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• Custom Balloon

  xdylanm • 10/29/2022 at 01:07 • 0 comments

  After some additional research & experimentation, I have a method to make and fill a custom helium balloon. 

  Background

  After some initial exploration, it appeared that "foil" helium balloons are the best choice for a lifting body. The balloon envelope is made of a lightweight, low-stretch plastic and they can hold helium for a couple of days. However, after a lot of research, it was very difficult to track down the exact material that foil balloons are made from. A few resources that I found had limited information:

  • https://www.ehow.com/how_7540897_create-own-foil-balloons.html
    
  • https://www.quora.com/Whats-a-foil-balloon-made-from
    

  There were also a few trade sites that provide some details, but some of the information was inconsistent. As far as I can tell,

  • Mylar (which is biaxially oriented PET or BoPET) is/was(?) used as a substrate, but maybe polypropylene (BOPP) or nylon is more common now
  • It is usually metallized with e.g. aluminium to reduce its permeability to gas 
  • One of the plastics involved needs to be a thermoplastic for heat sealing

  On the last point, PET appears to be a thermoset plastic, which would make it unsuitable on its own for balloons. If anyone reading this knows more about these materials, I would be very curious to learn more.

  Heat Sealing

  Previously, I tried using the material from an emergency blanket (which should be metallized BoPET, maybe?). The dollar store blankets appeared to be ideal, but they do not heat seal -- don't use those. I tried both a soldering iron at various temperatures and a heat sealer (i.e. a nichrome wire with a PTFE tape over it -- a future project if I ever need to make more than a few of these).

  I bought a few foil balloons and cut those up. They seal well with both the heat sealer & soldering iron, so that suggested it was a material issue. For 4x the cost, MEC sells a polypropylene emergency blanket with foil on one side, so I tried that: success! The non-foil side heat seals well with both the soldering iron & heat sealer (foil to foil & foil to non-foil does NOT seal).
  

  Some notes for heat sealing:

  • Using the heat sealer makes the best seams. Adjust the heating time to ensure a good seal without too much distortion.
  • Using a soldering iron with a large flat tip works, but tends to apply too much heat, which results in distortion and occasionally in some tears. Use a piece of parchment paper between the tip of the soldering iron and the plastic.

  Valves

  Helium balloons have a clever one-way valve system made from two layers of plastic that collapse on themselves when not held open by a nozzle/straw. [Make Things Fly] has a nice video where he deconstructs a balloon and illustrates this part.

  To make a custom valve, I found that you can use the material from a ziploc freezer bag (regular ziploc bags work fine, but the freezer bag material is a bit heavier). This is also a thermoplastic, and will heat seal to the polypropylene side of the emergency blanket. Construction is a bit involved

  1. Cut two strips 2-3cm wide, 15-20cm long
  2. Lay the strips on top of one another (making 2 layers). Heat seal the edges of the strips from the mid-point to the end. That end will be the opening of the valve inside the balloon.
  3. At the mid-point, fold back one layer of plastic so that it won't be subjected to heating. Place the other on the PP side of the balloon material where you want your valve and heat seal across the strip to fix it to the balloon envelope
  4. Repeat on the other side, again folding back the opposite side so that you're just attaching the valve to the balloon envelope.
  5. Cut back one layer of the valve material below the horizontal weld. The remaining layer will be a backing to guide the fill nozzle into the valve.
  6. Lay the strips of valve plastic on one another at the outlet area (now there are four layers: balloon-valve-valve-balloon). Heat seal through the balloon envelope along the edge of the valve to fix the valve in place and couple it to the envelope while closing...

  Read more »

• Helium

  xdylanm • 10/08/2022 at 15:07 • 0 comments

  Originally, I had assumed that difficulties finding a reliable source of helium would preclude using it as a lifting gas. It turns out that this is not the case: you can usually purchase small helium tanks for balloons at a party supply store (e.g. a Michael's or Party Time where I live). The current cost is approximately $4/cu ft. at retail. 3 cu ft. is roughly equivalent to 85L. The helium supplied this way is mixed with air: "at least 80% helium" (presumably 80% then...). This will reduce the buoyant force accordingly. As a next step, I'll call around to see if industrial gas suppliers can provide tanks at a better cost. In the meantime, I still haven't figured out how to heat seal seams in those foil space blankets.
  

• H2 Production - Experiment 1

  xdylanm • 09/18/2022 at 01:17 • 0 comments

  
  

  Materials

  • Balloon (a helium party balloon - unfilled - from the dollar store)
    
    • mass: 10g
    • diameter (uninflated): 440mm
    • approximate volume: 10L
  • NaOH: 11g
  • Al foil: 8g

  Expecting loss in H2, double amounts of NaOH & Al.

  Procedure

  • Fill water jug (bubbler) with water; leave 3cm air at top
  • Fill flask with 500mL warm water
  • Add 22g NaOH and dissolve
  • Add 1-2g crumpled sheets of Al * Collect gas in balloon

  Note: the procedure closely follows the approach demonstrated in NightHawkInLight's video, except using NaOH in place of HCl. More information on the reaction chemistry can be found here.
  

  Observations

  • With 2x NaOH mass, there was sufficient H2 production to also partially inflate a small grocery bag (a few L)
    • the reaction was slowing substantially towards the end, estimate 1.5x mass required next time
  • Approximate rate of production was 10L in 45 minutes
  • Add 1-2g of Al at a time and monitor temperature (reaction is exothermic)
    
    • adding Al requires removing the stopper from the flask, which likely mixes air in with the H2
  • Filled balloon (10g) was buoyant with 10cm attached string using approximately 10L of H2 (10L should give 12g lift)
    • balloon filled to taught (lightly pressurized) lost some gas within a few minutes of disconnecting the feed and would yield easily when poked
    • filled balloon has dimensions of approximately 32cm diameter and 12.5cm height (approx 10L -- it's not a perfect cylinder)

• Balloon Construction Attempt #1

  xdylanm • 09/11/2022 at 20:43 • 0 comments

  I tried constructing a custom balloon out of the Mylar film (from the emergency blanket). The method is

  • cutout the shape
  • heat seal a seam

  To seal the seam, I used a piece of aluminium foil as an intermediate layer between the tip of a soldering iron and the plastic at a set temperature of 360-380C. This partially worked, except

  • small holes develop at the interior seam edge (too hot?)
  • the seams are not very robust mechanically (while inflating the balloon with a straw, slight over-pressure causes the seam to fail)
  • it's very tedious

  More investigation is required.
  

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