Classifications

• • 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
  • B22C9/02—Sand moulds or like moulds for shaped castings
  • B22C9/04—Use of lost patterns
  • B22C9/046—Use of patterns which are eliminated by the liquid metal in the mould
• • 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

Definitions

• the invention relates to a method for casting castings, in which molten metal is poured into a casting mold that encloses a cavity that forms the casting to be produced, the casting mold being a lost mold consisting of one or more casting mold parts or cores made of a molding material are formed, which consists of a core sand, a binder and optionally one or more additives to adjust certain properties of the molding material.
• the casting mold provided in each case is housed in a housing in such a way that a filling space is formed between at least one inner surface section of the housing and an associated outer surface section of the casting mold.
• the filling space is then filled with free-flowing filling material, the filling material filled into the filling space having such a low bulk density that the filling material packaging formed there from the filling material after the filling space has been filled can be traversed by a gas flow.
• the molten metal is poured into the casting mold that is housed in this way, with the casting mold beginning to radiate heat as the molten metal is poured in, which is the result of the heat input caused by the hot molten metal, and the binder of the molding material increasing as a result of the heat input caused by the molten metal vaporize and begin to burn, losing its effectiveness and causing the mold to crumble into fragments.
• quartz sands, mixed with bentonites, lustrous carbon formers and Water is used as the molding material for the mold parts that form the outer end of the mold.
• the casting cores forming the inner cavities and channels of the casting are usually formed from commercially available core sands, which are bound with an organic or inorganic binder, e.g. B. are mixed with a synthetic resin or water glass.
• the basic principle in the production of casting molds made from molding materials of the type mentioned above is that after shaping, the binder is cured by a suitable thermal or chemical treatment, so that the grains of the core sand stick together and the dimensional stability of the respective molded part or core is guaranteed over a sufficient period of time.
• the internal pressure on the casting mold after the molten metal has been poured off can be very high.
• either thick-walled, large-volume casting molds or supporting structures must be used that support the casting mold on its outside.
• the housing is usually designed in the manner of a jacket, which surrounds the casting mold on its peripheral sides, but has a sufficiently large opening at its top to allow the melt to be poured into the casting mold.
• the housing is dimensioned in such a way that, after it has been put on, a filling space remains between the inner surfaces of the housing and the outer surfaces of the casting mold, at least in the sections that are decisive for supporting the casting mold. This filling space is filled with a free-flowing product, so that a large-area support of the respective surface section on the enclosure is guaranteed.
• filling material In order to achieve the most even possible filling of the filling space, an equally even contact of the casting mold with the filling material and a correspondingly even support of the fragile casting mold material, fine-grained, free-flowing filling materials such as sand or steel shot are usually used as filling material, which have a high have bulk density. After filling, the filling material is additionally compressed.
• the aim here is to create the most compact filling compound possible, which, like an incompressible monolith, ensures the direct transmission of the supporting forces from the housing to the casting mold.
• the molten metal is poured into the mold at a high temperature, so that the mold parts and cores that make up the mold are also heated to a great extent. As a result, the mold begins to radiate heat. If the temperature of the casting mold exceeds a certain minimum temperature, the binder of the mold material begins to evaporate and burn, releasing more heat. The binder loses its effectiveness as a result. As a result of this decomposition of the binder, the binding of the grains of the molding material from which the casting mold parts and cores of the casting mold are made is lost and the casting mold or its parts and cores made of molding material disintegrate into individual fragments.
• WO 2016/016035 A1 proposed using a preheated filling material to fill the filling space between the mold and the housing, with the filling temperature of the filling material being so high that, starting from the filling temperature, the process heat generated by the Heat radiated from the mold and formed by the heat released during the combustion of the binder, the temperature of the filling material rises above a limit temperature at which the out of the mold evaporating binders that come into contact with the filling material ignite and begin to burn.
• the filling material is used in the sense of a heat accumulator, which is temperature-controlled and designed in such a way that the decomposition of the binder of the mold material, from which the casting mold parts and cores of the casting mold are made, progresses as far as possible during the dwell time in the housing due to the effects of temperature .
