CA1259769A - Process for producing packing material particles - Google Patents

Abstract

ABSTRACT

In the case of a process for producing pourable spherical-segment-shaped packing material particles made of a plastic material which have an external convex and an internal concave surface, the plastic material is fed in by means of a feeding funnel through an opening in a bush surrounding the extrusion screw. The plastic material is plasticized and, because of the difference in speed existing of the cross section of the mass, comes out of an opening in the die with a bent surface. The extruded plastic material is cut offdirectly at the opening of the die and before any considerable expansion has taken place.
In this case, the plastic material is pulled into a space between the extrusion screw and a bush provided with longitudinal grooves in the material pull-in zone. The result is a possibility for some of the plastic granules to escape into the longitudinal grooves and an increased-and steadier transport of material through the extruder.

Description

37~

A PROCESS FOR PROD~CING PACKING MATERIAL PARTICLES
Thl~ lnventlon relutea to ~ proce~fi for produclng pourable spherical-segment-6haped packlng material partlcle6 made of a pla6tlc materlal which hsve an external convex and an ~nternal concave surfa~e, where the pla6tlc materlal, by mean~ of a feeding funnel, 16 fed lnto an extruder through an openlng ln 2 bush 6urroundlng the extruslon screw, ~here the plastic materlal ls pla~tlclzed over the course of the extruder and, because of the dlfference ln 6peed over the cross 6ection of the ~as6, comes out of an opening ln the dle wlth a bene 6urface and the extruded plastlc i~ cut off directly at the openlng of the dle and before any considerable expanslon has taken pl~ce.
A process of thl6 type is known from US-PS 3,961,000. In the case of thls pro~ess, expandible polyst~rene ~EPS~ and sdmlxture6, via a delivery funnel, are fed into an extruslon device~ An extrusion screw transports the plastic material SEPS) through the extruder, where the ~peclal design of the extrusion 6crew, i.e., an increasing core diameter, as well as a ~uitable temperature program result ln a plasticizing of the pla6tic over the course of the extruder. Immediately after the pla~tlc materlal comes out of an opening in the die, lt 16 cut off by mean6 of a cuttlng device, where lt i6 made po6sible for the cut-off particles ln a fir6t expanding proce66 to expand lnto the 6pecial ~hs p e, ~lth a surface that 16 convex on the outslde and concave on the lnslde. ln 6everal 6ub6equent expanding proce66es, the parking materlal partlcle~ are processed to their flnal co~dltlon.
Th16 continuous proce6~ depends on a large number of parameter6.
From an economlc polnt of view, the throughput of pla6tlc materlal through the extruder per tlme unit 16 of 6pecial lntere6t. Th10 throughput al~o 1B tependent on many parameter6. Thl6 value 18 6ignific~ntly lnfluenced by the deslgn of the extruder, l.e., the dimen6iDns of the extru~loL ~crew ~nd of the bush ~urrounding lt. In order to obtaln a reproducible ent product ~lth low fluctuatlon6 of quallty, lt 1~ b~olutely oece~ary to be ~m111ar vlth the chemlcal ~nd phy6ical proces~es oc~urring in61de the exeruder.

Io order to obteln n uniformly str3 ture~ ex~t~er packlng, the starting materlsl ~EPS) and the admlxtures, ~uch 8~ the colorlng ple-ment6, the bubble-formlng ~ubstances Mnd ~imllar mAterlals, must be sdded steadlly ln thls continuDus process. The 8teady feedlng 1~
ehls s~artlDg phase of the proce~s alrendy lnfluence~ the quallty ~nd naturally the quantlty of the end product. A steady feedln~ 18 made possible by a co-called "~tuffing" of the extruder. '~hl6 means ~hat the starting material 18 pressed lnto the extruder under pressure by means of 8 "stufflng devlce". Thls ~ay, for example, take place by pr&~sing tha plastlc material frDm a 6upply contalner by mean6 of 8 "601id-mstter screw" lnto the extruder. Thls lntrodurtlon process requires a control and forms a compDnent that is susceptible to trouble ln a mechanlsm for carrylng out the above-mentloned proce6s. A ~tuffing 8crew that presae~ the material into the extruder under pres6ure must itself be supplled wlth material from a 6upply container 60 that the steady feed~ng of plastic materlal into the extruder requires considerable constructive and operational expenditures.
In the case of a feeding without an addltlonal stuffing screw, the 6teadiness and the throughput are low, and the profitablllty of the above-mentioned proces6 18 therefore reduced.
It is the ob~ect$ve of the invention to lmprove a procesq of the initially mentioned type ln such a way that without stuffing devices, a high throughput of materlal and a ~ore 6teady transport of tbe ~aterial ln the extruder 18 made posslble.
Thls ob~ectlve 18 achieved by the fact that the pla8tlc material la pulled lneo the extruder in a space between the extruslon 6crew and the bush provlded with longitudlnal groove6 ln the zone where the material is pulled ln, where by means of the poaaibllity of escape of aome of the plastic granule~ lnto the longitudlnal grooves, an increased 0nd more steady transport of material through the extruder is made possible.
Iu the case of thl6 proce66, a feedlng funnel, wlth lte lower opening, re6ts on a corre6ponding openlng on the bu6h ln the pull-in zoue of the extruder. The pla6tlc granule6 are pre6~ed lnto the 60-called "groove ~ntrance zone" only through the force of their weight6.
The propelliug 81te6 of the 8plral-8haped screw cauHe the advancing v~ment of the granule~ through the extruder ~hlch can be dlvided lnto an axlal orsinrd l~,ovement nnd a clrcular movement. The rntlo of the ~ 6~9 speeds of the two movement6 determlneg the speed at whlch the gr0nule advnnce~ through the extnlder ln trnnsport dlrection. If the granule, for example, adheres at gmy polnt ln the extruder, ~t wlll only carry out a circular move~ent and wlll no longer be advanced ln axlal dlrectlon.
The lnrger thl~ proportion, the le6g the trnn6port of mnterial ln axlal tlrectlon, ln whlch ca6e the 6pace 18 nlso blocked for the material that follows. ~ nean~ that the more granule~ rotate ~lmultaneously with the screw in clrculnr dlrectlon, the les6 the overall nxinl advanclng quantlty, i.e., the throughput quantlty of tbe Eranule6, where at the ~ame tlme, the 6teadlness of the pulled-after materlal i6 not 6~ti6factory.
Tbe grooves ln the bush, for a certsin number of granule6 over n certaln cross-sectionsl area through an extruderln the entrance zone, offer an "escape corner". Thu6 lesc granules are 610wed down dlrectly at the screw, l.e., on the whole, le6~ granule6 "adhere" at the screw, and thu6 les6 grnnule6 rotate along 61multaneou61y ln circulnr direction, vhlch results in an lncrease materlal transport ln tran6port dlrec~ion.
~hus, the granules located in the grooves are agaln pulled more ln the directlon of the screw core, or through Lhe pres6ure are pres6ed out of the feedlng funnel, where on the whole, an lncrea6ed movement and a connected mlxlng of the granules i8 achieved. At the 6a~e time, because of the reduced "blockingl', the volume required for the ~ranules becomes smaller, and thu6 a more compact and more 6teady pscklng of granule6 per volume element i6 acbleved.
In the groove entrance zone, the g~oove6 have a con6tant depth of rece66.
~n comparl60n to a bu6h wlth a 6rnooth lnterlor surface, the materlal throughput at the aame rotating speed of the 6crew can be approxlmately doublet.
It 1~ of deci61ve ~ignlflcance that the granules do not become pla6ticlzed in thi6 pull-in zone. If thi6were the ca6e, the granules would ~queeze themselves into the groove6, and the posltlve effect would be 106t becau6e of a quasi-~mearing-over of the groove6. In the cnse of an lndlcated dlmension figure of the cut-ln groove6 (depth of reces6, wldth and nùmber), the size6 of the granule~ can be varied over a relstively wide ranBe without ~ignificantly llmitlng the advantngeous effect.

- The gro~ve~ very ~dv~nt~geously ~Bve a ~-sh~ped cross ~ectlonal l~S97~9 `~ proflle, ~her~ the two legs of the U ~re 011ghtly lncllned towsrd the out31de.
The recess depth of the groovea, ln n trnn~itlon zone connecting to the groove entrance zone, decreases to zero. The plastlclzlng zone having a completely smooth l~fiide surface of the bush then connects to sa1d transltion zone.
In the transltlon zone, becau~e Df the gradunl decrease of Gpace ~vallable to the materlsl, a careful further denfilflcatlon of the plastlc ~nterial tskes place. The resulting frlctlonal hest must not reach the qunntum of he~t that 18 sufflclent to plasticize the materlal. AD excess quantum of heat must be removed by coollng. The plasticizlng of the plastlc msterial will take place only in the plastlclzlng zone that follows this tran~itlon zone.
In an especially preferred embodiment, elght grooves 3re cut aplrally into a bush with a diameter of about 50 mm. The throughput of EPS, in comparlson to a ~mooth bush, could be lncreased from about 50 kg/h to 90 kg/h.
By means of the devlce accordlng to the inventlon, the process can be carrled out ln an especlally 61mple and cost-effectlve way vithout the use of stufflng screws or other stuffing devlces.
In the followlng, the l~ventloD wlll be explalned ln detall by means of the embodiment uhown ln the drawlng.
Figure l ls a diagrammatlc side vlew of ~ devlce for produclng packlng material particles;
Flgure 2 1B a partlal ~lde vlew of an extrudlng device ~lth the m~terlal pull-ln zone;
Flgure 3 ls B broken partlsl topv~wof a materlal pull-in ~one;
Flgure 4 ls a partlal enlarged uectlon of an extruder bush having grooves;
Flgure 5 la & cut ~long V-V ln Flgure 4; and F~gure 6 ls the deslg~ of the ~crew hellx of the groove6.
The tevlce requlred for cnrrylng out the process 1~ chown ln disgrum form ln Flgure 1 ~nd hafi an extruslon devlce 10 confiisting of a driving motor 11, ~ gear mechanlsm 12, a msterlsl pull-ln zone 13 and nn extruder 14. A cutting devlce 16 18 ~rr~nged dlrectly ln froDt of a dle openlng 15 of the extruder 14. Ti~e extrudnble expnnd~ble ~ 5i9~i9 thermoplastlc materlnl that 18 added preferably ln the form of granulated graln~ or tablets arrlves ln the extruder 14 through 8 feedlng funnel 17 through the materilll pull-in zone 13. Such materlal may, for example, consist of polystyrene or other sultsble polymers.
The materlal 18 plastlclzed over the longitudlnal course of the extruder and comes out of the openlng 15 ln the form of a n~ass of melted plastlc materlal. Because of the dlfference ln ffpeed occurrlng over the cross 3ectlo~i of the mass, the plastlc material squeezes out of the lnslde srea of the dle opening 15 having a bent surfece.
The extruded material 18 cut off dlrectly at the openlng 15 by ~e~s of the cuttlng device 16.
~ he cut-off plastlc partlcles expand in the free fall to a flrst expanded condltlon, in whlch case they already tske thelr shape baving ~ ~urface that i8 concsve on the lnside and convex on the outside.
A collectis~g container 19 catches the sollfied and cooled plastlc partlcle6 18.
The lntlally expanded foam partlcles, by mean6 of a blower 20, are tran6ported through a pipe 21 lnto a storage container 22.
After a certaln storage period, the lnltlally expanded plastlc partlcle6 18 are transported from the ~torage contalner 22 lnto B
re - expansion unlt 23, where the pla6tic particle6 are re-expanded.
After leavlng the re-expanslon unlt 23, the re-expanded plastlc partlcles 18 are led to a atorage contalner 24. Thls storage container 24 preferably conslst6 of a 61eve material or another open-mesh material 80 that a free circulstion of air and thu6 an ea61er drylng of the re-expanded pla6tlc parricles lB is possible.
The particles that were expanded to thelr end condltlon, ln order to carry out thelr function a6 packlng mater~al, must have a steady and unlform structure. In partlcular, the partlcles mu6t have such stablllty that the pre6sure affectln6 the packing materlal through the 6tacklng-together and durlng the transport toes not result ln a breaking of the packlng materlal particles. In addltlon, the lndivldual partlcle in lt~elf mu6t be clo6ed off by a relatlvely smooth ~urface ~o that there ~111 be no "crumbling" through the frlctlon among the lrdlvldual packlnK
aterial partlcles. Another factor that is decl61ve wlth re6pect to the qualltg and ehe unlformity of the materlal 18 the steadlness wlth whlch the plast1c materlal 18 fed lnto the extruder. Tbe ~ransport of material through the extruder per tlme unit determlnes the qusntlty of the plastic materlsl coming out of the extruder and therefore determines, st a constant cuttlng perform~nce of the cutting devlc~ 16, the ~lze of the packlng particle~ ln the flrst expanded condition.
Flgure 2 18 an enlarged vlew of the materlal pull-ln zone 13 wleh the feedlng funnel 17 placed on lt. The materlal pull-in zone 13, on ~he rlght-hand ~lde, i8 connected wlth a step-down gear 25 that ~8 drlven by a tor 11.
ID transport directlon, the materlal pull-ln zone 13 i8 followed by a plastlclzlng zone 26. The plasticizing zone 26 and the uaterial pull-in zone 13, along thelr connectlon 27, are thermlcally ln6ulated.
The extruslon screw (not shown here) reaches through the materlal pull-ln zone and the plaselclzlng zone and is drlven by the motor 11 via the step-down 8ear 25. The extruslon screw, ln the materlal pull-ln zone, 16 gulded by a bush 28 whlch ls held by a support 29. The bush 28 18 provlded wlth an opening 30 througb whlch the materlal 18 pulled from the feedlng funnel 17 into the extruder 14. The feedlng funnel 17, wlth lts bottom side ~ connected with 8 flange 32 of the support 29.
The area of the bush 28 that 18 bordered by the openlng 30 forms the groove entrance zone 33. The area of the bush connectlng ln transport dlrection to thi~ groove entrance zone couprlses a transltlon zone 34.
A,s seen best ln Figure 3, 6everal longitudlnally extendlng grooves 35 Are cut lnto the bush 28. In the ares of the groove entrance zone 33, the grooves 35 have a constant depth 36 of recess. In the transltlon zone 34 connectlng ln transport dlrectlon to the groove entrance zone 33, the depth 36 of recess ln transport dlrection decreases to zero.
The opening 30 ln the bush 28 1B about 80 mm long and about 50 mm wlde, The transltion zone 34 has a length of about 185 mm.
The bush 28 has a wall thlckness 37 of aoout 13 ~m.
Flgure 4 shows an enlarged cutout of a bush 28 in the area of the groove entrance zone 33 having grooves 35 wlth a constant depth 36 of recess.
The groove~ 35 have a proflle 38 that ls U-shaped ln lts cross-section, wlth the two legs 39 of sald U belng lncllned toward the outside by an Pngle ~ . In the present embodi~ent, the angle of lncllnation ~ is 15.

