[0001] The present invention relates to a system for dry forming of paper or other sheet
materials of particles or fibres and of the kind specified in the introductory clause
of claim 1. A system of this kind is known from the USA Patent Specification No. 4,157,724,
in which the distributor unit comprises an upwardly open container having lower side
wall portions of a classification screen material which enables the fibre material
in the container to be gradually let out through these wall portions, the outlet material
then being moved down to the top surface of the moving, foraminous forming web by
the downwardly directed air flow as caused by the suction means underneath the forming
web. Inside the distributor container is mounted a row of impellers, the rotating
wings of which serve to whip the fibre material in a recirculating flow one way along
one side of the container and the opposite way along the opposite side. The impeller
wings also impart to the material flow a movement component outwardly towards the
insides of the screen walls, whereby the material flow is generally held against the
respective walls, even through these project in a straight manner across the forming
web, and by the same action the material output through the screen walls is generally
promoted such that a high distributing capacity is achieved.
[0002] The said recirculation of the material in the container is highly advantageous partly
as a means for providing an even distribution of the material inside the container,
even if new material is supplied at one place only, and partly because the material
flow as generally passing across the forming web will prevent the formation of stripes
in the fibre web as deposited on the moving forming web; in other known systems, in
which the material in the container is not moved crosswise of the forming web, fibre
lumps in the material or other local irregulatities may give rise to stripe formation,
because they form local obstructions to a free fibre outlet and assume stationary
positions as seen in the transverse direction of the fibre web being formed.
[0003] The recirculation of the material along the sides of the container requires a considerable
driving effect of the said impellers, though in the known system this is to some degree
justified by the fact that the said whipping wings serve not only to effect the recirculation,
but also to whip the material for keeping it air fluidized, to increase the distributor
capacity by forcing material out through the classification screens, and to generally
hold the material flow against the inside of the screens, such that it maintains its
character of a well defined and confined flow, without individual fibres spreading
all over the container space and depositing themselves whereever possible. But still,
the impellers should be driven with considerable power for producing the desired effects,
and besides it can be operationally inconvenient that the single parameter constituted
by the speed of rotation of the whipping wings will thus determine several different
functions of the distributor in an interrelated manner.
[0004] It is the purpose of the invention to
pro- vide a dry forming system of the kind referred to, which is of a simple disign
essentially different from that of the known system, and which is usable or operable
in a more flexible manner.
[0005] According to the invention the outlet wall portion forms at least a part of a pipe
which is used for guiding the flow of material along the respective length or partial
length of the recirculation path, the latter preferably being located entirely within
a"closed pipe circuit.
[0006] The technical main effect of the invention is that the recirculation flow of the
material may be supported or maintained merely by way of transportation air through
the said pipe, because there is no longer any need to arrange for the material flow
to be held monolaterally against a guiding wall. The flow will be effectively confined
by the pipe, and basically the recirculation movement as such will then be produceable
by simple blower means in a very economical manner.
[0007] It will still be possible to arrange for special means inside the pipe for causing
the fibre material to be kept air fludized and to be urged against the inside of the
screen wall portion, i.e. the corresponding operational features'of the known system
will be retained, but now without necessarily having to be interrelated in any fixed
manner, neither mutually nor with the recirculation velocity.
[0008] In a preferred embodiment, however, use is made of a rotating needle cylinder extending
axially through the respective straight pipe lengths, this cylinder operating both
to contribute to the recirculation flow, to effect air fludization of the fibre material
in the'flow as well as even to effect disintegration of fibre lumps, and to cause
a general outthrowing action on the material in the flow. Then these functions, of
course, will be interrelated, but it is still possible to adjust the recirculation
velocity in an independent manner, by varying the supply of additional transportation
air or provide for a throttling somewhere in the pipe circuit.
[0009] When the pipe system is entirely closed, of course exept for the perforations and
the material inlet, a further adjustable parameter will be the general internal pressure
of the pipe system.
[0010] In a very important embodiment of the invention the screen wall portions of the pipes
crossing the forming web are extended to simply constitute the pipes entirely, i.e.
all the way round, and these pipes or pipe portions are arranged so as to be rotating
during the operation. As air is drawn down through the horizontal perforated pipe,
the fibres will leave the pipe through the lower portion thereof, and a tendency will
exist to fibres sticking to the edge portions of the perforations, whereby the free
area thereof may become reduced. However, when the pipe is rotating, even at slow
speed, the same perforations will soon be located adjacent the top side of the pipe,
and here the downwardly directed air flow will penetrate the perforations with opposite
relative direction, whereby the perforations will be cleaned in a successive manner.
Tonwise of the nine may even be arranged for special cleaning means such as air nozzles
blowing compressed air against a restricted area of the outside of the pipe, whereby
the perforations and the outside of the pipe may be cleaned most effectively.
