JPS61119359A - Continuous casting method of magnesium or ally thereof - Google Patents

Abstract

PURPOSE:To improve the quality of an ingot by providing an overhang part to the bottom surface of a molten metal receiving vessel and introducing a gas contg. sulfur hexafluoride to right under said part then applying a gaseous pressure to the outside circumferential surface of the melt of Mg or the alloy thereof. CONSTITUTION:The molten metal receiving vessel 2 made of refractories is disposed to the upper part of a casting mold 1 and the overhang part 9 forming a spacing 8 between said vessel and the mold 1 is provided. The spacing 8 communicates with an annular flow passage 7 and is connected via pipes 6, 6', 6'' to a gas supply source. A liquid lubricating oil supply port is further installed to the inside of the mold 1 and a cavity in which a cooling medium 4 flows is provided. The gas contg. sulfur hexafluoride is introduced into the part 9 and casting is executed while the gaseous pressure is applied to the outside circumferential surface of the calmner or cylindrical molten Mg alloy in the stage when the molten metal starts solidifying. The ingot having a smooth casting surface and less inverse segregation layer is formed by the above- mentioned method and therefore the quality thereof is improved.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is a continuous method for casting ingots such as magnesium and magnesium alloys, which are materials for plastic working such as forging, extrusion, and rolling, or billets for remelting. Regarding casting methods.

(Conventional technology) Ingots and billets for rimmel made of plastic working materials such as magnesium and magnesium alloys (hereinafter simply referred to as magnesium alloys) are produced using gouville casting methods, air-cooled cast iron molds (book molds), continuous casting methods, etc. It is manufactured by.

The Gouville casting method is excellent for producing small ingots on a small scale, but when producing large quantities of large ingots,
It is efficient to manufacture by continuous casting method.

As shown in Figure 7, in the continuous casting method, molten metal is poured into a water-cooled copper or aluminum alloy mold, and the outer shell of the molten metal is solidified by removing heat from the molten metal within the mold. In this method, a dummy block is pulled down using a hydraulic cylinder or the like, and molten metal is continuously injected and solidified. When the formed ingot reaches a certain length downward, casting is stopped and the ingot is pulled upward. In addition, the solidified ingot is pulled down with a vinyl roll, and the saw is moved in synchronization with the descent, cutting it into lengths and taking it out during the descent, so that the ingot is poured completely continuously and the ingot is It can also be manufactured.

The supply of molten metal from the sump to the mold is controlled by a pulp operation. The disadvantages of this casting method are that the molten metal permeates into the outer shell surface during the casting process due to fluctuations or fluctuations in the molten metal surface, which often causes sweating, and the cold welding phenomenon (Co1d).
5hut) is also likely to occur, resulting in poor casting surface. Furthermore, since the reverse segregation of alloy components to the surface layer is large, it is necessary to remove the reverse segregation layer by applying a large amount of surface agent during plastic working.

A major advance in continuous casting of nonferrous metals in recent years is so-called hot-top casting, in which a molten metal receiving tank made of an insulating refractory is installed above the mold to hold the molten metal under high hydrostatic pressure above the solidified layer of metal. It is in the casting method called the method. In this casting method, the molten metal surface exists in the molten metal receiving tank, so unlike traditional casting, there is no need to strictly adjust the height of the molten metal surface in the mold, and labor savings can be expected. . Although it has advantages such as less contamination of oxide film, this method is still far from a perfect technology for casting magnesium alloys whose molten metal tends to be easily oxidized. It is insufficient as a lump, and improvements in improving the casting surface are desired.

(Problems to be Solved by the Invention) The existing continuous casting method for manufacturing magnesium alloy ingots has problems in terms of the quality of the ingot, such as poor casting surface and reverse segregation of alloy components in the surface layer. There are many problems such as large oxidation, and since magnesium is very easily oxidized, there are safety issues.
Many considerations are required and the casting operation is also complicated.

Therefore, the present inventors have developed a continuous casting method for magnesium alloys that is simple in process and provides excellent quality of the cast ingot, and has completed the present invention.

Therefore, an object of the present invention is to efficiently obtain an ingot of excellent quality from a molten magnesium alloy by a continuous casting method.

