JPH03151151A - Core for forming receiving hole in cast iron tube - Google Patents

Abstract

PURPOSE:To prevent the generation of scale on the inner face of a receiving hole in a cast iron tube by penetrating a penetrant mixing graphite fine powder with a binder having high temp. resistance into the surface layer of a core for forming the receiving hole composed of sand mold loaded to a metallic mold for centrifugal force casting. CONSTITUTION:To one end of the water cooling metallic mold 2 for centrifugal force casting for forming the cast iron tube having the receiving hole, the core 1 for forming the receiving hole formed with the sand mold is loaded to form the receiving hole forming mold part 3. In the above core 1 for forming the receiving hole, the penetrant mixing the graphite fine powder with the binder holding caking property even at high temp. on surface layer at least in receiving hole forming side in this core 1. As the above binder, aluminous phosphate, colloidal silica, water glass, etc., are used. Further, as the above graphite, carbon black having about 0.01-0.5mum particle diameter is suitable. Further, the thickness of the formed penetrating layer 4 is desirable to about 3-10mm. By this method, at the time of executing annealing heat treatment to the cast iron tube attached to the core 1, the core 1 is not collapsed and the development of oxide scale in the inner face of receiving hole in the cast iron tube is prevented.

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. 2 shows the socket forming side end of the water-cooled mold 21 of the centrifugal casting apparatus for manufacturing cast iron pipes having the socket described above. A core 22 is attached concentrically to the mold 21, and the outer peripheral surface of the core 22 and the inner peripheral surface of the end of the mold 21 form the socket mold part 2.
3 is formed. The core 22 is closely fixed to the end surface of the mold 21 by a groove plate 24 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 22 attached by a drawing machine. After that, it is charged into an annealing furnace with the core 22 attached, and usually
Annealing treatment is performed at a temperature of about 950″C.Furthermore,
Surface oxides (so-called scale) are removed by shot blasting and the product is made into a product.

(Problem to be Solved by the Invention) However, the socket molding core 22 described above is usually formed from molding sand containing an organic binder such as furan resin or urethane resin, and during casting or annealing. The binder burns and the strength decreases, making it easy to disintegrate. For this reason, as shown in FIG. 3, the inner surface of the socket of the cast iron pipe 30 is exposed during annealing and exposed to the oxidizing atmosphere in the annealing furnace, so thick scale 31 is likely to form on the inner surface of the socket. .

On the other hand, as described above, since the core is formed by a sand mold, its cooling capacity as a mold is smaller than that of a water-cooled mold for molding the outer periphery of a cast iron pipe. Therefore, during casting, a position near the surface of the core, that is, a position near the inner surface of the socket of the cast iron pipe 30 becomes the final solidified part, and shrinkage cavities 32 are likely to occur at this position.

Therefore, in order to remove the above-mentioned thick scale 31, shot blasting is performed to remove the above-mentioned thick scale 31.
2 is exposed on the inner surface of the socket, which not only impairs the appearance of the product, but also requires repairs such as injecting resin into the exposed cavities or filling them with overlay welding. There is a problem in that it causes a decrease in productivity.

Further, when thick scale 31 is generated, the shot blasting process time becomes longer and productivity is lowered. Also,
Removal of thick scale increases the inner diameter, leading to problems such as loss of watertightness when joining iron pipes and the dimensions of the inner surface falling outside the specified tolerance range.

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. In the socket molding core, at least the surface layer on the socket molding side of the core is infiltrated with a penetrating liquid containing fine graphite powder mixed with a binder that maintains caking properties even at high temperatures. This is the structure of the invention.

(Function) In the present invention, a penetrating liquid is permeated into at least the surface layer on the socket molding side of the socket molding core to form a permeating layer. Therefore, even if the organic binder in the core burns during annealing, at least the molded socket side of the core will collapse because its shape is retained by the binder with high hot strength in the permeation layer. The inner surface of the socket of the cast iron pipe can be covered until the annealing process is completed.

Furthermore, the graphite in the permeation layer reacts with oxygen near the inner surface of the socket, thereby preventing the inner surface of the socket from being oxidized, and the COt gas generated by oxidizing the graphite,
The inner surface of the socket can be protected from the oxidizing atmosphere inside the annealing furnace.

Therefore, the inner surface of the socket of the cast iron pipe is prevented from being exposed to the oxidizing atmosphere in the furnace during the annealing treatment, so that it is possible to prevent scale from forming on the inner surface of the socket.

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

FIG. 1 shows that a socket molding core l 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 mentioned above, the core 1 is made of molding sand containing an organic binder, and the surface layer contains fine graphite powder mixed with a binder that maintains its caking properties even at high temperatures. A permeable layer 4 is formed by permeating the permeated liquid. In the same figure, the arrangement of the core l to the mold 2 and the method of mounting and fixing it are the same as in the prior art.

