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Stretched Polymer

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Some polymer fibres have steel's strength and stiffness thanks to stretching and keep a plastic's density. Stretched polymers could hence excel as fast-spinning parts, especially as impellers of gas compressors and vacuum pumps, as turbines too where the temperature fits.

These parts are uneasily made of fibres in a matrix. Intricate shapes hamper automatic production, thin sections held at thicker ones aren't quite natural to fibres. It's done at individual fan blades of turbofans, not at cheap small integral compressor impellers.

I suggested to deform polymer raw material. Here strength is needed in the radial direction, by squeezing a disk, and in the azimuthal too, by a torsion. Then the part could be machined by usual methods, accurate and automated - if everything works as hoped.

Or just inject the part. For instance LCP is known to harden much from small shear at injection. That would be perfect to harden the blades or thin disk of an impeller: Inject the polymer at the centre so shear is strong at the thin blades and disk periphery. Heat the resin and mould a bit less, compensate with more injection pressure.

The blades and disk periphery of impellers and turbine rotors hold at a massive ring or disk section near the axis, where the material needs azimuthal strength too. This would be achieved by a rotating part of the mould, or maybe a separate construction used as the unmoulded part is still warm. Azimuthal shear could occur in the polymer between concentric tools, an outer one (optionally a mould part) that holds the impeller at its blades and a rotating inner one where the shaft will be. Other arrangement are possible, this one limits the deformations of the impeller.

PA too hardens by deformation. Simple injection and rotation could make very strong and cheap impellers.


When extruding tubes, the kernel could rotate to give azimuthal shear. This can combine with the axial shear given by the extrusion.

Marc Schaefer, aka Enthalpy

Could the fan blades be of stretched polymer at a turbofan?

They demand strength-to-mass at room temperature. The air arrives at almost 0.95 Mach, the blades must rotate significantly faster. I know titanium alloy and graphite composite for them. Blades need impact resistance too, creep resistance, and more.

Stretched LCP would improve the strength-to-mass, other polymers too. Just milling the blades from stretched raw material would be simpler than now. Injecting the blades with high shear under limited heat to obtain strength would be fantastic.

Marc Schaefer, aka Enthalpy

"LCP" was too general here. I meant primarily Vectra. Maybe it has competitors.


Cutlery of stretched polymer would be lighter than metal and replace disposable plastic cutlery that becomes outfashioned. Vectra must fit. Polyolefins are cheaper if they keep transverse strength and withstand the washing temperature.

Ramblers, mountaineers would happily save weight. Airlines too, aiming towards reusability.

Spoons look easy, chopsticks anyway. Forks need adequate shape and stretching at the teeth, I suppose injection achieves it with less heat and more pressure.

I'd try knives too, they can only improve over the present disposable ones. The blade needs macromolecules stretched in the flat directions: maybe mold parts that glide against an other in several directions during the injection achieve it. The detailed blade shape can be finished later.

For some pieces, bamboo is the competitor.

Marc Schaefer, aka Enthalpy

I shouldn't forget plates, glasses, trays... And as users, children too.

Vectra makes already bearings and can be filled with Ptfe powder, graphite powder, graphite choppers.

Seals need similar properties as bearings. Vectra and more LCP may outperform PA, POM and the others for some parts, especially the seal backup rings that prevent the extrusion of the elastomer ring through the remaining clearance between the sealed parts.

Mechanical strength, temperature stability, resistance to oils and water favor Vectra and similar LCP. Stretching them when injecting or machining the parts would let them resist more pressure. This may involve an axial oscillation when injecting a polymer tube between concentric mold parts, or maybe injection at lower temperature and higher pressure suffices. Unless a tiny deformation in operation suffices to strengthen these polymers enough, better than PA does.

Stretch during manufacture may improve seal parts of other materials too, for instance PA.

Marc Schaefer, aka Enthalpy


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