Note: Descriptions are shown in the official language in which they were submitted.
Grunzweig + Hart~ann AG P 862
6700 Ludwigshafen, DE
'1
Apparatus for the production of wool, in particular
rock wool, from a melt
The invention relates to an apparatus for the production of wool,
in particular rock wool, from a melt in accordance with the
preamble of claim 1.
In the blast drawing process, primary filaments emerging from,
as a rule, a row of exit orifices of a melt distributor, are fed
into the drawing gap of a blast nozzle and are accelerated and
thus pre-drawn in a gas flow which likewise enters the drawing
gap. Downstream of the blast nozzle exit, the thus formed gas-
fibre dispersion has to be decelerated, and the static pressure
of the gas flow raised to approximately ambient pressure, in
order to be able to deposit the fibres which have solidified on
cooling to form, eventually, a nonwoven fabric. In this
connection, it is known, for example, from published German
patent application ~E-OS 38 07 420 that a subsonic diffuser is
employed for deceleration in the form of a so-called impact
diffuser with at least one sudden widening of the cross section
of the flow boundary. This has the effect that the fibre and/or
fibre-gas dispersion, downstream of the sudden widening of the
cross section, undergoes a relatively pronounced degree of
expansion, so that the mutual clearance between the filaments of
the fibres is increased and the probability of their coming into
contact with one another is minimised. Downstream of the sudden
widening of the cross section, so-called impact eddies are formed
on both sides in the backflow zones, said impact eddies forming,
in technical flow terms, the boundary of the main flow. Direct
wall contact of filament constituents is thus avoided in the
region of the impact eddies by virtue of the fact that the flow
boundary is formed by another flow and not by the solid wall.
Owing to the fibre contact which thus occurs, and the
accompanying thermal loading, the walls of the blast nozzle
undergo wear cO that the blast nozzle has to be replaced at
regular intervals. Although the blast nozzle may, for the
purpose of increasing its service life, be manufactured from pure
nickel or from high-alloy, wear-resistant steel, whereby in the
last-mentioned case a cooling arrangement for the side walls has
had to be added to further extend service life, the disadvantage
nevertheless remains that the impact diffuser arranged below the
blast nozzle as a separate part is likewise subject to
considerable wear, at least in the upper region, i.e. in the
region of the first stage of the impact diffuser, owing to the
fibre contact which occurs at the wall there, so that the impact
diffuser also wears out at regular intervals and has to be
completely replaced by a new impact diffuser.
The object of the present invention is to combat this problem
through the characterising features of claim 1.
By designing the blast nozzle as a single-piece component with
the first stage of the impact diffuser, an approach which
initially appears to contradict functional requirements, the
situation is created whereby the parts of the fiherisation unit
which undergo the most wear and tear can be replaced as a whole.
As claimed in claim 2, for the purpose of increasing service life
the first stage of the impact diffuser, designed together with
the blast nozzle as a single piece, is manufactured from the same
material, for example a high-alloy, wear-resistant steel.
As claimed in claim 3, the service life of the wearing parts can
be further extended to good advantage by cooling the side walls
of the blast nozzle and/or the impact diffuser by means of
cooling ducts which are swept by a coolant.
3 ~ )~"~
In a particularly advantageous further development of the
invention, the blast nozzle is designed, as claimed in claim 4,
in the form of a so-called flat-land blast nozzle.
Further details, features and advantages of the invention are
revealed in the following description of an embodiment by
reference to the drawing in which
ig. 1 shows in schematically simplified form a section
through an appliance according to the invention for
the fiberisation of mineral fibre melts, with a blast
nozzle and the first stage of an impact diffuser, and
with further stages of the impact diffuser,
and
ig. 2 shows in a representation essentially similar to that
of Fig. 1, a modified embodiment with a so-called
flat-land blast nozzle.
