Magnesium is an excellent thermal conductor, and as a physical object, the entire part must be heated to near the melting point temperature before it is ignited. Usually this does not happen unless the solid magnesium is surrounded by a fire from another source.
Precautions must be taken when magnesium is in the following states:
- in a molten state - fine, such as shavings, granules or fine powder - by a flame cage
Molten magnesium
1, safety clothing and equipment
As with any other object, molten magnesium, when exposed to your skin at 600 ° C, can cause severe burns. Those working around molten magnesium must wear adequate protective clothing and equipment. This includes:
- Safety glasses - Safety helmet with protective screen - Flame retardant overalls - Safety shoes - Thermal insulation gloves
All safety clothing and equipment are tested to ensure adequate protection. First aid preparations should include flame coverage and safety indicators. All personal protective equipment should comply with applicable legal standards.
2, the protection of the melt
Molten magnesium ignites and burns when exposed to air, so it must be protected during smelting operations. The traditional approach is to cover the fluidized chloride salt and remove the contact of air with the melt. The common practice today, though not all, uses a protective gas such as a mixture of a small amount of fluorine hexafluoride and air, or a mixture of air and carbon dioxide.
Fluorine hexafluoride or SF6 forms a film on the surface of the melt to prevent excessive oxidation.
3. Gas supply system
The gas supply system should be designed to prevent the formation of high concentrations of hexafluoride on the melt, as high concentrations of hexafluoride can severely corrode steel lids and smelting pots. Corrosive products can react with molten magnesium and can cause an explosion.
The system design should ensure that the interference of the airflow to the gas barrier is minimized. The fuel supply line shall be provided with combustion safety control and remote shutoff.
4, to prevent contact with water
Do not install automatic sprinklers in smelting operations, heat treatment furnaces or where fine magnesium particles are processed or stored. If the water is in contact with the molten magnesium, the explosion may occur regardless of whether the molten magnesium is in the casting furnace or in the combustion chamber pit. The water will expand to 1000 times its original volume, thus throwing the molten metal a considerable distance. In addition, magnesium has a strong affinity for oxygen, which will decompose water and release flammable hydrogen. When hydrogen combines with air, it can explode.
5, preheating of metal ingots and tools
Any material, such as ingots and tools that incorporate molten magnesium, must be preheated to above 100 °C to remove all moisture or other volatiles. Any cold surface may contain moisture from atmospheric condensation.
6, keep the smelting pot clean
Molten magnesium reacts exothermically with iron oxide to produce a high temperature of 2200 ° C and a large amount of heat. Since most smelting pots are made of steel, it is important to keep the pot clean and free of scale. Similarly, the iron should be periodically removed from the furnace to prevent it from reacting with the molten magnesium when the pan is broken. The refractory material used in the furnace should be high alumina or magnesia, because the molten magnesium will react violently with it even if it contains a very small amount of silica. The pan should be prepared to prepare for the damage of the melting pot. These pots should be kept dry and free of scale at all times.
7, fire extinguishing materials
Dry, Class D fire-extinguishing materials, such as G-1 powder and foundry flux, should always be kept nearby.
8, casting mold
Magnesium casting molds are made of non-combustible materials, and the ground around the smelting operation should be cauterized or glassy. The heat of molten magnesium releases the hydrogen from the moisture of the cement, which can cause ground fragmentation and sometimes even an explosion.
9, summary - molten magnesium
Despite the need for careful and certain measures to deal with molten magnesium, many magnesium producers and foundries around the world routinely smelt and process thousands of tons of magnesium per day without accidents by strictly following well-documented safe operating procedures.
Fine magnesium
Magnesium in a fine form is flammable and is self-ignitable in the presence of water or a fatty acid-containing cutting fluid. Hydrogen can also be generated and there is a danger of explosion in case of fire. Containing magnesium dust, when the air to dust concentration ratio reaches a critical value, if it is ignited, it will burn with a violent explosion. Smoking, open flames and electric welding must be prohibited in places where magnesium machining, sawing or milling is required. All electrical connections and motors must be explosion-proof. Tools that do not produce sparks must be used where magnesium dust is present.
Dust collector device
The dusting dust is collected using a special wet dust collector device for magnesium. The entire system must be grounded and the exhaust fan power supply and the water level controller should be interlocked.
