JPS586765A - Centrifugal casting method - Google Patents

Abstract

PURPOSE:To produce a two-layered pipe having high adhesiveness between both layers and having prescribed layer thicknesses by charging thermit after casting of the 1st layer and utilizing the molten metal formed by reaction as metal for the 2nd layer. CONSTITUTION:In a centrifugal casting machine, first, a required amt. of molten metal for the 1st layer is charged to cast the 1st layer 1 having a prescribed design wall thickness. The powdery mixture wherein metallic oxide and Al are compounded at thermit reaction ratios is charged to the inner side thereof. The charged thermit receives the heat of the 1st layer and covers the inner side surfaces of the 1st layer 1 as a mixture in a molten state. The layer 3 of such molten mixture is centrifugally separated to the molten metal and alumina by a difference in specific gravities under rotation of a mold M, whereby the molten metal layer 2 in contact with the layer 1 and the molten alumina layer 4 on the inner side thereof are formed. If the molten metal is solidified and the alumina layer 4 is stripped away, the two-layered pipe consisting of the 1st layer 1 and the 2nd layer 2 melt-stuck thereto is obtained.

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 tubes are made by casting two different metals in concentric circles to create a two-layer structure, making use of the characteristics of each layer of metal 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 pipe to exhibit the desired performance and characteristics, it is necessary to prevent the metals in both layers from mixing during the casting process, to form each layer to a predetermined uniform thickness, and to It is necessary to bring the layers into close contact metallurgically at the interface to create a strong bond.

Two-layer centrifugal casting tube has an outer layer (first layer) inside the centrifugal casting mold.
After injecting the molten metal as an inner layer, flux is applied to the inner surface of the molten metal, and then the molten metal that becomes the inner layer (second layer) is injected. If this is done at a relatively early point in time, Figure 1 [1
] As shown in the figure, the surface layer (1.1) of the first layer metal (1) inside the mold shaft is in an unsolidified state, and therefore the first layer and second layer metal (1) are in an unsolidified state.
Although layer (2) is easily adhered to by fusion, as a result of the molten metal of the first and second layers melting together, the first layer that is finally formed as shown in (1) of the same figure. (1) is thinner than the intended layer thickness, -1 second layer (me) is due to the incorporation of a large amount of metal in the first layer, resulting in an excessive layer thickness and a change in the original chemical composition. becomes different.

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, flux (2) is applied to the inner surface of the injected first layer molten metal (1), and the first layer (1) is solidified in that state. I]),
When the second layer molten metal (2) is injected (see figure [l]), the second layer forms a thin solidified shell (chill layer) (2) on the contact surface with the first layer.
・1) is formed (same figure [■]). Most of the flux (6) floats to the surface with the injection of the second layer at 0:00, but because the solidified shell (2/1) is formed early, some of the flux does not fully float and remains as it is. Solidification of each layer is completed in a state where it remains between the first layer (1) and the second layer (2) (Figure [■]). For this reason, the bond between the two layers is extremely incomplete, and the flux remaining between the two glabellas becomes a fatal defect in the tube material. This tendency becomes more pronounced especially when the melting point of the second layer metal is higher than that of the first layer metal. As a method to prevent this, the casting temperature of the second layer molten metal is increased or the amount of casting is increased, and the formation of the solid shell (2.1) is delayed by increasing the heat capacity □ of the molten metal, or It is also possible to try to remelt it.

However, the former method cannot raise the temperature of the molten metal so high, so its effectiveness is limited, while the latter method involves an increase in the thickness of the second layer, so it cannot be used when a thin second layer is required. cannot be applied.

The present invention has been made to address the above problem, and after casting the first layer, a mixture of metal oxide powder such as iron oxide powder and metal aluminum (iy!!& powder), so-called thermite, is administered. By using the molten metal generated with a large amount of heat due to the chilled reaction as the second layer metal, it is possible to obtain a double-layered pipe having a uniform and predetermined layer thickness with excellent adhesion between both layers. The present invention provides a centrifugal force casting method.

The present invention will be explained in detail below.

According to the method of the present invention, first, a required amount of molten metal for the first layer is injected in a centrifugal casting apparatus according to a conventional method to cast the first layer having a certain design thickness. On the inner surface of the first layer,
Fluxes commonly used for antioxidant purposes may be administered in a conventional manner.

After casting the first layer, at an appropriate time, a powder mixture containing a metal oxide and Al in a thermite reaction ratio is administered inside the layer.

The administered thermite undergoes an oxidation-reduction reaction upon receiving the heat of the first layer, and metal and A403 are generated along with a large amount of heat generation. The reaction formula when F 620B is used as the metal oxide is as follows.

Fe2O8+2Al-+2Fe+A#208+200K
The cal-generated metal and A 1208 form a mixture in a molten state due to the calorific value of the reaction, as shown in Figure 3 [■].
Cover the inner surface of layer (1). This molten mixture layer (3) is centrifuged into molten metal and alumina (i20.) due to the difference in specific gravity while the mold is rotating, and as shown in the figure (Ill), the first layer (1 ) and a molten alumina layer (5) inside it are formed.If it is solidified in this state and then the alumina layer (5) is peeled off, the first layer (1) is formed. A two-layer pipe is obtained, consisting of a and a second layer (2) welded thereto.The second layer (2) formed in the above
Since the layer thickness in 2) is determined by the amount of metal produced in the thermite reaction, any designed thickness can be obtained by appropriately weighing the amount of thermite.

By the way, the metal oxides that make up thermite are basically iron oxides such as Fe2O8 and Fe3O4.
If iron is desired as the layer material, the purpose can be achieved with it, but depending on the use of the two-layer pipe, alloy steel containing Or or other alloying elements is required. In such cases,
A part of the iron oxide is replaced with an oxide of one or more alloying elements, such as Or20B, and these oxides are mixed in a proportion corresponding to the desired second layer metal acid composition. You can use the one you made. For example, 13 as the second layer
%Or steel, by blending iron oxide powder and chromium oxide powder so that the Fe:Cr ratio is 87:13, and using thermite made by mixing this with Al powder. A second layer having a predetermined steel composition can be formed. Furthermore, depending on the steel composition of the second layer, in addition to the metal oxide, an alloying element such as Ni may be added in the form of a simple substance, or Or.

Elements such as Mn can also be blended with the thermite in the form of powder of ferroalloy such as ferromanganese.

Of course, if the amount of raw material powder added in a form that does not participate in the thermite reaction is too large, the temperature of the molten metal produced will be low and it will become viscous, making it difficult to separate it from alumina. It should be limited within a range that provides sufficient fluidity with the exothermic value of the reaction. Normally, if the proportion of thermite in the thermite is about 30% by weight or less, a desired steel composition can be obtained without causing the above-mentioned disadvantages.

In the method of the present invention, thermite may be administered through the pouring hole of the molten metal scattering prevention end plate attached to the open end of the mold, as in the case of pouring molten metal into a mold. The administration can also be carried out by an appropriate method such as a blowing method using a carrier gas or the like. In this case, it is desirable that the thermite be administered so as to cover the entire inner surface of the first layer. As a means for this purpose, it is effective to administer thermite mixed with flux. The flux fluidizes the thermite and promotes its spreading on the inner surface of the first layer. As this flux, a general flux commonly used for the purpose of preventing oxidation of the surface of the molten metal may be used.

Further, the thermite is administered after the first layer has solidified to its inner surface. This is because if the inside surface of the first layer is administered in an unsolidified state, the molten metal produced by the thermite reaction and the molten first layer will mix, causing the problem shown in FIG. 1 above. However, if the timing of administration is too late, the first
If the temperature drop in the layer is large, it will be difficult to secure the heat required for the thermite reaction to occur, so it is best to administer the product until the temperature on the inner surface of the first layer drops to ``melting point - 300℃''. preferable.

The molten metal generated by the thermite reaction may form a thin solidified shell (chill layer) at the boundary with the first layer.
Since the flux is remelted by a sufficient amount of heat generated by the reaction, residual flux in the chilled layer as shown in FIG. becomes complete.

Next, examples of the present invention will be described.

Example 1 In a centrifugal casting device, 0.4*C-251Or-2
0% Ni-Fe molten metal,? A first layer of silk with a thickness of 15 was cast by injecting 5 kQ, and then flux was administered to prevent internal oxidation. Wait until it solidifies to the inner surface of the first layer, then administer 1 kq of thermite having the following composition using air as a carrier gas, and use the resulting molten metal to form the second layer.
A layer was formed, and after solidification, the alumina layer inside the second layer was peeled off.

