GB2312184A

GB2312184A - Making a durable sand mould

Info

Publication number: GB2312184A
Application number: GB9707377A
Authority: GB
Inventors: David John Darby
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-04-17
Filing date: 1997-04-11
Publication date: 1997-10-22
Anticipated expiration: 2017-04-11
Also published as: GB9707377D0; GB2312184B

Abstract

A method for making a durable mould comprises forming a porous mould by applying sand 18 coated with thermo-setting resin to a heated pattern 14, cooling, removing the pattern and impregnating at least those interstices near its surface with a liquid chemical which sets hard and heat-resistant, such as cyanoacrylate, either by suction, pressure, immersion or coating. A porous mould incorporating a cooling jacket is made by applying sand (48) (Fig 5, not shown) coated with thermosetting resin to a heated pattern (44) removing surplus sand to leave a fused layer adjacent the pattern, laying a sheet (50) of a thermo-plastic material capable of being burned off, such as polystyrene, over the surface of the hot layer to follow the contours of the pattern, re-applying resin-coated sand over the sheet, and heating to fuse the re-applied sand whilst burning off the sheet to leave a void constituting the cooling jacket. Holes (52) may be formed in the sheet to accommodate resin-coated sand which forms supporting pillars in the jacket. This porous mould can be made durable by impregnating it with cyanoacrylate.

Description

"Making a Mould" This invention relates to making a mould, which expression is herein intended to include halves or parts of moulds, and dies.

So-calied rapid prototyping systems are a recent development. One such system uses ink-jet technology to produce three-dimensional patterns, layer by layer, in thermo-plastic materials. Another such system shapes nylon by means of a laser. A further such system uses adhesive layering of paper with semi-automated aligned assembly of the layers. However, rapid prototyping systems are not suitable for manufacturing articles in commercial quantities and/cr materials.

It is well known to make a porous mould by applying sand coated with thermo-setting resin to a heated pattern, removing surplus resin-coated sand when a requisite thickness thereof has fused into a layer adjacent to the pattern, and wallowing the mould to cool. Such sc-called shell moulds produce high definition articles but are not durable, being readily degraded or charred by hot materials introduced into them.

One object of the present invention is to provide a durable mould suitable inter alia for reproducing in commercial quantities and materials a rapid prototype of an article.

Another object of the invention is to -provide a porous mould incorporating a cooling jacket.

A further object of the invention is to provide a durable mould incorporating a cooling racket and suitable inter alia for reproducing in commercial quantities and materials a rapid prototype of an article.

According to one aspect of the invent ion, a method of making a durable mould comprises forming a porous mould by applying sand coated with thermo-setting resin to a heated pattern, allowing the porous mould to cool, and then impregnating at least those interstices near its surface with a liquid chemical which sets hard and heat-resistant.

The method preferably further comprises impregnating substantIally all the Interstices of the porous mould with the liquid chemical by differential pressure, that is to say by either pressure or suction.

Alternatively, the method further comprises impregnating at least those interstices near all the surfaces of the porous mould with the liquid chemical by immersion.

Alternatively, the method further comprises impregnating at least those interstices near the surfaces of the porous mold which are counterparts of the pattern with the liquid chemical by coating.

The liquid chemical may be cyanoacrylate or a functional equivalent thereof.

According to another aspect of the invention, a method of making a porous mould comprises applying sand coated with thermo-setting resin to a heated pattern, removing surplus resin-coated sand when a requisite thickness thereof has fused into a layer adjacent to the pattern, laying a sheet of a thermo-plastic material capable of being burned off over those surfaces of the hot layer which follow the contours of the pattern whereby said sheet takes up the contours of said surfaces, re-applying resin-coated sand over the sheet, and heating the ensemble to fuse the re-applied resin-coated sand whilst burning off the sheet of material so as to form a mould incorporating a cooling jacket.

The method preferably further oorrrlses making holes through the sheet of material after it takes up said contours and prior to re-applying the resin-coated sand, whereby the re-applied resin-coated sand fills said holes and fuses to form supporting pillars in the cooling jacket.

