Foundry core, use of a foundry core, and method for producing a foundry core

Abstract

A foundry core formed from a moulding sand, grains of which are bound together by a binder, and which is provided to form a cooling channel in an engine block for an internal combustion engine. The foundry core has a supporting section, two neck sections, which protrude from a lateral surface of the supporting section and are arranged at a distance from one another, and at least one bridge section which is held by the neck sections at a distance from the supporting section and a minimum thickness of which measured as the distance between its lateral surfaces is no more than 3 mm in an area which lies between the neck sections.

Claims

1. A method for producing a foundry core, which is intended for forming a cooling channel in an engine block for an internal combustion engine, the foundry core comprising a supporting section, two neck sections, which protrude from a lateral surface of the supporting section and are arranged at a distance from one another, and at least one bridge section which is held by the neck sections at a distance from the supporting section, the at least one bridge section comprising two lateral surfaces and having a minimum thickness, measured as the distance between the lateral surfaces and lying between the neck sections, that is 3 mm or less, wherein the foundry core consists of a moulding material, which comprises a moulding sand and a binder, wherein the moulding material is shot into a mould cavity of a core mould by a core shooting machine and subsequently the binder is hardened, in order to provide the foundry core with the required shape stability, and wherein at least the moulding material used for forming the bridge area of the foundry core is not a mixture of the moulding sand and the binder, and wherein at least the moulding material used for forming the bridge area of the foundry core comprises moulding sand wherein the grains of the moulding sand are each enveloped by the binder to form coated moulding sand and grains of the coated moulding sand have a mean diameter of 0.35 mm or less and are spherical in shape prior to being shot into the mould cavity of the core mould.

2. The method according to claim 1, wherein the lateral surfaces of the bridge section of the foundry core each merge in a transition into a peripheral surface of the neck sections of the foundry core and the thickness of the bridge section starting from a maximum thickness adjacent to each respective neck section decreases continually in a longitudinal direction of the bridge section to the minimum thickness.

3. The method according to claim 1, wherein the minimum thickness of the bridge section of the foundry core is 2 mm or less.

4. The method according to claim 1, wherein the minimum thickness of the bridge section of the foundry core is 1 mm or less.

5. The method according to claim 1, wherein a height of the bridge section in an area in which the bridge section has the minimum thickness is 4.5 mm or less.

6. The method according to claim 1, wherein the moulding material used for the entire foundry core comprises a moulding sand, the grains of which have a mean diameter of 0.35 mm or less.

7. The method according to claim 1, wherein the mean diameter of the grains of the moulding sand is 0.25 mm or less.

8. The method according to claim 1, wherein the mean diameter of the grains of the moulding sand is 0.23 mm or less.

9. The method according to claim 1, wherein the two neck sections have a cross-sectional shape formed like a cam, a tip of which faces the respective other neck section.

10. The method according to claim 1, wherein two or more bridge sections which are arranged spaced apart from one another are supported by the two neck sections and each of the bridge sections have an area in which a minimum thickness is 3 mm or less.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is explained in more detail below with the aid of the figures showing one exemplary embodiment:

(2) FIG. 1 schematically shows a foundry core in a view from below;

(3) FIG. 2 schematically shows the foundry core in a view directed at its one wide side;

(4) FIG. 3 schematically shows the foundry core in a view directed at its one narrow side;

(5) FIG. 4 schematically shows a part of a casting mould in a longitudinal section;

(6) FIG. 5 schematically shows a part of an engine block in plan view.

DETAILED DESCRIPTION OF THE INVENTION

(7) The casting mould 1 has a supporting section 2 which has the basic shape of a narrow truncated pyramid with opposing wide sides 3, 4 and likewise opposing narrow sides 5, 6 which join the wide sides 3, 4 to one another. Holding sections 8, 9 laterally protruding on the wide sides 3, 4 and extending over approximately one fifth of the height of the supporting section 2 are formed adjoining the upper face side 7.

