GB2118079A

GB2118079A - Casting moulds and their manufacture

Info

Publication number: GB2118079A
Application number: GB08308006A
Authority: GB
Inventors: Uwe Ehlbeck
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-03-23
Filing date: 1983-03-23
Publication date: 1983-10-26
Also published as: ES282773Y; IT8347962A0; ES282773U; JPS58173054A; IT1197612B; FR2523880A1; GB8308006D0; DE3210588A1

Abstract

A casting mould half for a metal casting process comprises a layer of a mould material (9), such as a moulding sand mixed with a binder, shaped by a pattern 8 to form the inner face of the mould half, and supported by a backing formed by a number of individual modules (5, 6) which are placed together side by side on a support plate (2) and are preferably held together by a binding (17) and/or a mould frame (4). Preferably the modules are selected and assembled so that the face of the backing remote from the plate (2) generally follows the contour of the pattern (8). By using a plurality of individual and different size modules a mould half of any desired shape can be constructed, and furthermore the modules are easily salvaged for re-use after a casting has been made. <IMAGE>

Description

SPECIFICATION Improvements relating to casting moulds and their manufacture This invention relates to casting moulds for making metal castings, and to a method and apparatus for use in making such moulds.

In the casting of metal, permanent moulds or lost moulds made by a compaction process or a solidification process are used, the moulds being made in two halves which are fitted together for the casting.

In the compaction process each mould half is formed by packing clay-bonded sand, or some similar material, into a mould box consisting of a mould plate and frame and a mould half-pattern, and compacting the sand against the pattern, for example by tamping or vibrating and pressing. The process is very cumbersome because the entire mould box cavity must be filled with sand and, having regard to the usual sand/casting ratio of from 6:1 to 12 :1, large quantities of sand are necessary. This necessitates a corresponding capacity for sand preparation with an expensive dust-removal plant. Also, for a high quality casting, a uniform and heavy compaction of the mould sand is necessary.Added to this is the fact that the cores required when making castings with cavities are usually made from a high-quality moulding material, so that special measures for recovering the core sand are necessary, if indeed this is possible, otherwise a mixture of core sand and mould sand is produced in the sand treatment. Furthermore, in the cooling of a mould of this type, the sensible heat of the metal or casting appears diffusely and at low temperature due to the high sand/casting ratio, with the result that difficulties arise in the recovery of heat.

Moreover, lost moulds of this type do not permit any controlled cooling as a whole or by zones, without special expensive measures for accelerated heat removal.

Some of these disadvantages are avoided by lost moulds made according to the solidification method, for example mask moulds made from a hot-hardening, resin-bonded sand. The strength of such moulds is based upon a chemical or physical bond of the mould material. In making each half of a mask mould a quartz sand to which a binding agent, for example phenolic resin, has been added at a temperature of, for instance, 120 to 1 500C, is applied to a pattern at a temperature of 200 to 2500C and coated with a release agent.

Depending upon the curing time and pattern temperature, the mould material solidifies as a coating of varying thickness on the pattern. After a hardening time of several minutes, the mould halfmask is removed from the pattern and, after the necessary cores have been inserted, is glued to the other half-mask and placed in a mould box.

Since the mask mould is frequently not capable of withstanding the pressure of the molten metal which is cast, it is usual to pack the box behind the mask with old sand, iron granules or scrap casting material. Only when there is a very large number or run of identical castings to be made is the use of a supporting shell, profiled to the form of the mask mould, justified on account of the high costs.

For this purpose German Patent Specification No.

725,946 describes a mould comprising a permanent form of sintered metal, and a thick coating of mould material, for example of sand or mortar material. In contrast, German Patent Specification No. 870,598 describes a casting mould consisting of an outer permanent concrete layer and an inner layer of usual mould material to the shape of the pattern and casting.

Disadvantages of mask moulds are the high costs, the risk of distortion of each mask half when removing it from the pattern, and the high likelihood of breakage. Furthermore, the production of the masks requires an accurate temperature control and comparatively long hardening times. The back filling of a mask mould is usually carried out in the mould box from above, and therefore requires a vertical division of the mould. A further disadvantage arises from the fact that the filiing forms part of the material cycle.

