JPH05285509A - Manufacture of composite roll for rolling - Google Patents

Abstract

PURPOSE:To manufacture a composite roll in which the generation of center defects of an internal layer is prevented and which is excellent in the soundness of internal quality by applying periodic pressure in the feeder head parts of molten metal for the internal layer at the time of manufacturing the roll for rolling. CONSTITUTION:After forming a cylindrical outer shell layer 1, an internal layer material 2 is poured into the inside of that outer shell layer 1, the feeder head part 3 is added to the molten metal for the internal layer and, at the time of manufacturing the composite roll for rolling which joins these outer shell layer 1 and inner shell layer 2 together metallurgically, periodic pressure is applied to the feeder head part 3 of the molten metal for the internal layer. In this way, even when a material such as cast steels having large solidification shrinkage is used for the internal layer material, a sound roll without the defect of drawing cavity can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a rolling composite roll, and more particularly to a method for producing a rolling composite roll which prevents the occurrence of inner layer center defects.

[0002]

2. Description of the Related Art Casting rolls are often used as rolls for hot rolling of steel sheets, but the layers used for rolling are required to have wear resistance and the shaft portion toughness. A composite structure composed of an outer shell layer and an inner layer is adopted.

The conventional composite rolls for rolling are obtained by centrifugally casting an outer shell layer having excellent wear resistance (for example, high chromium cast iron), and immediately after the outer shell layer is solidified, a tough inner layer is formed inside the outer shell layer. It is manufactured by casting a material and metallurgically joining an outer shell layer and an inner layer. At this time, a cast iron-based material with less solidification shrinkage is adopted as the inner layer material from the viewpoint of casting defects, and spheroidal graphite cast iron has been frequently used.

Since the body diameter of the conventional composite roll for hot strip rolling is φ500 to 800 mm and the shaft diameter is φ400 to 600 mm, the inner layer material made of spherical black smoke cast iron (tensile strength = 400 to 500 MPa) Was able to guarantee its strength sufficiently.

[0005]

However, as the rolling technology advances, the strength required for the inner layer of the composite roll may not be satisfied by the spheroidal graphite cast iron due to the reduction of the roll diameter, the introduction of a strong roll bender, and the like. Has occurred.

In order to secure necessary and sufficient strength for the inner layer of the composite roll, it is effective to strengthen the inner layer material, that is, to change the inner layer material from spheroidal graphite cast iron to higher strength cast steel material. It is conceivable that cast steel-based materials have larger solidification shrinkage than cast iron-based materials, and therefore shrinkage cavity defects occur in the center part, and shrinkage of the roll diameter causes more shrinkage cavity defects to occur. Difficult to manufacture. The inner layer center defect of the roll is dangerous because it causes the roll to break during rolling.

As a method for preventing shrinkage cavity defects due to solidification shrinkage, it is generally known to increase the size of the feeder and pressurize the feeder, but it is sufficient for castings having a long and slender shape such as rolls. In order to obtain the effect, it is necessary to raise the pressure of the molten metal, which is not practical because it is dangerous and requires a large capital investment. Also, even if a chill is used to promote directional solidification, no sufficient effect can be expected.

Further, as a roll manufacturing method in which a cast steel material is adopted as the inner layer material, a continuous casting method in which an outer shell layer is built up around a steel core material as described in JP-A-1-91901. Although a method has been proposed, since the manufacturing process is completely different from the conventional centrifugal casting method, enormous equipment investment is required, and it is not easy to switch the roll manufacturing method from the centrifugal casting method to the continuous casting method.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to make it possible to manufacture a composite roll for rolling which is free from center defects in the inner layer and which is excellent in internal quality and soundness.

[0010]

[Means for Solving the Problems] When casting a composite roll,
Shrinkage cavity defects do not occur if the molten metal is replenished from the feeder against solidification shrinkage of the inner layer material, but shrinkage cavity defects occur in the part where the molten metal replenishment is interrupted if the molten metal supply path in the middle solidifies. ..

