GB2088261A

GB2088261A - A method of manufacturing a core of a mold

Info

Publication number: GB2088261A
Application number: GB8126026A
Authority: GB
Original assignee: Sintokogio Ltd
Current assignee: Sintokogio Ltd
Priority date: 1980-11-27
Filing date: 1981-08-26
Publication date: 1982-06-09
Also published as: DE3133431A1; GB2088261B; FR2499433B1; CH654763A5; FR2499433A1

Abstract

Molding sand containing a gas hardenable binder is introduced into a cavity in a core box (6) through a sand feed opening (6b) therein from a hopper (13) under the influence of negative pressure applied, for example, by a suction box (1) connected to a vacuum pump. The hopper is then removed and a hardening gas source (20) is connected to the cavity. The hardening gas is then caused to flow through and penetrate the molding sand in the cavity under the influence of a negative pressure applied, for example, by the suction box (1) so as to harden the molding sand. In one example air is evacuated from the cavity before opening a valve (10) to allow sand into the cavity and again before opening a valve (18) to allow hardening gas into the cavity. Preferably, a flexible film sheet (7) is used to seal the core box against leaks. <IMAGE>

Description

SPECIFICATION A method of manufacturing a core of a mold The present invention relates to a method of manufacturing a core of a mold and, more particularly, to a method of manufacturing a core from molding sand containing therein a gas hardenable binder.

The method of manufacturing a core from molding sand containing a gas hardenable binder is known as a cold box process or SO2 process and comprises the steps of filling a core box with the molding sand containing the gas hardenable binder, and passing a gas for hardening the binder through the molding sand in the core box so as to harden the molding sand.

In general, the core box is charged with the mold sand as the primary step of the cold box process or SO2 process by so-called blowing method making use of compressed air. Also, the application of the hardening gas is made by blowing compressed air or compressed CO2 gas directly to the molding sand.

In the core making machine making use of the compressed air, it is essential to incorporate clamping means for firmly clamping the core box, as otherwise the core box may be undesirably opened by the internal pressure in the core box resulting in the discharge of the molding sand or hardening gas during blowing of the molding sand or during application of the hardening gas. In addition, the core box has to be made of a material which can withstand the internal pressure. In consequence, the core making machine is inevitably of impractically large size and complicated construction, which in turn makes the handling difficult.

The invention provides, in a first aspect, a method of manufacturing a core of a mold, in which a molding sand containing a gas hardenable binder is supplied from a hopper through a sand feed opening of a core box into a cavity in said core box to fill the latter, and a hardening gas is made to flow through and penetrate said molding sand to harden said molding sand, comprising the steps of (a) introducing sand into said cavity under the influence of a negative pressure to fill the cavity with said molding sand, (b) connecting a hardening gas source to said cavity, and (c) causing hardening gas from the hardening gas source to flow through and penetrate said molding said under the influence of a negative pressure so as to harden said molding sand.

The invention provides, in a second aspect, a method of manufacturing a core of a mold, in which a molding sand containing a gas hardenable binder is supplied from a hopper through a sand feed opening of a core box into a cavity in said core box to fill the latter, and a hardening gas is made to flow through and penetrate said molding sand to harden said molding sand, comprising the steps of: (a) sucking air from said cavity of said core box to evacuate said cavity to a negative pressure with the sand feed opening or openings closed; (b) opening said sand feed opening(s) to permit said molding sand to be introduced from said hopper into said cavity to charge said cavity; (c) connecting a hardening gas source to said cavity; (d) reducing the pressure in said cavity filled with said molding sand to a negative pressure; and (e) sucking said hardening gas from said hardening gas source and making said hardening gas flow through and penetrate said molding sand to harden said molding sand.

