JPH0218659B2 - - Google Patents

Description

[Detailed Description of the Invention] A. Purpose of the Invention a. Industrial Field of Application This invention relates to a shell casting method for hollow objects, and more specifically, to manufacture hollow objects without unevenness to the extent that no finishing is required on the inner surface of the hollow object. shell casting method,
and the shell mold used therein.

b. Conventional technology The shell casting method produces castings with high dimensional accuracy and smooth casting surfaces, and greatly reduces the cutting process.
It has advantages such as easy removal of sand after casting and improved productivity, so it is widely used in production. To manufacture a hollow object using this shell casting method, first heat a hollow shell mold by combining two molds, and then fill the mold with sand or coated sand that is a mixture of silica sand and resin. to attach it. After heating and hardening, it is removed from the mold, and the molded shell core is placed as a core in a hollow main mold made by combining two molds, and metal is cast and solidified. The molded product is taken out of the main mold and the shell core is removed.This casting has burrs on the outside surface due to the joints of the main mold, and on the inside surface there are cuts and unevenness caused by burrs and irregularities on the outside surface of the shell core. It has a department. Therefore, the conventional method for casting hollow shells is to remove them by cutting, shot blasting, or the like.

c Problems to be Solved by the Invention In the conventional hollow shell casting method described above, burrs occur on the shell core at the joints of the shell molds, but when these are polished and removed, uneven portions are inevitably formed in those areas. Therefore, uneven portions are formed on the inner surface of the casting. In addition, small burrs on the shell core may be overlooked, and if they create cuts in the inner surface of the casting, they are difficult to detect, and if the product is for water pipes, it may cause a rupture. . On the other hand, if the shell mold is used many times, wear and tear will occur between the positioning pin and the engagement hole, and this will cause the shell mold to shift in the direction of the joint, causing a difficult difference in level on the outside of the shell core. This may result in the failure to maintain the desired shape and dimensions. Furthermore, during shell molding, sand is often put into the shell mold using an air blowing method.
In this case, the joint of the shell mold acts as an air vent, resulting in a shell core in which the density of sand is low near the joint. Since that part is fragile, it is necessary to remove it in advance, but this creates a recess in the shell core and a convex part on the inner surface of the casting. In this way, with conventional hollow shell casting methods, cuts, irregularities, and deformations occur on the inner surface of the casting, so it is necessary to remove and deform them.
There is a problem in that multiple finishing operations are required for correction, which is time-consuming and increases costs.

The present invention attempts to solve the above-mentioned problems of conventional hollow shell casting means. In other words, the purpose is to be able to remove burrs that have formed on the shell core without creating uneven parts on the core itself, to be able to reliably remove small burrs without overlooking them, and to remove burrs that have formed on the shell core. Misalignment can be corrected without changing the predetermined shape and dimensions of the core, and it also prevents the creation of brittle areas in the shell core itself due to the thin sand density, and eliminates cuts, unevenness, and unevenness on the inner surface of the hollow casting. To provide a hollow shell casting method and a shell mold capable of manufacturing a hollow shell so precise that it does not undergo deformation and requires almost no finishing work.

B. Arrangement of the Invention a Means for Solving Problems The present invention is a shell casting method for hollow objects, in which sand 1 for shell molding is used at the joints 5 and 6 of a pair of molds 3 and 4.
The outer protrusions of the shell core 10 are blown into a shell mold 2 having a wide inner groove part 8 on the side of the hollow part 7 and an outer groove part 9 communicating therewith, and heated and hardened. The portion 12 is broken and removed at the boundary with the inner protruding strip 11, and the inner protruding strip 11 is polished and removed to obtain a predetermined shape and size, and the shell core 10 is placed in the main mold 13. Casting,
A hollow casting 14 is formed. As a shell mold for carrying out this casting method, between the joint parts 5 and 6 of the pair of molds 3 and 4, there is an inner groove part 8 which is widened on the side of the hollow part 7, and an outer groove part communicating with the inner groove part 8. A shell mold 2 provided with 9 is used.

