wherein the sizing additionally contains at least 1% by weight, based on the total weight of the sizing, of boron nitride, MoS ₂ and / or WS ₂ . A method according to the preceding claims, wherein the binder contains nanoscale particles. Process according to the preceding claims, wherein the application of the size takes place at a mold temperature of 90 to 200 ° C. Process according to the previous claims, wherein the solidification of the coating takes place at a mold temperature of 250 to 400 ° C over a period of 1 to 3 hours. Process according to the preceding claims, wherein the mold is heated to 80 to 150 ° C, preferably to about 120 ° C before filling the melt. A method according to the preceding claims, wherein the obtained coating has a hydrophobic surface. Reusable hydrophobic mold coating, producible from a sizing comprising
at least one inorganic oxide,
at least 1% by weight of polysiloxane, based on the total weight of the size, and
a binder. Coating according to claim 9, wherein the sizing additionally contains at least 1% by weight, based on the total weight of the sizing, boron nitride, MoS ₂ and / or WS ₂ . A coating according to claim 9 or 10, wherein the polysiloxane is selected from the group comprising polyalkylsiloxane, polyalkylphenylsiloxane, alkylsilicone resin and phenylsilicone resin. A coating according to claim 9, 10 or 11, wherein the at least one inorganic oxide is selected from the group consisting of alumina, zirconia, aluminum titanate, wollastonite, xonotlite, zirconium silicate, iron oxide and titanium dioxide. A coating according to claim 9, 10, 11 or 12, wherein the coating has a foam structure on the surface. Mold with extended service life comprising a hydrophobic die coating according to claims 9 to 12, wherein the mold is specifically temperature controlled in the range of 60 to 200 ° C. Use of a hydrophobic coating according to claims 9 to 13 for extending the service life of a mold. Use of the method according to one of claims 1 to 8 for reducing the zinc discharge during the casting of brass.

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