Method for Producing a Foundry Core and Foundry Core

Abstract

The invention proposes the following production step sequence, in order that foundry cores, which consist of a mould material which is mixed from a binder and a mould sand, as well as optionally added additives, which are also moulded in a complex way or are optimised with regard to their quality and which are provided for casting cast parts, can be produced simply by: a) moulding the foundry core by introducing the mould material into a foundry core mould; b) hardening the mould material; c) removing the foundry core from the foundry core mould; d) heating the foundry core to a deformation temperature; e) deforming the heated foundry core by applying a deformation force to the foundry core; and f) cooling the foundry core.

Claims

1. A method for producing a foundry core for casting a cast part, wherein the foundry core consists of a mould material which is mixed from a binder and a mould sand, as well as optionally added additives, comprising the following production steps: a) moulding the foundry core by introducing the mould material into a foundry core mould; b) hardening the mould material; c) removing the foundry core from the foundry core mould; d) heating the foundry core to a deformation temperature; e) deforming the heated foundry core by applying a deformation force to the foundry core; and f) cooling the foundry core.

2. The method according to claim 1, wherein the deformation force brings about a bending deformation, compressive deformation, tensile deformation, shear deformation or torsional deformation of the foundry core.

3. The method according to claim 1, wherein the deformation is carried out at a deformation rate of at most 2 mm/s.

4. The method according to claim 1, wherein the deformation force is 5-100 N.

5. The method according to claim 1, wherein the foundry core is fully hardened in production step b).

6. The method according to claim 1, wherein the binder of the mould material is an organic binder.

7. The method according to claim 1, wherein the deformation temperature is 180-300 C.

8. The method according to claim 1, wherein the heating-up rate when heating the foundry cores to the deformation temperature is 1-15 C/s.

9. The method according to claim 1, wherein by carrying out the production steps a)-c) a first foundry core is produced with a recess, in that a second foundry core is provided which has a protrusion which is adapted to the shape of the recess of the first foundry core, in that the second foundry core is joined to the first foundry core such that the protrusion of the second foundry core engages with the recess of the first foundry core forming a joining zone, and in that subsequently at least one of the foundry cores passes through the production steps d)-f) and in production step e) is deformed in such a way that in the area of the joining zone a tight form-fit connection is formed, by means of which the two foundry cores are joined together.

10. The method according to claim 1, wherein by carrying out the production steps a)-c) a first foundry core is produced with a recess, in that a second foundry core is provided and this foundry core is positioned on the first foundry core in a predetermined position, in that at least the second foundry core passes through production steps d)-f) and in production step e) by applying an external force is deformed in such a way that material of the second foundry core which is located in the area of the recess of the first foundry core enters the recess of the first foundry core and fills this recess, so that a tight form-fit connection is formed, by means of which the two foundry cores are joined together.

11. A foundry core which is produced from a mould material which consists of a mixture of a binder and a mould sand, as well as optionally added additives, wherein the foundry core is brought into its final shape by means of a deformation brought about by external application of force.

12. A foundry core which is produced from a mould material which consists of a mixture of a binder and a mould sand, as well as optionally added additives, wherein the foundry core is produced according to claim 1.

Description

[0038] The invention is explained in more detail below with the aid of the figures illustrating exemplary embodiments.

[0039] FIG. 1 schematically shows a rod-shaped foundry core before and after a deformation in a lateral view, wherein the shape before deformation is illustrated with dotted lines and the shape after deformation is illustrated with continuous lines;

[0040] FIG. 2 schematically shows a rectangular-shaped foundry core before and after a deformation in a lateral view, wherein the shape before deformation is illustrated with dotted lines and the shape after deformation is illustrated with continuous lines;

[0041] FIG. 3a schematically shows another rod-shaped foundry core with a plurality of branchings formed on to it before a deformation in a lateral view;

[0042] FIG. 3b schematically shows the foundry core according to FIG. 3a in an end view;

[0043] FIG. 4a schematically shows the foundry core according to FIG. 3 after a deformation in a lateral view;

[0044] FIG. 4b schematically shows the foundry core according to FIG. 4a in an end view;

[0045] FIGS. 5a-5d schematically show two foundry cores in the different production steps which are carried out when joining these foundry cores, in each case in a lateral, partly cutaway view.

[0046] The foundry cores G1, G3 illustrated in FIGS. 1 and 3a-4b represent, by way of example, elongated, delicate foundry cores which, for example, form delicately shaped oil supply channels or coolant channels when casting cylinder heads for internal combustion engines. Cylinder heads of this type nowadays are usually cast from aluminium casting materials.

[0047] The cylindrical foundry core G2 illustrated in FIG. 2 is provided to form a cavity for an internal combustion engine, for example when an engine block is being cast.

[0048] The foundry cores G4, G5 illustrated in FIGS. 5a-5d represent those foundry cores which are joined together to form a foundry core combination GK, in order to mould complex forms of cavities or channels in a cast part cast from any metal melt.

[0049] The foundry cores G1-G5 have each been produced in the so-called PU cold box process.

