A combination air knife and soft box attachment pins the web to the chill roll immediately after it exits the die?handling a range of CPP film thicknesses and reportedly reducing downtime for product changeover. Cast polypropylene film lines typically use either an air knife or a soft box because each handles different ranges of web thickness.An air knife expels air in a concentrated stream at high velocity. Its power makes it effective with webs of 30 µm or more in thickness. A soft box usually has a screened opening that expels a higher volume of air at lower velocity and over a wider area of the web than an air knife. It works best with films that are less than 30 µm thick.
The air knife/soft box combo handles a web thickness range of 20 to 150 µm. The design consists of an air knife mounted on top of the soft box. The component is attached in the same general area as a conventional air knife or soft box between the die and chill roll. To adjust the flow of air for a product change, the processor can make a mechanical adjustment to the component and index the correct side into place. The air knife/soft box unit does not have to be removed, eliminating the downtime associated with disconnecting one device and installing the other.
The first air knife/soft box component was installed on a Battenfeld Gloucester CPP line in the People's Republic of China late in 2003. The device is available for sale on new lines or for retrofit worldwide.
SMS Plastics Technology, Gloucester, MA
(978) 282-9268; www.bge.battenfeld.com
