GB2110578A - Method of making mold - Google Patents

Abstract

The method comprises the steps of introducing molding sand (8) containing a gas-hardenable binder into a space defined by a pattern plate (1) and a molding flask (6), covering the upper surface of the molding sand (8) in a gas-tight manner with a film sheet (9), bringing the space in the molding flask (6) into communication with a vacuum source to reduce the pressure in the space to compress the molding sand (8) by means of the film sheet (9), closing, after removing the film sheet (9), the upper opening of the molding flask (6), and connecting a hardening gas source to the space in the molding flask while reducing the pressure in the space to induce a hardening gas into the moulding flask to make the gas penetrate the molding sand (8), thereby to harden the molding sand (8). <IMAGE>

Description

SPECIFICATION Method of making mold The present invention relates to a method of making a mold and, more particularly, to a method suitable for carrying out so-called "cold box process" or "SO2 process" in which molding sand containing a gas-hardenable binder is supplied into a space defined by a pattern plate and a molding flask and, after compressing the molding sand, a hardening gas is supplied to penetrate the molding sand to harden the molding sand thereby to form the mold.

In general, the formation of a mold by the "cold box process" or "SO2 process" requires various devices such as a mechanical device for compressing the molding sand, gas blowing device for blowing the hardening gas into the molding sand, clamp device for clamping a pattern plate and a molding flask firmly to prevent the escape of the hardening gas, and so forth. The sizes of these devices get larger as the size of the mold to be formed becomes greater. The increased size of the mold to be formed also requires an increased force produced by the gas pressure which in turn requires a construction which has a strength high enough to withstand the increased force.

Generally, as the size of the mold to be formed is increased beyond a certain limit, it becomes difficult to mechanically compress the molding sand and a considerable time is required for satisfactory compression. In some cases, it is necessary to adopt a stamping operation requiring manual labour.

According to the invention, there is provided a method of making a mold in which molding sand containing a gas-gardenable binder is introduced into a space defined by a pattern plate and a molding flask and, after compressing said molding sand, a hardening gas is supplied to said molding sand thereby to harden the latter, comprising the steps of: covering, after introducing said molding sand into said space, the upper surface of said molding sand with a film sheet in a gas-tight manner, and bringing said space into communication with a vacuum source to establish a vacuum in said space to compress said molding sand by means of said film sheet; and, after removal of said film sheet, placing a cover member having a gas supplying port on the upper end of said molding flask, connecting said space to a hardening gas source through the port of said cover member, and reducing the pressure in said space to positively induce a hardening gas from said source into said space to make said gas penetrate the compressed molding sand thereby to harden said molding sand.

Thus, the compression of the sand, as well as the penetration of the hardening gas can be achieved quite easily. Sufficient hardening gas may be supplied to the sand without the escape of hardening gas to the outside. The method can be performed economically and without fear of environmental pollution and the consumption of sand can be minimised.

The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, wherein: Figure 1 is a sectional view of an apparatus for carrying out one embodiment of a method according to the invention, in the step of compressing the molding sand; Figure 2 is a sectional view of the apparatus shown in Figure 1, in the step of supplying the molding sand with a hardening gas; Figure 3 is a sectional view of an apparatus for carrying out a method in accordance with another embodiment, in the step of compressing the molding sand; Figure 4 is a sectional view of the apparatus shown in Figure 3, in the step of supplying the molding sand with a hardening gas; Figure 5 is a sectional view of an apparatus for carrying out a method in accordance with still another embodiment, in the step of compressing the molding sand; and Figure 6 is a sectional view of the apparatus shown in Figure 5, in the step of supplying the molding sand with a hardening gas.

A pattern plate 1 is composed of a suction box 4 and a pattern 5 attached to the upper side of the suction box 4. The suction box 4 has a vacuum chamber 2 formed therein and a plurality of vent holes 3 formed in the top wall thereof to communicate with the vacuum chamber 2. A molding flask 6 is placed on the pattern plate 1.

The molding flask 6 is located by locating pins which are not shown.

Each vent hole 3 receives therein a vent plug 7 which acts to prevent the molding sand from discharging therethrough.

The space defined by the pattern plate 1 and the molding flask 6 is charged with molding sand 8. A flexible film sheet 9 such as a synthetic resin film or a rubber sheet is placed on the sand 8 in a gas-tight manner. Reference numeral 10 designates a cover member which is provided in its lower side with a recess 11 and a central gas supplying port 12 as shown in Figure 2. The cover member 10 is placed on the molding flask 6 in such a manner that, due to the recess 11, a small gap is formed between the lower face of the cover member 10 and the upper face of the molding sand 8.

An inverse U-shaped cap 13 having a gas supplying hole 1 6 is placed to cover the gas supplying port 12. The space inside the cap 1 3 communicates with a hardening gas generating device 1 5 through a flexible conduit 14, and a stop valve 17, as shown in Figure 2. A suction pipe 18 is connected at its one end to the vacuum chamber 2 and at its other end to a vacuum pump via a deodorant device. The vacuum pump and the deodorant device are not shown.

