Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to apparatus for the production
oi lo~ density self-sustaining foams of cured urea/formaldehyde
resin material. Such ~oams can be used, for example,
in the building industry for thermal insulation purposes.
Low density in the present context means a dry density
of less than 20 kg/m in the absence o~ any inert ~iller,
corresponding to a resin solids content of less than
20 kg/m3. Such foams are made by forming a ~et f oam
containing an intimate mixture o~ a resin and a hardener
for the resin, both being initially in aqueous solution.
The wet foam can be injected, for example, into a cavity
wall and allowed to cure/clry in situ.
Conventional apparatus ~or producing low-denslty urea/
~ormaldehyde resin ~oams su~ers ~rom a variety oi de~ects
which result in optimum processing conditions being di~ficult
to achieve, mainly due to the many variables involved.
It is an object of the present invention to provide apparatus
in which the effects of at least some of these variables
can be minimised.
~ccording to the present invention apparatus ~or making
lo~v density cured urea/~ormaldehyde resin ~oams includes
a centri~ugal mixing head as hereina~ter defined. A
centri~ugal mixing head in this specification means
a casing and an impeller rotatably mounted therein,
the casing having an inlet directed generally a~ially
with respect to the axis ~ rotation o~ the impeller
and an outlet directed generally tangentially relative
to said axisO
Preierably the impeller is constituted by at least one
paddle projecting radially ~rom a central drive shaft.
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Advantageously, the paddle is per~orated to improve
the mi~ing action. Preferably the impeller has ~wo paddles
located on opposite sides of the sha~t in dynamically
balanced relation thereto, although more than two paddles
can be used, if desired. The paddles may also take the
form o~ a set of rods or bars extending radially fron
the central drive shaft.
The paddles pre~erably extend ~rom a central boss on
the drive sha~t, the boss having a conical portion directed
towards the inlet. The inlet to the casing may be offset
with respect to the axis of the drive sha~t so as to
provide a maximum duration ~or the mixing action.
The apparatus preferably includes feed means for supplying
resin and hardener to the inlet o~ the centri~ugal mixing
h~ad; the ~eed means ~re~erably includes ~oam generating
~eans operable to ~oc~m the resin or the hardener or both
prior to supplying them to the inlet. Advantageously,
the centrifugal mixing head is located immediately downstream
o~ the ~oam generating ~eans and where either the resin or
the hardener is unfoamed, the apparatus preferably includes
a nozzle ~or supplying the unioamed component to the
inlet. Preferably the nozzle is located in the inlet
and is directed towards the impeller.
Whilst it is normally more convenient to ~oam the hardener
solution prior to mixing in the resin, the apparatus
may also be used ~or the converse route, wherein a ~oam
o~ resin solution is mixed with an unfoamed hardener
solution. For practical purposes, however, it is normally
easier to ~oam the hardener solution - which usually
contains a surfactant - than the resin solution which
is viscous, espec~ally when relatively undiluted~ The
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resin solution normally also contains a surfactant, but
because it is viscous, considerable difficulty may be ex~
perienced in mixing it with the foamed hardener solution
to obtain a homogeneous wet foam. In conventional foam
making appara-tus it is necessary to inject the resin solu-
tion into the hardener foam by means of an atomising jet
and it is this that has hitherto effectively limited the
surfactant content of the hardener foam. Too much surfac-
tant in the hardener used in conventional apparatus results
in a fine foam which is very stable, but which also tends
to restrict the rate of dispersion of atomised resin and
give a badly mixed product.
This particular problem is more acute in hot weather but
attempts to remedy it by reducing hardener surfactant con-
tent can result in coarse-celled foams of inadequate sta-
bility.
By using the centrifugal mixing head of the present invention
the above-mentioned problems can be to a large extent
overcome, since the mixing operation is positive. It is
no longer necessary to atomise the resin, so the surfac-
tant content of the hardener foam is not critical and it
can be increased beyond conventional levels to give fine,
stable homogeneous foams, which allow formulations having
a relatively long gel time to be used, without encountering
the bad mixing problems frequently experienced when using
conventional apparatus.
Hardener foam can be produced by passing the hardener
solution through a foam generating column in such a way
as to produce an extremely fine foam. However, this feature
30 is particularly appropriate to the manufac-ture of specific .
low shrinkage foams, whereas the centrifugal mixing head
according to the present invention is equally applicable
to production of conventional foams.
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As mentioned above, the apparatus of the present invention
can also be used to mix a resin foam with a hardener foam.
This particular method of producing urea/formaldehyde resin
foams by mixing the resin and hardener as two foams is the
S subject of our British Patent No. 1313103.
In order that the apparatus of the invention be better
understood a preferred embodiment of :it will now be des-
cribed by way of example with reEerence to the accompanying
diagrammatic drawing in which:-
Figure 1 is a schematic cross-sectional side view through
a foam generating apparatus, including a centrifugal mixing
head, in accordance with the invention;
Figure 2 is a cross-sectional side view through the mixing
head of Figure l; and
Figure 3 is a sectional view through the mixiny head oE
Figure 2 on line A-A thereof.
In Figure 1, a foam generating column ~ has a feed pipe 5
to which hardener solution and compressed air are supplied.
The column is packed with glass beads 6 and discharges
into a coupling pipe 7 which connects it to the inlet 8
of a centrifugal mixing head, generally designated 9, and
which has an outlet pipe 11. A resin feed pipe 16 is also
provided at the inlet of the mixing head. Referring to all
three figures, the mixing head 9 comprises a cylindrical
(in plan) casing 10 containing an impeller 12 rotatably
mounted in a bearing assembly 15 and driven by an air motor
13 through a shaEt 14. The casing is divisible (not shown)
along a line parallel to line A-A to facilitate cleaning
and/or servicing. The impeller has four blades 17, each set
in a central boss 18. The blades are perforated to improve
the mixing action and the assembly is dynamically balanced
about the shaft 1~.
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In the example described later, the blades were each
about 30mm long, 20mm deep and had 5mm holes drilled
in them. The inlet 8 is essentially directed onto the
conical head o~ the boss 18) since this has been observed
to enhance the mixing ef~iciency.
Re~erring now to Figure 2, the driYe s~ha~t 14 passing
through the base of the mixing head is of course a potential
source of leakage and in view o~ the corrosive nature
o~ the acid hardeners normally used, a simple sleeve
bearing is not satisfactory. Accordingly, the bearing
assembly includes pair of garter seals 19 in a housing
20. Spring rings 21 urge the seals into contact with the
shaft 14. The garter seals are disposed i~ bac~-to-
back relation and the housing is supplied with grease
22 from a conventional spring loaded pressure lubricator
23, the grease forcing the seals apart and against the
housing, whilst ~t the same time both lubricating the
sha~t-to-seal contact area and repelling fluid leaking
down the shaft. It has been follnd that apparatus constructed
in this way is both reliable and reasonably robust, despite
the corrosiYe nature of the hardener used.
As mentioned earlier, the inlet may be offset with respect
to the axis oP the shaft 14 and the outlet, as indicated
in Figure 3 by dotted lines 24. This provides for a ;~
maximum duration of the mixing action.
~xample
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In a specific operation, an acid hardener solution containing
1.4% by weight of a sur~actant was fed to the column
4 at a rate of 2 litres/minute. The feed pipe S was
also supplied with air at 40 KN/m and in the coupling
pipe 7, a low density hardener foam resulted. The column
was in this case 360mm long, 45~m in diameter and packed
with 6mm glass beads.
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An aqueous urea/~ormaldehyde resin solution containing
45 ~ 0 reactive resin solids was supplied via pipe 16
at a rate o~ 2~ litres/minute and mixeld with the foam
in the ~ixer 9, the impeller being rotated at 900 r.p.m.
The resin was in this case "BEETLE" BU700 and the hardener
was "B~ETLE" FH100, an acidic solution containing an
anionic sur~actant. "BEETLE" is a Registered Trade
MarL of British Industrial Plastics Limited.
The product ~rom the outlet pipe 11 was a homogeneous
~et ioam which on curing/drying had .a ~inal dry density
o~ 14 kg/m.
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