duminică, 6 noiembrie 2011


Chapter I

General technical information fans

An external rotor motor is essentially constructed like a normal non synchronous motor,with ane difference : the ststor and the rotor have swapped ploaces. The stator with its windings is at the centre of the motor while the rotor is located is the casing itself.The motor shaft connected to the rotor turns on sealed ball bearings inside the stator and the impeller or fan blades are fitted to the rotor casing .With this design the rotor and fan form a compact unit at the centre of the air stream.Because the external rotor motor”s unique construction allows it to be cooled by the transported air the motor speed can be controlled by voltage regulation.

Most of the fans have an cuter casing made of hot - rolled galvanised sheet complying with with EN 10n142/10 147.The sheet steel has a layer of 20 μm zinc which provides excellent protection against corrosion.The galvanised sheet - metal parts are either spot –welded screwed or riveted together.
Fans with powder - coated surfaces are well protected against corrosions.The powder coating in at least 40 μm thick and produces a hard and impact resistant surface.To avoid environmental poliution ,no solvents are used at the Systemair powder-coating plant.

The material used in out insulated fans is water-repellent non-capillary mineral wool whose stability is unaffected by steam and moisture. The insulation is classified as noncombustible material which tolerates 200ºC.

Motors and impellers
The direction of rotation for three-phase fans is indicated by an arrow on the motor housing .
Fans with forward curved impellers are manufactured from galvanized sheet steel.
Backward - curved impellers have polyamid or galvanised steel plate blades.These blades are mounted on a galvanized steel plate.
The impellers are press-fited directly onto the rotor of the external rotor motor.
The motor complete with impeller is balanced dynamically in two planes in accordance with DIN ISO 1940.

The rotor”s ball bearings are completely maintenance - free and can be used in any installation position at the maximum indicated temperature for transported air.
At a 40ºC ambient temperature for transported air,the life expectancy of the bearings is at least 40.000hours.Low ambient temperature is not a problem for the motor ball bearings if the fan is operating .The reason in the 60÷90K temperature increase inside the motor during operation.

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