Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
  • B22C1/02—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by additives for special purposes, e.g. indicators, breakdown additives
  • B22C1/08—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by additives for special purposes, e.g. indicators, breakdown additives for decreasing shrinkage of the mould, e.g. for investment casting
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
  • B22C1/16—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents
  • B22C1/18—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of inorganic agents
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C9/00—Moulds or cores; Moulding processes
  • B22C9/10—Cores; Manufacture or installation of cores
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C9/00—Moulds or cores; Moulding processes
  • B22C9/12—Treating moulds or cores, e.g. drying, hardening

Definitions

• the invention relates to a method for producing castings from a molten metal, in particular a light metal melt, such as aluminum melt.
• the invention relates to a molding material and its use for the production of casting mold parts which are used for the casting of molten metal, in particular of molten light metal, such as molten aluminum.
• casting mold parts can be, for example, casting cores, through which cavities are formed in the interior of the casting to be produced.
• mold parts according to the invention can be components from which a multi-part mold is assembled, by means of which the outer shape of the cast part to be produced is determined.
• such casting mold parts are required, by means of which the inner and the outer shape of the workpiece to be cast are determined. Accordingly, such casting mold parts can be casting cores, through which cavities are formed in the interior of the casting to be produced, or are casting mold elements from which a multi-part casting mold is assembled, which determines the external shape of the casting to be produced.
• molding material systems are generally used, which are composed of a basic molding material and a binder. These two components are mixed together, shaped and processed into a compact body in a suitable curing process. Quartz sand, which is bound with an organic binder in the majority of applications, is usually used as the basic molding material.
• quartz sand as the basic material for the production of casting mold parts has proven itself in several ways, in particular in the field of casting light metal materials. Such quartz sand can be obtained inexpensively and is characterized by simple processability and good quality in the imaging of the mold elements of the casting mold part to be produced.
• the molding material used to manufacture the mold parts must have a high level of strength and dimensional accuracy, which is retained even when the mold is being built and the melt is poured off.
• the molding material should be easy to remove after pouring. The latter proves to be particularly important when casting cores are used which form complex interiors in the casting.
• the molded materials should be regenerable after use in such a way that the highest possible rate of reuse is achieved with the molded raw material.
• This can be achieved in a manner known per se by using inorganic binders which release low emissions during the production of the molded parts and which can be burned almost without residue after the casting process has ended by exposure to sufficiently high temperatures.
• Another problem with pouring complex shaped castings using conventionally produced mold parts is that the sand is difficult to remove from the casting after cooling.
• the cast part is usually shaken or subjected to impacts which are intended to disintegrate the casting cores located in the inside of the cast part and the shaped parts adhering to the outside of the cast part and to promote the trickling out of the molded material particles obtained.
• these mechanical methods for removing the molded parts entail the risk of damage to the cast part. This can lead to the formation of cracks, particularly in the case of filigree-shaped or thin-walled components.
• the object of the invention was to provide a method with which high-quality, complex-shaped castings can be produced and in which the casting mold parts can be removed from or from the casting in a simple and safe manner after the casting process has ended.
• a molding material should be made available, with which molded parts can be produced which are suitable for producing high-quality, complex-shaped castings and which can be easily and safely removed from or from the casting after the casting process has ended.
• the above-mentioned object is achieved by a molding material for the production of casting mold parts for pouring molten metal, in particular light metal melt, which consists of a mixture of a free-flowing mold base material inert to the metal melt and a binder mixed with the mold base material, the thermal expansion behavior of mold base material and binder are matched to one another in such a way that the thermal expansion coefficient of the molten metal is above the thermal expansion coefficient of the casting mold part produced from the molding material.
• the invention is based on the knowledge that, by choosing a suitable molding material, mold parts can be produced which optimally combine the properties required for the simple, safe and environmentally friendly production of high-quality, dimensionally accurate cast parts.
• the molding material according to the invention optimally combines the properties which are a prerequisite for the production of a high-quality cast part are at the same time a simple manufacturing method.
• the molding material according to the invention contains a granular or comparable particle-like form and as such a free-flowing base material which, when it inevitably occurs during the casting, exhibits a significantly low thermal expansion compared to conventionally used quartz sand.
• the basic molding material thus guarantees high dimensional accuracy in the production of complex shaped castings, even with a low material thickness.
• the free-flowing base material is mixed with a binder that has a different expansion behavior from the base material when heated. Due to the different thermal expansion of the base material and the binder, the binder is detached from the grains of the base material after the heat has been introduced from the casting heat. As a result, when the binder expands more than the base material, the binder bursts open so that it loses its solid shape and can be easily removed from or from the cast part. Conversely, the expansion behavior of the basic molding material can be such that the bond to the binder is broken by a change in volume associated with the heating and the basic material becomes free-flowing again. It is essential that the core or molded component breaks along with the heating, so that after the casting has cooled, it breaks down into easily removable, loose individual parts.
• the thermal expansion behavior of the molding material according to the invention in the manner according to the invention is matched to the thermal expansion behavior of the molten metal to be cast and by simultaneously producing this molding material on the basis of a free-flowing basic material, it is achieved that after the casting has cooled, the molding which is at least partially encompassed by the casting or which is adjacent to the casting due to the im Forces occurring during the cooling process are broken up into loose individual pieces that can be easily removed.
• the breakage of the mold parts is caused by the effects of the different expansion of the cast metal and the molding material.
• the invention has a particularly favorable effect when casting components from molten aluminum.
• Aluminum has a high coefficient of thermal expansion, so that the forces exerted in the course of the pouring and solidification of the melt on the molded parts in contact with the cast part are exerted such high forces that the molded part in question breaks safely into smaller parts. This proves to be particularly favorable if the molded part is a core mold.
• a further property of the molding material procured and used according to the invention which is advantageous for the invention is that the binder and the molding base material are matched to one another such that the particles of the base material are thermally stable and not elastically bound by the binder in the molded parts produced from the molding material.
• the cast part produced from such a basic molding material behaves brittle over the entire temperature interval that has passed through when the melt is poured off, as a result of which the Invention desired breaking of the molded parts is promoted.
• the binder of the molded parts is preferably chosen so that it does not decompose due to the action of heat. In this way it is avoided that volumes are released in the core which could lead to an undesired flexibility of the molded part in accordance with the invention.
• a further advantageous embodiment of the invention is that the particles of the basic molding material have an essentially round, spherical shape.
