JP5146172B2 - Method for preventing combustion of molten magnesium or magnesium alloy - Google Patents

Description

  The present invention relates to a method for preventing rapid oxidation and combustion of molten magnesium or a magnesium alloy.

  Molten magnesium, molten magnesium alloy (both of which are sometimes referred to as “molten magnesium / magnesium alloy” or “molten metal” in this application) reacts violently with oxygen in the air to form and burn oxides. It has been known. In order to prevent oxidation of molten magnesium or a magnesium alloy, a method of covering with a protective gas composition having a protective gas component is employed.

Until now, sulfur hexafluoride (SF ₆ ) has been mainly used as a protective gas component in magnesium and magnesium alloy manufacturing processes. However, because the substance has a global warming potential (GWP) of about 24,000 times that of carbon dioxide (CO ₂ ) and has a very long atmospheric life of 3,200 years, its emission is regulated by the Kyoto Protocol. It is a substance, and alternative substances are required.

Against this background, the present applicant has disclosed a protective gas composition containing a fluorinated olefin such as 1,3,3,3-tetrafluoropropene as a novel protective gas, and a molten magnesium / magnesium alloy using the same. Patent Documents 1 and 2 propose methods for preventing combustion.
Pamphlet of International Publication No. 2006/118157 Pamphlet of International Publication No. 2007/63674 Japanese Patent Laid-Open No. 11-140002

  The production method of existing magnesium or magnesium alloy (hereinafter sometimes referred to as “magnesium metal”) using sulfur hexafluoride as a protective gas component is changed to a production method using fluorinated olefin as a protective gas component. When it tried to replace it, it turned out that the casting of magnesium metal may not be performed stably only by changing the protective gas component.

  When using fluorinated olefins instead of sulfur hexafluoride as a protective component for existing magnesium metal casting equipment, the magnesium or magnesium alloy melt (hereinafter sometimes referred to as "metal melt") is smooth. In some cases, the protective gas composition is difficult to reach. Since the casting atmosphere is a high temperature of 500 to 900 ° C., a part of the fluorinated olefin is decomposed into hydrogen fluoride. When an excessive protective gas composition is introduced into the casting equipment to ensure that the molten metal surface is covered with the protective gas composition, a large amount of hydrogen fluoride is generated, which may promote deterioration of the equipment.

  The present invention relates to a method for covering a molten metal surface with a protective gas composition having a fluorinated olefin as a protective gas component to prevent rapid oxidation and combustion of molten metal, even if the production scale is increased. It is an object of the present invention to provide a method for preventing the molten metal from burning so that the casting can be stably performed.

  In the present invention, the protective gas composition having a fluorinated olefin as a protective component is less likely to reach the molten metal surface because the specific gravity of the fluorinated olefin is lower than that of sulfur hexafluoride. Standing and trying to solve the problem.

  That is, the method for preventing combustion of molten magnesium or magnesium alloy according to the present invention is a method for preventing combustion of molten metal stored in a furnace, and the method uses a protective gas composition having a protective gas component comprising a fluorinated olefin as a nozzle. From the nozzle to the molten metal surface, the flow rate at the nozzle outlet of the protective gas composition is 5 to 200 m / s when the protective gas composition is supplied from the nozzle. Preferably, the protective gas reaches the molten metal surface by setting the distance between the lower end of the nozzle and the molten metal surface to 10 to 190 mm / s, preferably 10 to 500 mm, and preferably 50 to 450 mm.

  Whether the present invention is to increase the flow rate when supplying a protective gas composition comprising a carrier gas component and a protective gas component comprising a fluorinated olefin, or to shorten the distance between the nozzle tip and the surface of the molten metal. Is based on overcoming the high decomposability and low specific gravity of fluorinated olefins.

  The protective gas component is on the surface of the molten metal, reacts with magnesium metal to form a protective film, and combustion of the molten metal is suppressed. When the flow rate exceeds 200 m / s, the protective film may be destroyed. On the other hand, if it is less than 5 m / s, the protective gas composition may not reach the molten metal surface sufficiently, and the protective film may not be sufficiently formed. In addition, when the distance is more than 500 mm, the protective gas composition may not reach the molten metal surface sufficiently, and when the distance is less than 10 mm, the protective film may be destroyed.