However, although it is known that the molten metal supply can be promoted by pressurizing the feeder part or the entire mold, in a casting having an elongated shape such as a roll, the molten metal supply path is long, so that a simple pressure is applied. In some cases, the supply of molten metal from the feeder tends to be incomplete. In particular, when a molten metal with a large solidification shrinkage, such as steel, is used as the inner layer material, it is necessary to raise the height of the riser or apply a very high pressure in order to secure sufficient melt supply. However, it is almost impossible to realize it on an industrial scale.

[0012] Therefore, as a result of earnest studies on stable replenishment of molten metal having a large solidification shrinkage, the present inventor suppressed the solidification of the molten metal replenishment passage by periodically pressurizing the molten metal to replenish the molten metal from the feeder. The present invention was created by finding that the above can be sustained.

That is, according to the present invention, after forming a cylindrical outer shell layer, an inner layer material is poured inside the outer shell layer, and a riser portion is added to the inner layer molten metal to form the outer shell layer and the outer shell layer. In the method of manufacturing a rolling composite roll for metallurgically joining the inner layer, a cyclic pressure is applied to the feeder portion of the inner layer molten metal.

[0014]

The present invention is to manufacture a composite roll for rolling according to the following (1) to (3). (1) First, a cylindrical outer shell layer having a predetermined thickness is formed. As the outer shell layer material, any material having wear resistance can be advantageously used, but high Cr cast iron is particularly advantageous.

Although the means for forming the cylindrical outer shell layer can be freely selected, the outer shell layer needs to be at a high temperature in order to metallurgically bond the cylindrical outer shell layer with the inner layer. It is most reasonable to form the outer shell layer by centrifugal casting. That is, as shown in FIG. 2, the molten metal forming the cylindrical outer shell layer 1 is poured into the casting mold 11 rotating at a high speed from the ladle 12 through the pouring pipe 13, and the casting mold 11 is rotated until it is completely solidified. .. 11A is a mold driving roller.

(2) Next, as shown in FIG. 3, immediately after the outer shell layer 1 is solidified, the mold 11 is vertically erected and the molten metal for the inner layer is poured from the ladle 12 at the top (or bottom) through the injection pipe 13. Make a bath. The inner layer material may be a cast steel system having a large solidification shrinkage, or cast iron having a small solidification shrinkage, spheroidal graphite cast iron, or graphite steel.

When the pouring is completed, a heat insulating material is sprinkled on the upper surface of the upper feeder to suppress the solidification of the feeder unit 3.

(3) After a while after the lubrication of the inner layer 2, a pressure is applied to the feeder portion 3 of the inner layer molten metal. Although various methods can be applied to pressurization, the method of pressurizing from the upper part of the feeder using the pressurizing device 14 including a hydraulic cylinder as shown in FIG. 1 is simple.

The timing of starting the cyclic pressurization is after the solidified shell is thickened to the extent that hot cracking does not occur due to the pressurization of the inner layer solidified shell such as the shaft portion, and the molten metal is supplied from the feeder. The effect of the present invention cannot be expected if the feeder is pressurized after the passage is solidified. Further, the periodic pressurization is stopped after the portion to be the product is completely solidified.

In the present invention, however, the reason why the occurrence of internal defects is reduced by the periodic pressure applied to the feeder part is considered as follows.

Since the amount of molten metal supplied through the gap serving as the molten metal supply path is proportional to the pressure difference, pressurizing the feeder facilitates the supply. However, the increase in viscous resistance due to the temperature decrease of the molten metal and the narrowing of the gap due to the progress of solidification increase the resistance for replenishing the molten metal.