• the invention has solved this problem by the method specified in claim 1.
• the invention therefore provides a method for casting castings, in which, in accordance with the prior art explained above, molten metal is poured into a casting mold which encloses a cavity that represents the casting to be produced, the casting mold being a lost form of a or several casting mold parts or cores, which are formed from a molding material, which consists of a core sand, a binder and optionally one or more additives for setting certain properties of the molding material, comprising the following work steps:
• the filling material filled into the filling space having such a low bulk density that the filling material packaging formed there from the filling material after the filling space has been filled can be flowed through by a gas flow;
• the casting mold begins to radiate heat as a result of the heat input caused by the hot molten metal as the molten metal is poured in
• the filling material temperature which the filling material has when it is filled into the filling space, is limited to less than 100.degree. What is essential for the invention here is that the filling material is not heated in a targeted manner to a specific target temperature. Rather, the filling material is advantageously filled into the filling space at the temperature it currently has, ie which it has adopted as a result, for example, of the ambient temperature at the location where the filling material has been stored, or of process heat that occurs, for example, in recycling - process or the like stops.
• the filling material temperature provided according to the invention is preferably at least equal to the room temperature in the vicinity of the storage location of the filling material or the respective Casting device prevails, or with which the filling material reaches the casting device without targeted, active supply of heat, in the filling chamber of which it is filled.
• the filling material temperatures at which the filling material is filled into the filling space are typically in the range of 10° C. to 45° C., in particular 18-45° C., with typical room temperatures in the range of 10-25, depending on the time of year °C, in particular 18-25 °C.
• the method according to the invention can be improved compared to the prior art of the technology to implement significantly simplified plant engineering.
• the filling material can be actively or passively cooled if necessary.
• the invention thus allows the process of filling the filling space with the filling material to be decoupled in terms of time from the filling of the casting mold with the respective molten metal. Since it is no longer important that the filling material in the filling chamber has a certain high temperature, such as at least 500 °C, which is considered to be practical in the prior art, but has a temperature at which there is no unfavorable influence on the molding material of the casting mold, the filling space can be filled long before the molten metal is poured off.
• the process control becomes significantly more robust and stable thanks to the temporal decoupling of the filling process from the casting process. As a result, an optimized operational safety is achieved with a simple practical implementation of the method at the same time.
• the cooling of the cast part in the method according to the invention runs faster than in the prior art explained at the outset, since the filling material that is filled in cold, i.e. at a temperature of less than 100 °C, in particular at most 45 °C, preferably at room temperature, acts as a heat sink acts, through which heat is withdrawn from the casting mold until the temperature has equalized.
• the faster solidification of the cast part that is achieved in this way leads to increased dimensional stability of the workpiece. Since, in addition, the use of energy is avoided, which is required in the prior art for heating the filling material, the method according to the invention also proves to be more energy-efficient.
• the cores have also broken down into at least coarse fragments, which form channels or fleas inside the cast part, so that the core sand and the fragments of molding material from these cores either trickle out of the cast part automatically in the housing or in a known manner Way, can be removed from the casting, for example by mechanical methods such as shaking, or by flushing with a suitable fluid.
• the core sand fragments can be crushed, for example, in a conventional grinder.
• the regenerated sand obtained after processing can be mixed with new sand in a manner known per se.
• the method according to the invention is based on the idea of not only stabilizing the casting mold with the filling material, but also accelerating the removal of heat in order to produce high-precision castings in a technologically and economically expedient manner.
• the filling material filled according to the invention in the filling space formed between the cast part and the housing is free-flowing, so that it completely fills the filling space even if there are undercuts, cavities and the like in the area of the outer surfaces of the casting mold.
• the filling material used according to the invention has a bulk density that is so low that a gas flow can still flow through it even after the filling space has been filled and the filling material placed in the filling space has been compacted.
• no highly compressed packing is produced in the filling space, which does ensure optimal support of the casting mold but is largely impermeable to gas.
