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
• • 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
  • B22C1/186—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 contaming ammonium or metal silicates, silica sols
  • B22C1/188—Alkali metal silicates
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C9/00—Moulds or cores; Moulding processes
  • B22C9/02—Sand moulds or like moulds for shaped castings
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C9/00—Moulds or cores; Moulding processes
  • B22C9/18—Finishing

Definitions

• the invention relates to a coating composition for molds and their use.
• the coating composition is suitable for cores and molds, especially those made using water glass as a binder.
• the coating composition comprises certain clay materials. Likewise, a method for sizing is claimed.
• Molds are available from a refractory material, such as quartz sand, to form into a casting mold and set by a suitable binder to ensure sufficient mechanical strength of the mold.
• a refractory molding material such as quartz sand
• a suitable binder for the production of molds is thus used a refractory molding material and a suitable binder.
• the refractory molding base material is preferably present in a free-flowing form, so that it can be filled into a suitable mold and compacted there.
• the binder produces a firm cohesion between the particles of the molding base material, so that the casting mold obtains the required mechanical stability.
• both organic and inorganic binders can be used, the curing of which can be carried out in each case by cold or hot processes.
• Cold processes are processes which are carried out essentially at room temperature without heating the casting mold.
• the curing is usually carried out by a chemical reaction, which is triggered for example by the fact that a gas is passed as a catalyst through the mold to be cured.
• hot processes the molding material mixture is heated to a sufficiently high temperature after molding to expel, for example, the solvent contained in the binder or to initiate a chemical reaction by which the binder is cured, for example, by crosslinking.
• Binder systems have been developed which can be cured by the introduction of gases. Such a system is for example in the GB 782205 described in which an alkali water glass is used as a binder, which can be cured by the introduction of CO 2 .
• an exothermic feeder composition containing an alkali metal silicate as a binder In the US 6972059 B1 describes an exothermic feeder composition containing an alkali metal silicate as a binder.
• binder systems have been developed which are self-curing at room temperature. Such, based on phosphoric acid and metal oxides system is eg in the US 5,582,232 described.
• inorganic binder systems are known which are cured at higher temperatures, for example in a hot tool.
• Such thermosetting binder systems are for example from US 5,474,606 in which a binder system consisting of alkali water glass and aluminum silicate is described.
• the waterglass-based binder system consists of an aqueous alkali silicate solution and a hygroscopic base, such as sodium hydroxide, added in a ratio of 1: 4 to 1: 6.
• the water glass has a modulus SiO 2 / M 2 O of 2.5 to 3.5 and a solids content of 20 to 40%.
• the binder system also contains a surface-active substance, such as silicone oil, which has a boiling point ⁇ 250 ° C.
• the binder system is mixed with a suitable refractory material, such as quartz sand, and then injected into a core box with a core shooter.
• a suitable refractory material such as quartz sand
• the hardening of the molding material mixture takes place by removal of the water still contained.
• the drying or hardening of the casting mold can also take place under the action of microwaves.
• inorganic binders also have disadvantages compared to organic binders, for example the known inorganic binders have a low stability of the casting molds produced therewith against high humidity or against water. For a storage of the molded body over a longer period, as usual with organic binders, not secured possible.
• the US 7770629 B2 proposed a molding material mixture containing a water-based binder in addition to a refractory molding material. A proportion of a particulate metal oxide is added to the molding material mixture. Precipitated silica or fumed silica is preferably used as the particulate metal oxide.
• the methods described for the production of molds and cores usually also include the application of a refractory mold coating, which is also called sizing, at least on those surfaces of the basic shape, which come into contact with the cast metal.
• a refractory mold coating which is also called sizing, at least on those surfaces of the basic shape, which come into contact with the cast metal.
• the purpose of the mold coatings is to influence the molding surface, to improve the casting appearance, to metallurgically influence the casting and / or to avoid casting defects.
• the commonly used sizing agents contain as base materials e.g. Clays, quartz, kieselguhr, cristobalite, tridymite, aluminum silicate, zirconium silicate, mica, chamotte and also coke and graphite. These bases are the purportive portion of the sizings which cover the mold surface and close the pores against the penetration of the cast metal.
• the surface of the casting mold can be modified and matched to the properties of the metal to be processed.
• the size can be used to improve the appearance of the casting by creating a smooth surface because the size compensates for irregularities caused by the size of the grains of the molding material.
• the sizing may metallurgically influence the casting by, for example, selectively transferring additives to the casting at the surface of the casting via the sizing which enhance the surface properties of the casting.
