Blown Film Extrusion Internal Bubble Cooling and Non-IBC

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.