Method for Casting Castings

Abstract

The invention relates to a process for casting castings, in which a metal melt is poured into a casting mold, The casting mold, formed as a lost mold, consists of one or more casting mold parts or cores which are formed from a molding material consisting of a core sand, a binder and optionally one or more additives for adjusting certain properties of the molding material. In the course of the method according to the invention, the casting mold is provided. The casting mold is enclosed in a housing, forming a filling space between at least one inner surface section of the housing and an associated outer surface section of the casting mold. The filling space is filled with a pourable filling material which has such a low bulk density that a gas flow can flow through the filling material package formed there from the filling material after the filling of the filling space, and the metal melt is poured into the casting mold. The casting mold begins to radiate heat as a result of the heat input caused by the hot metal melt, and wherein as a result of the heat input caused by the metal melt the binder of the molding material begins to evaporate and burn, so that it loses its effect and the casting mold disintegrates into fragments. In accordance with the invention, the filling material has a filling material temperature of less than 100? C. when it is filled into the filling space, so that the rapid and energy-efficient decomposition of the casting mold can be achieved with reduced effort.

Claims

1. A method for casting castings, in which a metal melt is poured into a casting mold which surrounds a cavity forming the casting to be produced, wherein the casting mold, formed as a lost mold, consists of one or more casting mold parts or -cores which are formed from a molding material consisting of a core sand, a binder and optionally one or more additives for adjusting certain properties of the molding material, comprising the following working steps: providing the casting; enclosing the casting mold in a housing, forming a filling space between at least one inner surface section of the housing and an associated outer surface section of the casting mold; filling of the filling space with a free-flowing filling material, wherein the filling material filled into the filling space has such a low bulk density that a gas flow; can flow through the filling material package formed there from the filling material after the filling of the filling space; and pouring the metal melt into the casting mold, wherein the casting mold begins to radiate heat as the metal melt is poured in, as a result of the heat input caused by the hot metal melt, and wherein as a result of the heat input caused by the metal melt, the binder of the molding material begins to evaporate and burn, so that it loses its effect and the casting mold disintegrates into fragments, wherein the filling material has a filling material temperature of less than 100? C. when it is filled into the filling space.

2. The method according to claim 1, wherein the filling material temperature is at most 45? C. when the filling material is filled into the filling space.

3. The method according to claim 1, wherein the temperature of the filling material is at least equal to room temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The invention is explained in more detail below with reference to a drawing showing an embodiment. The figures show schematically in each case:

[0051] FIGS. 1-10 different phases of the implementation of the method according to the invention, each with components shown in a section along their longitudinal axis.

DESCRIPTION OF THE INVENTION

[0052] As in the prior art known from WO 2016/016035 A1, casting mold parts and cores are provided in the method according to the invention.

[0053] The casting cores and -mold parts are conventionally produced in a cold-box process from a conventional molding material, which may be a mixture of a commercially available core sand, an equally commercially available organic binder and optionally added additives, which serve, for example, to improve the wetting of the grains of the core sand by the binder. After molding, the resulting casting cores and -mold parts are gassed with a reaction gas in order to harden the organic binder through a chemical reaction and thereby give the casting cores and -mold parts the necessary dimensional stability.

[0054] A casting mold 1 is assembled from the casting mold parts and -cores provided in this conventional manner in an equally known manner to form a casting mold 1 designed as a so-called core package. In addition, the casting mold 1 can comprise components made of steel or other indestructible materials. These include, for example, cooling molds 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 coming into contact with the cooling mold.

[0055] The casting mold 1 is intended for the casting production of a casting G, which in this example is a cylinder crankcase for a commercial vehicle combustion engine.

[0056] New filling material, for example granular, in particular spherical, ceramic granulate with a grain size of 1.5-25 mm determined in a conventional manner by sieving, is also provided, which is at room temperature (typically 18-25? C.), wherein filling material temperatures of up to 45? C. are practical here.

[0057] Furthermore, these raw materials can be reused in a cycle, as explained below.

[0058] 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 a cast iron melt is placed.

[0059] The casting mold 1 delimits a mold cavity 3 from the surroundings U, into which the cast iron melt is poured to form the casting G. The iron melt flows into the mold cavity 3 via an ingate system, which is not shown here for the sake of clarity.

[0060] The edge of the sieve plate 2 is supported on a circumferential edge shoulder 4 of a collection container 5. A sealing element 6 is incorporated into the circumferential contact surface of the edge shoulder 4.

[0061] After the casting mold 1 is positioned on the sieve plate 2, an enclosure 7, which is also part of the device T, is placed on the circumferential edge shoulder 4 of the collection container 5. The enclosure 7 is designed like a hood and encases the casting mold 1 on its outer circumferential surfaces 8. The circumference of the space enclosed by the enclosure 7 is oversized compared to the circumference of the casting mold 1, so that a filling space 10 is formed between the outer circumferential surface of the casting mold 1 and the inner surface 9 of the enclosure 7 after the enclosure 7 has been placed on the sieve plate 2. With its edge associated with the collection container 5, the enclosure 7 sits on the sealing element 6, so that a tight seal of the filling space 10 with respect to the surroundings U is ensured.

[0062] The enclosure consists of a sheet metal material whose thermal insulating properties are not subject to any special requirements. The sheet metal material is designed in a known manner to ensure the necessary dimensional stability of the enclosure 7. On its upper side, the enclosure 7 has a large opening 11 through which the casting mold 1 can be filled with cast iron melt and the filling space 10 with filling material F (FIG. 2).

