Magnesium alloys have many excellent properties such as low density, good specific performance, good shock absorption, good electrical and thermal conductivity, good process performance, poor corrosion resistance, easy oxidation and combustion, and poor heat resistance. Due to oxidative combustion, the editor will talk about the precautions for production safety.
Unsafe factors in machining process.
In the process of machining magnesium alloys, the chips and fine powders produced have the risk of burning or exploding.
1.During the processing of magnesium alloys, the influencing factors that make the chips heat up to the flash point or combustion are as follows.
a. Relationship between machining speed and cutting rate. The generation of cutting heat increases in proportion to the cutting speed, and the higher the relative temperature, the greater the possibility of fire.
b. Other factors. Feed rate or engagement is too low; dwell time during machining is too long; tool clearance and chip space are too small; high cutting speed is used without the use of cutting fluid; tool and nesting Sparks may occur when dissimilar metal core liners in castings collide; magnesium chips build up around or under machine tools, etc. insecurity in the process.
2.Safe Operating Procedures for Machining
a. The cutting tool should be kept sharp, and the larger relief angle and relief angle should be ground; blunt, chip-adhered or cracked tools are not allowed.
b. Under normal circumstances, try to use a large feed rate for processing, and avoid using a small feed rate to generate chips with a larger thickness.
c. Do not let the tool stop on the workpiece in the middle.
d. When using a small amount of cutting, use mineral oil coolant to reduce cooling.
e. If there is a steel core lining in the magnesium alloy parts, avoid sparks when it collides with the tool.
f. Keep the environment neat and clean.
g. It is strictly forbidden to smoke, make fire, and electric welding in the processing area.
3. Safety Problems in Grinding
Magnesium powder is easily combustible and can cause an explosion when suspended in the air. Therefore, the following precautions must be taken when grinding magnesium alloy parts:
a. There must be a grinder specially used for the processing of magnesium alloy parts. Before dressing the grinding wheel, the vacuum cleaner should be thoroughly cleaned.
b. When the surface of magnesium alloy parts washed with chromate is reworked and ground, sparks may be caused, so special care must be taken to never allow dust to accumulate nearby.
c. Grinding equipment operators should use smooth hats, smooth gloves and smooth flame-retardant clothing without pockets and cuffs. The apron or protective clothing used should be clean and dust-free and easy to take off.
d. The magnesium waste should be cleaned up in time, and the longest storage time limit should be set.
e. Sufficient yellow sand should be stored in the working area to prevent fire fighting.
4. Handling of Magnesium Chips and Fine Powder
Waste chips must be stored separately and cannot be exposed to rainwater
The magnesium waste chips produced by processing are packed in barrels and soaked in special cutting fluid for magnesium processing. Place it in a place that is ventilated but not exposed to rain or water, and do not cover the lid to allow the hydrogen that may be generated to volatilize naturally (the hydrogen may not be fully volatilized, which may cause an explosion).
Smoking, welding and other behaviors with ignition sources are strictly prohibited around.
5. Magnesium chip burning fire extinguishing
a. D class fire extinguisher.
The material is usually a sodium chloride-based powder or a passivated graphite-based powder, which works by smothering the fire by excluding oxygen.
b. Covering agent or dry sand.
It can be used to cover a small area of fire, and its principle is also to smother the fire by excluding oxygen.
c. cast iron debris.
It can also be used in the absence of other good fire extinguishing materials. The main function is to reduce the temperature below the ignition point of magnesium, rather than smothering the fire.
In conclusion, under no circumstances should water or any other standard fire extinguisher be used to extinguish fires caused by magnesium. Water, other liquids, carbon dioxide, foam, etc. all react with the burning magnesium and strengthen the fire rather than suppress it.
The above content is for reference only, if you have different opinions, please correct me!
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