EP0272471B1 - Process and mould for manufacturing a cast iron object, and object thus produced - Google Patents

Description

The invention relates to a method for casting a cast iron camshaft having an elongated cavity and intended for use in an internal combustion engine. It also relates to a casting mold with a core in the iron foundry and a cast iron body.

If an elongated cast iron part is to be cast as a hollow body with a correspondingly elongated passage, a core must be made and inserted into the mold into which the molten iron is to be poured. In GB-PS 11 91 202 it is proposed to use a steel tube with a steel rod inserted therein and coated with insulating material as the mold core. In this process, liquid iron is poured into the mold and then the steel rod is pulled out of the steel tube that becomes part of the cast body. A major disadvantage of this procedure is that a very hard, difficult-to-drill quench layer is formed at the boundary between the steel and the cast iron. The effort for the steel pipe is considerable.

In another from British patent application 84 03 355 from February 2, 1984 known process, the mandrel consists of a tubular steel core wrapped with ceramic paper or similar insulating material. In this process, the ceramic paper forms an insulating layer between the melt poured into the mold and the much cooler steel tube. The insulating layer is used up by the molten iron flowing in during casting, e.g. B. burned, so that the inner metal tube can be pulled out of the cast body after it solidifies. It is very tedious to wrap each mold core with the intended insulating material before inserting it into the mold; in addition, the surface of the winding is not completely flat, so that the inner surface of the through opening of the cast iron piece to be manufactured has to be reworked.

Relatively flat inner surfaces of through openings in elongated cast iron parts are obtained if, according to GB-PS 15 96 442, a graphite rod is used as the mandrel. With this procedure, the handling is extremely difficult and can hardly be carried out in practice, since graphite rods are very sensitive to breakage and have a very porous surface, so that, for example, moisture and fat residues caused by skin contact can lead to casting defects, such as bubbles. In addition, in the case of a graphite core, similar to a sand core, supports are also used in the central region of the rod length if the length / diameter ratio of the core exceeds a certain value.

From "Patent Abstracts of Japan", Volume 4, No. 164, Nov. 14. 1980, p. 110 (JP-A-55 114 435) the use of tubes made of glass for the production of cooling cores in turbine blades is known. The use of a quartz tube to form a thin hole open on one side in a metal casting is reported in "Patent Abstracts of Japan", Volume 9, No. 155, June 29, 1985 (JP-A-60 30 549). The iron foundry is not mentioned in the publications. The corresponding prior art has nothing to do with the casting of camshafts.

The invention has for its object to provide a method for producing a hollow cast camshaft, i.e. a cast iron body that is thin relative to the length, which allows both hollow bodies without a casting opening or hollow bodies with very thin through openings or, for example, only suitable for supplying oil to bearings Cast blind holes, as well as hollow bodies with, for example weight-reducing, relatively thick cylindrical and / or adapted to the outer contour of the workpiece cavity relative to the workpiece outer diameter. The inner surface of the cast part, if and insofar as it is attainable or of importance, should correspond to the surface quality of a mechanical bore without substantial reworking, after all a problem-free handling should also be possible in the practice of a foundry. A casting mold suitable for carrying out the method according to the invention should be able to have a mold core which can also be used without supporting its central region of its length even with length / diameter ratios of the core of up to 500 mm / 5 mm. A hollow cast camshaft should also be able to be produced by the method according to the invention.

The solution according to the invention for the method for producing a camshaft is that a mold core made of glass is used during casting. The mold core provided according to the invention can have a smooth cylindrical surface or a surface contoured to the requirements for stability, weight or the like. Improvements and further refinements of the invention are specified in the subclaims.

A casting mold which is suitable for carrying out an exemplary embodiment of the method can have a mold core consisting of glass, which is completely enclosed by the cast iron body to be produced. An exemplary embodiment of a cast iron body produced according to the invention can have a cavity which is enclosed on all sides during casting and on whose inner contour glass, in particular quartz material, bears.

The invention provides a casting method and a casting mold with a rod-like elongated mandrel, which allow an elongated camshaft to be cast as a hollow body in the iron foundry, without substantial reworking of the inner contour being necessary and without quenching layers or hard to drill through in the camshaft the like. The method and the mold with a glass tube as the mold core are particularly well suited for producing a camshaft, which is known to be relatively thin for its length, but a part for reasons of weight savings or as an oil supply line or should have a continuous longitudinal cavity.