(Means and effects for solving the problems) The present invention provides a refractory metal molten metal receiving tank provided above a forced cooling mold,
Magnesium or its alloy to be cast in the molten metal receiving tank is used using a forced cooling mold with a molten metal receiving tank in which the lower end surface of the inner periphery of the molten metal receiving tank extends inward from the inner peripheral surface of the mold to form an overhang part. The molten metal is held in a columnar or cylindrical shape in close proximity to the mold in which a molten metal is stored and a lubricating interface is formed on the inner peripheral surface, and the columnar or cylindrical body is cooled by a coolant passing through the mold. A continuous casting method for magnesium or its alloy, which includes a step of cooling a shaped body, in which a gas containing sulfur hexafluoride is introduced directly under the overhang, and the columnar or cylindrical molten magnesium or its alloy is continuously cast. The gist is a continuous casting method for magnesium or its alloy, which is characterized by casting by applying gas pressure to the outer peripheral surface.

Since molten magnesium alloy is more easily oxidized than copper, aluminum, etc., it is necessary to cover the surface of the molten metal with a non-oxidizing atmosphere. Conventionally, SO gas has been used for this purpose, but
There are disadvantages such as severe effects on the human body and severe corrosive effects on the metal materials of structures such as equipment. On the other hand, the sulfur hexatide gas used in the present invention does not have these drawbacks and is effective in preventing oxidation, and is suitable as a gas to be applied to the outer circumferential surface of a molten magnesium alloy metal.

The shapes of ingots to which the present invention is applied are mainly cylindrical ingots that are used as materials for extrusion or pultrusion molding, prismatic ingots that are used as materials for forming rolled plate materials, and wall thickness that are used as materials for extruded products in pipes. It is a cylindrical hollow ingot or a billet for remelting.

The present invention relates to an improvement in a continuous casting method called the direct chill method, in which the molten metal is held close to the mold in a columnar or cylindrical shape. At this time, the columnar or cylindrical body held in the mold comes into contact with the forcedly cooled inner surface of the mold, and the outer peripheral surface of the molten metal is rapidly cooled, forming a thin solidified outer shell, which then becomes thicker. It is believed that the solidified shell is separated from the peripheral surface of the mold, and that solidification begins near the entrance of the mold.

According to the present invention, the gas pressure of a gas containing sulfur hexafluoride is applied to the outer circumferential surface directly below the overhang portion.

For example, the gas is introduced parallel to the lower end surface of the magnesium alloy molten metal receiving tank forming an overhang and perpendicular to the axial direction of the casting. That is, the gas is introduced from one or more locations on the interface between the molten metal receiving tank and the mold, is then distributed over all the interfaces, and reaches the outer peripheral surface of the columnar or cylindrical body from all the interfaces. That is, in this case, there is no problem whether the gas branch flow is introduced facing the outer circumferential surface of the magnesium alloy columnar or cylindrical body, or the gas branch flow is introduced obliquely. However, all the gas may be introduced substantially perpendicular to the outer circumferential surface. The gas is introduced during the entire casting period and around the entire circumference.

As long as the introduced gas arrives at the outer peripheral surface of the predetermined area and in a predetermined direction, the flow path of the gas does not matter. However, in practice it is advisable for the gas to pass through the interface.

In the present invention, casting is performed by forming a lubricating interface on the inner surface of the mold.

As a method for forming a lubricating interface, one of the following known methods is employed.

(1) Liquid lubricating oil is continuously leached from a position below the Opart ring toward the inner surface of the mold.

(2) Before starting casting, apply lubricant to the inner surface of the mold.

(3) Use a mold made of a material such as graphite, which has a large contact angle with the molten metal and has self-lubricating properties with respect to the solidified metal shell.

Formation of the above-mentioned lubricating interface on the inner surface of the mold is one of the essential components for obtaining a smooth and good casting surface, which is a characteristic effect of the present invention. The above (1) and (2) are applied to a mold made of a metal with good thermal conductivity such as aluminum or copper.

In the casting apparatus used for carrying out the present invention, a refractory metal molten metal receiving tank is provided above a forced cooling mold, and the inner peripheral lower end surface of the molten metal receiving tank protrudes inward from the inner peripheral surface of the mold. An apparatus for continuous casting of magnesium alloys, comprising a forced cooling mold with a molten metal receiver forming a hang part, an outer region where the joint between the mold and the molten metal receiver is in airtight contact, and a slit between the mold and the molten metal receiver. an inner region formed therein and surrounded by the outer region, the slit being defined such that the molten metal does not enter therein and communicating with a gas source containing sulfur hexafluoride; This is a characteristic feature.

Next, the method according to the present invention will be explained based on the drawings.

