JPS62173068A - Production of compound roll - Google Patents

Abstract

PURPOSE:To improve the quality of a product by casting an outside layer then casting a small amt. of a molten metal having a low m.p. during the solidification or partial solidification of the inside surface of the outside layer to mix and solidify the same with the cast outside layer and casting an inside layer. CONSTITUTION:After the outside layer A is cast, the molten metal B having the low m.p. is mixed at the small amt. corresponding to the pouring thickness of 1-5% of the barrel diameter of the product during the solidification or partial solidification of the outside layer A to mix the molten metal with part of the outside layer. The inside layer C is cast after the inside surface of the mixed layer solidifies. The outside layer and inside layer are thoroughly metallurgically adhered by the above-mentioned method, by which the product having the extremely high quality is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention is applied to the manufacture of composite rolls by centrifugal casting for rolling steel.

[Conventional technology]

Conventionally, in order to bond the outer layer and the inner layer metallurgically, this type of roll was made by casting the outer layer, then casting the inner layer while the inner surface of the outer layer was solidified or partially unsolidified, and melting a part of the inner surface of the outer layer.
The eroded outer layer is diluted within the inner layer.

Note that a cast iron material with a low melting point is generally used for the inner layer, and this is to perform directional solidification from the roll surface to the inside and prevent the boundary from becoming the final solidified part.

[Problem that the invention seeks to solve]

In order to metallurgically bond the outer layer and the inner layer of the composite roll, a part of the inner surface of the outer layer must be melted away by casting the inner layer, and this must be diluted into the inner layer.

In this case, the higher the inner surface temperature of the outer layer when the inner layer is cast, the higher the diffusion ability of the chemical components between the two layers, and therefore the better the adhesion. However, the amount of erosion loss also increases, and the chemical composition of the diluted inner layer material differs greatly from that of the original inner layer, generally leading to loss of strength and structure and deterioration of roll quality. In particular, in recent years, materials to which various alloying elements have been added, including high-chromium cast iron with excellent wear resistance, have been adopted for the outer layer.While many of these alloying elements have a strong tendency to damage the cast iron inner layer material, they can also cause melting damage. If the timing of casting the inner layer is delayed and the inner surface temperature of the outer layer is lowered in order to suppress the amount, the adhesion may be impaired and may not bond.

[Means for solving problems]

The present invention aims to provide a manufacturing method that improves adhesiveness without damaging the material of the inner layer by suppressing the amount of erosion loss. That is, when manufacturing a composite roll using the centrifugal casting method, after casting the outer layer, while the inner surface of the outer layer is solidified or partially unsolidified, a small amount of low melting point molten metal is poured and mixed with a part of the outer layer, and then This method of manufacturing a composite roll is characterized in that after the inner surface of the mixed layer is solidified, the inner layer is cast, and the mixed layer is completely melted away or a part of it remains, thereby achieving complete metallurgical bonding.

[Effect]

In manufacturing composite rolls, the earlier the inner layer is cast after the outer layer is cast, that is, the higher the inner surface temperature of the outer layer, the better the adhesion, but as mentioned above, the amount of erosion increases. be. On the other hand, in centrifugal casting, the initial injection amount of the inner layer also has a large effect on the erosion loss, and by reducing this amount, it is possible to reduce the amount of erosion loss. Furthermore, if a low melting point molten metal is used as the first molten metal, the adhesion to the subsequently cast inner layer will be improved, making it possible to easily bond the inner layer even if the timing of casting the inner layer is delayed. In addition, even if the inner layer at this time completely melts away the aforementioned mixed layer, the outer layer with a high melting point has been further cooled, and the amount of melting away of the outer layer again is extremely small. This makes it possible to keep dilution to a small level.

In the present invention, the small amount of molten metal injected after the outer WJ casting is limited to a material with a low melting point in order to improve the adhesion with the inner layer material to be subsequently cast. That is, since the melting point is low, it is possible to lower the inner surface temperature of the mixed layer when casting the inner layer, and it is possible to bond the inner layer even if the casting of the inner layer is delayed. Therefore, there is no effect unless the melting point is at least lower than that of the outer layer.

In this respect, the intermediate layer shown in Japanese Patent Publication No. 50-37019 has a high melting point and is not effective. On the other hand, it is preferable that the melting point is higher than that of the inner layer. If the molten metal in the inner layer that is subsequently poured completely melts away this mixed layer, there will be no problem even if it has a low melting point, but if some of this mixed layer remains, the boundary with the inner layer will become the final solidified part, causing cavities etc. There is a risk of defects occurring.

