JPS59193747A - Mold for casting composite roll - Google Patents

Abstract

PURPOSE:To obviate generation of crazes and cracks of a roll occuring in the difference in the cooling rate of a molten metal by providing a boundary part mold having an intermediate heat extracting power to the neck part between a cylindrical metallic mold and end metallic molds and changing gradually the heat extracting power. CONSTITUTION:A mold for casting a composite roll is constituted by disposing a boundary part mold 12 having the heat extracting power smaller than that of a cylindrical metallic mold 2 and larger than that of sand molds 3, 4 for the end parts having the heat extracting power smaller than that of the mold 2 between the mold 2 and the molds 3, 4. The mold 12 is formed of a metallic mold 12a and a refractory sand layer 12b. The difference in the cooling rate when the molten metal charged into the casting mold is cooled to solidify is decreased and the concentration of the internal stress generated during cooling of the molten metal is prevented by the above-mentioned casting mold. The crazes and cracks of the roll are thus prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the structure of a mold used when casting composite rolls for rolling, such as rolls for hot strip mills.

Traditionally, so-called composite rolls have been used, with the inner layer having high strength and the outer layer having high hardness to provide good wear resistance.Recently, centrifugal casting has been used to cast these composite rolls. began to be practiced.

As shown in FIG. 1, a mold for carrying out this centrifugal casting method comprises an outer frame 1, a metal mold 2 as a body mold, and a sand mold 3 and a sand mold 4 as end molds.

Further, the continuous portions between the mold 2 and the sand molds 3 and 4, that is, the neck portions 5 and 6, are formed into curved surfaces by sand material, similarly to the sand molds 3 and 4.

In order to cast a composite roll using the above centrifugal casting mold, first, the outer layer molten metal 7 made of hard alloy roll material is poured into the mold. The injected outer layer molten metal 7 is cooled and solidified in the recess formed by the mold 2 and the neck portions 5 and 6. At this time, the heat extraction ability of the sand material in the neck parts 5 and 6 is very small compared to the mold 2, and while the outer layer molten metal 7 in contact with the mold 2 is rapidly cooled and solidified, the neck part 5 The outer melt field near the neck portion 6 is cooled and solidified relatively slowly.

Regarding this point, when we actually measured it by inserting a thermocouple into the mold, we found that the cooling rate of the outer layer molten metal 7 near the mold 2 was 10'C/n+m, whereas the neck part 5 and the neck part The cooling rate of the outer layer molten metal 7 near 6 was 6° C./h.

Because of this significant difference in cooling rate, the following problems arise when a composite roll is cast by centrifugal casting. That is, the outer layer molten metal 7 near the mold 2
Compared to the rapid solidification and contraction of the outer layer molten metal 7, the solidification and contraction of the outer layer molten metal 7 near the neck portion 5 is delayed, and as a result, the outer layer molten metal 7 near the mold 2 and the neck A large internal stress is generated at the boundary with the outer 1 part molten metal solidification layer near part 5. As a result, as shown in FIG. A crack 10 is generated in the portion 9a, and the entire internal stress based on the solidification contraction of the outer layer molten metal 7 is concentrated in the crack 10, so that the crack propagates along the body portion 9. The crack 10 created in this way eventually becomes the second
As shown in the figure, there is a risk that cracks 11 may develop along the roll body 9, and such cracks 11 may actually occur.
Occasionally, this occurred.

In addition, since there is a significant difference in cooling rate at the boundary between the outer layer molten metal 7 near the mold 2 and the outer first molten metal 7 near the neck portion 5, the structure of the solidified layer of the outer layer molten metal 7 is as described above. Critical non-uniformity occurs at the boundary.

Further, such a problem occurred not only in the neck portion 5 but also between the outer first molten metal solidified layer near the neck portion 6 and the outer first molten metal solidified layer near the mold 2. .

This invention has been made in view of the above-mentioned conventional circumstances, and aims to alleviate the significant difference in cooling rate that occurs when molten metal poured into a mold is cooled and solidified to cast a composite roll. We have created a composite roll casting mold that can prevent cracks in the roll body caused by excessive internal stress being locally generated and concentrated during cooling of the molten metal, and can make the roll structure as uniform as possible. The purpose is to provide.

That is, the composite roll casting mold of the present invention has a body mold and an end mold whose heat removal capacity is smaller than that of the body mold. It is characterized in that a boundary mold, which is smaller than the end mold and larger than the end mold, is disposed in a region where the body mold and the end mold are continuous.

An embodiment of the invention will be described below with reference to FIG.

FIG. 3 shows a partial sectional view of a composite roll casting mold according to an embodiment of the present invention, in which a mold 2 and a sand mold 3 or a sand mold 4 are shown.
A boundary mold 12 is disposed between the two. This boundary mold 12 is formed by covering a mold 12a fixed to the outer frame 1 with bolts and nuts 13 with a refractory sand layer 12b.

As shown in FIG. 4(A) and FIG. 4(B), a curved surface 12C is formed in the mold 12a, and the curved surface 12c is covered with refractory sand 1112b, so that the mold A neck curved surface that connects the second sand mold 3 and the sand mold 4 is formed. Note that the curved surface 12c has a depth of 3
1IIO1-8mm soil retaining groove is 30IIl-50mm
They are provided on the entire surface at intervals of . Thereby,
The refractory sand layer 12b covering the curved surface 12c
It is fixed to 0 and is not easily peeled off.