Alternatively, the sheet has pre-formed holes whereby the re-applied resin-coated sand fills said holes and fuses to form supporting pillars in the cooling jacket.

Rcds of heat-conducting material may be inserted through at least some of the holes prior to re-applying the resincoated sand to form heat-dissipating supporting pillar-s in the cooling jacket.

The material may be polystyrene or a functional equivalent thereof.

According to a further aspect of the invention, a method of making a durable mould comprises forming a porous mould incorporating a cooling jacket in accordance with any one of the twelfth to sixteenth paragraphs hereof, and then liapregnating at least those interstices near its surface with a liquid chemical in accordance with any one of the seventh to eleventh paragraphs hereof.

In all of the above three aspects of the invention, the pattern may be a rapid prototype.

Yet another aspect of the invent ion comprises a mould when made in accordance with any one of the seventh to eighteenth paragraphs hereof.

Yet a further aspect of the invention comprises an article produced from a Irould made in accordance with any one of the seventh to nineteenth paragraphs hereof.

The invention will now be described, by way of example, with reference to the accompanying drawings of which Figure 1 is a sectional view showing how one half of a porous mould is made; Figure 2 is a sectional view showing how the other half of the porous mould 15 made; Figure 3 is a sectional view showing the finished mold assembled ready for use, its two halves having been rendered durable by chemical Impregnation cf sjbstantlally all their interstices and the upper half having been provided with a runner for the introduction of hot material; Figure 4 is a sectional view showing basically the same finished mould fully impregnated and assembied ready for use as a cavity die.

Figure 5 is a sectional view showing an intermediate stage in the making of a cooling jacket in one half of a porous mould; Figure 6 is a sectional view showing the finished mould with cooling jackets assembled ready for use without Impregnation; and Figure 7 is a view corresponding to Figure 6 showing basically the same mould rendered durable by chemical impregnation throughout.

Referring now to Figures 1 to 3, a durable mould is made by placing within one half 10 of a mould-box on a flat bedplate 12 a nylon pattern 14 which may have been produced by rapid prototyping, and filling any hollow beneath said pattern so as to maintain its shape with a temporary support 16 consisting of a mixture of equal parts of sand coated with thermo-setting resin, and plastics filler paste of the type used in repairing car bodies. The bed-plate 12 and the items thereon are then placed in a pre-heated oven at say 150 degrees Celsius for about 10 minutes. The mould-box half 10 is then slightly overfilled with resin-ccated sand 18 and the bed-plate 12 and the items thereon are replaced in the oven for about 30 minutes. After their removal, the cured sand 18 is then machined flush with the top cf the mould-box half 10, said half is turned over, the support 16 is removed, and a parting agent such as talc, silver sand or silicone can be applied to the joint face 20 of the porous mould half thus formed. The other half 22 of the mould-box is secured on top of the half 10 and is slightly overfilled with resin-coated sand 18. The whole mold-box 10, 22 is replaced in the oven at say 150 degrees Celsius for about 45 minutes and then taken out to cool. The two mould-box halves 10 and 22 are then separated, the pattern 14 is removed, the cured sand 18 in the mould-box half 22 is machined flush with the top of said half, and a hole 24 is made through the cured sand 18 in either one of the mould-box halves, say 10 as illustrated, with a masonry drill to form a runner. Suction is then applied to each of the porous mould halves to draw liquid cyanoacrylate, which is of low viscosity, through the entire mould half from its joint face 20 so as to saturate each half thoroughly and impregnate all or substantially all of the interstices therein as indicated at 26. The cyanoacrylate sets extremely hard and heat-resistant, thus forming cooperating mould halves which are highly durable and capable of re-use for a very large rumber cf times. Chemicals which are functional equivalents of cyanoacrylate can equally well be used and fall within the scope of this invention. The finished mould halves are clamped together and hot material is introduced into the mould cavity corresponding in shape to the pattern 14 through the runner 24 in order to form an article. The finished mould shown In Figure 3 is suitable for plastics injection moulding, and can also be used to cast a metal die.

