Analysis on the explosion hazard of milling magnesium powders

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Analysis on the dangerous worksites in the milling process of magnesium block

As the internal capacity of milling machine is small, it may be possible to catch fire. Especially as the main pipeline of cyclone separator and dust ventilating net has large volume as well as the interior dust concentration is within the explosive range, the static spark, overheating dust cluster and mechanical spark that are leaked by milling machine will inevitably occur. Therefore, the dangerous worksites in milling workshop mainly include cyclone separator and main pipeline of dust ventilating net.

Cyclone separator is the most dangerous worksite. If cyclone separator explodes, the airwave and shock wave may raise the magnesium powder near the discharge opening, in which the unfired dust may erupt and spread in the workshop, thus the secondary explosion will be occurred. Secondary explosion is very dangerous, which may ignite other equipments and cause personal injury on the operators in the workshop. Therefore, cyclone separator should be segregated from the other equipments in the workshop, especially the operators.

The main pipeline of ventilating net and branch pipeline of each milling machine should be set up according to original arrangement. The main pipeline of ventilating net should be segregated from operators, in which light hanging shed, such as frame galvanized sheet can be used. Cyclone separator should be set up outside the wall or equipped alone in a room. It should be segregated from milling machine workshop by blast wall.

Magnesium powders

Analysis on the dangerous worksites in the smashing section

Magnesium metal powder that has been smashed can be called mixed powder. The mixed powder that has not been graded will contain different particle size of magnesium powder. In the smashing process, the inside of pulverizer where the cutter blade will rotate, will incessantly charge by vibratory feeder, besides, its interior dust cloud will continuously exist under working condition; dust cloud may form near discharge port as well as inside of cyclone dust collector and dust removal pipe; in the operation process, the overflow and scattering of dust will inevitably happen, which may lead to the dust deposition on the equipment surface, floor and wall.

a. When the scrap iron that is generated in the vibratory feeding has not been fully removed by magnet, it will form friction and shock ingnition source due to the adjustment and rotating of pulverizer.

b. Static will be easy to occur in the smashing, gas delivery, cyclone dust removal and blanking, which will lead to the electrification of powder particles. If the electric charge cannot be leaked in time, it may discharge in the blanking place and pipeline export, form static spark and become a kind of electrostatic ignition source.

c. Fan blade can remove the residual dust in the cyclone dust collector. It will inevitably generate shock ignition source if it is made by iron material that is easy to have spark, or under the existence of rust.

d. When the stellated feeder is rotating, the friction between blade and valve shell can be one of the main reasons that lead to the ignition of material receiving box.

e. The detonation inside of pulverizer, the ignition of discharge port and explode sound of draught fan export pipeline may all lead to serious dust explosion accident. Therefore, effective precautions should be adopted firstly and protective measures should be applied secondly so as to ensure the segregation between people and machine.

Screening of magnesium powder

Magnesium powders that have different particle size are classified in the mechanical vibration screen. Experiment shows that vibrating screen will have large risk as static disaster and mechanical shock friction will occur in the vibration process. Before taking the explosion-proof measures, the vibrating screen should be segregated from operators so as to ensure their safety. In order to prevent the vibrating screen from being destroyed by the overpressure that is generated in the explosion accident and causing large loss, low opening pressure should be used in the explosion venting device according to the experiment results.