A METHOD OF PRODUCING FROZEN CASTING MOULDS

Abstract: To produce frozen casting moulds or core boxes the binder is cooled till freezing at least partly before or during the moulding process. This allows the production rate to be increased to such a level that the working rate of automatic machines for the production of casting moulds and core boxes can be turned into full account.

Description: A method of producing frozen casting moulds The invention relates to a method of producing frozen casting moulds or- cores of a granular material and a binder in a mould chamber or a core box, comprising the use of a freezable binder which is in a gas or liquid state at positive temperatures calculated in C. The specification of the U.S. Patent 4150704 teaches a method in which the mould sand is admixed with a controlled quantity of water which after moulding is frozen to ice in a certain depth from the surface that is caused to contact molten metal e.g. by placing a layer of so-called dry ice or spraying liquid nitro¬ gen on the surface. This gives a very strong mould surface which retains its strength and shape until the surface of the metal has solidified. As the metal ■ gives off its heat, the water melts and evaporates so that the mould begins collapsing without the use of mechanical means. Practically no smoke is developed in the casting process, and the mould sand can be reused right away. An article in the Russian magazine Liteinoe Proizvodsto, 1975, no. 5, p. 21-22, describes the freezing of a sand mould containing 3 to 7% water by means of a coolant that circulates through the evaporator in a cooling system and through the mould. Freezing of the added water is by nature a rather slow process, and consequently it takes a relatively long time from the moment when the moulding process -is finished until the mould has frozen deep enough to be able to resist the effect of molten metal for a suf- ficiently long time, and this in turn causes the over- all mould production to become considerably more time- consuming than the conventional mould manufacturing processes. The object of the invention is to overcome this draw- back of the known embodiments of the present method, and this object is achieved in that the binder has been frozen before the moulding process or is rapidly brought down below its freezing point during said process in that at least one of the tools and/or ma- terials which the binder, which itself may have been precooled, is caused to contact in the moulding process, has been cooled in advance. In this embodiment part or the entire necessary cooling may have been effected in advance, i.e. before the moulding process, so that the molten metal may be poured into the mould immediately after the termination of the moulding process. This provides for such a great production rate that the method may be used in connection with fast working automatic machines for the production of casting moulds with or without cores, e.g. of the type dis¬ closed in the applicants' Banish Patent Specification No. 87462 and Patent Application No. 3501/74 to turn the high operation rate of these machines in"to account. When the binder has been frozen before the moulding process, it may be expedient, as stated in claim 2, that additionally at least one of the tools and/or materials which the binder is caused to contact in the moulding process or in the mould and which may contain a binder previously used, has been cooled be- low the freezing point of the binder or to a tempera¬ ture slightly above said freezing point. As stated in claim 3, the mould binder zia-y have been cooled before the mould manufacturing process so that it is present in the form of fine, dendritic particles, e.g. snow, in the mould material, and a compression during the moulding process may entail that the binder obtains part of or its entire binding capacity depending upon the temperature conditions at the time of the mould manufacturing process. The mould binder used may, as stated in claim 4, also havebeen cooled before the mould manufacturing pro¬ cess so that it is present in the form of a finely divided powdered material, e.g. in the mould material, and a compression during the moulding process may en¬ tail that the binder obtains part of or its entire binding capacity depending upon the temperature con¬ ditions at the time of the mould manufacturing process. When a suitable mixture of granular material and snow or broken ice is compressed in a mould box, the snow or the ice may thus be caused to bind the grains of the material together to impart a cohesive force to the mould or the core sufficient for it to resist the effect from liquid metal which is poured down into the finished mould with or without cores. A correspond¬ ing effect can be achieved by injecting one-of the mentioned mixtures of mould material into a core box with a sufficiently great force and at a sufficiently great rate. The precooled binder in the form of pulverized material may, as stated in claim 5, also be combined wit liquid gas. This permits the temperature of the mould material to be reduced to a very low value before and during the moulding process and during the. immediately following casting process. The mixture must be homogenous and easy flowing. Actually, there is nothing to prevent the use of conventional setting binders. Thus, to form a binder there may be used water glass and liquid carbon dioxide, as stated in claim 6, or a mixture of polyisocyanate and phenol resin which is activated by pr cooled, liquid dimethylethyl amine or triethyl amine, as stated in claim 7. This provides for a reduction in the use of an environmentally harmful binder. To obtain a better resistance to the heat effect of the molten metal and thereby a delay in the heating of the mould or the core in the casting process, the granular material used for the formation of the mould or the core may have been deep frozen in advance, as stated in claim 8. As stated in claim 9, the process ingredients may have been deep-frozen in advance by means of an admixed freezing agent, and the freezing agent used may ex¬ pediently be liquid gas as stated in claim 10. The use of an inert gas, as stated in claim 11, obviatesJ any risk of chemical attacks on the equipment used for the process or for chemical reactions with the casting metal. The required cooling may also be effected or be supported by deep-freezing the parts of the apparatus which the mould material contacts during the moulding process. In the production of casting moulds, parti¬ cularly the pattern board which contacts the same mould surface as the molten metal does later, may have been deep-frozen in advance, as stated in claim 12, and a core box deep-frozen in advance may be used, as stated in claim 13 , in the production of cores. Also, the core box with the core or cores may be cooled simultaneously and additionally, as stated in claim 14 , e . g . with liquid gas . A specific embodiment of the method of the invention in the production of casting moulds comprises the use of deep-frozen disposable patterns of a material which evaporates when heated, as stated in claim 15, and this material may expediently have been deep-frozen and foamed, as stated in claim Iβ. Such patterns may be produced currently in a particular bifurcate pattern mould box corresponding to a conventional core box and be placed in a closed chamber, following which the space between the pattern and the walls of the chamber is filled with the moulding material which is cooled by the pattern and may additionally have been cooled in advance as mentioned above. After the moulding process is finished the pattern evaporates rapidly owing to the heat received. This obviates the in¬ convenient development of gas, which otherwise takes place in the moulding of disposable patterns. This embodiment of the method results in particularly accurate castings because the inaccuracies which in the conventional mould manufacturing process result from wear on the pattern board caused by shootings of sand, are avoided. Moreover, bifurcation of the mould box is not required when readily evaporable patterns are used. The invention also relates to .a plant for carrying out the disclosed method, said plant comprising apparatus for the production of casting moulds and/or apparatus for the production of cores. As stated in the charac¬ terizing portion of claim 17, the plant of the inven¬ tion is characterized in that the apparatus or parts of it are contained in a cooling chamber whereby the ne- cessary temperature conditions may be readily and con¬ stantly maintained so that valuable production time is ot lost in waiting for cooling. When the plant is connected to a casting plant having melting apparatus, as stated in the introductory portion of claim 18, a considerable saving in energy may be achieved by an arrangement such that waste heat from the melting apparatus is used for the operation of the cooling system of the cooling chamber, as stated in the characterizing portion of claim 18. C PI