The use of a support shell for each mask half avoids the need for back-filling material but achieves this with expenditure in other respects. In the support shell method, a mould half is formed by injecting resin-coated quartz sand into a mould material space between a hot pattern on the one hand and a hot profiled support shell of metal on the other hand. In this way, firm and easily handled half-moulds and moulds are obtained.

The high expense of support shells contoured to suit the casting limits the use of this method, however, to the casting of large runs. Added to this is the fact that the cleaning of the support shells in the case of faulty moulds which cannot be used for casting, and the temperature control of the support shells, is expensive. The support shells moreover are not gas-permeable.

It is also known to form moulds using waterglass or a cold-hardening phenolic resin as the binding agent for the mould material. The advantage of this is that the mould sand hardens at room temperature, the waterglass requiring gasification with carbon dioxide. In this case, however, each mould half consists of a highquality mould material layer surrounding the pattern, and of a back-filling material possessing a low proportion of binding agent and high proportion of old sand, and optionally a covering layer of old sand with high binding agent content, in order to assure adequate handling strength of the mould. This in turn makes the sand recovery treatment difficult, because a fractionated separation of the different sands from the individual layers is hardly possible.

Permanent moulds, on account of their high cost of manufacture, are used only for long runs.

They are usually made of metal, a high-quality material being necessary due to the thermal stresses experienced when the cast molten metal comes into contact with the metal surface of the mould. A further disadvantage is the lack of gas permeability of the mould, a feature which can only be remedied by expensive special measures.

According to the present invention, we propose a casting mould half for use in a metal casting process, comprising a backing formed at least partly by a plurality of individual modules supported side by side, and a layer of mould material which is supported by the backing and which has been shaped by a pattern to form the moulding face of the mould half.

According to another aspect of the invention we propose a method of making a casting mould half for use in a metal casting process, in which a plurality of individual modules are positioned and supported on a support plate to form a backing, a pattern for the mould half is supported relative to the backing so that there is a space therebetween, and the space is filled with a mould material which hardens to form a layer which is supported by the backing and of which the surface in contact with the pattern forms the moulding face of the mould half.

This permits moulds to be made which have high gas permeability and which produce excellent quality castings, expecially regarding surface quality. The moulds are made with a relatively low quantity of mould material and the construction permits a simple recovery treatment resulting in a high amount of re-usable mould substances.

Furthermore, the construction is suitable both for small and for large runs of casting.

The invention stems from the consideration that the quality of a casting, i.e. especially its surface and contour sharpness, is determined predominantly by the nature of the boundary layer between the mould on the one hand and the cast metal on the other hand, whereas the mould backing determines the dimensional stability of the casting, the limits of casting and gating technique, the ease of handling or mechanization and automation, and decisively influences the mould costs. By constructing the backing of a mould half from a plurality of individual modules or elements of varying sizes, the backing can be assembled simply and to any desired shape which suits the casting to be made. Provided the modules are held in position sufficiently firmly, the backing provides a strong and stable support for the layer of mould material (sand) forming the inner face of the mould.After casting, however, the backing is easily disassembled, allowing the mould sand to be recovered easily and the modules to be re-used. The construction cost is sufficiently low for it to be practical even for single and small casting runs.

The modules are preferably arranged so that the surface of the backing which supports the layer of mould material substantially follows the contour of the pattern, thus keeping the volume of mould material required as small as possible. The requirement for sand and binding agent per casting is therefore small, which leads to a considerable reduction in the storage and transport capacity required, and permits the use of a high-quality mould sand, such as zirconium sand. Since the backing modules are easily separated from the mould material after the casting has been removed from the mould, a highly pure sand results which is immediately suitable for re-use. This permits the use of a mould material on the basis of core sand. The small requirement for binding agent furthermore makes possible a reuse of high-quality binding agent and leads to only little environmental pollution.

As binding agents, any organic binding agents, especially cold-hardening or hot-hardening resins or resins which harden with gasification, such as furan resins and phenols, are suitable. Inorganic binding agents, such as waterglass and cement, are also suitable.

As previously mentioned, casting moulds made in accordance with this invention possess high permeability to gas, as a result of the more or less large ventilating openings, usually gaps, which exist at the abutting surfaces and edges of the modules and which permit escape of air or gas over the greater part of the casting surface.

Furthermore, by an appropriate choice of the cross-section of the modules, venting and degassing openings can be created intentionally.

