Note: Descriptions are shown in the official language in which they were submitted.
AB ~kerlund ~ Rausing
A~ EXTRUDER DIE ARRANGEMENT.
The present invention relates to an extruder die
arrangement for accomplishing working of the flow of
material flowing from a die such that the mechanical
characteristics and the appearence of the end product will
be detoriated at a minimum *rom what is an optimum achiev-
able level.
The problem behind the invention is to make invisible!
inoperative the disturbances that arise from flow obstacles
located circumferentially along the extrusion slot, some-
where along the length thereof, for instance of the type
comprising radial mandrel carriers and/or circumferen-
tially distributed, discrete inflow channels for tne
material to be extruded. The type of defects which are to
be -~ound are for instance longitudinal stripes of the
extruded product, colour variations originating from colour
shift of the material that is e~truded, inhomogenous wall
thickness, etc.
It has previously been suggested to arrange so called
"Verwischgewinde", i.e. a threadlike/screw-shaped groove in
a sleeve on the mandrel of an extruder die.
However, it has been recognized that the thread method
leaves unacceptable distortion, i.e. grooves/marXs of the
obstacles causing the problems.
There are a number of other known methods aiming at
eliminating interfering effects, primarily caused by the
mandrel support means.
It has been suggested to eliminate "radial" mandrel
support means by attaching the manclrel axially directly to
the extruder screw.
It has also been su~gestecl to give the mandrel support
mean~ a specific de~ign.
Rotating elements rotating aro~lnc7 the longituditlal axis
oF t~e e~trllder die have also heen sllg~Jested.
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It has been suggested that the rnandrel support rQeans
should be coate~ by a material ~Ihich repells the materi~l
that is extruded.
It has also been suggested to extend the flow path or
the material.
Additionally, it has been suggestea that the mandrel
support means should be heated.
In spite of the large number of different proposals for
solving the problem, there is no simple, more or less gene-
rally applicable solution which may be used for eliminating
of disturbing stripes as well as for making the extruded
material homogenous, for making the wall thickness unilorm
and for allowing a quick cleaning of an extruder die, for
instance when the colour of the material that is extruded
is shifted.
The invention eliminates the present lack and provides
an extruder die arrangement cornprising a mandrel and a head
forming the extruder die therebetween for extruding hollow
bodies of an extrudable material, for instance a thermo-
plastic material. The characterizing Eeature of the
arrangement resides in that the mandrel is provided with an
arrangement for deflecting the flow of material and arran-
ged such that a flow of ma-terial is obtained in at least
two difEerent directions relative the longitudinal axis of
the extruder die.
At least one sleeve-shaped element preferably is arran-
ged on the mandrel and is provided with grooves in the sur-
face thereof defining ~aid directions.
Preferably the grooves also define mutually liFfqrent
cross section areas (flow cross section) for the flow of
material in the groove.s, meaning that the flows are mixed
ef~ectively.
In orcler tv prornote further the mixing of the rnaterial
frorll the dif~erent flows ancl provide a net movement eompo-
nent in anokller direction th~n axially in each cross sec-
tion o~ the sleeve one groove preferably has an axic~l
extension c~nd tlle otller groove Foflil.'; ~111 c~ngl e rel,-lti~e the
,lxi.. ~ll. t3ir~--ti.-)rl. ~?r~ ?r~ y, t~ ; cl~ ;ltl tl~t' ~:c~
~7~2
the hole length of the sleeve.
The object of this is that channels havins different
angle relative the longitudinal axis of t'ne extrusion die,
or channels of different direction having different cross
section area, are to provide a phase displace~ent of the
through flow of material and thereby a mixing ef~ect on the
material. This arrangement does not rnerely give an
equalizing effect onto the material but a directly ~ixing
or stirring effect.
In another embodiment the longitudinal axis forms yene-
rally a bisectrix to the angle between the grooves.
The invention will now be exemplified by reference to
the accompanying drawings, where
Figure 1 partly in a longitudinal section shows a straight
extruder die,
Figure 2 in a side view shows the "homogeni~.ing sleeve"
forming a part of the extrusion die in
Figure 1,
Figure 3 in a side view shows another embodiment of the
sleeve, and
Figure 4 partially in a longitudinal sec-tion shows an
angled extruder die.
The extruder die 10 in Figure 1 comprises a front head/
sleeve 11 forming together with a mandrel 12 a ring-shaped
gap 13 of varying width along the mandrel. In the area of
the external end of the head there is formed a ge~nerally
cylindric groove 13a through which a pipe-shaped member is
extruded.
The head 11 is demountable by means of a support rinq
14 on the extruder housing 15. ~n a n~anner known per se
this ho~sing contains an extruder s~rew and an adapter 16
having channels and sealed against the ~o-lsing by sealin~3
rings 17. In the pres-~n~ ~a~e there are ~href~ 0 separa-
te(l inflow ~hant)e1s 1~ ~or the Ina~erial that is extrn(led at
tll-* slot end of the a-iapter. rhe 0~ ow 0~ .erictl t:a`.~e~S
pla-e . :~f.~-~ discrete ~)eripherallv se~ rnllltl~ t~lo-:
C~ 5 .
~rhe al:la~-~tt-~r 16 is att~ t~-1 t-~ t:he h-~ns in9 1~ by mf'all
~2~73~
of radial screws and supports the mandrel 12. This "radii3 L '
support of the mandrel necessarily gives a type of loci~lly
distributed ou-tflow through discrete openings in the
adapter.
On the mandrel 12, between the adapter l6 and head,
there is clamped a "homogenization" sleeve 20. This slee~e
is fixed by a compression ring 21. The sleeve 20 has
cut-outs in the outer wall thereof ~orming grooves 22' and
23'. Said grooves baslcally define the flow of material in
the directions 22 and 23, between remainin~ broken through
ledges of an outer diameter corresponding to the slot
diameter in the area of the sleeve 20. The grooves 22' and
23', respectively, are generally parallel and moderately
spaced, a distance within the range of some millimetres.
In the embodiment according to Figure 2, the grooves
22' and 23' have the same cross section area measured
across a respective flow direction.
In Figure l t'ne flow taXes place in two different
directions relative the longitudinal axis 24 of the extru-
sion die.
This flow implies that no distinct flow-together zones
(stripes) are formed on the output side of the sleeve 20,
i.e. the peripheral flow tendency in a direction towards
120 separated flow-together zone~ which exist at tlle input
side o~ the sleeve, has been interrupted.
Any unevennessess in the wall of the proc3uct -that is
obtained will be cli~tributed at so many discrete areas that
the overall appearence will be almost perfect.
In Figure 3 there is shown a sleeve having a ~omewhat
different shape giving a ~low in tWQ different directions
relative the lc)r1gituclinal axis of the extr1~sioil die, but
where one c,,ro~v~? 22 is parallel to the loncJ~itudin~l a~is
ancl ~hefe the s~rooves 22' ail~l 23' 'nave di-~?ferlt cro6s-
section areas.
~ r~ re,-~i7~i? ill lro~; se~tion .~r~ t~
~1,3;~ J(~i~?l~ t},~ r~ls.
5 ~ 12
according to t'ne principles of the invention, but in tihis
case provided with an angled adapter 16. This adapter is
not attached by radial mandrel fastening means, but i~plies
a local discharge of the extrudable material to the slot
13, implying the same problems as for the radial mandrel
support/adapter 16 in Figure 1.
Directly adjacent to the .inlet from the adapter, there
is arranged a homogenization sleeve 20 according to the
principles in Figure 3.
Although specific embodiments have been described, it
is realized that the inventive idea may be applied more
generally within the scope of the c].aims.
