JPH02303666A - Core for molding sockets of cast iron pipes - Google Patents

Abstract

PURPOSE:To prevent the development of scale on inner face by covering the inner face of a socket till completing an annealing without collaps of a core during casting and annealing by penetrating binder caking property of which is held even at high temp. on surface layer of at least socket forming side in the core for forming the socket. CONSTITUTION:The core 1 for forming the socket is fitted at one end side of a water cooling metallic mold 2 for centrifugal force casting and the socket forming part 3 is formed at the one end part of the water cooling metallic mold 2. The core 1 is formed with molding sand containing the organic binder and in the surface layer, the penetrated layer 5 penetrated with the binder the caking property of which is held even at high temp. is formed. After executing the centrifugal force casting with the metallic mold 2, the cast iron tube as attaching the core 1 is charged in an annealing furnace and the core 1 covers the inner face of the socket till completing the annealing with the penetrated layer 5. By this method, the development of scale with oxidizing caused by exposing the inner face of the socket, is prevented and as the scale removing process can be eliminated, the productivity is improved.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a socket-forming device that is attached to one end of a centrifugal casting mold when manufacturing a cast iron pipe having a socket by a centrifugal casting method. Regarding the core.

(Prior Art) In recent years, many cast iron pipes have been manufactured by centrifugal casting, and usually a socket is formed at one end of the cast iron pipe for attaching another cast iron pipe.

FIG. 3 shows the socket-forming side end of the water-cooled mold 21 of the centrifugal casting machine for manufacturing cast iron pipes having the sockets described above. A core 23 for use is mounted concentrically, and the outer peripheral surface of the core 23 and the mold 21
A socket mold portion 26 is formed by the inner peripheral surface of the end portion. The core 23 is closely fixed to the end surface of the mold 21 by a groove plate 25 via a core setter equipped with a fixing device (not shown).

A cast iron pipe having a socket at one end is centrifugally cast using the mold 21, and after casting, the cast iron pipe is taken out from the mold 21 with the core 23 attached by a drawing machine. After that, it is charged into an annealing furnace with the core 23 still attached, and usually 800~
Annealing treatment is performed at a temperature of about 950°C. Furthermore, oxides on the surface (so-called
The scale) is removed and the product is made into a product.

(Problem to be Solved by the Invention) However, the socket molding core 23 described above is usually formed from molding sand containing an organic binder such as furan resin or urethane resin, and during casting or annealing. Since the binder burns and the strength decreases, the core 23 is likely to collapse. Therefore, as shown in FIG. 4, there is a problem that the inner surface of the socket of the cast iron pipe 30 is exposed during annealing, and thick scale 31 is likely to be formed on the inner surface.

When thick scale 31 is formed, the time required for the Shigot blasting process becomes longer and productivity is lowered.

In addition, the inner diameter becomes large due to the removal of thick scale, which impairs watertightness when joining iron pipes, and the dimensions of the inner surface fall outside the specified tolerance range. Alternatively, there may be a casting defect (
So-called "crow's nests" 32 may appear, spoiling the appearance of the product.

In addition, when an inorganic binder such as water glass or cement is used as the binder, no significant decrease in strength occurs in the core, and it is considered that the formation of scale as described above can be prevented. However, the core has poor disintegration properties after annealing, it takes time and effort to remove the core, and the molding sand after use becomes alkaline industrial waste, which is undesirable.

The present invention was made in view of the above-mentioned problems, and an object of the present invention is to provide a socket molding core that can prevent the formation of scale on the inner surface of the socket of a cast iron pipe.

(Means for Solving the Problems) The present invention, which has been made to achieve the above-mentioned object, is a method of forming a cast iron pipe with a sand mold attached to one end of a centrifugal casting mold to form a cast iron pipe having a socket. A core for socket molding according to the present invention is characterized in that at least the surface layer on the socket molding side of the core is impregnated with a binder that maintains caking properties even at high temperatures; It is preferable to increase the bulk density of the surface layer by infiltrating fine refractory powder into the surface layer of the core along with the penetration of the binder.