• the sizings form a layer which chemically isolates the casting mold from the liquid metal during casting. This prevents any adhesion between the casting and the casting mold so that the casting can be easily removed from the casting mold.
• the sizing can also be used to specifically control the heat transfer between the liquid metal and the casting mold in order, for example, to effect the formation of a specific metal structure by the cooling rate.
• the curing of the inorganic binder used is nowadays increasingly via a condensation reaction initiated by elevated temperatures, in which the formation of the binder bridges takes place via the splitting off of water.
• this is a reversible reaction, i. by contact and reaction with water, the bonds can be cleaved again, the extent of this back-reaction is highly dependent on the process parameters for core production.
• the process parameters typically used in series production fast cycle times, high temperatures
• the casting molds lose their strength through contact with water and partly also through contact with alcohol, the surface softens and the casting mold loses its shape.
• the invention had the object of proposing a sizing, by which a defect-free coating, especially inorganic cores and molds, can be ensured without negatively affecting the stability of the cores or molds and thus the processing and storage.
• the sizing composition according to the invention is provided according to a preferred embodiment in the form of a paste or a suspension.
• the sizing composition contains a carrier liquid.
• the total clay content of the size of the above clays is 0.1 to 4.0% by weight, preferably 0.5 to 3.0% by weight and more preferably 1.0 to 2.0% by weight.
• Palygorskit is a magnesium-aluminum hydrosilicate, which under the CAS no. 8031-18-3 is listed. Palygorskit is part of attapulgite marketed commercial products. Attapulgite contains Palygorskit, but should not be used because of other disturbing components and missing rod-shaped crystals. Palygorskite is in the form of rod-shaped crystals. The particles have the following dimension: 1 to 3 .mu.m, in particular 1.5 to 2 .mu.m in length with a diameter of 1 to 5 nm, in particular about 3 nm.
• Palygorskit has other properties than attapulgite. Palygorskit does not swell or shrink, is shear stable and leads in a slurry with water or water-based liquids with (A2) or (A3), for example, at low levels such as 0.01 to 3 wt.%, To a pseudoplastic or thixotropic liquid , When the shear stops, the higher initial viscosity quickly recovers. With shear the viscosity is low. Attapulgite is loaded with smectite, SiO 2 , and / or CaCO 3 and other impurities.
• palygorskite e.g. the product Acti-Gel® 208 of the company "Active Minerals” can be used.
• hectorite e.g. Bentone CT of the company “Elementis” are used.
• the sizing composition e.g. as a basecoat or as a topcoat, and desired layer thickness of the coating made from the sizing composition, other characteristic parameters of the sizing composition may be adjusted.
• the carrier liquid may be proportionate or completely formed by water.
• the carrier liquid is the constituent which is vaporizable at 160 ° C and atmospheric pressure and in this sense, by definition, that which is not solids content.
• the carrier liquid contains greater than 50% by weight, preferably 75% by weight, in particular greater than 80% by weight, if appropriate greater than 95% by weight of water.
• the other ingredients in the carrier liquid may be organic solvents.
• Suitable solvents are alcohols, including polyhydric alcohols and polyether alcohols.
• Exemplary alcohols are ethanol, n-propanol, isopropanol, butanol and glycol.
• the solids content of the ready-to-use size composition is preferably adjusted in the range from 10 to 90% by weight, in particular greater than 80% by weight to 85% by weight.
• the size composition according to the invention may contain further constituents customary for sizes.
• the sizing composition according to the invention comprises at least one pulverulent refractory material.
• This refractory material serves to close the pores in a mold against the penetration of the liquid metal.
• the refractory thermal insulation between the mold and liquid metal is achieved by the refractory thermal insulation between the mold and liquid metal.
• refractory material conventional refractory materials can be used in metal casting.
• Suitable refractory materials are quartz, aluminum oxide, zirconium oxide, aluminum silicates such as pyropyllite, kyanite, andalusite or chamotte, zirconium, ciconsilicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolins, calcined kaolins, kaolinite, metakaolinite, iron oxide and / or bauxite.
• the refractory material is provided in powder form.
• the grain size is chosen so that a stable structure is produced in the coating and that the size can preferably be distributed without problem on the wall of the casting mold by means of a spraying device.
• the refractory material has an average kite size (measured by means of light scattering in accordance with DIN / ISO 13320) in the range from 0.1 to 500 ⁇ m, particularly preferably in the range from 1 to 200 ⁇ m.
• materials are suitable as a refractory material which have a melting point which is at least 200 ° C. above the temperature of the liquid metal and, irrespective of this, do not react with the metal.
