JPS5938866B2 - Continuous casting mold - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention improves continuous casting molds, and more specifically, the thickness of the bottom of the continuous casting mold is defined by the mold material, mold diameter, and casting material, thereby improving the radial direction during casting. This invention relates to a continuous casting mold that aims to eliminate dimensional changes and prevent defects in the ingot.

In the belt-and-wheel casting method, in which ingots are continuously produced by injecting molten metal into a mold consisting of a rotating ring with grooves on the outer periphery and an endless metal belt facing the rotating ring, the cast Periodic temperature fluctuations occur in the longitudinal direction of the lump, and at the same time, defects occur along with these temperature fluctuations.

The inventors investigated the causes of this periodic ingot temperature fluctuation and defect occurrence, and found that this was caused by the surface of the rotating wheel in contact with the ingot changing from its reference surface. It was done.

Figure 1 uses a mold with a diameter of 2000 mm and a rotation speed of 2.
1 of the rotating wheel when aluminum is cast using EC
This figure shows the relationship between the displacement from the reference position of the bottom of the rotating ring groove in contact with the ingot during rotation, the ingot temperature, and the amount of defects measured by a flaw detector.

Note that the number of defects is the number of defects when casting was continued for one hour under the same conditions.

As is clear from this figure, in locations where the bottom of the rotating ring groove is lower than the reference surface, that is, locations where there is poor contact between the rotating wheels and the ingot, the ingot temperature decreases because heat transfer from the ingot to the cooling system deteriorates. It was observed that the surface area became high and defects occurred in this area.

These results show that in order to improve the quality of ingots in belt-and-wheel casting, it is most important to prevent fluctuations in the bottom of the rotating ring groove.

On the other hand, in the conventional belt and wheel casting method, the second
A rotating ring with a cross-sectional shape as shown in Figures a, b, and c is used, and the mold 1 has mold holding plates 2 called side plates.
The side plate is fixed by bolts 4 and nuts 5 to a fitting plate 3 called a mounting plate which is connected to the rotating shaft.

In such conventional molds, for example, when a pure copper mold is used, the positions at which the mold 1 is fixed with the side plates 2 etc. have the following relationship.

In the mold of Fig. 2 a 0.5t≦h≦1.5t 20mm≦h≦80run In the same mold, t≦h≦2t 40mn<h≦100 fights In the mold of C in the same figure .

≦h≦tO≦h≦501m However, t: Thickness of the ingot h: Distance from the bottom of the mold groove to the clamp position The dimensional accuracy of the radius length from the center of the mold to the bottom of the groove after grinding is ±
Although it is within 0.1 mm, after it is installed in a casting machine and during casting, this dimensional accuracy decreases to about ±0.8 mm.

By the way, as shown in Figure 1, if the dimensional accuracy of the mold in the radial direction is ±3 mvt or more, ingot temperature fluctuations and ingot defects are likely to occur. It is necessary to keep the deviation within ±0.2 mm after mounting on the device.

The same thing can be said about the dimensional accuracy of the mold in the width direction, so it is necessary to maintain the accuracy within 0.4 runs in the radial and width directions when the mold is installed in the casting machine.

Therefore, in the past, in order to improve the precision in the width direction of the mold, a spacer 6 was inserted between the mold and the side plate, and in order to improve the precision in the radial direction, a spacer was inserted in the upper part 7 of the mounting plate that fixed the mold. 6 is installed.

However, with this method of fixing the mold to the mounting plate and improving accuracy in the diameter and width directions of the mold, the mold temperature heat cycle unique to the belt-and-wheel casting method involves a rapid rise in mold temperature after pouring, followed by cooling. Due to this phenomenon, the mold repeatedly expands and contracts, so there is a problem that the above-mentioned spacer may move from its initially installed position during casting, or the accuracy may deteriorate significantly.

As a result, within 1 to 2 hours after the start of casting, the precision in the diameter and width directions of the rotating ring deteriorates, causing periodic ingot defects as shown in Figure 1, making it difficult to stably produce high-quality ingots over a long period of time. It was particularly difficult.

In view of these points, the present inventors conducted research and study on a method for preventing deterioration of the dimensional accuracy of the rotating ring during casting, and obtained the following knowledge.

Figure 3 shows aluminum casting using copper molds of the type shown in Figure 2 with rotating wheel diameters of 1,500 mm, 2,000 mm, and 2,500 mm, and various changes in the position of clamping the mold with the side plate. , which shows the relationship between the deterioration of the mold dimensional accuracy in the radial direction during temperature fluctuation during casting of the clamp part and the deterioration from before casting.

As is clear from this, as the temperature fluctuation during casting at the point where the mold is clamped increases, the dimensional accuracy during casting of the mold deteriorates and the quality of the ingot deteriorates.

In addition, this deterioration in dimensional accuracy is also affected by the diameter of the rotating ring.
When T (°C) and the length of deterioration in mold dimensional accuracy are Δh (mm), their relationship can be expressed by the following equation.