In the above configuration, the outer convex strip 12 formed in the outer groove 9 is formed in the gap between the joint parts 5 and 6 of the molds 3 and 4 when sand 1 is blown into the shell mold 2 during shell core molding. The air escapes from the sand 1 in the vicinity.
This corresponds to the fact that the density of
That is, a low-density part of the sand 1 is formed on the outer protruding part 12, and is broken and removed along with the burr (not shown) generated at the tip at the boundary with the inner protruding part 11. . Therefore, the size of the outer protruding strip 12 corresponds to the part where the sand 1 becomes thinner, and the shape of the outer protruding strip 12 is such that the boundary with the inner protruding strip 11 is shaped as shown in FIG.・Fourth
As shown in Figures 5 and 5, it is desirable to have an inverted triangular cross section with a narrow width.

In addition, the inner convex portion 11 formed by the inner groove 8
refers to uneven portions 18 caused by breaking the outer convex stripes 12 and uneven steps on the outside of the shell core 10 caused by misalignment of the shell mold 2 (not shown)
It serves as a polishing margin for correcting. That is, by polishing the inner protruding stripes 11 with sandpaper or the like, the uneven portions 18, steps, etc. on the outer side of the shell core 10 are eliminated, and the shell core 10 is made into a predetermined shape and size. Therefore, the size of the inner protruding strip 11 is made slightly larger than the expected uneven portion 18, step, etc., and the boundary portion with the outer protruding strip 12 is As shown in the figure, it is desirable to have a triangular cross-section with a narrow width.

The shell mold 2 has the inner convex portion 11.
The structure is different from the conventional structure in that concave grooves 8 and 9 are formed between the joints 5 and 6, each of which is divided into two, as shown in FIGS. 2 and 3, so that the outer convex strip 12 can be formed. The difference is that

Note that the present invention can be implemented even if the casting 14 as a product is cylindrical, triangular, square, or other hollow as long as it has a hollow portion 15. Also, on the outer surface of the completed shell core 10,
In order to make the inner surface of the casting more beautiful, graphite and
It is desirable to apply zircon or the like. Furthermore, if sand with small particles is used for shell molding, the present invention will be even more effective.

In the figure, 16 indicates a guide rod for moving the shell mold, and 17 indicates a sprue.

b. Effect This hollow shell casting means, as described above,
An inner groove portion 8 as shown in FIG. 3 is provided in the joint portions 5 and 6.
Sand 1 for shell molding is blown into a shell mold 2 having an outer concave groove portion 9. Therefore, on the outer surface of the cylindrical shell core 10, as shown in FIGS. 4 and 5, an inner protruding strip 11 and an outer protruding strip 12 are formed on the outside thereof in parallel to the center line. In this outer convex strip 12, a part with a low density of sand is formed due to air flowing out from the gap between the joint parts 5 and 6, and the main body of the shell core 10 is formed with a uniform one with a high density. has been done.

Then, from the shell core 10 as shown in FIG. 5 taken out, first, as shown in FIG. 6, the outer protruding stripes 12 are broken off, and the low-density portions of the sand 1 are removed together with the burrs. At this time, since the boundary portion with the inner convex strip 11 is formed to have a narrow width, it can be easily broken by pinching with fingers, and small burrs that are easily overlooked are also reliably removed.

Next, the remaining inner convex stripes 11 of the shell core 10 are polished and removed using sandpaper or the like. This is due to the difference in level that occurs on the outside of the shell core 10 due to the misalignment between the shell molds 2, and the above-mentioned outer convex strip 1.
In order to eliminate the irregularities 18 and the like caused by cutting the inner protrusions 11, the inner protrusions 11 are polished and removed. As a result, a shell core 10 having a predetermined shape and dimensions is obtained as shown in FIG.

Thereafter, by putting this shell core 10 into the main mold 13 as shown in FIG. 8 and casting as shown in FIG. 9, the inner surface of the hollow part 15 is free from irregularities as shown in FIG. A hollow casting 14 that requires almost no finishing work can be manufactured.

c Example The inner convex portion 11 formed on the shell core 10 is
It is preferable that the inner side, that is, the side of the shell core 10 main body, has a wide cross-section of a triangular, fan-shaped, or trapezoidal shape, and that the outer convex strip 12 is formed at the narrow portion at the tip. Further, it is preferable that the outer protruding strip 12 has an inverted triangular cross section with a small width in the portion following the inner protruding strip 11, but it may have a rectangular cross section, for example, as shown in FIG. 11. The shell mold 2 is provided with an inner groove part 8 and an outer groove part 9 for molding them.

