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
  • 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
  • B22C1/183—Sols, colloids or hydroxide gels
• • 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
  • B22C1/20—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 organic agents
  • B22C1/22—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 organic agents of resins or rosins
  • B22C1/2233—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 organic agents of resins or rosins obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
  • B22C1/2246—Condensation polymers of aldehydes and ketones

Definitions

• the present invention relates to foundry cores with improved gutting properties, a process for their preparation and their use.
• Shapes and cores are usually sand cast from quartz sand, for special applications but also from other sands (alumina, zirconia, olivine, chrome ore) produced in which the grains of sand are bonded together by polymeric binder and a dimensionally stable for the duration of mold filling with liquid metal Forming a composite.
• sands alumina, zirconia, olivine, chrome ore
• mechanical aids shaking, shaking, tapping
• thermal aids or pressurized water can be used for coring or dissolution of the mold.
• binders Today, phenolic resins, polyurethanes, ureas and furan resins, which are complexly chemically modified (chemical additives), are used as binders to meet the requirements of the foundries. Likewise aerogels are known. The binders are optimized to the applications in their chemical composition to meet the conflicting requirements, such as An example of high thermal stability with low outgassing and low binder use and yet easy gutting and high surface quality.
• binders of the prior art can not yet be regarded as optimal at the present time. Adhesion of molten metal to the mold and core material as well as the mineralization of the casting surface affect the casting quality, the demolding and the coring as well as the subsequent use of the casting. Almost all binders are difficult to remove on filigree or complex shaped castings, leaving buildup and mineralization, and a coarse, rough casting surface.
• the problem underlying the present invention is solved by a foundry scientist comprising sand, binder and resorcinol-formaldehyde airgel granules (RF airgel granules).
• Binders for the sands may be inorganic or organic in nature, the inorganic binders being divided into natural and synthetic inorganic binders.
• Natural inorganic binders include clays such as montmorillonite, glauconite, kaolinite, illite or attapulgite.
• Synthetic inorganic binders include, among others, water glass, cement and gypsum.
• Organic binders include synthetic resins such as phenolic, urea and furan resins as well as ethyl silicate.
• Oils, carbohydrate binders, water-soluble liquid binders based on sulfite waste liquors, molasses, dextrose processes, alkanolamines and pitch binders are still used ( KE Höner "Founding", Ullmann's Encyclopedia of Industrial Chemistry, pp. 271-287, Vol. 12, 4th edition, Verlag Chemie Weinheim, 1976 ).
• RF aerogels according to the invention comprise colloidal substances which are gelled and subcritically dried. They have a low density and high, open porosity. They consist only of about 10 to 30 vol .-% of a solid, while the rest of their volume through the it is filled surrounding gas or even a vacuum, that is, they have a high surface area (up to 50 - 300 m 2 / g).
• Inorganic aerogels but also, for example, the RF airgel of the present invention as an organic airgel are usually inherently hydrophilic. Aerogels are considered one of the lightest materials and the best heat insulators.
• Airgel granules are obtained in particular by the milling of airgel monoliths.
• Hydrophilic means water-loving, that is, the used RF-Aerogelgranulat shows a strong interaction with polar solvents such as water.
• the hydrophilic RF aerogels used have a wetting angle with water of ⁇ 10 °.
• a possible explanation for the improvements observed by the foundry core according to the invention could be related to the fact that the RF aerogels used have macroscopic dimensions but are nanostructured (like all aerogels).
• the use of a sufficient proportion of this airgel granules could now cause the melt can no longer adequately wet the mold sufficiently reactive, since the nanostructure of the airgel granules only punctiform contacts allows. In this way, attachments and mineralization would be suppressed. It is surprising, however, that such an effect can be achieved with an organic airgel, since it inevitably at least partially decomposes under the thermal stresses during the casting, that is charred to form a carbon airgel granulate.
• the castings obtained via the use of the foundry cores according to the invention prove to be very smooth (exact casting quality), adhesions and mineralization are clearly suppressed compared to castings of the prior art.
• the sand preferably comprises quartz sand, an Al 2 O 3 -based and / or a mullite-based sand.
• corundum sands of similar size (0.1 to 0.9 mm) can also be used.
• the quartz sands shown above are new sands, in fact these are only added to the "old sands" in foundries to a limited extent.
• Used sand is the sand that accumulates when the castings are emptied out of the molds, which, after appropriate cooling and reconditioning, is returned to the molding shop.
• the reprocessing has two tasks to accomplish: cleaning the quartz grain from adhering binders and removing dusty constituents. In this process, any remaining agglomerates are mechanically comminuted and thus the binder coats partially removed from the quartz grains. In this process, the originally rather rounded surface of the grain of sand undergoes a change. From around she is too fragmented. This grain shape is important for the process of forming material, thus ensuring that only a comparatively small amount of binder is needed.
• the mixture of which the foundry core is made a sand content of 83 to 95 wt .-% wherein here 1 to 20 wt .-% virgin sand and 80 to 99 wt .-% regenerate (cycle molding material, that is purified recycled sand) preferred are.
• the addition of regenerated sand can be dispensed with, especially in red, brass and bronze castings.
• the proportion of binder is preferably 1 to 10 wt .-%.
• Sand, binder and Airogelgranulatanteil (and optionally the proportions of other ingredients) add up to 100 wt .-% or vol .-%.
• the airgel granules preferably have a particle size distribution in the order of magnitude of the sand.
• the airgel granules and / or the sand have / have a particle size distribution in a range from 0.1 to 0.9 mm.
• the airgel granules preferably have a particle size / particle size distribution in a range of ⁇ 0.5 mm.
• the proportion of airgel granules is preferably in a range from 5 to 15, particularly preferably from 8 to 12,% by volume. Alternatively or cumulatively, the proportion of airgel granules in the core is in a range from 0.18 to 0.93, in particular from 0.5 to 0.75 wt .-%.
• the binder is preferably an organic binder, in particular a binder or a binder mixture which comprises at least one member selected from phenolic resins, urea resins, furan resins, polyurethane resins and resorcinol-formaldehyde resins and RF airgel binders.
• Organic binders have been found to be preferred, as charring of the binder occurs during casting and this contributes to further ease of gutting and reduces mineralization.
• the compaction is done for example by core shooting, shaking, tapping and / or pounding.
• temperatures of 20 to 300 ° C have been found to be particularly suitable, in particular 80 to 250 ° C.
• the duration of the curing is preferably a few seconds to minutes. Drying of foundry cores is either completed after curing or by storage of the cores at room temperature or at temperatures above room temperature to 300 ° C from 1 to 24 hours or in the microwave.
• the object underlying the invention is achieved by the use of the foundry core according to the invention in metal casting, in particular in non-ferrous metal, light metal or cast iron.
• the core is removed after the solidification of the melt by a thermal treatment at elevated temperature, in particular a temperature of ⁇ 350 ° C, or mechanically (shaking, ultrasound, knocking).
• the removal with a thermal treatment is advantageous because here the core decomposes without leaving any residue.
• RF airgel granules were used.
• monoliths were prepared via the sol-gel process to produce RF airgel granules.
• the following molar ratios were used: resorcinol (MERCK, very pure) to water (deionized): 0.044, formaldehyde (VWR, 37%, aqueous solution) to resorcinol: 1.38 and resorcinol to catalyst (sodium carbonate anhydrous for analysis, Merck): 1,512.63.
• resorcinol MERCK, very pure
• VWR formaldehyde
• VWR formaldehyde
• resorcinol to catalyst sodium carbonate anhydrous for analysis, Merck
• RF Aerogel binder proved to be particularly advantageous:
• sand mixture (MinSand 230 / natural sand, mixing ratio 1: 0.208), 10% by volume of RF airgel granules (3.4 g, grain size ⁇ 0.5 mm) and 62 g of RF binder (own production , Sol aqueous solution, composition according to the molar ratios: resorcinol (MERCK, purest) to water (deionized): 0.044, formaldehyde (VWR, 37%, aqueous solution) to resorcinol: 1.38 and resorcinol to catalyst (sodium carbonate anhydrous to Analysis, Merck): 1512.63).
• resorcinol resorcinol
• VWR formaldehyde
• VWR formaldehyde
• resorcinol to catalyst sodium carbonate anhydrous to Analysis, Merck

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Dispersion Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Mold Materials And Core Materials (AREA)

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• 2008
  • 2008-11-12 DE DE102008056856A patent/DE102008056856A1/de not_active Withdrawn
• 2009
  • 2009-11-06 EP EP09175206.3A patent/EP2204246B1/fr active Active

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