JPS5937150B2 - Method for casting composite rolls - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for casting a composite roll, and more particularly to a method for casting a sound composite roll in which the materials of the outer layer and the inner layer are continuously changed.

Generally, the properties required for rolling rolls are excellent wear resistance of the outer layer of the body and excellent toughness of the inner layer and shaft.
A composite roll was developed to meet these demands.The composite roll uses high-alloy steel for the outer layer of the body to provide wear resistance, and uses low-alloy steel for the inner layer including the shaft. A double-layered roll with breakage resistance has been manufactured.

The specific method for manufacturing this composite roll is as follows (
4)～(Tsugo is known.

(a) A centrifugal casting method in which the outer layer of the body is made of high-alloy steel, and the shaft and inner layer are made of low-alloy steel.

(b) The high alloy steel constituting the outer layer is cast as primary molten metal into the lower part and body of the mold, and after a sufficient solidified layer is formed on the surface of the body, the mold is turned over and the unsolidified molten metal is poured away; A hollow casting method in which secondary molten low-alloy steel is then poured into the shaft and inner layer.

(-j A composite casting method using a partition plate method in which a partition plate is provided in the mold, and high alloy steel is cast as the outer layer material and low alloy steel is cast as the inner layer material at the same time.

However, a common drawback of these composite roll casting methods is that the interface between the outer and inner layers is not only compositionally discontinuous (in addition, complete metal welding is often not achieved). There are things I haven't done yet.

When such a roll is used for rolling, it may peel off from the interface between the inner and outer layers and breakage due to residual stress caused by heat treatment after casting and stress during operation due to the rolled material.

Other disadvantages unique to the centrifugal casting method include the segregation of impurities on the inner surface of the outer layer, which can cause cracks or breakage of the roll, and the uneconomical nature of discarding the primary molten metal in the hollow casting method. However, the casting method using the partition plate method has disadvantages such as not only the cost of manufacturing the partition plate but also the assembly cost, and the workability is not good.

An object of the present invention is to eliminate the drawbacks of these conventional composite casting methods and to provide a casting method that provides a continuous boundary between the outer layer and the inner layer and provides a sound composite roll.

The present invention is a composite roll casting method characterized by having the following steps (1) to (n*).

(1) It has a roll shape and the body of the roll is a mold.

a step of casting primary molten metal constituting the outer layer of the body of the roll into a mold in which the upper and lower shaft parts and the riser part are sand molds; (11) the secondary molten metal is solidified to a predetermined thickness in the vicinity of the mold; Thereafter, a step of immersing the elongated nozzle into the secondary molten metal in the mold of the lower shaft portion to near the bottom of the mold, (111) While pouring the secondary molten metal through the elongated nozzle, the nozzle is immersed at the end of casting. The step of pulling up the nozzle so that the tip reaches near the bottom of the riser surface and mixing the secondary molten metal and the secondary molten metal to form the inner layer part and the shaft part of the roll.

The details of the present invention will be explained with reference to the accompanying drawings.

FIG. 1 shows a mold for manufacturing a composite roll of the present invention, which is composed of a feeder mold 1, an upper shaft mold 2, a body mold 3, and a lower shaft mold 4, in a top pouring method or a bottom pouring method. Then, the primary molten metal that is to form the outer layer of the composite roll is cast, and left to stand for a certain period of time, so that only the molten metal part that comes into contact with the body mold 3 has a solidified layer 6 of a constant thickness.
, and the other portion is unsolidified molten metal 5.

Since it takes a considerable amount of time for the solidified layer 6 to reach a certain thickness, the secondary hot water is prepared during that time.

FIG. 2 shows the positions of the ladle 7 and the elongated nozzle 10 in the mold at the initial stage when the secondary molten metal is poured, and FIG. 3 is a similar layout diagram at the final stage when the secondary molten metal is poured.

Once the solidified layer 6 of a predetermined thickness has been formed, as shown in FIG. Lower it to approximately the center position and start pouring the secondary hot water 9.

Primary in the mold 4 for the lower shaft part. Secondary molten metal 9 is added to unsolidified molten metal 5 to form mixed molten metal 11.

Next, the elongated nozzle 10 is pulled upward while pouring the secondary molten metal (.