The modules may have a circular or polygonai, preferably square or rectangular, cross-section, and may be arranged to create between adjacent modules gusset-shaped ducts extending from the moulding material layer to the back of the mould.

If desired, the modules may be so profiled that they may be interlocked one with another. The modules may be hollow, solid or porous, allowing the weight of the mould to be adapted in optimum manner to the requirements of casting. In the case of modules of square cross-section, the edge length is preferably from 10 to 1 00 mm, whereas for cylindrical modules the diameter is preferably from 10 to 100 mm.

The vent openings and gaps are of course clogged as soon as the mould material is injected into the space between the pattern and the backing formed by the modules, but nevertheless there is still high permeability to gas, which makes possible the use of less flowab[e sands and in particular gasification of the mould material, for example with carbon dioxide or sulphur dioxide.

The penetration of the mould material into the openings and gaps also results in effective locking of the mould material layer or mask to the modules of the backing. This can be still further intensified by the modules being profiled at the end contacted by the mould material, for example being angled or possessing depressions.

The assembly of modules forming the backing may be surrounded by a mould frame and/or may be clamped or braced together, for example with a surrounding binding of wire. Bracing is possible, however, also with the help of a sliding plate on at least one side of the mould frame by which the modules can be pressed against one another and against the opposite wall of the mould frame. In this way, generally stable half-moulds which can be handled without difficulty are obtained, and which can also be turned over without special equipment and connected to the complementary half. The mould frame can then be removed, so that it does not subsequently enter into the material cycle.

If desired, it is possible to provide a seal between the mould frame and the modules of the backing e.g., by means of a peripheral inflatable tube, which simultaneously makes possible easy but elastic wedging of the modules in the frame and, by subsequently releasing the pressure, rapid loosening of the module connections.

Depending upon the nature of the casting, the peripheral modules may extend to the plane in which the mould half meets the other when the two halves are assembled to form the complete mould. The peripheral modules of the two halves therefore meet and touch one another in the edge zone of the mould, so that the mould material contact between the two halves of the mould is limited to a minimum.

The modules are preferably made of metal, for example steel or light metal, or of ceramic material, and due to their high thermal conductivity, they achieve rapid cooling of the casting in the mould without adversely influencing shrinkage of the casting. The individual modules and the gaps inevitably formed by them at their abutting surfaces impart to the mould, in contrast to conventional moulds, a degree of resilience, which can be further increased by loosening the bond between the modules at an appropriate time after casting. This may be done, for example, by removing a frame surrounding the modules or by loosening a binding eveloping the modules.The casting can then immediately be unpacked, because the mould easily breaks down into its constituents, i.e. the modules on the one hand and the mould and core sand on the other hand, which then only need to be separated from one another.

The material cycle is therefore limited to a few, easily transported and separated, robust components and materials.

The rate of cooling of a casting in the mould may be controlled locally by arranging individual modules or module groups to be at a particularly small or a particularly large distance from the mould face and hence the surface of the casting.

The module or modules may even extend as far as the surface of the casting, i.e. right through the layer of mould material. Basically, the rate of cooling depends upon the thickness of the mould material layer or mass, which can be adjusted by appropriate selection of the modules in relation to the spacing between the pattern and the support plate in any particular area.

After casting and hardening, the moulds are moved without frame by means of simple pallets or a continuous conveyor into a cooling tunnel, in which they rapidly give up their heat at a high temperature level. This enables economical heat recovery to be achieved at a comparatively low tunnel volume.

Examples of casting mould halves in accordance with the invention and of methods of making them will now be described with reference to the accompanying drawings, in which: Figure 1 is a cross-section through a first example of a mould half for a horizontally split casting mould, showing the mould half during a stage in its manufacture; Figure 2 is a view similar to that of Figure 1 but showing a second example of a casting mould half; Figure 3 is another view similar to that of Figure 1 and showing a third example; Figure 4 is a cross-section through a casting mould assembled from two mould halves similar to that shown in Figure 1; Figure 5 is a sketch illustrating schematically apparatus for use in making casting half-moulds in accordance with the invention;; Figure 6 is a schematic sectional view illustrating a stage in the manufacture of two halfmoulds in accordance with the invention for a vertically split casting mould; Figure 7 is an enlarged scrap section showing the mounting of modules in the arrangement shown in Figure 6; and, Figure 8 is a view similar to Figure 7 but showing an alternative mounting arrangement.

