What about building some kind of ultrasonic welding tool? You could build something with a small tip and surrounded by a collar. The tip would stick out only a very short way past the collar so that when you press down on two sheets the tip would only be able to dig in a short way. The collar would stop it going in too deep and cutting the sheet. It would only melt where you supply adiquate pressure between the tip and the platic and the pressure would drop off as the tip digs into the platic and the collar comes into play. Regards Sergio Masci http://www.xcprod.com/titan/XCSB - optimising PIC compiler ----- Original Message ----- From: Russell McMahon To: Sent: Thursday, June 17, 2004 3:22 AM Subject: [EE]: Queries re heat sealing polythene sheet > Summary: Looking for information on heat sealing polythene sheets together: > > I wish to heat join polythene (polyethylene) flexible sheet - similar to > standard plastic bags but thicker. > My application is the (very) experimental fabrication of an > air-solar-heating envelope ** using clear plastic sheet as the top layer and > black plastic as the bottom. I'm using 250 micron plastic, which is > considerably stiffer than standard plastic bags (which are perhaps 50 to 100 > micron) but is still very flexible. > > I want to seal the edges of a rectangular "bag" completely reliably so that > it neither leaks or separates accidentally. > My trial bag is 1.5m x 4m and my final target bags are about 4m x 5m. > > You can buy small thermal sealers for a few dollars which are meant for heat > sealing plastic bags for eg food storage. I believe and am told that these > are too low powered for what I want to do. They have a heated element on one > side and two ?Teflon (= PTFE) coated jaws which grip the plastic as you > slide the sealer across the bag. I do not have one to hand at present but > recall that they work OK once you establish a considerable knack for best > speed of travel. Factors include plastic thickness and exact makeup. > > Commercial "pulse" units are not useful as they are intended for a fixed > width of plastic - eg a relatively small bag. > > You can buy commercial continuous units which would probably work well. > Typical units use hot air applied at a number of points, rollers or feed > belts and multiple PID temperature controllers.They melt a zone of plastic > which is then compressed and cooled. Such a machine would probably be ideal > but I have no access to one and the price is extremely unattractive for > "playing". > > My experiments with a soldering iron at various temperatures are not > promising. One can achieve a good weld but with cutting of the sheet or only > partial (or no) sealing. I'm probably going to have to go to something which > at least crudely approximates the commercial machines operation. Perhaps a > small sealer with a heater element running on speed*. > > I could attempt gluing/sealing (maybe silicon rubber) but this is an > unattractive alternative and polythene is an extremely difficult plastic to > deal with. > > I'd welcome any comment from people who have had experience in this area. > > > > > Russell McMahon > > > > > * cf Niven-Pournells "Legacy of Heorot" - marvellous story. > > ** I'm aware of the issues of mechanical strength, UV lifetime etc. > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics