Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
4'~
T~ MAN111;`/\CTURE OF LIG~l'rWE CGHT E~XTE~IJDED Sl'RUCTUl~AI, PROFII,F:
This invention is concerned with the manufacture o~
lightweigh-t extruded struc-tural profile, particularly but
not exclusively profile suitable for use in the building
or joinery industries instead of timber, for example in
the construction of window and door frames and the like,
but also for floor boards, joists, rafters and other
building components.
In International patent specification
No. WO 81/00588 there is described a method of
manufacturing window and door frames from cored extruded
plastics profiles in which the core material may be of
high quality plywood or other suitable material (for
example a cement-bonded fibrous material such as
cement-bonded chipboard or cement-bonded glass fibres)
provided with a cladding of plastics material e.g.
polyvinylchloride.
For such frames the core material is required to
possess a high degree of dimensional and shape stability
and ~o be of adequate strength to bear the loads
encountered by the frames in use in various weather
conditions. Furthermore, as a timber substitute it may
be desirable that the core material should possess good
screw-holding properties.
In U.K. patent specification No. 2 028 406 B there
is disclosed a method of manufacturiny an extruded
construction strip which is suitable for use in the
manufacture of frames for windows and the like and which
comprises a tubular section of thermosoftening plastics
material ~specifically PVC) filled with a matrix of
me~hylmethacrylate with hollow silicate spherules as a
filler. As described, the construction strip may
'IL'ZV~
incorporate with:in the matr:ix a number of fi]arnents
(specifically glass rovlngs) extend;ng leng-thwise of the
strip for reinforcement purposes. In manufacturing -the
strlp the plastics sheath forming the hollow section is
extruded by a first extruding machine and the sheath is
Eilled by extruding -thereinto (by a second extruding
machine) the plastics matrix of methylmethacrylate incor-
porating the silicate spherules, being extruded in the
cold state into the hollow sheath whilst the latter is
still hot. The glass rovings are drawn into the matri~
during its extrusion by some means not disclosed. Curing
of the matrix takes place as the strip is fed through a
sizing bush of cons:iderable length. It is apparent
that the matrix must comprise a relatively high propor-
tion of resin (methylmethacrylate) enabling the matrixto flow freely under pressure to fill the hollow section.
Furthermore, there is described in International
patent specification No. WO 82/03243 a method of making
somewhat similar structural profile, in which method:
(i) a core comprising an unsaturated polyester resin
incorporatin~ a silicate filler and an additional mineral
filler, thoroughly mixed and tightly compacted together,
is extruded through a die, (ii) a sheath of a plastics
material is extruded around the core, and (iii) the
sheathed core is cured by means of haat, so as to effect
curing of the core and cross-linking between the core and
the sheath. The preferred silicate filler for that
process, as described thereinr is in the form of
lightweight hollow microspheres, and an acrylic coating
is preferred for the plastic~ sheath.
According to the process described in specification
No~ WO 82/03243, a very close packin~ of the selected
fillers could be achieved, resulting in a considerable
reduction in the amount of resin required. However, a
~2442V~
Eurther reducl:ion ~ he re.qin content can be clesirable.
Furthermore, there coul.d be an advanta~e in usincJ, at
leas-t as the primary filler for the core of such
str~ctural profile, a reaclily manufacturable material
that could reduce the dependence on commercially supplied
fillers.
There are known, and described for example in
European patent specification No. 0 0~6 489 ~A1), rigid
inorganic foams of cellular structure comprising one or
more layer minerals (hereinafter referred to as layer
mineral foams). The term "layer minerals" includes
vermiculite, kaolinite, kaolin-containing clays such as
ball clays, china clays and fire clays, montmorillonite
and sepiolite. Mixtuxes of layer minerals may be
employed in making foams, as also may mixtures of one or
more layer minerals with one or more materials other than
layer minerals. Where the foam comprises at least a
major proportion of clays (hereinafter referred to as a
clay foam) it may be sintered to confer improved strength
and water~stability.
Such rigid foams have been proposed for various
uses, including insulation uses and the fire-protection
of substrates. Whilst often produced in the form of
extruded board or slab-stock, the foams are also produced
in a coarse particulate extruded form known as prills,
the prills comprising short extruded strands of the foam
material. Production of such foams can be effected
utilising readily available materials and relatively
simple machinery.
It has now been found by the applicant that such
rigid foam materials can be used most effectively and
advantageously in a method of manufacturing lightweight
extruded structural profile in which there is formed in
: .