The issue here is the melting point of the mixed layer after the melted outer layer is diluted. Considering that the outer layer generally has a higher melting point than the inner layer, the original molten metal is slightly higher than the inner layer. Even if the melting point is low, the mixed layer will eventually have a high melting point and no problem will occur. Furthermore, even if the material is the same as that of the inner layer, the above-mentioned effects will not be diminished, and compared to using three molten metals, there will be no equipment constraints such as a melting furnace, resulting in lower costs.

Now, the injection amount is preferably a small amount corresponding to an injection thickness of 1 to 5% of the product barrel diameter. In other words, the main purpose is to suppress the amount of melting loss in the outer layer, and if it is more than 5%, this effect will not be achieved and melting loss will increase, but if it is less than 1%, it will cause cooling of the molten metal during injection and non-uniform distribution on the inner surface of the outer layer. There is a risk of local adhesion failure.

For the inner layer to be cast last, it is possible to freely select the conditions for metallurgical bonding with the mixed layer, which has a low melting point, but if the mixed layer is completely melted away, the result will be the same as before. The same composite roll as the method is obtained, but there is less erosion of the outer layer and less dilution to the inner layer, making it easier to obtain the original material properties. Further, if the mixed layer does not become brittle, even if a portion of this mixed layer remains, it will not damage the product of the roll.

〔Example〕

Product body diameter 1. A roll having a body length of 4,800 mm and a total length of 8,000 mm was manufactured under the conditions shown in Table 1 using high-chromium cast iron for the outer layer and high-grade cast iron for the mixed layer and inner layer. In this case, the outer layer and the mixed layer were cast by horizontal centrifugal casting, and the inner layer was cast by static casting and top pouring.

FIG. 1 is a schematic diagram showing the casting of an outer layer and a mixed layer in the horizontal centrifugal casting method, and FIG. 2 is a schematic diagram showing the casting of the inner layer in the static casting top pouring method.

In the figure, A is the outer layer, B is the mixed layer, C is the inner layer, 1 is the mold, and 2 is the sand mold.

As a result, as shown in FIG. 3, it was possible to obtain a healthy roll with no adhesion defects or casting defects.

For reference, an example is shown in Fig. 4 using the conventional method under the manufacturing conditions shown in Table 2. Although the inner layer was injected early, poor adhesion was observed and cracking occurred from this defective adhesion.
The effect of washing with water is remarkable. In this example, most of the mixed layer was completely eroded away by the inner layer, but a maximum of 8 mm of the mixed layer remained in some parts. However, the boundary strength of all parts was good as shown in Table 3.

Further, the Cr content of the inner layer after final dilution was 0.7%, and the amount of erosion was suppressed and the material properties were not impaired.

In the above example, high chromium cast iron was used for the outer layer and high-grade cast iron was used for the inner layer, but the outer layer was made of a cast steel material with a high melting point, and the inner layer was made of a low-melting point material that is commonly used in conjunction with high-grade cast iron. It is easy to understand that the same effect can be obtained even if ductile cast iron or the like is used.

−〇 − [Effects of the Invention] As mentioned above, according to the manufacturing method of the present invention, the outer layer and the inner layer can be easily bonded together without impairing the characteristics of the inner layer material, and a high-quality composite roll can be supplied. This makes it possible and has great industrial value.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing the casting of the outer layer and mixed layer in the horizontal centrifugal casting method, Figure 2 is a schematic diagram showing the casting of the inner layer by the static casting overcasting method, and Figure 3 is a schematic diagram showing the casting of the inner layer by the static casting method. Figure 4 shows a cross-sectional sketch of a roll manufactured by a conventional method. Fig. 1 ■ Fig. 2, “ 10.2 ′°゛ A Outer layer I B Mixed layer Fig. 3 ■ - Cedar (

Claims (1)

[Claims] When manufacturing a composite roll using the centrifugal casting method, after casting the outer layer, while the inner surface of the outer layer is solidified or partially unsolidified, a small amount of low melting point molten metal is poured and mixed with a part of the outer layer.
Furthermore, after the inner surface of this mixed layer has solidified, the inner layer is cast, and the mixed layer is completely melted away or a portion remains, thereby achieving complete metallurgical bonding.