After the casting and cooling of a camshaft according to the invention, which is at least open on one side, any remaining glass can be left in its passage sack cavity or the like with the simplest means, e.g. B. are known for removing sand cores, in particular by simple drilling, by vibration, blasting media or high pressure water.

The mold core itself can be designed as a hollow body or solid. Hollow mold cores are preferred, particularly with regard to mechanical or thermal stability. When casting a camshaft, the mandrel can be longer than the shaft and therefore be supported at least on one of its longitudinal ends outside the outer contour of the camshaft. If the mandrel is only supported at one longitudinal end outside the outer contour of a camshaft, it is within the mold with the help of a core support. e.g. B. position as usual with the help of steel pieces, especially to rule out floating in the initially liquid iron. If the mandrel completely protrudes from the mold with its two longitudinal ends, it usually requires no supports up to a diameter / length ratio of only about 1: 100, so that there is a rod-like or rod-like elongated mandrel, with the help of which an appropriately elongated core is provided To produce a continuous hollow cast iron body. Cores that are relatively long are appropriately supported in the middle at the top against floating.

If the mandrel ends on one side within the mold and - as I said - is positioned at this end with a core support, a correspondingly elongated thin blind hole is formed in the finished cast workpiece with a correspondingly elongated rod-like thin mandrel.

The method according to the invention preferably also relates to producing a cast iron body which has a defined cavity without any access to the outside due to the casting. Such a cavity can also be elongated in a rod-like manner and take into account any value of stability, weight or the like of the workpiece to be produced be specified by its contour. In the simplest case, a mandrel for casting a cast iron body having a defined cavity (without an access caused by the casting) consists in melting a glass tube at both longitudinal ends and using core supports at the longitudinal ends inside the mold in a manner which is sufficiently stable for the casting is positioned. The core supports can preferably consist of an iron ring to be pushed over the mold core, on which support legs are attached, for example at a mutual distance of 120 °. In general, however, e.g. B. three or four, separate supports used. In principle, the closed mold core, which remains completely within the mold during casting, can have any configuration as a closed glass bulb, but also as a solid glass body.

According to the foregoing, the term “cavity” of the cast iron body is understood according to the invention to mean a through opening with two — possibly axial — entrances, a blind hole or a space that is completely enclosed by the cast iron during casting. While in the presence of an opening leading to the outside due to the casting, the glass remaining inside the cavity or on the walls thereof can be removed after the casting, such a post-treatment is not always necessary or desirable in the cavity enclosed on all sides.

A cavity enclosed on all sides is particularly advantageous if only a reduction in weight is desired and / or if the cavity is fully defined should not have blind holes to be produced by casting with sufficient accuracy or should have openings that penetrate into the interior, which can be subsequently created with the aid of a drill, which is not disturbed by any casting hole. When drilling blind holes in general - usually already during the design of the cast body - it must be ensured that the drill does not reach or penetrate the glass core, because otherwise it is usually necessary to dispose of the glass completely. If, on the other hand, through-holes are to be drilled, the interior of the cavity should generally be treated in the same way as in the case of cavities which are cast on one or more sides.

Various glasses can be used to produce the mold core according to the invention. Quartz glass is preferred, and quartz material in particular because of the reduced expenditure. Quartz glass is made from crystalline quartz by complete melting and degassing. In contrast, the quartz material which has proven particularly useful in the context of the present invention can already be produced by partially melting or sintering quartz sand. In practice, glasses that have previously been used to draw samples from a steel or iron melt for analysis by pipette type are also favorable. If contoured cores are required, a mold core according to the invention consisting of glass can be combined with glass parts of larger or smaller diameter or with a conventional mold core made of sand. The contoured cores of the type according to the invention can also run through the shape or end on one side or even all around within the shape.

Fig. 1

eine Gießform im Schnitt quer zur Längsrichtung eines langgestreckten Formkerns;

Fig. 2

eine untere Halbschale einer Gießform und einen als Glasrohr ausgebildeten Formkern; und

Fig. 4

eine Form im Schnitt mit einem allseitig eingeschlossenen Formkern.

Details of the invention are explained on the basis of the schematic representation of exemplary embodiments. Show it:

Fig. 1

a casting mold in cross section to the longitudinal direction of an elongated mandrel;

Fig. 2

a lower half-shell of a casting mold and a mold core designed as a glass tube; and

Fig. 4

a shape in section with a mold core enclosed on all sides.

