Note: Descriptions are shown in the official language in which they were submitted.
CA 02220362 1997-11-06
WO 96/38391 PCT/EP96/02068
1
Man-Made Vitreous Fibre Products and
Processes and Apparatus For Their Production
This invention relates to apparatus and processes for
' making man-made vitreous fibre (MMVF) products by a
~ centrifugal spinner technique in which the or each rotor is
mounted to rotate about a substantially horizontal axis.
It also relates to products having particularly useful
combinations of properties and which can be made by the
centrifugal spinner technique.
The centrifugal spinner can have a single rotor
mounted for rotation on a substantially horizontal axis,
for instance as in the system known as the Downey spinner.
More usually the centrifugal spinner is a cascade spinner
comprising a first rotor and one or more subsequent rotors
each mounted for rotation about a substantially horizontal
axis and arranged such that melt poured on to the ffirst
rotor is thrown on to the or each subsequent rotor in turn
and is thrown centrifugally off the or each subsequent
rotor and optionally off the first rotor as fibres.
It is necessary to carry the fibres away from the
rotors. In US 3709670 a cascade spinner discharges into a
collection chamber which is closely coupled to the spinner.
In this instance the fibres are not collected as a web but
. are merely sucked out of the chamber as fibres entrained in
air.
In most processes the fibres are carried towards and
onto a collector where they form a web, which is then
carried away from the spinner by the collector.. The web
may be laminated on itself. It is important to deposit the
3o fibres on the collector in ..as laminar a fashion as
possible. If fibres are deposited perpendicular to the
plane of the web, for instance as clusters or balls of
ffibres, this tends to detract from the properties of the
web and products made from it.
It is conventional to provide air flowing axially
forward around the spinner so as to carry fibres from
adjacent the rotor towards and onto the. collector. This
CA 02220362 1997-11-06
WO 96!38391 PCT/EP96/02068
2
transport air can be blasted out of transport air supply
orifices positioned around and a few centimetres from the
periphery of the rotors as described in GB 867299 or it can
be sucked around the spinner by suction applied through the
collector, as described in GB 961900, or both by blast and
by suction.
The collector is usually the inclined base of a
collection chamber. Usually the chamber is open in the
spinner end of the chamber, i.e., distant from the
collector, and the spinner is positioned in this open end
leaving a relatively large and variable open area around
the spinner for the entry of induced air which is sucked
into the chamber. The spinner with its associated motors
for driving the rotors usually has a bulky cross-sectional
area, for instance as shown in Figure 1 of U.S. 5,131,935.
Although the spinner may present a substantially
rectangular profile as shown in that, often it presents a
very irregular profile both in transverse and longitudinal
cross-section. Accordingly the cross-section of the open
area around the spinner is highly variable with sudden
changes in open area along the length of the spinner. Air
flow along the length of the spinner is liable to be highly
turbulent due to its variable longitudinal profile.
Additionally it is necessary to provide sufficiently
powerful suction through the collector to suck air in
through the open area around the spinner with sufficient
axial velocity to carry the fibres onto the collector.
In GB 961900 the spinner end of the collecting chamber
is substantially closed except for an opening in which the
spinner is located. A tubular duct leads to this opening
and the rotors of the spinner are mounted within a spinner
housing in this tubular duct, so as to define a relatively '
narrow passage, which is described as a nozzle, between the
spinner housing and the outer tubular wall of the duct. Air '
is sucked through this narrow passage as a result of
suction through the collector, so as to carry fibres away
from the spinner rotors and on to the collector. The air
CA 02220362 1997-11-06
WO 96/38391 PCT/EP96/02068
3
flow through the duct is said to be at 1,000 to 5,000 feet
per minute (about 5 to about 30m/s) and it is stated that
the passages which conduct the air to the rotors are
designed to avoid or to eliminate eddy currents or other
turbulence within the fluid stream.
Accordingly it seems to be intended that substantially
steady flow conditions should prevail in the passage
leading up to the rear of the rotors. However these
steady flow conditions will inevitably be destroyed as the
air emerges from the passage past the rotors because of the
very large area occupied by the front of the spinner
housing (through which no air is emerging) relative to the
open area of the passage. The quantitative relationship
between the open area and the area of the end of the
housing is not capable of determination from the drawings
of GB 961,900 because of inconsistencies in the drawings.
However the passage does not even extend around the entire
spinner housing and is instead merely C-shaped with a large
area above the spinner blocked off. It is therefore
inevitable that even if a boundary layer is attached to the
spinner housing and the outer tubular wall of the duct as
the passage leads up to the rotors, wholly turbulent
conditions will prevail as the air emerges from this
passage. This turbulence will be further promoted by the
fact that the air emerges from a passage which is narrow
into a wide spinning chamberdefined at its rear by a wide
partition wall. There will therefore be a very significant
amount of back eddys being formed in the chamber both
within the area of the front end of the spinner and outside
the area of the passage. Back flow of air within the
chamber is shown in the drawings, and it is also shown that
the air is considered to be drawn substantially
perpendicular through the collector. It is therefore
inevitable that a considerable amount of formation of tufts
or balls of fibres will occur
When forming MMVF products by a centrifugal spinner,
it is known to improve initial fibre formation and
CA 02220362 1997-11-06
WU 96!38391 PCT/EP96/02068
4
transport of fibres away from the rotor surface by
providing primary air supply means associated with each of
the subsequent rotors (and optionally also with the first
rotor) for blasting air substantially axially forwards
across the surfaces of the rotors. Thus this air blast
D
travels substantially axially along the surface of the
rotors. It may also have a helical or tangential
component, and may adopt the form of a diverging cone.
Such a system is described in, for instance, WO 92/06047
and in US 5131935. This air blast will normally have very
high velocity, typically above 100 metres per second
(20,000 feet per minute).
The air that is blasted along the surface of the
rotors emerges with substantially steady flow conditions
across the surface of the rotors so as to attach to the
rotors as a boundary layer which is a wall jet, so as to
promote fibre formation.
Despite the steady flow conditions leading up to the
rotors, normal commercial practice results in very
turbulent conditions prevailing immediately in front of the
rotors. For instance when steady flow conditions prevail
in the primary air, very turbulent conditions usually
prevail in any air that is flowing around the spinner. For
instance in U.S. 5,131,935 a typical arrangement is shown
in which the spinner is bulky and of irregular shape and
has motors offset from the rotors. Accordingly any air
flowing along the spinner is unlikely to have a boundary
layer attached to the spinner and the large area of the
front end of the spinner also co-operates to ensure
3o significant turbulence immediately in front of the spinner.
Accordingly, even if any induced air flowing along the
spinner had steady flow conditions as it approached the
rotors, the primary air has such a high axial velocity
relative to the axial velocity of the induced air that
there is a very high velocity gradient in the radial
direction. This gradient, and the spacing between the
primary air and the induced air, in practice is so large
CA 02220362 1997-11-06
WO 96!38391 PCT/EP96/02068
that significant turbulence and back eddys inevitably occur
immediately in front of the front end of the spinner. In
practice, as mentioned above, the air flowing along the
spinner towards the rotors is liable to be turbulent in
5 contrast to being under steady flow conditions and this
will further increase turbulence. Turbulence immediately
in front of the spinner will also be increased by the fact
that, in practice, the area occupied by the rotors is
normally a relatively small proportion (e.g., below 25%) of
the area of the front end of the spinner. All these
factors combine to result in a substantial degree of
turbulence where the primary air merges with the air which
has flowed along the spinner. The air flow immediately in
front of the spinner is therefore inherently turbulent and
not under steady flow conditions. Accordingly, it is
inevitable that a significant proportion of the fibres will
be formed into tufts or otherwise deposited on the
collector in the thickness direction of the collector.
-- In conventional centrifugal spinner apparatus, air
which is sucked in around the spinner necessarily has a
much lower velocity, generally less than 5% of the velocity
of the primary air. This is essential because the volume
of air that has to be transported towards and through the
collector would be excessive, with present designs of
apparatus, if the velocity is higher than this, especially
having regard to the variable and generally large open area
around some parts at least of the spinner in conventional
apparatus.
In practice therefore conventional centrifugal
spinners provided with a primary air supply, as described
above, necessarily generate a very high central primary air
. velocity and a relatively low induced air velocity around
it but spaced away from it. In WO 88/06146 a unit is shown
- which comprises a single rotor mounted in a relatively
streamlined housing that contains both the rotor and a
motor coaxial with the rotor for driving the motor, but no
details are given about how such a unit should be utilised
CA 02220362 1997-11-06
WO 96/38391 PCT/EP96/02068
6
in practice to form fibres, or about the relationship
between air that is forced internally of the housing and
any air that may flow around the housing.
In WO 93/13025 a cascade spinner discharges towards a
steeply inclined collector surface and a primary air blast
and a plurality of other air blasts are provided through
and around the spinner. Suction is applied from behind the
collector so that there is no pressure drop across the
collector and the collection chamber is described as being
essentially wall-less. Thus it seems that sufficient air
blasts are provided that the collection area can be
entirely open to the atmosphere, the fibres being confined
solely by the movement of air. This has the advantage that
potential fouling of the chamber walls is avoided but it
makes it very difficult to control the process in practice.
MMVF wool made using a horizontally mounted
centrifugal spinner, and in particular a cascade spinner,
is generally formed from stone melt (otherwise known as
rock or slag melt) in contrast to glass wool which is
usually made from a glass melt by, for instance, a Tel
spinner. Stone wool made by such spinners has several
advantages over glass wool. The stone wool has better
fire resistance and water repellancy, and production costs
can be lower, for instance due to reduced raw material
costs. In order to obtain equivalent insulation value it
__ is, however, generally necessary to make the stone wool
with a higher density than glass wool. For instance MMVF
wool from a cascade spinner tends to contain a proportion
of shot (particles having a diameter of at least 63~m) and
this tends to be inert as regards the properties of the
wool.
