When shotblasting products of aluminium alloys, which contain impurities of silicon, magnesium, zinc, coopper, etc., it is necessary to adapt the equipment for shotblasting and dedusting to the studies on the risk of explosion. The basic document for safe work in explosive environments is the explosion protection regulations, which combine two European directives 2014/34/EU and 99/92/EC.
The explosive physico-chemical properties of aluminum powder in inadequate concentrations, when shotblasting different aluminum alloys in a mixture with the powder of different abrasives, can represent serious and potentially dangerous explosive environments.
In the explosion risk studies, the zones of explosion danger must be precisely defined for these environments and spaces (Zones represent the frequency of the presence of an explosive atmosphere), sources of ignitionn and their effectiveness, defined devices, substances, procedures and their mutual influences and the extent of the expected effects.
Protection of work process and equipment
Zones are determined on the basis of the explosion hazard analysis. Equipment that can be installed in these zones is provided on the basis of certain zones. Usually the Ex zones includes the dust collector and also the parts of the machine for which we cannot prevent the ignition, but it is necessary to protect it properly to mitigate the harmful consequences of the explosion.
Depending on the class of dusty combustile substance St.1 - St.3 (determined according to the explosion constant Kst), protective elements or devices that relieve the working device are defined.
Passive elements in the dust collector unit
The selection and equipment of such a dust collector unit must include:
- Housing of cartridge dust collector with structural resistance up to 2 bar and built-in burst flap, which enables release at the time of explosion in the direction of defined zone.
- Antistatic dust collector cartridges,
- Fan manufactured in EX protection,
- A non-return flap that prevents the spread of the explosion from the dust collector towards the machine,
- A diverter-drain with an anti-explosion membrane is usually installed at the exit part of the pipeline from the room, which allows release at the moment of an explosion in the direction of a defined area.
- All element of the pipeline between the machine, the dust collector unit and the fan must be grounded in accordance with the regulations on the discharge of static electricity.
- In cases where the dust collector equipment must be installed inside the building, a water dust collector is recommended. If a dry dust collector is installed, it is aboslutely necessary to install a fire detection system and explosion suppression systems on the dust collector unit and pipelines.
Passive elements of the machine
The following measures must be taken into account:
- Intensive dust extraction from the machine,
- Explosion flaps are installed on the machine so that in the event of an explosion the pressure in the machine does not rise to more than 3,000 Pa.
- A negative pressure indicator is installed on the machine, which immediately stops the shot blasting machine in case of insufficient ventilation.
- All parts of the machine must be grounded to eliminate static electricity.
- The temperature of the surface where the dust settles must in any case be lower than 75°C.
- The machine must be designed in such a way that the possibility of dust accumulation is reduced.
- Before putting the machine into operation, it is necessary to set the correct water level in the dust collector and set both indicators with the instrument for measuring flows and negative pressures.
Protection with active elements
Active elements include elements that, based on a sensor signal, trigger a certain function of protecting the working device.
- Protection with temperature or pressure sensors and fire extinguishers or explosion suppressors.
For more information, contact us at marketing@gostol-tst.eu.
