Extruder with roller die

An extruder with a roller die in which a plastic or rubber material fed from a mixer is formed into a sheet, said extruder comprising:

• a screw feeder having said roller die located at the fore end thereof, said screw feeder comprising:
• a cylinder:
• a revolving screw;
• a variable pitch screw shaft including a driven base portion thereof rotatably supported in said cylinder and a non-contacting screw portion forming a feed portion and a compression portion and which is disposed in said cylinder so as to form a small gap with respect to the inner periphery of said cylinder;
• and
• means for maintaining the maximum pressure of the extruding material in said compression portion and the pressure at the fore end of said screw feeder in the ranges of 52.times.10.sup.3 to 200.times.10.sup.3 gr/cm.sup.2 and 20.times.10.sup.3 to 60.times.10.sup.3 gr/cm.sup.2, respectively, said means for maintaining said pressure further comprising means for measuring said pressure of said material at a position between said roller die and said screw feeder.