Description
Depending on the type of application and on the basis of the required work performance, boxes and cabins are equipped with anti-corrosion or renovation electric arc coating (metallization) equipment (see Arc spraying equipment M45).
For decorative and renovation metallization (e.g. bronze, molybdenum, brass, copper, stainless steel), boxes and cabins are equipped with standard dry dust separators for the separation of metal dust, which are non-flammable, non-sticky and do not form an explosive mixture with air (see Dust separators).
For anti-corrosion metallization (Zn, ZnAl 85/15, Al), boxes and cabins are equipped with dry dust separators, which are designed to separate flammable or explosive powders, i.e. reinforced structure of the separator body, filter cartridges in an antistatic design, depending on the location of the separator and the distance of the intake air duct, the pipe system can be fitted with a non-return valve to prevent the flame from “whipping” back when the dust in the separator is ignited back into the box or cabins.
In addition, the dust separators are equipped with explosion membranes to release the explosion pressure or an automatic self-extinguishing device or explosion suppression system.
When the explosion suppression system is activated, the control unit of the dust separator registers an increase in pressure and temperature, and by injecting a fire extinguisher, it eliminates the explosion before it develops. Thanks to this system, the unit does not need to be equipped with explosion membranes and a check valve. Furthermore, in the event of an explosion, the internal equipment of the unit and mostly the filter cartridges are not damaged.
Working with hazardous materials is determined by Government Regulation no. 23/2003 Coll., which establishes min. technical requirements for equipment and protective systems intended for use in an environment with a risk of explosion, as amended by Government Regulation no. 286/2000 Coll. This Government Regulation contains (“copies”) the European Directive 94/9/EC, or ATEX 100a.
The requirements for safety when working with devices and systems in an explosive environment are determined by the European directive ATEX 137, in the Czech version Government Regulation no. 406/2004 Coll.
ATTENTION!!! According to the BGIA manual, zinc dust produced during thermal spraying is explosive at an average grain size of 40 mm, it is classified in the St 1 category (with electrometalization, the average grain size is even lower).
Surface preparation
The surface of the treated parts before hot spraying of zinc (aluminum) carried out by electric arc spraying equipment must be free of all grease and oil and must be blasted to a surface cleanliness of Sa 2.5 to 3 (Sa 3) according to ČSN ISO 8501. The blasted surface should be (aluminum) coating with a thickness of approx. 100 µm should have the surface roughness of Ramin. = 4 µm – we recommend 10 µm (Ramin. = 6 µm – we recommend 12 µm ) and Rmmin.= 25 µm – we recommend 60 µm (Rmin.= 35 µm – we recommend 80 µm).
The above-mentioned roughness value can only be achieved by blasting with a sharp-edged abrasive.