It is possible to reduce the amount of shot and to
improve the properties of MMVF wool made by a cascade or
other horizontally mounted centrifugal spinner by operating
the spinner under carefully controlled conditions, and in
particular by reducing the throughput of the spinner.
However this tends to increase production costs. An
CA 02220362 1997-11-06
WO 96/38391 PCT/EP96/02068
7
example of MMVF wool which can be made by a cascade spinner
and which can have good qualities, but which is generally
made at rather low throughput per unit hour, is described
in W092/12941.
It would be desirable to be able to improve the
production of MMVF wool by such a spinner so as to allow
improvement in the productivity of the process or the
product quality or both. In particular, it would be
desirable to modify existing processes and apparatus so as
to allow improved control and operation of the process and
so as to allow improved lay-down of the fibres in the web
which is produced in the process, at convenient rates of
production.
The invention provides a novel apparatus comprising a
horizontally mounted centrifugal spinner and a collecting
chamber, novel components for use in that apparatus
including a novel spinner and assembly of spinner with a
surrounding housing, and a novel process __for making MMVF
products using the novel spinner and/or novel apparatus.
By the invention it is possible to produce high
quality MMVF products in an economic manner, and these
products include new products.
In the apparatus embodiment of the first aspect of the
invention, novel apparatus for making MMVF (especially
stone) products comprises
a centrifugal spinner having a front end, a first
rotatable rotor or a set of rotatable rotors consisting of
a first rotor and one or more subsequent rotors, wherein
the or each rotor is mounted for rotation about a
substantially horizontal axis in front of the front end
whereby melt poured onto the first rotor is thrown off as
fibres or, in a set of rotors, is thrown onto the or each
subsequent rotor in sequence and is thrown off the or each
subsequent rotor and optionally off the first rotor as
fibres, and primary air supply means at least in the outer
peripheral regions of the spinner associated with the first
rotor or, in the set of rotors, with each subsequent rotor
CA 02220362 1997-11-06
WO 96/38391 PCT/EP96/02068
8
and optionally with the first rotor for blasting primary
air substantially axially forwards across the surface of
the or each rotor with which the primary air supply means
are associated, and motor means for rotating the or each
rotor,
a chamber which comprises a collecting portion which
has a spinner end adjacent to the cascade spinner and which
extends forwards from the spinner end and which comprises
side and top walls and an upwardly inclined base defined by
a collector mounted to receive fibres blown from the
spinner and to carry the fibres as a web out of the
chamber, and
suction means for applying suction through the
collector, and in this apparatus
the chamber also comprises a spinner portion which has
a rear end which is open to the atmosphere and a front end
which opens into and merges with the collecting portion,
and a substantially tubular duct which extends between the
front end and the rear end,
2o the collecting portion of the chamber is substantially
closed to the ingress of air except for air forced through
the spinner and air whichis sucked through the tubular duct
and, optionally, a lesser, non-interfering, amount of air
sucked or forced through supplementary air passages in the
spinner end of the collection portion,
the front end of the spinner and the front end of the
spinner portion together define a substantially open
annular collar between them,
at least 50% of the cross-sectional area of the front
end of the spinner portion is open to the flow of air
sucked through the spinner portion by the suction means,
and -
the spinner and the tubular duct are constructed to
provide substantially steady air flow conditions through
the collar.
As a result of providing the induced air under steady
f low conditions through the collar, coupled with
CA 02220362 1997-11-06
WO 96/38391 PCT/EP96/02068
9
appropriate choice of the forced or primary air, it is
easily possible to provide substantially non-turbulent
conditions in the region in the collecting portion where
the primary air initially merges with the air from the
collar.
The process first aspect of the invention utilises
apparatus comprising
a centrifugal spinner having a front end, a first
rotatable rotor or a set of rotatable rotors consisting of
a first rotor and one or more subsequent rotors, wherein
the or each rotor is mounted for rotation about a
substantially horizontal axis in front of the front end
whereby melt poured onto the first rotor is thrown off as
fibres or, in a set of rotors, is thrown onto the or each
subsequent rotor in sequence and is thrown off the or each
subsequent rotor and optionally off the first rotor as
fibres, and primary air supply means at least in the outer
peripheral regions of the spinner associated with the first
rotor or, in the set of rotors, with each subsequent rotor
2o and optionally with the first rotor for blasting primary
airsubstantially axially forwards across the surface of
the or each rotor with which the primary air supply means
are associated, and motor means for rotating the or each
rotor,
a chamber which comprises a collecting portion which
has a spinner end adjacent to the centrifugal spinner and
which extends forwards from the spinner end and which
comprises side and top walls and an upwardly inclined base
defined by a collector mounted to receive fibres blown from
the spinner and to carry the fibres as a web out of the
chamber, and
suction means for applying suction through the
collector, and in this apparatus
- the chamber also comprises a spinner portion which has
a rear end which is open to the atmosphere and a front end
which opens into and merges with the collecting portion,
CA 02220362 1997-11-06
WO 96/38391 PCT/EP96/02068
and a substantially tubular duct which extends between the
front end and the rear end,
the collecting portion of the chamber is substantially _
closed to the ingress of air except for air forced through
5 the spinner and sucked through the tubular duct and,
optionally, a lesser, non-interfering, amount of air sucked
or forced through supplementary air passages in the spinner
end of the collection portion,
the front end of the spinner and the front end of the
10 spinner portion together define a substantially open
annular collar between them,
at least 500 of the cross-sectional area of the front
end of the spinner portion is open to the flow of air
sucked through the spinner portion by the suction means,
and
the spinner and the tubular duct are constructed to
provide substantially steady flow conditions through the
collar,
and the process comprises pouring melt onto the first
rotor while the rotor or rotors are spinning, forming
fibres off the first rotor or, in a set of rotors, off the
or each subsequent rotor and optionally the first rotor
while forcing primary air through the primary air supply
means under substantially steady flow conditions, and
collecting the fibres as a web on the collector while
applying suction through the collector and carrying the web
out of the chamber on the collector,
and in this process the air sucked through the collar
flows through the collar under substantially steady flow
conditions with an axial velocity which is 5 to 400 of the
axial velocity of the primary air as it is forced out of
the air supply means.
Throughout this specification, unless otherwise
stated, axial velocities are calculated on the basis of the
rate of flow (Nm3 per second) through the area of the
passage through which the air is flowing. Thus the axial
velocity of the primary air is calculated on the basis of
CA 02220362 1997-11-06
WO 96/38391 PCT/EP96102068
11
the open area of the slots and the axial velocity of the
air sucked through the open area in the front end of the
spinner portion is calculated on the basis of the area of
the collar or, if there is an open area within the spinner,
on the area of the collar plus the open area within the
spinner.
As a result of flowing the air through the collar
under substantially steady flow conditions and as a result
of selecting the axial velocity of the air which flows
through the collar appropriately within the range of 5 to
40% of the axial velocity of the primary air, it is
possible to provide essentially non-turbulent conditions in
the collecting chamber where the primary air initially
merges with the air from the collar. This is facilitated
by arranging for the primary air and the air from the
collar to emerge from the spinner as close together as is
conveniently possible.
The spinner used in the apparatus and process aspects
of the invention can comprise a single rotor but preferably
has a plurality of rotors (as a cascade spinner).
The cascade spinner can have an open outer periphery
in which event it does not have a housing enclosing the
spinner. Instead, the cascade spinner may comprise, for
instance, a plurality of individual units each of which may
comprise a single rotor mounted in a relatively streamline
- -housing that contains both the rotor and a motor co-axial
with the rotor for driving the motor, for instance as
illustrated in Wo88/06146. For instance one such unit may
provide the top rotor and one, two or three such units may
provide the subsequent rotors, and each of the units may be
mounted independently on an outer tubular duct. More
- usually, however, the rotor units are inter-connected as an
assembly, by rods or other supports which allow the passage
of air between the rotor units as well as between the
assembly of rotor units and the surrounding tubular duct.
Preferably, however, the spinner which is used in the
apparatus and process aspects of the invention has a
CA 02220362 1997-11-06
WQ 96/38391 PCT/EP96/02068
12
housing which is substantially closed to the free axial
flow of air, for instance due to being closed at its front
or rear ends and the rotors are mounted on means (such as
shafts) within or substantially behind this housing for
rotation in front of the housing.
Accordingly, the preferred spinner comprises a housing
which is substantially closed to the free axial flow of air
through the spinner and which has a front face, a rear end
and a substantially tubular housing wall which extends
between the front face and the rear end and which is
substantially streamlined to air flowing axially along the
front end of the outside of the housing,
a first rotor and one or more subsequent rotors each
mounted in the housing for rotation in front of the front
face about a substantially horizontal axis and arranged
such that melt poured onto the first rotor is thrown onto.
the or each each subsequent rotor in turn and is thrown off
the or each subsequent rotor (and optionally off the first
rotor) as fibres, and
2o primary air supply means associated with the
subsequent rotor or with each of the subsequent rotors ( and
optionally with the first rotor) for blasting air axially
forward across the surfaces of the or each rotor at least
in the outwardly facing regions of the or each rotor, and
motor means for driving the rotors and located within
the housing or substantially behind the rear end, i.e.,
with the motors all being arranged so that their periphery
is substantially within the area defined by the periphery
of the rear end of the housing, when viewed from the rear.