In the vicinity of the body mold 3, the surface is a solidified layer 6 of primary molten metal, the inside is a semi-solidified molten metal with secondary molten metal interposed therein, and the innermost layer is a mixed molten metal of primary molten metal and secondary molten metal. It becomes 11.

The tip of the long nozzle 10 should eventually reach near the bottom of the feeder surface. Specifically, as shown in FIG. Nearby (
so that

During this time, the stopper 8 of the ladle 7 is kept open, so the secondary molten metal 9 in the ladle I gradually dilutes the unsolidified molten liquid inside the mold, but it does not dilute the semi-solidified primary molten metal. Since the degree of dilution is low and the solidified layer on the surface of the mold 3 remains as it is, the boundary between the primary and secondary molten metals exhibits a very natural continuous change in composition.

Moreover, metallic bonding based on diffusion can be obtained.

By ejecting the secondary molten metal outward from the tip of the long nozzle 10, the secondary molten metal rotates within the mold, increasing the diffusion effect to the primary molten metal and increasing the degree of dilution.

By gradually pulling up the long nozzle 10 from inside the mold 4 in the lower shaft part to inside the mold 2 in the upper shaft part, the primary molten metal inside is pushed up and mixed with the secondary molten metal, so that the vertical axis The middle layer of the body is completely diluted with secondary hot water, and the middle layer of the body is a mixture of semi-solidified primary hot water and secondary hot water with a low degree of dilution (a continuous boundary where composition changes are extremely natural). It can be a layer without.

By pouring secondary molten metal while pulling up the long nozzle,
A positive temperature gradient is also applied to the molten metal.

As a result, the impurities that have gathered in the center of the mold during the solidification stage of the second molten metal come to float up to the feeder part, and a high-quality composite roll with fewer inclusions can be obtained.

Next, preferred embodiments of the present invention will be described.

Body diameter 1500mm, body length 1500mm, total length 4000mm
The results of casting a composite roll of mm and weight of 34.5 tons according to the present invention will be described.

The mold uses the body as a metal mold to speed up the cooling rate, and the lower shaft, upper shaft, and feeder part as sand molds for slow cooling. An induction heating device is embedded in the round lower shaft mold 4 to increase the cooling rate at 50 Hz.
Induction heating is performed using a power source, and a heating agent is sprayed on the surface of the hot water in the open riser section to prevent coagulation from the surface, and an electric arc heating device is installed to enable electric arc heating. .

First, carbon (C) 0.88% by weight, chromium (Cr) 3.7%
A molten metal of high alloy steel containing 0% by weight at 1525° C. was poured into a lower shaft mold 4 and a body mold 3 by a top pouring method using a long nozzle 10.

During casting, the tip of the long nozzle 10 was positioned 300 mm from the bottom of the lower shaft mold.

The long nozzle 10 is raised in synchronization with the rise of the hot water level,
Finally, it was brought to a position 300 mm below the hot water surface.

Molten metal was ejected from the tip of the long nozzle 10 toward the outside of the nozzle.

25.6 tons of the above-mentioned hot water was poured into the mold and left as it was for 120 minutes.

The theoretical calculation results of the temperature distribution inside the roll and the state of the molten metal after being left for 120 minutes are shown in Figure 4. The liquidus line γ of the molten metal is 1485°C and the solidus line α is 1380°C. 175 from the roll surface in contact with mold 3 is solid phase α1.
In the range of 175 to 370 mm, it is a mixed phase of solid phase and liquid phase β1, that is, a semi-molten state, and from 370 mm onwards, it is a liquid phase γ1.
It is estimated that the

After leaving for 120 minutes, 0.29% by weight C1
A long nozzle 1 is made of low alloy steel containing 0.15% by weight of Cr.
0 was used to dilute the primary casting molten metal in the same manner as in the case of the secondary molten metal described above.

At this time, the stopper 8 is opened once at the moment when the tip of the long nozzle 10 touches the surface of the primary hot water, and after a small amount of secondary hot water is discharged and the air inside the long nozzle 10 is exhausted, the stopper 8 is opened once. Close it and lower the long nozzle 10 in that state,
When the tip of the nozzle reached 300 degrees from the bottom of the mold 4 for the lower shaft portion, the stopper 8 was opened again, and at the same time as the secondary hot water was poured, the tip of the nozzle was pulled up at a speed faster than the rising speed of the hot water.

