JPS586763A - Centrifugal casting method - Google Patents

Abstract

PURPOSE:To produce a two-layered centrifugally cast pipe wherein both layers have prescribed uniform layer thickness and the adhesiveness between the layers is high by remelting the chill layer produced at the boudary between the 1st layer and the 2nd layer, and discharging the excess unsolidified melt of the 2nd layer. CONSTITUTION:The 1st layer of a prescribed layer thickness is cast in a rotary mold for centrifugal casting installed horizontally, and after the molten metal solidifies down to the inner side thereof, the 2nd layer 2 is cast. Here, the molten metal for the 2nd layer is charged at the amt. sufficient for remelting of the chill layer of the 2nd layer produced in the boundary part with the 1st layer by the heat retained by the molten metal of the 2nd layer. If the layer thickness of the molten metal charged for the 2nd layer is larger than the design value of the casting wall thickness, the mold M is tilted at the point of the time when the thickness of the solidified layer attaining the design value, then one of end plates 3 for preventing scattering of the molten metal is removed and the residual melt 4 is flowed out through the opening part on the bottom end side and is discharged into a suitable vessel 5.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a centrifugal casting method, and particularly to a method for producing a two-layer centrifugally cast tube in which each layer has a predetermined uniform layer thickness and excellent adhesion between layers.

Double-layer centrifugally cast pipes are made by casting two different metals concentrically to form a two-layer structure, making use of the characteristics of each layer of metal to withstand harsh usage conditions. It is used as a reaction tube for thermal decomposition and reforming of hydrocarbons, a so-called cranking tube. In order to make this double-layer centrifugally cast pipe exhibit the desired performance and characteristics,
In the casting process, it is necessary to prevent the metals in both layers from mixing together, to form each layer to a predetermined uniform thickness, and to bring the two layers into metallurgical contact at the interface to create a strong bond. be.

Two-layer centrifugal casting tube has an outer layer (first layer) inside the centrifugal casting mold.
It is produced by injecting molten metal as a layer, then applying flux to the inner surface of the molten metal, and then injecting molten metal to form the inner layer (second layer). If this is done at a relatively early point in time, Figure 1 [
1) As shown in K, the surface layer (1.1) of the first layer metal (1) in the mold (goods) is in an unsolidified state, so the first layer and second layer (2) are fused to form a container. Although the solidified layer (l.2) of the first layer is also in a high temperature state, it is remelted by the heat of the second layer molten metal. As a result, the first layer (f) that is finally formed is thinner than the intended layer thickness, and the second layer (d) of the first layer is made up of a large amount of metal in the first layer (as shown in the previous figure). As a result, the layer thickness becomes excessively thick and the chemical composition becomes different from the original one.

In order to avoid the above-mentioned disadvantages, it is necessary to completely solidify the first layer to the inner surface and cool it to a temperature at which it will not re-melt even when it receives the heat of the second layer molten metal, and then pour the second layer molten metal. However, if this is done, a problem will arise in the adhesion between the two layers. That is, as shown in FIG. 2, a flux (F) is applied to the inner surface of the injected first layer molten metal (1),
After solidifying the first layer (1) in this state (the same figure [, 1
]), when the second layer molten metal (2) is injected (same figure [■]
), the second layer forms a thin solidified shell (chill layer) (2.1) on the contact surface with the first layer (Figure [■]). In that case, most of the flux (F″) floats to the surface with the injection of the second layer molten metal, but because a solidified shell (2·l) is formed early, some of the 7 fluxes cannot float completely. , solidification of each layer is completed with tIc remaining between the first layer (1) and the second layer (2) (Figure [N]).This tendency is
Particularly, the higher the welding point of the second layer metal is than that of the first layer metal, the more conspicuous it becomes. As a result, the bond between the two layers becomes extremely incomplete, and the 7 lux remaining between the two layers becomes a fatal defect in the resulting two-layer tube.

One way to prevent this is to raise the casting temperature of the second layer molten metal to increase the heat capacity of the molten metal.
It is possible to delay the formation of 2.1) or try to remelt it, but since the temperature of the molten metal cannot be raised that much, there is a limit to its effectiveness, and in the end it is impossible to obtain a sound two-layer pipe. Can not.

