GB2068279A

GB2068279A - Permanent mould

Info

Publication number: GB2068279A
Application number: GB8102099A
Authority: GB
Original assignee: BRUEHL EISENWERK
Current assignee: BRUEHL EISENWERK
Priority date: 1980-01-25
Filing date: 1981-01-23
Publication date: 1981-08-12
Also published as: FR2474359A1; IT1135147B; DE3002576A1; DE3002576C2; FR2474359B1; GB2068279B; IT8119286A0; ES8200025A1; ATA18781A; AU6653981A; AT381259B; BR8100365A; ES498736A0; JPS56111549A

Abstract

A casting mould comprising inner and outer shells (2, 3) the inner shell consisting of a steel unit having side walls (4) and a base part 5 defining the casting cavity and the outer shell consisting of a grey iron body having side parts (6) that support said side walls (4) of the inner shell and a base part (7) that supports said base part (5) of the inner shell; the side walls and base part of the inner shell being in connection with the side parts and base part of the outer shell by means merely of contact surfaces (45) of limited size, while the adjoining surfaces of the shells have no point of contact with each other; said contact surfaces (45) serving for heat dissipation from the inside to the outside and being arranged in the middle region with respect to the length of the casting cavity where distortion of the inner shell is at its lowest as a result of temperature drop. Spaces (34-37) exist between the inner and outer shells in other regions, some of these spaces, which are ventilated, containing insulation (41). <IMAGE>

Description

SPECIFICATION Casting moulds This invention relates to permanent moulds (chill moulds) for manufacturing castings from light-metal alloy, more particularly for long castings, for example cylinder heads of internal combustion engines. The invention is concerned with chill moulds that are constructed with a double shell with the inner shell consisting of a steel unit and the outer shell of a grey cast iron body.

During the chill casting of long castings, for example of a length of 0.3 m to 1 m and more, there is a great risk that the casting will not remain straight but will distort to a greater or lesser degree, i.e. that-the casting itself, seen over the longitudinal axis, will be curved.

Any such distortion of the casting is undesirable. The tolerances at the surfaces to be processed must be maintained at a high level.

This means, on the one hand, a higher material expenditure and, on the other hand, greater processing costs. Different ways of avoiding distortion of long castings during chill casting have already been tried. One way of achieving this consists of cooling the chill mould. This results in additional expense in the development and formation of the chill mould. The parts of the chill mould must be dimensioned so that a sufficient number of cooling ducts may be arranged within the wall thickness of the chill mould. This leads to an additinal expense in terms of operation.

Another way of avoiding distortion of long castings during chill casting is by designing the chill mould itself in an extremely massive manner. The chill mould itself is provided with excessively strong wall thicknesses. This is based on the idea that, by their mass alone, the thick walls can absorb the heat to be conducted off from the casting so that the chill mould remains straight and does not become distorted. This is because, in the case of chill casting, it is not only the casting which becomes distorted but also the parts of the chill mould, i.e. the steel unit and the outer grey cast iron body forming the outer shell. These may contribute further to the distortion of the casting. Common to the two instances of the previous formation and development of the chill moulds for producing long castings is that the chill moulds produced are very material intensive.The chill moulds produced are very heavy. In the case of the previous constructions the ratio of specific weights, i.e. one kp for the chill mould to the kp for the cast material or casting, inclusive of casting header, reaches the values of 200 to 500 to 1. This means that the chill mould is at least two or three hundred times heavier than the casting. In operation weights of this kind are very expensive in terms of work and energy, particularly with chill moulds which are divided in the longitudinal plane making it necessary for the chill mould parts to be displaceably mounted for closing and opening. The previous construction of chill moulds is also disadvantageous when the castings are to be produced in continuous operation in a circulating system.