• the filling material used according to the invention should be selected in such a way that it is permeable to a gas flow is, which occurs, for example, as a result of thermal convection. This occurs when the casting mold is heated by the molten metal poured into it and the evaporating binder components of the molding material of the casting mold parts and cores begin to evaporate and begin to burn with the release of heat.
• Casting molds whose molded parts and cores consist of molding material bound by an organic binder are particularly suitable for the method according to the invention.
• Commercial solvent-based binders or those binders whose effect is triggered by a chemical reaction can be used for this purpose, for example.
• Corresponding binder systems are used today in the so-called "cold box process”.
• the filling material temperature, which the filling material has when it is filled into the filling space, is, as mentioned, selected according to the invention in such a way that even if the filling material is filled into the filling space before pouring, there are no negative effects on the mold material and in particular on the Set binder, through which holds together the grains of the molding material from which the parts and cores of the mold are formed.
• typical filling material temperatures provided according to the invention are in the range of up to 45.degree.
• the parts and cores of the casting mold made of molding material disintegrate into loose fragments, which can either be disposed of after the housing has been removed and processed or, advantageously, already during the period between the Pouring off the molten metal and the removal of the housing elapsing residence time can be deducted from the housing.
• the casting mold can be placed on a sieve bottom and the fragments of the casting mold trickling through the sieve bottom can be caught.
• the openings in the sieve bottom are designed in such a way that the fragments of the casting mold and the filling material trickle through the sieve bottom together, are caught, processed and then separated from one another after processing.
• the housing of the casting mold can consist of a sufficiently dimensionally stable sheet metal material which surrounds the casting mold at a distance sufficient for the formation of the filling space and no special requirements are placed on the thermal insulation of this material.
• a perforated support plate acting as a sieve plate can be provided, on which the casting mold is placed.
• An exhaust gas opening can be provided in order to enable the exhaust gases forming in the filling chamber to be discharged in a controlled manner.
• the filling material filled into the filling chamber can also be compressed in a manner known per se in order to generate a prestress between the casting mold and the housing, which ensures that the casting mold is held together securely and in the exact position even when the casting mold is a multiplicity of molded parts and cores composite core package is formed.
• the through-flow of a gas stream is ensured even with a filling material compacted in this way.
• Channels introduced specifically into the casting mold can also be used to accelerate cooling of certain zones on or in the casting or to avoid such accelerated cooling in order to achieve certain properties of the casting in the respective zone.
• Granules or other granular bulk material have proven suitable as filling material.
• Bulk materials of this type with bulk densities of at most 4 kg/dm 3 , in particular less than 1 kg/dm 3 or even less than 0.5 kg/dm 3 are particularly suitable for the purposes according to the invention.
• the grains of the filling material are spherical.
• the diameter of the balls is preferably in the range of 1.5-100 mm, in particular 1.5-40 mm.
• all thermally resilient bulk materials that meet the conditions specified above and are sufficiently temperature-resistant are suitable as filling material.
• Non-metallic bulk materials such as granules made of ceramic materials, are particularly suitable for this purpose. These can be irregularly shaped, spherical or provided with cavities in order to achieve good gassing through of the filling material filled into the filling space while at the same time having a low heat storage property.
• the filling material can also consist of ring-shaped or polygonal elements which only touch one another at points when they come into contact with one another, so that sufficient space remains between them in order to ensure good flow.
• the filling material can consist of ceramic or refractory materials.
• the cast part exposed after demolding according to the invention can undergo a heat treatment in a known manner after the mold has disintegrated, in which it is cooled in a known manner according to a specific cooling curve in order to produce a specific state of the cast part.
• casting molds can be accommodated together in one housing and these casting molds can be filled with molten metal in parallel or in close succession in time.
• the method according to the invention is suitable for any type of metallic casting material, during the processing of which a sufficiently high level of process heat is generated.
• the method according to the invention is particularly suitable for producing castings from cast iron, because due to the high temperature of the cast iron melt, the temperatures provided according to the invention for the combustion of the binder are reached particularly reliably.
• the method according to the invention is particularly suitable for the production of cylinder crankcases and cylinder heads for internal combustion engines by casting.