Also, the thickness of the refractory sand layer 121) is 11 mm at the mold 2 side end.
11m to 3m111, sand mold 3 and sand mold 4 side edge 5mm
~101III, and its thickness gradually increases from the mold 2 side end toward the sand mold 3 and sand mold 4 side ends. As a result, in the mold shown in FIG.
The heat removal capacity gradually decreases in the sand molds 3 and 4, and the heat removal capacity becomes the minimum in the sand molds 3 and 4.

When a composite roll for rolling is cast using the mold of the above embodiment, the outer layer molten metal poured into the inside of the mold is cooled and solidified in the recess formed by the mold 2 and the boundary mold 12. At this time, the solidification rate of the outer layer molten metal changes slowly from the vicinity of the mold 2 to the vicinity of the boundary mold 12. That is, as the sand mold 3 and the sand mold 4 are approached, the solidification rate of the molten metal in the outer layer gradually decreases. Therefore, no large internal stress is generated or concentrated at the boundary between the boundary mold 12 and the mold 2.

The refractory sand material forming the refractory sand layer 12b is made by adding mallet viscosity, bentonite, an activator, and water to aggregate made by adding chamotte powder to refractory sand. As the refractory sand, zircon, chromite sand, etc. can be used in addition to crushed sand, and a mixture of these may also be used.

The mixing ratio of each of the above components was such that the aggregate was 100, Honda viscosity was 0 to 8, bentonite was 3 to 10, activator was 0.01 to 0.05, and water was 30 to 50. Moreover, the aggregate used has a mixing ratio of refractory sand of 60 to 100 and chamotte powder of 0 to 40 in terms of weight ratio.

The composition of the above refractory sand material is shown in Table 1.

When pressure was applied in a dry state to the refractory sand layer 12b formed using the above refractory sand material, no damage occurred even under a pressure of about 35 kg/d.

In addition, fireproof sand materials have lower air permeability than ordinary sand molds.
There is no penetration of molten metal.

A rolling composite roll was actually cast using the composite roll casting mold described above. The composite roll to be cast has a body diameter of 75 mm.
5 +++m, body length is 2146mm, 135
The outer layer molten metal at 0°C was injected into the mold, and after a predetermined period of time, the inner layer molten metal at 1370°C was injected into the mold.The resulting composite roll for rolling was shown in Figure 2. There were no defects such as cracks at the end of the body or cracks along the body.

Although the boundary part mold 12 of the above-mentioned example is formed by covering the mold 12a with a refractory sand layer 12b, the boundary part mold 12 of the present invention is not limited thereto. The boundary mold 12 may be formed of a material mixed with the above.

As described above, according to the present invention, the boundary mold whose heat removal capacity is smaller than that of the body mold and larger than that of the end mold is disposed in a region where the body mold and the end mold are continuous. By this,
In a region where the body mold and the end mold are continuous, that is, in the neck part, the heat removal ability can be made to gradually decrease from the body mold to the end mold. Therefore, cracks in the roll caused by a significant difference in the cooling rate of the molten metal at the boundary between the end of the body mold and the neck;
It is possible to prevent the occurrence of cracks. Further, it is also possible to eliminate the non-uniformity of the structure of the outer molten metal solidified layer that occurs at the boundary.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a conventional centrifugal casting mold, Fig. 2 is a perspective view showing a part of a rolling composite roll cast using the centrifugal casting mold of Fig. 1, and Fig. 3 is a cross-sectional view of a conventional centrifugal casting mold. FIG. 1 is a partial sectional view of a centrifugal casting mold according to an actual example of the invention. FIG. 4 is a diagram showing the state of the retaining groove formed in the boundary mold.
Figure 4 (A) is a front view of the mold, Figure 4 (B) is Figure 4 (
It is a B-Bii plane view of A). 1... Outer frame, 2... Mold, 3... Sand mold, 4
...Sand mold, 5.6...Neck part, 7...Outer layer molten metal, 8...Roll, 9...Body part, 10...
・Crack, 12... Boundary mold, 12a... Mold,
12b... Fireproof sand layer, 12c... Curved surface, 14
...Tsuchimochi ditch. Applicant Kawasaki Steel Co., Ltd. Agent Patent attorney Takehisa Toyota (and 1 other person)

Claims (3)

[Claims] (1) In a composite roll casting mold having a body mold and an end mold whose heat removal capacity is smaller than the body mold, there is a boundary where the heat removal capacity is smaller than the body mold and larger than the end mold. A mold for composite roll casting, characterized in that a part mold is arranged at a part where a body part mold and an end part mold are continuous. (2) The body mold is a mold, the end mold is a sand mold, and the boundary mold is comprised of a mold and a refractory sand layer covering the mold. A composite roll casting mold according to claim 1. (3) The composite according to claim 2, wherein the refractory sand layer is formed so that the thickness gradually increases from the side end of the body mold to the side end of the end mold. Mold for roll casting.