[0063] To fill the filling space 10 with the unheated and provided filling material F, i.e. at a filling material temperature that is at least equal to room temperature and at most 45? C., a storage container V is positioned above the opening 11, from which the 14 untampered filling material F is then allowed to trickle into the filling space 10 via a distribution system 12 (FIG. 3).

[0064] When the filling process is complete, the filling material package filled into the filling space 10 can be compacted if necessary. A lid 13 is then placed on the opening 11, which also has an opening 14 through which the cast iron melt can be poured into the casting mold 1 (FIG. 4).

[0065] The cast iron melt is then poured into the casting mold 1 (FIG. 5).

[0066] Meanwhile, oxygen-containing ambient air can enter the filling space 10 via a gas inlet 15 formed in the lower edge area of the enclosure 7. Similarly, ambient air that enters the collection container 5 via an inlet 16 is drawn into the filling space 10 through the sieve bottom 2 (FIG. 6).

[0067] The intentional destruction of the casting mold 1 that begins with the pouring of the cast iron melt and the associated demolding of the casting G takes place in two phases.

[0068] In the first phase, the solvent contained in the binder evaporates. The vaporous solvent escaping from the casting mold 1 burns due to the heat radiated by the casting G as it exits the casting mold 1. The burning of the binder components and other potential pollutants escaping from the casting mold 1 continues without further energy input until no more binder evaporates from the casting mold 1. The vaporous substances that may still be escaping from the casting mold 1 are oxidized or otherwise rendered harmless by the high temperature prevailing in the filling space 10.

[0069] The oxygen-containing gas flows S1, S2 formed from ambient air, which enter the filling space 10 of the enclosure 7 via the gas inlet 15 and the sieve bottom 2, also contribute to the complete burning of the gases emerging from the casting mold 1.

[0070] As the bulk density of the filling material F is so low that even after compaction, good gas permeability of the filling material package present in the filling space 10 is ensured, good mixing of the gases emerging from the casting mold 1 with the gas flows S1, S2 providing oxygen for its burning is guaranteed. At the same time, the filling material package in the filling space 10 supports the casting mold 1 at its circumferential surfaces 8 and thus prevents the cast iron melt from breaking through from the casting mold 1.

[0071] 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. Depending on the progress of the destruction of the casting mold 1, the sieve bottom 2 can be opened so that filling material F also reaches the collection container 5 (FIG. 7).

[0072] The progress of the destruction of the casting mold 1 and the solidification process of the cast iron melt poured into the casting mold 1 are adapted to each other in such a way that the casting G is sufficiently solidified when the disintegration of the casting mold 1 begins. The low temperature of the filling material F helps to ensure that the casting mold 1 and the casting G cool down quickly. In this way, a particularly good dimensional accuracy of the casting G is achieved.

[0073] After the casting mold 1 has essentially completely disintegrated, the collection container 5 with the mixture of molding material and filling material it contains is separated from the sieve bottom 2 and the enclosure 7 is also removed from the sieve bottom 2 (FIG. 8). The largely desanded casting 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).

[0074] Due to the process, the casting G has a high temperature during removal, at which the austenite transformation is not yet complete and rapid cooling would lead to residual stresses and therefore cracks. For this reason, the casting G is cooled slowly in a cooling tunnel 17 in accordance with the annealing curves during stress relief annealing. The cooling air supplied is dimensioned so that the cooling profile is achieved for the specific product.

[0075] 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.

[0076] The core sand obtained from the processing is made available for the production of new casting mold parts and -cores.

[0077] The filling material F obtained from the processing is cooled to room temperature in the air without additional energy input and stored in the storage container V for a refilling the filling space 10.

[0078] The invention thus provides a method for casting castings (G), in which a metal melt is poured into a casting mold 1, the casting mold 1, formed as a lost mold, consists of one or more casting mold parts or -cores which are formed from a molding material consisting of a core sand, a binder and optionally one or more additives for adjusting certain properties of the molding material. In the course of the method according to the invention [0079] the respective mold 1 is provided, [0080] the casting mold 1 is enclosed 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, [0081] the filling space 10 is filled with a free-flowing filling material F which has such a low bulk density that a gas flow S1, S2 can flow through the filling material package formed there from the filling material F after the filling of the filling space, and [0082] the metal melt is poured into the casting mold 1,
wherein the casting mold 1 begins to radiate heat as the metal melt is poured in, as a result of the heat input caused by the hot metal melt, and wherein as a result of the heat input caused by the metal melt, the binder of the molding material begins to evaporate and burn, so that it loses its effect and the casting mold 1 disintegrates into fragments B.

[0083] By the filling material F having according to the invention a filling material temperature of less than 100? C. when the filling material is filled into the filling space 10, the rapid and energy-efficient decomposition of the casting mold 1 can be achieved with reduced effort.

REFERENCE SIGNS

[0084] 1 Casting mold [0085] 2 Sieve plate [0086] 3 Mold cavity [0087] 4 Circumferential edge shoulder [0088] 5 Collection container [0089] 6 Sealing element [0090] 7 Enclosure (housing) [0091] 8 Circumferential surfaces of the casting mold 1 [0092] 9 Inner surface of the enclosure 7 [0093] 10 Filling space [0094] 11 Opening of the enclosure [0095] 12 Distribution system [0096] 13 Lid [0097] 14 Opening of the lid 13 [0098] 15 Gas inlet [0099] 16 Inlet [0100] 17 Cooling tunnel [0101] B Fragments [0102] F Filling material [0103] G Casting [0104] S1,S2 Oxygen-containing gas flows [0105] T Device [0106] U Surrounding [0107] V Storage container