• the proportion of refractory (e.g. in the form of sale paste, based on the solids content of the size composition, is preferably greater than 70 wt .-%, preferably greater than 80 wt .-%, more preferably greater than 85 wt .-% selected.
• the fraction of the refractory material for use after dilution (eg the paste) with water is less than 80% by weight, according to another embodiment less than 70% by weight and according to further embodiment selected less than 60 wt .-%.
• the size according to the invention may comprise at least one setting agent.
• the adjusting agent causes an increase in the viscosity of the size, so that the solid components of the size in the suspension do not or only to a small extent decrease.
• organic and inorganic materials or mixtures of these materials can be used.
• Suitable inorganic actuators are, for example, highly swellable clays, e.g. Sodium bentonite.
• organic thickening agents may alternatively or additionally be selected, since these can be dried to the extent that they hardly give off any more water upon contact with the liquid metal after application of the protective coating.
• Suitable organic adjusting agents are, for example, swellable polymers, such as carboxymethyl, methyl, ethyl, hydroxyethyl and hydroxypropyl cellulose, mucilages, polyvinyl alcohols, polyvinylpyrrolidone, pectin, gelatin, agar agar, polypeptides and / or alginates.
• the proportion of the adjusting agent, based on the total size composition is preferably selected to be from 0.1 to 5% by weight, preferably from 0.5 to 3% by weight, particularly preferably from 1 to 2% by weight.
• the size according to the invention comprises as further constituent at least one binder.
• the binder allows for better fixation of the size or of the protective coating prepared from the size on the wall of the mold.
• the binder increases the mechanical stability of the protective coating so that less erosion is observed under the action of the liquid metal.
• the binder cures irreversibly, so that an abrasion-resistant coating is obtained.
• binders which do not soften upon contact with atmospheric moisture. All binders which are used in sizing can be contained per se. Both inorganic and organic binders can be used. For example, clays can be used as binders, in particular bentonite.
• the proportion of the binder is preferably selected in the range of 0.1 to 20 wt .-%, particularly preferably 0.5 to 5 wt .-%, based on the solids content of the sizing composition.
• the size contains a proportion of graphite.
• the proportion of graphite is preferably selected in the range of 1 to 30 wt .-%, particularly preferably 5 to 15 wt .-%, based on the solids content of the size.
• Graphite has a favorable effect on the surface quality of castings during iron casting.
• the size composition according to the invention may also contain further components customary for sizing, for example wetting agents, defoamers, pigments, dyes or biocides.
• the proportion of these further constituents in the ready-to-use coating composition is preferably less than 10% by weight, preferably less than 5% by weight and more preferably less than 1% by weight.
• Suitable wetting agents are, for example, anionic and non-anionic surfactants, in particular those having an HSB value of at least 7.
• An example of such a wetting agent is disodium dioctyl sulfosuccinate.
• the wetting agent is preferably used in an amount of 0.01 to 1 wt .-%, preferably 0.05 to 0.3 wt .-%, based on the ready-to-use sizing composition.
• Defoamers or anti-foaming agents, can be used to prevent foaming in the preparation of the sizing composition or in applying it. Foaming on application of the sizing composition can result in uneven layer thickness and holes in the coating.
• defoamers for example, silicone or mineral oil can be used.
• the defoamer is preferably present in an amount of from 0.01 to 1% by weight, preferably from 0.05 to 0.3% by weight, based on the ready-to-use sizing composition.
• pigments and dyes may be used in order to achieve a different contrast, for example between different layers, or to bring about a greater separation effect of the size of the casting.
• pigments are red and yellow iron oxide and graphite.
• dyes are commercially available dyes such as the Luconyl ® color range of BASF AG, Ludwigshafen, Germany.
• the dyes and pigments are preferably contained in an amount of 0.01 to 10 wt .-%, preferably from 0.1 to 5 wt .-%, based on the solids content of the sizing composition.
• the sizing composition contains a biocide to prevent bacterial attack, thereby avoiding a negative impact on the rheology and binding power of the binding agents.
• the carrier liquid contained in the sizing composition is formed substantially in water with respect to the weight, that is, the sizing composition according to the invention is provided in the form of a so-called water sizing.
• suitable biocides are formaldehyde, 2-methyl-4-isothiazolin-3-one (MIT), 5-chloro-2-methyl-4-iosthiazolin-3-one (CIT) and 1,2-benzisothiazolin-3-one (BIT).
• MIT, BIT or a mixture thereof are used.
• the biocides are usually used in an amount of from 10 to 1000 ppm, preferably from 50 to 500 ppm, based on the weight of the ready-to-use sizing composition.
• the size composition of the invention can be prepared by conventional methods.