According to the present invention there is provided a casting mould comprising inner and outer shells, the inner shell consisting of a steel unit having side walls and a base part which gives the casting its contour, and the outer shell consisting of a grey cast iron body having side parts that support said side walls of the inner shell and a base part that receives said base part of the inner shell; the side walls and base part of the inner shell being merely in connection with the side parts and base part of the outer shell by means of contact surfaces of limited size, while the adjoining surfaces of the shells have no point of contact with each other; said contact surfaces serving for heat dissipation from the inside to the outside and being arranged in the middle region with respect to the length of the casting where distortion of the inner shell is at its lowest as a result of temperature drop. Such a chill mould when used for the production-of long castings, for emample internal combustion engine cylinder heads, chiefly by gravity die-casting, enables castings to be produced which remain straight, seen over their length, and the ratio of the weight of the chill mould to that of the casting is substantially reduced as compared with previous moulds, thereby making the handling of the chill moulds easy and fast with the use of less energy.The construction of the chill mould consisting of an inner shell and an outer shell is based on the knowledge that as far as possible there is no transfer of heat between the shells, i.e.

that insulations are provided whenever possible, and that heat transfer points between the inner shell and the outer shell are arranged in a controlled manner only at predetermined points, that is these transfer points, through common contact surfaces, should be provided where, in view of the distortion of the level of the inner shell, heat is to be given off to the outer shell. The temperature pattern between the cast material and the inner shell, i.e. the steel unit, decreases from the inside to the outside so that, as a consequence, the steel unit tends to curve outwards at the ends of its length. This tendency must be counteracted by drawing-off heat from the inside to the outside by means of contact surfaces at controlled points between the ends of the inner shell. This is usually in the middle region between the two shells.At the point where the bulging out of the inner shell, i.e. the steel unit, will have the greatest effect, any heat transfer is prevented by means of insulation. The end result of this method of arranging the contact surfaces is that the forces being produced as a result of heat expansion of the grey cast iron part, that is the outer shell, counteract the forces being produced by the heat on the inner shell, that is the steel casting. The distortions of the shell parts must cancel each other out so that overall the chill mould, and above all the inner mould, that is the steel unit, remains straight during the casting. In this way the casting itself also remains straight, that is is of extremely exact size, so that desired tolerance limits are not exceeded. In order to assist these processes the shells forming the chill mould should be kept extremely light.The wall thicknesses of the shells should be kept relatively thin. They may be approximately 1 5 to 20 mm. Overall this leads to an extremely light construction of the chill mould. The ratio of weights, namely one kp of the chill mould to the kp of the cast material is reduced to 70 to 90 : 1, i.e. to a third or almost a sixth compared with the previous constructions. The considerable weight reduction has as a consequence the further advantages of making the chill mould parts of the divided chill mould easier to handle. Less energy is required for the displacement. Furthermore, the chill mould is suitable for use in a circulating system. No dead weights need be involved, which again leads to a considerable saving in operational energy. The cost for the production of the chill mould and for the operating the mould are considerably reduced.

The opposite-lying surfaces of the shell parts have insulations outside the contact surfaces arranged at controlled points. An effective insulation may be achieved by these surfaces being offset from one another outside the contact surfaces by recesses. The recesses also have the advantage of considerably reducing the weight. They form controlled insulation spaces. In order to aid this type of insulsation, that is-to bar heat transfer or convention, heat insulating bodies of a suitable type, for example insulating boards or also shielding plates or such like, can be arranged in the recesses. Advantageously, the insulation which is arranged in the recesses can be made of asbestos. The heat insulating bodies or boards set in the recesses may be secured in their position by spacers made of insulating material.Where support surfaces are required between the inner shell and the outer shell, the support is provided by means of insulating components. In particular ceramic bodies may be used for this purpose.

The result of the controlled arrangement of contact surfaces and insulation between the two shells should be to ensure that the inner shell is straight by means of point heating of the outer shell at predetermined places. This applies not only for the side walls of the steel unit of the inner shell but also for the bottom part of the mould.

To avoid build-up of heat of the air in the recesses, the recesses are preferably provided with ventilation and extraction openings or passages. When the hollow spaces formed by the recesses are deaerated the heat or hot air can pass off unhindered. The ventilation openings are provided so that colder air may always pass back into the hollow spaces so that true cold bridges are produced by the recesses.

In the case of chill moulds having chill mould parts produced by longitudinal division which have to be displaced for opening and closing in the transverse direction to the longitudinal axis, the present measures are additionally supported by keeping these chill mould parts free of actuating members for opening and closing the mould parts and also for the ejection of the casting. The actuating members are preferably arranged in a stationary manner. This contributes to a reduction of the weight of the chill mould. In contrast to moulds in which these actuating members are arranged on the outer shell, these actuating members if arranged as herein proposed are not involved in the thermal economy of the double-shell chill mould. As a result, it is possible to control with greater accuracy the thermal conditions and the thermal stress ratio of the shell parts in respect of each other.