The binder forming the penetrating liquid is capable of maintaining the shape of the core 1 without losing its caking properties even when the core 1 is heated to a high temperature by pouring molten cast iron or annealing. . Examples of the binder include aluminum phosphate, colloidal silica, and water glass.

The graphite mixed in the binder is preferably a fine powder that can penetrate into the gaps in the casting sand that forms the core.For example, carbon black has a particle size of 0. O1
This method is suitable because it yields ultrafine powder with a surface of μ■ to 0.5μ.

To form the penetrating liquid, a predetermined amount of fine graphite powder may be added and mixed into a solution in which the binder is dissolved in a suitable solvent such as water or methanol.

On the other hand, the thickness of the permeation layer 4 formed by permeating the core with the above-mentioned permeation liquid may be approximately 3 to 10 m+ from the surface of the core 1. This is because if it is less than 3M, it will be difficult to retain the shape of the core 1 at high temperatures, and on the other hand, even if it is made thicker than 1011II11, no particular improvement in the shape retention effect will be observed.

In order to form the permeation layer 4, the core may be immersed in the above-mentioned permeation liquid for several tens of seconds. Also, while the core is immersed in the penetrating liquid inside the sealed container, the air inside the container is degassed to reduce the pressure inside the container, and then the pressure is returned to atmospheric pressure to form the core under negative pressure. The penetrating liquid around the core may be forcibly sucked into the gaps in the casting sand. According to this method, even if the viscosity of the penetrating liquid is high or the affinity between the core surface and the penetrating liquid is low, the penetrating layer 4 is formed on the surface layer of the core 1, so it is suitable. The permeable layer 4 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.

As a specific example, a manufacturing example of a ductile cast iron pipe having a nominal diameter of 150 mφ and having a JIS T-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.

■ To 100 parts by weight of 20% colloidal silica aqueous solution,
A penetrating liquid was prepared by mixing and dispersing 10 parts by weight of carbon black having an average particle size of 0.2 μm.

(2) The penetrating liquid obtained in (2) was poured into a sealed container, and the core obtained in (2) was immersed therein, followed by sealing the container. Then, the air inside the container is degassed using a vacuum pump to reduce the pressure inside the container to -0.7.
The pressure was reduced to kg/ctA, held for 1.0 minutes, and then returned to atmospheric pressure to infiltrate the surface of the core with the penetrating liquid.

The thickness of the permeation layer formed at this time is 5 mm from the surface of the core.
It was about 10 nn+.

(2) After drying the core obtained in (2), it was closely fixed to one end of the mold (2) via a core setter to form a socket mold portion 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 rotational speed of the mold was GNo. 50, and the pouring temperature was 1315°C.

■ After the molten metal has completely solidified, the cast iron pipe is taken out from the mold by a drawing device, charged into an annealing furnace, and heated to 95°C in the annealing furnace.
Annealing was performed by holding at 0"C for 1.5 hours. 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 the core did not collapse after the core collapsed. No scale was observed on the inner surface of the mouth.

Furthermore, 50 ductile cast iron pipes of the same shape were produced by the same operations as described in (1) to (2) above, but no scale was observed on the inner surface of the socket of any of the cast iron pipes.

(Effects of the Invention) In the present invention, at least the surface layer on the socket molding side of the core for socket molding is infiltrated with a penetrating liquid that is a mixture of a binder with excellent hot strength and finely powdered graphite. Until the annealing treatment of the cast iron pipe is completed, at least the socket forming side of the core can cover the inner surface of the socket of the cast iron pipe without collapsing, and the vicinity of the inner surface of the socket can be maintained in a non-oxidizing atmosphere. Therefore, the inner surface of the socket is protected from the oxidizing atmosphere in the furnace by the core, so it is possible to prevent scale from forming on the inner surface of the socket.

Therefore, the shot blasting process for removing scale can be omitted. For this reason, not only productivity is improved, but also the cavities directly under the inner surface of the socket do not appear on the surface, so the appearance of the socket is not impaired, contributing to quality improvement.

[Brief explanation of the drawing]

Fig. 1 is a partial sectional view of a water-cooled mold for centrifugal force casting in which a socket molding core according to an embodiment of the present invention is attached to one end, and Fig. 2 is a partial cross-sectional view of a water-cooled mold for centrifugal force casting in which a socket molding core according to an embodiment of the present invention is attached to one end. FIG. 3 is a partial cross-sectional view of a water-cooled mold for centrifugal casting mounted on the side, and FIG. 3 is a cross-sectional view of the socket portion of the cast iron pipe formed by the mold of FIG. 2 after annealing. 1... Core, 2... Water-cooled mold for centrifugal force casting, 3...
- Socket mold part, 4... penetration layer. Figure 2 Figure 2

Claims (1)

[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 forming a socket of a cast iron pipe, characterized in that the layer is impregnated with a penetrating liquid in which fine graphite powder is mixed with a binder that maintains its caking properties even at high temperatures.