• the relevant components are intended for commercial vehicles, they and the casting mold required for their manufacture have a comparably large volume, in which case the advantages of the procedure according to the invention have a particularly clear effect.
• casting mold parts and cores are provided in the method according to the invention.
• the casting cores and molded parts are produced in a conventional manner using the cold box process from a conventional molding material, which can be a mixture of commercially available core sand, an equally commercially available organic binder and optionally added additives, which, for example, improve wetting of the core sand grains through the binder.
• a conventional molding material which can be a mixture of commercially available core sand, an equally commercially available organic binder and optionally added additives, which, for example, improve wetting of the core sand grains through the binder.
• the resulting casting cores and molded parts are gassed with a reaction gas to form the organic binder through a chemical reaction to harden and thereby give the casting cores and molded parts the necessary dimensional stability.
• a casting mold 1 is assembled from the casting mold parts and cores provided in a conventional manner in a likewise known manner to form a casting mold 1 designed as a so-called “core package”.
• the casting mold 1 can comprise components made of steel or other indestructible materials. These include, for example, chills and the like, which are arranged in the casting mold 1 in order to achieve directional solidification of the casting G by accelerated solidification of the melt that comes into contact with the chill.
• the casting mold 1 is intended for the production of a cast part G, which in the present example is a cylinder crankcase for a commercial vehicle internal combustion engine.
• new filling material for example granular, in particular spherical, ceramic granules with a grain size of 1.5-25 mm, determined in a conventional manner by sieving, is provided, which has room temperature (typically 18-25 °C), with filling material temperatures of up to up to 45 °C are practical here.
• the device T shown in FIGS. 1-8 in various phases of the method according to the invention has a sieve plate 2 on which the casting mold 1 prepared for pouring an iron cast melt is placed.
• the casting mold 1 delimits a mold cavity 3 from the environment U into which the cast iron melt is poured to form the casting G .
• the molten iron flows into the mold cavity 3 via a gating system, which is not shown here for the sake of clarity.
• the perforated plate 2 is supported with its edge on a circumferential shoulder 4 of a collecting container 5 .
• a sealing element 6 is incorporated into the circumferential contact surface of the marginal shoulder 4 .
• the housing 7 is designed in the manner of a flake and encases the casting mold 1 on its outer peripheral surfaces 8.
• the circumference of the space bounded by the housing 7 is oversized compared to the circumference of the casting mold 1, so that after the housing 7 has been put on the sieve bottom 2 between the outer peripheral surface of the mold 1 and the inner surface 9 of the housing 7, a filling space 10 is formed.
• the housing 7 sits on the sealing element 6, so that a tight seal of the filling space 10 with respect to the environment U is ensured here.
• the enclosure consists of a sheet metal material with no special requirements for its thermally insulating properties.
• the sheet metal material is designed in a manner known per se in such a way that it ensures the necessary dimensional stability of the housing 7 .
• the housing 7 On its upper side, the housing 7 encloses a large opening 11 through which the casting mold 1 can be filled with molten iron and the filling space 10 with filling material F (FIG. 2).
• a storage container V is positioned over the opening 11, from which the untempered filling material F can then trickle through a distribution system 12 into the filling space 10 (Fig. 3).
• the filling material pack filled into the filling space 10 can be compacted if necessary. Then a cover 13 is placed on the opening 11, which also has an opening 14 through which the cast iron melt can be filled into the casting mold 1 (FIG. 4).
• the cast iron melt is then poured into the casting mold 1 (FIG. 5).
• Ambient air containing oxygen can meanwhile enter the filling chamber 10 via a gas inlet 15 formed in the lower edge region of the housing 7 .
• Ambient air, which enters the collection container 5 via an access 16 is also sucked through the perforated bottom 2 into the filling space 10 (FIG. 6).
• the solvent contained in the binder evaporates.
• the vaporous solvent escaping from the casting mold 1 burns as it exits the casting mold 1 due to the heat radiated by the cast part G.
• the combustion of the binder components and other potential pollutants escaping from the casting mold 1 continues without any further supply of energy until no more binder can be discharged from the casting mold 1 evaporates.