Thermite composition iron oxide (Fe208) powder: 0.75kg (Fe content 0
．． 5 kg) Metal An: 0.25 to 9 By the above casting, the first layer (0.4%G!-25%0r-
A two-layer tube with a layer thickness of 151aI11 (20%N1-Fe), a second layer (iron) layer thickness Q, 5ff, and an outer diameter of 1350 was obtained.

Example 2 Centrifugal force casting was carried out in the same manner as in the previous example except that 1 kg of thermite having the following composition was used.

Thermite composition iron oxide (Fe2OB) powder: 0.6# (Fe part, 4
2kg) Chromium oxide (Cr208) powder: 0.15
-# (Or part, 1 kg) Metallic Al powder: 0.25&q By the above casting, outer diameter 135r+++, first layer (0,4
%C-25%0r-20%Ni2Fe) layer thickness 15U, second layer (18%Cr steel) layer thickness 0. EIIO double layer pipe full thickness pipe.

Example 3 Centrifugal casting was carried out in the same manner as in the previous example except that thermite to which ferrochrome powder was added as an alloying element source was used.

Thermite composition iron oxide (Fe20B) powder: 0.754g (Fe portion: 055kg, metal Al: 0.25kg, ferrochrome powder (8%C-60% Cr): 0.15k
g (Cr content: 13% by weight), by the above casting, the outer diameter was 13
5jj1% 1st layer (0,4%C-25%0r-2(HN
A two-layer pipe with a layer thickness of 15 mm (i-Fe) and a second layer (13% Cr steel) layer thickness of 0.711 M was obtained.

The two-layer pipes cast in each of the above examples have each layer having a predetermined chemical composition and a predetermined designed wall thickness, and also have excellent adhesion with no 7 lux remaining between the two layers. It was confirmed that it has.

As described above, according to the present invention, the second layer is formed by administering thermite after the first layer has been solidified to the inner surface, so that the mixing of metal between both layers and the resulting There is no reduction in the thickness of the first layer or a change in the chemical composition of the metals in each layer.

Furthermore, even if a chill layer is formed in contact with the first layer, it will be remelted due to the sufficient amount of heat generated by the thermite reaction, so even if 7 lux is captured in that area, it will be floated and separated, and both The adhesion between the layers is made metallurgically perfect,
A strong bond can be obtained. Further, the second layer can be easily formed into a desired layer thickness by adjusting the dosage of thermite, and the metal material thereof can be easily formed into a desired composition by adjusting the thermite composition. In this way, a two-layer tube with good adhesion can be obtained, which is made of a combination of various metal materials and has arbitrary layer thicknesses.

[Brief explanation of the drawing]

Figure 1 [1], [:ID and Figure 2 [ID, [i],
], [IV'] are cross-sectional explanatory diagrams showing the solidification status of each layer of metal in the centrifugal casting mold, and FIG. FIG. (1)...First layer, (2)-...Second layer, (4)...Alumina layer, ■...Mold, (g)...Flux. Patent Applicant Kubota Iron Works Co., Ltd. Agent Patent Attorney Miyazaki -18 Part 111 rl) [Engineering] I3 [TVI No. 3I! ! 1 [Z] Word j

Claims (5)

[Claims] (1) Inject the required amount of molten metal into a centrifugal casting mold to cast the first layer, and after solidifying to the inner surface of the first layer, metal oxide powder and metal aldinium are added to the inner surface of the first layer. A centrifugal force casting method for a two-layer pipe, characterized in that a required amount of thermite mixed with a thermite reaction ratio is administered, and a second layer is formed of the metal produced by the thermite reaction. (2) The centrifugal casting method according to item (1) above, wherein the metal oxide is iron oxide. (3) The metal oxide is a mixture of iron oxide and oxides of one or more other metal elements in a mixing ratio depending on the desired alloy steel composition of the second layer. The centrifugal casting method according to item (1) above. (4) Thermite is a powder of a single metal element and/or an iron alloy powder added in a proportion corresponding to the desired alloy steel composition of the second layer.
) or (3). (5) The centrifugal casting method according to any one of items (1) to (4) above, characterized in that thermite is administered as a mixture with flux.