In a typical conventional cascade spinner, such as is
illustrated in W092/12941 or W092/06047 or U.S. 5,131,935,
the rotors typically occupy only a very small proportion '
(for instance 5 to 20%) of the total cross-sectional area
of the cascade spinner. Accordingly the parts of the '
spinner housing around the rotors necessarily provides the
opportunity for undesired turbulence and eddy formation.
In the invention, the total cross-sectional area of the
CA 02220362 1997-11-06
R'O 96/38391 PCT/EP96/02068
13
rotors is preferably at least 40% of the maximum cross-
sectional area of the cascade spinner.
When the spinner is an open assembly of individual
rotor units, then the cross-sectional area of the spinner
is the area that partially blocks the axial flow of air
past the spinner, i.e., the total cross-sectional solid
area of the spinner. When as is preferred the cascade
spinner has a substantially closed outer housing defined by
a substantially tubular wall then the maximum cross-
sectional area is the maximum area defined by this closed
housing except that if there is a central open duct through
the spinner, to allow induced air to flow through the
spinner as described in U. S. 5, 131, 935, the area of this
open duct is excluded from the area of the spinner.
The second aspect of the invention provides a novel
spinner as described above having a housing which is
substantially closed to the free axial flow of air through
the spinner and in which the total cross-sectional area of
the first and subsequent rotors is at least 40%, usually 40
to 95%, of the maximum cross-sectional area defined by the
housing.
The novel spinner may be mounted in a substantially
tubular duct that surrounds the housing and which is open
at each end to define an annular passage between the
spinner housing and the duct, as explained below.
-- -- The front face of the spinner housing and/or the rear
end are preferably closed in order that the housing is
substantially closed to the free axial flow of air through
the spinner. Appropriate air supply means and apertures
for the axles and orifices for the supply of binder may be
provided in a solid front face of the housing. Preferably
- both the front and rear of the housing are closed.
The substantially tubular housing wall which encloses
. the spinner is substantially streamlined at 1-east along the
front end of the wall and preferably along the entire
length of the wall. The extent of streamlining should be
such that the air flowing along the wall has a boundary
1 CA 02220362 1997-11-06
WO 96!38391 PCT/EP96/02068
14
layer which is attached to the wall at least along the
front end of the wall (for instance at least the front 25%
of the length of the housing) so as to allow substantially _
steady flow conditions along the front end of the wall, and
preferably along the entire length of the housing.
In order that the boundary layer remains substantially
attached, the wall is preferably substantially free of
flow-distorting steps having a radial depth of more than
about 5cm or lOcm at most, and preferably they are
substantially free of such steps having a radial depth of
more than about 1 or 2cm. A step can be considered to be
flow-distorting if the step has a substantial radial depth
(for instance a depth greater than 2cm or 5cm at the most)
and which has a face, and especially a downstream face
(i.e., the face which faces towards the collecting chamber)
which has a significant radial depth and makes an angle of
more than about 30° to the axis. The angle of any such
face which is present should therefore be not more than 30 °
and is preferably less than 20°, most preferably less than
10°, to the axis (i.e., the downstream face should make an
angle of at least 150°, and preferably approaching 180°
with the downstream surface of the housing).
The upstream face (i.e., the face which faces towards
the rear end of the spinner) preferably makes an angle of
not more than about 45° to the axis (i.e., the upstream
face and the upstream surface of the housing makes an angle
of more than 135°), and preferably the angle is less than
30° and is preferably less than 15°.
The total cross-sectional area of the rotors is
preferably as large as possible with respect to the maximum
cross-sectional area of the spinner housing, and is
preferably at least 50%, and most preferably at least 55%
of the area. It can be up to 85% or 900, but it is often
adequate that it is up to, say, 70 or 750 of the maximum
area. For instance the spinner cross sectional area
typically is 0.3 to 0.6m2 and the rotor area is 0.15 to
0.4mZ.
CA 02220362 1997-11-06
WO 96/38391 PCT/EP96/02068
The rotors can be slightly conical or domed, but
preferably are substantially cylindrical.
The spinner may contain solely the first rotor and
one, or more usually two, subsequent rotors, but preferably
5 there are three subsequent rotors.
The first rotor generally has a diameter in the range
100 to 250mm, often around 150 to 200mm. Each subsequent
rotor generally has a diameter in the range 150 to 400mm,
often around 220 to 350mm. Typically the first rotor has
l0 a diameter in the range 220 to 300mm and the subsequent
rotors have a diameter in the range 300 to 350mm.
The rates of revolution of the rotors are generally
such that the f first rotor has an acceleration f field of 8 to
100km/sec2 while the subsequent rotors provide an
15 acceleration field which is normally at least as much as
the field on the first rotor and is often at least 1.5
times the acceleration field on the first rotor, and is
generally in the range 20 to 300km/sec2. For instance when
relatively coarse fibres are required the acceleration
field on the first rotor is typically in the range 8 to
25km/secZ while the acceleration field on each of the
subsequent rotors is higher and is typically in the range
15 to 70km/sec2. However when finer fibres are required,
the acceleration field on the first rotor is typically in
the range 30 to 100km/sec2 and the field on the subsequent
rotors is typically higher and is in the range 80 to
3 50km/ sect.
The front part of the spinner housing can be
streamlined by being tapered inwardly towards the base of
rotors in the front face, for instance at an angle of up to
45°, preferably at an angle of not more than about 20 or
30°. This tapering can be over a relatively short
distance, for instance up to 5cm or perhaps lOcm. The
defined percentages of the area of the housing can then
apply to the front portion only of the housing, for
instance the first 5 or lOcm of the housing. In
particular, preferably the rotors havean area of at least
CA 02220362 1997-11-06
WO 96/38391 PCT/EP96/02068
16
50~ of the cross-sectional area defined by the front lOcm
of the housing. Any wider part of the housing behind this
front part may have little or no effect on the potential
for turbulence around the front face if the housing is
shaped appropriately. However if desired the tapering can
be over a longer distance.
Generally, however, the housing has substantially
parallel sides leading from adjacent the front face (e.g. ,
within 5cm) to its extreme rear end or to a position near
its rear end sufficiently far from the front face to avoid
having significant turbulence-inducing consequences on the
air flowing around the front end. For instance steps or
other shapes due to supply pipes or motors in the rear 25%,
and usually in the rear 10%, of the total length of the
cascade spinner are usually acceptable. Further, as
explained below, if any outer tubular duct is shaped
appropriately it can be suitable for the streamlined part
of the housing to extend only along a minor part of the
total length of the spinner.
2o It is also possible for the substantially parallel
sides to merge into an inwardly tapered rear section, so
that the diameter of the housing expands gradually outwards
from the rear end towards the front end of the spinner
housing. Thus particularly effective streamlining can be
achieved by having the housing tapering rearwards towards
a narrow housing end and having an air supply inlet pipe
subtantially co-extensive with that narrow end.
In order to avoid the inconvenience, and the
turbulence, created by having motors for the rotors all
substantially off-set from the respective rotors, for
instance as shown in U.S. 5,131,935, it is desirable that
the motor means for driving the motors are confined
substantially within the periphery of the cascade spinner.
If the cascade spinner has a closed outer housing, it is -
permissible for there to be, for instance, a single motor
located within the housing and provided with appropriate
drive belts and/or appropriate gearing to transmit the
CA 02220362 1997-11-06
WO 96/38391 PCTlEP96102068
17
drive from that motor to the individual rotors. However it
is strongly preferred that the motor means in the cascade
spinner should comprise a motor for each rotor
substantially co-axial with that rotor. This eliminates
the need for belts or other means for transferring the
drive laterally from the motor to the rotor. The provision
of a motor for each rotor substantially co-axial with that
rotor is a convenient way of providing a streamlined
cascade spinner consisting of a series of individual rotor
units, each containing a rotor and a motor.
The motors may be wholly enclosed within the housing
of the spinner. However often the motors are located
beyond the rear of the housing or at least beyond any rear
wall in the housing, in order that they can be exposed to
the cooling effect of air flowing along the housing. Any
step at the front of a motor which would tend to distort
flow is preferably provided with a baffle that faces
downstream and that is at an angle of less than 30° to the
axis. Since total streamlining at the rear end may not be
critical, it can be permissible for the motors to extend
slightly outside the area of the peripheral housing.
Preferably there are means for adjusting individually
the speed of rotation of one or more of the rotors separate
from one or more of the other rotors. For instance if each
rotor is driven by its own associated, substantially co-
axial, variable speed motor then it is possible to adjust
the speed of rotation of each rotor independently of the
speed of rotation of all the other rotors.
The cascade spinner must be provided with the primary
air supply means for blasting air across the surfaces of
the rotors at least in the outer periphery region of the
rotors, that is to say in the regions of the rotors that
are adjacent to the outer periphery of the cascade spinner.
The primary air supply means generally extend around
at least one third, and usually at least half, of each of
the subsequent rotors.
CA 02220362 1997-11-06
WO 96/38391 PCT/EP96/02068
18
The primary air is intended primarily to assist in the
formation and transport of fibres and so it should be
provided for each of the subsequent rotors, off which fibre
formation occurs. However it may also be provided for the
first rotor, especially when the construction of rotors and
the method of use of the rotors involves significant fibre
formation off the first rotor.
Each primary air supply means generally comprises an
annular slot. This may be a continuous slot or it may be a
series of orifices that are adjacent to each other. The
inner diameter of the slot (or the orifices) can be larger
than the diameter of the associated rotor, for instance by
up to 20 or even 50mm in some instances, but it is
generally preferred that the inner diameter should be
substantially the same as the diameter of the associated
rotor or not more than about 10 or l5mm more.