The invention provides in a third aspect, a method of manufacturing a core of a mold, in which a molding sand containing a gas hardenable binder is supplied from a hopper through a sand feed opening of a core box into a cavity in said core box to fill the latter, and a hardening gas is made to flow through and penetrate said molding sand to harden said molding sand; comprising the steps of: (a) communicating said cavity with a tank through one or more shut-off valves; (b) closing said shut-off valve(s) and evacuating said tank down to a negative pressure; (c) opening said shut-off valve(s) to induce said molding sand from said hopper into said cavity to fill said cavity with said molding sand; (d) connecting a hardening gas source to said cavity; (e) closing said shut-off valve and reducing the pressure in said tank to a negative pressure; and (f) opening said shut-off valve to induce said hardening gas from said hardening gas source into said cavity to make said hardening gas flow through and penetrate said molding sand to harden said molding sand.

Thus it is possible to provide a method of manufacturing a core of a mold, without the need for means for firmly clamping the core box and with a core box of reduced strength.

The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, wherein: Fig. 1 is a sectional view of core making apparatus for carrying out one embodiment of the method according to the invention, the apparatus being shown in a state ready for charging a core box with the molding sand; Fig. 2 is a sectional view of the apparatus shown in Fig. 1, in a state ready for applying hardening gas to the molding sand; Figs. 3 and 4 are sectional views of core making apparatus for carrying out further embodiments of the method according to the invention.

A first embodiment of the invention will be described hereinunder with specific reference to Figs. 1 and 2.

A suction box generally designated by reference numeral 1 has a vacuum chamber 2 formed therein. The vacuum chamber communicates with the upper surface side of the suction box through a plurality of vent holes 3 formed in an upper panel portion of the suction box 1. A core box 6 mounted on the suction box 1 comprises left and right half core box parts 4 and 5. The left half core box part 4 is provided at its lower end with a recess 4a which cornmunicates with a vent passage 4b opening in the inner side surface of the left half core box part 4. Similarly, the right half core box part 5 is provided at its lower end with a recess 5a which communicates with a vent passage Sb opening in the inner side surface of the right hand half core box part 5.Reference numeral 6a designates a cavity defined by the left and right half core box parts 4, 5 in the assembled state. A film sheet 7 having a sand feed aperture 7a covers the core box 6 and upper part of the suction box 1 such that the sand feed aperture 7a is aligned or substantially aligned with a sand feed opening 6b of the core box 6. The vent holes 3 and vent passages 4b and Sb are provided with vent plugs 8 so that only air is allowed to flow through these holes and passages.

A connecting pipe 9 mounted on the core box 6 is arranged to communicate with the sand feed opening 6b of the core box, and is connected to a hopper 11 through a shut-off valve 10. A suction pipe 12 is connected at its one end to the vacuum chamber 2 and at its other end to a vacuum pump (not shown). Molding sand containing a gas hardenable binder is designated by reference numeral 13.

To assemble the apparatus shown in Fig. 1 the core box 6 is mounted on the top of the suction box 1, the suction box 1 and core box 6 having alignment pins and alignment holes. The film sheet is then positioned as shown. Subsequently the pipe 9 (with valve 10 and hopper 11) is mounted on the top of the core bore 6 so as to communicate with the sand feed opening 6b.

Then the cavity 6a of the core box 6 is depressurized by a vacuum pressure applied by the vacuum pump through the suction pipe 12, the vacuum chamber 2 and vent holes 3, and the film sheet is caused to adhere to the outer surface of the core box 6 by suction. The molding sand 13 in the hopper 11 is then fed into the cavity 6a through the connecting pipe 9 by opening the shut-off valve 10.

Then, the vacuum pump is stopped and, after closing the shut-off valve 10, the pipe 9 (with valve 10 and hopper 11) and the film sheet 7 are demounted from the core box 6. Then, after placing a plate member 14 on the upper central portion of the sand 13 filling the cavity 6a, a cover member 17 having a recess 1 5 in its lower end and a central gas supplying port 1 6 is placed on the top surface of the core box 6 in such a manner as to cover the molding sand 13, as will be seen from Fig. 2. Subsequently, the film sheet 7 is positioned as shown in Fig. 2 to cover the core box 6 and the cover member 1 7 in such a manner that a gas supplying aperture 7b in the sheet 7 is aligned or substantially aligned with the gas supplying port 1 6 of the cover member 17.A cap 21 c; inverted U-shaped cross-section, which communicates with a hardening gas source 20 through a shut-off valve 1 8 and a conduit 19, is mounted on the film sheet 7 in such a manner as to cover the gas supplying aperture 7b.