• the then possibly still emerging from the mold 1 vaporous substances are oxidized by the high temperature prevailing in the filling chamber 10 or rendered harmless in some other way.
• the filling material pack in the filling space 10 supports the casting mold 1 on its peripheral surfaces 8 and thus prevents the cast iron melt from breaking through from the casting mold 1.
• the mold parts and cores of the casting mold 1 disintegrate into fragments B or individual grains of sand, which fall through the sieve bottom 2 into the collection container 5 and are collected there.
• the perforated bottom 2 can be opened in such a way that filling material F also reaches the collection container 5 (FIG. 7).
• the progress of the destruction of the casting mold 1 and the course of solidification of the molten iron poured into the casting mold 1 are matched with each other so that the casting G is sufficiently solidified when the casting mold 1 starts to collapse.
• the low temperature of the filling material F contributes here to the fact that the casting mold 1 and with it the cast part G cool down quickly. In this way, a particularly good dimensional accuracy of the casting G is achieved.
• the collection container 5 with the mold material/filling material mixture it contains is separated from the sieve bottom 2 and the housing 7 is also removed from the sieve bottom 2 (FIG. 8).
• the largely desanded cast part G is now freely accessible and can be cooled in a controlled manner in a tunnel-like space 17 provided for this purpose (FIG. 9).
• the casting G Due to the process, the casting G has a high temperature when it is removed, in which the austenite transformation is not yet complete and rapid cooling would lead to residual stresses and thus cracks. For this reason, the cast part G is slowly cooled in a cooling tunnel 17 according to the annealing curves during stress-relief annealing.
• the cooling air supplied is measured in such a way that the cooling profile is achieved in a product-specific manner.
• the still hot mixture of filling material F, core sand and fragments B collected in the collection container 5 is processed in the manner described in WO 2016/016035 A1.
• the core sand obtained as a result of the processing is made available for the production of new casting mold parts and cores.
• the filling material F obtained by the processing is cooled to room temperature in air without any additional supply of energy and stored in the storage container V for refilling the filling space 10 .
• the invention thus provides a method for casting castings (G), in which molten metal is poured into a casting mold 1, the casting mold 1 being a lost mold consisting of one or more casting mold parts or cores which are formed from a molding material , which consists of a core sand, a binder and optionally one or more additives for setting certain Properties of the molding material.
• a lost mold consisting of one or more casting mold parts or cores which are formed from a molding material , which consists of a core sand, a binder and optionally one or more additives for setting certain Properties of the molding material.
• the casting mold 1 is housed in a housing 7, forming a filling space 10 between at least one inner surface section 9 of the housing 7 and an associated outer surface section 8 of the casting mold 1,
• the filling space 10 is filled with a free-flowing filling material F, which has such a low bulk density that the filling material packaging formed there from the filling material F after filling the filling space 10 can be flowed through by a gas flow S1, S2, and
• the molten metal is poured into the casting mold 1, with the casting mold 1 accompanying the pouring of the molten metal beginning to radiate heat, which is the result of the heat input caused by the hot molten metal, and the binder of the mold material increases as a result of the heat input caused by the molten metal vaporize and start to burn so that it loses its effect and the mold 1 breaks up into fragments B.
• the filling material F has a filling material temperature of less than 100° C. when it is filled into the filling chamber 10, the rapid and energy-efficient decomposition of the casting mold 1 can be achieved with reduced effort.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Mold Materials And Core Materials (AREA)
• Molds, Cores, And Manufacturing Methods Thereof (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=82270664

Family Applications (1)

Country Status (5)

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• 2021
  • 2021-06-17 DE DE102021115727.7A patent/DE102021115727A1/de active Pending
• 2022
  • 2022-06-15 CN CN202280042946.7A patent/CN117529375A/zh active Pending
  • 2022-06-15 BR BR112023025405A patent/BR112023025405A2/pt unknown
  • 2022-06-15 EP EP22734570.9A patent/EP4355512A1/de active Pending
  • 2022-06-15 WO PCT/EP2022/066323 patent/WO2022263517A1/de active Application Filing

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