• a sizing composition according to the present invention can be prepared by initially charging water and breaking up a clay acting as a sizing agent using a high shear stirrer. Subsequently, the refractory components, pigments and dyes and the metallic additive are stirred until a homogeneous mixture is formed. Finally, wetting agents, antifoams, biocides and binders are added.
• the sizing composition according to the invention can be prepared and sold as ready-to-use sizing.
• the size according to the invention can also be prepared and sold in concentrated form. In this case, to provide a ready-to-use size, the amount of carrier liquid necessary to adjust the desired viscosity and density of the size is added.
• the size composition according to the invention can also be provided and sold in the form of a kit, wherein, for example, the solid component (s) and the solvent component (s) are present side by side in separate containers.
• the solid component (s) can be provided as a powdery solid mixture in a separate container.
• further liquid component (s) to be used e.g. Binders, wetting agents, wetting agents / defoamers, pigments, dyes and biocides may in turn be present in a separate container in this kit.
• the solvent component (s) may comprise either the optional additional components to be used, e.g. in a common container, or it may be separate from other optional components in a separate container. To prepare a ready-to-use size, the appropriate amounts of the solid component, the optional further components and the solvent component are mixed together.
• the sizing compositions according to the invention are suitable for coating casting molds.
• the term "mold” includes all types of bodies necessary to make a casting, such as cores, molds and molds.
• the use of the size compositions according to the invention also includes partial coating of casting molds.
• the sizings are used for metal working molds obtainable from inorganic molding material mixtures comprising at least one refractory molding base, a water glass based binder, and preferably a portion of a metal oxide selected from the group of silica, in particular amorphous silica, alumina, titania or Zinc oxide and mixtures thereof, which is preferably particulate and in particular has particle sizes of less than 300 microns (sieve analysis).
• Amorphous silica is accessible, for example, via precipitation processes starting from water glass, which is obtainable by digesting quartz sand with sodium carbonate or potassium carbonate. SiO 2 produced in this way is called precipitated silica depending on the process conditions.
• Another important production variant is the production of so-called pyrogenic SiO 2 in a blast gas flame, starting from liquid chlorosilanes such as silicon tetrachloride.
• the mold is then removed from the sizing composition and excess sizing composition drained from the mold.
• the time taken to drain the excess sizing composition after dipping depends on the flow behavior of the sizing composition used.
• the sizing composition is filled in a dilute state in a pressure vessel.
• the sizing can be pressed into a spray gun via the overpressure to be set, where it is sprayed with the aid of separately adjustable atomizing air.
• the conditions are preferably selected so that the pressure for sizing composition and atomizing air are adjusted to the gun such that the sprayed sizing composition still wet on the mold or the core, but gives a uniform application.
• the casting mold in the mold cavity of which optionally a base coat has been applied, is poured over with the aid of a hose, a lance or similar instruments with a ready-to-use size composition according to the invention.
• the mold is completely covered with the sizing composition, the excess sizing composition drains from the mold.
• the time taken for the flow of excess sizing composition after flooding depends on the flow behavior of the sizing composition used.
• the sizing can also be applied by brushing.
• the carrier liquid contained in the size is then evaporated so that a dry sizing layer is obtained.
• any conventional drying method can be used, such as air drying, dehumidified air drying, microwave or infrared radiation drying, convection oven drying, and similar methods.
• the coated casting mold is dried at 20 to 250 ° C, preferably at 50 to 180 ° C, in a convection oven.
• the size composition according to the invention is preferably dried by burning off the alcohol or alcohol mixture.
• the coated casting mold is additionally heated by the heat of combustion.
• the coated casting mold is dried in the air without further treatment or using microwaves.
• the size can be applied in the form of a single layer or in the form of several layers arranged one above the other.
• the individual layers may be the same or different in their composition.
• a base coat can be made from a commercially available size which does not contain a metallic additive according to the invention.
• a primer coating for example, water-based or alcohol-based sizing can be used.
• the layer which later comes in contact with the liquid metal is always made from the size of the invention.
• each individual layer can be completely or partially dried after application.
• the coating prepared from the sizing composition preferably has a dry film thickness of at least 0.1 mm, preferably at least 0.2 mm, more preferably at least 0.45 mm, most preferably at least 0.55 mm.
• the thickness of the coating is chosen to be less than 1.5 mm.
• the dry layer thickness here is the layer thickness of the dried coating, which was obtained by drying the sizing composition by substantially complete removal of the solvent component and optionally subsequent curing.
• the dry layer thickness of the base coat and the top coat are preferably determined by measurement with the wet film thickness comb. If necessary, the casting mold can then be completely assembled. The casting is preferably carried out for the production of cast iron and steel castings.
