Cooling in harsh environments with 'Enviro-shield'
Robin Cook explains how fans can be protected for long life even in the
harshest of environments
With today's modern electronics systems, protecting fans and blowers
against harsh environments is more important than ever before.
Miniaturisation means that portable equipment has become increasingly
complex and powerful and so more sophisticated systems can now be used on
site, on the shop floor and in the field where they are often subjected
to the vagaries of the weather, wide temperature fluctuations, airborne
contaminants and transportation shocks.
These developments have prompted a major USA manufacturer of fan and
blower based thermal management solutions, Comair Rotron, to introduce a
three-tier system of protection known as 'Enviro-shield', which provides
environmental integrity up to IP65. Protection to at least IP56 is
available across all fan sizes from 60mm to 255mm in diameter and in all
voltages.
Standard fans normally conform to IP24, but any improvement in the level
of protection will dramatically increase product life as it eliminates
electrophoretic corrosion, an inevitable consequence of moisture and dust
invasion, which will ultimately cause fan failure. In addition, the
fundamental processes of environmental protection are to spray or
encapsulate with a silicone material that is non-corrosive, fungus
resistant and has elastomer properties that increases the fan's
resistance to vibration and shock.
Three levels of protection are offered to cater for different
applications. With Type 1, the basic level, a thin silicone coating is
sprayed over the complete motor assembly, including the motor winding,
lamination stack and circuit board. This caters for mildly harsh
environmental conditions such as the occasional spray of water to the
fan, exposure to fine dust particles, morning dew that may condense
inside the fan and similar conditions.
Type 2 level involves applying Type 1 material to the motor winding and
lamination stack and a thicker silicone coating to the motor assembly.
The circuit board is dipped, dried and then dipped again into a heavier
grade of silicone. This thick barrier gives added protection especially
over sharp edges such as solder points. The Type 2 level is designed to
meet harsher environmental conditions including the direct or indirect
spray of water onto the fan and the long term exposure to salt spray and
salt fog.
The highest grade of protection is Type 3, where the complete motor
assembly and circuit board is placed into a mould into which the heavy
grade silicone is poured and then vibrated to release any air bubbles
that may be trapped. In addition, the total encapsulation process ensures
the highest possible levels of protection against shock and vibration.
During development the results were rigorously checked using accelerated
life testing in a salt fog chamber and although there is a cost penalty
to provide extra protection, this is comparatively small when compared
with product life savings and the reduction in repair bills.
'Enviro-shield' fans are already successfully employed by a number of
companies including Ericsson Microwave for outside cabinets in
telecommunication systems and Atlet AB where they are used to solve
thermal shock problems encountered in fork-lift trucks that are
continually moving in and out of cold storage rooms.
Comair Rotron fans and blowers are available in the UK from Aerco