Method for demoulding a casting, cast from a light metal melt, from a casting mould

Abstract

A method for demolding a casting from a casting mold having at least one casting core which images a passage opening in the casting connecting two outer sides of the casting and is produced from a molding material bound by a binder which decomposes under the influence of temperature, wherein the casting mold undergoes a heat treatment in a furnace for the demolding, during which it is heated to a temperature at which the binder loses its binding effect. In the furnace, hot gas is flowed through a passage formed in the casting core of the casting mold, the temperature of the hot gas corresponding at least to the temperature at which the binder of the molding material loses it binding effect such that the casting core decomposes into fragments or separate sand particles as a consequence of the influence of the hot gas.

Claims

1. A method for demoulding a casting, cast from a light metal melt, from a casting mould, the method comprising: providing a casting mould, wherein internal passageways of the casting mould defining the casting have been filled with the light metal melt which has been at least partially solidified, the casting mould comprising a moulding material which is bound by means of a binder which decomposes under the influence of temperature, the casting mould including at least one casting core having an outer surface that mirrors an inner surface of a passage opening in the casting that connects two outer sides of the casting, and an inner passageway; heating the casting mould in a furnace to a temperature at which the binder loses its binding effect; and flowing hot gas, the temperature of which corresponds at least to the temperature at which the binder of the moulding material loses its binding effect, through the inner passageway of the at least one core while the casting mould is heated in the furnace such that the at least one casting core decomposes into fragments or separate sand particles as a consequence of the influence of the hot gas.

2. The method according to claim 1, wherein the inner passageway of the at least one casting core of the casting mould is aligned vertically in the furnace.

3. The method according to claim 1, wherein the inner surface of the passage opening of the casting is mirrored by two or more casting cores which each have an inner passageway and the inner passageways of the casting cores are connected.

4. The method according to claim 1, wherein the casting mould is formed as a core package composed of two or more casting cores.

5. The method according to claim 4, wherein indentations are moulded into the casting cores which form outer side parts of the casting mould.

6. The method according to claim 1, wherein the at least one casting core abuts an outer side part which forms an outer surface of the casting mould, and the inner passageway of the casting connects with a passageway in the outer side part that extends to an outer surface of the casting mould.

7. The method according to claim 1, wherein the heating of the casting mould in the furnace is conducted at a temperature that solution anneals the casting.

8. The method according to claim 1, wherein the fragments of the at least one casting core, which are formed by the decomposition of the binder and which fall away from the casting, are collected and are held in the furnace until the binder still contained in the fragments is combusted.

9. The method according to claim 1, wherein the casting is an engine block for a combustion engine, and the passage opening is a cylinder opening.

10. The method according to claim 1, wherein the casting mould and the casting pass through the furnace in a continuous run.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a casting mould in a perspective view;

(2) FIG. 2 is the casting mould according to FIG. 1 in a view from above;

(3) FIG. 3 is the casting mould according to FIG. 1 in a cut along the intersection X-X recorded in FIG. 1;

(4) FIG. 4 is the sequence of the work steps completed in the production of a casting involving the method according to the invention; and

(5) FIG. 5 is the temperature development in the engine block casting during the run through a continuous furnace until reaching the solution annealing temperature applied over time.

DESCRIPTION OF THE INVENTION

(6) The rectangular casting mould 1 serves for the casting of an engine block M for a combustion engine which is not shown further here.

(7) The casting mould 1 is assembled as a core package made from a plurality of casting cores. The casting cores are respectively produced in an intrinsically known manner from a moulding material which has been moulded into the casting cores as a mixture of a moulding sand and an organic binder as well as, if necessary, optionally added additives in a core shooter not depicted here, said casting cores having been subsequently solidified by gassing with a reaction gas.

(8) The cores can alternatively be produced with all organic core production methods known in prior art, such as, for example warm box, hot box, croning, hand moulding methods and self-hardening methods without catalysts.

(9) Included in the casting cores of the casting mould 1 are a casting core 2 which forms the base of the casting mould 1 and on which the other casting cores of the casting mould 1 are constructed, two casting cores 3, 4 of which one is respectively allocated to one of the longitudinal sides of the casting mould 1 and which delimit the casting mould 1 on its longitudinal sides, two casting cores 5, 6 of which one is respectively allocated to one of the front sides of the casting mould 1 and which delimit the casting mould 1 on its front sides, as well as a cover core 7 which completes the casting mould 1 on its upper side.

(10) Respectively, several indentations 8, 9 are moulded into the casting cores 3, 4 forming the lateral border of the casting mould 1 on the longitudinal sides thereof and the casting cores 5, 6 forming the lateral border of the casting mould 1 on the front sides thereof. The indentations 8, 9 are thereby arranged such that, and recessed into the respective casting core 3-6 over such a depth that, on the one hand a wall thickness remains in the region of their base which is sufficient in order to securely enclose the casting chamber surrounded by the casting mould 1, but on the other hand respectively only bars 10, 11 remain between the indentations 8, 9 with a thickness which ensures a strength which is sufficient for the inherent rigidity of the respective casting core 3-6, however at the same time enables a simple breakup of the bars 8, 9 and in an accompanying manner of the respective casting core 3-6 if the binder of the moulding material from which the casting cores 3-6 are formed is ineffective.

