CN1400325A

CN1400325A - Method for fire-resisting protection for smelting magnesium alloy

Info

Publication number: CN1400325A
Application number: CN 01108697
Authority: CN
Inventors: 龙思远; 游国强
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-07-31
Filing date: 2001-07-31
Publication date: 2003-03-05
Anticipated expiration: 2021-07-31
Also published as: CN1132949C

Abstract

The present invention relates to a fire-resisting protection method for smelting magnesium alloy. In the course of smelting, heat-insulating, refining and pouring processes of magnesium alloy said ivnention adopts a mixture of carbon and sulfur or carbon and sulfide and oxygen gas compressed air or mixed gas of oxygen gas and compressed air, and makes them produce on-site reaction in smelting workshop, smelting furnace or heat-insulating furnace to produce mixed gas containing SO2 and CO2 to implement fire-resisting protection.

Description

Flame-retardant protection method for magnesium alloy smelting

The invention relates to a method for flame-retardant protection of alloy melt, in particular to a method for flame-retardant protection of melt in the processes of magnesium alloy smelting, heat preservation, refining and pouring.

Magnesium alloy is the lightest metal material in practical application and has many advantages, but magnesium has active chemical property and large chemical affinity with oxygen, and is easy to oxidize and burn or even explode in the smelting process. Therefore, the smelting process of magnesium must take effective measures to prevent its oxidative combustion. The existing flame retardant methods mainly comprise three methods: (1) one is a physical barrier method using flux covering during the melting process. Although the method has good flame retardant effect, the magnesium melt is inevitably polluted, the mechanical property of the alloy is influenced, and the process quality and the corrosion resistance of the casting are reduced. (2) The other method is to adopt an alloying method, namely, a large amount of Be, rare earth or Ca and the combination thereof are added into the magnesium alloy melt, so that a compact oxide film is formed on the surface of the melt, and the purpose of flame retardance is achieved. However, this method causes a large increase in melting cost, coarsening of crystal grains, a decrease in mechanical properties, and an increase in the tendency to hot cracking, and also causes a drastic increase in the use of BeThe toxic Be vapor and the Ca-added magnesium alloy melt are easy to burn when being stirred and impacted. (3) Still another is the currently commonly used SF₆The mixed gas is smelted for protection, and the method has the advantages of no pollution to the magnesium melt and good protection effect. But SF₆The gas is expensive, and the capability of destroying the ozone layer of the atmosphere to cause the greenhouse effect is CO₂24000 times of the total usage of the product is forbidden. At present, SO has been used₂Etc. other gases being substituted for SF₆A method for carrying out magnesium alloy mixed gas protection smelting. There are several disadvantages: one is SO₂When the gas is bottled or canned, the transportation and the use are inconvenient; and secondly, a special gas mixing device and a corresponding control device are needed, and the equipment is complex.

The invention aims to overcome the defects of the existing method and provide a magnesium alloy smelting flame-retardant protection method which has good protection effect and low cost, does not pollute magnesium melt and does not destroy the environment.

The purpose of theinvention is realized by the following technical scheme: modifying a smelting furnace or a heat preservation furnace, installing a reactor in the smelting furnace or the heat preservation furnace, adding a mixture of carbon and sulfur or carbon and sulfide into the reactor, heating to 300-800 ℃ by using a heating system of the smelting furnace or the heat preservation furnace to enable the mixture to reach an ignition point, generating required mixed protective gas in situ, and introducing O into the reactor₂Compressed air or O₂Mixed gas with compressed air

The protective gas adopted by the invention contains SO₂、CO₂The mixed gas comprises the following main components in percentage by mass: SO (SO)₂：0.5-10％，CO₂：0-90％，N₂：0-80％，O₂：0-10％。

The method for obtaining the mixed protective gas comprises the following steps: oxygen, compressed air or a mixed gas of oxygen and compressed air is introduced into a reactor which is arranged in a smelting workshop, a smelting furnace or a holding furnace, is heated to the temperature range of 300-800 ℃, and is internally provided with a mixture of carbon and sulfur or a mixture of carbon and sulfide for oxidation reaction, and in-situ (on-site) generation is carried out (as shown in figure 1). The reaction is as follows (reaction formulas (1), (2) and (3), and the sulfide takes pyrite as an example):

(1)

(2)

(3) the ignition point of the pyrite is about 400 ℃ and 20 ℃, and the addition of carbon plays a role in supporting combustion, so that the ignition point of the pyrite is slightly lowered, and the ignition point of the mixture of the pyrite and the carbon powder is about 400 ℃; the ignition point of sulfur is about 360 ℃. Because the working temperature of the magnesium alloy smelting, heat preservation and refining equipment is generally about 700 ℃, the requirement of full combustion of the mixture of carbon and sulfur or carbon and sulfide can be well met, the smelting furnace or the heat preservation furnace is only required to be slightly modified, the mixture of carbon and sulfur or carbon and sulfide is added into a reactor arranged in the smelting furnace or the heat preservation furnace, and O is introduced into the reactor₂Compressed air or O₂The mixed gas with the compressed air is beneficial to a heating system of a smelting furnace or a heat preservation furnace, so that the ignition point of the smelting furnace or the heat preservation furnace can be reached, and the required mixed protective gas is generated in situ; or adding a reactor in the smelting plant, adding carbon and sulfur or a mixture of carbon and sulfide, and introducing O₂Compressed air or O₂And generating the required mixed protective gas in situ by the mixed gas of the compressed air and the protective gas.

Introducing the mixed protective gas generated by the reaction directly above a magnesium alloy molten pool, reacting with the magnesium melt at high temperature (such as reaction formulas (4), (5) and (6)), generating a thin and compact MgS-MgO composite surface film with metal color on the surface of the magnesium melt,

(4)

(5)

the amorphous carbon generated in the reaction (6) exists in the gaps of the surface film, so that the compactness of the surface film can be improved. The composite surface film can effectively inhibit magnesium oxidation under the conditions of smelting, heat preservation, refining and pouring temperature of magnesium alloy, thereby achieving the purpose of flame-retardant protection.

FIG. 1, schematic diagram of the process for obtaining mixed shielding gas

The method has the characteristics of practicability and economy. The mixed protective gas has good protective effect and can replace covering agent protection and SF₆Conventional methods of mixed gas shielding; meanwhile, the method adopts cheap raw materials and in-situ reaction generation, so that the use is particularly convenient and the cost is low.

Claims

1. A method for flame-retardant protection of magnesium alloy smelting is characterized by comprising the following steps: introducing oxygen, compressed air or mixed gas of the oxygen and the compressed air into a reactor which is arranged in a smelting workshop, a smelting furnace or a heat-preserving furnace, is heated to the temperature range of 300-800 ℃, is internally provided with a mixture of carbon and sulfur or a mixture of carbon and sulfide for oxidation reaction, and generating SO-containing gas in situ (on-site)₂And CO₂The generated mixed gas is directly introduced above a magnesium alloy molten pool and reacts with a magnesium alloy melt to generate a compact MgS-MgO composite surface film, thereby achieving the flame-retardant protection effect of preventing the magnesium alloy from being continuously oxidized.

2. The magnesium alloy melting protection method as set forth in claim 1, wherein: the mass percentages of main components in the mixed protective gas are as follows:

SO₂：0.5-10％，CO₂：0-90％，N₂：0-80％，O₂：0-10％