In one modification, cyanoacrylate or equivalent is forced through the whole of each porous mould half by pressure so as to impregnate substantially all of the interstices therein. In another modification, at least those interstices near all the surfaces of each porous mould half are impregnated with cyanoacrylate or equivalent by brief total immersion of said half. In a further modification, at least those interstices near the surfaces of each porous mould half which are counterparts of the pattern are impregnated with cyanoacrylate or equivalent by coating, for example with a brush.

In yet another modification, pressure can be applied to the resin-coated sand during its fusion by heating, to produce a denser and therefore stronger mould.

Referring now to Figure 4, basically the same mould, turned on its end as shown and provided with a runner 30 instead of the runner 24, can be used to produce a cavity die.

Referring now to Figures 5 and 6, a porous mould incorporating a cooling jacket is made by placing within one half 40 of a mould-box on a flat bed-plate 42 a nylon pattern 44 which may have been produced by rapid prototyping, and filling any hollow beneath said pattern so as to maintain its shape with a temporary support 46 consisting of a mixture of equal parts of sand coated with thermo-setting resin, and plastics filler paste of the type used In repairing car bodies. The bed-plate 42 and the items thereon are then placed in a pre-heated oven at say 150 degrees Celsius for about 10 minutes. Resin-coated zircon sand, which is finegrained and therefore good for facing, is then poured into the mould-box half 40, and the bed-plate 42 and the items thereon are replaced in the oven for sufficient time to enable a requisite thickness of said sand to fuse into a layer 48 adjacent to the pattern 44. Upon their removal, surplus unfused sand is removed by simply turning the mouldbox half 40 over. Said half is then turned back and the bedplate 42 and the items thereon are replaced in the oven at say 200 degrees Celsius for about one minute and then removed. A sheet of polystyrene 50, which is thermo-plastic and capable of being burned off, is laid over those surfaces of the hot layer 48 which follow the contours of the pattern 44 and is pressed down whereby it takes up the contours of said surfaces. Materials which are functional equivalents of polystyrene can equally well be used and fall within the scope of this invention. When set in shape, the sheet 50 is removed, holes 52 are made in it, ad it is replaced closely on the layer 48. This is the stage of the procedure illustrated in Figure 5. Rods 53 of copper or other heatconducting material are optionally inserted through at least some of the holes 52 in order to form heat-dissipating pillars in the cooling jacket. The mould-box half 40 is the slightly overfilled with resin-coated silica, chromite or zircon sand 54 which hoids down the sheet 50 and flows into any holes 52 without rods 53 to contact the layer 48. The bed-plate 42 and the items thereon are replaced in the oven at say 200 degrees Celsius for about 30 minutes or longer depending on the amount of sand to be cured. During this time the heat burns off the polystyrene completely, leaving a void 56 with supporting pillars 58 to form a cooling jacket (see Figure 6). After removal from the oven and cooling, the cured sand 51 is machined flush with the top of the mould-box half 40, said half is turned over, and a parting agent can be applied to the joint face 60 of the mould half thus formed.

The other half 62 of the mould-box is secured on top of the half 40, and the whole procedure is repeated to form the zither half of the mould. Two holes 64 are made in each half of the mould with a masonry drill to intersect the void 56 therein to enable old air to be circulated through the cooling jackets to cool the assembled mould. Another hole (not shown) is made in either one of the mould halves to form a runner. The finished mould described so far in this paragraph is an air-cooled porous mould. It can, however, readily be made into a very durable mould by appropriate treatment with cyanoacrylate or equivalent as indicated at 70 in Figure 7, for example by temporary filling the cooling jackets therewith to render them water-proof, whereby cold water can be used for cooling, and by applying suction as hereinbefore mentioned to draw cyanoacrylate or equivalent through each entire mould half from its point face 60 so as to impregnate substantially all of the interstices in said half.