On the other hand, if the feeder is periodically pressurized, the molten metal moves while being pressurized and moves away from the feeder, and when the pressing is stopped, the molten metal pressure inside the feeder rises. Will try to flow in the opposite direction due to the higher As a result, a passage for the molten metal is formed in the gap, and even if the solidification of the gap progresses, solidification is suppressed in the passage where the molten metal always flows, and the molten metal supply from the feeder is continued.

That is, the present invention secures the path of molten metal by artificially generating convection in the molten metal supply path. In the molten metal supply path of the present invention, as long as there is an area requiring molten metal supply ahead of it, the flow of the molten metal is caused by the cyclic pressurization, so that solidification is suppressed and the molten metal supply path continues to function.

Further, in the molten metal supply path of the present invention, since the molten metal has good fluidity, high pressure such as static pressure is not required. The pressure of this cyclic pressurization is preferably 0.1 to 1.0 MPa. Further, the cycle of the periodic pressurization does not have to be a fast cycle, and 0.1 to 5 Hz is suitable.

[0025]

[Examples] A composite roll for hot rolling was produced in which the body had an outer diameter of 700 mm, a length of 2000 mm, and an outer shell layer having a thickness of about 70 mm. The outer shell layer was formed by centrifugal casting using high chromium cast iron. Inside the outer shell layer, a cast steel-based molten metal was poured as an inner layer. The feeder had an outer diameter of 600 mm and a length of 800 mm, and a heating sleeve was placed around it. Two types of composite rolls were manufactured: one in which the feeder part was cyclically pressed (example of the present invention) and one in which it was not pressed (conventional example).

In the example of the present invention, the pressurizing method is to press the upper surface of the feeder with a hydraulic cylinder. The pressurization of the feeder was started 40 minutes after pouring, and the pressure of 500 MPa was applied at 2 Hz for 240 minutes.

The control items other than the pressurization of the feeder in manufacturing the roll are the same in the present invention example and the conventional example.

In each of the present invention example and the conventional example, the chemical compositions of the outer shell layer and the inner layer are as shown in Table 1, and there is no difference in terms of the chemical composition of the inner layer which tends to cause shrinkage cavity defects.

In order to investigate the occurrence of shrinkage cavity defects in the center of the roll, the roll was cut in the axial direction and the cross section was observed. As a result, it was found that the roll manufactured by the conventional method had a diameter of 50 to 100 mm in the longitudinal direction of the center of the roll. Pipe-shaped or Zaku-shaped shrinkage cavity defects were recognized. On the other hand, the roll produced by the method of the present invention had shrinkage cavity defects having a diameter of 10 mm or less. The shrinkage cavity defect of the roll by the conventional method is larger than the problematic point in the strength of the roll. On the other hand, the shrinkage cavity defects obtained by the method of the present invention are very slight and have no problem during rolling use.

[0030]

[Table 1]

[0031]

According to the present invention, a sound roll having no shrinkage cavity defect can be obtained even when a material such as cast steel having a large solidification shrinkage is used as the inner layer material. Therefore, it is possible to manufacture a rolling composite roll having excellent inner soundness, which prevents the occurrence of inner layer center defects, and to manufacture a rolling composite roll having high axial strength. Further, since the flowability of the molten metal is improved, the volume of the feeder can be reduced, which is also effective in improving the yield.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a method for periodically pressurizing a roll inner layer feeder according to the present invention.

FIG. 2 is a schematic view showing a centrifugal casting method for a composite roll outer shell layer.

FIG. 3 is a schematic diagram showing a casting method of an inner layer of a composite roll.

[Explanation of symbols]

 1 Outer shell layer 2 Inner layer 3 Feeder 11 Mold 14 Pressurizing device

Claims (1)

[Claims] 1. After forming a cylindrical outer shell layer, an inner layer material is poured inside the outer shell layer, and a riser portion is added to the inner layer molten metal,
A method for manufacturing a rolling composite roll for metallurgically joining the outer shell layer and the inner layer, wherein a cyclic pressure is applied to the feeder portion of the inner layer molten metal. .