, ~
, ' . ,
~z~z~
an extruc.lon process a core compr:ising close:L~ compacted
alld bonded part:iculate fi]ler compr;sing Lay~r mineral
Eoam in a coarse part:iculate Eorm.
In a technique developed by the applicant for the
purpose of enabling loose particulate layer mineral foam
(i.e. not pre-mixed with liquid resin) to be introduced
into an extrusion die in an efficient manner, applied
vacuum is utilised to draw in and pack the ~iller. This
technique could Pind wider application in use with other
fillers in manufacturing lightweight extruded structural
profile, and the invention provides in one of its aspects
a method of manufacturing lightweight extruded structural
profile in which there is formed in an extrusion process
a core comprising closely compacted and bonded
particulate filler, the method comprising packing loose
particulate filler into an extrusion die by means of
applied vacuum and progressing the packed filler through
the die to become bonded in formation of the core.
It is to be clearly understood that any references
herein to extrusion (e.g. to an extrusion process and
die, and to the core and profile being extruded) are
intended to be read broadly as applicable to a pultrusion
process, in which it may be that only pulling forces are
applied to move the profile, in formation, thxough the
die.
Such a vacuum packing techni~ue can enable
particularly high packing densities to be achieved where
the filler comprises a relatively coarse primary filler
(e.g. layer mineral foam prills) and a relatively fine
free-flowing addi~ional filler ~e.g. hollow silicate
microspherest, the additional filler being drawn in
separately to occupy lnterstices in previously packed
primary filler.
~2 ~ 3
To enclble vacuum to be c~ppliecl, t,he~ walls o~ the di,e
can be provided with airways leaclinq rom khe interior of
the die. The airways may lead to one or more manifolds
maintained at reduced pressure, a stream of air (or other
gas) so being drawn into -the die, and filler consequently
being drawn into the die and packed. A suitab]e filter
arrangement can prevent filler particles ~rom entering or
obstructing the airways in the die walls.
For certain products it might be desirable to
arrange to have filler of a higher specific gravity
towards the outside of the core than in the middle. This
could be achieved by first packing by vacuum the heavier
filler against the walls of the die and thereafter
packing (also by means of vacuum) lighter filler into the
middle.
The manufacturing method can advantageously employ a
pultrusion process similar to that described in U.R.
patent specification No. 2 143 768 A. That is to say,
glass fibre rovings, or equivalent materials, can be
provided trapped between outer surfaces of a body of
packed filler and walls of the extrusion die, the rovings
being pulled with the packed fiIler through the die as
the profile is extruded. Such use of glass fibre rovings
can be of particular benefit in easing the extrusion
process, serving to keep down the back pressure in the
die with a consequent saving of wear in the apparatus
generaIly and minimising any breakdown of the filler by
crushing owing to excessive pressures. The fibres may
provide a complete resin-bonded sheath for the core. If
required, a plastics coating can be applied to the
outsid~ of the fibre-clad core, again as referred to in
patent specification No. 2 143 768 A, though with
suitable resins and pigments this may be unnecessary to
~ , .
,
~Z~2(~b~
provlde Einlshed profile with a fully satisfactory outer
surface.
In a preferred method, after the loose filler has
been vacuum packed within the extrusion die a bonding
resin is caused to permeate the interstices of the packed
filler (and the surrounding sheath of fibres, if present)
the xesin thereafter being caused or allowed to cure or
set. Advantage may be gained from at least the surface
of the filler being at an elevated temperature when the
bonding resin is introduced.
Preferably, after initial packing by means of
applied vacuum the packed filler is progressed through a
convergent portion of the extrusion die to achieve
further consolidation of the packed filler. Introduction
of a bonding resin into the packed filler preferably
occurs as the filler is progressed through the convergent
portion.
The coaxse particulate layer mineral foam can
conveniently be in the form of short extruded strands
("prills"). An additional filler, being of a less coarse
particulate form, can be introduced; a preferred such
additional filler comprises (primarily if not
exclusively) a silicate filler in the form of hollow
microspheres.
The densities and strengths of layer mineral foams
can vary over a wide range but can be readily controlled.
Their use, together with careful selection of secondary
fillers as appropriate, affords a corresponding
versatility in determining the properties of structural
profile so manufactured.
