GB2116889A

GB2116889A - A process of moulding a metal casting mould

Info

Publication number: GB2116889A
Application number: GB08208392A
Authority: GB
Inventors: Sidney Devereux Little
Original assignee: Acme Conveyors & Constr
Current assignee: Acme Conveyors & Constr
Priority date: 1982-03-23
Filing date: 1982-03-23
Publication date: 1983-10-05
Also published as: GB2116889B

Abstract

The process comprises the steps of positioning a pattern (10), in a container (11) on a base (12), applying a thin covering (17) of a chemically bondable moulding material to the top and sides of the pattern surface, thereafter adding sand (19) to the container (11) to surround the top and sides of the thus covered pattern (10), causing the sand (19) to compact e.g. by vacuum and/or vibration, and removing the pattern (10) to form a mould cavity defined in the chemically bondable material (17). A reinforcing pattern net (16) may be applied over the pattern surface, and an air impervious, or partly impervious sheet (18) may be applied between the covering (17) and the sand (19), and an impervious sheet (18a) may be applied over the sand (19). <IMAGE>

Description

SPECIFICATION Moulding process This invention relates to a moulding process.

Many moulding processes are in use today.

Perhaps the most well known is sand casting which comprises the steps of taking a pattern, surrounding the pattern with sand, compacting the sand by the application of pressure, and then removing the pattern to provide a cavity into which metal can be cast. The sand can be green or dry. Generally two such cavities are thus formed and then closed to provide a single cavity into which metal is cast. This method does not give very accurate high quality castings and in particular cannot be used for intricate patterns as the sand cannot take up and hold intricate shapes. Many attempts have been made to provide improved methods of moulding including the following four which are most relevant to the present invention.

One of these methods, known as the "Vee" method comprises the steps of providing an air porous pattern, connecting the interior of the pattern to a vacuum source, applying an air impervious sheet over the surface of the pattern, placing a container over the assembly of pattern and film, introducing dry sand into the container to surround the top and sides of the pattern, applying an air impervious sheet to the top of the sand, connecting a vacuum source to the interior of the container, thereby causing the sand to be compacted, relieving the vacuum applied to the interior of the mould, removing the pattern from the container and sand thereby leaving a cavity into which metal can be cast whilst continuing to apply a vacuum to the interior of the container.

Usually two, or more, such moulds made in the above manner will be assembled together to provide a closed cavity into which the metal is cast whilst a vacuum is applied to the containers of each mould.

A second method, known as the "Full Mould" process, comprises the steps of introducing a layer of sand into a container, introducing a pattern made of polystyrene into the container on top of said layer, adding further sand to the container to surround the pattern, applying an air impervious layer to the top of the sand, connecting the interior of the container to a vacuum source, to cause the sand to be compacted, metal is then poured into the mould and this causes the the polystyrene pattern to volatilise and the metal to occupy the cavity thus vacated.

After the metal has solidified, the vacuum is released from the interior of the container.

Athird method, known as the "Shell Mould" process comprises the steps of sprinkling a chemically bondable moulding material over a heated pattern so that the heat of the pattern causes the chemical bond to occur aided, if necessary, by heating in an oven and then removing the pattern to provide a cavity for casting. Again, usually two, or more, moulds made in the above way will be assembled together to provide the cavity into which metal is cast.

Afourth method, known as the "Chemically Bonded" system is similar to sand casting but utilises for the moulding material moulding sand to which a chemical bonding agent has been added such as a furane resin so that a strong mould is achieved as a result of a chemical bond.

The "Vee" process has the disadvantage that the pattern required is expensive because of the need to provide it with an ability to apply a vacuum and in addition it is necessary to apply two layers of thin, relatively expensive, sheet. The process does however have the advantage that a high quality casting is produced and it is not necessary to provide sand having a chemical binder as in the case of the fourth method.

The "Full Mould" method has the disadvantage that it is necessary to provide a polystyrene pattern for each casting produced and this is a relatively expensive operation since the patterns are not re-usable. In addition, it is necessary to provide relatively expensive tools to produce the polystyrene patterns. Furthermore, a considerable amount of toxic fumes are produced when the polystyrene burns off and it is necessary to provide appropriate fume collecting equipment.

The "Sheli Mould" process has the disadvantage of requiring the use of expensive moulding material, a pattern capable of being heated to, typically 20"C, the provision of a means to heat the mould and, usually, an oven to heat the pattern and moulding material after sprinkling; all which renderthe process expensive.

The "Chemically Bonded" system has the disadvantage of requiring the use of a large amount of expensive moulding material.

It is accordingly an object of the present invention to provide a moulding process which leads to high quality castings and which does not suffer from the disadvantages of known moulding processes.

According to the present invention we provide a moulding process comprising the steps of taking a pattern, causing said pattern to be positioned in a container on a base, applying a thin covering of a chemically bondable moulding material to the top and sides of the pattern surface, thereafter adding sand to the container to surround the top and sides of the thus covered pattern, causing the sand to compact and removing the pattern to form a mould cavity defined in the chemically bondable material.

The invention may include the steps of providing at least two moulds, each formed by the method set out in the preceding paragraph, and assembling two or more such moulds together so that the moulds together define a casting cavity into which metal is cast.

The sand may be caused to compact by the application of vibration and/or a vacuum to the sand.

A vacuum may be applied to the sand during casting of metal into the casting cavity.

An air impervious sheet or a partly air impervious sheet may be applied over the covering layer so as to lie between the covering layer and the sand.

An air impervious sheet may be applied over the top ofthe sand after the container has been filled with sand.

The vacuum may be released temporarily during removal of the pattern followed by re-establishment of a vacuum which is maintained during casting.

If desired, a pattern net may be applied over the surface of the pattern before application of the chemically bondable covering material to support the chemically bondable layer.

The method of the present invention has the advantage that the pattern may be of any desired material including wood, which is a very economical material to use for pattern manufacture, and the pattern does not have to have any special characteristics such as porosity or ability to burn off when metal is poured or ability to withstand high temperatures. In addition, the majority of the moulding material is dry sand, again a relatively economical material, and only a relatively small amount of expensive chemically bondable moulding material is required for the relatively thin covering layer. For example, the covering layer may have a thickness lying in the range one sixteenth of an inch to two inches and generally being approximately one inch thick.

There may be little or no delay in the carrying out of the moulding operation because the relatively thin covering layer can bond whilst the remainder of the container is filled with dry sand.

It is preferred that the sand introduced into the container has a size lying in the range : 2 so as to get a grain distribution so that, on vibratidn, a relatively solid mass is achieved, particularly when the vibration is carried out in association with the application of a vacuum.

In practice of the invention, a relationship can be established between the amount of vibration required to compact a mould in combination with a specified degree of vacuum so that, if desired, less vibration but more vacuum can be applied, or alternatively more vibration and less vacuum. An empirical relationship is determined by simple observation in practice.

In order to facilitate removal of the pattern, the container is inverted so as to permit the pattern to be lifted from the, now inverted, base of the container and if desired, the vacuum applied to the interior of the container may be reduced or eliminated to faciliteate pattern withdrawal. To facilitate this, the air impervious sheet applied over the covering material may be only partially air impervious so that whilst it is sufficiently impervious to restrict air flow therethrough so that a vacuum is created within the sand when a vacuum souce is connected to the interior of the container, nevertheless air can pass through the layer to a sufficient extent when the vacuum source is disconnected or reduced to release the vacuum acting upon the pattern.

The provision of the covering layer of chemically bondable material provides for basic shape retention of the mould cavity, particularly during pattern removal, thereby avoiding the need for a high vacuum during pattern removal thereby enabling the vacuum to be released to reduced to permit of removal of the pattern. The vaccum may be reapplied as necessary after the pattern has been removed during metal pouring in dependence upon the decree of compaction of the sand achieved by vibration.

A further advantage of the present invention is that, compared with for example, the shell moulding process, or the chemically bonded system, the material used for the covering layer has considerably less chemically bondable material therein than the material used in these known processes and therefore expense is minimised, and in addition the need to provide equipment to heat a pattern as is necessary in the shell moulding process is avoided.

In the present invention the covering material contains of the order of 1% of resin and the amount of chemically bondable material to the total amount of sand in the container is relatively small, preferably in the order of 1:10, although the ratio may be as low as 1: 2.

One embodiment of the invention will now be described in more detail by way of example, with reference to the accompanying drawings, wherein: Figures I to 6 are diagrammatic cross-sectional views illustrating successive steps in a method embodying the present invention.

Referring to the drawings, Figure 1 illustrates a pattern 10 of a desired configuration and made in any suitable material. In the present example the pattern is made of wood.

As shown in Figure 2, a container 11 is then placed on a base part 12 and secured thereto by appropriate securing means S. The container 11 has an opening 13 in the wall thereof which is connected by a pipe 14 to a vacuum pump 15.

