Manufacturer of I.D.
blowers, F.D. blowers, force draft fans, force draft blowers, blow off
ventilators / fans, PVC FRP SST ventilators, squirrel cage blower fans,
high pressure centrifugal ventilators, Chicago blowers, aluminum fans,
stainless steel ventilators, hot air blowers, heating fans, high
temperature oven ventilators, high pressure air blowers, squirrel cage
blower wheels, Peerless Dayton ventilators, Sheldons blowers, New York
fans NYB, TCF, Delhi fans blowers. Industriall fans and blowers
engineering sales, roof and wall air make up and exhaust fan
ventilators, high temperature pressure blowers and high capacity
centrifugal and axial blowers, fans and high CFM ventilators.
Large Industrial Fans, Blowers, Ventilators
Designers and manufacturers of industrial process air handling systems,
blow-off air-knives, dust collectors, wet air scrubbers, industrial
process air curtains and vacuum systems. Sales of packaged dust
collectors, fans, blowers and air knives.
Sales of big industrial process and OEM fans, blowers and ventilators,
high temperature oven fans and pressure blowers. Supply of centrifugal
and axial fans, radial blowers, tubeaxial and vaneaxial ventilators,
roof and wall exhaust and supply fan ventilators, airfoil and backward
inclined scroll cage blowers and fan wheel blades.
When fans are exposed to elevated temperatures, many aspects of the fan
design must be reviewed to make sure the fan will withstand the extreme
temperatures and that the fan is appropriately designed for the
application. The fan engineer must understand the limitations of
materials and various failure mechanisms, such as high stress, stress
to rupture, and creep. Sometimes, it is necessary to consider high
cycle fatigue, low cycle fatigue in cyclical operation with speed
changes, and numerous start-stop cycles. If rapid temperature changes
are encountered, transient analysis may be required due to thermal
stresses. Depending on the exposed temperature levels, the following
are to be considered:
• Materials of construction for the wheel, shaft, and hub
• Wheel to hub attachment
• Materials of construction for the housing including insulation
• Bearings and lubrication
• Shaft seals
• Shaft cooling (air-cooled, water-cooled, etc.)
Limits on the operating temperature for standard fans are defined by
the arrangement of the fan. For example, the maximum temperature for a
standard fan that does not have a bearing in the airstream can run up
to 300°F. For standard fans that have a bearing in the airstream,
the maximum operating temperature is limited to the maximum temperature
that the bearing can handle, which is typically about 130°F.
Carbon steel, low alloy high strength steels, and chrome moly steels
are satisfactory for a temperature range of 900° to 1000°F,
depending on stress levels. Heat resistant alloys such as stainless
steels (304, 316, 347), Incalloy 800HT, 230, Inconel (600, 625, 617),
Multimet, Haynes 25, etc. should be used for higher temperatures up to
1800°F. Again, the material chosen also depends on the stress
levels and the material properties at elevated temperatures.
Temperature derates lower the maximum speed of a wheel to account for
the lower material strength at elevated temperatures. The wheel must
sustain the highest stress of all the fan components. It is very
important that the material used on the wheel is strong enough to
handle the stress at high temperatures. At higher temperatures,
material eep must be considered.
Bearings usually require high temperature lubricants and sometimes
circulating oil or static oil in a monoblock. Bearings can be kept cool
in high temperature applications by using a shaft cooler and a shaft
seal. For higher temperature fans, water cooling can be used to cool
the shaft. In this case, the fan should be belt driven in order to
install a rotating union to circulate the water over the shaft.
Bearings should be kept out of a high temperature airstream and should
never run in air temperatures hotter than 130°F. The inboard
bearing, which is the bearing nearest the fan housing, should be moved
away from the fan housing to create some space for the heat to
dissipate. The space created between the inboard bearing and the fan
housing allows for the use of a shaft cooler and shaft seal. Bearing
temperatures should be monitored and should not be allowed to exceed
200°F at speeds higher than 2500 RPM and 220°F at speeds below
2500 RPM. Bearings should be selected to allow for free movement of the
shaft lengthwise due to temperature changes. One bearing should be
fixed, serving as an anchor bearing to locate the shaft lengthwise. The
bearing closest to the drive end is normally fixed. All other bearings
should be expansion bearings to permit the shaft to move lengthwise.
The thermal growth of the shaft may limit the bearing used.
A shaft cooler is a small fan that clamps on the shaft between the fan
housing and the inboard bearing. The shaft cooler draws cool air over
the shaft and bearings as the shaft rotates to dissipate the heat. A
shaft cooler is recommended for all applications over 300°F.
Generally, the pedestal must be modified to allow room for the shaft
cooler. This will increase the distance between the inboard bearing and
the wheel. This dimension, referred to as the overhang dimension, is
critical in determining the safe speed of the shaft. As the overhang
dimension is increased, the shaft safe speed becomes lower. During
maintenance repairs, it is very important that the overhang dimension
is never increased. When the temperature exceeds 800°F, it is
necessary to separate the fan pedestal from the fan housing. By doing
this, the amount of heat conducted through the pedestal and to the
bearings and motor is greatly reduced.
For housing material, carbon steels are satisfactory for temperatures
up to 800°F and Corten is often used for temperatures up to
1000°F. For higher temperatures, stainless steels and Inconel may
be required. A customer may want to keep the heat of the airstream from
heating up the fan housing and radiating out to the surrounding area.
Insulating the fan accomplishes this. There a few ways to insulate a
fan, but the main idea is to create a second fan housing offset from
the main fan housing and then fill the gap between the two with
insulation. It is common to have 2" - 6" of insulation depending on the
temperature of the airstream and the need for the outer skin to be
cool. For fans that require an access door and also have an insulated
housing, the access door is raised from the fan housing to the outer
insulation skin by building a box between the two housings.
Up to this point, the discussion has centered on centrifugal fans. It
should be mentioned that there are a few modifications that are
specific to axial fans. Standard axial fans are good to 200°F. By
moving the bearing housing upstream of the wheel, opening the bearing
housing to the wheel, and by adding a cooling wheel to the shaft to
pull cool air over the shaft and bearings, the maximum operating
temperature goes up to 300°F. With a change of wheel material to
aluminum A240, some axial fans can be made to run in temperatures as
high as 600°F.
When a fan is installed in a high temperature application, it is
important for the engineer to properly design the components of the
fan. This includes, but is not limited to, the wheel, shaft, bearings,
and housing. The wheel material should be selected to provide adequate
strength at the elevated temperature. The shaft and bearings may
require a cooling system or other means to keep them from overheating.
The bearings should have proper lubrication that can handle the higher
operating temperatures. Sometimes an insulated housing should be
manufactured to keep the heat from radiating out to the surroundings of
the fan. High temperature fans, if designed properly, can provide years
of dependable service.
