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INDOSSABILI
PTFE (Polytetrafluoroethylene)
On 6. April 1938 Roy Plunkett at DuPont opened the valve on a cylinder of tetrafluoroethylene gas, a candidate refrigerant, and nothing came out - though the cylinder still weighed full. Sawn open, it held a white waxy powder: the gas had polymerised by itself. The powder resisted every solvent and acid tried on it, did not melt like other plastics, and almost nothing would stick to it.
**US 2,230,654**, "Tetrafluoroethylene polymers", Plunkett, assigned to Kinetic Chemicals, granted 4. February 1941. Its first claim is two words: "Polymerized tetrafluoroethylene."
**Tetrafluoroethylene is explosive and is never handled outside a plant.** You build what the material is for: a hinged tilting ramp that measures the coefficient of friction of PTFE against steel, beside nylon, acrylic and steel itself.
Principiante
3 hours
Istruzioni
1
1
The rig
The rig
The whole rig: a 400 mm base, a hinged ramp with a steel strip on top, a prop under the raised end, and a faced sled.
2
2
Cut base and ramp
Cut base and ramp
From 18 mm plywood saw two boards 400 x 120 mm. Sand the edges.
Materiali per questo passaggio:
Pannello di compensato1 pezzoStrumenti necessari:
Sega a mano
Righello
Morsetto a C3
3
Hinge them
Hinge them
Lay the boards end to end and fit the butt hinge across one short joint with 4 wood screws, pilot-drilled 2 mm. The ramp must lift from flat to 45° without rocking.
Materiali per questo passaggio:
Cerniera a libro1 pezzo
Viti da legno4 pezziStrumenti necessari:
Trapano a batteria
Serie di punte da trapano
Set di cacciaviti4
4
Fit the steel counterface
Fit the steel counterface
Stick a 360 x 100 mm strip of mild steel sheet to the ramp's top face with double-sided tape. Wipe it with isopropyl alcohol - grease halves any reading.
Materiali per questo passaggio:
Lamiera di acciaio dolce1 pezzoStrumenti necessari:
Occhiali di sicurezza trasparenti
Alcol isopropilico al 99 %
Nastro biadesivo5
5
Make four sleds
Make four sleds
Saw four 60 x 60 mm plywood blocks. Face one each with PTFE, nylon, acrylic and steel cut to 60 x 60 mm, fixed with double-sided tape. Clean every face with alcohol.
Materiali per questo passaggio:
Lamiera di acciaio dolce1 pezzoStrumenti necessari:
Sega a mano
Taglierino
Lastra di PTFE
Lastra di nylon (6/6)
Lastra di acrilicoNastro biadesivo6
6
Tilt until it goes
Tilt until it goes
Set a sled 100 mm from the top. Raise the ramp slowly, about 1° per second. Stop the instant it slides and read the angle finder on the ramp. Five tries per sled.
Strumenti necessari:
Goniometro / misuratore d'angoliRighello7
7
Load it
Load it
Repeat the PTFE sled with a weight taped on top. The angle should not change.
Strumenti necessari:
PesoGoniometro / misuratore d'angoli8
8
Angles into friction
Angles into friction
Caricamento del notebook Jupyter…
9
9
History & Context
History & Context
**What the patent specifies:** the polymer of tetrafluoroethylene itself, a solid insoluble in ordinary solvents. **Modern build (derived):** machined PTFE sheet against clean mild steel on a tilting plane.
Its first large use was seals and gaskets for the Manhattan Project's uranium hexafluoride plant, a gas that attacked everything else. DuPont registered Teflon in 1945; non-stick pans followed in the 1950s, and stretched PTFE became Gore-Tex. Its limits: it creeps under steady load, wears quickly without fillers, cannot be glued without etching, and above about 260 °C in use it begins to give off harmful fumes.
Materiali
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Strumenti richiesti
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