FIG. 5 shows the relationship between the nozzle tip position B and the hot water surface position A from the start to the end of injection of the secondary hot water.

In other words, at the beginning of the injection of secondary hot water, the level of the primary hot water almost reaches the top of the body mold 3 as described above, and as the secondary hot water is poured, the primary hot water is pushed up, and the secondary hot water is raised inside the mold. The primary molten metal is diluted with hot water to form a mixed molten metal, and the molten metal level in the mold gradually rises, and when the secondary molten metal is poured, the tip of the long nozzle 10 is 300 mm below the molten metal level in the riser mold 1. It was like being located in .

The amount of secondary molten metal poured was 8.9 tons, and the time required for casting was 107 seconds.

After finishing the injection of the secondary hot water, the induction heating of the lower shaft part is stopped, cooling water is flowed into the induction coil to promote cooling of the lower shaft part, and the upper part of the riser part is heated by electric arc, The mixed melt inside is solidified from the lower shaft part, and the inside and the feeder part are kept in a molten state for a long time to prevent the concentration of internal impurities in the feeder part and the generation of shrinkage holes.

According to the present invention, after completing the casting as described above, samples were taken from each part of the roll and the chemical components were checked.

By the way, as shown in Figure 6, the results of measuring the amount of Cr at three locations at the top, middle, and bottom of the body are approximately 15 mm from the roll surface.
Up to 0m71L, the Cr content was about 3.7% by weight, indicating that the molten metal was solidified as it was, and the Cr content was about 200 to 30% from the surface.
Although the Cr content rapidly decreases at 0 vtm, the state of the decrease is extremely natural and shows a continuous change.

Furthermore, the amount of Cr becomes approximately constant at about 2.2 wt % Cr inside 300 mm.

According to the examples of the present invention, it was confirmed that the drawbacks of the conventional composite roll manufacturing method were eliminated and the following effects were achieved.

(Since the boundary between the uniform outer layer and the inner layer is not clear and shows a very natural continuous change, there is almost no residual stress caused by heat treatment after casting, and there is no risk of breakage due to stress during rolling.) There is no sex.

(b) Segregation of impurities on the inner surface of the outer layer is completely prevented by casting the molten metal with a long nozzle and pulling it up, and combined with the heating of the feeder, most of the impurities are concentrated in the feeder. It is possible to obtain a healthy composite roll with no internal shrinkage holes.

() Since both the secondary and secondary molten metals are used 100% without wasting any part of them, there is no uneconomical effect as in the hollow casting method.

As is clear from the above description, according to the present invention, primary hot water and secondary hot water can be mixed from the lower shaft portion to the upper shaft portion.

At the same time, since the molten metal has a positive temperature gradient, impurities and inclusions can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the structure of the mold used in the present invention and the solidification state of the outer layer of the body. FIG. FIG. 3 is a sectional view showing the position of the elongated nozzle at the final stage of secondary hot water injection. Figure 4 is a theoretical diagram showing the temperature distribution inside the roll and the state of the molten metal after it has been left for 120 minutes after casting the primary metal.
The figure is a correlation diagram of the position of the tip of the long nozzle during injection of secondary hot water and the position of the hot water level over time from the start of injection.
FIG. 6 is a correlation diagram showing the change in Cr content and distance from the roll center of a composite roll cast according to the present invention. 1...Mold for riser part, 2...Mold for upper shaft part, 3...Mold for body part, 4...Mold for lower shaft part Mold, 5... Unsolidified molten metal, 6...
Solidified layer, 7... Ladle, 8... Stopper, 9... Secondary hot water, 10... Long nozzle, 11...・Mixed hot water.

Claims (1)

[Claims] 1. A step of casting the primary hot water constituting the outer layer of the body of the roll into a mold having a roll shape, in which the body of the roll is a mold, and the upper and lower shaft parts and the feeder part are sand molds, After the hot water has solidified to a predetermined thickness near the mold, a step of immersing a long nozzle into the secondary hot water in the mold of the lower shaft portion to near the bottom of the mold, and passing the secondary hot water through the long nozzle. While casting, the nozzle is pulled up so that the tip of the nozzle reaches near the bottom of the feeder surface at the end of casting, and the secondary molten metal and the secondary molten metal are mixed to form the inner layer and shaft of the roll. A method for casting a composite roll, comprising the steps of: