GB2047141A - Mould production - Google Patents

Abstract

A process for the production of moulds comprises producing a pattern from a combustible material, surrounding the pattern with mould forming material, rendering the mould forming material form stable and igniting the pattern to burn the pattern out, to leave a cavity conforming to the shape of the pattern. The pattern may be formed from wood pulp slurry to which may be added materials to improve combustibility, dimensional stability and rigidity thereof.

Description

SPECIFICATION Mould production This invention relates to mould production and is particularly concerned with the production of moulds into which molten metal can subsequently be poured.

Hitherto moulds have tended to be formed around a pattern in two parts to allow the removal of the pattern, the mould parts formed from a suitably bonded material subsequently being secured together to define between them a mould cavity, often with mould cores strategically placed in the resulting cavity. With such materials, the recovery of mould material is extremely difficult and can be impossible dependent upon the nature of bonding. It is also the case that a high proportion of the resultant castings require subsequent fettling to remove flash caused by the mould parting lines and the cores.

It has already been recognised that in many casting processes, the use of a mould formed from unbonded sand or other mould forming material has many advantages in comparison with conventional moulds. Thus, it has already been proposed that unbonded sand should be placed in a mould flask around a suitably shaped pattern, with vacuum applied to the sand at least during the casting of the metal, and for the pattern to be made from a material capable of being removed by the molten metal as it is poured. Traditionally such patterns have been formed from a suitable plastics material, e.g., polystrene. Inevitably during the pouring of molten metal a carbon residue is formed which can have and frequently does have an effect on the composition of the poured metal, the effect which in certain circumstances is not acceptable.It is also the case that fume is caused during the pouring of molten metal which can only escape through the unbonded sand material of the mould. If, however such fume were to pass into the downrunners of the gating system, it could encourage the creation of cavities within the casting or blow holes and which would be highly undesirable.

According to the present invention, a process for the production of a mould for use in the casting of molten metal comprises producing a pattern from a combustible material, surrounding the pattern with mould forming material, rendering the mould forming material form stable and igniting the pattern to burn the pattern out, to leave a cavity conforming to the shape of the pattern.

The combustible material for the pattern is preferably a combustible fibrous material. Thus, the pattern can be formed from a wood pulp slurry to which can be added materials to improve the combustibility of the pattern and to improve its dimensional stability and rigidity.

One of the main advantages of the process in comparison with the prior art is that there is the complete removal of the residue of carbonaceous material in the cavity prior to casting taking place and as a direct consequence the elimination of carbon pick-up by the casting. It is equally the case that fume can readily escape from the cavity during burning out and is completed before casting takes place.

The invention is therefore applicable to conventional mould manufacture where mould forming material with suitable bonds can be applied around the pattern with the advantage that the mould need not be in two parts and therefore there is the complete elimination of mould parting lines, with consequent reduction in fettling, and is well suited to other mould forming techniques such as by investing a layer of mould forming material on the surface of the pattern. The invention is equally applicable to the use of unbonded sand or other mould forming materials where after casting, and on removal of vacuum which vacuum holds the mould forming material form stable during casting, the material is fully recoverable and shake-out considerably simplified.

1. A process for the production of a mould for use in the casting of molten metal comprising producing a pattern from a combustible material, surrounding the pattern with mould forming material, rendering the mould forming material form stable and igniting the pattern to burn the pattern out, to leave a cavity conforming to the shape of the pattern.

2. A process as in Claim 1, wherein the combustible material for the pattern is a combustible fibrous material.

3. A process as in Claim 2, wherein the pattern is formed from a wood pulp slurry.

4. A process as in Claim 2 or Claim 3, wherein materials are added to improve the combustibility of the pattern and to improve the dimensional stability and rigidity of the pattern.

5. A process as in any of Claim 1 to 4, wherein mould forming material with suitable bonds are applied around the pattern.

6. A process as in any of Claims 1 to 4, wherein a layer of mould forming material is invested on the surface of the pattern.

7. A process as in any of Claims 1 to 4, wherein unbonded sand is applied around the pattern with vacuum applied to hold the mould forming material form stable during casting.

8. A mould when produced by the processes of any one of Claims 1 to 7.

9. A process for the production of a mould for use in the casting of molten metal substantially as hereinbefore described.

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

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Mould production This invention relates to mould production and is particularly concerned with the production of moulds into which molten metal can subsequently be poured. Hitherto moulds have tended to be formed around a pattern in two parts to allow the removal of the pattern, the mould parts formed from a suitably bonded material subsequently being secured together to define between them a mould cavity, often with mould cores strategically placed in the resulting cavity. With such materials, the recovery of mould material is extremely difficult and can be impossible dependent upon the nature of bonding. It is also the case that a high proportion of the resultant castings require subsequent fettling to remove flash caused by the mould parting lines and the cores. It has already been recognised that in many casting processes, the use of a mould formed from unbonded sand or other mould forming material has many advantages in comparison with conventional moulds. Thus, it has already been proposed that unbonded sand should be placed in a mould flask around a suitably shaped pattern, with vacuum applied to the sand at least during the casting of the metal, and for the pattern to be made from a material capable of being removed by the molten metal as it is poured. Traditionally such patterns have been formed from a suitable plastics material, e.g., polystrene. Inevitably during the pouring of molten metal a carbon residue is formed which can have and frequently does have an effect on the composition of the poured metal, the effect which in certain circumstances is not acceptable.It is also the case that fume is caused during the pouring of molten metal which can only escape through the unbonded sand material of the mould. If, however such fume were to pass into the downrunners of the gating system, it could encourage the creation of cavities within the casting or blow holes and which would be highly undesirable. According to the present invention, a process for the production of a mould for use in the casting of molten metal comprises producing a pattern from a combustible material, surrounding the pattern with mould forming material, rendering the mould forming material form stable and igniting the pattern to burn the pattern out, to leave a cavity conforming to the shape of the pattern. The combustible material for the pattern is preferably a combustible fibrous material. Thus, the pattern can be formed from a wood pulp slurry to which can be added materials to improve the combustibility of the pattern and to improve its dimensional stability and rigidity. One of the main advantages of the process in comparison with the prior art is that there is the complete removal of the residue of carbonaceous material in the cavity prior to casting taking place and as a direct consequence the elimination of carbon pick-up by the casting. It is equally the case that fume can readily escape from the cavity during burning out and is completed before casting takes place. The invention is therefore applicable to conventional mould manufacture where mould forming material with suitable bonds can be applied around the pattern with the advantage that the mould need not be in two parts and therefore there is the complete elimination of mould parting lines, with consequent reduction in fettling, and is well suited to other mould forming techniques such as by investing a layer of mould forming material on the surface of the pattern. The invention is equally applicable to the use of unbonded sand or other mould forming materials where after casting, and on removal of vacuum which vacuum holds the mould forming material form stable during casting, the material is fully recoverable and shake-out considerably simplified. CLAIMS

1. A process for the production of a mould for use in the casting of molten metal comprising producing a pattern from a combustible material, surrounding the pattern with mould forming material, rendering the mould forming material form stable and igniting the pattern to burn the pattern out, to leave a cavity conforming to the shape of the pattern.

2. A process as in Claim 1, wherein the combustible material for the pattern is a combustible fibrous material.

3. A process as in Claim 2, wherein the pattern is formed from a wood pulp slurry.

4. A process as in Claim 2 or Claim 3, wherein materials are added to improve the combustibility of the pattern and to improve the dimensional stability and rigidity of the pattern.

5. A process as in any of Claim 1 to 4, wherein mould forming material with suitable bonds are applied around the pattern.

6. A process as in any of Claims 1 to 4, wherein a layer of mould forming material is invested on the surface of the pattern.

7. A process as in any of Claims 1 to 4, wherein unbonded sand is applied around the pattern with vacuum applied to hold the mould forming material form stable during casting.

8. A mould when produced by the processes of any one of Claims 1 to 7.

9. A process for the production of a mould for use in the casting of molten metal substantially as hereinbefore described.