• the core sizes 1 and 2 used had the compositions and physical properties shown in Tables 1 and 2.
• Table 1 Composition of the sizes Simple 1 Simple 2 Name, company (name) % By weight % By weight water 15.0 21.0 Attagel 40; Solvadis (attapulgite) - 1.2 Actigel 208, Active Minerals (Palygorskit) 0.3 - Bentone CT, Elementis (hectorite) 0.4 - Volclay, South chemistry (sodium bentonite) 0.6 0.6 Zirconium flour 45 ⁇ m 30.5 24 Zirconia 75 ⁇ m 51 51 PVA solution (25%) 1.2 1.2 Surfynol® SEF (wetting agent 1) 0.2 0.2 Dynol® 604 (wetting agent 2) 0.05 0.05 Foamstar® MF324 (defoamer) 0.2 0.2 Acticide® F (N) (Preservative 1)
• the cast molding was prepared as follows: water is initially introduced and the clay or clays are digested for at least 15 minutes using a high-shear unit and a toothed disc. Subsequently, the refractory components, pigments and dyes are stirred for at least 15 minutes until a homogeneous mixture is formed. Finally, additives such as wetting agents, defoamers and preservatives and the binder are stirred for 5 minutes.
• non-patented sizing composition the products available from the company ASK Chemicals Trioflex® WK-HP or Solitec® W 3 can be used.
• Georg Fischer test strip illustrates the behavior of the sized test specimens on thicker core geometries
• long cores illustrates the behavior of the sized test specimens on thin geometries.
• Georg Fischer test bars are cuboid test bars measuring 150 mm x 22.36 mm x 22.36 mm.
• the long cores have dimensions of 13 mm x 20 mm x 235 mm.
• the composition of the molding material mixture is given in Table 3.
• the Georg Fischer test bars were prepared as follows: The components listed in Table 3 were mixed in a laboratory paddle mixer (Vogel & Schemmann AG, Hagen, DE).
• the quartz sand was introduced and added with stirring the water glass.
• a sodium water glass was used, which had proportions of potassium.
• the modulus SiO 2 : M 2 O of the water glass was about 2.2, where M is the sum of sodium and potassium.
• amorphous silica was added, if necessary, with further stirring.
• the amorphous silica is pyrogenic silica from RW silicon. The mixture was then stirred for an additional 1 minute.
• the molding material mixture was transferred to the storage bunker, a H 2.5 hot-box core shooter from Röperwerk-G manmaschinen GmbH, Viersen, DE, whose mold was heated to 180.degree.
• the molding material mixture was introduced into the mold by means of compressed air (5 bar) and remained in the mold for a further 35 seconds.
• hot air (2 bar, 150 ° C on entering the mold) was passed through the mold during the last 20 seconds. The mold was opened and the test bars removed.
• the coating compositions were applied to the test bars by dipping, the application parameters are listed in Table 2.
• the test bars were coated either immediately after removal from the mold or after a 30 minute cooling time.
• the coated test bars were stored after application of the coating in a drying oven for 30 minutes at 150 ° C.
• test bars were placed in a Georg Fischer strength tester equipped with a 3-point bending device (DISA Industrie AG, Schaffhausen, CH), and the force was measured, which leads to the breakage of the test bars.
• the quality of the inorganic cores and molds coated with these sizes is sustainably improved and, for example, a storage stability of the cores and forms of several days can be achieved without problems.
• Particularly noteworthy here is that despite the unusually high solids content, the viscosity of the size is in a range customary for sizing. The size can be brought into the application state without the use of special additives or larger amounts of water.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Mold Materials And Core Materials (AREA)
• Paints Or Removers (AREA)
• Silicates, Zeolites, And Molecular Sieves (AREA)

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• 2011
  • 2011-09-30 DE DE102011114626A patent/DE102011114626A1/de not_active Withdrawn
• 2012
  • 2012-10-01 RU RU2014117287/02A patent/RU2014117287A/ru not_active Application Discontinuation
  • 2012-10-01 CN CN201280047222.8A patent/CN103826775A/zh active Pending
  • 2012-10-01 EP EP12773196.6A patent/EP2760607B1/de not_active Not-in-force
  • 2012-10-01 MX MX2014003804A patent/MX2014003804A/es unknown
  • 2012-10-01 BR BR112014007623A patent/BR112014007623A2/pt not_active IP Right Cessation
  • 2012-10-01 US US14/348,232 patent/US20140255601A1/en not_active Abandoned
  • 2012-10-01 JP JP2014532247A patent/JP2014527915A/ja active Pending
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• 2014
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