The section through a casting mold according to FIG. 1 shows the lower mold 1, the upper mold 2 and a glass tube 3 serving as the mold core. During the casting, the hatched cavity between the lower mold 1 and the upper mold 2 is filled with the cast iron which later forms the cast iron body 4. Although the softening point of the glass 3 used to manufacture the glass tube is far below the temperature of the liquid iron, the casting and subsequent cooling of the cast iron body 4 result in a smooth inner surface 5 of the casting 4 corresponding to the surface quality of the glass tube 3.

Fig. 2 shows a perspective view of a lower mold 6 and a mandrel 7, with the aid of which a camshaft can be produced. The lower mold 6 has the recesses 8 corresponding to the outer shape of the cast iron body 4 to be produced. Corresponding to these depressions 8, raised zones 9 are provided on the surface of the molded core 7 designed as a glass tube. The material distribution or removal is preferably made such that the cast iron body 4 to be produced has largely the same wall thickness everywhere.

Fig. 3 shows a shape in section with mold core 7 enclosed on all sides between lower mold 1 and upper mold 2. This is positioned in the cavity remaining between lower mold 1 and upper mold 2 with the aid of three core supports 10 each such that the cast iron piece 4 to be produced has the desired inner contour receives. the core supports 10 are to be dimensioned such that they not only support the mandrel 7 but can also resist its buoyancy in the liquid iron.

According to FIG. 3, depressions 8 and raised zones 9 on the lower and upper mold 1, 2 or on the mold core itself can also be provided with an enclosed mold core 7, which correspond to a cam of the cast iron piece 4 to be produced.

The mold core 7 to be used in a casting mold according to FIG. 3 can be designed both as a hollow body and as a solid body made of glass, preferably quartz. Since the core is to be built into the cast iron body essentially for the purpose of saving weight, it is of course particularly expedient to use a hollow body made of glass as the mold core. Because of the relatively low (compared to iron) specific weight of glass, there is also a considerable reduction in the weight of the cast iron body produced, even when using a solid glass body.

Without damaging the finished cast iron body, it cannot be readily determined whether the cast cavity has the intended position, that is, whether the thickness of the wall around the cavity has the same desired thickness everywhere. The corresponding quality check can, however, be carried out, for example, with the aid of ultrasound measuring methods. The foundry is therefore able to guarantee the customer a constant quality.

Experiments have shown that the mandrel, in addition to being a tube that is open on one or both sides, is also — and preferably — designed as a hollow body made of glass. In experiments, a glass bulb was sealed under normal pressure, so there was normal air pressure in the bulb. Such a piston was positioned with the aid of core supports between the upper and lower molds so that they had the desired distance from the outer mold everywhere. After casting and cooling the cast iron body, it could be determined by ultrasound that the hollow piston had not changed its position during casting. The further check by sawing the cast body also showed a perfect design and exact position of the cavity enclosed on all sides in the workpiece.

Claims (9)

1. Method of casting a cast iron camshaft having an elongated central space and intended for use in an internal combustion engine, characterized in that a moulding core (7) of glass is used during the casting process.
2. Method according to claim 1, characterized in that a glass tube extending throughout the length of the camshaft is used as moulding core (7).
3. Method according to claim 1, characterized in that a hollow glass body to be surrounded on all side by the cast iron, particularly a closed glass body, is used as moulding core (7).
4. Method according to claim 1, characterized in that a solid glass body, preferably remaining inside the cast iron, is used as a moulding core (7).
5. Method according to one or more of claims 1 to 4, characterized in that the moulding core (7) is positioned with the aid of core supports (10) formed particularly of a ring to be pushed over the moulding core (7) with supporting legs mounted thereon.
6. Method according to one or more of claims 1 to 5, characterized in that the moulding core (7) is made of a material of the type of a glass tube, particularly quartz glass, suitable for taking samples from a steel or iron melt.
7. A method according to one or more of claims 1 to 5, characterized in that the moulding core (7) is made of translucent fused quartz.
8. A casting mould with a moulding core particularly elongated in the manner of a rod in the iron foundry for carrying out the method according to at least one of claims 1 to 7, characterized in a moulding core (7) made of glass to be completely surrounded by the cast iron body (4) to be produced.
9. A cast iron body (4) made by the method according to at least one of claims 1 to 7, characterized in a hollow space surrounded on all sides during the casting process, on the inner outline of which glass, particularly translucent fused quartz, applies.

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