The device should be designed to prevent dry dust from accumulating at any point before it is converted into mud, avoiding high-speed moving parts in dry dust. The dust collector must also be designed to ventilate hydrogen from the mud at all times, even in the event of a power outage.
Magnesium with chromate on the surface or magnesium with a steel insert cannot be used for milling because both can produce sparks. Any spark can cause the dust to ignite and cause the flame to pass through the system. The mud of the liquid separator should be removed at least on the same day and transported to the disposal site or to the covered and ventilated iron bucket classification zone.
Magnesium machining
Magnesium processing consumes less power than any other commonly used metal, allowing the production of long chips at maximum speed and infeed. Keep the tool sharp and never allow the tool to rest against the metal without cutting. A blunt tool can be overheated and ignited by turning it against the metal.
Storage and transportation of magnesium
Magnesium of any shape should be stored on a well drained, spilled floor. The preferred storage of magnesium ingots and magnesium parts is a single-layer, non-combustible building, but perhaps this is not true in all situations. If stored with other combustibles, the volume of storable magnesium recommended by the National Fire Protection Association is:
1. Recommended automatic sprinkler system
Unlike where molten magnesium is present, it is highly recommended to have an automatic sprinkler system in place where magnesium ingots or magnesium parts are stored. Because they are used to prevent the ignition of magnesium into nearby nearby combustibles.
The passage should be wide enough for firefighters to use the equipment effectively.
2, powder, chips, grains and chips
Dry magnesium, magnesium, magnesium and magnesium chips should be stored in closed, non-combustible containers, such as iron drums that are sufficiently isolated from other combustible materials. Automatic sprinkler systems should be prohibited in these areas.
Wet magnesium chips, magnesium powder or magnesium mud should be stored underwater in a covered, ventilated, non-combustible container and placed outdoors. When wet magnesium is exposed to the atmosphere, it generates heat to accelerate evaporation, which ultimately leads to spontaneous combustion. Do not stack containers, and keep the source away from the exhaust of the container.
3. Transportation of magnesium
Most industrialized countries classify magnesium as a “dangerous†product. There are provisions for air, rail, road or water transport of dangerous goods. The regulations usually cover packaging, shipping documents, labels and announcements. Make sure to verify your country's compliance with regulations, or if it is international transportation, make a UN document – ​​a proposal for the transport of dangerous goods.
If a fire breaks out
Magnesium fires are spectacular because they emit bright light and smoky white clouds. White smoke is a magnesium oxide that is itself non-toxic, but avoids inhalation because excessive amounts can cause symptoms of metal smoke. You must also realize that other toxic smoke may be mixed in this white smoke. The best chance to control the flame is to subdue it when it is still very young, and magnesium is no exception. Dry magnesium particles burn very slowly and smoothly, but if they are stirred or have moisture or cutting oil, the fire will suddenly become fierce.
1, asphyxiant
Magnesium is burned by direct oxidation, so the only way to control the magnesium flame is to use a dry, air-free fire-extinguishing agent to hold it or burn it out. In the face of a fire that is out of control, firefighters may have to take damage control to nearby buildings.
Suitable magnesium flame asphyxiants are:
- G-1 dry powder - Met-L-X powder - Magnesium casting solvent - Special material for magnesium
In a restricted area, such as a storage tank, the magnesium flame can be suppressed with argon.
2, never use water to destroy magnesium flame
Never use water to destroy the magnesium flame, as the water will break down into oxygen and hydrogen, increasing the fire and creating an explosion hazard.
Many commonly used fire extinguishing agents also exacerbate the fire of magnesium, they are:
- Foam - Carbon dioxide - Halogenating agent - Some dry chemicals containing mono or diammonium phosphate - Sand
Staff training and response team
If you are manufacturing, processing or storing magnesium, you must train all operators for safety procedures and establish a skilled internal emergency team.
In many countries, there is a legal requirement that if you are processing or storing magnesium, you must notify the local fire department and jointly develop an emergency response plan. This work is done even without any legal requirements.
to sum up
Magnesium can be burned, especially in molten or fine form. Magnesium reacts with water to produce hydrogen causing a fire or explosion. However, as long as there are reasonable safety precautions, you can prevent fire or explosion.
Globally, the use of magnesium is growing rapidly. The fact is that millions of tons of magnesium have been melted or processed without incident by adhering to well-defined safe operating procedures.
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