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Public Lab Research note

Making a balloon-making jig

by mathew | May 18, 2012 19:33 18 May 19:33 | #2135 | #2135

We haven't had much luck finding someone willing to manufacture mylar balloons bigger than 1 meter (3 feet). Which got me thinking about how to manufacture balloons myself.

I've done a lot of plastic heat seaming with an iron, but find the results with helium-resistant laminated foils not really flight-grade. I get good seams on thin polyethylene and that's about it.

The highest quality seams are made with a bag sealer because with a bag sealer, the plastic is held perfectly still through the heating and cooling process. The professional equipment is the same and hasn't changed much in the past 100 years-- heat welding rubber or plastic is done with a gigantic, shaped bag sealer.

materials inside a bag sealer

The heating element is nichrome wire. covered in a sheet of PTFE (teflon). The plastic is pressed down against the heating element with high-temperature silicone, and the nichrome wire controlled by a simple timed on/off circuit. These products aren't too expensive from McMaster-Carr: Nichrome Wire-wire/=hlaehj) Conformable PTFE Tape Extreme Temperature Silicone-Backed Rubber Strips

To do more precision heating, a temperature control unit should be added. This could be a DIY setup with an arduino, a thermocouple, and a solid-state relay, but there are also commercial units that are quite affordable: digital temperature controller and another

thermocouples that can squeeze next to nichrome

making a curved jig

the bag sealer is easy because the heating element is straight. Nichrome wire needs to be handled gently while heating, and keeping it in a smooth curve (like we want for balloon making) is potentially problematic. My speculation is that it can be embedded into a routed channel in some material like MDF, so long as it is protected by more PTFE tape on both sides of the channel. I'm going to try this out.

Plastics that can be used

Mylar is not a thermoplastic, but laminated mylar(usually with LDPE) will work. EVOH does as well but is finicky about heat. Both of these are purchasable from Gary at balloonkits. Gary also sells reusable balloon valves that can be heat seamed in.


Why not make a long rectangle? Straight edges and it might lend some stability to the camera if rigged right. Also, it seems that there would be glues that are strong and fast drying and even available in tape form.. 3m adhesive tapes

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from a construction standpoint you're certainly right, a rectangle would be easier-- but for legal reasons we have to keep the balloon less than 6' long. A 6' rectangle won't hold much gas unless its fairly square.

also, a rectangle is an unstable balloon shape, a circle is much more structurally sound.

carefully taped seams can be air tight with special care, but I don't recommend that as a balloon seaming method. it gets especially hard when the seam is longer than can easily be done with one piece of tape (about 3'), and the corners are especially difficult.

Glues don't work very well on plastic films. 3M makes a good epoxy for the purpose but it is very, very pricy.

ultimately the goal here is to make a whole lot of balloons, not a one-off. The jig, if it works, will be well worth the time.

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