(11) Four passage openings 13-16 aligned perpendicularly to the flat outer cover surface 12 of the cover core 7 and arranged at equal distances are moulded into the cover core 7, said passage openings 13-16 leading from the cover surface 12 into the space surrounded by the casting cores 2-7.

(12) A circumferential recess is moulded into the edge region of the passage openings 6 abutting onto the cover surface 12. A cover E which is produced from the moulding material from which the cover core 7 itself is also formed, from cardboard or combustible felt, and is approximately 1 cm thick and which is laid loosely in the opening 13-16 sits respectively on this recess in order to hold the passage openings 13-16 closed after the decantation of the engine block casting M until the heat treatment which is implemented to desand and solution anneal begins. Alternatively to a separate cover E, the passage openings 13-16 can also be closed with a membrane-like cover layer which is connected in one piece to the surrounding core material of the cover core 7 and which, if it is exposed to the temperature existing during the heat treatment, decomposes quickly and releases the respective passage opening 13-16. In FIGS. 2 and 3, the covers E are left off such that the free passages D1-D4 through the casting mould 1 formed in the manner described below and provided according to the invention are visible.

(13) In the space surrounded by the casting cores 2-7, four pairs of two annular casting cores 18a, 18b, 19a, 19b, 20a, 20b and 21a, 21b respectively which are stacked one on top of the other sit on a central casting core 17 which images the upper part of the crank case K of the engine block casting M in a seat provided for this respectively. The casting core pairs 18a, 18b, 19a, 19b, 20a, 20b and 21a, 21b respectively border with their outer peripheral surfaces one of the four cylinder chambers of the engine block casting M, of which, for the sake of clarity, in FIG. 4 only three cylinder chambers Z1-Z3 are depicted symbolically. The cylinder chambers respectively form a passage opening of the engine block casting M. The annular openings surrounded by the casting cores 18a-21b are, at the same time, aligned in alignment with one other and with regard to the respectively allocated passage openings 13-16 of the cover core 7 sitting flush on the edge of the respective upper casting core 18b, 19b, 20b, 21b allocated to it, such that they form the continuation of the passage openings 13-16.

(14) In an extension of the annular space of the respective lower casting core 18a, 19a, 20a, 21a of the casting cores 18a-21b, a further passage opening 22-25 is moulded into the planar casting core 17, which is likewise arranged in alignment with the allocated passage opening 13-16 of the cover core 7.

(15) The passage openings 22-25 respectively merge into a passage opening 26-29 at their lower end allocated to the base core 2. The passage openings 26-29 are moulded in a funnel shape in the direction of the base core 2 in an extending manner into a further casting core 30 which moulds the lower part of the crank case K and sits on the base core 2.

(16) Finally, four further passage openings 31-34 are moulded into the base core 2, of which one respectively is allocated to the passage openings 26-29.

(17) The passage openings 13, 22, 26 and 31 which are aligned in alignment with each other and coaxially to a mutual longitudinal axis L1 form, together with the annular openings enclosed by the casting cores 18a, 18b, a first passage D1 which leads from the flat contact surface 35, with which the base core 2 stands on the respective ground during use, to the likewise flat cover surface 12 of the cover core 7.

(18) In a corresponding manner, the passage openings 14, 23, 27 and 32 which are aligned in alignment with each other and coaxially to a mutual longitudinal axis L2 arranged axially parallel to the longitudinal axis L1 form, together with the annular openings enclosed by the casting cores 19a, 19b, a second passage D2, the passage openings 15, 24, 28 and 33 aligned in alignment with each other and coaxially to a mutual longitudinal axis L3 arranged axially parallel to the longitudinal axis L1 form, together with the annular openings enclosed by the casting cores 20a, 20b, a third passage D3 and the passage openings 16, 25, 29 and 34 aligned in alignment with each other and coaxially to a mutual longitudinal axis L4 arranged likewise axially parallel to the longitudinal axis L1 form, together with the annular openings enclosed by the casting cores 21a, 21b, a fourth passage D4.

(19) To produce an engine block M, the casting mould 1 is assembled in a first processing station from the casting cores 2-7, 17, 18a-21b and 30 as well as further casting cores which are not shown here for the sake of clarity.

(20) Subsequently, the casting mould 1 is filled with aluminium melt. The casting mould 1 is thereby aligned around a horizontally aligned rotational axis such that it is arranged above and the cover core 2 is arranged below in the direction of the force of gravity. In this way, a filling opening which is not visible in FIGS. 1-3 of a feeder which is likewise not depicted in FIGS. 1-3, via which the filling of the casting mould 1 occurs, is arranged above for filling, whilst the feeder is located below in the direction of the force of gravity. After completion of the filling procedure, the casting mould 1 is pivoted again around the horizontally aligned pivot axis such that now the feeder and the cover core 7 lie above, whilst the filling opening of the feeder is arranged below in the direction of the force of gravity. Using this method, also referred to as rotational moulding, an even solidification of the casting in the casting mould 1 is achieved.

