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Nitrile Rubber (Buna-N)
At IG Farben in 1930 Erich Konrad and Eduard Tschunkur copolymerised butadiene with acrylonitrile. The nitrile group makes the chain polar, so oil and petrol - which are not - stay out. Sold as Buna N, nitrile rubber became the standard material for oil seals, fuel hoses and, much later, disposable gloves.
**US 1,973,000**, "Rubber like masses from butadiene hydrocarbons and polymerizable nitriles", Konrad and Tschunkur, assigned to IG Farbenindustrie, filed 20. April 1931, granted 11. September 1934. It requires the butadiene to be more than about 60 % by weight of the mix.
**You build the part nitrile made universal: an O-ring seal.** Turn two plugs with sized grooves, close a clear pipe with them, and leave it under water overnight.
Intermediate
3 hours plus an overnight soak
Instructions
1
1
The plug
The plug
One turned acetal plug: a flange that stops against the pipe end, a spigot that fits the bore, and a groove carrying the O-ring.
2
2
Measure and choose
Measure and choose
Cut 150 mm of clear PVC pipe and deburr both ends. Measure the bore at three angles and average. Pick a nitrile O-ring about 3 mm thick whose inside diameter is a little under bore minus 5 mm.
Materials for this step:
Clear PVC Pipe1 piece
O-Ring Assortment Kit1 kitTools needed:
Hacksaw
Sandpaper
Digital Caliper 6-Inch3
3
Size the groove
Size the groove
Loading Jupyter Notebook...
4
4
Turn the spigot
Turn the spigot
Chuck acetal rod. Face it. Turn 12 mm of length to the bore minus 0.1 mm, leaving a 5 mm flange at full pipe outside diameter behind it.
Materials for this step:
Delrin/Acetal Rod1 pieceTools needed:
Metal Lathe
Lathe Tool Set (HSS)Digital Caliper 6-Inch
Clear Safety Glasses5
5
Cut the groove
Cut the groove
3 mm from the spigot's end, plunge the parting tool to the root diameter from the notebook, then widen to 4.0 mm. Check the root with the caliper. Break the sharp edges.
Tools needed:
Parting ToolMetal LatheDigital Caliper 6-Inch6
6
Part off, make the second
Part off, make the second
Part off behind the flange. Make a second identical plug.
Materials for this step:
Delrin/Acetal Rod1 pieceTools needed:
Parting ToolMetal Lathe7
7
Grease and fit
Grease and fit
Wipe a thin film of petroleum jelly on each O-ring and roll it into its groove without twisting. Put a folded dry paper towel in the pipe and press both plugs home.
Materials for this step:
Petroleum Jelly2 g
Paper Towel1 sheet8
8
Overnight under water
Overnight under water
Weigh the capsule down in a bucket of water for 12 hours. Dry it outside, open it, and check the towel. Any damp spot shows which end leaked.
Tools needed:
Bucket9
9
History & Context
History & Context
**What the patent specifies:** a butadiene hydrocarbon (over about 60 % by weight) polymerised with a polymerisable nitrile, by heating or in emulsion. **Modern build (derived):** commercial NBR O-rings in an acetal gland.
Wartime Germany needed a rubber that fuel could not ruin, and nitrile answered it. More nitrile in the chain means more oil resistance and less flexibility in the cold. Its limits: ozone and sunlight crack it, and it swells in brake fluid and many solvents.
Materials
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Tools Required
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Design Files
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