The depth 36 of recess of the grooveg 35 1B nbout l.S mnn I~e wldth 40 ~LZ~;9 of the grooves 35 18 about lO ~nm. The grooves ln the embodlment shown here have a con~tnnt dlstnnce 41 from one another ~hlch a~ounta to about 15.5 mm.
The dlstance of the grooves 18 determlned by the diameter ofthe bush Z8 snd the number of cut grooves ~8 well ~8 thelr wldth.
Flgure 5 shows a cut along the Llne V-V ln Flgure 4 whlch extends through a groove 35. The grooves 35, seen ln transport dlrectlon, at the beglnning of the bu6h 28, have a starting area 42 after whlch they reach thelr m~u;imum depth 36 of recess whlch then ln the groove entrance zone 33 is constant.
Figure 6 shows the design of the groove hellx ln the mater$al pull-in zone 13. The bush 28 18 cut open ln longltudlnal dlrection and ln the rolled-out condition has a "rectangular contour". Around the clrcumference 43 of the bush 28, elght grooves 35 are cut 1D at regular dlstances. After a distance 44 ln tran6port dlrectlon, the helix w111 hAve made a complete 360 turn. The dls~ance 44 in the preaent embodiment 18 about 203 mm.
As`best 6hown ln Figure 3, the material, durlng the operatlon, 18 pulled through the opening 30 into the bush 28. The extrufiion screw (not 6hown here~ pu118 the plastlc granule~ lnto the ~pace between the screw and the groove entrance zone 33 provlded wlth groove~ 35 wlth a constant depth 36 of recess.
The plastlc partlcles whlch have, for example, a mezm core dlameter of 0.5 mm, ln the groove entrance zone 33, may escApe lnto the grooves. Because of thls moblllty and the possiblllty to escape, less plastlc partlcle~ rotate clrcularly simultsneou61y ~l~h the ~crew~
BO that more materlal can be brought ln transport dlrectlon by the screw into the transltion zone 34.
Because of the lnherent pressure of ehe plastlc ma~erlal and the moblllty ln the groove entrance zone, on the whole, re materlal can be tranaported in longltudlnnl dlrection by the extruslon acrew.
Bec~use of the fafiter conveying and the l~rger moblllty, le~6 plastic psrtlcles "bloc1c" the apace for the ~aterlal in the groove entrance Yone 33 that follow& by belng pushed out of the feeding funnel 17.
In the trAnsltion zDne 34, the depth 36 of recess of the grooves '7~t in transport directlon decreaaes to zero. The plDatlc materisl thus 18 packed more densely and more uniformly. The resultlng frlctlonal heat muat not be ~ufflclent to plastlclze the m~terial. Therefore, ln thl~ embodiment, cooling rlbs 45 are arranged around the bu6h 28 ln the tranaitlon ~one 34 (eee Flgure 2), ln order to make it pa~6ible to decrea6e the heat.
Ibe materlal wlll not be pln~tlclzed before lt reaches the plasticlzing zone 26. The transltlon zone 34 ls therefore ther-mlcally lnsulated wlth re6pect to the plasticlzlng zone 26.
The eore slze of the material to be processed can be varied within a certain range without slgniflcantly llmlting the advaDtageous effect.
Ascordlng to the pull-in speed and the material, the bush 28 ln the groove entrance zone 33, may also be provided with cooling rib6, 80 that ~t 16 alway~ ensured that the materlal ifi not plastlcized in the whole materlal pull-in zone 13. A pla~tlclzlng of the materlal would "smear over" the grooves and the advantageoufi effect of the groovea could not occur.
By mean6 of the materlal pull-ln zone with the grooves according to the lnvention, an lncreased pulling-in of materlal and a ateadier flo~ of material can be uchleved without atuffing device6, havlng a poslti~e effect on the quallty and ehe quantlty of the end product.

