Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C3/00—Selection of compositions for coating the surfaces of moulds, cores, or patterns
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K7/00—Use of ingredients characterised by shape
  • C08K7/22—Expanded, porous or hollow particles
  • C08K7/24—Expanded, porous or hollow particles inorganic
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
  • C09D5/18—Fireproof paints including high temperature resistant paints

Definitions

• the invention relates to a size or, in general, to a coating material which is used in foundry technology for coating foundry moldings, such as molds, cores and models.
• Ready-to-use sizes are suspensions of fine-grained refractory to highly refractory inorganic materials in a carrier liquid, which are applied to the molded parts by a coating process adapted to the respective application, for example by brushing, spraying, pouring or dipping, drying there and thus forming the desired coating.
• the fine-grained refractory to highly refractory inorganic materials represent the part of a size intended for casting purposes. They are also referred to as "base materials” and are suspended in the carrier liquid with the aid of suspending agents. In the carrier liquid, binders are also still used, which serve to fix the base material particles on the surface of the molded part after the liquid has been removed. If necessary, wetting agents, defoamers and Bactericides are added.
• Typical examples of basic materials include (individually or in a mixture with one another) mineral oxides such as corundum, magnesite, mullite, quartz and chromite, also also silicates such as zirconium silicate, olivine and chamotte and also coke and graphite. Swellable sheet silicates or cellulose derivatives which are capable of storing water are used as suspending agents.
• the carrier liquid can be water or a solvent such as light petroleum, methanol, ethanol, isopropanol or isobutanol, and starch derivatives such as dextrins, lignin derivatives such as lignin sulfonates, natural resins, synthetic resins or plastics such as PVA are suitable as binders, the binders corresponding to theirs Solubility in the carrier liquid can be selected.
• a solvent such as light petroleum, methanol, ethanol, isopropanol or isobutanol
• starch derivatives such as dextrins, lignin derivatives such as lignin sulfonates, natural resins, synthetic resins or plastics such as PVA are suitable as binders, the binders corresponding to theirs Solubility in the carrier liquid can be selected.
• the coatings are intended to perform the following tasks in foundry technology:
• Tasks 1 and 2 can generally be performed well by combining different suitable raw materials, and task 4 is only a peripheral area, because metallurgically effective sizes, e.g. with sulfur, are only partially used. With regard to task 3, however, there is still a need for action.
• Task 3 is becoming increasingly important today and in the future because all resin-bonded sand molds and cores tear at high temperatures due to the expansion of the sand and the melt then penetrates into the mold or core. The elimination of the resulting surface Defects from the casting is very difficult and time consuming.
• Mold coating materials have already been developed and used which counteract these errors and which, for example, in the literature references J. Levelink, foundry, year 66; 1979 pp. 456-458 and D. Bartsch, Report of Technica l Forum, 58th World Foundry Congress. Krakow 1991, are described.
• the mode of action of such coatings is based on the fact that platelet-like layered silicates such as kaolinite, pyrophillite, talc and mica are used as the base material and can be deformed better under the action of tensile stress.
• the mineral substances are combined in such a way that temporary softening phases form, which likewise improves the deformability of the coating.
• the invention is intended to provide an improved size which avoids the shortcomings described above and which, with unchanged good casting properties, permits the production of coatings with high gas permeability.
• This goal is achieved according to the invention in that the size, in addition to the fine-grained or platelet-shaped base material, also contains inorganic hollow spheres, in an amount of 1-40% by weight, based on the ready-to-use size.
• inorganic hollow spheres is understood to mean small gas-filled hollow spheres with a diameter of the order of 5 to 500 ⁇ m (preferably 60 to 250 ⁇ m), the shell of which consists of silicates, in particular of aluminum, calcium, magnesium and / or zircon, from oxides like Aluminum oxide, quartz, magnesite, mullite, chromite, zirconium oxide and / or titanium oxide, borides, carbides and nitrides such as silicon carbide, titanium carbide, titanium boride, boron nitride and / or boron carbide, made of carbon, glass or metals such as copper and the like Gas filling is usually a mixture of inert gases, for example consisting of 70% CO 2 and 30% N 2 . These hollow spheres have been developed in recent times and are used in particular as a light filler for plastics.
• fibers with a diameter of 1 to 30 ⁇ m (preferably 3 to 10 ⁇ m) and a length of 10 to 5000 ⁇ m (preferably 100 to 500 ⁇ m), inorganic fibers e.g. from aluminum silicates, zirconium oxide, aluminum oxide, titanium oxide, carbon, silicon carbide, titanium carbide, titanium boride, boron nitride, boron carbide, glass, basalt and mineral wool can be used as well as fibers made from organic material.
• the organic fibers can be plastic fibers of all kinds or natural fibers such as Cellulose fibers.
