JPH04100653A - Manufacture of ceramic ball for mold packing - Google Patents

Abstract

PURPOSE:To manufacture this ceramic ball for preventing crack in high temp. by setting a magnetic core body in an almost spherical shape of ceramic-made outer shell body having inner part space communicating with an outer space with a communicating hole. CONSTITUTION:The outer shell body in the ceramic ball 12 has almost the spherical shape as whole and is also composed of a spherical body 14 arranging the prescribed depth of a recessed part 16 opened at the outer face thereof and a cover body 18 clogging the opening part, and in the spherical body 14, a through-hole 15 penetrating into this is arranged and communicated through the recessed part 16 and the outer air. After setting a core body 10 composed of magnetic material in the recessed part 10 of this spherical body 14, by coating inorganic-based adhesive paste on joining face 18a of the ceramic sintered body (cover body) 18, this is joined to the spherical body 14, the opening part of recessed part 16 is closed in a condition remaining the prescribed gap between this and the core body 10, and drying is executed and heating operation is applied to make the ceramic ball 12.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a method for manufacturing ceramic balls for filling molds, and particularly to a method for manufacturing such ceramic balls with a high yield.

(Background Art) Conventionally, various casting methods such as the green mold method and the self-hardening mold method have been appropriately adopted in the production of cast parts for general industrial machines and machine tools, etc., to achieve the desired casting shape. It has been realized. Therefore, the molds used in these casting methods include:
Along with foundry sand, various binders are used as organic or inorganic binding materials, but such binders are expensive, leading to high casting costs.Therefore, efforts have been made to reduce costs. , various efforts have been made. In particular, in the case of non-mass production, such as casting parts for machine tools, sand metal (S/M) This increased ratio led to an increase in product costs.

Therefore, in the past, consideration has been given to reducing the amount of molding sand used by embedding an appropriate volume increasing material behind the surface sand layer that contacts the molten metal in the molding sand filling area that makes up the mold. The present inventors also previously
In Japanese Patent Application No. 1-40948, it has been disclosed that a ceramic ball containing a magnetic material in the center is embedded in a mold as a volume increasing material.

However, such ceramic balls, especially those having a structure in which a core made of a magnetic material is encased in the center, are exposed to high temperatures after being poured into a mold. Therefore, there is a problem in that the core expands, causing cracks in the ceramic layer forming the surface of the ceramic ball.

Therefore, the present inventors further proposed Utility Application No. 1-100958.
In the above issue, the volume increasing material is composed of a core made of a magnetic material and a substantially spherical ceramic outer shell surrounding the core so as to accommodate the core in the center, and the outer shell is composed of a plurality of outer shells. The present invention has proposed a ceramic ball in which the plurality of outer shell segments are joined together with a predetermined gap left between the core body and the core body. An example thereof is shown in FIG.

That is, the outer shell is composed of a spherical main body 4 in which a recess 6 of a predetermined depth is provided, and a lid 8 disposed to close the opening of the spherical main body 4. A core body 10 is accommodated in the recess 6 , and the opening of the recess 6 is closed with a lid 8 while leaving a predetermined gap between the core body 10 and the core body 10 . This makes it possible to effectively prevent the outer shell from cracking due to thermal expansion of the core even at high temperatures after pouring.

However, when manufacturing such a ceramic ball, the core body is housed in the internal cavity of the divided body constituting the outer shell body, and then the core body is divided by using an appropriate adhesive paste such as an inorganic adhesive. It is necessary to form the body into an integral joined body, and then heat it for about 30 minutes at a temperature of about 100 to 300°C to complete the joining of the divided bodies with adhesive paste. During this heating, since the internal space within the outer shell is sealed from the outside space, the gas existing within the internal space thermally expands and increases the internal pressure, thereby increasing the internal pressure of the outer shell. One of the divided bodies (lid body) comes off and the desired product (ceramic balls) cannot be obtained, resulting in a problem that the product yield is reduced.

(Problem to be solved) The present invention has been made against this background, and the problem to be solved is that when manufacturing ceramic balls for filling molds,
Avoiding that the divided bodies constituting the outer shell body housing the core body separate or separate from each other due to thermal expansion of the internal gas,
Therefore, it is an object of the present invention to provide a method for manufacturing ceramic balls with a high yield, which can be effectively used as a volume increasing material in the production of various molds.

(Solution Means) In order to solve the above problems, the present invention has the following features:
In a method for manufacturing ceramic balls as a volume increasing material filled in place of the molding sand behind a skin sand layer in a mold obtained by molding using a predetermined molding sand, the ceramic balls are made of a magnetic material. It consists of a core body of a predetermined size and a substantially spherical ceramic outer shell body having a space in the center to accommodate the core body, and the outer shell body is divided into a plurality of parts to form a plurality of a plurality of outer shell division bodies, and at least one of the plurality of outer shell division bodies is provided with a communication hole through which the housing space and the external space communicate with each other. The core body is accommodated in the accommodation space formed in the outer shell body, which is configured by The structure was such that the outer shell segments were integrally joined.

Further, in the present invention, preferably the outer shell body is
A spherical body having a recess large enough to accommodate the core body, the recess opening to the outside, and a lid body closing the opening of the spherical body. , which is composed of two outer shell segments.

As described above, the present invention provides a method for manufacturing a ceramic ball in which a core body made of a magnetic material is housed, in which the core body is housed in a form in which the outer shell body constituting the ceramic ball is divided into a plurality of parts. After forming an integral bonded body by applying an appropriate adhesive to the joints of these outer shell segments, a predetermined heating operation is performed to obtain the desired ceramic ball. In order to prevent an increase in internal pressure due to thermal expansion of the gas, usually air, present in the void during operation, a plurality of outer shell segments (one of which is provided with a communicating hole) is prevented. It has its characteristics in certain places.

(Specific Structure) By the way, one example of a preferable form of the ceramic ball obtained according to the present invention is shown in FIGS. 2 and 3, respectively.

First, the outer shell of the ceramic ball 12 shown in FIG. 2 has a generally spherical shape as a whole, and includes a spherical main body 14 provided with a recess 16 of a predetermined depth that opens on the outer surface, and a recess 16 with a predetermined depth that opens on the outer surface. Lid body 1 provided to close
It consists of 8. Further, the spherical body 14 is provided with a communication hole 15 passing through it, thereby allowing the recess 16 to communicate with the external space.

A ceramic ball using an outer shell having such a configuration is manufactured as follows.

First, a predetermined ceramic powder raw material is blended for press molding, and the blend is press-molded into a predetermined shape, followed by firing to obtain a spherical body 14 made of a ceramic sintered body. Next, after the core body 10 made of a magnetic material is placed in the recess 16 of the spherical body 14, a ceramic sintered body (
When the lid body 18 is bonded to the spherical body 14 by applying an inorganic adhesive paste to its joint surface 18a, the opening of the recess 16 forms a predetermined gap between it and the core body 10. The conjugate is closed while leaving a spherical shape, thereby obtaining a zygote having an approximately spherical shape as a whole.

Thereafter, the bonded body thus formed is dried according to a normal method, and then heated under predetermined conditions to bond the spherical body 14 and the lid 18 with the adhesive. By completing the process, the desired ceramic ball 12 can be obtained. The temperature and time of this heat treatment are appropriately determined depending on the adhesive components used, but are preferably 100 to 30
A heating operation is performed for about 30 minutes at a temperature of 0°C.

In addition, in such a joined body, the communication hole 15 is provided only in the spherical body 14, but in the present invention, it may be provided in the lid body 18 so as to penetrate therethrough.
Alternatively, it is also possible to provide them on both the spherical main body 14 and the lid body 18. In addition, when the communication hole 15 is provided only in the spherical body 14, the communication hole 15 is arranged with the lid 18 side facing downward so that the opening on the recess 16 side is not blocked by the core body 10. It is desirable that the internal gas of the joined body easily escapes to the outside through the communication hole 15 during heating.

Furthermore, although FIG. 3 shows a ceramic ball in which the outer shell division body constituting the outer shell body is composed of two hemispherical division bodies 20 and 20, it is difficult to understand in this figure. For ease of illustration, it is shown in an exploded state.

Here, a recess 22 of a predetermined size is formed in the center of each of the hemispherical divided bodies 20 on the dividing surface side, and at the bottom of the recess 22 of the hemispherical divided body 20, Communication holes 21 passing through the hemispherical divided bodies 20 are provided respectively. And those two divided bodies 2
0.20, the split surfaces of the shells are joined so that they face each other, so that the outer shell has a spherical outer shape and has a hollow part made up of hemispherical recesses 22, 22 inside. It consists of Moreover, the core body 10 will be accommodated in the hollow part formed in this way.