2()6
'I'here now :Eollows a cle~ai.:Lecl de~cription, to be re~acl
with refer~nce to the accompany.i.n~ draw:irlgs, of a method
of making lightwel~ht extruded s-tructural profile which
illus-trates the invention by way o~ exarnple.
In the accompanying drawings:
Figure 1 is a diagrammatic illustration of a packing
sectiorl of pultrus.ion apparatus for producing
extruded profile;
Figure 2 is a diagrammatic cross-sectional view of
the apparatus on the line II-II of Fiyure 1; and
Fi~ure 3 is a schematic illustration of the
apparatus as a whole.
In the manufacture of lightweight extruded
structural profile comprising a core of closely compacted
resin-bonded particulate fill.er within a sheath of
resin-bonded reinforcing fibres, an extrusion die 10
lined with continuously supplied reinforcing fibres in
the form of glass rovings 12 is packed from one end wi-th
loose particulate filler, from feeding means comprising a
conduit 14, as the rovings are continuously drawn through
the die (in the direction of the arrow E in Figure 1).
Reference can be made to U~K. patent specification
No. 2 143 768 A for a further example of the manufacture
of extruded profile comprising a fibre~sheathed core in
such a pultrusion process.
A nose portion 1~ of the conduit 14 is received
within an entry portion 18 of the die 10 and is shaped
similarly to the interior cross-section of the die in
that region to define a suitable gap ~all around the nose
portion) to permit and control introduction of the glass
.~,
.
124~2~;
rovings 12 on to tlle wall surEace~ defining the die
cavity 20. The CJla5S rovings are ~ecl in, itl COlltillllOU~
lencJ-ths, Erom supply dru~s 21 ~Figure 3) and ~re caused
to line the clie cavity 20 substantially uniformly over
all its wall surfaces.
A generally annular array of airways, comprising
fine radial bores 22 in the walls 24 of the die 10,
connect the die cavity 20 with the interiors of low
pressure mani~olds 26. The manifolds are connected to a
vacuum pump 27, whereby air can be drawn from the
manifolds to reduce air pressure within the die cavity.
By this means, particulate filler supplied to the die
cavity from the feeding means through the conduit 14 can
be vacuumed into a packing region 28 of the cavity
~within the array of airways) and so packed within the
sheath o glass rovings 12 in that region. Ths sheath of
rovings itself serves to some extent as a filter
preventing filler particles from entering or obstructing
the airways 22, but additional filtering means (not
shown) can be provided to prevent the passage o fine
filler particles.
In the construction shown in Figures 1 and 2, a
resin feeding tube 30 of resin feeding means extends
longitudinally through the conduit 14 and the die
cavity 20 substantially to the limlt of the packing
region 28 ~which is to say~ it extends to the limit of,
Qr very slightly beyond, that portion o the die lO
provided with the bores 22~. Alternatively, and as
indicated in Figure 3, resin can be introduced through a
feeding tube 31 through the die wall to a feeding channel
33 in the die wall extending in a loop around the die
~ ~ ~ cavity.
:
~1 :7
, :~,
~z~z(~
~ -t th~ start of operation, a plucJ 32 (Figure L) i3
positloned to occupy the die cavlty 20 immedia~ely beyond
the packincJ region 28. The plug 32 is shaped similarly
to the interior cross-section of the die in that region
to define a suitable gap to accommodate and hold the
glass rovings 12 against the interior die wall surfaces.
The plug provides, in effect, a dummy section of core
which together with the sheath of rovings around it
blocks the die to permit :Lnitial vacuum packing of the
filler. Once filler has been packed by vacuum into the
packing region 28/ continuous formation of profile can
commence by withdrawal (in the forwards direction) of the
plug 32 at noxmal extrusion speed. 1'he plug is of a
compressible foam material which permits it to be drawn
through the convergent die. The plug is drawn from the
die in a similar manner to that in which the profile will
thereafter be drawn through and from the die, which is to
say by applying a pulling force in the direction of
extrusion to the glass rovings 12 held to the plug/core
(in a similar manner to that described in U.K. patent
specification No. 2 143 768 A, hereinbefore referred to).
Liquid resin is fed through the feeding tube 30 or 31 to
permeate the packed filler and the glass rovings 12, the
resin thereafter being caused or allo~ed to cure or set
to provide an extruded body of predetermined
cross-section of sheathed resin-bonded filler.
More or less im~ediately following the packing
region 28, there is a compressing region 34 within the
die 10 in which a convergence of the die walls causes
compression and further consolidation of the core as it
passes to a final forming region 36 of the die.