(Function) In the present invention, at least the surface layer on the socket molding side of the socket molding core formed of molding sand retains caking properties even when heated to high temperatures by pouring molten metal or annealing. A permeable layer was formed by permeating the binder. Therefore, even if the organic binder in the core burns after casting or during annealing, at least the molded socket side of the core will not collapse because its shape is retained by the permeation layer, and the annealing process will be completed. Can cover the inner surface of the socket of cast iron pipes up to Therefore, the inner surface of the socket is not exposed and oxidized during annealing, and the generation of scale on the inner surface can be prevented.

Further, since the permeation layer is formed only on the surface layer of the core, it is possible to easily prevent the core from collapsing after annealing.

Furthermore, when the bulk density of the surface layer is increased by infiltrating fine refractory powder into the gaps between the casting sand in the surface layer of the core along with the penetration of the above-mentioned binder, the cooling capacity of the core can be increased. Therefore, when casting the socket, the final solidified portion can be moved from the vicinity of the inner surface of the socket to the center of the thickness of the socket. For this reason, it becomes difficult for mold porosity to occur near the inner surface of the socket, and even if thick scale occurs on the inner surface of the socket, it is possible to reliably prevent mold porosity from being exposed.

Incidentally, since the fine powder of the refractory material enters only the surface layer of the core, the air permeability of the core is not impaired by the fine powder.

(Example) The present invention will be described below with reference to the drawings.

FIG. 1 shows that a socket molding core 1 according to the present invention is attached to one end side of a water-cooled mold 2 for centrifugal force casting, and a socket mold part 3 is formed at one end of the mold 2. It shows the state that has been applied.

As usual, the core 1 is made of molding sand containing an organic binder, and a permeation layer 5 impregnated with a binder that maintains its caking properties even at high temperatures is formed on the surface layer. has been done. In the figure, the arrangement of the core 1 to the mold 2, the mounting and fixing method, etc. are the same as those of the prior art.

The binder forming the permeation layer 5 is capable of maintaining the shape of the core 1 without losing its caking properties even when the core 1 is heated to high temperatures by pouring molten cast iron or annealing. be. Examples of the binder include aluminum phosphate and colloidal silica.

The thickness of the permeation layer 5 may be approximately 2 to 10 cm from the surface of the core 1. This is because if the thickness is less than 211I11, it will be difficult to retain the shape of the core 1 at high temperatures, and on the other hand, even if it is formed thicker than 10 m, no particular improvement in the shape retention effect will be observed.

In order to form the permeation layer 5, the core may be immersed for several tens of seconds in a solution in which the above-mentioned binder is dissolved in an appropriate solvent.
The permeable layer 5 may not only be formed over the entire surface layer of the core 1, but may also be formed only on the outer peripheral surfaces of the two molds by spraying or the like.

Figure 2 shows that after being centrifugally cast using the mold 2 in Figure 1,
This figure shows the socket after annealing of a cast iron pipe 7 that has been charged into an annealing furnace with the core 1 still attached. 7 covers the inner surface of the socket. Therefore, the inner surface is prevented from being exposed to the oxidizing atmosphere in the annealing furnace, and the generation of scale 8 is prevented. Therefore, the work of removing scale from the socket after annealing can be omitted, and no cavities 9 will appear on the inner surface.

Moreover, as mentioned above, the permeation layer 5 is 2 to 1 mm deep from the surface of the core 1.
Since the core l is only formed in a length of about 0 m, the collapsibility of the core l is not impaired and it can be easily removed from the cast iron pipe.

By the way, when forming the above-mentioned permeation layer, fine powder of refractories such as zircon and waxite is mixed in the above-mentioned binder solution, and the binder permeates into the surface layer of the core. It is advisable to carry out the infiltration of fine refractory powder at the same time. This is because the bulk density of the surface layer can be increased and the cooling ability of the core can be improved. When the cooling capacity of the core improves, the final solidified part at the socket during casting moves from near the inner surface of the socket to the thick center of the inner wall of the socket, and as a result, the position of the cavities also moves. Since it moves, it is possible to reliably prevent the nest from being exposed on the inner surface of the socket. The particle size of the refractory is preferably fine so that it can easily penetrate into the gaps in the casting sand that forms the core.

As a specific example, a manufacturing example of a ductile cast iron pipe having a nominal diameter of 100 m-φ and having a JISSN type socket shape will be described below.

■ A water-cooled centrifugal casting mold for manufacturing cast iron pipes of the above shape was prepared.

■ Molding sand containing warm furan as an organic binder was molded and solidified to obtain a core of a predetermined shape.

■ 15-50% aqueous aluminum phosphate solution 10
0 parts by weight, zircon powder with particle size of 1350 mesh 2
1 part of the core obtained in step (■) was added to the liquid in which 7 parts by weight were mixed and dispersed.
The core was immersed for 5 seconds to penetrate the aqueous aluminum phosphate solution and the zircon powder into the surface layer of the core.

The thickness of the permeation layer and the penetration layer formed at this time was approximately 3 to 5 mm from the surface of the core. In addition, the bulk density of this portion was improved by 6%.

(2) The core obtained in (2) was closely fixed to one end of the mold (2) via a core setter, and a socket mold portion was formed at the same end.

(2) While rotating the mold, molten ductile cast iron was injected from the other end to form a cast iron pipe having a socket at one end. At this time, the rotation speed of the mold was 50 GNIIL, and the pouring temperature was 1'310°C.

(2) After the molten metal had completely solidified, the cast iron pipe was removed from the mold using a drawing device, taken out, placed in an annealing furnace, and subjected to annealing treatment at a maximum temperature of 980°C for 1.5 hours in the annealing furnace. At this time, the core of this example covered the inner surface of the socket without collapsing until the end of the annealing process, and not only scale was observed on the inner surface of the socket after the core collapsed, but also cavities were exposed. I couldn't.

(Effects of the Invention) In the present invention, at least the surface layer of the socket molding side of the core for socket molding is coated with caking, which maintains its caking properties even when heated to high temperatures, by pouring molten metal or annealing. penetrated with the agent. Therefore, even during casting or annealing, the core does not collapse and maintains its shape, and can cover the inner surface of the socket of the cast iron pipe until the end of the annealing process, so that the inner surface is prevented from being oxidized. It is possible to prevent scale from occurring.

Therefore, since the scale removal step can be omitted, productivity is improved.

Furthermore, when the bulk density of the surface layer is increased by infiltrating fine refractory powder into the surface layer of the core along with the penetration of the above-mentioned binder, the cooling ability of the core can be improved. can.

For this reason, it is possible to move the shrinkage cavities near the inner surface of the socket of the cast iron pipe to the thickness center side of the socket, so that it is possible to reliably prevent the shrinkage cavities from being exposed on the inner surface of the socket. Therefore, the appearance of the socket of the cast iron pipe is not impaired and the quality can be improved.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view of a water-cooled mold for centrifugal force casting with a socket molding core attached to one end according to an embodiment of the present invention, and FIG. Figure 3 is a cross-sectional view of the socket after annealing the cast iron pipe; Figure 3 is a partial cross-section of a water-cooled mold for centrifugal casting with a conventional socket-forming core attached to one end;
The figure is a sectional view of the socket portion of the cast iron pipe formed by the mold of FIG. 3 after annealing. l... Core, 2... Water-cooled mold for centrifugal force casting, 3...
- Socket mold part, 5... penetration layer. Figure 3 Figure 4 Figure 1 Figure 2

Claims (2)

[Claims] (1) In a socket forming core formed by a sand mold that is attached to one end of a centrifugal casting mold to form a cast iron pipe having a socket, at least the surface of the socket forming side of the core. A core for molding sockets of cast iron pipes, the layer of which is impregnated with a binder that maintains its caking properties even at high temperatures. (2) The core for forming a socket of a cast iron pipe according to claim (1), wherein fine powder of a refractory material is infiltrated into the surface layer of the core to increase the bulk density of the surface layer. .