The primary air blast may be wholly axial or may have
a tangential component, so that the blast emerges from the
slot in a helical direction. If it has a tangential
component, there may be means in the slot for varying the
angle of the air blast, for instance as described in
W092/06047, within the length of one or more of the slots.
The primary air supply means may consist of inner and
outer slots, where the outer slot merges with or is close
to the inner slot and wherein the slots are constructed so
as to impart different directions of movement to the
primary air as it is blasted through the inner and outer
primary slots.
The primary air flows through the slot under
substantially steady flow conditions such that it
preferably flows along the rotor surface as a wall jet.
There can be secondary air supply means for blasting
a secondary supply of air from the spinner. The secondary
air supply means may be arranged as a further annulus
outside the primary air supply slots or may be positioned
in some parts only of the front face of the cascade
spinner, for instance primarily beneath the rotors. This
CA 02220362 1997-11-06
WO 96!38391 PCT/EP96/02068
19
secondary air supply serves primarily to promote transport
of the fibres away from the spinner.
Although the primary air blast, and any secondary air
' blast, generally emerges from the respective air supply
means in a direction which is substantially parallel to the
' axis of the rotors, it may emerge with a non-axial
component, or it may acquire a non-axial component after
emergence, for instance due to helical rotation of the
primary air stream, and thus may have an overall direction
which is a diverging cone.
The primary air axial velocity is generally in the
range 60 to 170m/s, preferably 70 to 120m/s. These values
are calculated on the basis of the rate of flow (Nm3 per
second) through the area of the primary air supply means,
i.e., the open area of the slots. If secondary air is
blasted from the spinner, its axial velocity (measured in
the same manner) may be in the same range or may be less,
for instance down to 30m/s.
The novel cascade spinner (with or without a
surrounding tubular duct) can be used in a wide variety of
cascade spinning processes for making MMVF, especially
stone products. It can be used as a replacement for a
conventional cascade spinner. It has the advantage that it
can be lightweight and compact and its operation can use
less energy than many conventional spinners. Accordingly
the invention includes, inter alia, all processes for
making MMVF products which utilise the defined cascade
spinner which is enclosed within a spinner housing which
defines a substantially closed outer periphery and in which
the cross-sectional area of the first and subsequent rotors
is at least 40% of the maximum cross-sectional area defined
by the spinner housing, as explained above.
The benefit of the spinner is particularly significant
when it is desirable or necessary to regulate the flow of
air around the spinner, especially the flow of induced air
around the spinner. In order to maximise the benefit of
this, the cascade spinner is preferably mounted within a
CA 02220362 1997-11-06
WO 96/38391 PCT/EP96/02068
substantially tubular duct that surrounds the housing. For
instance a substantially tubular duct may be mounted around
and relatively close to the spinner so as to define a
relatively narrow passage between the duct and the outer
5 housing of the cascade spinner, often along the entire
length of the spinner.
Preferably the tubular duct and the outer housing are
both constructed to define between them a passage which
provides for steady flow conditions to prevail in the air
10 which is flowing through the passage. Thus the boundary
layers of the air should remain substantially attached to,
respectively, the outer wall of the spinner housing and the
inner wall of the tubular duct, at least close to the front
end of the spinner housing. Accordingly the inner wall of
15 the tubular duct should be substantially streamlined, at
least in the region close to the front end of the tubular
duct and so should be substantially free of steps which
have a radial depth and a downstream face angle such as to
distort flow by separating the boundary layer from the
20 inner surface of the duct.
If there is a relatively narrow passage between the
spinner and the duct, it may be desirable to force air, for
instance by a blower, through this relatively narrow duct
to serve as secondary air for a spinner in which primary
air is blasted through annular slots around the rotors.
In order to achieve sufficient primary air and
transport air with conventional spinners, it is necessary
to force very large volumes of air through the spinner.
However the compact nature of the novel and other preferred
cascade spinners, and the small.cross-sectional area of the
closed housing relative to the area of the rotors, and the
ability to mount it in a substantially tubular duct that
can optimise induced air flow, combine to allow for a
significant reduction in the amount of air which has to be -
forced through the spinner. For instance the volume
(Nm3/s) of primary air typically can be less than half or
even a quarter or less of the volume that is required in a
CA 02220362 1997-11-06
WO 96/38391 PCT/EP96/02068
21
conventional cascade spinner of similar fibre-forming
capacity. This allows for a great reduction in the
pipework and other equipment associated with the air supply
means in the spinner. In particular, it allows for a very
great saving in the energy which is required to provide the
necessary primary air since the energy consumption is
related to the third power of the volume (in Nm3) of air.
The spinner can be mounted for pivotal or oscillatory
movement alone or with the tubular duct and a preferred
arrangement providing for such pivotal or oscillatory
movement is described in more-detail below.
Although the passage between the spinner and the outer
substantially tubular duct can be relatively narrow,
preferably there is a relatively large passage as a result
of the open cross-sectional area in the open end of the
duct around the spinner being quite large. The part of the
passage which primarily controls the nature of the air flow
that is carrying the fibres away from the spinner is the
annular collar around the front end of the spinner and the
front end of the spinner portion. Preferably at least 50%
of the cross-sectional area of the front end of the spinner
portion should be open to the flow of air sucked through
the spinner portion by the suction means. Since the
spinner is preferably closed to the flow of air sucked
through the spinner housing, the cross-sectional area of
the annular collar is preferably at least 50% of the cross-
sectional area of the front end of the spinner portion.
The open area is generally 50 to 950 of the total cross-
sectional area of the open end of the tubular duct. Often
the open area is at least 60%, but often not more than 80%,
of the total area of the open end of the duct.
In order that subtantially steady flow conditions
exist in the air passing through the collar the collar must
. be substantially streamlined (i.e., substantially free of
f low-distorting protruberances) and must have a sufficient
length that substantially steady flow conditions exist in
the air emerging from the collar as a result of the air
CA 02220362 1997-11-06
WO 96!38391 PCTlEP96/02068
22
adjacent to each of the spinner and the tubular duct being
attached as a boundary layer as it passes through the
collar. The length of the collar required in order to
provide substantially steady flow conditions in the air
emerging through the collar will depend upon the
construction of the spinner and tubular duct upstream of
the collar (i.e., towards the rear end of the spinner).
For instance steady flow conditions can be achieved in a
relatively short collar if the tubular duct is constructed
so as to provide acceleration of the air as it passes
through the collar, due to the collar having a narrower
cross-sectional area than the upstream parts of the passage
leading to it. Thus it can be in the form of a nozzle. The
collar can have a substantially uniform width over a very
short axial length when a nozzle effect is being achieved
but generally has an axial length of at least 5cm where it
has substantially uniform width relative to the spinner
housing. Often the collar has a substantially uniform
width over at least 25~ of the length of the spinner
housing.
The collar can be regarded as the annulus between the
front ends of the spinner and the housing that controls the
flow of air that emerges from the collar, and so can be
very short in some instances where there may be
acceleration within the passage, or longer when the passage
has parallel sides.
The outer tubular duct can be generally cylindrical .
but if desired it can be conical or it can be conical
merging into cylindrical at its front end. Often it is
preferred that the substantially tubular outer duct should
be substantially cylindrical except for a wider inlet area
at its rear end which tapers towards a cylindrical body.
Its cross section can be circular or non-circular, e.g.,
elliptical.
The substantially tubular wall of the spinner housing
is generally non-circular and instead approximately follows
the configuration def fined by the arrangement of rotors , but
CA 02220362 1997-11-06
WO 96/38391 PCT/EP96l02068
23
if desired it can be truly cylindrical. Accordingly the
annular passage between the housing and the tubular duct
generally is not a regular annulus.
The width of the annular collar around the spinner can
be subtantially uniform or it can be variable, with the
collar usually being wider below the spinner than above it,
as explained below. ~It is usually preferred that the collar
is, however, substantially complete, in that preferably
there is an open air passage around the entire periphery of
the spinner. If any part of the collar is closed (which is
usually undesirable) it is important that the collar should
taper in width towards its closed part, so as to avoid
turbulence at the point where the collar is closed.
Usually the assembly of the spinner in the tubular
duct consists solely of the spinner, the substantially
tubular duct, and means for suspending or otherwise
mounting the spinner in the tubular duct so as to define a
complete annular collar around the spinner. However if
desired the tubular duct may contain one or more
concentrically mounted or eccentrically mounted ducts
within the main tubular duct, provided that these inner
ducts do not create undesirable turbulence or eddies in air
being induced through the annulae defined between the inner
and outer ducts and provided these inner ducts do not
reduce unacceptably the overall open area of the collar and
through which air can flow through the duct. For instance
they may be a tubular duct surrounding and close to the
spinner housing and an outer tubular duct surrounding it.
The total passage for the flow of induced air, and the
collar, is thus divided into inner and outer annuli by the
inner duct but the passage, and the open area, is not
. significantly altered by the presence of the inner duct.
It is also possible to provide for tubular pipes or
other pipework to extend, generally substantially parallel
to the spinner and outer tubular duct, from at or near the
rear of the spinner to the front end of the duct. For
instance a secondary air blast may be introduced beneath or
CA 02220362 1997-11-06
WO 96/38391 PCT/EP96102068
24
around the spinner in this manner. It is generally
desirable to keep such pipes or other supply devices to a
minimum since they reduce the open area between the spinner
and the tubular duct. Again such supply pipes or other
devices should be sufficiently streamlined to avoid
creating undesirable turbulence in air flowing through the
annular passage.