Figure 1 shows a supporting plate 2 which is furnished in the usual way with slit nozzles 1 and an injection opening 3, and on which there is peripheral frame 4 surrounding an assembly of individual block or rod-like modules 5, 6 of like cross-section but different heights disposed on the plate 2 in rows beside and behind one another.

The end faces 7 of the modules 5 remote from the plate 2 are spaced from a half-pattern 8 supported by the frame 4 so that between the modules and the half-pattern there is a space 9 which is of substantially uniform thickness except at the periphery where the outermost modules 6 extend to the mould parting plane as defined by the pattern 8. The pattern and the frame are centred with respect to each other by pins (not shown) which are pushed through holes 14, 1 5 in the pattern 8 and corresponding holes in the frame 4.

The mould frame 4 possesses a somewhat greater width than the assembly of the modules 5, 6 permitting easy fitting and removal of the mould frame, and to seal the gap 10 between the outermost modules 6 and the mould frame when the frame is in position, the frame possesses a peripheral groove 11 housing an inflatable sealing tube 12. When the pressure in the sealing tube 12 is released, the mould frame can be lifted clear of the modules 5, 6.

The pattern 8 possesses openings 13 for injecting into the space 9 the mould material for forming the moulding face layer of the mould half. The openings 1 3 are provided with inserts 1 6 which project somewhat beyond the lower face of the pattern and thereby create points of intentional rupture for removing the pattern. The inserts 1 6 can be easily pushed upwards out of the openings 13 after the pattem 8 has been removed, due to their conical form.

The mould material is injected through at least one of the openings 3, 13 into the space 9 and completely fills this space. It penetrates slightly into the gaps and openings situated between neighbouring modules 5, 6 and keys the mould material layer to the backing. These openings and gaps, in conjunction with the usual openings in the support plate prevent the occurrence of air pockets and thus assure a homogeneous distribution of mould material, even of a moulding sand possessing low flowability is used. At the same time, due to the high injection pressure, wedging of the individual modules 5, 6 in position within the mould frame 4 takes place, so that after the mould material has hardened and the pattern has been removed, the half-mould so formed can be immediately turned over and placed upon another half-mould to form a complete mould, such as illustrated in Figure 4.The turning over may be carried out, where the modules are of a magnetic material, by means of an electromagnetic device, which can be used to fix the modules in their intended position instead of, or in addition to a binding 17 or the mould frame 4.

The mould frame may be removed after turning over and bringing the half-moulds together.

In the embodiment shown in Figure 2, one of the modules 1 8 extends as far as the pattern 19, so that when the mould half is used in making a casting a more rapid removal of heat occurs in the region of the contact surface between this module and the casting. Also in contrast to the first example, in the example shown in Figure 2 the peripheral modules do not reach the pattern 1 9 and the mould material 20 is able to extend as far as the mould frame 4. Furthermore, a sprue core 32 is inserted in the backing in place of two of the modules in the central zone. Otherwise, the embodiment of Figure 2 is similar to that of Figure 1.

The third example shown in Figure 3 is similar to that of Figure 2 except that some of the modules in a central region are absent so that the mould material space 20 extends right down to the support plate 2 in this region.

In Figure 4, a complete casting mould including a central core 21 is illustrated after removal of the mould frame from each half mould and pouring of the casting 22. In this state the modules are held together only by the mould material and the bindings 1 7.

After the pouring and cooling of the casting, only small forces are necessary for removing the casting from the mould and the mould material from the modules. The mould material is supplied to a usual sand regeneration and treatment system, while the modules are cleaned and, provided they do not need repairing, are used again. The repair of the modules is advantageously limited to straightening, grinding and possibly repaire welding. A high degree of measurement accuracy is not important, since intermediate spaces between the modules are in any case desired for the reasons explained earlier.

The modules used in carrying out this invention can be combined with one another in various ways and are suitable for all types of castings.

Thus having regard to the weight of the mould and/or a locally varying temperature stressing, modules of different materials, for example steel and light metal can be used simultaneously. In each individual case, the different distances between the surface of the mould half pattern and a reference plane are first established, and the modules are then selected and assembled according to these distances and taking into account the intended thickness of the mould material layer, i.e. the mask thickness, at different positions.