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Claims (7)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for producing pourable spherical-segment-shaped packing material particles made of a plastic material which have an external convex and an internal concave surface, where the plastic material, by means of a feeding funnel, is fed into an extruder through an opening in a bush surrounding the extrusion screw, where the plastic material is plasticized over the course of the extruder and, because of the difference in speed over the cross section of the mass, comes out of an opening in the die with a bent surface and the extruder plastic is cut off directly at the opening of the die and before any considerable expansion has taken place, characterized in that the plastic material is pulled into a heated plasticizing zone of the extruder by passing through a bush having first an entrance zone and secondly a transition zone having spiral grooves the depths of which steadily decrease in the transport direction to zero, said transition and plasticizing zones having a thermal insulation there-between.

2. A process according to claim 1, further characterized in that the entrance zone has grooves the depths of which are constant.

3. In an apparatus for producing pourable spherical-segment-shaped packing material particles which comprises a feeding funnel, an extruder comprising an extruder bush having an extrusion screw therein to form a plasticizing zone, a cutting means attached directly at the opening of the die of said extruder, the improvement wherein said bush further includes a transition zone having spiral grooves the depths of which steadily decrease in the transport direction to zero, said transition and plasticizing zones having a thermal insulation therebetween.

4. A device according to claim 3, characterized in that the bush has a diameter of about 5 cm, and the grooves in the groove entrance zone, have a depth of recess of about 1,5 mm and a width of about 10 mm.

5. A device according to claim 3, characterized in that the grooves have a profile that is U-shaped in its cross section and has legs that are inclined toward the outside.

6. A device according to claim 5, characterized in that the legs of the U-shaped profile are inclined toward the outside by about 15°.

7. A device according to claim 1, characterized in that the groove entrance zone has a length of about 80 mm, and the transition zone has a length of about 180 mm.