Search

EP-4545204-B1 - INORGANIC BINDERS SYSTEM AND A PROCESS FOR PRODUCING A NON-FERROUS METAL ARTCILE

EP4545204B1EP 4545204 B1EP4545204 B1EP 4545204B1EP-4545204-B1

Inventors

  • HAANAPPEL, Vincent
  • LINKE, THOMAS

Dates

Publication Date
20260513
Application Date
20220712

Claims (4)

  1. A composition for making a core for use in a non-ferrous metal casting process, the composition comprising a particulate refractory material and comprising, relative to the weight of the particulate refractory material : 0.5 wt% to 5 wt% of an inorganic binder comprising one or more of sodium silicate, potassium silicate, lithium silicate, or a combination thereof; 0.1 wt% to 2 wt% of a pozzolanic additive comprising one or more of silica fume, fused silica and pyrogenic silica; and 0.1 to 1.5 wt% of a weak lustrous carbon former having a lustrous carbon content of less than 15%, wherein the weak lustrous carbon former comprises one or more of: graded coal, coal dust, and seacoal, wherein said lustrous carbon former is a foundry additive which comprises organic compounds which volatilise under the effect of casting conditions thereby forming lustrous carbon.
  2. The composition according to claim 1, wherein the particulate refractory material comprises sand.
  3. A core formed from the composition of any one of the preceding claims.
  4. A process for producing a non-ferrous metal article by non-ferrous metal casting, the process comprising: (i) mixing a composition according to any one of the preceding claims to form a mixture; (ii) moulding and hardening the mixture to produce a core in the shape of an internal cavity of the article; (iii) assembling the core with a mould for metal casting, such that the mould and the core together define a casting cavity; (iv) supplying molten metal into the mould cavity until the mould cavity is filled at a temperature of less than 1200°C; (v) cooling and solidifying the molten metal to form the article.

Description

Technical field The present invention relates to a composition for making a core for use in a non-ferrous metal casting process, a core formed from the composition, and a method for producing a non-ferrous metal article by non-ferrous casting using a core comprising the composition. Background In a gravity casting process, molten metal (or metal alloy) is poured into a pre-formed mould cavity which defines the external shape of the casting, with the molten metal filling the mould cavity under the force of gravity. The shape of hollow sections or internal cavities in the casting may be defined by a disposable core. The cores may be bound with organic resins, binders in powder form, clay minerals or water glass, the latter often referred to as liquid inorganic binder. Nowadays binding of sand cores and moulds with organic binders for example with organic resins in general is not the preferred method since the decomposition products of organic binders are often toxic and the compositions release toxic fumes upon curing or during casting which introduce risks for the foundry workers and have other negative environmental impacts, and can be expensive to mitigate. A further problem with many existing core binder systems is the quality of the finished surface of the cast component. The long casting times and harsh conditions involved frequently leads to surface on the casting such as sand adhesion, as well as the breaking of, and metal ingress into, the cores themselves. US patent no. 4,316,744 discloses high ratios of silicate foundry sand binders comprising an aqueous solution of sodium, potassium or lithium silicate and containing amorphous silica. The core and mould compositions as disclosed in US 4,316,744 are cold setting and are set with carbon dioxide or a suitable acid releasing curing agent. The disadvantage of such moulding compositions and particularly the method of setting binder systems with carbon dioxide is that purging of the moulded composition with carbon dioxide results in a strength which is always lower than in case of the use of the technology comprising hot curing with a heated metal core box and heated air to purge the sand cores. It is thus an object of the present invention to provide a foundry moulding composition which is particularly suitable for moulding of high strength cores in a so-called heated core box in which the moulded material simply can be cured by purging with heated air. US2015/306658 describes mould mixtures containing at least one aluminium oxide and a water glass-based binder. US7770629 describes moulding mixtures for producing casting moulds for metalworking, wherein the moulding mixtures comprise a binder based on water glass. CN111889616 describes a curing agent for casting, which comprises inter alia a metal alkali. US2010/224756 describes a moulding material mixture for production of casting moulds for metalworking, wherein the moulding mixture comprises a waterglass-based binder and a carbohydrate. It is thus an object of the present invention to mitigate or ameliorate the above problems. Summary of invention Composition According to a first aspect of the invention, there is provided a composition for making a core for use in a non-ferrous metal casting process according to Claim 1. As used herein, the term 'lustrous carbon former' refers to foundry additives which form lustrous carbon under the effect of casting conditions. The additives typically comprise organic compounds which volatilise under the conditions at the mould-metal interface thereby forming lustrous carbon. The inventors have found that cores made from the composition of the first aspect have sufficient strength to withstand the forces experienced during the casting process, have excellent de-coring properties and avoid or minimise the number of surface defects of the metal casting. In a further advantage, the composition of the first aspect can be used without requiring a coating applied to the core prior to use in a moulding or casting process. Lustrous carbon former The lustrous carbon former is a weak lustrous carbon former. The composition is suitable for making a core for use in a non-ferrous metal casting process. E.g. the composition may be for making a core in a low temperature non-ferrous metal casting process. In context, low temperature means below 1000°C, or optionally, below 900°C or below 800°C. The weak lustrous carbon former comprises one or more of: graded coal, coal dust, and seacoal. The weak lustrous carbon former has a lustrous carbon content of less than 15%. In some embodiments, the weak lustrous carbon former may have a lustrous carbon content of less than 14%, less than 13%, less than 12%, less than 11%, less than 10%, less than 9%, or less than 8%. The weak lustrous carbon former comprises 0.1 to 1.5 wt% relative to the weight of the particulate refractory material. In some embodiments, the weak lustrous carbon former may comprise 0.2 to 1.4 wt%, 0.3 to 1.3 wt%, 0.4 to