The present invention has been made in view of the above, and provides a centrifugal force casting method for obtaining a two-layer pipe having a predetermined uniform layer thickness of any thickness and excellent adhesion between the two layers.

The method of the present invention will be explained below.

According to the method of the present invention, a first layer having a predetermined layer thickness is first cast in a horizontally installed rotary mold for centrifugal casting, and after solidifying to the inner surface, the second layer is cast. Let's do it. The amount of second layer molten metal injected during casting of the second layer is sufficient to remelt the chill layer of the second layer that occurs at the boundary with the first layer using the heat possessed by the second layer molten metal itself. shall be. In addition, after casting the first layer, 7 lux may be administered inside the first layer according to a conventional method.

As mentioned above, the second layer molten metal has enough heat to remelt the chilled layer, so even if a part of the 7 lux is captured between the chilled layer and the first layer, the second layer melts due to the remelting of the chilled layer. The molten metal floats to the top of the layer and is separated.

That is, in the present invention, the second layer molten metal also serves as a heat source for remelting the chilled layer.

The amount of molten metal injected required to cover this amount of heat is determined as appropriate, but usually the molten metal layer thickness is approximately 1/1/1 of the thickness of the first layer.
It is preferable that the amount is 2 or more.

The second layer of molten metal gradually solidifies from the outside (the side in contact with the first layer) as the poem progresses. Of course, the thickness of the solidified layer is determined by the elapsed time after the injection of the molten metal. If the thickness of this second layer of injected molten metal is larger than the design value of the casting wall thickness, excess unsolidified molten metal (residual metal ) is discharged out of the mold.

To discharge the surplus second layer remaining metal, for example, as shown in Figure 3, the mold (goods) is tilted at an appropriate angle t with respect to the horizontal plane, and the I/C (in the figure, the (The drive mechanism and the drive mechanism that rotates the mold around its axis are omitted).
The end plate for preventing molten metal scattering (3
) and remove the remaining hot water (4) from the opening on the lower end side.
) may be drained and discharged into a suitable container (5).

As a result, the first layer (1) and the second layer (2) having a predetermined layer thickness are formed.
) is obtained.

As another method for discharging the remaining hot water, a method as shown in FIG. 4 may be used. This method requires that a ring-shaped container (a) with an open side facing the mold be placed around the mold (b) in a horizontal T/C
At the same time as installing the mold (goods), place the mold (goods) at its longitudinal center (
A drive means (not shown) is provided to rotate the mold in a horizontal plane around C), and when the second layer (2) of a predetermined thickness is formed, the end plates (3° 3) At the same time as the mold is removed, it is rotated around the shaft (Q), and its centrifugal force causes the residual metal (4) in the mold to be discharged into the surrounding container (A).

By the way, after the solidified layer thickness of the second layer reaches the designed thickness, the remaining metal should be quickly drained to avoid an unnecessary increase in the layer thickness. In this case, the larger the designed wall thickness is, the longer it takes to form a solidified layer of the designed wall thickness, and accordingly the temperature drop of the remaining metal is greater, and the degree of viscosity increases. . Therefore, when discharging the remaining metal by the inclination method shown in Fig. 3, the greater the design thickness of the second layer, the greater the inclination angle of the mold (goods) will be to increase the flow out of the remaining metal. If you are using the rotation method shown in Figure 4, it is better to increase the rotation speed to increase the centrifugal force on the remaining hot water.

In addition, in the method of the present invention, there are no particular restrictions on other casting conditions, and for example, the casting temperatures of the first layer and the second layer may be set as usual.

Next, examples of the present invention will be described.

Example 1 As shown in Fig. 3, using a centrifugal casting device equipped with a drive mechanism for tilting the mold, a 0.4%
Inject 22 kg of C-25%Cr-20%Ni-Fe molten metal and cast the first layer with a layer thickness of 15ffil at a casting temperature of 16.
30°C), and flux was added to prevent oxidation of the inner surface. After solidifying to the inner surface of the first layer, 9.6 Kf of 18% (r) steel melt was injected (casting temperature 1600°C).

The molten metal layer thickness is 8fi. Next, in order to remelt the chilled layer, the mold was tilted (tilt angle θ: 50°) and the lower end plate was removed to remove the molten metal equivalent to a layer thickness of 6fi, and the end plate was reattached. At the same time, the mold is returned to the horizontal position and solidification is completed, resulting in an outer diameter of 134sog and a first layer thickness of 1511I11. 2nd layer thickness 2
A double layer tube of 11g1 was obtained.