Claims: P a t e n t C l a i s : 1. A method of producing frozen casting moulds or cores of a granular material and a binder in a mould chamber or a core box, comprising the use of a binder which is in a gas or liquid state at positive tempera- tures calculated in °C, c h a r a c t e r i z e d in that the binder has been frozen before the mould¬ ing process or is rapidly brought down below its freezing point during said-process in that at least one of the tools and/or materials which the binder, which itself may have been precooled, is caused to contact in the moulding process, has been cooled in • advance. 2. A method according to claim 1, wherein the binder has been frozen before the moulding process, c h a r a c t e r i z e, d in that at least one of the tools and/or materials which the binder is caused to contact in the moulding process or in the mould and which may contain a binder previously used, has been cooled below the freezing point of the binder or to a temperature slightly above said freezing point. 3. A method according to claim 1 or 2, c h a r a c - t e r i z e d in that the mould binder used has been cooled before the mould manufacturing process so that it is present in the form of fine, dendritic particles e\g. snow, in the mould material, and that a compression during the moulding process entails that the binder obtains part of or its entire binding capacity depending upon the temperature conditions at the time of the mould manufacturing process. 4. A method according to claim-1, c h r a c t e r - i z e d in that the mould binder used has been cooled before the mould manufacturing process so that it is pres'ent in the form of finely divided powdered material, e.g. ice, in the mould material, and that a compression during the moulding process entails that the binder obtains part of or its entire binding capacity depending upon the temperature con¬ ditions at the time of the mould manufacturing process. 5. A method according to claim 4, c h a r a c t e r - i z e d in that the precooled binder in the form of pulverized material is combined with liquid gas. β. A method according to claim 1, c h a r a c t e r ¬ i z e d by the use of water glass and liquid carbon dioxide to form a binder. 7. A method according to claim 1, c h a r a c t e r ¬ i z e d in that a mixture of polyisocyanate and phenol resin which is activated by pre-frozen, liquid dimethylethyl amine or triethyl amine, is used for the formation of a binder. 8. A method according to any one of the preceding claims, c h a r a c t e r i z e d in that the granular material used has been deep-frozen in advance. 9. A method according to any one of the " claims 3-8, c h a r a c t e r i z e d in that the process ingre- dients have been deep-frozen in advance by means of an admixed freezing agent. 10. A process according to claim 9. c a r a c t e r ¬ i z e d by the use of liquid gas as freezing agent. 11. A method according to claim 10, c h a r a c t e r ¬ i z e d by the use of an inert gas. 12. A method according to any one of the preceding claims in the production of a casting mould, c h a r a c t e r i z e d by the use of a pattern board deep-frozen in advance. 13. A method according to any one of the claims 1-11 in the production of a core, c h a r a c t e r i z e, d by the use of a core box deep-frozen in advance. 14. A method according to claim 13 * c h a r a c t e r ¬ i z e d ±n that core box with the core or cores is cooled simultaneously and additionally. 15. A method according to any of the claims 1-11 in the production of casting moulds, c h a r a c t- e r - i z e d by the use of deep-frozen disposable patterns of a material which evaporates when heated. 16. A method according to claim 15, c h a r a c t e r ¬ i z e d by the use of disposable patterns manufactured from a deep-frozen, foamed material. 17. A plant for carrying out the method according to ■ any one of the preceding claims and comprising appara¬ tus for the production of casting moulds and/or apparatus for the production of cores, c h a r a c t e r i z e d in that the apparatus or parts of it are contained in a cooling chamber. 18. A plant according to claim 17, connected to a casting plant with melting apparatus, c h a r a c t e r ¬ i z e d by an arrangement su.ch that waste heat from O PI the melting apparatus is used for the operation of the evaporator in the cooling system of the cooling chamber,

Inventors: JESPERSEN E, SINGH B
Applicants: DANSK IND SYNDIKAT, JESPERSEN E, SINGH B, DANSK IND SYNDIKAT AS
Application year: 1981
Main classification: B22C9
IPC codes: B22C9