  The method for preventing combustion of molten magnesium or magnesium alloy according to the present invention is effective in efficiently operating casting of magnesium or magnesium alloy using a halogenated olefin as a protective gas component.

  An example of an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a view for explaining the outline of a molten metal holding furnace to which a method for preventing combustion of molten magnesium or magnesium alloy according to an embodiment of the present invention is applied. The molten metal 1 is retained in a furnace 2 used when casting magnesium metal. The furnace 2 is constituted by a furnace body 3, and a furnace body 3 ′ above the furnace passes through the nozzle 4 while the nozzle 4 maintains a sealed structure. Further, the furnace body 3 or 3 ′ may be provided with a mechanism for exhausting the gas in the furnace.

It is preferable that at least two nozzles 4 are installed per unit molten metal area (1 m ² ). The upper limit of the number of nozzles 4 per 1 m ² may be set to 10, preferably 8, and more preferably 5 in order to reduce the waste of supply of protective gas.

  The nozzle 4 is connected to a cylinder (not shown) in FIG. 1 through a pipe (not shown) outside the furnace 1, and the gas coming out of the cylinder is introduced into the furnace 1 through the nozzle 4. The flow rate of the gas in the nozzle is adjusted, for example, by controlling a cylinder valve or a gas pressure in the pipe. In order to adjust the flow rate more accurately, a volume type, an area type, a mass type flow meter or the like, or an electronic type flow rate controller may be used.

  By adjusting the distance between the surface of the molten metal 1 and the tip of the nozzle 4 and the flow rate of the gas in the nozzle as claimed in the present invention, the protective gas composition is flown as shown in FIG. It reaches the surface of the molten metal 1. A cylinder filled with a protective gas composition may be prepared, or a cylinder filled with a protective gas component and a cylinder filled with a carrier gas are prepared, and both gases are mixed in a pipe. Thus, a protective gas composition may be used.

  Examples of the material of the nozzle 4 include iron, copper, and stainless steel. When the nozzle 4 has an outlet diameter of preferably 1 mm to 25 mm, more preferably 2 to 15 mmφ, and more than 25 mmφ, it is necessary to supply a large amount of the protective gas composition in order to obtain a desired flow rate of the protective gas composition. It is not economical. On the other hand, if it is 1 mm or less, the supply of the protective gas composition is small in order to make the flow rate of the protective gas composition as desired, and more nozzles 4 need to be arranged, which is not economical. Moreover, in order to maintain the rigidity of the nozzle 4, the thickness of the nozzle 4 is preferably 0.1 to 2 mm, more preferably 0.2 to 1 mm.

  Examples of the material of the furnace body 3 or 3 'include heat-resistant steel.

  The tip of the nozzle (gas outlet) is directed toward the surface of the molten metal so that the nozzle 4 can supply the protective gas composition to the surface of the molten metal. At this time, the nozzles 4 may be arranged substantially perpendicular to the surface of the molten metal.

  The flow rate of the protective gas composition in the nozzle 4 is further 5 to 100 m / s, preferably 10 to 95 m / s when the distance between the nozzle 4 and one surface of the molten metal is 10 to 100 mm. Further, when the distance is more than 100 to 500 mm, it is more than 100 m / s to 200 m / s, preferably 110 to 190 m / s.

  The protective gas composition used in the present invention has a carrier gas component and a protective gas component composed of a fluorinated olefin. The fluorinated olefin preferably has at least one double bond in the molecule. Among them, 1,1,3,3,3-pentafluoropropene, 1,2,3,3,3-pentafluoropropene, 2,3,3,3-tetrafluoropropene, 1,3,3,3-tetra Preferred are fluorinated propenes selected from the group consisting of fluoropropene, 3,3,3-trifluoropropene, 1,1,2-trifluoropropene and mixtures thereof. The fluorinated propene is used in cis form, trans form, or a mixture of both cis form and trans form.