The length of the tubular duct extending rearwards of
the front face of the spinner is usually at least 30%, and
preferably at least 60%, of the length of the spinner, that
is to say the distance from the front face of the rotors to
the rear end of the housing or, if further, to the rearmost
part of the rearmost motor. Often the duct is at least as
long as the spinner and frequently is three times, or even
five times the spinner length or more.
The front end of the tubular duct l S T1YP'fAYalll
substantially coplanar with the front end of the spinner,
and in particular it is generally substantially coplanar
with the front face of the spinner. If the tubular duct
has a front face that is too far downstream of the spinner
the fibres and shot that are thrown off the rotors will be
liable to foul the front end of the tubular duct, instead
of being thrown into the collecting portion of the chamber.
If the tubular duct has its front end undesirably upstream
of the spinner housing there is a reduction in the control
of the induced air around the front end of the spinner.
It is necessary to be able to pour melt on to the top
rotor from outside the chamber. It may be sufficient to
provide an opening in the top of the tubular duct to allow
melt to be poured through this opening direct on to the top
rotor, but often there is an opening in the tubular duct
and a gutter leading from beneath this opening to above the
rotor. Melt can thus be poured through the opening on to
the gutter and from the gutter on to the top rotor.
When the cascade spinner is mounted in the spinner
portion of the chamber or in some other tubular duct
defining a relatively large open area around the spinner,
CA 02220362 1997-11-06
WO 96!38391 PCT/EP96/02068
it is preferred to mount the spinner in a position higher
than the central position of the tubular duct. This allows
for a larger amount of air to be induced beneath the
spinner than around and above the spinner, and this can
5 provide for improved transport of fibres towards the
collector.
. Generally the spinner is mounted so that the vertical
separation between the lowermost subsequent rotor and the
lower part of the tubular wall of the tubular duct is at
10 least 1.2 times and preferably at least 1.5 times the
vertical separation between the top of the first rotor and
the uppermost part of the wall of tubular duct. The ratio
between these lower and upper separations is usually at
least 2 and often at least 3 or 4. It can be as high as
15 10 and indeed in some instances it may be unnecessary to
have any significant air flow along the top of the spinner,
in which event the ratio may be very high. Generally,
however, the ratio is below 20, and frequently below 10.
The maximum horizontal transverse dimension of the
20 spinner is frequently the width of the spinner on a
horizontal line extending substantially through the axis of
the second subsequent rotor. The width of the spinner
measured through this axis is generally from 25 to 75~,
often around 30 to 60%, of the width of the chamber
25 measured at the same horizontal position. This ensures
that there is an adequate open area around each side of the
spinner.
The spinner is normally mounted within the tubular
duct so that the ratio of the separation between the
lowermost subsequent rotor on one side and that side of the
tubular duct to the separation of the lowermost subsequent
rotor on the other side and that other side of the tubular
duct is reasonably close to 1:1, for instance in the range .
3:1 to 1:3, preferably 2:1 to 1:2.
Conventional cascade spinners are mounted on a solid
base, typically a concrete floor or on rails. Because of
their weight, they are relatively difficult to move, even
CA 02220362 1997-11-06
WO 96!38391 PCTIEP96/02068
26
though they may be mounted on wheels. An advantage of the
novel spinners of the invention is that they are very
compact and lightweight and so do not have to be mounted on _
a solid base. Instead they can be suspended from suitable
supports. In particular, the spinner can be suspended
from the sides and/or upper parts of the tubular duct. The
spinner can be suspended by a hanger from the top of the
tubular duct or it can be suspended by a plurality of
supports, such as plates or rods, which extend from the
sides and/or upper parts of the tubular duct.
The means for suspending or otherwise mounting the _
spinner in the tubular duct can include means allowing for
oscillation of the spinner, with respect to the tubular
duct, about a substantially vertical axis or about a
horizontal axis which can be substantially parallel to the
axes of rotation of the rotors or substantially
perpendicular to them. Alternatively, the entire assembly
of tubular duct and spinner may be mounted for such
oscillation or pivoting.
Preferably the spinner and its surrounding tubular
duct are mounted for oscillation together about a vertical
axis since this ensures that induced and forced air flowing
through the duct will tend to oscillate with the
oscillation of the spinner. Oscillation of the spinner
about a substantially vertical axis is typically through a
relatively small oscillation angle, often 5 to 30° (e. g.,
2.5 to 15° either side of a central axis). The total
angle of oscillation is generally at least 7° and usually
at least 10 ° . It is generally unnecessary for it to be
more than about 25° and often it is not more than about
20°. A range of around 14 to 20° is often suitable.
The oscillation is preferably conducted at a frequency
of at least 0.05Hz, usually at least O.lHz. It can be
conducted at values of up to, for instance, 2Hz but 1Hz is
normally a convenient maximum. A frequency of about 0.3 to
0.6 or 1Hz is usually preferred. The oscillation can be
applied continuously or occasionally. The frequency of
CA 02220362 1997-11-06
WO 96/38391 PCT/EP96/02068
27
oscillation can be varied in accordance with process
conditions. For instance the rate of travel of the
collector may be varied in proportion to the rate of
' collection of web so as to provide a substantially uniform
weight per unit area of web despite variations in the
throughput of melt. Preferably the frequency of
oscillation is varied in accordance with the rate of travel
of collector in that the frequency can increase as the rate
of travel increases and can decrease as the rate decreases .
Preferably the frequency is varied in substantially direct
proportion to the rate of travel of the collector so that
one cycle of the oscillation corresponds to a substantially
constant length of travel of the collector.
The oscillation about a substantially vertical axis
can have a beneficial effect on the uniformity of fibre
lay-down on the collector and can improve properties of
batts, for instance made by cross-lapping the web that is
formed on the collector.
Oscillation of the spinner, or the spinner and duct,
2o about a substantially horizontal axis which is
substantially perpendicular to the axes of rotation
likewise can be at a similar rate and can have a beneficial
effect on fibre lay-down.
Oscillation of the spinner is preferably about a
substantially horizontal axis substantially parallel to the
axes of rotation of the rotors and can be a repeated
oscillation but preferably takes the form of an adjustable
pivoting of the spinner from one fixed position to another
ffixed position. Usually the spinner pivots within the
duct, but if desired the duct and spinner can pivot
together. By this means it is possible to vary the angle
between a horizontal line passing transversely through the
centre of the first rotor and a line drawn between the
centre of the first rotor and the centre of the first
subsequent rotor. Typically the spinner is mounted so that
it can be controllably pivoted such that the described
angle can have any selected value generally within the
CA 02220362 1997-11-06
WO 96!38391 PCT/EP96/02068
28
range zero to 30°, often zero to 20° most usually around 5
to 10°. Varying this angle, and consequently the angular
disposition of the second and any third subsequent rotor
relative to each other, can significantly influence fibre
formation.
Although it is desirable that the annular passage
defined between the spinner and the tubular duct should be
substantially streamlined, it can be desirable to include
guides in the passage for imparting a non-axial component
to air flowing through the passage. These guides can be
arranged so as to provide an overall helical component to
the air passing through the passage means. Preferably
however the guides are constructed so that each can impart
a non-axial movement to an axial segment of the air flowing
through the passage, since this allows for the guides being
shaped to provide different non-axial movement to different
axial segments of air flowing through the passage. For
instance the guides in one lowermost quadrant of the
tubular duct may tend to impose a clockwise rotation to the
air passing through that quadrant, while the guides in the
adjacent quadrant may tend to impose a counter-clockwise
rotation to the air passing through that quadrant, or vice
versa. For instance the air flow in any particular region,
e.g., beneath the spinner, can be maximised by this
technique.
The guides can be fixed and permanently shaped blades
to provide these different non-axial movements to different
parts of the air flow, but preferably the guides are
adjustable so that the direction of air flow can be
adjusted during use of the apparatus in response to
variations in performance.
In addition to the guides causing rotational movement,
it is generally preferred that they are shaped and
positioned to promote an outward conical component to the
air flowing out of the tubular duct, for instance away from
the spinner and towards the collector.
CA 02220362 1997-11-06
WO 96!38391 PCT/EP96/02068
29
The guides are usually in the front end of the
substantially tubular duct surrounding the spinner. The
guides can be on the spinner but preferably they are blades
mounted on the inner wall of the tubular duct extending in
a substantially longitudinal direction so that they do not
create unacceptable blockage of the passage between the
spinner and the tubular duct.
Small jets of forced air can also act as guides, in
which event such jets may be on or in the spinner housing
or on the tubular duct.
The spinner of the second aspect of the invention is
preferably used in the first aspect wherein the described
tubular duct is the tubular duct of the spinner portion of
the chamber of the first aspect. The collecting portion of
the chamber in the first aspect is preferably constructed
so as to minimise, and preferably substantially prevent,
the opportunity for air to be sucked into the collecting
por tio:. ~by t he suction ~earis - that- apply suction through
the collector) except through the tubular duct and,
optionally, other known inlets that allow for the entry of
non-interfering amounts of air. For instance some leakage
into the chamber will usually occur from the pit that is
preferably provided beneath the open end of the duct for
_ collecting shot, but the amount of air that enters through
this can easily be controlled so that it does not
significantly influence the performance of the process.
Generally the chamber is substantially closed except
for the collector through which suction is applied and the
open area of the open end of the duct around the spinner
3o and except for inlets for desired additives. For instance
recycled MMV fibres entrained in air can be introduced into
the collecting chamber through one or more inlets in the
walls of the chamber.