With particular reference to Figure 3, the feeding
means for supplying particulate filler to the extrusion
die 10 comprises two feed shutes 38 and 40 leading into
z~
the feed conduit 14~ Each o~ the shute~ :Ls valved to
enable measured portiGns of filler materlals to be
delivered into the conduit 14 as required. The vacuum
pump 27 in operation draws an air stream through the
conduit 14, and heating means 42 within an entry portic,n
of the conduit enahles the air to be heated if required.
Resin is supped to the resin feeding tube 30 or 31 by
means of a supply pump 44. The resin supply can be
controlled by monitoring the pressure in the feeding
tube. Profile drawing means 46, of a kind well known in
the pultrusion art, acts continuously to draw the glass
rovings 12 (and the profile core) through the extrusion
die ]0.
The particulate filler comprises layer mineral foam
in a coarse particulate form as a primary filler.
Suitable clay foam prills (being short extruded strands)
are as promoted in the U.K. by Imperial Chemical
Industries PLC as "K4 Inorganic Foam". The prills may,
for example, have a mean extruded length of around 5 mm
and a diameter of about 2 mm, and their specific gravity
can fall (at choice) anywhere ~ithin as wide a range as
0.1 to 0.6; partly reflecting that, the proportion ~by
weight) of filler in the resin-bonded product can vary
hetween, say~ 25~ and 80~ (dependiny also on the type of
resin used).
Whilst the particulate layer mineral foam alone may
constitute the filler, it is usually preferable that a
suitable secondary filler be incorporated. This
additional filler should be a relatively fine filler, and
to permit efficient incorporation by the vacuum packing
technique it should be a free~flowing material. A
preferred secondary filler comprises (at least as the
primary constituent) silicate material in the form of
hollow microspheres; such material is widely known as a
:~24~
filler and :is avai:lable comrnarcially eit,ller as recovered
from power station waste or as manllfactured "cJlass
bubble" E:i:Ller.
Chopped glass strands may al.so be introduced in
addition to the foam clay and hollow silicate fillers.
Employing the vacuum pack.i.ng techni.que lhereinbefore
descri.bed) the primary and secondary fillers are
introduced into the extrusion dle separately in discrete
measured portions. A first of the feed shutes 38 is used
to supply the primary filler (the prills), and the second
feed shute 40 is used to supply the secondary filler (the
microspheres), measured portions of the two fillers being
supplied alternately. Accordingly, a porti.on of primary
filler is first released from the first feed shute 38,
and the filler is drawn by vacuum into the packing region
28 of the extrusion die. A portion of secondary filler
is then released from the second feed shute ~0 and drawn
into the packing region 2~ and into the interstices of
the packed portion of primary filler. A next measured
portion of primary filler can be released from the first
feed shute 38 at a suitable time, bearing in mind that
extrusion is taking place continuously, with the glass
rovings 12 being drawn continuously through the die 10 by
means of the profil2 drawing means 46.
Further consolidation of the inltially vacuum packed
primary and secondary fillers occurs as the core material
is progressed next through the compressing region 34 of
; the die 10. With the resin-feeding arrangement as shown
in Figure 3, a bonding resin is introduced through the
feeding tube 31 shortly before the end of the compressing
region of the die. The resin (whether introduced at the
centre of the packed filler as from the tube 30 in
Figures 1 and 2, or,at the periphery as from the tube 31)
.
~LZ~ 6
permeates the rem.~ ing interstices of~ the packed fi:Ller
(and the glass Eibre rovings 12) by capillary attraction
and the eEfec-ts of increasiny pressure as the material
moves through the die. A non-foaming phenoli.c resin
system which has been used successfully is one available
in the U.K. from BP Chemicals under the trade marks
Cellobond J25/4251, resin and Phencat lO catalyst.
Typically, in use of that resin system, with about 5~ of
the catalyst, the heating means 42 is utilised to result
in the foam clay filler having a surface temperature of
around 70C when the resin (i.e. mixed resin and
catalyst) is introduced, the extruding die 10 itself
being at a temperature ranging from not more than about
90C at its entry end to around 130C towards its outlet
end.
In the finished profile the proportions of the
constituents (by volume) can be within the following
ranges:
Layer mineral foam prills (prirnary filler) : 50% 60%
Hollow silicate filler (additional filler) : 28%-32.5
resin : 12%-17.5~
The finished sheath thic~ness may typically be
O.S rnm to 0.75 mm.