(8) In addition, on its lower plane face side 10, two neck sections 11, 12 are formed onto the supporting section 2 which extend axially parallel to one another and protrude perpendicularly aligned from the face side 10. The neck sections 11, 12 have a cam-like cross-sectional form, the cam tip 13, 14 of which respectively points in the direction of the respective other neck section 12, 11.

(9) Two bridge sections 15, 16 extend between the neck sections 11, 12 in the longitudinal direction of the neck sections 11, 12 spaced apart from one another and from the face side 10 of the supporting section. The longitudinal axes L1, L2 of the bridge sections 15, 16 are aligned parallel to one another and to the face side 10 of the supporting section 2.

(10) The bridge sections 15, 16 merge with their ends into the respectively assigned neck section 11, 12. To that end, the lateral surfaces 17, 18 of the bridge sections 15, 16 are thus nestled on the peripheral surface 19, 20 of the respective neck section 11, 12. They run out tangentially and smoothly into the peripheral surface section 21, 22 of the neck sections 11, 12 which extends between the cam tip 13, 14 and the thickest point in each case of the cross-section of the neck sections 11, 12.

(11) At the respective connection point, where the bridge sections 15, 16 are joined to the respective neck section 11, 12, the thickness d of the bridge sections 15, 16 measured as the distance between its lateral surfaces 17, 18 corresponds to a maximum thickness dmax of approximately 5 mm, wherein in practice the thickness dmax can also be greater. Starting from this maximum thickness dmax, the thickness d of the bridge sections 15, 16 decreases continually in the direction of the respective other neck section 11, 12 until it reaches its minimum thickness dmin of approximately 1.5 mm in a central area 23, 24 arranged centrally between the neck sections 11, 12.

(12) In a corresponding manner, the height h of the bridge sections 15, 16, which is measured as the distance between the upper side and the lower side of the bridge sections 15, 16, starting from a maximum height hmax at the respective connection point continually decreases in the direction of the central area 23, 24 until a minimum height hmin of approximately 4.3 mm is reached there.

(13) The foundry core 1 was shot in one piece in a conventional core shooting machine (not shown here) from a commercially available so-called Croning moulding sand, the quartz sand grains of which had a mean grain diameter of 0.21+/0.02 mm (corresponding to AFS grain fineness number 68+/3) and were coated with a synthetic resin serving as a binder. The moulding sand was to that end shot at a pressure of 2-6 bar into a core box heated to 200-350 C., in which the binding resin of the quartz sand grains are baked together and hardened due to the supply of heat occurring via the core box. After a dwell time of 30-120 seconds required for this purpose, the foundry core 1 could be removed from the core box. It had a sufficient shape stability, despite the delicate form of its bridge sections 15, 16, to be able to supply it for further use. It also had, particularly in the area of the bridge sections 15, 16, a uniformly finely ground surface, the quality of which was of such a high-grade that it could be directly supplied for further use. The application of a coating or of another auxiliary agent, which would have been necessary in the case of coarser surface structures in order to obtain the required quality, was not necessary.

(14) Foundry cores 1 formed and produced in the manner mentioned above, are used as part of a casting mould 25 which is only shown in part in FIG. 4, is otherwise formed conventionally as a core package and is used for casting an engine block 26 for an internal combustion engine with cylinder chambers 27, 28, 29 arranged in a row which is cast from an aluminium fusible alloy and is also only shown in part in FIG. 5. The foundry cores 1 are arranged by means of covering cores 30, 31, 32 between the cylinder cores 33, 34, 35 forming the cylinder chambers 27-29, so that their bridge sections are arranged centrally in the upper area, which is assigned to the covering cores 30-32, of the narrow free space 36, 37 present between the cylinder cores 33-35. The respective free space 36, 37 forms the cylinder partition wall 38, 39 respectively in the finished engine block 26, by means of which the respectively adjacent cylinder chambers 27, 28; 28, 29 are separated from one another. In the area 40 in which the adjacent cylinder chambers 27, 28; 28, 29 come closest to one another, the minimal thickness dmin of the respective cylinder partition wall 38, 39 is approximately 5 mm.

