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PTFE Sheet: Compact-Extruded Films, Sintered, Laid at 45° and Fused (MacFarland, Hills-McCanna, US 3,130,954)
Thick PTFE was cut from a sintered billet with a knife, and the skived sheet tore along the knife marks. MacFarland built his sheet up instead, from thin extruded films laid crosswise and fused together, for the liner of a valve diaphragm.
Result: a dense PTFE sheet, about 7,000 psi tensile and 450 % elongation, much the same in every direction.
Source: MacFarland, US 3,130,954 (Hills-McCanna, 1964). Not given: furnace temperature, mill pressure. Picture drawn by Youblob.
Advanced
Factory process
Instructions
1
1
Compact-extrude a film
Compact-extrude a film
Feed finely divided PTFE resin from a hopper through a screw extruder to a slot die, usually without added heat. It comes out as a compact film that holds together unsintered, up to 24 in wide.
Materials for this step:
PTFE Resin Powder1 as requiredTools needed:
Plastic Extruder
Extrusion Die2
2
Sinter and coin the film
Sinter and coin the film
Carry the film through a sintering furnace to its fusion (gel) state and coin it in a mill as it goes. It comes out dense, with few pores, 5-8 mils thick. Ours: muffle furnace and calender rolls.
Tools needed:
Muffle Furnace
Calender Rolls3
3
Lay the films crosswise and fuse them
Lay the films crosswise and fuse them
Each film is a little stronger lengthwise, so stack several with their lengthwise axes turned by the same angle each time; 45° works well (MacFarland shows five plies). Feed the stack into a final sintering and compacting mill to fuse it into one sheet (over 20 mils thick). Ours: muffle furnace and calender rolls.
Tools needed:
Muffle FurnaceCalender RollsMaterials
1- 1 as requiredPlaceholder
Tools Required
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