[0011] It has been observed that the cleaning here discussed has a remarkable influence
on the entire system not only because the screen perforations are kept open to maintain
a high capacity of the system, but also because the system as here described is able
to handle a fibre material, in which the length of the fibres may substantially exceed
the fibre lengths which have until now been considered as a maximum in connection
with dry forming processes. Thus, a conventional fibre length maximum is some 3-4
mm, while experiments have shown that a system according to the embodiment of the
invention as here discussed can easily handle a material in which the fibre length
is some 20-25 mm, perhaps even higher.
[0012] Thus, the general concept of enclosing the recirculated material flow in a pipe system
at least along the more relevant portions of the entire circuit is indeed conditioning
an important row of advantages as seen in the various aspects of the invention.
[0013] In the following the invention is described in more detail with reference to the
accompanying drawing, in which:-
Fig. 1 is a perspective view of a system according to the invention,
Fig. 2 is a cross sectional view thereof,
Fig. 3 is a plan side view, partly in section, and
Fig. 4 is a cross sectional view of a modified detail.
[0014] The system shown in Figs. 1-3 comprises a foramia- ous forming web 2 which is moved
continually through a closed path (not shown in full) so as to pass underneath a distributor
unit 4. Underneath this unit and the web 2 is mounted a suction box 6 having an exhaust
pipe 8 connected to a suitable suction blower. The distributor unit 4 comprises an
outer housing 10, which is open downwardly towards the web 2, and two horizontal pipes
12 extending through the housing across the web, these pipes being made of classification
screen material, i.e. a net material or perforated sheet material. The end portions
of the pipes 12 are supported by rotation bearings 16 mounted in the opposed end walls
14 of the housing.10, and outside the walls 14 the respective pipe ends are interconnected
through exterior, stationary U-pipes 18 and 20, of which the U-pipe 20 is provided
with a tangential inlet pipe 22 projecting in line with one of the pipes 12. The end
portions of the pipes 12 are provided with non-perforated sleeves 24 cooperating with
the bearings 16 and received in a sealed, rotary manner in or by the ends of the U-pipes
18 and 20.
[0015] Adjacent at least one end of the pipes 12 the sleeves 24 cooperate with driving means
for rotating the pipes
12,
24, e.g. as shown in fig. 1 a driving belt 26 driven by a motor pulley 28.
[0016] The top side of the housing 10 is provided with slot openings 30, which may be width
adjustable by means of valve plates 32.
[0017] The system already as described so far may be operative in the manner that a flow
of air fluidized fibre material is supplied through the tangential inlet pipe 22 from
a blower (not shown), whereby is created a recirculating material flow in the pipe
system 12, 18, 20. From this flow individual fibres will be let our through the screen
pipe walls together with the surplus of transportation air as supplied through the
inlet pipe 22. From the suction box 6 air is sucked down through the foraminous forming
web 2 and down through the housing 10 from the upper slots 30. This generally vertical
air flow will pass both across the screen pipes and along the outsides thereof thus
promoting the outlet of fibres from the pipes and conveying the outlet material down
to be deposited on the forming web 2.
[0018] The air as drawn downwardly from the upper slots 30 will show the additional effect
that it serves to successively clean the outside and the perforations of the screen
pipes as these are rotated, such that fibre material deposited adjacent and inside
the perforations in the lower outlet portion of the pipes will now be removed by the
"counterflow" action of the downflowing air. Possible fibre collections on the outside
of the pipes may be blown off when they pass through the upper path of rotation of
the pipes, whereby is prevented the formation of lumps which are otherwise liable
to occur on the outside of the classification screen, e.g. due to static electricity;
it is well known that such lumps are disadvantageous, because after growing to a considerable
size thet will fall off and be deposited on the forming web.
[0019] The cleaning of the perforations and the outside of the screen pipes 12 may be substantially
amplified by means of additional exterior cleaning means such as a rotary brush or
- as shown in fig. 2 - a nozzle system 44 on a pipe 46 connected to a source of compressed
air, whereby air jets are blown against the outside of the pipes 12 either continually
or intermittently. In this way a very efficient cleaning is obtainable, and as a result
it will be possible to handle fibres of a considerable length and with a durably high
capacity of the system.
[0020] In a large scale production system the mere recirculation of the material through
the pipes by virtue of the air supply through the pipe 22 may be insufficient for
ensuring that the material is kept properly air fluidized. Therefore, in each pipe
12 is arranged an axially oriented agitation cylinder 34 provided with radial agitation
needles 36 all along the length thereof, the cylinders having shaft portions 38 mounted
in bearings 40, these shafts at least at one end being extended outwardly and provided
with pulleys 42 or similar means enabling the cylinders 34 to be rotated relatively
fast by suitable driving means (not shown).
[0021] Preferably the external diameter of the needle cylinders 34, 36 is pronounced smaller
than the internal diameter of the pipes 12, and the cylinders are mounted eccentrically
such that the needles 36 sweep closely over the lower inside portion of the screen
pipe 12. Hereby the needle tips will brush off any possible fibre collections at the
inside of the pipe, and moreover the needles will show a pronounced desintegrating
effect on the material, should the same contain fibre lumps.
[0022] Furthermore the needles 36 will act to directly throw material out through the screen,
such that a very high outlet capacity can be achieved.
[0023] As shown in Fig. 3 the needles 36 are mounted on the cylinder with small mutual distance
along a screw line on the surface thereof, and during their rapid rotation the needles
will thus act as a conveyor worm, which will promote the general material flow through
the pipe 12. The recirculation flow may well be produced by conventional blower means,
e.g. axial blower wings mounted direct on the cylinders near the ends thereof. Another
possibility is to cause transportation air to be injected into the system through
nozzles located inside the U-pipes 18 and/or 20. However, it seems to be fully sufficient
to use the cylinders 34 for this purpose, when the needles 36 are arranged along a
screw line. Of course, the needles or some of them may be shaped slightly propeller
formed for extra contribution to the main flow.
[0024] Inside the pipes 12, adjacent their top side, may be arranged a stationary shield
plate 48 supported endwise by means of brackets (not shown) inside the U-pipes 18
and 20. This plate serves to limit the direct downflow of air through the screen pipes
to the forming web 2, as it may be desirable to effect an increase of the air flow
down along the outsides of the screen pipes. However, air from above can still enter
the screen pipes through the side portions thereof.
[0025] The needle cylinder 34,36 shows a remarkable des- integration effect on fibre lumps,
perhaps due to its eccentric location in the pipe 12, and in an extreme case it could
be possible to supply the material to the pipe system solely as fibre lump material
e.g. injected through a top or inner side opening in one of the U-pipes 18,20. The
supply pipe 22 may then be avoided or used solely for supply of extra air.
[0026] In Fig. 4 it is illustrated that in stead of a needle cylinder in the screen pipes
it is possible to use one or more throughgoing pipes 50 connected to a source of compressed
air and provided with nozzle means 52 for directing an air jet towards the inside
of the screen pipe, whereby an outthrowing and agitating effect on the fibre material
is obtained. The jets may have a velocity component downstream in the pipe.
[0027] The flow and pressure conditions inside the pipes 12 will vary somewhat along the
length thereof, and if neccessary it will be possible to cause some differentiation
of these conditions, e.g. by arranging for the top shield plate 48 to be axially inclined
or to have varying width along the pipe. The screw line of the needles 36 along the
cylinder 34 may show a non-constant pitch, and the degree of perforation of the screen
pipes may be graduated.
[0028] It would be possible to make use of only one screen pipe 12, when the remaining pipe
system is non-perforated; however, the pronounced movement of the material inside
the pipe may tend to effect a varying outlet capacity along the pipe, and for obtaining
an even fibre distribution in the web to be produced it will normally be recommendable
to use the scfeen pipes 12 pairwise, since the return flow through the other screen
pipe may compensate for a non-uniform capacity of a single pipe. On the other hand
the recirculation system may well comprise more than two screen pipes 12, for instance
four such pipes.
[0029] The rotation of the screen pipes, which is very important for the said cleaning of
the perforations, may well take place at such speed that the associated centrifugal
forces hereby contribute to increase the outthrowing effect on the fibres located
in or adjacent the perforations.
[0030] The invention also comprises the described method of producing a web material by
guiding a material flow through distributor pipes 12 and preferably rotating the pipes
during the operation and cleaning them in a successive manner during the rotation.
1. A system for dry forming of paper or other web material of particles or fibres,
comprising a moving foraminous forming web (2) and a distributor unit (4) placed thereabove
as a container provided with a perforated outlet wall portion, through which a particle
or fibre material supplied to the container can gradually leave the container, suction
means (6) being arranged underneath the foraminous web (2) for sucking air down through
this web to convey the outlet material to be deposited onto the web, said distributor
unit being of the type having means for guiding the material supplied thereto in an
air flow through a recirculation path , of which at least a partial length extends
over the foraminous web i2) alonq the interior side of said outlet wall nortion of
the container, characterized in that the outlet wall portion forms at least a part
of a pipe (12) used for guiding the flow of material along the respective length or
partial length of the recirculation path, the latter preferably being housed entirely
within a closed pipe circuit (12,18,20).
2. A system according to claim 1, characterized in that said pipe (12) is rotatably
arranged, and that substantially stationary screen cleaning means such as air nozzles
(44) are provided for cleaning the perforations from outside the pipe.
3. A system according to claim 2, characterized in that the screen pipe (12) is made
entirely of classification screen material and is arranged for continuous or intermittent
one-way rotation.
4. A system according to claim 1, 2 or 3, characterized in that there is arranged,
inside the screen pipe (12), separate or combined means for agitating, desintegrating,
outthrowing, and/or axially conveying the material in the pipe (12).
5. A system according to claim 4, characterized in that said means comprise a rotating
needle cylinder (34,36) preferably mounted eccentrically in the pipe.
6. A System according to claim 5, characterized in that the needles (36) are arranged
along a screw line on the cylinder.
7. A system according to claim 4, characterized in that said means comprise a system
of air nozzles (52) mounted on stationary carrier means (50) and blowing an air jet
against the inside of the screen pipe (12).
8. A system according to claim 3, characterized in that a shield plate means (48)
is mounted stationarily inside the screen pipe (12) adjacent the top portion thereof.