(21) At the earliest at the beginning of the solidification and at the latest after complete solidification of the aluminium melt in the casting mould 1, the casting mould 1 passes into a continuous furnace O in which the engine block M is desanded, the engine block M passes through a solution annealing treatment and the moulding material of the casting cores of the casting mould 1 falling away from the engine block M is prepared for reuse.

(22) The casting mould 1 passing into the furnace O is heated for this purpose to the solution annealing temperature which typically lies in the range from 450-550 C. depending on the respectively processed Al casting alloy. This solution annealing temperature is higher than the temperature from which the binder of the moulding material of the casting cores of the casting mould 1 combusts.

(23) As a consequence of natural convection, hot gas flows H thereby begin which flow from below through the passages D1-D4 of the casting mould 1. In this way, the decomposition of the casting mould 1 begins not only in the region of the outer casting cores 2-7, but also in the regions of the casting cores 17, 18a-21b and 30 covered by the hot gas flows H1-H4 inside the casting mould 1. At the same time, the light metal of the engine block M is also not only heated quickly to the solution annealing temperature from the outer side of the casting mould 1, but also from inside.

(24) With progressive heating and consequently combustion of the binder of their moulding material, the binder becomes increasingly ineffective and the lateral casting cores 2-7 and the inner casting cores 2-7, 17, 18a-21b and 30 begin to decompose. The fragments and sand particles B falling away from the engine block casting M are collected in a sand bed SB provided under the conveyor path F of the casting mould 1 in the furnace O.

(25) In order to keep the fragments B collected in the sand bed SB moving in order to promote their fragmentation and regeneration, hot gas HG is blown into the sand bed SB via nozzles embedded in the base of the furnace O. Due to the thus achieved fluidisation and tempering of the sand bed SB, the residual binder still contained in the casting core fragments B combusts and the fragments B are decomposed into their separate sand particles. The moulding sand S obtained by this processing is conducted back for reuse to the core shooter which produces the casting cores from which the respective casting mould 1 is assembled.

(26) The further the engine block casting M is conveyed in the direction of the output of the furnace O, the more complete the desanding of the engine block M is, until finally even the smallest fragments B have trickled out from it.

(27) When the output of the furnace O is reached, then the time necessary for the solution annealing treatment is also completed, such that the engine block casting M can be quenched to room temperature in a station which is subsequently directly passed through. After that, a mechanical processing occurs during which the feeders are separated and further machine processing operations take place on the engine block M. Subsequently, optionally a further relocation treatment then occurs.

(28) In FIG. 5, the temperature profile of the engine block casting M is depicted in the furnace O for an engine block casting which is desanded and solution annealed in a conventional operating method (dashed line) and a similar engine block casting part which is desanded and solution annealed in the manner according to the invention (solid line). The casting moulds containing the respective casting enter the furnace O after falling below the liquidus temperature of the aluminium melt from which the casting parts are cast, however when the respective engine block casting has still not completely solidified. In that the engine block castings are conducted into the furnace O in the only partially solidified state, the casting heat which is still inherent in this state can be used.

(29) The temperature of the casting during conventional operation and that according to the invention during entry into the furnace O, amounted respectively to approx. 430 C. The casting which is flowed through by hot gas according to the invention, however, reached the solution annealing temperature TLG of approx. 485 C. clearly more quickly than the casting heated conventionally without through-flow. As a consequence, the casting flowed through with hot gas according to the invention stays at the solution annealing temperature TLG in the conventional furnace O approx. 90 minutes longer than the conventionally treated casting. As, at the same time, the desanding took place in a substantially more effective manner in the procedure according to the invention, the procedure according to the invention therefore enables the desanding and solution annealing process to be shortened by approx. 30% compared to the conventional procedure.

REFERENCE NUMERALS

(30) 1 Casting mould 2 Base casting core 3, 4 the casting cores bordering the longitudinal sides of the casting mould 1 5, 6 the casting cores bordering the front sides of the casting mould 1 7 Cover core 8, 9 Indentations 10, 11 Bars 12 Cover surface of the cover core 7 13-16 Passage openings of the cover core 7 17 Casting core 18a-21b Annular casting cores 22-25 Passage openings of the casting core 17 26-29 Passage openings of the casting core 30 30 Casting core 31-34 Passage openings of the base core 2 35 Contact surface of the base casting core 2 B Casting core fragments D1-D4 Passages E Cover H Hot gas HG Hot gas flows K Crank case of the engine block M M Engine block casting O Continuous furnace S Prepared moulding sand SB Sand bed Z1-Z3 Cylinder chambers of the engine block M F Conveyor path