JPS601109B2 - Centrifugal casting method - Google Patents

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 into the same D-circle shape to create a two-layer structure, making use of the features of each layer of metal and making it able to withstand harsh usage conditions. For example, it is used as a reaction tube for thermal decomposition and reforming of hydrocarbons, a so-called cracking tube.

In order for this two-layer centrifugally cast tube to exhibit the desired performance and characteristics, it is necessary to prevent the two layers of metal from coming together during the casting process.
It is necessary to form each layer to a predetermined uniform thickness, and to bring the two layers into close metallurgical contact at the interface to form a strong bond. Two-layer centrifugal casting tubes are made by injecting molten metal as the outer layer (first layer) into the centrifugal casting mold, then applying flux to the inner surface, and then forming the inner layer (second layer).
In this case, if the second layer molten metal is injected at a relatively early stage, the first layer in the mold M as shown in FIG. The surface layers 1 and 1 of the layer metal 1 are in an unsolidified state, and therefore the first layer and the second layer 2 are easily adhered by fusion, but the solidified layers 1 and 2 of the first layer are also in a high temperature state. It receives the heat of the second layer molten metal and remelts it.

As a result, as shown in FIG. As a result, the layer thickness becomes excessive and the chemical composition becomes different from the original one. In order to avoid the above-mentioned disadvantages, the first layer must be completely solidified to the inner surface, and the second layer lacquer must be injected after the temperature has reached such a temperature that it will not re-melt even when it receives the heat of the second layer molten metal. However, if this is done, there will be a problem with the adhesion between the two layers.

That is, as shown in Fig. 2, after administering flux F to the inner surface of the injected first layer metal port bath 1 and solidifying the first layer 1 in that state (Fig. 1 [1]), When the second layer molten metal 2 is injected (FIG. 2B), the second layer forms a thin solidified shell (chill layer) 2.1 on the contact surface with the first layer. (
Same figure [m]). In that case, most of the flux F is
As the layer molten metal is injected, it floats to the surface, but the solidified shell 2
・Because 1 is formed early, ``some of the flux does not float up completely and solidification of each layer is completed with it remaining between the first layer 1 and the second layer 2 (Figure [W]). For this reason, the bonding state between the two layers becomes extremely incomplete, and the flux remaining between the two layers becomes a fatal defect in the pipe material.This tendency is particularly caused by the fact that the melting point of the second layer metal is higher than that of the first layer metal. The higher the temperature of the metal, the more noticeable it becomes.To prevent this, increase the casting temperature of the second layer molten metal or increase the amount of the molten metal, and increase the heat capacity of the molten metal.・It is also possible to delay the formation of 1 or try to remelt it. However, the former method has a limited effect because the molten metal temperature cannot be raised that high, while the latter method 2
Since this involves an increase in layer thickness, it cannot be applied when a thin second layer is required. The present invention has been made in view of the above, and when casting the second layer after casting the first layer, it is possible to simultaneously cast the second layer.
Then, by administering a melting flux having a temperature higher than the melting point of the metal of the second layer, it is possible to obtain a single-layer tube having any layer thickness, which is thin or thick, with the tight contact between both layers broken.
Provides a force casting method.

The method of the present invention will be explained below.

According to the method of the present invention, first, in a centrifugal casting apparatus, a required amount of metal Luoyang is injected in a conventional manner to cast a first layer having a designed wall thickness.

A flux commonly used for the purpose of preventing oxidation on the inner surface may be applied to the inside of the first layer according to a conventional method. Then, after the first layer has solidified to its inner surface, a second layer of metal hot water is injected, and a second layer of the designed thickness is cast. Since the second layer is cast after solidifying up to the inner surface of the first layer, the metal between the two layers will not mix. When casting the second layer, molten flux is applied at the same time as the molten metal is injected, or after that, "the thin solidified shell (chill layer) of the second layer that occurs at the boundary with the first layer is It is remelted by the retained heat.

As a result of this remelting of the chill layer, even if the flux (part of the flux administered after casting the first layer) that had been pushed laterally into the chill layer is present, it floats to the top of the second layer port flaws and separates. The first layer and the second layer are fused and their adhesion becomes good. After solidification of the first layer, the administration of molten flux during casting of the second layer is carried out at the same time as the injection of the second layer metal port hot water or after the injection is completed, as described above.