Subsequently, the shut-off valve 1 8 is opened and the vacuum pump (not shown) is started, so that the interior of the core box 6 is evacuated through the suction pipe 12 and the vacuum chamber 2, and so that the hardening gas in the hardening gas source 20 is sucked into the recess 15 via the conduit 19, shut-off valve 18, cap 21 and the gas supplying port 16. The gas is then diffused by the plate member 14 and is induced by a deodorant device (not shown), passing through the molding sand 13 in the core box 6 and then through the vent holes 3, vacuum chamber 2 and the suction pipe 1 2. The hardening gas is thus made to flow through the molding sand 1 3 in the core box 6 for a predetermined time length to harden the molding sand 13.Then, the shut-off valve 18 is closed and the cap 21 is taken off from the top surface of the cover member 1 7.

Subsequently, the vacuum pipe (not shown) is started to suck and remove the residual gas in the sand 13 through the vent holes 3, vacuum chamber 2 and the suction pipe 1 2.

In the illustrated embodiment, the core box 6 and the cover member 1 7 are covered with the film sheet 7 in order to prevent any air leakage.

Needless to say, however, the placement of the film sheet is not essential and the hardening of the core can be made even without such a film sheet.

It is also possible to place the film sheet 7 directly on the core box 6 and mount the cap 21 on the core box, while eliminating the cover member 1 7 and the plate member 14.

In the above embodiment, the apparatus may include means for evacuating the chamber from the upper end as well as from the lower end.

The method of charging molding sand as illustrated in Fig. 1 may be substituted by a charging method as shown in Fig. 3. Referring to Fig. 3, after reducing the pressure in a tank 33 by closing the shut-off valve 31 and then starting the vacuum pump 32, the shut-off valve 31 is opened to evacuate the cavity 6a of the core box 6 through the suction pipe 12, vacuum chamber 2 and the vent holes 3. In consequence, the molding sand 13 is induced from the hopper 11 to fill even very small spaces or corners of the cavity 6a.

It is also possible to substitute a sand charging method shown in Fig. 4 for the charging method shown in Fig. 1. Referring to Fig. 4, the tank 33 is evacuated by starting of the vacuum pump 32 after closing of shut-off valves 31, 31 a. Then, the shut-off valves 31, 31 a are opened and vacuum is applied to the cavity 6a from the upper side through a chamber 34 and vent holes 35 and from the lower side through the vacuum chamber 2 and the vent holes 3, so that the cavity 6a is evacuated to a negative pressure to suck and induce the molding sand from the hopper 11 through sand feed apertures 36. In this case, since the vacuum is applied to the cavity 6a from both of upper and lower ends, the core box 6 can be packed with molding sand even when the core box 6 has such a shape that this is difficult at upper and lower positions thereof.

In the embodiments referred to by reference to Figs. 3 and 4, after the cavity has been charged with molding sand, a hardening gas source is connected to the cavity, e.g. in a manner similar to that shown in Fig. 2, and with shut-off valve 31 or valves 31 and 31 a closed the tank 33 is evacuated or at least the pressure therein is reduced by the vacuum pump. The shut-off valve or valves is/are then opened to induce the hardening gas into the filled cavity in the core box to make the gas flow through and penetrate the molding sand to harden the latter.

As will be understood from the foregoing description of the preferred embodiments, according to the invention, an undesirable discharge and leak of the molding sand and hardening gas are conveniently avoided in spite of the elimination of the core box 6 clamping means, because the charging with the molding sand and the application and penetration of the hardening gas are achieved making use of a sucking action.

For the same reason, the method of the invention permits the use of a less expensive wooden core box.

The method of the invention which offers the above described advantages can effectively be carried out with a simple apparatus, thus contributing greatly to the development of this field of industry.