Also, for this purpose, the other parts which receive or carry the chill mould may be provided with insulation against heat transfer.

Also involved in this respect is the fact that a base plate for an underframe or undercarriage receiving the mould may be insulated by heatinsulating intermediate layers. Also, the casting header may be arranged so that no heat can reach the chill mould from this.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a digrammatic cross-sectional view of a chill mould, Figure 2 is a schematic longitudingal sectional view of the chill mould of Fig. 1, and Figures 3 and 4 are detail views of alternative embodiments.

Referring to Figs. 1 and 2, the chill mould 1, which is for manufacturing castings from light metal alloy, more particularly long castings, for example cylinder heads of internal combustion engines and such like, has an inner shell 2 comprising a cast-steel part and an outer shell 3 comprising a grey cast iron body. The inner shell parts serve to shape the casting and consist of side walls 4 and a base part 5, while the outer shell components, as grey cast iron bodies, are side portions 6, which keep the side walls 4 supported, and a base part 7. Located inside the inner shell walls 4 and the base part 5 are the cores forming the shaping of the casting, for example a bottom core 8 and cores 9 and 10 which are provided with extensions for forming inlet ducts.A top core 11 is a pressure pig for gravity die-casting, the material additionally required because of the contraction of the cast material being extracted from a supply chamber of the pressure pig core.

The base part 7 is mounted and centered by means of feet 7a on a plate 1 2 of an underframe or under carriage 1 3. The undercarriage 1 3 has a running wheels 14 which travel along on rails 15, which rails 1 5 are supported by an underframe 1 6.

A lifting beam 1 7 has push rods 1 8 for ejecting the casting from the chill mould, the lifting beam being slidably mounted on pins 1 9. Connected with the lifting beam 1 7 is a shaft 20 which, by means of a flange 20a, may run in fixedly arranged hook-type retainers 21 when the chill mould is moved in the longitudinal direction and may run out of these again, the retainer 21 being actuated by a hydraulic cylinder 22 provided in a fixed position.

For dividing the chill mould in the direction of the longitudinal axis, the side walls 4, together with the side parts 6, are displaceable in the transverse direction to the longitudinal axis, slide guides 23 and 24 being provided for this purpose. Hydraulic cylinders 25 and 26 are used to effect this displacement, these cylinders having hook portions 27 and 28 arranged on their pistons 25a and 26a, which hook portions engage with projections 29 and 30 of the outer shell parts 6 for opening and closing the chill mould parts 4.

For displacing the chill mould parts in the transverse direction to the longitudinal axis the outer shell parts 6 slide on small rails 31a (Fig. 2) and engage under further guide rails 31b. The casting header is designated by 32.

To achieve a rectilinearly extending casting within a prescribed narrow tolerance limit, insulation and, to a limited degree only, contact surfaces are provided between the parts 4 and 5 of the inner shell and the parts 6 and 7 of the outer shell. The insulation preferably consist of recesses or hollow spaces 34, 35, 36, 37 which are provided as far as possible around the portions of the inner shell so that the opposite-lying surfaces of the parts of the inner shell and the parts of the outer shell are not in direct contact with one another. Hollow spaces 38, which may be in connection diagonally with the hollow spaces 36 and 37, are also provided on the longitudinally sides of the side walls 4 of the inner shell parts.

Leading to these hollow spaces or recesses are ventilation ducts 39 and at the upper end of the hollow spaces extraction ducts 40 are provided in order to avoid a build-up of heat inside the recesses or hollow spaces. Furthermore, heat insulation bodies or insulation boards 41, 42 which stop and absorb heat radiation to the inner shell parts are arranged in some of the hollow spaces, as illustrated in the spaces 34 and 38. These insulating bodies 41 and 42 are secured in place by spacers 43 and advantageously consist of ceramic material.

The base part 5 of the inner shell 2 is supported by the base part 7 of the outer shell 3. In this connection contact surfaces are provided, in a controlled arrangement, for conducting-off heat from the inside to the outside. One such contact surface 45 is located in the middle region, seen over the length of the components, by means of an upwardly directed projection 46, while the other support parts have intermediately placed insulation bodies 47 and 48. By this arrangement heat dissipation from the inner shell base part 5 to the outer shell base part 7 takes place in a controlled manner in the central region where deformation by means of the heat is at its lowest. At the ends of the long portions, at which deformation is at its greatest, there are no direct touching or contact surfaces, the support here being provided by heat insulation bodies.In this manner the tendency of the cast steel base part 5 to bulge, with the greatest curvature deformation at the ends, is counteracted by the grey cast iron base part 7 in which the middle region is hotter than the end portioris, thereby producing an oppositely directed convexity. The forces thereby produced are arranged to cancel each other out, making it impossible for the cast material to be damaged. It will be appreciated that wherever it is possible for there to be ventilation and extraction ducts to the recesses they are arranged in the shell portions.