Method of the Invention FIG. 1 is a longitudinal sectional view showing a mold, a molten metal receiving tank, and an ingot for carrying out the method of the invention. Molten magnesium alloy is supplied to the molten metal receiving tank from a molten metal holding furnace (not shown). The surface of the molten metal in the molten metal receiving tank is covered with a gas containing sulfur hexafluoride to prevent oxidation. (Not shown) The mold 1 made of a material such as metal or graphite has a suitable shape defining the outline of the ingot 17, for example, a circular shape in the case of a cylindrical ingot, or a cross section, so that the ingot 17 It surrounds the space that is formed.

The mold 1 has a cavity through which a cooling medium, for example water, 4 flows for forced cooling of the metal columns 16,17. Connected to the mold 1 is a pipe 3 that supplies a cooling medium to the cavity from a cooling medium supply source (not shown). The heat of the molten metal 16 is absorbed from a part of the inner peripheral surface of the mold 1, and the molten metal starts solidifying as shown by diagonal lines. In order to secondarily cool the metal that has been primarily cooled by the mold in this way, the trap and cooling medium is ejected from the spout 5 toward the ingot 17.

The spout ports 5 are holes provided at equal intervals in a part of the lower end corner of the mold 1, or are provided in the form of slits around the entire circumference. Note-
The medium for the secondary cooling and the secondary cooling need not be the same, but usually cold water is used.

Marinite (Marinite) is applied to the upper end surface of mold 1.
) or fiber flux
A molten metal receiving tank 2 made of a heat-insulating refractory material well known under the trade name of .

The molten metal receiving tank 2 is arranged coaxially with the mold 1 and has an inner peripheral surface substantially parallel to the inner peripheral surface of the mold 1. As is well known, the molten metal receiving tank 2 stores molten metal and prevents the solidification start surface from changing due to fluctuations in the amount of poured metal.

The solidified ingot 17 is continuously drawn downward from the mold 1 by lowering a bottom plate (not shown) at a constant speed (ie, casting speed).

Next, the structure of the mold used for introducing gas according to the present invention will be explained based on FIGS. 2 to 4.

Three pipes 6, 6', 6' branch out from the outer peripheral surface of the mold 1 at an angle of 120° in the diametrical direction and are communicated with a gas supply source (not shown). This gas supply pipe 6.6', 6'' communicates with an annular channel 7 extending around the entire upper circumference of the mold 1. The gas is therefore evenly distributed over the entire upper circumference of the mold.

It has been confirmed through experiments that even with one supply pipe, the same results can be obtained as with two or three supply pipes.

The outer upper surface 1a of the mold 1 is a flat surface that comes into close contact with the lower surface of the molten metal receiving tank 2, and a groove 12 extending around the entire circumference of the mold is formed in a part of the outer surface 1a. This groove 12 is filled with a packing material (not shown) such as heat-resistant rubber.
This prevents the gas flowing through the flow path 7 from leaking to the outside.

The inner upper surface 1b of the mold 1 is slightly lower than the outer surface 1a, and a very small gap 8 is formed between it and the lower surface of the molten metal receiving tank 2. This gap 8 communicates with the flow path 7 and is open over the entire inner peripheral surface of the mold. The inner end of the lower surface of the molten metal receiving tank 2 extends horizontally so as to cover the inner peripheral surface of the mold 1, so that an overhang portion 9 is formed over the entire inner peripheral surface. Therefore, gas is introduced from the gap 8 directly below the overhang portion.

A means for supplying liquid lubricating oil between the metal solidified by the primary cooling action of the mold and the inner peripheral surface of the mold is provided inside the mold 1. In other words, two supply pipes (not shown) connected to a liquid lubricant supply source (not shown) have a lubricant population of 1.
It is fixed at 4. The lubricating oil port 14 communicates with a passage 13 extending diametrically inside the mold l. Furthermore, this passage 13 communicates with a liquid lubricant supply tubular passage 10 extending circumferentially inside the mold 1 . A large number of liquid lubricant fine supply ports 11 branch from this supply passage 10 and open to the inner peripheral surface of the mold. The supply rows 1 extend radially into the mold and are inclined in a direction opposite to the casting direction.