Example 2 As shown in Fig. 4, 0.4%C-25%Cr was first cast using a centrifugal casting device equipped with a drive mechanism that rotates the mold in a horizontal plane with its longitudinal center as the rotation axis. -20%
A first layer with a thickness of 15 fl+ was cast by pouring 22 Kf of Ni--Fe molten metal (casting temperature: 1650 DEG C.), and 7 lux was administered to prevent internal oxidation. After solidifying to the inner surface of the first layer, 12 kg of molten 18% Cr steel was injected (casting temperature 1590°C). The thickness of the molten metal layer is 10fi. Next, in order to re-melt the chilled layer, remove the end plates at both ends of the mold, and at the same time rotate the mold at a rotating speed of 100 around the center in the longitudinal direction.
rl) rllVc and rotate in the horizontal plane, layer thickness 8III
After removing the molten metal corresponding to IIVC, the rotation was stopped, the end plate was reattached, and the pipe was solidified to obtain a two-layer tube with an outer diameter of 134 cm, a first layer thickness of 15 fi, and a second layer thickness of 2 fi.

The two-layered pipes obtained in each of the above examples were confirmed to have no intermixing of the metals in each layer, to have a predetermined composition and designed wall thickness, and to have perfect adhesion between the layers. ! It has been certified.

As described above, according to the method of the present invention, the second layer molten metal is injected after solidifying up to the inner surface of the first layer, so that the thickness of the first layer may be reduced due to the mixing of metal between both layers, and the metal of each layer may be reduced. There is no change in the chemical composition of the product. In addition, since the chilled layer that forms in contact with the first layer is remelted, even if flux is trapped in that area, it is floated and separated, and the adhesion between both layers is made metallographically perfect. A strong bond can be created. Furthermore, the second layer can be easily made to a desired layer thickness by removing residual metal, and thus a two-layer centrifugally cast tube with good adhesion, having a predetermined chemical composition and arbitrary layer thicknesses can be obtained.

Furthermore, in the past, when the molten metal for the second layer was injected after solidifying the inner surface of the first layer as in the present invention in order to prevent mixing of the first and second layers, the adhesion between the two layers was poor. As mentioned above, this tendency becomes more pronounced when a metal with a higher melting point than the first layer metal is used for the second layer, and therefore there are strong restrictions on the selection of materials for each layer metal. However, according to the method of the present invention, such restrictions are not imposed, and it is possible to manufacture a double-layer pipe using any combination of materials.
It can also be tailored to meet the various required characteristics for various uses.

[Brief explanation of the drawing]

Figure 1 CI], [II3 and Figure 2 [I], [■],
[II[] and [■] are cross-sectional explanatory diagrams showing the solidification status of each layer of metal in a rotary mold for centrifugal casting, and Figs. 3 and 4 respectively show specific examples of the method for discharging residual metal in the mold in the method of the present invention. FIG. 1: Outer layer (first layer), 2: Inner layer (second layer), 4: Remaining hot water,
5.5': Container, M: Mold for centrifugal casting. Patent applicant Kubota Iron Works Co., Ltd. Agent Patent attorney Arata Miyazaki (Eng.)
[and] [engineering]
[Anus] [■]

Claims (3)

[Claims] (1) After the first layer is cast in a centrifugal casting mold and solidified to its inner surface, when the second layer is cast, a chill occurs in the second layer at the boundary with the first layer. The second layer molten metal is injected in an amount sufficient to remelt the layer (solidified shell), and when the solidified layer thickness of the second layer molten metal reaches its design thickness, the excess second layer unsolidified metal is immediately poured out. A method for centrifugal force casting of double-layered tubes, which is characterized by discharge outside the mold. (2) Centrifugation of the two-layer pipe according to item (1) above, characterized in that the surplus unsolidified molten metal of the second layer is discharged outside the mold by tilting the mold and letting it flow from the lower end side. Power casting method. (3) The mold is rotated in a horizontal plane with its longitudinal center as the rotation axis, and the excess unsolidified molten metal of the second layer is discharged out of the mold by the centrifugal force. )
The centrifugal casting force of the two-layer pipe described in Section 0