JPH01202345A - Method for casting al-mg alloy twin roll - Google Patents

Abstract

PURPOSE:To cast an oil free twin roll by feeding the Al-Mg alloy molten metal whose Mg contg. amt. is more specified value between specified shall thickness rolls and casting an Al-Mg alloy plate by cooling the molten metal by a roll without coating a lubricant. CONSTITUTION:A pair of rolls 1, 2 are of the cylindrical shape having 35-60mm shell thickness (t) and the cooling member 3 circulating a cooling water is fixed onto the cylindrical face thereof. A cylindrical nozzle 4 is arranged at the upperstream side in the turning direction of the rolls 1, 2. The molten metal 5 of the Al-Mg alloy whose Mg contg. amt. is >=3.5wt.% is poured between the rolls 1, 2 via the nozzle 4 and solidified by cooling it by the rolls 1, 2 to obtain a casting plate 7. A solid-liquid coexisting phase exists between the molten metal 5 and casting plate 7. The Al-Mg alloy molten metal is cast by oil free without coating a lubricant on the shell outer peripheral face of the rolls 1, 2. The ununiform cooling due to this coating unevenness is eliminated because of no lubricant being used and the surface defect of the casting plate can thus be prevented.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention involves disposing a pair of rolls at an appropriate distance, and supplying molten AJ2-Mg alloy between the rolls to produce Al-Mg.
The present invention relates to a method for casting an Aβ-Mg alloy using twin rolls for casting an alloy plate.

[Prior Art] It is a widely known technique to cast an aluminum or aluminum alloy plate using a twin-roll casting machine, then roll it to a predetermined thickness and use it for a desired purpose. The casting rolls of this twin-roll casting machine have a core portion through which cooling water flows, and a shell portion with which the molten aluminum or aluminum alloy comes into direct contact. This pair of casting rolls are arranged to face each other with an appropriate distance between them,
The molten metal is injected between the two water-cooled rolls through a nozzle, cooled, and solidified. Then, the slab obtained by solidifying the molten metal is further rolled slightly by rolls to become a so-called cast plate. “When casting thick-walled ingots using a continuous casting machine, in order to improve the peelability between the mold and solidified aluminum and to ensure smooth casting, a release agent (lubricating agent) such as rapeseed oil is applied to the walls of the mold. ). When casting with a twin-roll casting machine, a lubricant is used in the same way as with a continuous casting machine, but this lubricant is a suspension of graphite powder or magnesia powder dissolved in water. The lubricant was applied to the peripheral surface of the roll by spraying the suspension onto the roll.

[Problem to be solved by the invention] However, in this prior art, since the lubricant is a suspension, it tends to settle in areas where the flow velocity is slow, so the concentration is not constant at the time it is sprayed onto the roll. , has the disadvantage that the lubricant concentration changes over time.

Furthermore, the roofing applied by the spray is not consistent depending on the part of the roll, and there are local variations.

Furthermore, the lubricant on the peripheral surface of the roll is removed by contact with the cast plate, and the amount removed differs depending on the location of the roll.

Due to these factors, the amount of lubricant becomes non-uniform on the circumferential surface of the roll, resulting in localized uneven cooling, which tends to cause surface defects (solidification defects) on the cast plate.

Moreover, such surface defects occur in Al-M with high Mg content.
This occurs significantly in alloys with a wide solidification temperature range, such as g-alloys.

The present invention has been made in view of such problems, and includes:
An object of the present invention is to provide a method for casting an Al-Mg alloy using twin rolls, which can reliably prevent surface defects caused by uneven lubrication, even in AfI-Mg alloys with a high Mg content where surface defects are likely to occur. purpose.

[Means for Solving the Problems] In the twin-roll casting method of Al-Mg alloy according to the present invention, a pair of rolls each having a shell thickness of 35 to 60 mm are arranged at an appropriate distance, and a Mg content is 3.
The present invention is characterized in that an Al-Mg alloy molten metal containing 5% by weight or more is supplied, and the molten metal is cooled by a roll without applying a lubricant to the circumferential surface of the roll to cast an Al-Mg alloy plate.

[Function] In the present invention, AfI-M is based on the completely new idea of casting molten metal without applying lubricant to the peripheral surface of the roll.
g-alloy is cast. Therefore, since there is no lubrication, surface defects on the cast plate due to uneven cooling caused by applying a conventional lubricant suspension are eliminated.