The supply port 11 may extend horizontally or obliquely in the drawing direction, the inclination being defined so that the lubricant flows down from the required height within the mold. Passage 1 in one mold
Since it is almost impossible to process the passage 10 and the supply port 11, it is easy to understand that it is a good idea to use two members that have been pre-processed so that the passage 10 etc. are defined and then fix them together by welding or the like. be understood. According to the structure described above, the liquid lubricating oil supplied from the inlet 14 leaks out from the supply port 11 and is constantly supplied to the inner circumferential surface of the mold from below the overhang portion 9.

Further, according to the apparatus shown in FIGS. 1 to 4, casting is performed in a state in which gas is introduced across the outer peripheral surface of the columnar metal directly under the overhang, and lubricant is supplied to the inner surface of the mold.

(Example) Experiments were conducted using the method according to the present invention by changing gas introduction conditions, lubricating oil supply conditions, etc.

Magnesium alloy AZ31 was cast into a cylindrical ingot with a diameter of 62 mm using the continuous casting apparatus shown in Figures 1 to 5.

The temperature of the self-molten metal in the receiving tank is 680℃, the cooling water temperature is 20℃, the cooling water supply amount is 20t/rr+tn, and the casting speed is 150℃.
Minted at Kaku/min.

Gas introduction conditions A sulfur hexafluoride gas source with a pressure of 5 kg/cm2 was introduced through the supply pipes 6.6' and 6'' via needle pulp and a float type flow meter.Casting period The test was conducted by introducing a gas flow regulated at a specific rate between 0.2 and 4.0 A/min directly below the over-ring section 9.

Castor oil is used as the lubricant, and the head pressure is
Adjustment was made to +20 gates above the positive gas value corresponding to each gas flow.

When the gas flow rate was low, the surface of the obtained ingot had a burnt surface as shown in the reference photo in Figure 1.

The appropriate gas flow rate to obtain a good casting surface is 0.5~
The flow rate was in the range of 3.0 t/min, and at flow rates exceeding this upper limit, bubbles were observed blowing out from the molten metal surface of the molten metal receiving tank. As shown in the reference photo in Figure 2, the optimum flow rate for obtaining a very smooth and good casting surface is 1.0 to 2. Ot/
The range is min. The appropriate value for the gas pressure of the introduced gas (substantially equal to the gas pressure applied to the outer peripheral surface of the columnar or cylindrical molten metal directly under the overhang) is the value equivalent to the hydrostatic pressure of the molten metal stored in the molten metal receiving tank. The upper limit is determined by the hydrostatic pressure of the molten metal at which gas does not float through the molten metal in the receiving tank, and the lower limit is determined by the pressure at which the contact area between the metal and the inner surface of the mold is substantially determined by the pressure that can be reduced. Eventually, the introduced gas forms an elastic space with a gas pressure close to the hydrostatic pressure of the molten metal just below the overhang, and the excess gas flows downward through the fine gap at the contact interface between the inner surface of the mold and the thin solidified shell of the molten metal. leak.

Conditions for using lubricating oil: The minimum head pressure of lubricating oil for continuous lubrication is the pressure on the gas pressure plate that is applied directly below the Opart ring, if the amount of gas introduced is selected within the appropriate range. However, normally, stable oil supply is performed at a gutter pressure of 10 to 50 degrees higher than this gas pressure. In this range, a good casting surface can be obtained. If the lubricating oil supply pressure falls below this lower limit, gas enters the oil supply port 11 and pushes back the oil, which prevents continuous oil supply and makes it impossible to obtain a good casting surface.

Next, even if the oil head pressure H0 increases and the amount of oil used increases, no effect on the casting surface is observed. Therefore, from the perspective of reducing oil usage, it is preferable to have a low oil head pressure as long as it does not cause interruptions in oil supply.As for the type of lubricating oil, the higher the viscosity, the better the casting surface will be. However, if oil spills are taken into consideration, the number is 5 to 40.
Preferred are those having an industrially appropriate poise viscosity, such as castor oil, rapeseed oil, and salad oil.

Effect of introduced gas In order to investigate how the gas introduced into the overhang is acting, we observed the solidification region of the ingot under (a) gas pressure and (b) no gas pressure. did. During casting, a tracer was injected into the molten metal in the hengoo, and at the same time, the lower die table of the casting machine was stopped from descending. Thereafter, the solidified ingot was cut along the plane including the shaft and etched with a casein-da solution. According to this, a solidified shell 5o was observed to grow from directly under the header in the case where gas pressurization was not effective (Fig. 6 a), but in the case where gas pressurization was effective (Fig. 6 b).
), no solidified shell growth was observed.