When administering the molten flux at the same time as the injection of the second layer molten metal, the entire prescribed amount is administered within a short period of time at the beginning, middle, or end of the injection from the start to the end of the injection of the molten metal. Alternatively, the drug may be administered continuously or intermittently from the initial stage to the final stage. However, in order for the molten flux to act directly on the chilled layer as a heat source for remelting the chilled layer, it is advantageous to administer it at the beginning to middle stage of pouring the second layer molten metal. On the other hand, when administering molten flux after the injection of the second layer molten metal is completed, the molten flux with a temperature higher than the melting point of the second layer metal coats the top surface of the second layer molten metal, which is used to remelt the chill layer. Thermal compensation is provided. In that case, it is thermally disadvantageous to leave a time interval between the injection of the second layer molten metal and the administration of the flux, and it is preferable to administer the flux immediately after the injection is finished. That is, the present invention
The molten flux administered during layer casting functions as a heat source for remelting the chilled layer.

For this reason, the molten flux must be heated to a temperature higher than the melting point of the second layer metal, and the amount administered must be an amount that can cover enough heat to remelt the tell layer. There must be. The dosage varies depending on the casting amount of the second layer, the specific heat/melting point of the metal, the specific heat/temperature of the molten flux used, etc., but it is usually about 2X9 or more for the second layer molten metal amount lk9. Bye. Note that this flux is a general flux that is normally used to prevent oxidation of cast molten metal, such as Na2007, S
It may have a composition consisting of i02, CaC03, etc. In addition, it is also possible to use molten slurk 11 (slag) generated during melting of steel. After casting the second layer and administering the molten flux, solidification is completed, and then the inner flux layer of the second layer is peeled off to form a layer with good adhesion and a predetermined layer thickness and chemical composition. A double layer tube is obtained. In addition, in the method of the present invention, there are no particular restrictions on other casting conditions, and for example, the casting temperature of each layer may be the same as usual.

Next, examples of the present invention will be described.

Example 1 In a centrifugal casting device, 0.4%C-25%Cr-20
%Ni--Fe molten metal was injected to cast the first layer with a designed wall thickness of 15, and flux was applied to the inside of the layer to prevent oxidation.

Then, after solidifying to the inner surface of the first layer, Rakuyo 2.5k9 of 18% Cr steel was injected to cast the second layer on the layer thickness 2 side, and molten flux (Ca○-S02 heated to a temperature of 160,000 A two-layer tube with an outer diameter of 134 mm, a first layer thickness of 15 mm, and a second layer thickness of 2 mm was obtained by administering 5 kg of Na20-NaF) and solidifying it as it was. In addition, the time required from the start to the end of pouring the second layer molten metal (time required for pouring) is 6
The administration of the molten flux started 3 seconds after the start of the injection of the second layer lacquer, and it took 1 second to administer the entire predetermined amount. Example 2 Melt flux (Ca○-Si02-Na20-NaF
) was administered in the same manner as in Example 1 above, except that instead of being administered during the pouring of the second layer molten metal, one portion of sand was administered immediately after the pouring was completed. Ta.

However, the temperature at the time of administration of the molten flux was 160,000 °C, and the dose was 5K9. It was confirmed that the two-layered pipes obtained in each of the above examples had no metal interaction between the layers, had the prescribed composition and designed wall thickness, and had perfect adhesion between the two layers. It was done. As described above, according to the method of the present invention, the second layer molten metal is injected after the first layer has solidified to the inner surface. No change in component composition occurs.

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 can be floated and separated, and the adhesion between both layers can be made metallurgically perfect. It can be tightened to form a strong bond. In this way, a two-layer centrifugally cast tube with a predetermined chemical composition and arbitrary layer thicknesses and good adhesion 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 the first layer and the second layer from stirring against each other, the adhesion between the two layers was incomplete. The trend is the first
As mentioned above, this becomes noticeable when a metal with a higher melting point than the layer metal is used as the second layer, and therefore, there have been strong restrictions on the selection of materials for each layer metal, but according to the method of the present invention, Since such restrictions are not imposed, it is possible to manufacture double-layer pipes using any combination of materials, and it is possible to meet various required characteristics for various uses.

[Brief explanation of drawings]

Figure 1 [1],

[0] and Figure 2 [1], [B], [
[m] and [W] are cross-sectional explanatory views showing the solidification state of each layer of metal in a rotary mold for centrifugal casting. 1: first layer, 2: second layer, M: mold, F: flux. Figure 1 Figure 2

Claims (1)

[Claims] 1. In the production of a two-layer centrifugally cast tube consisting of an outer layer and an inner layer, after the outer layer is cast and the inner layer is solidified, when the inner layer is cast, the inner layer metal is poured during or immediately after the injection of the molten metal. A centrifugal force casting method characterized in that the chill layer at the boundary with the first layer is remelted by administering molten flux heated to a temperature higher than the melting point of the first layer.