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I am working on a 50-micron BO-PET film (basically Mylar) which will need welding. I don't know if I'll be able to obtain an ultrasonic/HF welding machine and since the project will need extensive low-cost prototyping, I found that it has many things in common with the Echo I, II balloons. I know that the Echo I seams were bonded with an adhesive, whilst the Echo II seams were heat welded. But I wasn't able to find technical details on these two processes. I would be interested in replicating them, especially the heat welding part.

Does anyone have any in-depth info about this?

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  • $\begingroup$ Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. $\endgroup$
    – Community Bot
    Mar 28, 2023 at 12:37
  • $\begingroup$ I was mainly interested in finding heat welding methods and relative relevant parameters to weld BO-PET on BO-PET. And it would have been very interesting to see how they did that as they probably used more archaic methods. I will probably have to use similar archaic methods. Consider I have to do almost the same thing, welding parts of a balloon. $\endgroup$
    – Gianf DS
    Mar 28, 2023 at 13:34

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NTRS has Development of the fabrication and packaging techniques for the Echo II SATELLITE (I've finally started to learn from Organic Marble to check NTRS early), which is extremely detailed. Though I'm only skimming it, I believe section 3.6 "Gore Sealing" (starting on page 75 of the PDF / page 3-53) indicates that the gores were machine-sealed together using a sealing tape with an adhesive called "GT-301" at sealing temperatures of 300${}^\circ$F at a rate of 6 feet per minute. See particularly section 3.6.2.4 and Figs 3-29, 3-31. Section 3.9 indicates the "electrical continuity jumper strip" was installed with "a Gulton ultrasonic sealer, electronically and pneumatically operated"; Section 3.10 indicates the pole caps were also "attached to the sphere with GT-301 heat sealable adhesive." See Fig 3-37 for views of all the seals, despite its title.

Fig 3-31 "Rigid Sealing Rail", a cross-section diagram showing top-to-bottom the sealing wheel, sealing tape, gore edges, tacking tape, rubber surface and aluminum channel rail

crop from Fig 3-37 showing the gore seal and polar cap seals

The second picture is cropped from Fig 3-37.

Before finding that report, I was going to leave a slightly impoverished version of the following as a comment on the question but it seems at more constructive to leave these here instead:

  • Amusing Planet and SP-4308 indicate that the Echo I adhesive is owed to Gilmore Schjeldahl, and the Echo II report linked above says the GT 301 used for both lamination and gore sealing is also "a proprietary item of the G. T. Schjeldahl Co" (section 3.1.4).

  • BBBlimp and RCGroups appear to prefer adhesives to heat; so far, I've only found food bloggers sealing mylar with heat happily.

Good luck with your seals!

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PET melts at 250C and decomposes at 350C So the welding temperature would need to be within that range. https://en.wikipedia.org/wiki/Polyethylene_terephthalate

I've seen PVC welded using a heated Teflon block to apply heat. (Teflon melts at 325C).

There are sealers which heat with closely spaced aluminum blocks. The film is drawn through the space between the blocks, then pressed together with rollers. enter image description here

Or there is a one-sided heated roller which offers less control.enter image description here

Reliable welds are dependent on uniformity of time, temperature and pressure parameters. What design of seams are you using and what are you making?

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  • $\begingroup$ Thank you and sorry for late reply. I've been absorbed by other things and wanted to review this matter with much attention. I can't disclose the nature of the project unfortunately. But consider it's some kind of helium balloon with geometry slightly different than spherical. The balloon is subject to high mechanical stress. The seams should be welded in shear lap configuration for better strength. Theoretically speaking perfect butt joints with perfect polymer interdiffusion would yield the highest strength, but considering the thickness of the film I highly doubt the butt joint is doable. $\endgroup$
    – Gianf DS
    Apr 21, 2023 at 13:04

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