On the other hand, the releasability between the cast plate and the roll shell is achieved by increasing the Mg content of the molten metal to 3.5% by weight or more and forming an oxide film on the surface of the cast plate, without relying on lubricants as in the conventional method. This is ensured by forming the In addition, since the shale thickness was set to 35 to 60 mm to increase the cooling rate of the molten metal, instantaneous volumetric contraction occurred, which also contributed to improving the mold releasability.

[Examples] Examples of the present invention will be specifically described below with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view showing a molten metal injection part of a twin-roll type casting apparatus illustrating an embodiment of the present invention.

A pair of rolls 1.2 are arranged with their axial directions parallel to each other and vertically opposed to each other with an appropriate distance between them. The rolls 1 and 2 have a cylindrical shape with a constant shell thickness t, and a cooling member 3 through which cooling water flows is fixed to the inner peripheral surface thereof. Cooling water flows through the cooling member 3,
As a result, one shell of roll 1.2 is cooled.

The roll 1.2 is rotatably driven in the direction of the arrow, and a cylindrical nozzle is installed at a position upstream in the rotational direction of the roll 1.2 from the position where the rolls 1 and 2 face each other at the shortest distance. 4 is placed. The nozzle 4 is connected to a molten metal supply source, such as a molten metal pot, through which molten aluminum alloy 5 is injected into the gap between the rolls 1.2.

This molten metal 5 is cooled and solidified by rolls 1 and 2, and a cast plate 7 is obtained. Note that a solid-liquid coexisting phase 6 exists between the molten metal 5 and the rolls 1, 2 or the cast plate 7.

Conventionally, in such a twin-roll casting machine, in order to ensure mold releasability between the shells of rolls 1 and 2 and the casting plate 7, a lubricant in a suspension was applied to the outer periphery of the shells of rolls 1 and 2. It was spray painted on the surface.

However, the method of the present invention is characterized in that the molten Al--Mg alloy is cast without lubrication without applying a lubricant to the outer eight peripheral surfaces of the shell of the roll 1.2.

Uneven cooling (heat transfer) occurs due to uneven lubricant application, so in order to ensure uniform cooling and prevent surface defects on the cast plate, it is natural to consider ways to apply the lubricant evenly. It is common knowledge that this is the case, and the inventors of the present invention initially conducted experimental research in that direction. However, when the Mg content is high, no matter what method is used, it has not been possible to prevent uneven coating and completely eliminate surface defects caused by uneven coating.

Therefore, the inventors of the present application aimed at a method of omitting the process of applying lubricant itself, that is, performing casting without lubrication, which had not been considered at all in the past, and as a result of various experimental studies,
This has led to the completion of the method of the present invention.

As mentioned above, the purpose of lubrication is to release the cast plate from the roll shell, and if the release property is poor, problems such as sticking may occur. This poor sticking is caused by
This refers to a defect in which the cast plate adheres to the roll and remains attached to the circumferential surface of the roll for a while even after passing the roll exit.

The surface gloss of the part where this sticking defect has occurred is completely different, resulting in a defective matte surface, and the board shape is also disordered.

Therefore, when a lubricant is not used, it is necessary to ensure mold releasability by other methods. As a result of conducting various experimental studies on mold release methods other than using lubricants, the inventors of the present application found that if the cooling rate of the molten metal is made sufficiently high, Mg
It has been found that alloys with sufficiently high content can be cast without lubrication. This is because when the Mg content is high, an oxide film is likely to be formed on the surface of the cast plate 7, and this oxide film has a certain degree of mold releasability.

In addition, if the cooling rate is sufficiently high, the instantaneous volumetric contraction when the molten metal cools and solidifies increases the mold releasability in combination with the formation of an oxide film.

As mentioned above, in order to fully bring out the effect of improving mold releasability due to the oxide film, it is necessary for the molten metal to contain 3.5% by weight or more of Mg, and this Mg content is 3.5% by weight. If it is less than , the mold releasability will be poor, and significant sticking failure will occur without lubricant. In addition, in order to achieve the object of the present invention, it is not necessary to set an upper limit to the Mg content, but from the viewpoint of swirling flow, it is desirable that the Mg content is 5.5% by weight or less.