. The air forced through the spinner is usually only the
primary air but, as mentioned above, there can be secondary
air forced through the spinner as well as primary air.
optionally a controlled and non-interfering amount of air,
CA 02220362 1997-11-06
WO 96/38391 PCT/EP96/02068
less than the air that is forced through the spinner and
sucked through the open area of the duct, can also be
allowed to enter the collecting portion of the chamber
through the spinner end. For instance a controlled amount
5 of secondary air can be forced through passages in the
spinner end of the collecting portion or a controlled
amount of air may be sucked through annular or other
openings in the spinner end of the collecting portion.
Preferably at least 50%, and generally at least 75% or
10 at least 850 of the total volume of air (in Nm3/s) that is
sucked out of the chamber (through the collector) enters
through the tubular duct and spinner.
Air is sucked through the collar as a result of the
suction which is applied through the collector into the
15 substantially closed collector portion. Usually the air
flow through the collar is induced in this manner and there
are no means for forcing any air, or signfiicant quantities
of air forward through the duct. _H_owevPr i~ somfl i"~.~~.,..
~.~~a.~~es
it may prove useful to provide such means (for instance a
20 blower at the open rear end of the duct) to assist in
control of the induced air sucked through the duct.
As a result of constructing the chamber so that most
or substantially all the air sucked through the collector
has to be provided by the air blasted through the spinner
25 and induced through the tubular duct, and as a result of
ensuring that the open area around the spinner through the
duct is sufficiently large, it is possible easily to
control the induced air flow through the passage so as to
minimise turbulence in the collecting portion of the
30 chamber. With conventional spinners having a very high
primary air velocity and a low air velocity around (and
often spaced away from) the spinner, very high velocity -
gradients prevail in a radial direction around the spinner
and these necessarily cause significant turbulence. In the
invention, it is easily possible to control the supply of
primary air and the degree of suction so as to minimise
unacceptable velocity gradients.
CA 02220362 1997-11-06
WO 96/38391 PCTlEP96/02068
31
In particular, the forced air and the dimensions of
the apparatus are preferably such that the mean axial
velocity of the air induced through the open cross-
' sectional area of open end of the tubular duct is 5 to 40%,
usually 5 to 30%, of the mean axial velocity of the primary
' air. Generally it is 10 to 20 or 25% of the axial velocity
of the primary air. The mean axial velocity of the induced
air is calculated from the rate of flow of the air (Nm3/s)
and the open area of the open end around the spinner and
through which it is flowing.
Generally the mean axial velocity of the induced air
is 5 to 50m/s, preferably 10 to 35m/s. For instance in a
typical process the primary air may be forced at 100m/s and
the induced air may have a mean velocity of 25m/s. This
contrasts with corresponding figures of, for instance,
above l3om/s and below lOm/s in a conventional spinner.
A particular advantage of the apparatus is that it is
now possible for the amount (in Nm3/s) of forced primary
(o-r-primary and secondary) air to be a smaller proportion
of the total amount of air (in Nm3/s) entering the spinner
portion, and/or sucked through the collector, than with
conventional spinners. For instance good results can be
obtained when the proportion is below 10% and often below
8%, for instance in the range 3 to 6%. This not only
reduces energy requirements, as discussed above, but it
also facilitates maintaining substantially steady flow
conditions for as long as possible where the primary air
merges with the induced air. This is because there is less
tendency for turbulence to occur when the primary air
stream has, for instance, a maximum axial velocity of
120m/s and provides 5% of the total volume of air and the
- secondary air stream has a maximum velocity of 4om/s and
provides 95 % of the volume than when the primary stream has
- a maximum velocity of 160m/s and provides l0% of the volume
and the secondary air stream as a maximum velocity of lOm/s
and provides 90% of the volume. Additionally, the non-
turbulent merging of the streams is facilitated by their
CA 02220362 1997-11-06
WO 96!38391 PCT/EP96/02068
32
close juxtaposition as they emerge from the front of the
spinner, in contrast to their juxtaposition when there is
a significant radial step between the outer edge of the
housing and the outer edge of the primary air slot.
Thus it is now possible to promote the maintenance of
substantially steady flow conditions in the air stream even
after it has left the collar and, in particular, after the
air sucked through the collar has passed the rotors and is
merging with the primary air in the collecting portion.
to Accordingly, in the region in front of the spinner in the
collecting portion, for instance in the first 20cm or
perhaps 50cm the path lines of the air, i.e. , the paths
followed by fibres entrained in the air, are preferably
substantially all non-turbulent and lead from the
substantially streamlined path lines through the collar in
an essentially non-turbulent manner towards the collector.
By minimising turbulence and disruption of the path
lines in the collecting portion the formation of tufts and
balls in the fibres entrained in the conveying air is
minimised.
In order that substantially steady flow conditions do
tend to prevail in, for instance, the first 20cm in front
of the rotors where the primary and secondary air streams
merge, it is necessary that the front end of the spinner
portion should merge with the collecting portion in
preference to merely leading into a collecting portion
having an abruptly increased width for the travel of
entrained fibres, because of the back eddys that would be
formed in the region where the width does increase
abruptly.
However it is generally preferred that the collector
(and therefore the base of the chamber) is wider than the '
width of the spinner end of the collecting portion. In
order to provide the desired merging, rather than an -
unacceptable, flow-disrupting, step, it is preferred that
the side walls of the collecting chamber, or air guide
baffles within the side walls, should diverge outwardly
CA 02220362 1997-11-06
R'~ 96/38391 PCT/EP96/02068
33
substantially conically from adjacent to the open end of
the spinner portion and towards the collector. This avoids
any significant sudden increase in the effective width of
the collecting chamber such as to create unnecessary
turbulence in the chamber. Similarly it is desirable that
' the top wall which defines the upper part of the collecting
portion should also be shaped in a substantially
streamlined manner, and thus it preferably extends
substantially conically upwardly from the top of the open
30 end of the spinner portion.
Although the majority of the melt is converted by the
centrifugal spinner to f ine f fibres which are carried by the
air towards the collector, some of the melt is thrown off
the fibres as unacceptable shot, that is to say coarse
fibres or larger lumps of melt. There is generally a pit
below the open end of the spinner portion in which shot may
collect, and generally there are means for collecting into
the pit shot which is thrown radially outwards from
adjacent the open end of the spinner portion. Preferably
this collecting means comprises a collecting zone that
opens inwardly around the open end for reception of shot,
and leads downwardly to the pit, and the substantially
conical air guide baffle separates this collecting zone
from the remainder of the collecting chamber.
The main flow of fibres and air is thus constrained
within the area defined by the substantially conical air
guide baffle while the shot is thrown through the gap
between the baffle and the open end and falls down into the
pit, from which it may be removed by a screw or other
continuous or batch removal device.
The collector generally has a width greater than the
width of the open end of the spinning portion, for instance
1.1W to 2W, were W is the maximum width of the open end of
the spinning portion.
As a result of arranging that the air flow through the
open area of the tubular duct and into the collecting
portion is as non-turbulent as possible, the amount of
CA 02220362 1997-11-06
WO 96/38391 PCT/EP96l02068
34
balling and tufting of the fibres is minimised. Also, as
the fibres are carried from the spinner towards the
collector, the proportion of fibres that are arranged
substantially parallel to the direction of travel, and thus
in a substantially laminar configuration, is maximised.
It is desirable to collect the fibres while they have
as high a proportion as possible in a substantially laminar
arrangement and with a minimum proportion in a ball or
perpendicular arrangement. Preferably therefore the
collector should be positioned so as to minimise the length
of travel of the fibres from the spinner to the collector.
This minimises the opportunity for loss of laminar
configuration and attainment of a ball configuration.
The horizontal distance from the bottom of the
lowermost subsequent rotor to the collector is therefore
preferably not more than 2W or 2.4W, where W is the maximum
width of the open end of the spinner portion. Preferably
it is at least about 0.8W, often at least about W.
Typically it is less than 2 metres, or at the most 3
metres, but is usually more than half a metre or, more
usually, more than 1 metre.
The collector should be as steep as is practicable, so
as to minimise the horizontal travel of fibres through the
chamber to the top of the collector. Generally the
collector is positioned in the collecting chamber at an
angle of at least 60° to the horizontal. It can be at an
angle of up to 80 ° or even 90 ° ( i . a . , perpendicular ) and
if
desired the top of the collector can even lean towards the
spinner, for instance with the collector at an angle of as
much as 110° or even 120° to the horizontal. Naturally the
suction applied through the collector must be sufficient to
hold the web on the collector, but since the web can have -
a light density only a relatively low suction is required
for this. _
The collector is usually a continuous permeable belt
through which the desired degree of suction is applied
subtantially uniformly over the area of the belt and by
CA 02220362 1997-11-06
WU 96!38391 PCT/EP96/02068
which the web of fibres which collects on the belt can be
substantially continuously carried out of the chamber.
Generally the collector carries the web upwardly out of the
" chamber. However it can, if desired, be arranged to carry
5 the web downwardly out of the chamber.
The web can then be subjected to conventional post-
treatments such as cross-lapping and consolidation.
Preferably the rate of removal of the web is sufficiently
fast that the web is very light, e.g., below 400g/m2, often
10 200-300g/m2 if the web is then cross-lapped or otherwise
laminated to form the final batt.
Binder may be introduced into the web in conventional
manner, for instance by binder sprays located in or on the
spinner, for instance coaxial with one or more of the
15 rotors, or by binder sprays around the spinner or in the
collecting chamber.
