[0001] This invention is related to a feeding system for the former of a dry-paper machine,
in which feeding system the fibre material is disintegrated in such a form as is required
by the former.
[0002] The former of a dry-paper machine usually comprises a screening tanklike or tubular
treating space, into which the web-forming fibre material is fed with air stream.
In these apparatuses an even distribution of fibre material is sought by recirculating
it and spreading it into a layer of even thickness on the forming wire. The former
is normally fed with chemical pulp shredded, or disintegrated, in a hammer mill; and
into the hammer mill the chemical pulp is fed direct from the roll.
[0003] In comparison with other paper manufacturing methods, known systems of this type
have the drawback that the raw material's fineness is relatively modest and the controllability
of its properties poor. For this reason the manufacture of dry paper of finer quality,
for instance, has been if not impossible then at least too costly as compared to other
paper manufacturing methods.
[0004] The object of this invention is to eliminate the above-mentioned disadvantages and
create a system that has none of them and with which the forming stage in the manufacture
of dry paper is at least technically raised to the level of other paper manufacturing
methods. To achieve this, a system according to the invention is characterized by
that it comprises a shredder, in which the chemical pulp web gets preshredded, a disc
refiner, in which the preshredded chemical pulp gets defibrated, and fibre material
transport devices between the various parts of the system for a continuous feeding
of the former.
[0005] By using a refiner type known in the first place from the manufacture of TMP and
CTMP pulps as a defibrator in connection with a dry paper former, it is possible to
achieve with the help of a preshredder a defibration more effective and more controllable
and thus obtain better paper quality. For the controllability of the process, a disc
refiner is much better than a hammer mill because the width of the refiner gap, the
profile of the cutting elements, and other parameters can be freely determined, ever
according to the raw material and the required product. Even at its highest, the cost
of defibration here will not exceed the cost of defibration with other pulp production
methods because the same kind of apparatus is used.
[0006] The main explanation why the disc refiner has so far not been used in connection
with the manufacture of dry paper is that the low humidity of the raw material of
dry paper in comparison with other defibrated raw materials (for instance wood chips)
seems to mean less steam generated and a smaller process pressure and therefore a
decrease in the effect of the refiner. It should also be borne in mind that the manufacture
of dry paper as a whole is still relatively new technology; for instance formers frequently
constitute a quality bottleneck (tendency to form fibre lumps) in dry-paper machines
that easily nullifies the benefits of a finer raw material (produced for instance
with a disc refiner). In these circumstances there has been little incentive to think
about ways of getting the raw material even finer, especially as it might have only
aggravated the existing problems.
[0007] Accordingly, the invention is based on the insight new to a person skilled in the
art that it is both possible and economical to use a disc refiner in the manufacture
of dry paper and that it is possible to construct the former so that it, for instance
in continuous interaction with the defibration equipment, can fully utilize the defibration
capacity of the disc refiner.
[0008] Thus an advantageous embodiment of a system according to the invention is characterized
by that it includes devices for conveying into the disc refiner for a new defibration
the material that has been rejected or otherwise remained unscreened in the former.
[0009] Other advantageous embodiments of a system according to the invention are characterized
by what is presented in the patent claims below.
[0010] In the following, the invention is explained in more detail by using an example,
with reference being made to the attached drawing showing an embodiment of a system
according to the invention.
[0011] The figure shows a dry-paper machine's former unit 1, which has a rotating cylindrical
former drum 2 with a perforated mantle. The fibre material is fed through a pipe 3
into the drum 2, which disperses the fibres into an even fibre web 9 on the wire running
under the drum. In the example the fibre material is formed in accordance with the
invention by shredding rolled chemical pulp 4 in a preshredder 5 and, sped up by a
blower 7a, transporting it into a disc refiner 6 equipped with a feeding funnel and
a conveyor screw, where the actual defibration occurs. A blower 7b raises the pressure
in the pipe 3 if the process pressure of the refiner is not enough for transporting
the fibres into the former drum 2.
[0012] Fibres and fibre flocks that have travelled through the drum 2 are fed with a blower
7c through a pipe 8 back into the refiner 6. In the figure is also seen a secondary
circuit for the blast air of the drum, in which the air that has been sucked through
the wire is returned with a blower 7d through a pipe 10 to act as a cleaning jet over
the drum. Thus all air and fibre material circuits in the system are essentially closed.
[0013] It is obvious to a person skilled in the art that the various embodiments of the
invention are not restricted to the example presented above, but can be varied within
the scope of the following patent claims. Accordingly, the refiner can be equipped
with various accessories for instance for feeding arrangements or to control the steam
generated in the process. And for a multiphase refining of the fibre material, the
refiner can also have more than one phase.
1. Feeding systems for the former of a dry-paper machine, in which feeding system
the fibre material is disintegrated in such a form as required by the former, wherein
the system comprises a shredder, in which the chemical pulp web gets preshredded,
a disc refiner, in which the preshredded chemical pulp gets defibrated, and fibre
material transport devices between the various parts of the system for a continuous
feeding of the former.
2. System according to claim 1, the system including devices for conveying into the
disc refiner for a new defibration the material that has been rejected or otherwise
remained unscreened in the former.