Claims

1. A method of manufacturing a core of a mold, in which a molding sand containing a gas hardenabie binder is supplied from a hopper through a sand feed opening of a core box into a cavity in said core box to fill the latter, and a hardening gas is made to flow through and penetrate said molding sand to harden said molding sand comprising the steps of: (a) introducing sand into said cavity under the influence of a negative pressure to fill the cavity with said molding sand; (b) connecting a hardening gas source to said cavity, and (c) causing hardening gas from the hardening gas source to flow through and penetrate said molding sand under the influence of a negative pressure so as to harden said molding sand.

2. A method of manufacturing a core of a mold, in which a molding sand containing a gas hardenable binder is supplied from a hopper through a sand feed opening of a core box into a cavity in said core box to fill the latter, and a hardening gas is made to flow through and penetrate said molding sand to harden said molding sand; comprising the steps of: (a) sucking air from said cavity of said core box to evacuate said cavity to a negative pressure with the sand feed opening closed; (b) opening said sand feed opening to permit said molding sand to be induced from said hopper into said cavity to charge said cavity; (c) connecting a hardening gas source to said cavity; (d) reducing the pressure in said cavity filled with said molding sand to a negative pressure; and (e) sucking said hardening gas from said hardening gas source and making said hardening gas flow through and penetrate said molding sand to harden said molding sand.

3. A method of manufacturing a core of a mold as claimed in claim 1 or claim 2, wherein prior to step (a), a flexible film sheet having a sand feed aperture is placed on said core box to cover the latter with said sand feed aperture in or substantially in alignment with said sand feed opening of the core box.

4. A method of manufacturing a core of a mold as claimed in claim 2, wherein step (c) comprises placing a cover member having a gas supplying opening, over said sand feed opening and connecting said gas supplying opening to said hardening gas source.

5. A method of manufacturing a core of a mold as claimed in claim 4, wherein after placing the cover member over said sand feed opening, a flexible film sheet having a gas supplying aperture is placed on said core box to cover the latter with said gas supplying aperture in or substantially in alignment with said gas supplying opening of the cover member.

6. A method of manufacturing a core of a mold, in which a molding sand containing a gas hardenable binder is supplied from a hopper through a sand feed opening of a core box into a cavity in said core box to fill the latter, and a hardening gas is made to flow through and penetrate said molding sand to harden said molding sand; comprising the steps of: (a) communicating said cavity with a tank through one or more shut-off valves; (b) closing said shut-off valve(s) and evacuating said tank down to a negative pressure; (c) opening said shut-off valves to induce said molding sand from said hopper into said cavity to fill said cavity with said molding sand; (d) connecting a hardening gas source to said cavity; (e) closing said shut-off valve and reducing the pressure in said tank to a negative pressure; and (f) opening said shut-off valve to induce said hardening gas from said hardening gas source into said cavity to make said hardening gas flow through and penetrate said molding sand to harden said molding sand.

7. A method of manufacturing a core of a mold as claimed in claim 6, wherein step (d) comprises: placing a cover member having a gas supplying opening over said sand feed opening and connecting said gas supplying opening to a hardening gas source.

8. A method of manufacturing a core of a mold as claimed in claim 1 or claim 2, wherein the reduction of pressure in said cavity is made from the upper and lower ends of said cavity to uniformly charge said molding sand into the upper and lower parts of said cavity.

9. A method of manufacturing a core of a mold as claimed in claim 6 or claim 7, wherein said tank is connected to upper and lower ends of said cavity, whereby the upper and lower portions of said cavity are uniformly packed with said molding sand.

10. A method of manufacturing a core of a mold as claimed in claim 9, wherein said core box is provided at its upper end with an upper vacuum chamber connected to said tank through a first shut-off valve and at its lower end with a lower vacuum chamber connected to said tank through a second shut-off valve, said upper vacuum chamber having one or more vent holes communicating with the upper portion of said cavity while said lower vacuum chamber has one or more vent holes communicating with the lower portion of said cavity, whereby the vacuum is applied to said cavity from the upper and lower sides of said cavity.

11. A method of manufacturing a core of a mold, substantially as hereinbefore described with reference to Figures 1 and 2, or Figure 3 or Figure 4 of the accompanying drawings.

12. A core of a mold manufactured according to the method of any one of the preceding claims.