Even in the case of a ceramic ball having an outer shell of this type, similarly to the above, a predetermined ceramic powder raw material is used to form a press-formed product that has a substantially hemispherical shape and has a recess in the center of its flat surface. A plurality of hemispherical divided bodies 20 are obtained by producing a plurality of them and firing them according to a usual method. After the same core body 10 as described above is accommodated in the recess 22 of this hemispherical divided body 20, another hemispherical divided body 20 is used to divide the core body 1 into two divided bodies 20 and 20.
0 is included, a predetermined adhesive is applied to the joint surfaces 20a of the divided bodies 20.20, the divided bodies 20.20 are joined, and heat treatment is performed under the same conditions as above. By applying the adhesive, the bonding of the divided bodies 20, 20 using the adhesive is completed, and the desired ceramic ball 24 as shown in FIG. 4 is obtained.

Then, using such a hemispherical outer shell divided body 2o,
When manufacturing the ceramic ball 24, only one mold is required for press molding, which provides the advantage of reducing manufacturing costs.

Note that the communication holes (15, 21) in the ceramic ball (1224) as described above are formed at the same time as the press molding of the outer shell segments (14, 18i20) that constitute such a ceramic ball. The size is such that it can function as an escape hole for the gas in order to prevent the internal pressure from increasing due to thermal expansion of the gas existing in the internal cavity of the outer shell, and it does not reduce the strength of the ceramic ball. Depending on the degree and size of the intended ceramic ball, it will be selected as appropriate.
Generally, a size of about 1 to 1.5 mm is sufficient.

In addition, a recess (16,
The size of 22) is generally such that the core body is configured such that it can sufficiently allow expansion due to heat of the core body to be accommodated, in other words, such that there is a sufficient gap between the core body and the core body. It will be appropriately selected depending on the coefficient of thermal expansion of the magnetic material.

In this way, in the present invention, a plurality of outer shell segments (one
4, 18; 20), a communicating hole (15,
21), the outer shell segment (14) is heated during heating to complete the adhesive bonding.
, 18; 20) Even if the gas, usually air, present in the internal housing space expands due to heat, the communication holes (15, 2
The outer shell segments (14 and 18, 20 and 20) are discharged to the outside through 1) and form the outer shell.
There is no separation or separation.

Further, the ceramic balls (12; 24) having the above-mentioned configuration obtained according to the present invention can be used as a volume increasing material behind the surface sand layer in any of the various molds obtained by molding a predetermined foundry sand. Instead of such foundry sand,
They can be adopted to take advantage of this.

In addition, in the present invention, the outer shell (1418; 2
The ceramic material for forming 0) is appropriately selected from alumina, cordierite, silicon carbide, silicon nitride, zirconia, and the like.

Furthermore, as the adhesive used to join the plurality of outer shell segments made of ceramic materials, any known heat-resistant inorganic adhesive can be suitably used. However, in general, alkali silicate,
Inorganic adhesives such as phosphate adhesives and silica sol adhesives are preferably used. Furthermore, as an oxide adhesive, BzO with a low melting point
* It is also possible to use PbOZnO based adhesives and perform bonding heating at a temperature of 300 to 700"C. These adhesives solidify through appropriate heat treatment and exhibit strong bonding strength. .

Furthermore, the magnetic materials constituting the magnetic core (10) as described above include soft magnetic materials and hard magnetic materials, both of which have the function of imparting magnetism to the pole. It is something that will be done.

For example, when used in organic self-hardening molds,
Soft magnetic materials are advantageously selected due to the ease of maintenance of the ceramic balls. A magnetic separation device in the automated casting and casting line allows
After the mold has been dismantled, when separating the foundry sand from the ceramic balls, which are the volume increasing material, if the lines are still magnetic even after they are separated from the magnet, most of the lines are soft magnetic, so the core will be hard. If magnetic materials are used, there is a risk of line troubles due to the poles becoming magnetically attached to the line, or the ceramic balls becoming magnetically attached to each other and forming a lump-like shape. be. Moreover, since soft magnetic materials are mainly composed of oxides, their raw materials are inexpensive, they can be easily molded into desired shapes, and the materials are easily available. .

(Examples) Examples of the present invention are shown below to clarify the present invention more specifically, but the present invention is not limited in any way by the description of such examples. That goes without saying.

