CA1227312A

CA1227312A - Extruder die arrangement

Info

Publication number: CA1227312A
Application number: CA000458496A
Authority: CA
Inventors: Ove Wendel
Original assignee: Akerlund and Rausing AB
Current assignee: Akerlund and Rausing AB
Priority date: 1983-11-28
Filing date: 1984-07-10
Publication date: 1987-09-29
Also published as: SE449457B; SE8306553L; ZA845436B; SE8306553D0

Abstract

ABSTRACT

An extruder die arrangement comprising a mandrel and a head forming the slot of the extrusion die therebetween for extruding hollow bodies of an extrudable material, pre-ferably a thermoplastic material. A sleeve is arranged on the mandrel and gives a flow of material in at least two different directions relative the longitudinal axis of the die and of mutually different cross section areas.

Description

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.

73~

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.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An extrusion die arrangement, comprising a mandrel and a head for forming a slot of the die between the mandrel and the head, the die being arranged for extruding hollow bodies of an extrudable material, the mandrel having an arrangement for deflecting the flow of material compris-ing grooves crossing each other and having different flow cross sections thereby providing a flow of material which at each crossing point provides flow in at least two different directions relative the longitudinal axis of the die.

2. An arrangement as in claim 1, in which said means also provide a flow of material having mutually dif-ferent flow cross sections.

3. An arrangement as in claim 2, in which a sleeve shaped element is supported by the mandrel and pro-vided with grooves in the envelope surface thereof defining said directions.

4. An arrangement as in claim 3, in which the longitudinal axis generally forms the bisectrix to the angle between said grooves.

5. An arrangement as in claim 3, in which one flow of material occurs in a direction parallel to the longitudinal axis or in a direction forming an angle rela-tive the longitudinal axis of the die and the flow of material in another direction.

6. An arrangement as in claim 3, 4 or 5, in which said flow directions are defined by crossing sets of grooves in the external wall of the sleeve, where the grooves in each set are generally parallel and spaced at a moderate distance, within the range of some millimetres.