Where other contact surfaces may otherwise occur they are also insulated . This applies for example, to the points at which the base part 5 of the inner shell is fixed to the base part 7 by screw bolts 52; heat insulation rings 53 are inserted here for support. The occurrence of heat bridges are completely avoided except for the controlled arrangement of heat contact surfaces between the parts of the inner and the outer shells. Consequently, the heat insulation between the parts of the inner and outer shells is effected on all sides in order to achieve and make calculable the controlled effect for the straightness of the cast material.

It is also advantageous for the running wheels 14 and 1 4a to be mounted in a heat insulated manner, which can be achieved by means of a heat insulating sleeve 54 (Fig. 3).

Alternatively, if the base part 7 is movable directly on driven or non-driven rollers 55 of a roller conveyor, as shown in Fig. 4, an intermediate rail 56 may also consist of heat insulating material.

The described development of the doubleshell chill mould is also considerably advantageous in terms of expense as a result of the reduced wall thicknesses, with, at the same time, improved achievement of the desired advantage of straightness of the cast material.

For a kp-cast material (selling weight) approximately one third to almost one fifth only of the costs of the chill mould need be used, with otherwise the same components and using inlet-outlet-, water jacket- and pressure pig-core in silical sand. The cost ratio becomes even more advantageous in the case of cylinder heads or more than approximately 10 kp. The chill mould weight (inclusive of casting header) relative to the weight of the casting can be arranged to be in the ratio of less than 1 00:1, preferably 90 to 70:1.

Claims

1. A casting mould compising inner and outer shells, the inner shell consisting of a steel unit having side walls and a base part which give the casting its contour, and the outer shell consisting of grey cast iron body having side parts that support said side walls of the inner shell and a base part of the inner shell; the side walls and base part of the inner shell being merely in connection with the side parts and base part of the outer shell by means of contact surfaces of limited size, while the adjoining surfaces of the shells have no point of contact with each other; said contact surfaces serving for heat dissipation from the inside to the outside and being arranged in the middle region with respect to the length of the casting where distortion of the inner shell is at its lowest as a result of temperature drop.

2. A mould as claimed in claim 1, wherein the opposing surfaces of the inner and outer shells have insulation outside said contact surfaces.

3. A mould as claimed in claim 1 or 2, wherein opposing surfaces of the inner and outer shells are offset from one another outside said contact surfaces by means of recesses.

4. A mould as claimed in claim 3, wherein heat insulating bodies are arranged in said recesses.

5. A mould as claimed in claim 3, wherein heat insulating bodies are arranged in said recesses.

6. A mould as claimed in claim 3, wherein shielding plates for preventing heat radiation are arranged in said recesses.

7. A mould as claimed in claim 3, 4, 5 or 6, wherein said recesses and corresponding hollow spaces are provided with ventilation and extraction ducts.

8. A mould as claimed in any one of the preceding claims, wherein insulating members are provided at support surfaces between.the inner shell and the outer shell.

9. A mould as claimed in claim 8, wherein said insulating members are formed as ceramic bodies.

10. A mould as claimed in any one of the preceding claims, wherein the base part of the outer shell and an underframe receiving this base part is insulated from means along which the underframe can move.

11. A mould as claimed in any one of the preceding claims, wherein the mould is free of actuating members for opening and closing the mould, and is also free of such members for ejecting the casting.

1 2. A mould as claimed in any one of the preceding claims, wherein the chill mould weight (inclusive of casting header) relative to the weight of the casting is in the ratio of less than 100:1.

1 3. A mould as claimed in claim 11, wherein the chill mould weight (inclusive of casting header) relative to the weight of the casting is in the ratio of 90 to70:1.

14. A casting mould substantially as hereinbefore described with reference to Figs. 1 and 2, with or without either Fig. 3 or Fig. 4, of the accompanying drawings.