As shown in Figure 3, the pattern 10 is then covered with a net material 16 such as ordinary wire netting to provide a reinforcement for a covering layer of chemically bondable moulding material which is then applied over the pattern 10 and wire netting 16 as indicated at 17. The covering material 17 may be any chemically bondable moulding material such as a furane resin or sodium silicate material and may, if desired, be provided with a cereal additive to give good green strength to the covering material.

In certain applications it may be found unnecessary to provide the covering net 16 and if this is the case it can be omitted.

Afterthe application of the layer 17, if necessary a period of time may be allowed to elapse to allow the chemical bond to take place or sulphur dioxide gas may be passed over the pattern to cause the bond to take place.

As shown in Figure 4, a thin sheet or film 18 is then applied over the covering layer, the thin film being made of polythene and thereby providing an air impervious sheet. It is preferred that the film 18 is only partly air impervious, for example by being provided with a plurality of small apertures for a reason hereinafter to be described.

Thereafter, as shown in Figure 5, dry moulding sand 19 is introduced into the container 11 to surround the pattern and, when the container is filled, a further film 1 8a is provided over the top of the sand to provide an air impervious sheet. In this case, the film is preferably totally air impervious.

The container and contents are then vibrated and the vacuum pump 15 caused to operate to apply a vacuum within the container 11, the vibration and application of vacuum serving to compact the sand 19.

When the sand has been thus compacted, the assembly is inverted, as shown in Figure 6, and the vacuum pump switched off and air allowed to enter the sand 19 so as to remove the suction applied to the pattern 10, thereby permitting the base part 12 and pattern 10 to be lifted thereby leaving defined in the material 17 a mould cavity.

If desired, the vacuum may be re-applied to the interior of the container 11 as soon as the pattern has been removed, although this may prove unnecessary where the sand has been sufficiently compacted by the application of vibration and vacuum prior to pattern removal.

A similar operation is performed for a second pattern to provide a further mould cavity and the two containers, after the patterns have been removed, are then assembled together so that the two mould cavities co-operate to define a single casting cavity into which metal is cast in conventional manner.

As mentioned above, the vacuum may be maintained during metal casting. Where the metal has been cast and adequately solidified, the vacuum is released and the cast metal allowed to cool.

If a sufficient amount of compaction has taken place, it may prove possible to remove the container 11 prior to metal casting or shortly thereafter so as to expediate cooling.

This latter is particularly the case if the air impervious sheet 16 is arranged to provide a form of "skirt" as indicated at 20 in Figure 6, around the side of the box.

When the metal has solidified, the metal is shaken out in conventional manner and the sand 19 can be separated from the chemically bondable material 17 and the sand 19 and material 17 treated. The material of the layer 17 is preferably treated by the method described in British Patent Application No.

80.

In the present example, the chemically bondable layer 17 is one inch thick and the volume of material in the layer 17 to the volume of sand 19 lies in the range 1 10. The sand 19 has a size range of particles lying in the range 5: 2 and the container and sand therein is vibrated at a frequency of 3000 cps at an amplitude of 1 mm approximately.

It is preferred that the container is vibrated with a variable vibrator in which the "out of balance" force can be adjusted, for example by transferring mer cury from one location to another during operation, and therefore the desired "out of balance" can be determined empirically for a particular mould when the first mould is made and thereafter similar moulds made at the same setting.

In the present example the chemically bondable material of the layer 17 comprises less than 1%.

The binder is of a self-setting proprietory type with a suitable catalyst.

If desired, the binder could be of the gas-curable type but in this case the pattern would have to be suitable for gassing via the pattern, or pipes for the gas supply could be provided through the sand mould.

CLAIMS (Filed on 3.3.83) 1. A moulding process comprising the steps of taking a pattern, causing said pattern to be positioned in a container on a base, applying a thin covering of a chemically bondable moulding material to the top and sides of the pattern surface, thereafter adding sand to the container to surround the top and sides of the thus covered pattern, causing the sand to compact and removing the pattern to form a mould cavity defined in the chemically bondable material.

2. The process according to Claim 1 which includes the steps of providing at least two moulds, each formed by the process claimed in Claim 1 and assembling two or more such moulds together so that the moulds together define a casting cavity into which metal is cast.

3. A process according to Claim 1 or Claim 2 wherein the sand of the or each mould is caused to compact by the application of vibration and/or a vacuum to the sand.

4. A process according to Claim 3 wherein a vacuum is applied to the sand during casting of metal into the mould or casting cavity.

5. A process according to any one of Claims 1 to 4wherein an air impervious sheet or a partly air impervious sheet is applied over the covering layer so as to lie between the covering layer and the sand.