• the spherical shape of the base material and the associated predominance of point contacts between the base material particles promotes the automatic disintegration of the molded parts as a result of the mechanical forces that occur during the pouring and solidification of the melt.
• a basic molding material that fulfills this requirement particularly well is synthetically produced mullite.
• the molding base material has at least a portion, preferably more than 50% or more than 70%, of the aluminum oxide sand (mullite) which constitutes quartz sand.
• Mullite has a round grain shape and a density comparable to that of quartz sand.
• the molded materials made from it are much easier to process than known Zr0 2 sands, for example.
• the round spherical shape of the mullite particles in practice leads to a simplified processability of the particles Mold raw materials produced molding materials and, consequently, to a reduced wear of the tools and machines used for the production of the molded parts.
• a molding material with high mullite contents due to its low thermal expansion, even with low material thickness, has a high dimensional stability in the production of complex shaped castings.
• molded material composed according to the invention is particularly suitable for the production of casting cores. These can be removed after casting without the risk of damaging the finished casting.
• a molding base material composed of a mullite-quartz sand mixture and a molding material produced from it have a rather insulating effect. Therefore, these substances can be used specifically for casting technology applications in which there is a temperature rise above the critical temperature of 573 ° C for quartz sands, in which the thermal conductivity of the molded parts produced from the substances in question plays a subordinate role or heat conduction should be deliberately restricted. Practical tests have shown that by adding a sufficient amount of mullite sand to a quartz sand, the problems of spontaneous changes in geometry can be overcome, which occur when quartz sand is used alone as the basic molding material for the production of slim, filigree castings. It is essential that the proportion of Al 2 Si0 5 sand is sufficiently high in each case to be able to compensate for the change in length of the quartz that otherwise occurs with quartz sand due to the heating above the critical temperature.
• the binder and base material are moreover preferably matched to one another in such a way that a casting mold part produced from the molding material has a low thermal conductivity. This property causes the temperature difference between the casting material and the molded part to remain large after the metal melt has been poured off, so that the risk of premature thermally or chemically triggered decomposition of the molded part is reduced to a minimum.
• the disintegration of the casting cores can be supported by coordinating the components of the molding material in such a way that the molding base and binder expand differently when heated, with the result that the bonds between them break when the melt is poured off.
• the invention can be implemented in a particularly practical manner by processing a molding material which is formed from a mixture of a granular or comparable particle-like form and as such a free-flowing base material and an inorganic binder.
• molding materials which have been found to be particularly suitable are those which are mixed from a binder based on water glass and a molding base material composed according to the invention. It is essential, however, that the expansion behavior of the components mixed with one another sufficiently differentiates from one another.
• the base material and the binder expand differently.
• the binder after the heat input from the casting heat, the binder is detached from the grains of the base material.
• the binder expands more than the base material, it bursts the molded part in such a way that it loses its solid form and breaks up into fragments. These can easily be shaken off or from the cast part without the risk of mechanical damage.
• the respective casting mold part is also produced in the method according to the invention in that a molding material mixture composed according to the invention is injected into the core box of a core molding machine in a known manner.
• the molding material is then hardened, for example, according to the process described in DE 196 32 293 A1, by applying a vacuum to the hollow mold of the core box heated to a temperature of 100 ° C. to 160 ° C. and the core molding over a period of 20 to 30 seconds is heated by the core box.
• the mold part becomes so solid that it can be removed from the core box and placed in a heating device, for example a microwave oven, which is arranged outside the core box.
• a heating device for example a microwave oven, which is arranged outside the core box.
• this heating device it is heated with sufficient heat output to such an extent that an amount of water sufficient for complete hardening is withdrawn.
• the Dehydration can also be done by sufficient heating of the core box itself or by hot air fumigation. These measures can each be combined with heating outside the core box. It is also possible to effect the water removal by means of a microwave heating which acts directly on the core molding which is still in the core box.
• the respective molded part can be used to increase the molded part
• Core surface strength can be sprayed with binder liquid.
• the molded parts treated in this way have an increased stability with an equally increased abrasion resistance, so that they can be stored without problems and meet the highest requirements for their dimensional accuracy. This proves to be particularly favorable with regard to an optimized quality of the casting to be produced if a water glass binder is used.
• the invention is explained in more detail below on the basis of a drawing illustrating an exemplary embodiment.
• the single figure shows schematically in section a camshaft core 1 of a mold, not shown, for casting a cylinder head from an aluminum casting alloy.
• two recesses 3, 4 are formed, spaced apart in the longitudinal direction, through which the shape of the bearing blocks of the cylinder head to be manufactured, which are provided for mounting the camshaft, is determined.
• the length A of the branches 5, 6 is in this case many times greater than its diameter B.
• the length C of the main section 7 of the oil channel core 8 is many times greater than its diameter D.
• the ole channel core 8 has been produced in a conventional manner in a conventional molding machine from a molding material according to the invention which has been produced by mixing a molding base material consisting of mullite sand and quartz sand with a water glass binder. Due to the proportion of mullite sand, it is ensured that the ole channel core 8 expands evenly and consequently clearly predeterminable even when it heats up to over 573 ° C. in the course of the casting of the cylinder head to be produced.
• the casting cores 1.8 deform due to the peculiarities coordinated with one another in the manner according to the invention only insignificant of the basic molding material and binder.
• the low thermal expansion of the base material thus supports the process-reliable achievement of the dimensional requirements of the casting.
• the fragments into which the respective casting core 1, 8 automatically disintegrates due to the action of the casting heat and due to the different thermal expansion behavior of the base material and the binder , emptied from the casting and processed.
• the solid core contraction of the cast metal which is considerably higher than that of the casting cores 1.8, subjects the casting core 1.8 to high mechanical stresses. Due to the brittle, inelastic nature of the casting cores 1.8, these cause the casting cores 1.8 to shatter into bulb-like fragments.
• the processing of the casting core fragments can include gentle breaking into granular particles.
• the granular particles obtained can then be subjected to metal deposition and dedusting to produce the condition necessary for their reuse.
• the casting mold parts recycled to granular material are then used again as the base material for the molding material composed according to the invention.
• molding materials are used in the manner according to the invention which consist of molding base material, such as synthetic mullite, mixed with water glass binder, then no significant emissions occur during the production of the moldings. As a result, casting errors that occur repeatedly as a result of gas formation, extensive precautions for the extraction of gases and complex tool cleaning can be avoided in the conventional procedure. This reduces the burden on the environment and operating personnel to a minimum.
• a further advantage of the invention is the chemical resistance of the molding base material to binder and melt. This property ensures that when the procedure according to the invention is obtained, a casting is obtained whose surface is completely free of residual sand buildup after the fragments of the mold cores and moldings have been emptied, without additional cleaning measures.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Mold Materials And Core Materials (AREA)
• Molds, Cores, And Manufacturing Methods Thereof (AREA)
• Powder Metallurgy (AREA)

