Multi-layer web formation section

A multi-layer web formation section comprising:

• a first wire unit for forming a first partial web, the first wire unit having a first wire, a forward end, and an output end;
• a first headbox, arranged to supply a first pulp suspension jet to the forward end of the first wire unit;
• a second wire unit succeeding the first wire unit, the second wire unit having a two-wire stretch defined by a second wire and a third wire, the second wire and the third wire forming a closing jaw at a forward end where the second wire and the third wire come together, and forming an output end where the second wire and the third wire are separated from one another, the two-wire stretch defining a first side and a second side;
• a second headbox located at the forward end of the two-wire stretch of the second wire unit and which is arranged to supply a second pulp suspension jet into the closing jaw;
• a joint formed in between the second wire unit and the first wire so that a second partial web formed in the second wire unit will join to a first partial web carried on the first wire;
• a first dewatering zone defined by at least one fixed first formation shoe having a leading edge and a curved cap positioned on one side and at the forward end of the two-wire stretch, the at least one fixed first formation shoe having the curved cap placed against the first side or the second side of the two-wire stretch, the cap having portions defining openings which extend through the cap, which openings are connected to a source of under-pressure, wherein the openings are formed by holes or by gaps extending essentially in the lengthwise direction of the machine, the at least one fixed first formation shoe arranged such that fiber pulp traveling in-between the second and third wires of the two-wire stretch is subjected to non-pulsating dewatering in an area following after the leading edge of the at least one fixed first formation shoe and wherein the leading edge of the at least one fixed first formation shoe is arranged not to remove water from the fiber pulp traveling in-between the second and third wires of the two-wire stretch;
• and
• a second dewatering zone positioned after the first dewatering zone along the two-wire stretch of the second wire unit and defined by fixed dewatering cross machine direction extending lists placed against the first side or the second side of the two-wire stretch, the lists defining gaps between the lists, the gaps connected to a source of under-pressure such that a fiber pulp traveling in between the second forming wire and the third forming wire is subjected to pulsating dewatering by the fixed dewatering lists and by under-pressure.

A method of forming a multi-layer web in a formation section, comprising the steps of:

• forming a first partial web on a first wire of a first wire unit with a first pulp suspension jet supplied by a first headbox at a forward end of the first wire unit;
• forming a second partial web in a second wire unit from a second pulp suspension jet supplied by a second headbox, wherein the second pulp suspension jet is supplied to a jaw defined by a second wire of the second wire unit, and a third wire of the second wire unit, the second wire of the second wire unit, and the third wire of the second wire unit forming a two-wire stretch which begins with the jaw, and defining a forward end of the two wire stretch where the second wire of the second wire unit, and the third wire of the second wire unit meet;
• non-pulsatingly dewatering the second partial web in a first dewatering zone of the two-wire stretch of the second wire unit by moving the second wire of the second wire unit, and the third wire of the second wire unit, in the two-wire stretch, over a curved cap of a least one fixed first formation shoe having a leading edge and located at the forward end of the two-wire stretch such that the cap engages one side of the two-wire stretch, and drawing water with under-pressure through holes or gaps which extend through the cap and are essentially lengthwise in a machine direction and wherein the leading edge of the at least one fixed first formation shoe does not remove water from the second partial web in the first dewatering zone;
• after the non-pulsating dewatering, pulsatingly dewatering in a second dewatering zone of the two-wire stretch of the second wire unit with fixed dewatering lists placed against a side of the two-wire stretch, the lists extending in the cross machine direction and forming cross machine direction gaps therebetween, and through said gaps applying under-pressure to the two-wire stretch;
• bringing one of the second wire of the second wire unit, or the third wire of the second wire unit, having the second partial web thereon into engagement with the first wire of the first forming unit having the first partial web thereon to join the first partial web to the second partial web at a joint;
• wherein pulsating dewatering in the second dewatering zone of the two-wire stretch of the second wire unit is effected with loadable dewatering lists loaded in a controlled manner on a side of the two-wire stretch opposite the fixed dewatering list, the loadable dewatering lists positioned opposite the gaps between the fixed dewatering lists;
• wherein in the step of forming the first partial web on the first wire with the pulp suspension jet is by supplying the suspension jet into a jaw at a forward end of the first wire unit, the jaw formed by the first wire and a superpositioned wire forming a first two-wire stretch, the first two wire stretch defining a beginning where the first wire and the superpositioned wire first meet;
• wherein dewatering of the first partial web formed on of the first wire unit is accomplished in a first dewatering zone of the first wire unit as non-pulsating dewatering at the beginning of the first two-wire stretch of the first wire unit with a further fixed formation shoe which has a leading edge and a curved cap, the further fixed formation shoe being placed against an inner surface of the first wire;
• and
• applying under-pressure through portions of the further fixed formation shoe cap forming holes or gaps which extend through the cap and are essentially lengthwise in the machine direction, which holes or gaps extend through the further fixed formation shoe cap whereby fiber pulp from the first pulp suspension jet traveling in between the first wire and the superpositioned wire, is subjected to a non-pulsating dewatering area following after the leading edge of the further fixed formation shoe and wherein the leading edge of the further fixed formation shoe does not remove water from the first partial web in the first dewatering zone of the first wire unit;
• wherein pulsating dewatering of the first partial web formed on the first wire unit is accomplished in a second successive dewatering zone in the first two-wire stretch of the first wire unit with fixed dewatering lists placed against one side of the first two-wire stretch in a cross machine direction, and applying under-pressure through cross machine direction gaps defined between the lists and subjecting the fiber pulp between the first wire and the superpositioned wire formation wire to pulsating dewatering;
• and further accomplishing dewatering by loading in a controlled manner movable lists located on an opposite side of the first two-wire stretch in relation to the fixed dewatering lists at the gaps between the fixed dewatering lists.