Figure 5 shows diagrammatically apparatus for use in making a casting mould half in accordance with the invention. The apparatus comprises a module magazine 23 which is subdivided by intermediate walls 24 into individual rows of modules 5, 6, 18 of different sizes. Behind each individual row of modules there is a pusher device, indicated by arrows 25, by means of which the modules can be fed to a module grab 26 comprising a row of individual module compartments 28 separated by walls 27, and a movable bottom 29. The module grab is able to travel in the directions of the arrows 30, and can therefore be moved past the ends of the rows of modules of the module magazine 23 in order to receive successively the individual modules required for one of the rows of modules of the mould half.As soon as the module grab contains the required modules, it is moved from the open side into a mounting frame 31, and deposits the row of modules in the required position on the support plate 2.by opening the bottom 29 of the grab. In this way the backing of the casting mould half is built up row by row from individual modules. This can be done completely automatically if the apparatus is constructed in the manner of a mounting machine.

For the construction of a mould with a vertical parting plane, Figure 6 shows a support frame 33 with a closure batten 34 situated between two patterns 8 and 19. The individual modules 5, 6 are connected by dovetail guides 35 to the support frame 33 in the manner shown in Figure 7, and the moulding sand is injected through openings 13 in a cover 36 into the mould material spaces 20 formed between the modules and the patterns 8 and 19.

In the alternative embodiment indicated in Figure 8, pairs of modules 5, 6 are connected together end to end by a web 37, and adjacent pairs are held in position by filler and retaining bars 38 extending between the webs 37 and secured by a locking batten 34.

Claims

1. A casting mould half for use in a metal casting process, comprising a backing formed at least partly by a plurality of individual modules supported side by side, and a layer of mould material which is supported by the backing and which has been shaped by a pattern to form the moulding face of the mould half.

2. A casting mould half according to claim 1, in which the surface of the backing which supports the layer of mould material substantially follows the contour of the pattern.

3. A casting mould half according to claim 1 or claim 2, in which vent apertures are situated between the modules.

4. A casting mould half according to any one of claims 1 to 3, in which the modules are blocks having a circular or polygonal cross-section.

5. A casting mould half according to any one of claims 1 to 4, in which the modules are hollow, solid or porous.

6. A casting mould half according to any one of claims 1 to 5, in which the modules are clamped or braced together.

7. A casting mould half according to claim 6, in which the modules are clamped together by a binding wrapped around the modules.

8. A casting mould half according to any one of claims 1 to 7, including a mould frame surrounding the modules.

9. A casting mould half according to claim 8, in which a peripheral seal is situated between the mould frame and the peripheral modules.

10. A casting mould half according to any one of claims 1 to 9, in which the peripheral modules extend to the plane in which the mould half meets the other when the two halves are assembled to form the complete mould.

11. A casting mould half according to any one of claims 1 to 10, in which one or more of the modules extends through the layer of mould material to the moulding face.

12. A casting mould half according to any one of the preceding claims, in which the modules are made of metal.

13. A casting mould half according to any one of the preceding claims, in which the mould material is mould sand together with a binder.

14. A casting mould half according to claim 1, substantially as described with reference to any one of Figures 1 to 3 of the accompanying drawings.

1 5. A method of making a casting mould half for use in a metal casting process, in which a plurality of individual modules are positioned and supported on a support plate to form a backing, a pattern for the mould half is supported relative to the backing so that there is a space therebetween, and the space is filled with a mould material which hardens to form a layer which is supported by the backing and of which the surface in contact with the pattlern forms the moulding face of the mould half.

1 6. A method according to claim 15, in which the modules are selected and positioned according to the shape of the pattern so that there is a predetermined spacing between the backing and the pattern producing a layer of mould material of substantially uniform thickness.

1 7. A method according to claim 15, substantially as described with reference to any one of Figures 1 to 3, Figures 6 and 7, or Figures 6 and 8 of the accompanying drawings.

18. Apparatus for use in a method of making a casting mould half according to claim 15, comprising at least one module magazine containing a store of modules of different sizes, a travelling module grab, and a mounting frame.

19. Apparatus according to claim 18, in which the mounting frame comprises a sliding bottom.

20. Apparatus according to claim 18, substantially as described with reference Figure 5 of the accompanying drawings.