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Publications (1)

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Citations (6)

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• 2002
  • 2002-09-13 MX MXPA04002424A patent/MXPA04002424A/es active IP Right Grant
  • 2002-09-13 JP JP2003528331A patent/JP2005502473A/ja active Pending
  • 2002-09-13 BR BR0212534-0A patent/BR0212534A/pt not_active IP Right Cessation
  • 2002-09-13 EP EP02772298A patent/EP1425121B1/de not_active Expired - Lifetime
  • 2002-09-13 WO PCT/EP2002/010301 patent/WO2003024642A1/de active IP Right Grant
  • 2002-09-13 PL PL02367736A patent/PL367736A1/xx unknown
  • 2002-09-13 HU HU0401547A patent/HUP0401547A2/hu unknown
  • 2002-09-13 DE DE50206490T patent/DE50206490D1/de not_active Expired - Fee Related
  • 2002-09-13 ES ES02772298T patent/ES2262845T3/es not_active Expired - Lifetime
  • 2002-09-13 US US10/489,485 patent/US20040261969A1/en not_active Abandoned
  • 2002-09-13 KR KR10-2004-7003845A patent/KR20040070330A/ko not_active Application Discontinuation
  • 2002-09-13 CA CA002461797A patent/CA2461797A1/en not_active Abandoned
  • 2002-09-13 AT AT02772298T patent/ATE323563T1/de not_active IP Right Cessation
  • 2002-09-13 CN CNB02820431XA patent/CN1298456C/zh not_active Expired - Fee Related

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