Metal spraying boxes and chambers
Our company produces and delivers metal spraying boxes and chambers, including complete accessory equipment. Boxes and chambers are intended for anticorrosive, decorative, and restorative metal spraying processes.
Following the application type, and based on required operating performance, the boxes and chambers are equipped with a gas metal spraying gun or electro-arc metal spray equipments (see Electro-arc metal spray equipments).
For decorative and restorative metal spraying (e.g. bronze, molybdenum, brass, copper, and stainless steel) the boxes and chambers are equipped with standard dry dust collectors for collecting metallic dusts that are inflammable, tack free, and that do not create an explosive mixture when mixed with air (see Dust collectors above 2000).
For anticorrosive metal spraying (Zn, Zn Al 85/15, Al), the boxes and chambers are equipped with dry dust collectors. These are adjusted for collecting flammable or explosive dust, i.e. with a stronger body construction of the collector; and antistatic version of filtering cartridges. According to the position of the collector and air induction piping distance, a clap valve can be fitted on the piping system to prevent fire back flashing when the dust in the collector burns back into the box or chamber.
Further, the dust collectors are equipped with either explosion valves for releasing explosion pressure or automatic self-extinguishing equipment/system for explosion suppression.
When the explosion suppression system is activated, the dust collector control unit records an increase in pressure and temperature; it eliminates the explosion by releasing an extinguishing agent. Owing to this system, the unit does not need to be equipped with explosion valves and a clap valve. Furthermore, in case of an explosion, the inner equipment of the unit is not damaged. The filtering cartridges are often undamaged as well.
In the Czech Republic, handling dangerous materials is controlled by government regulation no. 23/2003 of the law code. It sets minimum technical requirements for both equipment and safety systems intended for use in environments where there is an explosion risk, as amended by government regulation no. 286/2000 of the law code. This government regulation includes (or copies) European regulation 94/9/EC or ATEX 100a. Work safety requirement concerning working with equipment and system in an explosive environment are given by European regulation ATEX 137, in the Czech Republic this is represented by GOVERNMENT REGULATION no. 406/2004 of the law code. It is an amendment of law no. 65/1965 of the law code, Labour Code, as amended by law no. 155/2000 of the law code. In the CR, ATEX 100 is valid from 01.07.2003. ATEX 137 is valid from 01.09.2004.
According to the BGIA guide, for example, zinc dust produced during plasma spraying is explosive at the grain medium size of 40um. St 1 category classification.
Surface pre-treatment
Before zinc (aluminium) metal spraying with electro-arc metal spray equipments, the surface of the treated components must be clear of all grease and oils, and it must be blasted to reach the surface cleanliness Sa 2.5 to 3 (Sa 3), following the ČSN ISO 8501.
In order to retain a quality zinc (aluminium) coating of ca 100 um, the blasted surface should have the surface roughness of Ramin = 4 um – we recommend 10 um (Ramin. = 6 um – we recommend 12 um ) and Rmmin.= 25 um – we recommend 60 um (Rmmin.= 35 um – we recommend 80 um).
The above mentioned roughness figures can only be accomplished when blasting with grit abrasive.
Selected references
Elektrizace Železnic Praha a.s.
place of realization: station Vlkov
application: aluminium anticorrosive surface treatment of column footings
application: an automatic line for aluminium anticorrosive surface treatment of columns (see Electro-arc metal spray equipments)
OMC Scientific Czech, s.r.o., Louny
application: high roughness functional aluminium coatings
ON Semiconductor Czech Republik, s.r.o., Rožnov pod Radhoštem
application: high roughness functional aluminium coatings
ArcelorMittal Poland S.A., Katowice
application: applying functional coatings to a pipe production line guide rollers.