  Among these fluorinated propenes, 1,3,3,3-tetrafluoropropene and 2,3,3,3-tetrafluoropropene are particularly preferred as protective gases because of their boiling point, low toxicity and easy handling. In the case of these fluorinated propenes, it is particularly preferable to use a trans form (boiling point −19 ° C.) because it can be handled as a gas rather than a cis form (boiling point 9 ° C.).

Fluorinated propene is obtained by hydrogenation and deHF from readily available hexafluoropropene to obtain 1,2,3,3,3-pentafluoropropene, and further by hydrogenation and deHF, 2,3,3,3- It is known that tetrafluoropropene can be obtained. 1,3,3,3-tetrafluoropropene can be obtained by deHFing 1,1,1,3,3-pentafluoropropane which is industrially produced and easily available. (For example, Patent Document 3)
The concentration of the protective gas component is 0.01 to 10% by volume, preferably 0.02 to 5% by volume, more preferably 0.02 to 1 when the total amount of the protective gas composition is 100% by volume. It is preferable to set it as volume%.

  Examples of the carrier gas include dry air, carbon dioxide, nitrogen, helium, neon, argon, krypton, xenon, and future products thereof. In particular, the carrier gas is composed of 0.5 to 50% by volume of dry air and 50 to 99.5% by volume of nitrogen, preferably 1 to 30% by volume of dry air and 29 to 70% by volume of nitrogen. It is preferable.

  The combustion prevention method of the present invention is applied to the surface of the molten metal in the melting furnace at the time of casting the magnesium alloy and the protective gas for the molten metal from the outlet of the melting furnace, as well as to forging and rolling of the magnesium alloy at a high temperature. May be.

  EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

Example 1
About 130 kg of magnesium alloy (AZ91D) is put into a furnace for casting magnesium metal, and the furnace is heated to 700 ° C. to melt the magnesium alloy to form a 0.5 m ² molten magnesium alloy. The protective gas composition was introduced into the furnace from a nozzle having a diameter of 4 mmφ, and a protective film made of a reaction product of the protective gas component and magnesium was formed on the surface of the molten metal.

  At this time, one nozzle 4 is arranged above the center of the surface of the molten metal, the distance between the surface of the molten metal and the tip of the nozzle 4 is 50 mm, and the flow rate of the protective gas composition in the nozzle 4 is 10 m / s. did. Further, as the protective gas composition, 0.2% volume 1,3,3,3-tetrafluoropropene (trans form) as a protective gas component, and 99.8% by volume carrier gas component (95% by volume nitrogen and What consists of 5 volume% dry air) was used.

  The protective gas composition was continuously supplied from the nozzle at the above flow rate, and the protective film in a range of 15 × 40 cm square was broken with an iron scratching rod every 10 minutes, but a protective film was formed immediately. This operation was repeated 10 times, but combustion from the molten metal was not confirmed.

Example 2
The same procedure as in Example 1 was performed except that the flow rate of the protective gas composition at the nozzle outlet was 30 m / s. As a result of this example, combustion from the molten metal was not confirmed.

Example 3
The same procedure as in Example 1 was performed except that the flow rate of the protective gas composition at the nozzle outlet was 50 m / s. As a result of this example, combustion from the molten metal was not confirmed.

Example 4
The same procedure as in Example 1 was performed, except that the distance between the molten metal surface and the tip of the nozzle was 100 mm, and the flow rate of the protective gas composition at the nozzle outlet was 10 m / s. As a result of this example, combustion from the molten metal was not confirmed.

Example 5
The same procedure as in Example 1 was performed, except that the distance between the molten metal surface and the tip of the nozzle was 100 mm, and the flow rate of the protective gas composition at the nozzle outlet was 30 m / s. As a result of this example, combustion from the molten metal was not confirmed.

Example 6
The same procedure as in Example 1 was performed, except that the distance between the molten metal surface and the tip of the nozzle was 100 mm, and the flow rate of the protective gas composition at the nozzle outlet was 50 m / s. As a result of this example, combustion from the molten metal was not confirmed.

