JPS586764A - Centrifugal casting method - Google Patents

Abstract

PURPOSE:To produce a two-layered centrifugally cast pipe wherein respective layers have prescribed uniform layer thicknesses and the adhesiveness between the layers is high by moving a partition plate of a mold to discharge the molten metal that exceeds the design thickness of the 2nd layer. CONSTITUTION:A partition plate 4 is located spacially by a suitable distance from an end plate 3, and a required amt. of molten metal is charged through the hole 6 in the central part of the plate 3, whereby the 1st layer having a design thickness t1 is cast. After waiting for the molten metal to solidify down to the inner side surfaces thereof, the molten metal for the 2nd layer is charged to cast the 2nd molten metal layer 2 (layer thickness t2). Said metal is charged at the amt. sufficient for remelting of the chill layer. After the chill layer is remelted, the plate 4 is slided to the other opening end B side to form a space part V and the excess molten metal that exceeds the design wall thickness t3 of the 2nd layer is flowed out into the space V. Thus, the molten metal of the 2nd layer is held at the design wall thickness t3 on the inner side of the 1st layer 1 and is solidified, whereby the two-layered pipe wherein the respective layers have the prescribed layer thickness is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a centrifugal casting method, particularly a method for manufacturing 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 manufactured by injecting molten metal as a layer, then applying 7 lux to the inner surface of the molten metal, and then injecting the molten metal that will form the inner layer (second layer). If the injection is performed at a relatively early point in time, Figure 1 [
As shown in I), the surface layer (1-1) of the first layer metal (1) in the mold (2) is in an unsolidified state, so the first layer and the second layer (2) are fused together. Although it adheres easily, since the first coagulated layer (1 and 2) is also in a high density state, IX2
Re-melts after receiving zero heat during layer melting. As a result, the same figure [I[
] As shown in K, the first layer (i) that is finally formed is thinner than the expected layer thickness, while the second layer (a) is thinner due to the large amount of first layer metal mixed in. The amount becomes too large 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, Vc7 lux (g) is administered to the inner surface of the injected first layer molten metal (1),
After solidifying the first layer (1) in this state (see figure [1]
), when the second layer molten metal (2) is poured (same figure [■])
, the second layer has a thin solidified shell (chill layer) on the contact surface with the first layer.
(2.1) is formed (same figure [■]). In that case, most of the flux (D) floats to the surface with the injection of the second layer molten metal, but since a solidified shell (2.1) is formed early, some 72 fluxes do not fully float and remain as they are. @1
Solidification of each layer is completed with the layer remaining between layer (1) and the 124th layer (2) (Figure [■]). This trend is particularly
The higher the melting point of the second layer metal is than that of the first layer metal, the more pronounced this becomes. For this reason, the bond between the two layers becomes extremely incomplete, and the flux remaining between the two layers becomes a fatal defect in the resulting two-layer tube.

Here's how to prevent this! The solidified shell (
It has been considered to delay the formation of 2.1) or to try to re-melt 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 difficult to create a healthy two-layer pipe. You can't get it.

The present invention has been made in view of the above,
□Providing a method for centrifugal force casting of a two-layer pipe having arbitrary layer thicknesses with excellent adhesion between the two layers.

One method of the present invention will be explained below.

According to the method of the present invention, first, a required amount of molten metal for the first layer is poured into a centrifugal casting mold to cast the first layer having a designed thickness. Inside the first layer, flux may be applied in a conventional manner. After the first layer has solidified to the inner surface, the second layer is cast. In the casting of the second layer, the solidified shell (chill layer) of the second layer molten metal that is generated in contact with the first layer is remelted by the heat possessed by the second layer molten metal itself. That is, the present invention allows the second layer molten metal to also serve as a heat source for remelting the chilled layer.

Therefore, the amount of the second layer molten metal injected must be at least sufficient to cover the amount of heat required to remelt the chilled layer.

As mentioned above, the second layer molten metal has a sufficient amount of heat, so even if some of the flux is trapped in the chilled layer formed in contact with the first layer, the remelting of the chilled layer will cause the flux to reach the upper surface of the second layer molten metal. They float to the surface and are separated.

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

After the chilled layer redissolves, the second layer molten metal solidifies sequentially from the outside (the side in contact with the first layer) over time, increasing the thickness of the solidified layer. Of course, the layer thickness is determined by the elapsed time after pouring the molten metal. In the present invention, the injection amount of the second layer molten metal is determined independently of its design thickness as described above, so if the thickness of the second layer molten metal in the mold exceeds the design thickness, if the second layer molten metal is allowed to solidify as it is, then The excess wall thickness will have to be removed. Therefore, in the solidification process of the second layer, the present invention eliminates molten metal whose thickness exceeds the design thickness. Of course, the removal must be performed after the remelting of the chilled layer is completed and just before the solidified layer thickness of the second layer reaches the designed thickness.

The above-mentioned centrifugal force casting can be carried out using a centrifugal casting mold shown in FIG. 3 [I].