6. A process according to any one of Claims 1 to 5 wherein an air impervious sheet is applied over the top of the sand after the container has been filled with sand.

7. A process according to any one of Claims 3 to 6 when appendantto Claim 3 where the sand is caused to be compacted by applying a vacuum, wherein the vacuum is released temporarily during removal of the pattern followed by re-establishment of a vacuum which is maintained during casting.

8. A process according to any one of the preceding claims wherein a pattern net is applied over the surface of the pattern before application of the chemically bondable covering material to support the chemically bondable layer.

9. A process according to any one of the preceding claims wherein the covering layer has a thickness lying in the range one sixteenth of an inch to two inches.

10. A process according to any one of the preceding claims wherein the sand introduced into the container has a size lying in the range : 2.

11. A process according to any one ofthe preceding claims wherein to facilitate removal of the pattern, the container is inverted so as to permit the pattern to be lifted from the, now inverted, base of the container.

12. A process according to Claim 11 wherein the vacuum applied to the interior of the container is reduced or eliminated during pattern removal to facilitate pattern withdrawal.

13. A process according to Claim 12 where appendant to Claim 4 wherein the sheet applied over the covering layer is only partially air impervious so that air can pass through the layer to a sufficient

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. vacuum within the container 11, the vibration and application of vacuum serving to compact the sand 19. When the sand has been thus compacted, the assembly is inverted, as shown in Figure 6, and the vacuum pump switched off and air allowed to enter the sand 19 so as to remove the suction applied to the pattern 10, thereby permitting the base part 12 and pattern 10 to be lifted thereby leaving defined in the material 17 a mould cavity. If desired, the vacuum may be re-applied to the interior of the container 11 as soon as the pattern has been removed, although this may prove unnecessary where the sand has been sufficiently compacted by the application of vibration and vacuum prior to pattern removal. A similar operation is performed for a second pattern to provide a further mould cavity and the two containers, after the patterns have been removed, are then assembled together so that the two mould cavities co-operate to define a single casting cavity into which metal is cast in conventional manner. As mentioned above, the vacuum may be maintained during metal casting. Where the metal has been cast and adequately solidified, the vacuum is released and the cast metal allowed to cool. If a sufficient amount of compaction has taken place, it may prove possible to remove the container 11 prior to metal casting or shortly thereafter so as to expediate cooling. This latter is particularly the case if the air impervious sheet 16 is arranged to provide a form of "skirt" as indicated at 20 in Figure 6, around the side of the box. When the metal has solidified, the metal is shaken out in conventional manner and the sand 19 can be separated from the chemically bondable material 17 and the sand 19 and material 17 treated. The material of the layer 17 is preferably treated by the method described in British Patent Application No. 80. In the present example, the chemically bondable layer 17 is one inch thick and the volume of material in the layer 17 to the volume of sand 19 lies in the range 1 10. The sand 19 has a size range of particles lying in the range 5: 2 and the container and sand therein is vibrated at a frequency of 3000 cps at an amplitude of 1 mm approximately. It is preferred that the container is vibrated with a variable vibrator in which the "out of balance" force can be adjusted, for example by transferring mer cury from one location to another during operation, and therefore the desired "out of balance" can be determined empirically for a particular mould when the first mould is made and thereafter similar moulds made at the same setting. In the present example the chemically bondable material of the layer 17 comprises less than 1%. The binder is of a self-setting proprietory type with a suitable catalyst. If desired, the binder could be of the gas-curable type but in this case the pattern would have to be suitable for gassing via the pattern, or pipes for the gas supply could be provided through the sand mould. CLAIMS (Filed on 3.3.83)

1. A moulding process comprising the steps of taking a pattern, causing said pattern to be positioned in a container on a base, applying a thin covering of a chemically bondable moulding material to the top and sides of the pattern surface, thereafter adding sand to the container to surround the top and sides of the thus covered pattern, causing the sand to compact and removing the pattern to form a mould cavity defined in the chemically bondable material.

extent when the vacuum source is disconnected or reduced to release the vacuum acting upon the pattern.

14. A process according to any one of the preceding claims wherein the covering material contains of the order of 1% of resin.

15. A process according to any one of the preceding claims wherein the ratio of chemically bondable material to the total amount of sand in the container is less than 1:10.

16. A process according to Claim 15 wherein said ratio is in the order of :2.

17. A moulding process substantially as hereinbefore described with reference to the accompanying drawings.

18. Any novel feature or novel combination of features disclosed herein and/or shown in the accompanying drawings.