The melt that is supplied to the spinner to form the
MMV fibres can be any suitable melt___ of the type
conventionally used for forming stone wool (i.e., material
20 described as rock, stone or slag wool rather than glass
wool) and thus typically contains various elements
including significant amounts of Si02 and usually at least
15% alkaline earth oxides (Cao and Mg0) and relatively low
amounts (usually below 10%) alkali metal oxides. The
25 amount of A1203 can be low (below 10% and often below 4%)
or it can be higher, e.g., up to 300. Any of the
conventional melt-forming compositions can be used. A
typical melt is given in W092/12941. The melt temperature
is generally in the range 1400°C to 1600°C on the top
30 rotor.
In order to increase the production of a plant without
reducing product quality, it can be convenient to restrict
the throughput of melt on a cascade spinner and to increase
_ the number of cascade spinners.
35 For instance there can be two cascade spinners in
side-by-side relationship within an appropriately shaped
spinner portion (generally a substantially elliptically
CA 02220362 1997-11-06
WO 96/38391 PCT/EP96/02068
36
shaped tubular duct) but more usually there are at least
two of the cascade spinners each positioned within its own
associated spinner portion. These spinner portions may be
arranged substantially parallel to one another so that each
opens to the spinner end of a single collecting portion.
Thus a single collecting portion may be supplied by two or -
more spinner portions and there may be a single collector
for receiving the fibres from both spinners.
Often, however, two or more assemblies of the spinner
and chamber are arranged in side-by-side relationship.
Thus one apparatus comprising the defined spinner and
chamber may be arranged in side-by-side relationship with
at least one other assembly of spinner and chamber.
Each spinner may be provided with melt from its own
dedicated cupola or other furnace, but often a single
furnace will supply melt to two or more spinners.
By the invention it is easily possible to adjust the
rate of supply of melt and the conditions of operation so
that the fibre diameter can be relatively coarse, for
instance 3.5 to 5.5/cm, or relatively fine, for instance 2
to 3.5/cm, and the product can have relatively low density,
for instance 20 to up to 100kg/m3, or relatively high
density, for instance 100 to 300kg/m3. This can be
achieved easily merely by altering the speed of rotation of
one or more of the rotors and/or by pivoting the spinner
about a horizontal axis so as to change the angles between
the first and subsequent rotors.
The resultant MMVF materials can be used as, for
instance, fire, heat or sound insulation or protection, as
3o an agricultural growing medium, or as a filler, or for
other conventional MMVF purposes.
A particular advantage of the invention is that it is -
easy to control and perform the process efficiently, thus
allowing for reduced production costs or improved products,
or both. For instance it is easily possible to obtain a
good combination of lambda, density and tensile strength
using very economically advantageous operating conditions
CA 02220362 1997-11-06
WU 96/38391 PCT/EP96/02068
37
such as melt capacity and energy input (for the forced air
supply and for the rotors).
The shot content can easily be below 35% by weight,
for instance below 32%, and often in the range 25 to 30%.
The tensile strength (measured in conventional manner on a
slab 100mm thick having a density of 30kg/m3 and 1.2%
binder content) can easily be, as initially manufactured,
at least 10 and often at least l3kN/m2 up to for instance
18 or 2 OkN/m2.
A particlar advantage of the products of the invention
is that they can maintain an unusually high proportion of
their tensile strength after being compressed 30 to 60% for
24 hours. This test gives an indication of the tensile
strength after conventional compression packing, and
usually results in a reduction of 40% or more. In the
invention the reduction is less than this, typically in the
range 10 to 20 or 30%.
By the invention it is easily possible to make a
product which, after compression, has a tensile strength of
8 to 15, often 9 to 14, kN/mz. Since the products of the
invention can retain more of their tensile strength after
compression than conventional products, and since the
choice of product for any particular purpose is often
dictated in part by its tensile strength, it follows that
a benefit of the invention is that it is possible to
provide a tensile strength after compression much more
economically than can be achieved when the initial product
loses a large amount of its tensile strength during
compression. By the invention it is possible to achieve
products having, for instance, a density-lambda
relationship approaching or equivalent to the relationship
defined in W092/12941, in a very economical and convenient
manner.
The invention is now illustrated in the accompanying
drawings in which:-
CA 02220362 1997-11-06
WO 96/38391 PCT/EP96102068
38
Figure 1 is a longitudinal horizontal cross section of
apparatus according to the invention (taken on the line I-I
in Figure 2)
Figure 2 is a longitudinal vertical cross section of
the same apparatus (taken on the line II-II in Figure 1)
Figure 3 is a transverse cross section taken on line
III-III in Figure 2 and shows the novel spinner in more
detail (it is shown diagrammatically in Figures 1 and 2)
Figure 4 is a longitudinal cross section of the
spinner shown in Figure 3, taken on the line IV-IV (not to
scale)
Figure 5 is a view similar to Figure 1 but of an
apparatus having a shorter tubular duct
Figure 6 is a cross section similar to Figure 1 but of
an apparatus having two spinners
Figures 7A and 7B are two schematic diagrams of air
velocity profiles where V is velocity and R is the radial
distance from the centre of a primary air slot.
The apparatus comprises a cascade spinner 1 located
within a chamber 2 which comprises a collecting portion 3
which has a spinner end 4 adjacent to the cascade spinner
1, and a spinner portion 5. This spinner portion 5 has a
rear end 6 which is open to the atmosphere and a front end
7 which opens into the spinner end of the collecting
portion 3.
There is a substantially tubular duct 8 extending
between the front end 7 and the rear end 6. The front ends
of the cascade spinner 1 and the duct 8 define between them
an open annular collar 9. Air can be induced to flow
through this collar from along a passage 10 extending back
from the collar 9 towards the rear end 6.
In the apparatus which is shown, the collar 9 merges '
with and is coextensive with the passage 10, since the
spinner and duct are both shown as being substantially -
parallel sided. However if the tubular duct 5 is, for
instance, in the shape of a converging cone the annular
passage 10 will have decreasing open area towards the front
CA 02220362 1997-11-06
WO 96/38391 PCT/EP96/02068
39
of the spinner, and the relevant open cross sectional area
around the spinner for axial forward flow of induced air
from the passage will then be the collar 9 between the
spinner and the front end 7 of the spinner portion 5.
The collecting portion 3 has side walls 12, end walls
' 13 merging with the spinner portion, a top wall 14 merging
with the spinner portion and with the side walls, and a
base comprising a pit section 15. and an inclined conveyor
16. Behind the collector 16 there is a suction chamber 18
from which air is drawn by a suction pump 19. The suction
chamber 18 is coextensive with the collector 16 and thus
sucks air from the collection portion over the entire area
of the collector, although the greatest amount of suction
will be applied where the web is thinnest.
The collector 16 is conveniently a slatted conveyor
belt or other porous carrier that can run continuously
around rollers 20, 21 and 22.
During operation of the apparatus, fibres collect on
the collector 16 to form a thin web 23 which is carried
upwardly by the collector and is taken off by the take-off
apparatus 24. From that position it can be subjected to
conventional treatments such as cross lapping and
consolidation. Rollers 25 act as seals to prevent
significant ingress of air around the conveyor.
The pit zone 15 includes a trough 26 set in the base
of the pit area and having a closed end and a sluice or
rotary valve at the opposite end (not shown). A screw
conveyor 27 rotates within the trough 26 to carry shot
which collects in the trough out through the sluice or
valve. This openable end may be permanently open,
provided that it is designed such that only a limited
. amount of air can enter through it, or it may be opened
from time to time to allow the discharge of shot by the
conveyor from the trough.
There are air guide baffles 32 in each side of the
collecting chamber extending from the wall 12 to an open
edge 33. These air guide baffles 32 diverge outwardly
CA 02220362 1997-11-06
WO 96/38391 PCT/EP96/02068
substantially conically from the edge 33 which is adjacent
to the open end 7 of the spinner portion. The top wall 14
also extends substantially conically upwards. Preferably
the angle that the top wall and each of the air guide
5 baffles makes to the axial direction is not more than about
45°, preferably about 15 to 30°.
There is a shot collecting zone 35 around the open end
7 of the spinner portion. One side of the collecting zone
is defined by the chamber end wall 13 and the other is
10 defined by the edge 33 and the baffle 32. Shot thrown
radially outwards from the spinner is thrown through the
gap between edge 33 and wall 13 into the zone 35. The
side wall 12 merges inwardly near its base with the baffle
32 so as to cause shot that slides down the collecting zone
15 35 to fall into the trough 26.
The spinner 1 comprises a peripheral tubular housing
40 closed at its rear end by an end plate 41 and at its
front end by a facing plate 42. A top first rotor 43 and
subsequent rotors 44, 45 and 46 are mounted as a cascade in
20 conventional manner, so that melt thrown on to rotor 43 is
accelerated and thrown on to rotor 44 , optionally with some
fibre formation on rotor 43, some of the melt on rotor 44
is thrown off as fibres while the rest is thrown on to
rotor 45. Some of the melt on rotor 45 is thrown off as
25 fibres while the rest is thrown on to rotor 46, off which
it is thrown as fibres. Each rotor is mounted on an axle
47, which conveniently rotates within a fixed sleeve 48
around bearings 49. Rotation of the axle is caused by a
motor 50, there being one motor 50 mounted on each axle.
30 The motors 50 may be enclosed within the housing 40 or may
be positioned behind the rear plate 41 if desired.
It is necessary that there should not be any '
significant inward steps in the passage 9 sufficient to
disrupt severely the flow of air past the front of the
35 spinner. Disruption of the flow at the back of the spinner
is less important and so small steps there can be
tolerated.