In making the mold, the molding flask 6 is placed on the pattern plate 1 and the molding sand containing a gas-hardenable binder is charged into the space formed by the pattern plate 1 and the molding flask 6. Then, after covering the upper surface of the molding flask 6 with the film sheet 9 in a gas-tight manner, the vacuum pump (not shown) is started so that the space inside the molding flask 6 is evacuated through the vacuum chamber 2 and the vent holes 3, so that the molding sand 8 in the molding flask 6 is compressed by means of the film sheet 9 so as to be compacted uniformly. This step is illustrated in Figure 1.

Thereafter, the film sheet 9 is taken away, and the molding sand 8 in the upper part of the molding flask 6 is scraped and removed, so that the upper surface of the molding sand is flat. Then, the cover member 10 is placed on the molding flask 6 and the cap 13, the hole 1 6 of which communicates with the hardening gas generating device 1 5 through the conduit 14, is placed on the cover member 10 to cover the gas supplying port 12.

At first, the vacuum pump (not shown) is started, and then the stop valve 1 7 is opened, so that the hardening gas generated and stored in the gas generating device is induced and sucked into the molding flask 6, through the conduit 14, hole 16 of the cap 13, gas supplying hole 12, recess 11 and so forth. The hardening gas is then sucked so as to penetrate the molding sand 8, and further pass through the vent plugs 7, vent holes 3, vacuum chamber 2 and the suction pipe 18. The gas is then sucked through the deodorant device (not shown) by the vacuum pump (also not shown).

After supplying the molding sand with the hardening gas for a predetermined time, the cap 13 is removed while continuing the operation of the vacuum pump to suck and remove the residual hardening gas from the molding sand 8, which is followed by a stripping thus completing the making of the mold.

In the described embodiment, the major operations i.e. the compression of the molding sand and the penetration by the hardening gas, are achieved solely by the sucking action of the vacuum pump. This fact offers various advantages.

For instance, the components such as the pattern plate 1, molding flask 6, cover member 10 and so forth need not have any pressure-resistant construction nor any specific structure for preventing the leak or escape of the gas.

Figures 3 and 4 illustrate another embodiment of the invention in which the molding sand 8 is introduced to provide a substantially uniform thickness of the sand along the upper surface of the pattern plate 1 as shown in Figure 3, and, after placing the film sheet 9 in a gas-tight manner on the molding sand 8, compression of the molding sand 8 is effected in the same way as in the embodiment shown in Figures 1 and 2, which is followed by the penetration by the hardening gas as shown by Figure 4, to obtain a shell-type mold.

According to this embodiment, it is possible to reduce the consumption of the hardening gas and the molding sand.

Figures 5 and 6 illustrate still another embodiment of the invention which applies to the case where the prevention of introduction of ambient air is essential during the process including the compression step and the hardening gas supply step. In this case, the film sheet 9 is made to have a width large enough to cover all inclusive of the junction between the pattern plate 1 and the molding flask 6. In addition, during the supply of the hardening gas, another film sheet 9 having a hole 20 is placed on the cover member 10 as illustrated in Figure 6 to prevent the ambient air from entering the molding sand.

Although the invention has been described through specific terms, it is to be noted that the described embodiments are not exclusive, and various changes and modifications may be imparted thereto without departing from the scope of the invention which is limited solely by the appended claims.

Claims (6)

1. A method of making a mold in which molding sand containing a gas-hardenable binder is introduced into a space defined by a pattern plate and a molding flask and after compressing said molding sand, a hardening gas is supplied to said molding said thereby to harden the latter, comprising the steps of: covering, after introducing said molding said ir,to said space, the upper surface of said molding sand with a film sheet in a gas-tight manner, and bringing said space into communication with a vacuum source to establish a vacuum in said space to compress said molding sand by means of said film sheet; and, after removal of said film sheet, placing a cover member, having a gas supplying port, on the upper end of said molding flask, connecting said space to a hardening gas source through the port of said cover member, and reducing the pressure in said space to positively induce a hardening gas from said source into said space to make said gas penetrate the compressed molding sand thereby to harden said molding sand.

2. A method of making a mold as claimed in claim 1, wherein said molding sand is introduced into said space defined by said pattern plate and said molding flask to provide a substantially uniform thickness of the sand over the upper surface of the pattern plate.

3. A method of making a mold as claimed in claim 1 or claim 2, wherein said film sheet placed on said molding sand after compression of the sand, has a size large enough to cover the upper surface of said molding sand, the outer surface of said molding flask and the outer surface of said pattern plate down to a portion of the latter adjacent to the junction between said pattern plate and said molding flask.

4. A method of making a mold as claimed in any one of claims 1-3, further comprising the step of laying, after placing said cover member having said gas supplying port on said molding flask, a film sheet having a gas supplying port corresponding to the gas supplying port of said cover member, in such a manner that said film sheet covers in a gas-tight manner the outer surface of said cover member, the outer surface of said molding flask and the outer surface of said pattern plate down to a portion of the latter adjacent the junction between said pattern plate and said molding flask, said hardening gas source being then connected to said space in said molding flask through said gas supplying port in said film sheet and through said gas supplying port in said cover member.

5. A method of making a mold substantially as hereinbefore described with reference to Figures 1 and 2 or Figures 3 and 4, or Figures 5 and 6 of the accompanying drawings.

6. A mold made according to the method of any one of the preceding claims.