PTFE

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For a list of PTFE tubing suppliers see --> Bowden.

PTFE, also known under the brand name Teflon, has the lowest coefficient of friction of any known solid material and melts between 260°C and 327°C.

It's fairly hard and fairly stiff too, so it's ideal for RepRap parts including things low friction bushings to main assembly parts. Thermoplastics often swell just before they melt, so PTFE tube inserts are used in many extruder hot ends so that the swelled plastic slides on this insert, instead of wedging itself in, preventing extrusion. PEEK tubing can also be used for this purpose.

PTFE is used in lubricants, and PTFE-filled oil is highly recommended by many in the community as being the best all-round low friction and inert lubricant for RepRap machines. PTFE is also sold in very thin tape, known as plumbers tape or thread-sealing tape.

Despite it's relatively low melting temperature, "liquid" PTFE is much more of a thick gel than a true liquid. Because of this it cannot be injection molded; it is shaped and compressed in powder form, and then sintered. For this reason, PTFE is surprisingly expensive. It will likely remain a RepRap vitamin, unless powder printing takes off.

Properties

Property PTFE (unfilled) PTFE (25% glass filled) PTFE (25% carbon filled)
PHYSICAL
Density (lb/in³) (g/cm³) 0.078 (2.16) 0.081 (2.25) 0.075 (2.08)
Water Absorption, 24 hrs (%) < 0.01 0.02 0.05
MECHANICAL
Tensile Strength (psi) 3,900 2,100 1,900
Tensile Modulus (psi) 80,000 - -
Tensile Elongation at Break (%) 300 270 75
Flexural Strength (psi) No break 1,950 2,300
Flexural Modulus (psi) 72,000 190,000 160,000
Compressive Strength (psi) 3,500 1,000 1,700
Compressive Modulus (psi) 70,000 110,000 87,000
Hardness, Shore D D50 D60 D62
IZOD Notched Impact (ft-lb/in) 3.5 - -
THERMAL
Coefficient of Linear Thermal Expansion(x 10-5 in./in./°F) 7.5 6.4 6.0
Heat Deflection Temp (°F / °C) at 264 psi 132 / 55 150 / 65 150 / 65
Melting Temp (°F / °C) 635 / 335 635 / 335 635 / 335
Max Operating Temp (°F / °C) 500 / 260 500 / 260 500 / 260
Thermal Conductivity (BTU-in/ft²-hr-°F) (x 10-4 cal/cm-sec-°C) 1.70 (5.86) 3.1 (10.6) 4.5 (15.5)
Flammability Rating V-O V-O V-O
ELECTRICAL
Dielectric Strength (V/mil) short time, 1/8" thick 285 - -
Dielectric Constant at 1 MHz 2.1 2.4 -
Dissipation Factor at 1 MHz < 0.0002 0.05 -
Volume Resistivity (ohm-cm)at 50% RH >10^18 > 10^15 10^4

from boedeker-infopage.

Availability

PTFE rods suitable for RepRap extruders can be purchased from:

Plastock.co.uk

External Links