'') In Figure 2, ゛ and (to) are molds for centrifugal force casting, which are rotated at an appropriate rotational speed by a rotary drive means (not shown) K with the center in the longitudinal direction aligned. ) of one open end (A
) is equipped with an end plate (3) to prevent the molten metal from scattering inside the mold, while inside the mold there is an inner wall surface (S) at the end of the mold.
A circular partition plate (4) corresponding to the cross-sectional shape of is slidably mounted. The partition plate (4) is connected to an operating rod (5) of a suitable drive means (not shown) such as a hydraulic device so as not to interfere with the rotational movement of the mold, and is connected to the operating rod (5) of a suitable driving means (not shown) such as a hydraulic device so as to prevent the rotational movement of the mold from occurring.
It can move along its axial direction (longitudinal direction). In addition, if the partition plate (4) is slidable within the mold and maintains airtightness that prevents molten metal from flowing out between its outer peripheral surface and the mold inner wall surface (S), Its material, shape, etc. are arbitrary, and it may be a circular plate-like body similar to the end plate (3), for example.

In the above device, the partition plate (4) is positioned at an appropriate distance from the end plate (3), and in that state, the end plate (3)
) The required amount of molten metal is injected through the hole (6) in the center of the hole (6) to cast the first layer (1) having the designed wall thickness (tl), wait for it to solidify to the inner surface, and then Two-layer molten metal is injected, and a first two-layer molten metal layer (2) [layer thickness (t2)] is cast. Of course, the amount of injection must be sufficient to remelt the generated chill layer.

When the second layer molten metal (2) is injected, a chill layer is generated at the boundary with the first layer (1), which has already solidified, but this is remelted by the heat retained in the molten metal. After finishing the remelting, slide the partition plate (4) to the other open end ■ side. By moving this partition plate, a space M is formed, and the design thickness of the second layer (
Excess molten metal exceeding t3) is discharged into the space (b). Therefore, the amount of movement of the partition plate (4) is determined so that the volume of the pool in the space (b) to be formed is equal to the amount of excess molten metal [layer thickness (j4)] in the second layer to be removed. Should.

In this way, each layer has a predetermined layer thickness by maintaining the second layer thickness 2 mm (t3) that matches the inner I/C design thickness of the first layer (1) and completing solidification. A double layer tube is obtained. The sump portion (7) may be removed by cutting after the casting tube is removed from the mold.

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.Examples of the present invention will now be described.

Example As shown in Fig. 3, in a centrifugal casting mold equipped with a partition plate that is movable in the axial direction, 0.4% C-2 was first added.
Inject 22 kg of 5% Cr-20% Ni-Fe molten metal,
Casting the first layer with a layer thickness of 15fi (casting temperature: 1600℃)
A flux was applied to the inner surface to prevent oxidation.

After solidifying to the inner surface of the first layer, 18% Cr steel molten metal 9
．． 5 KIF was injected (casting temperature 1580°C). The molten metal layer thickness is 8 fl. Then, in anticipation of the remelting of the chilled layer, the partition plate was moved, and an amount of molten metal corresponding to a layer thickness of 6 fl was expelled into the pool, where it was allowed to solidify. After solidification was completed, it was taken out from the mold and the base metal in the pool area was cut off to obtain a two-layered tube with an outer diameter of 134 fins, a first layer thickness of 15 fi, and a second layer thickness of 2 mm.

It was confirmed that the two-layered pipe obtained in the above example had no intermixing of the metals in each layer, had a predetermined composition and designed wall thickness, and had perfect adhesion between the layers.

As described above, according to the method of the present invention, the molten metal for the second layer is injected after the first layer has solidified to the inner surface. There is no change in the chemical composition of the metal. 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, by eliminating the remaining molten metal in the second layer, it is possible to easily obtain a desired layer thickness, and thus a two-layer centrifugally cast tube with a predetermined chemical composition, arbitrary thickness, and good adhesion can be obtained. It will be done.

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 would be incomplete. As mentioned above, this tendency becomes more noticeable when a metal with a higher melting point than the first layer metal is used as the second layer, and therefore, there are strong restrictions on the selection of materials for each layer metal, but the method of the present invention According to the above, since such restrictions are not imposed, it is possible to increase the production of double-layered pipes by combining arbitrary materials, and it is possible to meet various required characteristics for various uses at will.

[Brief explanation of the drawing]

Figure 1 CI], []I] and Figure 2 CI], [Old, [
■], [■] are cross-sectional explanatory diagrams showing the solidification status of each layer of metal in the rotary mold for centrifugal casting, and Figure 3 [■] and [II] are each layer in the mold for centrifugal casting used to carry out the present invention. FIG. 1: First layer, 2: Second layer, 3: End plate, 4: Partition plate, 5:
Operating rod for moving partition plate, M: Mold for centrifugal casting. Patent applicant Kubota Iron Works demutualization agent Patent attorney Arata Miyazaki Part 8 Part 1ml [Eng.] [11”I]
Obstacle〕〕〔■】

Claims (1)

[Claims] (1) An end plate having a hole in the center is attached to one open end of the mold, and a circular partition plate placed inside the mold is driven into the mold by a driving means connected to the end plate. In a mold for centrifugal force casting in which a partition plate is provided so as to be slidable in its longitudinal direction, the partition plate is positioned in the mold at an appropriate distance from the end plate, and the partition plate is placed in the mold at an appropriate distance from the end plate. A sufficient amount to remelt the solidified shell (chill layer) that is generated in contact with the first layer when pouring molten metal to cast the first layer and solidify to the inner surface, and then casting the second layer. The second layer molten metal is injected into the space formed by moving the partition plate to the other open end side after the chilled layer has remelted, exceeding the design thickness of the second layer. A method for centrifugal force casting of a two-layer pipe, characterized in that the second layer molten metal is excluded.