[0050] The binder used in the PU cold box process comprises two components, namely phenol formaldehyde resin as the first component and isocyanate as the second component. A polyaddition of these two components to form polyurethane is brought about by gassing with a tertiary amine.

[0051] To produce the mould material, the foundry sand is mixed with the phenol formaldehyde resin and the isocyanate for two to five minutes, in particular for three minutes, in a suitable mixer, e.g. an oscillating mixer or paddle mixer. The added amount of both components of the binder can vary depending on the application and the foundry sand. They are typically between 0.4 and 1.2% for each part in relation to the added amount of mould material. A ratio of 0.7% for each part has proved to be particularly favourable.

[0052] When parts are mentioned as the metering measure here, then this is taken to mean that the amount of the constituent, measured in parts in each case, is measured by means of a standard measure which is the same for all constituents and the parts, provided according to the invention for the individual constituents in each case, constitute the respective multiple of this standard measure.

[0053] The fully mixed mould material was formed in a conventional core shooting machine into the foundry cores G1-G5. The mould material was shot into a core box at a shooting pressure of approximately 2-6 bar, in particular 3 bar, and compacted there. Then, the foundry cores G1-G5 were gassed in the core box with the gaseous catalyst, the tertiary amine, in order to bring about the hardening of the cores. The hardening process was carried out until the foundry cores G1-G5 had obtained a strength of 150-300 N/cm.sup.2 typical for PU cold box cores. A value of 220 N/cm.sup.2, regarded as optimum, was deemed to be the target value here.

[0054] The rod-shaped foundry core G1 produced in this way has, for example, a circular cross-section of 10 mm and a length of 200 mm. The foundry core G3 was correspondingly dimensioned.

[0055] The foundry cores G1-G3 obtained in each case were now heated through in a convection oven at a heating-up rate of 5 C./s to a preheating temperature of 220 C.

[0056] The foundry cores G1-G3 heated in this way were subsequently deformed.

[0057] To that end, the foundry core G1 was positioned with its end sections on two supports B1, B2 arranged spaced apart from one another with rounded rests. Subsequently, force was applied by a force K acting in the direction of gravity. This external force K was applied by means of a punch not illustrated in detail here which is aligned centrally in relation to the longitudinal extension of the foundry core G1 and is rounded on its abutting face coming into contact with the foundry core G1, in order to prevent compressive load peaks on the foundry core G1 during deformation. The load via the force K occurred in a quasi-static way at a deformation rate of 0.5 mm/s. The force K introduced was 40 N.

[0058] The deformation process was completed after the target deformation angle of approximately 20-30 degrees was obtained. During the deformation process, the foundry core G1 was constantly held in a range around the deformation temperature of 220 C.30 C.

[0059] The foundry core G1 plastically deformed in this way was cooled in quiescent air down to room temperature. Subsequently, it was able to be used in the casting process like a conventionally formed foundry core.

[0060] The foundry core G2, like the foundry core G1, was heated in the above described way and subsequently deformed by means of a punch-like tool (likewise not shown here) by external application of force KA such that it obtained the shape of an hour glass. In the process, the mould material was compacted, which had a positive effect on its dimensional stability and its surface quality. At the same time, the foundry core was calibrated, so that its shape corresponded to the geometrical specifications in an optimum way.

[0061] The foundry core G3 was also heated to the deformation temperature in the way described above for the foundry core G1. Subsequently, the heated foundry core 3 was clamped with its one end into a holder and on its other end a torque M acting about its longitudinal axis L was applied as an external force. In this way, the foundry core G3 could be twisted about its longitudinal axis L by an angle of 90.

[0062] The two foundry cores G4, G5 were also produced in the way described above for the foundry cores G1-G3. The foundry core G4 had a protrusion V on its one front end, whereas a recess A was formed into the assigned front end of the foundry core G5, the shape of which with a certain excess represents a negative of the shape of the protrusion V of the foundry core G4.

[0063] Correspondingly, the foundry core G4 could be inserted with its protrusion V into the recess A of the foundry core G5, so that the foundry cores G4, G5 were joined in the area of a joining zone F defined by the recess A.

[0064] Subsequently, at least the foundry core G5 was brought to a deformation temperature in the range from 180-300 C. by concentrated heating for example in a hot air jet. Then, the foundry core G5 had an external force KX applied to it by means of a suitable tool (not shown here) such that the material of the foundry core G5 surrounding the recess A was compressed. The material of the foundry core G5 surrounding the recess A was in this way pressed against the protrusion V until the protrusion V was tightly enclosed by the material of the foundry core G5 and a tight form-fit connection was formed, by means of which the foundry core G4 was permanently fixed in every degree of freedom in relation to the foundry core G5 and the foundry core formation GK was formed.

REFERENCE SYMBOLS

[0065] deformation angle

[0066] A recess of the foundry core G5

[0067] B1, B2 supports

[0068] F joining zone

[0069] G1-G5 foundry cores

[0070] GK foundry core combination

[0071] K, KA, KX external forces

[0072] L longitudinal axis of the foundry core G3

[0073] M torque

[0074] V protrusion of the foundry core 4