Example 7
The same procedure as in Example 1 was performed except that the distance between the molten metal surface and the tip of the nozzle was 100 mm and the flow rate of the protective gas composition at the nozzle outlet was 90 m / s. As a result of this example, combustion from the molten metal was not confirmed.

Example 8
The same procedure as in Example 1 was performed except that the distance between the molten metal surface and the tip of the nozzle was 200 mm and the flow rate of the protective gas composition at the nozzle outlet was 30 m / s. As a result of this example, combustion from the molten metal was not confirmed.

Example 9
The same procedure as in Example 1 was performed except that the distance between the molten metal surface and the tip of the nozzle was 200 mm and the flow rate of the protective gas composition at the nozzle outlet was 60 m / s. As a result of this example, combustion from the molten metal was not confirmed.

Example 10
The same procedure as in Example 1 was performed except that the distance between the molten metal surface and the tip of the nozzle was 200 mm and the flow rate of the protective gas composition at the nozzle outlet was 90 m / s. As a result of this example, combustion from the molten metal was not confirmed.

Example 11
The same procedure as in Example 1 was performed except that the distance between the molten metal surface and the tip of the nozzle was 200 mm and the flow rate of the protective gas composition at the nozzle outlet was 120 m / s. As a result of this example, combustion from the molten metal was not confirmed.

Comparative Example 1
The same procedure as in Example 1 was performed except that the flow rate of the protective gas composition at the nozzle outlet was 220 m / s. In the result of this example, destruction of the protective film occurred when the protective gas composition was introduced, and combustion from the molten metal was observed. In addition, excessive hydrogen fluoride was generated in the furnace.

Comparative Example 2
The same procedure as in Example 1 was performed, except that the flow rate of the protective gas composition at the outlet of the nozzle 4 was 2 m / s. In the result of this example, the protective gas composition did not reach the surface of the molten metal smoothly, and a portion where no protective film was formed appeared. As a result, combustion from the molten metal 1 was observed.

Comparative Example 3
The same procedure as in Example 4 was performed except that the distance between the molten metal 1 and the tip of the nozzle 4 was 520 mm. In the result of this example, destruction of the protective film occurred when the protective gas composition was introduced, and combustion from the molten metal 1 was observed.

Comparative Example 4
The same procedure as in Example 4 was performed except that the distance between the molten metal 1 and the tip of the nozzle 4 was 5 mm. In the result of this example, the protective gas composition did not reach the surface of the molten metal smoothly, and a portion where no protective film was formed appeared. As a result, combustion from the molten metal 1 was observed.

It is a figure explaining the outline of the holding furnace of the molten metal to which the combustion prevention method of the molten metal of magnesium or magnesium alloy by one Embodiment of this invention is applied.

Explanation of symbols

1 Molten metal of magnesium or magnesium alloy 2 Furnace 3 Furnace 3 ′ Furnace 4 Nozzle 5 Flow of protective gas composition in the furnace

Claims (2)

A method of preventing combustion of molten magnesium or magnesium alloy stored in a furnace, the method comprising supplying a protective gas composition having a protective gas component comprising a fluorinated olefin from a nozzle toward the molten metal surface, In the step of covering with the protective gas component, a furnace having at least two nozzles per unit molten metal area (1 m ² ) is used, the flow rate at the nozzle outlet of the protective gas composition is 5 to 200 m / s, the nozzle tip and the molten metal surface A method for preventing combustion of molten magnesium or magnesium alloy, wherein the protective gas composition is allowed to reach the molten metal surface by setting the distance to 10 to 500 mm. The fluorinated olefin is 1,1,3,3,3-pentafluoropropene, 1,2,3,3,3-pentafluoropropene, 2,3,3,3-tetrafluoropropene, 1,3,3 2, at least one selected from the group consisting of 1,3-tetrafluoropropene, 3,3,3-trifluoropropene, 1,1,2-trifluoropropene, and mixtures thereof. A method for preventing combustion of molten magnesium or magnesium alloy.

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