(15) After casting the aluminium fusible alloy in the casting mould 25, the aluminium cast material solidifies. The binder which binds the sand grains of the foundry core 1 begins to decompose due to the accompanying heat. The thermal energy introduced in this way is normally only sufficient to start the decomposition process. If the broken pieces of the foundry core 1 obtained as a consequence are still too large to trickle out of the channels formed by the foundry core 1, the core material is subsequently further broken up into small pieces in a known way by means of a targeted treatment. A suitable thermal treatment, also known in the specialised technical language under the term thermal desanding, can be carried out for this purpose, in which the decomposition of the binder by the targeted supply of heat is continued and, as a consequence, the binding between the individual moulding material grains is broken up until such time as the moulding material is able to trickle out. Alternatively or additionally, breaking up the foundry core into small pieces can also be supported mechanically by exposing the casting mould or the cast part itself to hammer blows, knocking, shaking or vibrating. In order to optimise the removal of the broken up moulding material of the foundry core 1 from the respective channel, the respective channel can be additionally flushed with water or another liquid.

(16) At least the neck and bridge sections 11, 12, 15, 16 of the foundry cores 1 decompose in this way into fine particles such that their moulding sand, despite the minimised dimensions of the channels formed by them, freely trickles out of the complete cast part or, if necessary, can be rinsed out.

(17) The neck sections 11, 12 of the respective foundry core 1 can be coupled to a water jacket core (not shown here) which forms a cooling channel in the engine block 26, via which the walls of the engine block 26 defining the cylinder chambers 27-29 on their outsides are cooled. In this way, when the internal combustion engine is in operation, coolant flows via the inflow and outflow channels 41, 42 formed by the neck sections 11, 12 through the narrow cooling channels 43, 44, which are formed by means of the bridge sections 15, 16 and which in the area 40 are only approximately 1.5 mm wide and approximately 4.2 mm high, in the cylinder partition walls 38, 39 and provides effective cooling in the thermally highly stressed area of the cylinder partition walls 38, 39.

REFERENCE SYMBOLS

(18) 1 Foundry core

(19) 2 Supporting section

(20) 3, 4 Wide sides of the supporting section 2

(21) 5, 6 Narrow sides of the supporting section 2

(22) 7 Upper face side of the supporting section 2

(23) 8, 9 Holding sections

(24) 10 Lower plane face side of the supporting section 2

(25) 11, 12 Neck sections of the foundry core 1

(26) 13, 14 Cam tip of the neck sections 12, 11

(27) 15, 16 Bridge sections of the foundry core 1

(28) 17, 18 Lateral surfaces of the bridge sections 15, 16

(29) 19, 20 Peripheral surface of the neck sections 11, 12

(30) 21, 22 Peripheral surface section of the peripheral surface 19, 20

(31) 23, 24 Central area of the bridge sections 15, 16

(32) 25 Casting mould

(33) 26 Engine block

(34) 27, 28, 29 Cylinder chambers of the engine block 26

(35) 30, 31, 32 Covering cores

(36) 33, 34, 35 Cylinder cores

(37) 36, 37 Free space between the cylinder cores 33-35

(38) 38, 39 Cylinder partition walls of the engine block 26

(39) 40 Area in which the adjacent cylinder chambers 27, 28; 28, 29 come closest to one another

(40) 41, 42 Inflow and outflow channels of the engine block 26

(41) 43, 44 Cooling channels in the cylinder partition walls 38, 39

(42) d Thickness of the bridge sections 15, 16

(43) dmax Maximum thickness of the bridge sections 15, 16

(44) dmin Minimum thickness of the bridge sections 15, 16

(45) h Height of the bridge sections 15, 16

(46) hmax Maximum height

(47) hmin Minimum height

(48) L1, L2 Longitudinal axes of the bridge sections 15, 16