C. Effects of the Invention As is clear from the foregoing, the hollow shell casting method and shell mold of the present invention have the following effects.

a) Burrs generated during molding of the shell core can be easily and reliably removed without damaging the core itself. That is, conventionally, when removing burrs, uneven portions may be formed on a part of the outer surface of the core, or small burrs may be overlooked and cuts may be made on the inner surface of the casting. However, in the present invention, all burrs can be removed by breaking the outer convex stripes. Further, even if an uneven portion occurs on the folded surface, the shell core itself is not affected at all because it is on the inner protruding strip that will be removed later. Therefore, no cuts or uneven portions occur on the inner surface of the hollow casting product.

b. The areas of low sand density that occur during shell core molding do not occur in the core itself. That is, in the past, due to air outflow from the joint of the shell mold, a brittle part where the density of sand was thin was created in the shell core near the joint. If that part of the shell core is removed, it becomes a recess, which creates a convex part on the inner surface of the cast product, which requires time and effort to cut. However, in the present invention, since the portion where the sand is thin is formed on the outer convex strip, the portion where the sand is thin is eliminated by breaking and removing the outer convex strip, and the core itself is not affected. Therefore, no convex portions are formed on the inside of the cast product, and there is no need for cutting.

c) It is also possible to easily correct the difference in level on the outer surface of the core that occurs due to misalignment of the mold during shell core molding. That is, in the past, when the mold was misaligned, a difficult difference in level difference occurred on the outer surface of the shell core. If you shave the core to correct it, it may no longer be the specified shape, the dimensions may change, or uneven parts may appear.
This influenced the inner surface of cast iron products. On the other hand, in the present invention, even if a step occurs, since there is an inner protrusion, the uneven step can be eliminated by cutting this protrusion. It is also possible to eliminate uneven parts. Moreover, since this modification processing does not reach the core itself, it is possible to obtain a shell core with the specified shape and dimensions, and the inner surface of the resulting cast product will be exactly as specified, allowing for finishing processing. There's no need.

d As mentioned above, the inner surface of the hollow casting has a predetermined shape and dimensions, and almost no finishing is required, which improves productivity, reduces costs, and reduces wear and tear on finishing machines. There will be no waste.

[Brief explanation of drawings]

The figures show an embodiment of the present invention, and Fig. 1 is a longitudinal cross-sectional perspective view during shell core molding with a shell mold, and Fig.
The figure is a longitudinal sectional front view when the shell mold is separated, Fig. 3 is a longitudinal sectional front view when they are joined, Fig. 4 is a longitudinal sectional front view when the shell core is molded, and Fig. 5 is the inside of the shell taken out from the mold. Fig. 6 is a longitudinal sectional front view of the shell core after the outer protruding stripes are broken, Fig. 7 is a longitudinal sectional front view of the shell core after polishing the inner protruding stripes, and Fig. 8 mainly shows the shell core. Fig. 9 is a longitudinal sectional front view when it is placed in a mold, Fig. 10 is a longitudinal sectional perspective view of the hollow casting, and Fig. 11 is a shell core of another embodiment. FIG. Drawing code 1... Sand for shell molding, 2... Shell mold, 3, 4... Mold, 5, 6... Joint part, 7... Hollow part,
8... Inner concave groove portion, 9... Outer concave groove portion, 10... Shell core, 11... Inner convex stripe, 12... Outer convex stripe, 1
3...Main mold.

Claims (1)

[Scope of Claims] 1 Sand 1 for shell molding is placed between the joints 5 and 6 of the pair of molds 3 and 4 in the wide inner concave groove 8 on the hollow part 7 side.
The shell core 10 is blown into a shell mold 2 having an outer concave groove 9 communicating therewith, and heated and hardened. In addition to breaking and removing the
A hollow product characterized in that the inner convex strip 11 is polished and removed, the shell core 10 is corrected to a predetermined shape and dimensions, and the shell core 10 is placed in a main mold 13 to cast a casting 14 of the cast hollow product. shell casting method. 2. A shell mold characterized in that an inner groove part 8 having a wider width on the side of the hollow part 7 and an outer groove part 9 communicating therewith are provided between the joint parts 5 and 6 of the pair of molds 3 and 4. .