△h=1.3X10-' ・R・△T ・・・・・・
...... (1) Also, as mentioned above, in order to produce a high-quality ingot, △h must be within 0.4 mm, so from equation (1), during temperature fluctuations at the mold clamp part, The following formula must be satisfied.

ΔT l<3. I X 10'/R・・・・・・・・・
・・・・・・・・・(2) Next, using molds made of various materials, we investigated the relationship between the distance from the mold groove bottom and the temperature fluctuation at that point during casting. Experiments were conducted using molds with a diameter of 700° C. and a casting wheel diameter of 1500 mm, and the relationship between the distance from the mold groove bottom and the temperature fluctuation when these molds were used as shown in FIG. 4 was obtained.

Table 1 shows the materials of commercially available molds and the temperature conductivity α of the molds.

The following is recognized from the results shown in Figure 4.

1) Temperature fluctuation ΔTo at the bottom of the mold groove is 70°C when molten aluminum is used, regardless of the type of mold material.

11) During temperature fluctuations, the temperature decreases as the distance from the mold groove bottom increases.

111) When the distance from the mold groove bottom is l (mm) and the temperature during temperature fluctuation is △Tl ('C), the relationship between the two is affected by the temperature conductivity α, which changes depending on the mold material, and is shown by the following equation. .

1n6T, g--d-exp(-2,08α-2,69
) + ln△T, ・・・・・・・・・・・・・・・
......(3) exp(-2-08α-2,69
) represents e-2,08α-2,69.

Further, as a result of conducting experiments on the influence of cast metal on equation (3), as the melting point of the cast metal becomes higher, ΔTo increases during temperature fluctuation at the bottom of the mold groove, and is expressed by the following equation.

△T-0,106・CT ・・・・・・・・・・・・
...(4)- However, CT indicates the melting point ('C) of the cast material.

From the above equations (2), (3), and (4), the bottom thickness l of the mold required to stably produce high-quality ingots in the belt-and-wheel casting method is expressed by the following equation.

*The present invention minimizes ingot temperature fluctuations and prevents ingot defects by defining the length l from the bottom of the mold groove to the position where the mold is fixed so as to satisfy the above formula (5). The aim is to improve quality.

The present invention will be explained below by way of examples thereof.

Figure 5 shows the cross-sectional shape of a rotary casting machine for continuous casting manufactured for aluminum and copper alloys. Mold 1 has a figure-7 groove on both sides of its bottom, and a figure-7 protrusion at that part. The mold is clamped by a mounting plate 3 and a side plate 2, and the mold and the mounting plate are fixed with bolts 4 and nuts 5.

The diameter of this rotating ring is 2000 mm, and when a copper mold with a temperature conductivity α of 0.90 is used, the required distance l from the mold groove bottom to the clamp part is 133 mm in the case of aluminum casting according to formula 5.
mm, and in the case of steel casting, 180mvt or more is required.

In this example, in order to improve accuracy for aluminum and steel casting, the distance from the mold groove bottom to the clamp was set to 160 mm and 2.
It was set to 00.

Table 2 shows the characteristics of the temperature fluctuation of the clamp part during casting, the change of dimensional accuracy of the mold groove bottom, and the obtained ingot quality when casting was performed using the mold of this example and the conventional mold, respectively. Ta.

As is clear from Table 2, by using the mold of the present invention, it became possible to prevent deterioration of mold dimensional accuracy and to produce defect-free ingots stably for a long period of time.

As described above, according to the present invention, it is possible to cast an ingot without defects for a long time by using a rotary mold having a bottom thickness as defined by formula (5) or a length from the groove bottom to the fixed point. This allowed the dog to be recognized as an industrial profit dog.

[Brief explanation of drawings]

FIG. 1 shows the relationship between the dimensional change in the radial direction of the mold groove bottom, the ingot temperature, and the amount of defects in the ingot during casting. Figures 2a, b and c show mold shapes used in the belt and wheel casting method. FIG. 3 shows the relationship between the temperature change of the rotary casting fixing part and the dimensional change in the radial direction of the mold groove bottom. FIG. 4 shows the relationship between the distance from the groove bottom of the rotary mold and the temperature fluctuation. FIG. 5 is a sectional view showing the shape of a mold used in an example of the present invention. 1...Mold, 2...Side plate,
3...Mounting plate, 4...
・Bolt, 5...Nut, 6...Spacer.

Claims (1)

[Claims] 1. A mold is continuously formed by a rotating ring with grooves on the outer periphery and an endless belt in contact with the circumferential surface of the rotating ring, and molten metal is continuously poured into the mold to form an ingot. A continuous casting mold used in a belt-and-wheel casting method for producing a continuous casting mold, characterized in that a length l from the bottom of the mold groove to a position where the mold is fixed satisfies the following formula.