In addition to the following examples and the above-mentioned specific explanation, the present invention may include various modifications and changes based on the knowledge of those skilled in the art, as long as they do not depart from the spirit of the present invention.
It should be understood that modifications, improvements, etc. may be made.

First, the outer shell division body (14,
A ceramic ball (12) consisting of 18) was manufactured. That is, alumina is used as the material, and a recess (16) capable of housing the core (10) from the outside and the recess (
A substantially spherical press-molded body (spherical body 14) in which a communication hole (15) was formed to communicate the spherical body 16) with the external space was produced. Thereafter, the spherical body (14) of 28 fflInφ was obtained by firing under predetermined conditions according to a conventional method.

The diameter of the opening of the recess (16) was 12 mmφ, and the depth was 20°. The lid body (18) that covers the recess (16) is similarly made of alumina, and is press-formed into a cylindrical shape in a separate process, and then fired in the same manner to obtain a 12-hole diameter x 10 mm. A ceramic sintered body was used.

Further, as the magnetic core (10), a steel ball of 11 m+φ made of 5S41 material was used.

Using 100 spherical bodies (14) thus obtained, a steel ball as a core body (10) was placed in each recess (16), and then a lid body (18) produced in a separate process was placed.
) was joined to the spherical body (14) via a phosphate-based inorganic adhesive paste. As a result, the recess (16)
The opening was covered to obtain a bonded body having an approximately spherical shape as a whole. Thereafter, the thus formed bonded body is dried according to a normal method and further heated at 200"C for 15 minutes to bond the spherical body (14) and the lid (18). was completed, and the desired ceramic ball (12) was obtained.

In all of the thus obtained ceramic balls (12), there was no case where the lid body (18) came off from the spherical body (I4) during heat bonding, and in a good bonding state, an integral outer shell was formed. It had a body.

On the other hand, for comparison, as shown in Figure 1,
When the same heating bonding operation as above was performed using 100 spherical bodies (4) without communication holes,
In about half of the cases, the lid body (8) protrudes from the recess (6) of the spherical body (4) by more than five points and separates, and in the remaining half, a protrusion of about 2 to 411II11 is observed. It became.

(Effects of the Invention) As is clear from the above description, in the present invention, at least one of the plurality of outer shell segments constituting the outer shell of the ceramic ball that accommodates the core is Since it adopts a configuration with a communication hole that communicates the housing space with the external space, there is no possibility that the core body will be present in the space that houses the core body during heating to complete the joining of the outer shell segments with adhesive. Even if the gas expands thermally, the expanded gas can be discharged to the external space through the communication hole, thereby ensuring a good bonding state without separating or detaching the outer shell segment. Therefore, ceramic balls that can be advantageously used in various molds can be obtained at a high yield.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional explanatory diagram showing an example of an outer shell segment constituting a ceramic ball previously proposed by the present inventors, and FIGS. 2 and 3 respectively show an outer shell body according to the present invention. FIG. 4 is a cross-sectional explanatory view of what constitutes a ceramic ball in a different embodiment, and FIG. 4 is a cross-sectional explanatory view of a ceramic ball obtained by the structure of FIG. 3. 0: Magnetic core 2. 24: Ceramic ball 4: Spherical body 15, 21: Communication hole 6. 22: Recess 18: Lid 0: Hemispherical divided body

Claims (2)

[Claims] (1) A method for manufacturing ceramic balls as a volume increasing material filled in place of the foundry sand behind a skin sand layer in a mold obtained by molding using a predetermined foundry sand, , consisting of a core body of a predetermined size made of a magnetic material, and a substantially spherical outer shell body made of ceramics having a space in the center to accommodate the core body, and the outer shell body is divided into a plurality of parts. A plurality of outer shell division bodies are formed, and at least one of the plurality of outer shell division bodies is provided with a communication hole that penetrates the plurality of outer shell division bodies to communicate the accommodation space and the external space, so that the plurality of outer shell division bodies While the core body is accommodated in the housing space formed in the outer shell body constituted by the divided bodies, an adhesive is applied to the joints of the plurality of outer shell divided bodies, and heat treatment is applied to the plurality of outer shell divided bodies. A method for manufacturing a ceramic ball for filling a mold, characterized by integrally joining the outer shell segments of. (2) a spherical body in which the outer shell has a recess large enough to accommodate the core, and the recess is opened to the outside; The manufacturing method according to claim 1, wherein the manufacturing method is comprised of two outer shell divisions, including a lid that closes the opening.