GB2133338A - Injection molding of moisture- containing inorganic materials - Google Patents

Abstract

An apparatus for injection molding of inorganic materials or a mixture of inorganic materials and synthetic resin materials in kneaded clay state and containing moisture or other solvent, is provided for producing a hard molding which has not been shrunken by drying, and which has become half-dry during the molding process, without the necessity of applying heat. The apparatus comprises mold parts A, A formed of a material having a capillary structure a, b so that the space defining the mold cavity e can be evacuated through the capillary mold structure using pumps 4 before and during the injecting of the molding material into space e so that moisture and air contained in the molding material is suctioned off. <IMAGE>

Description

SPECIFICATION Process for wet type injection molding of inorganic materials and apparatus therefor The present invention relates to a process for wet type injection molding of inorganic materials and an apparatus therefor. More particularly, the invention relates to a process for wet type injection molding of inorganic materials, high in water content, or a mixture of inorganic materials and synthetic resin materials in kneaded clay state (owing to the water or solvent contained therein), so as to produce a hard molding or form which has not shrunk by drying, and which is half-dried instantaneously during the molding process, without the necessity of applying heat, and an apparatus for carrying out the process.

Conventionally, in order to mold kneaded clay state inorganic materials or a mixture of them with synthetic resin materials, without the application of heat, jiggering, extrusion, or wet type press molding processes have commonly applied. An injection molding process also has been developed but is rarely used.

Among the conventional processes, the jiggering process and the casting process used kneaded soil or mud of high water content, i.e. 20 through 40% by weight and they are molded on the jigger surface or in plaster molds, and then the molded product is heated from tenths of a minute to several hours for drying or to remove moisture, so as to obtain a half-dry molding. Since the drying process requires such a long period of time, several hundreds to several thousands of plaster molds are necessary for molding one lot of products. Furthermore, the plaster molds are inferior with regard to water-resistance, heatresistance and wear-resistance. Therefore, plaster molds cannot be used more than 100 times at most.

According to the conventional wet type press molding of kneaded inorganic materials, only one pair of molds is necessary. With extrusion molding, however, a mold is not necessary, but since high-water content materials should be used for these processes, materials used are pliant and, therefore, the product is apt to be deformed while being molded and, therefore, it should be carefully placed in a heated chamber until it becomes half-dry.

In the case of the conventional wet type press molding process, since granules of materials of lower water content about 10%, for example, are used, a half dried molding can be obtained, but even with this process, heated-air treatment is necessary for controlling the granules to reduce the water content. According to the conventional dry press molding, since pressure is applied to only one side, it is difficult to obtain complex form molding as is the case with jiggering extrusion or wet type press molding processes.

The types of injection molding processes are carried out in quite a limited area. One of the processes utilises a mixture of inorganic materials and thermoplastic materials. The process includes the steps of melting materials under heat in a cylinder as is used in injection molding of synthetic resin, injecting the melted materials into metal molds, and then withdrawing a molding from the molds after its having been cooled and hardened.

Another process is to use inorganic materials, or a mixture of them with synthetic resin materials which are in a kneaded clay state, and to inject it into metal molds to produce a molding.

These processes, are no different from the conventional injection molding process except that synthetic resin materials used in the conventional process are replaced by inorganic materials or a mixture of them with synthetic resin materials. In other words, since the mold is used only for forming molding materials, the water or solvent content in the material is still high and no means are available to reduce the water or solvent content.

In conclusion, no process has been proposed to date which acts to produce a complex haif-dry molding in a short time, without causing a great deal of shrinkage by drying.

Accordingly, in view of the above-mentioned disadvantages in the prior art, it is the general purpose of the present invention to provide a new injection molding process and an apparatus therefor, by which a hard, half-dry molding is obtained instantaneously without the need for application of heat, from kneaded clay type inorganic materials or a mixture of them with synthetic resin materials, which are used also in conventional jiggering, extrusion and casting molding processes, and without the necessity of using of thermoplastic materials.

According to the invention there is provided a process for injection molding of fluent material which comprises or includes inorganic materials and moisture or other solvent, comprising the steps of injecting the material into an evacuated mold space deformed by mold parts which have a capillary structure, the process including the step of sucking water or other solvent and air contained in the material through said capillary structure, so as to harden the molding in the mold space by dehydrating it and removing air.

Aiso, according to the invention there is provided apparatus for injection molding of fluent material which comprises or includes inorganic materials and moisture or other solvents, comprising mold parts defining a mold space, said mold parts having a capillary structure, whereby the mold space may be evacuated through said capillary structure.

Embodiments of the present invention will now be described by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a longitudinal side sectional view of the first embodiment of the apparatus for wet type injection molding of inorganic materials or their mixture, illustrating the mold in a shut position; Fig. 2 is a view similar to Fig. 1, but illustrating the mold in an opened position; Fig. 3 is a longitudinal side sectional view of the second embodiment of the invention, showing the mold in a closed position; and Fig. 4 is a view similar to Fig. 3, but illustrating the mold in an opened position.

The first embodiment of the invention may be explained with reference to Figs. 1 and 2. In these drawings, mold (A) consists of surface layer (a) and lower or backing layer (b), and is made from a powdered mixture of synthetic resins such as stylene, urethane or phenol resin and of inorganic compounds such as silica, feldspar or alumina.

Lower layer (b) is formed so as to have a thin capillary structure (c) of 50-200 ,u in diameter, which surface layer (a) of 0.3-5 mm thick is provided with dense capillary structure (c) in which the capillary tubes are less than 10,u in diameter.

Surface layer (a) contains slightly watersoluble inorganic compounds which can generate di-valent cation, such as magnesium carbonate, calcium carbonate, calcium sulphate or magnesium hydrogen-phosphate, di-valent cation which as will be explained later, are exchanged, with ion generated form the molding (D) of a mixture of inorganic materials and/or a mixture of them with synthetic resin material (d), so as to convert the molding material (d) into aggregates.

Surface layer (a) is contoured to produce the desired shape of the molding (D).

This mold (A) is connected to air suctioning and/or jetting apparatus (B) at its two sides, in such a manner that air can be withdrawn or injected through capillary structure (c) at will. One half of the pair of molds (A) is provided with injection in that (5) connecting with molding space (e), so that molding material (d) may be injected into space (e).

Air apparatus (B) which opens and shuts at certain intervals is provided with openings (1), so that said openings may be connected with capillary structure (c). One half of apparatus (B) is provided with an injection channel (6) for injecting molding material (d) into space (e). Openings (1) are connected with pipe (2) which, in turn is connected with pump (4) via vacuum meter (3).

Behind a suctioning apparatus is positioned an injector (E). Injector (E) injects molding material (d) through injection channel (6) of apparatus (B) and injection port (5) of mold (A), into molding space (e).

Figs. 3 and 4 illustrate the second embodiment of the invention. In this embodiment, only the surface layer (a') of mold (A') has a capillary structure (c). Mold (A'), consisting of two mold halves facing each other, is attached to mold support (F) in such a manner that suctioning and jetting ducts (7) provided in support (F), connect with mold (A'). Air suctioning and jetting apparatus (B') is fixed to mold support (F) so that its openings ( 1 ') communicate with duct (7) of support (F). Opening (1') connects with pump (4') via vacuum meter (3') as similar way to that of structure of the first embodiment. Furthermore, injector (E') is provided behind one half air apparatus (B) so that molding material (d') can be injected through injection channel t6') of apparatus (B) and injection inlet (5') of one half of mold (A').

According to this second embodiment, when mold (A') becomes worn or defective, only the mold need to be removed for replacement, and there is no necessity of replacing a mold support (F).

The operational process of the apparatus of the invention is explained below; During the first step, two half molds (A) are firmly shut, and aligned to each other. Then air in molding space (e) defined by the surface layers of two half molds is suctioned out by pump (4) of air suctioning and jetting apparatus (B), through channels (1) and (2) until the vacuum meter (3) indicates a reading of 500-760 mm/Hg.

During the second step, precisely weighed inorganic material (d) or a mixture of it with synthetic resin material, in a kneaded clay state, is injected into molding space (e), from injector (E) via its hopper (8) and cylinder (9), by means of piston (10) at an injection speed of 4 m/sec., while the air is being suctioned out.

Simultaneously, with the completion of the injection process, moisture and air contained in molding material (d) is suctioned from molding space (e) through capillary structure (c) by means of pump (4). As a result, half-dried molding (D') consisting of inorganic material, or a mixture of it with synthetic resin material, is obtained without causing shrinkage by drying.

In the third step, after the molding or shaping has been completed, compressed air is injected into the mold by pump (4) of air suctioning and injecting apparatus (B) provided at another or second half mold (A) while air is suctioned out of first half mold (A) by means of pump (4) of air apparatus (B).

While injecting compressed air into a space (e), and suctioning air from the said space, two half molds are separated in opposite directions. Then air apparatus (B) is switched to counter direction, that is, the suction side is changed to injection, and injection side is changed to suction. In this way, molding (D) is detached from mold (A).

According to the process as explained above the step of water or solvent removal and de-airing is effected simultaneously with the step of injection of molding material in kneaded clay state. Since a half-dry molding (D) is obtained in a state in which no shrinkage by drying has occurred, there is no necessity for the preliminary 0 ying by means of hot air, which is required by conventional molding processes, wherein inorganic material or a mixture of it with synthetic resin, in a kneaded clay state is used as a molding material. Furthermore, it is not necessary to cool and harden the molded product in the mold, as has been required in conventional injection molding processes where a mixture of inorganic material and thermoplastic resin material is used.

Since it is not necessary to apply secondary drying treatment in order to avoid shrinkage during drying to the completed molding, it can be immediately put into a kiln or left as it is for natural hardening after having been removed from the mold.

According to the molding process of the invention, dehydration for removal of solvent and de-airing steps are carried out in the moulding space (e) in a manner designed to prevent shrinkage by drying. Therefore, it is not necessary to limit molding materials to those of particularly low water or solvent content. Inorganic materials or their mixture with synthetic resin materials in kneaded clay state which has been used for ordinary molding, can be used as it is in the process of the present invention.

Conventionally it was difficult to produce a non-conventional form differing from circularsymmetric or simple oval form. Furthermore, it was difficult to produce a deep bottom molding with conventional casting molding and press molding processes.

With respect to the present invention, molding material (d) is of such consistency and under such pressure that it is injected at high speed of 4 m/sec. or greater from the injection inlet (5) into the molding space (e) of the mold (A). Therefore, the material (d) is forced into every corner of the space (e). Consequently, since uniform pressure is applied to even complex form or deep bottom form, a moulding (D) of complex or deep bottom form can be obtained after having expelled the gas and moisture.

The greater the moisture or solvent content in the inorganic materials or a mixture of them with inorganic materials and synthetic resin becomes, or the higher velocity of the material flowing through the injection inlet (5) is, the more the material flow takes the form of Newton's flow, i.e.

the pressure distribution takes the form of hydrostatic pressure distribution and, thus, the injection pressure from one point is applied uniformly to all over the space (e).

When a mixture (d), composed of inorganic material and water, or inorganic material, synthetic resin and water or solvent, is injected and contacts with the mold surface (A), water or solvent is separated from the solid material, since the mixed material (d) is injected at a high speed.

The separated moisture or solvent is suctioned by the capillary tube (c) at a pressure above 500 mm/Hg. In this way, since the mold space (e) is suctioned and retained in vacuum state, the separated moisture is absorbed swiftly by the mold (A) and is expelled by a pump (4) via a passage (2).

In the event the injection speed is less than 4 m/sec., the pressure applied to every corner of the space (e) may not be uniform, and the effect of separating moisture or solvent is lessened. When the pressure in the space is lower than 500 mm/Hg., its ability to swiftly suction and separate moisture or solvent is lowered and, accordingly, the effect of dehydrating and releasing the gas from the molding (D) is weakened.

According to the invention, the injecting pressure need not be limited to a certain value.

The pressure may be varied according to levels of the moisture or solvent content in the materials to be injected. Any way, the pressure required for injecting the material at high velocity is far below that required for conventional injection molding processes, such as dry or wet type press molding.

A sample formula for producing a projected molding from inorganic materials mixed with kneaded clay, is as follows: Injected materials (percent by weight): Kaolin Feldspar 16% Clay 23% Water 22% Molding conditions: Injection speed 1 5 m/sec.

Injection duration 0.9 sec.

Injection pressure 900 kg/cm2 Degree of vaccuum in the space between the molds 650 mm Hg.

The mixture of materials listed above, were molded under the molding conditions given. The obtained molding (D) has a water content of 12.7% and 0% shrinkage rate by drying. After having been molded, the molding (D) was dried for one hour at 1 3O0C and then sintered. No defect has been preceived in the obtained product.

A sample formula for producing a molding from inorganic materials mixed with kneaded clay is as follows: Injected materials (percent by weight): pH adjusted alumina 75% Water soluble binder 5% Water 20% Molding conditions: Injection speed 20 m/sec.

Injection duration 0.5 sec.

Injection pressure 1000 kg/cm2 Degree of vacuum in the space between the molds 580 mm/Hg.

The mixture of inorganic materials listed above, were molded under the conditions stipulated above. The obtained molding (D) has a water content of 7.8% and 0% level of shrinkage during drying. After having been molded, the molding (D) was dried for one hour at 1 3O0C and then sintered. No defect was found in the completed product.

As has been seen from the examples, even the inorganic materials of high water content, can be half dried simultaneously with the production of a molding (D) without incurring shrinkage. Since uniform pressure is applied to every portion of the molding, complex form moldings can be mass produced. Since the molding does not shrink during drying and since it is applied with uniform pressure, a highly precise form can be obtained even after the molding is sintered.

According to the invention, the mold itself is made of powder mixture containing synthetic resins and inorganic materials and is formed so as to be provided with a capillary structure. The surface layer is so formed to contain a slightly water soluble compound powder which can generate divalent ions. One half of the mold is provided with an injection duct. Furthermore, air suction and jetting apparatus is connected to the back side of each mold.

In producing the mold structure mentioned above, the capillary structure including water and/or air absorbing properties, can be controlled by selecting the materials used, depending on the application of the mold, so as to obtain the best results. Thus the produced mold can form a halfdry or substantially dried molding swiftly and without causing shrinkage.

Since pressure is applied with uniformity to every point, of complex molding, a large sized and/or deep bottomed molding, can be produced.

This mold can be repeatedly and continuously used without the necessity of replacement, and thus productivity is improved and economy in labour is realised.

Claims (10)

Claims

1. A process for injection molding of fluent material which comprises or includes inorganic materials and moisture or other solvent, comprising the steps of injecting the material into an evacuated mold space deformed by mold parts which have a capillary structure, the process including the step of sucking water or other solvent and air contained in the material through said capillary structure, so as to harden the molding in the mold space by dehydrating it and removing air.

2. A process according to claim 1, including the further step of injecting air into the molding cavity at one side thereof, whilst sucking air therefrom at another side for detaching the molding from the molding space.

3. A process according to claim 1 or 2, wherein the mold parts have a dense capillary structure at their surfaces backed by a thin capillary structure.

4. A process for injection moulding of fluent material substantially as hereinbefore described with reference to the accompanying drawings.

5. Moldings produced by the method according to any one of the preceding claims.

6. Apparatus for injection molding of fluent material which comprises or includes inorganic materials and moisture or other solvents, comprising mold parts defining a mold space, said mold parts having a capillary structure, whereby the mold space may evacuated through said capillary structure.

7. Apparatus according to claim 6, wherein the mold parts have a dense capillary structure at their surfaces backed by a thin capillary structure.

8. Apparatus according to claim 7, wherein said mold parts comprise a powdered mixture of synthetic resins and inorganic compounds the said dense capillary structure being defined by slightly water-soluble inorganic materials which are able to generate divalent cation.

9. Apparatus according to claim 6, 7 or 8, wherein the said mold parts are sandwiched between an air suction apparatus and an air injection apparatus.

10. Apparatus for injection molding of fluent material which comprises or includes inorganic materials and moisture or other solvent, substantially as hereinbefore described.