Method and distributor for air-laying of fibers
A fiber distributor is used for air-laying fibers on an endless, air pervious forming wire in a plant for producing non-woven webs. The fiber distributor includes a forming head with a perforated bottom and rows of rotatable wings situated at a distance above the bottom for during production sweeping supplied fibers along the rows of wings in an air stream before they successively leave the forming head through the openings of the perforated bottom for being deposited in a layer on the upper part of the forming wire. The fibers are, while being swept along in this way, inclined to form nits. The wings are therefore adapted to rotate with an optimal speed of rotation in an interval where the fiber's inclination to form nits changes from being lesser to being larger when the rotation speed of the wings grows. By use of the method and the fiber distributor according to the invention, it is possible to produce non-woven webs with a minimum of fiber loss in form of nits and at the same time also with an extremely high rate of production.
1 . A method for air-laying fibers on an endless, air pervious forming wire which comprises:
supplying fibers to a forming head having a perforated bottom and at least one row of rotatable wings situated at a distance above the bottom,
sweeping the fibers along the at least one row of wings in a first air stream by rotating the wings, during which sweeping the fibers are inclined to form nits,
regulating the speed of rotation of the wings into an interval around an optimal speed wherein the inclination of the fibers to form nits changes from being lesser to being greater as the rotation speed of the wings increases, and
successively depositing the fibers into a layer on an upper part of the forming wire by sucking the fibers down through the openings in the perforated bottom in a second air stream.
2 . The method of claim 1 , which further comprises regulating the rotation speeds of the wings in agreement with the composition of the fibers.
3 . The method of claim 1 , which further comprises choosing an interval of speeds of rotation of the wings around an average optimal rotation speed that provides a relatively small number of nits, with the interval having a value between 0.5 and 1.5 times the rotation speed of the wings generating the average optimal velocity.
4 . The method of claim 1 , which further comprises choosing an interval of speeds of rotation of the wings around an average optimal rotation speed that provides a relatively small number of nits, with the interval having a value between 0.9 and 1.1 times the rotation speed of the wings generating the average optimal velocity.
5 . The method of claim 1 wherein the speed of rotation of the wings is increased to a velocity that decreases the number of nits per m 2 of non-woven web to 117 n/m 2 while increasing output to 60 kg/w/h.
6 . The method of claim 1 , which further comprises:
detecting the percentage of nits in the fiber layer on the forming wire or in the resulting non-woven web,
sending signals representing the results of the detecting as input to a computer,
using this input to calculate, by means of a program of the computer, a value which represents an optimal rotation speed where the number of nits at a given moment is small or smallest, and
sending signals representing this value as output from the computer to order the wings to rotate with rotating speeds represented by the value.
7 . A method for air-laying fibers on an endless, air pervious forming wire which comprises
supplying fibers to a forming head having a perforated bottom and at least one row of rotatable wings situated at a distance above the bottom,
rotating the wings with such a rotation speed that the fibers are swept along the bottom with a velocity between 5 m/sec and 26 m/sec, and
successively depositing the fibers into a layer on the upper part of the forming wire by sucking the fibers down through the openings of the perforated bottom in a second air stream.
8 . The method of claim 7 , wherein the wings are rotated with such a rotation speed that the fibers are swept along the bottom with a velocity of between 9 m/sec and 16 m/sec.
9 . A fiber distributor of the kind used for air-laying fibers on an endless, air pervious forming wire in a plant for producing non-woven webs, comprising forming head with a perforated bottom and at least one row of rotatable wings situated at a distance above the bottom for during production sweeping supplied fibers along the at least one row of wings in an air stream before they successively leave the forming head through the openings of the perforated bottom for being deposited in a layer on the upper part of the forming wire, whereby the fibers while being swept in this way are inclined to form nits and the wings are rotated with an optimal speed of rotation in an interval where the inclination of the fibers to form nits changes from being lesser to being greater as the rotation speed of the wings increases.
10 . The fiber distributor of claim 9 , further comprising a regulator for regulating the optimal speed of rotation in agreement with the composition of the fibers and the arrangement of the actual fiber distributor.
11 . The fiber distributor of claim 10 , wherein the regulator is adapted for regulating the optimal speed of rotation into an interval that provides a relatively small number of nits, with the interval having a value between 0.5 and 1.5 times the rotation speed of the wings generating the average optimal velocity.
12 . The fiber distributor of claim 10 , wherein the regulator is adapted for regulating the optimal speed of rotation into an interval that provides a relatively small number of nits, with the interval having a value between 0.9 and 1.1 times the rotation speed of the wings generating the average optimal velocity.
13 . The fiber distributor of claim 9 , further comprising
a detector for detecting the percentage of nits in the fiber layer on the forming wire or in the resulting non-woven web and sending signals representing the results of this detecting as input to a computer,
a program of the computer for by means of the input, calculating a value, which represents an optimal rotation speed where the number of nits is small or smallest and generating output representing the value, and
one or more actuators for, by receiving the output, rotating the wings with rotation speeds represented by such values.
14 . The fiber distributor of claim 9 , comprising that the mutual distance between each of two neighboring rows of wings is the mutual distance between two wings in a row plus between 50 mm and 135 mm.
15 . The fiber distributor of claim 9 , wherein the distance between the wings and the perforated bottom is between 1 mm and 12 mm.
16 . The fiber distributor of claim 9 wherein the speed of rotation of the wings is increased to a velocity that decreases the number of nits per m 2 of non-woven web to 117 n/m 2 while increasing output to 60 kg/w/h.