|
 
| Internal
Bubble Cooling Pressure Blowers |
|
For
an internal bubble cooling (IBC) control system to function,
there has to be forced movement of cold air into the bubble
and hot air out of the bubble. This is done with high pressure
blowers like the one shown.
For maximum possible air exchange rate the blowers must be
properly sized based on the physical dimensions of the air
flow passageways, the die diameter, and the maximum required
volume. If the IBC blowers are not sized properly, loss in
potential production rate will be the result.
|
|
| Typical
Arrangement 4 Pressure Blower Courtesy of New York Blower Company |
| Each
of the elements (flow, pressure and horsepower) are described
below. To provide optimum control of the flow rates, DRJ recommends
the use of variable
speed drives. Two added benefits of using variable
speed drives include improved electrical efficiency and reduced
noise levels when not running at maximum speed. The ABB
version of the IBC system provided by DRJ uses a
variable speed drive on blower drives to provide easy operator
adjustment of the cooling flow rate and to allow automatic balancing. |
| Flow
(Volume) |
Pressure
(Static) |
HorsePower |
| This
is the first element that must be specified when sizing a blower.
The flow required for internal cooling varies from extrusion
line to extrusion line. In general, the larger the line the
more flow is required. Many extrusion manufacturers use a simple
rule of thumb to of 75-100 cubic feet per minute per inch of
die diameter. |
After
the flow value is derived, the static pressure required to produce
that flow must be calculated. To do this properly, DRJ uses
proprietary software that calculates the velocity pressure and
friction losses through any style blown film die. In addition,
the air temperature and elevation above seal level must also
be considered to account for air density, which affects pressure
and power requirements. |
Once
the flow and pressure are derived, the blower wheel diameter,
width and horsepower are calculated. One of the most common
misconceptions is that more horsepower means more flow. Without
added pressure (which comes from a combination of wheel diameter
and wheel speed), there is no additional flow. Also, there is
a physical limit to the amount of air that can pass through
a given area. |
| |
|
|