As is apparent from Fig. 1, melt, in the illustrative example
mineral melt, is fed from a melting tank, not depicted in any
further detail, to a distributor tank, signified by 1, which is
manufactured from platinum, emerging in the present embodiment
in the form of a plurality of adjacently arranged primary
filaments from exit orifices 2 of the distributor tank 1. For
reasons of clarity, the melt itself is not depicted. The exit
orifices 2 arranged in a row exhibit in the embodiment a diameter
of approx. 1 to 2 mm and are spaced at intervals of approx. twice
the orifice diameter. These dimensions may, however, be modified
upward or downward depending on the melt. The exit zone of the
distributor tank in the present case is heated by hot combustion
gases 3, these latter passing through a narrow gap 4 on both
sides of the exit zone of the distributor tank 1 at high velocity
and enveloping the divided flows of melt in the zone where
formation and movement of the primary filaments takes place. The
mass flow of melt per exit orifice is determined by the
temperature and the geostatic pressure of the melt, the orifice
2~r,9~
diameter and the level of static partial vacuum in the exit plane
of the orifices 2. This partial vacuum is generally generated
by injection of a blown medium 5 through nozzle orifices, said
blown medium being supplied to a blast nozzle unit, generally
signified by 6, and entering through, in the present embodiment,
slit-like nozzle orifices 7 in the upper region of a nozzle slot
8 of the nozzle unit. The injection of the blown medium 5
through the blow-in slits 7 takes place on both sides of the
nozzle slot 8 in a pattern which is essentially wall-parallel or
parallel to the centreline 9 of the blast nozzle units 6. In
this process, the pre-drawn primary filament in the suction zone
is excited such that it oscillates in a direction transverse to
the main flow direction, is entrained by the rapid wall jets and
is further accelerated and drawn. The flow velocity of the
drawing gas streams, which are composed of the actual blown
medium 5 as the propellant, the sucked-in hot combustion gases
3 and the ambient medium (secondary air) depicted at 10, and
which can easily assume supersonic speed in accordance with the
converging-diverging contour of the blast nozzle units 6, is
reduced in a downstream subsonic diffuser 11. The narrower the
subsonic diffuser 11, the finer, and also shorter are the fibres
obtained.
The point at which the flow leaves the subsonic diffuser 11
generally marks the end of the fibre formation process. Normally
the fibre-air dispersion is then further decelerated and cooled
in the chute with the addition of coolants, sizing/slashing
agents, binders and/or further conditioning means, and also with
further false air being sucked in. The fibres are deposited in
the form of a wool non-woven fabric on a perforated accumulating
conveyor located below, and are separated from the drawing and
entrained gases (process air) by vacuum chambers with downstream
fans arranged below the accumulating conveyor.
The subsonic diffuser 11 is designed as an impact diffuser with,
in the present illustrative embodiment, three stages 13, 14 and
15 within its flow boundary, with sudden inward or outward
changes in cross section, 16, 17 and 18. The customary single
or multiple impact diffusers, which are known per se, are
characterised by the fact that the main flow at those points
where there is a sudden widening of the cross section breaks down
and only returns to the solid flow boundary after a certain flow
length over which a backflow zone is formed. The higher the
number of stages 13, 14 or 15, the better is the efficiency with
which dynamic pressure energy is converted into static pressure
energy.
In the case of the apparatus according to Fig. 1, the individual
inward or outward changes in cross section 16, 17, 18, and the
length of the individual stages 13, 14 and 15 can be dimensioned
such that the melt and fibre constituents, which follow the
drawing gas flows with a certain degree of slippage, only come
into contact with the solid flow boundary at the end of each
stage, with any wall contact occurring virtually parallel to the
wall, thus resulting in the melt filaments only being exposed to
insignificant deceleration and cooling phenomena with ensuing
bead formation.
The length of the individual stages 13, 14 and 15 should be
selected such that, in the stage exit-plane, no further backflow
zones are formed, as these can lead to large-volume flows which
are mostly unstable and have as their consequence a non-uniform
fibre flow pattern. From this point of view, the preferred
minimum length of the stages 13, 14 and 15 is approximately 5 to
6 times the difference of the roots of the respective exit and
entry cross sections of each stage 13, 14 and 15.