In this experiment, the molten metal is thought to have solidified as shown in Figure 5. That is, the molten metal is removed from the area directly below the overhang portion 9 by the applied gas pressure. The molten metal starts contacting the inner peripheral surface of the mold at a position considerably lower than the top end of the mold 1, immediately forms a thin solidified shell, and then separates from there. The length of the molten magnesium alloy in the casting direction in contact with the inner circumferential surface of the mold is quite short, and therefore the effect of secondary cooling is reduced. The realization of the solidification process as shown in FIG. 5 is considered to be one of the reasons for the effects of the present invention. Another reason is that the effects of fluctuations in the molten metal level in the receiving tank and disturbances in the flow path of the inflow into the receiving tank are alleviated by the gas that exists directly under the mold. It does not reach the molten metal that solidifies directly, so solidification progresses under certain conditions. Such a process is considered to be an important basis for bringing about the effects of the present invention.

Reverse segregation of alloy components in the ingot The quality of the ingot formed by continuous casting is determined by the casting surface and other factors.
It is evaluated by the magnitude of reverse segregation of alloy components in the ingot.

Magnesium alloy AZ31 was cast by the method of the present invention and the conventional continuous casting method shown in FIG. 7 to obtain cylindrical ingots each having a diameter of 62 mm. The segregation layer immediately below the surface of the ingot and the reverse polarization layer inside the ingot were compared, and results 2 in Table 1 were obtained.

1st Thickness of the segregation layer just below the surface Thickness of the opposite side plate layer Conventional method
200 μm or more Method of the present invention 5
0 μm or less Group 0.1 (Effects of the invention) An excellent ingot with a smooth casting surface and few reverse side plate layers was obtained by continuously casting magnesium alloy using a hot-top casting method that pressurized gas containing sulfur hexafluoride. 0 Therefore, plastic processing such as extrusion and rolling can be performed by omitting skin scraping or by removing a very small amount of skin, and it is also possible to use the material as a forging material after cutting without going through the extrusion process. Ta.

[Brief explanation of the drawing]

FIG. 1 is a vertical sectional view showing a specific example of a casting apparatus according to the present invention, FIG. 2 is a plan view of a mold of the apparatus shown in FIG. 1, FIG. 3 is a sectional view AB of FIG. 2, and FIG. is the CD sectional view of Figure 2, and
The figure is a partially enlarged view of Fig. 1 to explain the cooling mechanism, and Fig. 6 is a cross-sectional view of the ingot showing the solidification area of the ingot (a) under gas pressure (b) without gas pressurization. The sketch diagram and FIG. 7 are explanatory views showing the conventional continuous casting method. DESCRIPTION OF SYMBOLS 1...Mold, 2...Refractory molten metal receiving tank, 3...Cooling medium supply hole, 4...Cooling medium, 6...Sulfur hexafluoride gas supply port, 8...Gap, 9... Overhang part, 10... Lubricating oil supply tubular port, 11... Lubricating oil inlet, 16... Molten metal of magnesium alloy, 17.
...Magnesium alloy ingot, 20...Valve, 21
... Magnesium alloy molten metal transfer pipe, 22... Nozzle,
24...Distribution cup. Patent Applicant Showa Light Metal Co., Ltd. Patent Attorney Sei Kikuchi - Figure 1 Figure 3 Figure 4 l: S type 2: Fireproof sacrificial bath ellipse / 7゛ Magnesium 8-karat gold kaburi tane Figure 6 (α) (b) I6: Magnesium alloy molten metal 17: Magnesium alloy ingot 50 near 7 nenium alloy solidified shell

Claims (1)

[Claims] A refractory metal molten metal receiving tank is provided on the upper part of the forced cooling mold, and the inner peripheral lower end surface of the molten metal receiving tank extends inward from the inner peripheral surface of the mold to form an overhang part. A cooling mold is used to store a molten metal of magnesium or its alloy to be cast in the molten metal receiving tank, and the molten metal is held in a columnar or cylindrical shape close to the mold, which has a lubricated interface formed on its inner peripheral surface. , and a continuous casting method for magnesium or its alloy, which includes a step of cooling the columnar or cylindrical body with a coolant passing through the mold, and in which a gas containing sulfur hexafluoride is placed directly under the overhang. 1. A method for continuous casting of magnesium or alloy thereof, characterized in that the columnar or cylindrical molten magnesium or alloy thereof is introduced and cast by applying gas pressure to the outer peripheral surface of the columnar or cylindrical molten magnesium or alloy thereof.