• fibers compared to hollow spheres, fibers have the considerable disadvantage that they cannot be easily introduced into sizes and that the processability of such sizes is also poorer. Thus, high shear forces are necessary when introducing fibers to ensure adequate uniform distribution, because fibers tend to form clumps.
• a smooth application is hardly possible when processing fiber-containing sizes because, for example, the fibers are drawn through the brush bristles when brushing. For this reason, only small amounts of fibers are used in the invention, and only when otherwise sufficient strength of the coating cannot be achieved.
• the gas permeability of size coatings can be significantly improved without adversely affecting the desired casting properties if the size contains a proportion of these hollow spheres, possibly with the addition of small amounts of fiber materials. This enables the deficiencies described at the beginning to be eliminated without having to accept other disadvantages. Due to their shape, the hollow spheres can be easily introduced into sizes, and the processability of such sizes corresponds to that of conventional sizes, with an even shorter drying time of the coatings being found.
• the insulating properties of the hollow spheres and the gas-permeable coatings cause a delayed heat transfer through the size into the molding material.
• the hollow spheres later melt in the casting heat and / or break under the casting pressure, as a result of which numerous micro-defects occur in the size coating, through which the coating acquires an extremely high gas permeability without becoming permeable to the casting metal.
• An advantageous side effect of the melting and / or breaking of the hollow spheres also consists in the fact that the inert gas filling of the spheres is released and takes on a protective gas function, which the Protects metal surface against oxidation.
• the invention can be used universally in all types of sizes. It is of particular importance in the case of those sizes which contain platelet-shaped base material particles and is almost indispensable for the practical usability of such sizes. But the advantages of the invention also apply to other sizes, because the fine-grained base particles of conventional sizes can also form relatively dense packs because the grains usually have an angular to splintered shape.
• the invention creates a size which is suitable for all uses and which allows the gas permeability and mechanical strength of the coatings to be adapted to the requirements of the casting process with the aid of fibers and hollow spheres or solely hollow spheres, the drying speed is increased and good deformability and smooth surfaces remain guaranteed.
• Size A none none (comparative example) Size B 10% by weight no size C 5% by weight 1% by weight Size D 10% by weight 1% by weight
• Size E none none (comparative example) Size F 10% by weight no size G 4% by weight 1% by weight
• hollow spheres made of aluminum silicate were used, the particle size of which was 80% between 250-90 ⁇ m.
• Fibers were aluminum silicate fibers with an average diameter of 3 ⁇ m and a length of ⁇ 3 mm.
• the sizes AF were applied to portafilter, and then their gas permeability was determined using a test device + Georg Fischer +, in which air was pressed through the samples at a predetermined pressure and the amount of air passed in the time unit was measured.
• the attached graphic shows the gas pressure curve of a coldbox core, which has been conventionally constructed with a coating material (size A), compared to an unfinished core (0).
• the determination was carried out using cylindrical coldbox cores which melt in a Eisen ⁇ of about 1430 * C were immersed.
• the gas pressure generated in the core was measured as a function of the diving time and is given in centimeters of iron column.
• the plain core After an initial maximum still a second gas pressure maximum at a later point in time, while only one initial maximum and two smaller further pressure maxima are observed in the unclosed core. (The non-butchered core has the maximum possible highest gas permeability).
• the graph shows the gas pressure curve of a coating material (size C) according to the invention. Only a high initial pressure maximum is observed. At the critical times during casting and solidification, no high gas pressure builds up here. The errors described above, such as gas bubbles and inclusions in the casting, do not occur.
• the sizes according to the invention show an excellent result in the evaluation of casting surfaces with regard to the stated requirements for sizes (points 2 and 3).
• the advantages of using hollow spheres or hollow spheres and fibers in sizes are due to the relevant properties of the hollow spheres for the casting process.
• Table 1 Water finishing with various hollow spheres / fiber components

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• 1993
  • 1993-05-17 DE DE9307468U patent/DE9307468U1/de not_active Expired - Lifetime
• 1994
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  • 1994-05-11 KR KR1019950700153A patent/KR950702459A/ko not_active Application Discontinuation
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  • 1994-05-11 CA CA002139871A patent/CA2139871A1/en not_active Abandoned
  • 1994-05-11 HU HU9500128A patent/HU213910B/hu not_active IP Right Cessation
  • 1994-05-11 CN CN94190284A patent/CN1109678A/zh active Pending
  • 1994-05-11 WO PCT/DE1994/000555 patent/WO1994026440A1/de active IP Right Grant
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• 1995
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