Magnesium Alloy Plant Anti-corrosion Centrifugal Fan

Overview

Magnesium alloy melting and refining uses fluxes such as MgCl2, KCl, BaCl2 and CaF2, so the exhaust carries both chloride and fluoride compounds. Where these occur together, ordinary stainless steel fails through chloride pitting and the material scheme has to be chosen for combined chloride and fluoride service.

Material Selection by Medium Composition

Attack comes from chloride and fluoride bearing dust and from fumes released when the flux is heated.

Location	Material / process	Basis
Impeller	FRP or PVDF lined impeller	Resists chloride and fluoride bearing dust
Casing	FRP with reinforced lining	Easy to form for large and irregular parts
Shaft	Duplex 2205 or sheathed 316L	Better chloride pitting resistance
Sealing	PTFE or fluoroelastomer seal set	Keeps dust out of the bearings
Lining anchors	Stiffeners with anchors	Prevents the lining detaching under dust laden flow

Construction and Operating Measures

Location	Material / process	Basis
Dust pre-separation	Pre-separator or settling section ahead of the fan	Reduces impeller wear and deposit build up
Anti-sediment design	Sloping casing floor with dust outlet	Limits accumulation and caking
Equipotential earthing	Casing, impeller and duct bonded and earthed	Controls static build up
Inspection openings	Removable covers on casing and inlet	Allows lining and impeller inspection
Wash down	Periodic washing and drying of the interior	Reduces attack after chlorides absorb moisture

Applications

Applications include magnesium melting and refining furnace exhaust, die casting shop ventilation, flux conveying dust collection and magnesium dust collection.

Magnesium dust is combustible, so the dust collection system also has to meet dust ignition protection requirements and both aspects must be designed together.

Where SF6 or SO2 protective gas is also used, the gas composition becomes more complex and the material and sealing scheme has to be reviewed for the actual composition.

Acceptance and Verification

Standard	Title	Purpose
HG/T 20679	Design code for external anti-corrosion of chemical equipment and piping	Anti-corrosion design for chemical media
GB/T 3854	Barcol hardness test for reinforced plastics	Hardness acceptance of FRP parts
GB 12476.1	Electrical apparatus for use in the presence of combustible dust - Part 1: General requirements	General requirements for dust ignition protected equipment
GB/T 1236	Industrial fans - Performance testing using standardized airways	Air flow, pressure and efficiency testing
GB/T 9239.1 / ISO 21940-11	Mechanical vibration - Balance quality requirements for rigid rotors	Impeller balancing grade

Please provide the medium composition, dust concentration, medium temperature and air flow. Size and motor power are calculated for the actual duty.

FAQ

Why is ordinary stainless steel not used in a magnesium shop?

Chloride dust releases chloride ions when it absorbs moisture, which breaks the passive film and causes pitting; fluorides also attack some grades. FRP and PVDF are therefore common, and metal parts tend towards duplex grades with better pitting resistance.

Does magnesium dust require explosion protection?

Yes. Magnesium dust is combustible, so the exhaust and dust collection system has to be designed for dust ignition protection, including motor selection, earthing and anti-sediment construction. The specific rating depends on the dust characteristics.

How can lining life be managed?

Lining life depends on dust concentration, moisture and the number of starts. Setting a replacement interval from visual inspection and thickness measurement during the first year is more reliable than assuming a fixed life, with anchors and welds checked first.

Related pages: Anti-corrosion fan range  Explosion proof fan range  Rubber and plastic lined fan