7n one modification, the sheet cf polystyrene or equivalent has pre-fored holes for forming the supporting pillars without the need to remove, perforate and replace said sheet after it has taken up the contours of the initial layer of sand. These pre-formed holes are equally capable of having rods of copper or other heat-conducting material inserted through them. In another modification, the holes 52 and thus the pillars 58 and any rods 53 are dispensed with.

The durable impregnated moulds made in accordance herewith are very speedily made with only moulding (not metal tooling) skills, very light-weight, very hard and re-usable with very little wear, totally oil and water resistant, totally faithful to pattern dimensions, heat resistant to more tan 200 degrees Celsius, poor conductors of heat, capable if desired of retaining the same porosity after impregnation as before, capable of being machined befcre impregnation, capable of being polished to a mirrcr finish, capable of being fitted with dowels or the like before impregnation, and capable of akin cores. patterns, models, kitchen. tiles, sculptures, figures and the like. They can be used for all forms of plastic injection moulding, for clay or ceramic casting, as vacuum moulds, and as dies for the extrusion of plastics. Porous unimpregnated moulds with cooling jackets made in accordance herewith are well suited for the casting of metals.

The scope of this invention extends to moulds when made in accordance with the methods hereinbefore described, and to articles produced from such moulds.

Claims

Claims:

1. A method of makIng a durable mould comprising forming a porous mould by applying sand coated with thermo-setting resin to a heated pattern, allowing the porous mould to cool, and then impregnating at least those interstices near its surface with a liquid chemical which sets hard and heatresistant.

2. A method according to claim 1, further comprising impregnating substantially all the interstices of the porous mould with the liquid chemical by differertial pressure.

3. A method according to claim 1, further comprising impregnating at least those interstices near all the surfaces of the porous mould with the liquid chemical by immersion.

4. A method accordinq to claim 1, further comprising impregnating at least those interstices near the surfaces of the porous mould which are counterparts of the pattern wtth the liquid chemical by coating.

5. A method according to any one of the preceding claims, wherein the liquid chemical is cyanoacrylate or a functional equivalent thereof.

6. A method of making a porous mould comprising applying sand coated with thermo-setting resin to a heated pattern, removing surplus resin-coated sand when a requisite thickness thereof has fused into a layer adjacent to the patter, laying a sheet of a thermo-plastic material capable of belng burned off over those surfaces of the hot layer which follow the contours of the pattern whereby said sheet takes up the contours of said surfaces, re-applying resin-coated sand over the sheet, and heating the ensemble to fuse the re-applied resin-coated sand whilst burning off the sheet of material so as to form a mould incorporating a cooling jacket.

7. A method according to claim 6 , further comprising making holes through the sheet of material after it takes up said contours and prior to re-applying the resin-coated sand, whereby the re-applied resin-coated sand fills said holes and fuses to form supporting pillars in the cooling jacket.

8. A method according to claim 6, wherein the sheet of material has pre-formed holes whereby the re-applied resincoated sand fills said holes and fuses to form supporting pillars in the cooling jacket.

9. A method according to claim 7 or claim 8, wherein rods of heat-conducting material are inserted through at least some of the holes prior to re-applying the mixture to form heat-dissipating supporting pillars in the cooling jacket.

1O. A method according to any one cf claims 6 to 9, wherein the material is polystyrene or a functional equivalent thereof.

11. A method of making a durable mould comprising forming a porous mould incorporating a cooling jacket in accordance with any one of claims 6 to 10, and then impregnating at least those interstices near its surface with a liquid chemical in accordance with any one of claims 1 to 5.

12. A method according to any one of the preceding claims, wherein the pattern is a rapid prototype.

13. A mould when made in accordance with any one of the preceding claims.

14. An article produced from a mould made in accordance with any one of the preceding claims.

15. A method of making a durable mould substantially as hereinbefore described with reference to Figures 1 to 3 of the acccpanying drawings.

16. A method of making a porous mould incorporating a cooling jacket substantially as hereinbefore described with reference to Figures 5 and 6 of the accompanying drawings.