With respect to further details, features and advantages of the
impact diffuser 11, express reference is made to printed German
patent application DE-OS 38 07 42Q of the present assignee, filed
on the same day, the full contents thereof being hereby
incorporated by reference.
6 ~ 7~
According to the invention, provision is now made for those parts
which, owing to the fibre material impinging on the wall and the
thermal loads associated therewith, undergo the most wear, i.e.
the blast nozzle unit 6 and the section corresponding to the
first stage 13 of the impact diffuser 11, to be designed as a
single-piece component which can be completely replaced if
required.
As shown in the drawing, the walls of the nozzle slot 8 of the
blast nozzle unit 6, and the subsonic diffuser 11 feature cooling
ducts which are individually and severally signified by 19.
These result in intensive cooling of the flanks of the nozzle
slot 8, and/or of the solid flow boundary of the subsonic
diffuser 11. As a result of the cooling of the surfaces which
are directly involved in heat exchange with the fibre dispersion,
operational reliability is increased on the one hand, as melt
constituents randomly impinging on otherwise hot surfaces are
more likely to adhere thereto, eventually causing a melt overflow
at the blast nozzle unit 6. However, as a result of provision
of a cooling means, the blast nozzle flanks, which are preferably
manufactured from nickel, can be manufactured from a cheaper
material, for example stainless steel, which is, in addition,
more wear-resistant. On the other hand, so much heat is removed
by the coolant that the microclimate in the downstream chute is
less thermally loaded, i.e. the danger of premature curing of
binder while still in the chute is avoided. The heat removed
with the coolant can, where appropriate, be utilised elsewhere.
A further advantage derived from provision of cooling ducts 19
lies in the fact that the blast nozzle halves can be brought
closer together, as a result of which the proportion of entrained
ambient media is reduced. Consequently, the quantities of gas
which have to be extracted through the product and treated are
also correspondingly smaller. Moreover, with the distances
between the flanks reduced, there is an increase in the
temperature level in the fiberisation zones, thus promoting the
formation of finer and less beaded fibres.
7 ~ 'I ' ' ' ~.
Fig. 2 shows a further embodiment according to the invention, in
which the blast nozzle unit 6 is designed in the form of a so-
called flat-land blast nozzle.
In contrast to blast nozzle unit 6 according to the embodiment
shown in Fig. 1, the upper part, signified by 20, of the blast
nozzle unit 6 is provided not with a rounding but with a flat
land, and features a sharp-edged corner 21 of the upper part 20.
As a result of this measure, it is possible to generate a more
centrally concentrated, and better centred intake flow of the
secondary air which, in terms of its entrainment behaviour, acts
more intensively in the vertical direction than the
aerodynamically smoother and rounder inlet as shown in the
embodiment depicted in Fig. 1.
With respect to further details, features and advantages of the
guide cells which may be employed in this context, and the
injection there of water and binder, and of the construction of
the chute and the blast nozzle unit 6, reference is made to the
six co-pending German applications of the present assignee
entitled "Apparatus for producing mineral wool from silicate raw
materials, in particular basalt, by blast drawing" under patent
agent folio No. llGH06312; "Apparatus for producing mineral wool
from silicate raw materials such as basalt by blast drawing"
under patent agent folio No. llGH06322; "Process and apparatus
for the continuous production of mineral wool nonwovens" under
patent agent folio No. llGH06332; "Process for the melting of
silicate raw materials, in particular for the production of
mineral wool, and apparatus for the preheating of the raw
material mixture" under patent agent folio No. llGH06342;
"Apparatus for the continuous production of mineral wool
nonwovens" under patent agent folio No. llGH06362; and
"Apparatus for the continuous production of mineral wool
nonwovens" under patent agent folio No. llGH06372, all filed on
the same day, the full contents thereof being hereby incorporated
by reference.
