Hi All,
Worth a read if you have 10 minutes, this describes the 'old fashioned' method of RF sealing, Greenseal is much better, utilising solid-state devices, rather than oscillator tubes, therefore making it more controllable, thinner welds, tighter welds, and less electricity per weld. The other advantages mentioned on this page, also apply to Greenseal .... note that ultrasonic and induction are nowhere near as good as old-RF, let alone Greenseal ....
http://www.devicelink.com/mddi/archive/99/12/003.html
In fact I will just edit in this bit, as it stuffs ii's drivel completely :))))
"Other methods, such as thermal, impulse (a switched thermal), or ultrasonic sealing, do not share this advantage. For example, temperature profiles taken during thermal and impulse processing indicate that the hottest spot is where the dies touch the outside of each layer of plastica condition that often causes degradation of the outside of each layer before the interface reaches melt temperature. (Thermal and impulse sealing functions best with certain very thin [<0.006 in.] films and with polyethylene, polypropylene, or polystyrene.) Ultrasonics, on the other hand, works like a jackhammer, pounding the plastic from 20,000 to 40,000 times per second, with the resulting friction creating heat and thus melting the plastic. Again, the temperature profile is less desirable than that with RF. These alternative processes are limited in area of seal, lack repeatability of acceptable seal quality, and do not have the ability to produce tear seals. They are often employed in small-area spot sealing or in applications for which product appearance is not important, such as polybagging or tack sealing to locate parts. "
Cheers,
PM