Abstract: Wood chips are fed into a sheath containing two parallel screws that mesh with each other, their respective threads having, at least an upstream series of segments and a downstream series of segments, each of which comprises a drive upstream zone in which the chips are driven downstream and a braking downstream zone through which the chips are forced, the chips thus being driven through the sheath while being braked in the braking zones and while being transformed into fibers. The transit time for which the chips remain in the sheath lies in the range 1.5 s to 80 s, and provision is made for the pressure to be at least substantially equal to 90 bars upstream from the braking zone of the upstream series, so that a temperature lying in the range 120° to 150° C. is reached inside the sheath (10) without supplying external heat.

Abstract: The installation comprises a defibration sheath with an inlet for wood chips, an outlet for fibers, and two parallel rotative screws. The screws mesh with each other via their respective threads, which have at least an upstream and a downstream series of segments, with a drive upstream zone having forward threads, and a braking downstream zone having reverse threads with notches that are smaller in the braking downstream zone of the downstream series than in the braking downstream zone of the upstream series. The number of notches per thread in each braking zone is 2 to 6, and the section-to-output ratio RSO of the sum of the sections of the notches of a thread of the braking downstream zone of the downstream series to the fiber output rate is 60 mm2/m3h?1 to 80 mm2/m3h?1.

Abstract: Wood chips are fed into a sheath containing two parallel screws that mesh with each other, their respective threads having, at least an upstream series of segments and a downstream series of segments, each of which comprises a drive upstream zone in which the chips are driven downstream and a braking downstream zone through which the chips are forced, the chips thus being driven through the sheath while being braked in the braking zones and while being transformed into fibers. The transit time for which the chips remain in the sheath lies in the range 1.5 s to 80 s, and provision is made for the pressure to be at least substantially equal to 90 bars upstream from the braking zone of the upstream series, so that a temperature lying in the range 120° to 150° C. is reached inside the sheath (10) without supplying external heat.

Abstract: The installation comprises a defibration sheath with an inlet for wood chips, an outlet fir fibers, and two parallel rotative screws. The screws mesh with each other via their respective threads, which have at least an upstream and a downstream series of segments, with a drive upstream zone having forward threads, and a braking downstream zone having reverse threads with notches that are smaller in the braking downstream zone of the downstream series than in the braking downstream zone of the upstream series. The number of notches per thread in each braking zone is 2 to 6, and the section-to-output ratio RSO of the sum of the sections of the notches of a thread of the braking downstream zone of the downstream series to the fiber output rate is 60 mm2/m3h?1 to 80 mm2/m3h?1.