In addition, in order to increase the cooling rate and improve mold releasability due to volumetric shrinkage, it is necessary to make the shell thickness of the casting roll 35 mm or more. If the shell thickness is less than 35 mm, when the molten metal contacts the shell of the roll and starts to solidify, water vapor will create an adiabatic state between the shell and the cooling water, and the cooling ability of the shell will decrease significantly. . Also,
If the shell thickness exceeds 60 mm, the cooling effect of the cooling water in the roll on the roll surface will be reduced, and the shell surface will not be cooled in the time it takes for the roll to rotate once. Therefore, the shell thickness is set to 60 mm or less. That is, the cooling ability of the molten aluminum alloy due to the heat capacity of the roll shell is extremely high when the shell thickness is in the range of 35 to 60 mm, and it is necessary that the roll shell has a thickness within this range. In order to further enhance the cooling ability of the roll shell, it is desirable to keep the shell thickness within a narrow range of 40 to 55 mm.

In this way, by setting the composition of the molten metal 5 of Al-Mg alloy to contain 3.5% by weight or more of Mg, A,
An oxide film is formed on the surface of the R alloy cast plate 7, and even though no lubricant is applied to the outer circumferential surface of the shell of the roll 1.2, the cast plate 7 is coated on the outer circumferential surface of the shell of the roll 1.2. Releases from mold without sticking.

Further, since the shell thickness is set to 35 to 60 mm, the heat capacity of the roll shell is optimal in terms of cooling efficiency, and the molten metal is cooled at a high cooling rate. Therefore, the cast plate 7 quickly shrinks in volume and separates from the roll shell.

Due to these effects, in the method of this example, excellent mold releasability is ensured even though no lubrication is required. Also,
Since no lubricant is used, uneven cooling caused by uneven application is eliminated, and surface defects on the cast plate are prevented.

Next, the results of manufacturing Ag-Mg alloys by the example method of the present invention will be explained together with comparative examples.

Example 1 A heat-resistant steel casting roll with a roll diameter of about 900 mm and a shell thickness of 55 mm was used, and the thickness was in the order of 7 and the Mg content was 2.5% by weight, 4% by weight, and 5% by weight. Three types of Al-Mg alloy plates were cast. The casting conditions were a roll peripheral speed of 100 cm/min, a casting temperature of 700°C, a roll cooling water temperature of 30°C, and a roll cooling water flow rate of 3001/min. As a result, the relationship between the surface quality, Mg content, and the presence or absence of lubrication of the manufactured cast plate was as shown in Table 1 below. However, S: The surface quality was extremely poor due to significant sticking. △: Some stains due to uneven lubricant application △: Some stains due to uneven lubricant application ○: No defects In addition, the lubrication condition with lubrication is 1% of graphite.
The suspension was sprayed onto the roll surface at a flow rate of 0.3 min/min per 10 l.

Furthermore, a stain defect is a segregation with a length of 1 to 5 cm extending in the casting direction, and if it is severe, it will result in a crack.

Spot defects are formed because solidification in this area is slower than in the surrounding area.

As is clear from Table 1, the Mg content is 4% by weight.
or 5% by weight, and in the case of this example without lubrication, an excellent surface quality without defects was obtained.

Chestnut" 1 chestnut 3 erol diameter is about 900 dragons, shell thickness is 25 mm, 45 cities,
Four types of casting rolls, 5511III+ and 70 mm, were used to cast an AA5182 alloy plate (containing 4.8% Mg) to a thickness of 7 m+a. The casting conditions are a roll circumferential speed of 1
The casting speed was 20 cm/min, the casting temperature was 700°C, the temperature of the roll cooling water was 30°C, and the cooling water flow rate was 300β/min. Also,
No lubricant was used.

The relationship between the surface quality and shell thickness of the cast plates produced in this manner is shown in Table 2 below.

Table 2 However, the method for evaluating surface quality is the same as in Example 1.

As is clear from Table 2, in the case of the present example in which the shell thickness was 45 mm or 55 mm, excellent surface quality with no defects was obtained.

[Effects of the Invention] As explained above, according to the present invention, the A! Since the molten metal of two alloys is cast, it is possible to perform casting using a twin roll method without lubrication, which was completely unthinkable in the past, and it is also possible to manufacture a cast plate with excellent surface quality.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an injection section of a twin roll casting apparatus showing an embodiment of the present invention. 1.2; roll, 4; nozzle, 5; molten metal, 7; cast plate

Claims (1)

[Claims] (1) A pair of rolls with a shell thickness of 35 to 60 mm are arranged at an appropriate length interval, and between these rolls the Mg content is 3.
．． A twin-roll method characterized in that an Al-Mg alloy molten metal containing 5% by weight or more is supplied, and the molten metal is cooled by a roll without applying a lubricant to the circumferential surface of the roll to cast an Al-Mg alloy plate. Method for casting Al-Mg alloy.