CA 02220362 1997-11-06
WO 96!38391 PCT/EP96/02068
41
Annular slots 53, 54, 55 and 56 extend around the
outer peripheral regions of each of rotors 43 to 46
respectively, except that slot 53 is around only a small
part of the outer peripheral portion of rotor 43. The
inner edge of each slot has the same diameter and is co-
axial with the associated rotor. Blades 57 are positioned
within each slot to regulate the angle at which air emerges
from the slot. All the blades in.a slot can be aligned in
a similar manner or they can be aligned at different angles
so as to impart variable amounts of tangential flow to the
air that emerges from each slot.
There is an air chamber 59 within the housing 40 for
leading air simultaneously to each of the slot and for
blasting it out of the slots at, for instance, 100m/s.
This chamber leads from an air supply pipe 60 by which air
is forced under pressure and at high speed towards the
slots 53 to 56. This air emerges as the primary air.
-3n--order to modify the air flow, air can also be
forced out of the housing through other positions, for
instance thorough orifices 58 leading from supply duct 64,
and this is the secondary air.
The outer profile of the housing 40 follows throughout
most of the length of the spinner, towards the front, the
line 61. However if the spinner followed this line up to
the rotors, the junction of this shaped outer housing with
_ the front face 42 would create a significant inwards step
in the areas 62 between each adjacent pair of rotors.
Accordingly the housing in these areas 62 is tapered
inwardly, at an angle of around 20 to 30° so that the area
of the front face 42 is less than the total area defined by
the line 61. This tapering is usually conducted over, for
instance, the 5 to lOcm closest to the rotors.
Although the duct 8 and the spinner housing 40 are
shown as being parallel sided and defining a substantially
parallel sided annular passage they can have other shapes,
provided they are adequately streamlined. There is an
CA 02220362 1997-11-06
WO 96/38391 PCT/EP96/02068
42
outward flare 63 in the tubular duct 8 so as to facilitate
the collection of air into the duct.
The spinner is provided with binder sprays 65 coaxial
with and on the front edge of each of the rotors and
supplied by pipe 66, in conventional manner. Binder sprays
may also be provided elsewhere on the front face of the
spinner and/or on jets positioned around the spinner in the
open end 7 of the spinner chamber 5.
The spinner is suspended by plates or rods 70 from the
sides and top of the tubular duct 8. These rods can be
rigid but if desired they can be provided with means for
synchronised extension and contraction so as to provide
means for pivoting the spinner about its longitudinal axis
or for oscillating it about a transverse horizontal axis or
a vertical axis. Pivoting about a longitudinal axis is
useful since it allows for adjustment of the angle A, that
is to say the angle between the horizontal and the line
joining the centres of the rotors 43 and 44.
The tubular duct 8 is provided with an opening 71
through which melt can be poured on to the top rotor 43 or
on to a gutter (not shown) which leads towards the
collection portion and discharges melt on to the top rotor.
There are a series of guide blades 72 to 79. These
are shaped so as to impose the desired air flow direction
on air that is flowing through the passage 9 and the open
area around the spinner. They can be fixed or adjustable.
Forinstance the segment of air flowing past blades 72 and
73 can be directed counterclockwise whilst the segment
flowing past blades 74 and 75 could be directed clockwise,
so as to increase the flow of air beneath the spinner. The
blades 77 and 78 could be shaped so as to cause the segment
of air passing them to flow conically upwards, so as to
follow the line of the chamber top wall 14. Other
configurations of blades can be selected and preferably '
they are provided with means for adjusting their
configuration during operation.
CA 02220362 1997-11-06
WO 96/38391 PCT/EP96/02068
43
The separation B between the lowermost subsequent
rotor 46 and the lower part of the tubular wall 8,
vertically below the rotor, is considerably greater than
the separation C between the uppermost part of the first
rotor 43 and the part of the tubular duct 8 vertically
' above it. As shown, the ratio B:C in the drawing is around
4:1.
The transverse horizontal line D through the axis of
the second subsequent rotor 45 (i.e., the third rotor in
the fascade) is generally at a position which is at or
close to the widest part of the spinner.. At this position,
the distance between points E, where the line intersects
the spinner housing in the drawing is around 50% of the
total width of the chamber at this position. The
separation, that is to say the horizontal distance, between
rotor 45 (which is the lowermost subsequent rotor on the
righthand side) and the adjacent side of the chamber in the
drawing is approximately the same as the separation between
the lowermost rotor on the other side, rotor 46, and the
horizontally adjacent wall of the duct 8.
The total area of the front faces of the rotors 43,
44, 45 and 46 is at least 40% of the maximum cross
sectional area of the housing, defined by the line 61 and
preferably it is at least 50% of the maximum area in the
front lOcm of the housing.
The angle F between the collector 16 and the
horizontal can be, for instance, 70°. The distance G of a
horizontal line from the bottom of the lowermost rotor to
the conveyor is, in the illustration, approximately the
same as the diameter of the tubular duct 8 but is
preferably about 1.5 to 3 times (usually about twice) the
- diameter of the duct 8. The maximum width of the collector
16 is, in the illustration, almost twice the diameter of
the tubular duct.
Instead of or in addition to mounting the spinner on
supports 70 that provide for pivoting or oscillation, the
entire duct 8 may be mounted for pivoting or oscillation
CA 02220362 1997-11-06
WO 96/38391 PCT/EP96/02068
44
with respect to the collecting portion 3. If this is done,
it is necessary to ensure that the movement of the duct
relative to the end walls 13 of the collecting portion does ,
not allow for unacceptable ingress of air. Appropriate
gasketing maybe required around the duct to prevent this.
If it is desired to increase the yield from a single
collecting chamber 3, the chamber may be equipped with two
spinning portions 5, as shown in Figure 6. Spinner lA is
located in spinner portion 5A and spinner 1B is located in
spinner portion 5B, and they are each directed ii.to a
single collecting portion 3. This portion can be divided,
on the spinner side of the collecting screen, by inclined
walls 80 which co-operate with the inclined walls 32 to
provide an outwardly diverging collecting zone for each
spinner.
In the spinner shown in Figure 5, the tubular section
8 of the spinner portion is only about half the length of
the spinner. It can be made even shorter, for instance
about a quarter of the length of the spinner, especially if
the flared portion 63 is increased in length and depth, so
as to create a nozzle effect in the annular collar 9
between the tubular portion 8 and the spinner 1.
In a typical spinner of the type shown in W092/06047
it is often convenient for the primary air to have a mean
velocity of about 150m/s and the air which flows around the
spinner to have a mean axial velocity of around 5m/s, and
for the volume of primary air to be about 15,000Nm3/h and
the volume of induced air to be about 150,000Nm3/h.
However in a typical process of the invention the mean
velocity of the primary air may be about 100m/s giving a
volume of around 5,o0oNm3/h while the mean velocity of the
induced air through the collar around the spinner may be
about 25m/s and may give a volume only of about
100, OOONm3/h.
In a spinner as described in W092/06047 steady flow
conditions may prevail in the primary air slot but would
not prevail in the air flowing around the spinner housing,
CA 02220362 1997-11-06
WO 96/38391 PCT/EP96/02068
because of the irregular shape of it. However if that
spinner was modified and the induced air was passed at the
same quantitative velocity and volume but through a
streamline annular passage similar to the passage 9 in
5 Figure 1 (in order to eliminate turbulence), while
retaining the same front face of the spinner (so that the
rotors occupy only a small portion of the air of the front
face) the radial velocity profile might be as shown in
Figure 7A.
10 In this figure, point K corresponds to the centre of
the primary air slot, point L corresponds to its outermost
wall, point M corresponds to the outer edge of the housing
1 and point N corresponds to the inner surface of the
tubular wall 8. The solid line represents the velocity of
15 the air at the front face of the spinner housing, i.e., as
the primary air emerges from the slot. The dashed line
represents a typical velocity profile some distance in
front of the slot. It will be seen that there is still a
very steep velocity gradient and accordingly there is
20 therefore a very strong tendency for turbulence to occur in
front of the spinner quite close to the spinner rotors.
It must be remembered that, in practice, a
conventional spinner will not give the air flows shown in
Figure 7A and, instead, the induced air between M and N is
25 turbulent, further increasing the turbulence in front of
the spinner.
In a typical process of the invention, the greater
control of the process and the improved streamlining of the
apparatus allows suitable air flows to be, typically,
30 primary air flow of about 100 metres per second giving a
volume of about 5, OOONm3/h and an induced air flow of about
. 25m/s giving a volume of about 100,000Nm3/h, where the
induced air and the primary air are very close to one
another. An idealised velocity profile of such air flows
35 is shown diagrammatically in Figure 7B where K and N
represent the same points as in Figure 7A but P represents
the wall which defines the outside of the slot and the
CA 02220362 1997-11-06
WO 96/38391 PCT/EP96/02068
46
outside of the spinner housing. The solid line represents
the air flows at the front face of the spinner and the
dashed line represents the air flows in the collecting .
portion, in front of the spinner. It will be seen that the
velocity gradient can be free of any region where the
gradient is extremely steep, and thus there is very much
less tendency for turbulence to occur.
Example
Apparatus as shown in Figures 1 to 4 is used wherein
A = 15°
B:C = 6
rotor area = 0.20m2
spinner cross section area = 0.35mZ
duct cross section area = 1.54m2
rotor diameters 1, 2, 3, 4 - 185, 250, 310, 330 mm
respectively
rotor acceleration fields - 36, 49, 72, 89 km/sz
respectively
primary air flow = 4150 Nm3/h
induced air flow = 90,000 Nm3/h
melt throughput = 4500 kg/h
web density = 250 g/mz
product quality - tensile strength of bonded product
- 10 to 12 kN/mz after 60o compression
