DE2350674A1 - EXTRUDING SCREW FOR THERMOPLASTICS OR ELASTOMERS - Google Patents

Description

i. B.

.Patent attorney

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Maillefer S. A., ■ 1020 Renens (Canton of Vaud, Switzerland) rue Neuve 19

"Extruder screw for thermoplastics or Elastomers "

The subject of the invention is an extruder screw for thermoplastics or Elastomers that have a backwater thread along their entire length, which is intended to work together with the cylinder "of the extruder screw in order to move the material to be extruded towards the valley side, and which is divided into a loading zone, a plasticizing zone, a decompression zone and a pumping zone, the plasticizing zone is determined by the presence of a through thread, which an inlet and an outlet throat between the turns of the backwater thread forms, these grooves are arranged so that the material to be extruded progressively above the thread and through moves the plasticizing zone through from the entry throat to the exit throat.

Screws of this type with a plasticizing zone as in Swiss U.S. Patent No. 363,149 are known and have been used for several years used regularly. They have the advantage of being safe get a homogeneous product at the valley end of the Extrudierma chine whose all parts have the same temperature and the same Have degree of plasticization. In fact, it was found that the through-going thread running along the entire length of the plasticizing

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zone extends the completely liquid material from the still partially solid separates and activates the plasticization of the latter.

However, the quality of the product extruded at the end of the machine depends not only from a good homogenization of the material, but also relies on the most complete removal of the gases contained in the raw material or with it into the feed zone can be entered. The removal of these gases is then particularly difficult, if the raw material used is powder instead of granules; however, the use of granules also poses the problem of Degasing.

It has already been proposed to insert gas discharge pipes through the cylinder of the Attach the extruder to the decompression area. The screw has a diameter constriction in the mountain-side part of the pumping zone on and the drainage pipes are in the Zyftider at this part with reduced Diameter attached. However, this arrangement does not lead to as complete a degassing as would be desirable.

The object of the invention is therefore to create an extruder screw from the above Type that meets the requirements of practice better than before, in particular as it allows for a more complete degassing of the extruded product, especially in the case where the raw material allows is a powder.

Accordingly, the screw according to the invention is characterized in that that the entrance throat cut a pass cross at most equal to that Has total passage cross-section at the entrance of the plasticizing zone and in that the profile of the exit throat is such that the entire Passage cross-section, regardless of the point in the named plasticizing zone, is larger than at the entrance to this zone.

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Further features and advantages essential to the invention can be found in the following Description in the, with reference to the drawings, exemplary embodiments explained.

In the drawings show:

The only figure is a longitudinal sectional view of part of an extrusion cylinder with the corresponding part of the screw.

The cylinder 1 has a cylindrical inner surface all over Length on. The diameter is adapted to the outside diameter of the screw thread 2 with a constant pitch of the screw 3, i.e. it exists a relatively small play between the thread'2 and the cylinder 1. The Screw 3 is driven in rotation (by means not shown) in such a way that that the plastic material is jammed from left to right in the drawing. Around the cylinder 1 are neck means (not shown) arranged, which are able to bring the material transported by the screw progressively to its melting temperature. That said Material is fed into the cylinder through a funnel at the left end of the cylinder. It then has the form of a powder or granules. At the right end of the extrusion machine, the material is under pressure ejected through the screw in a completely molten state and at the temperature desired for the extrusion operations.

The screw 3 is divided into four zones: the loading zone 4, the Plasticizing zone 5, the decompression zone 6 and the pumping zone 14. The plasticization zone is defined by the presence of the through thread 7, whose step here is larger than that of the backwater thread 2, while the outside diameter is slightly smaller, so that between the The inner surface of the cylinder 1 and its tip have a greater amount of play than that existing between the thread 2 and the cylinder 1. Each-

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however, in a variant, the clearances between threads 2 and 7 and the cylinder also be the same. The through thread 7 is with the Ruckstaugewin.de at the two valley and mountain side ends of the zone 5 in the Connected way that between the turns of the thread 2 a helical, Valley-side groove 8 is formed, the cross-section of which decreases progressively and a helical groove on the mountain side 9 with progressively increasing cross-section. The valley-side recess 9 can be referred to as the entrance recess, because it follows the loading zone directly 4 and the material to be extruded arrives there without hindrance from the loading zone. The mountain side zone can be the starting groove because, in contrast to the above, it is directly with. the decompression zone at the end of the plasticizing zone on the valley side is connected, but completely through from the loading zone the passage thread 7 is separated. As can be seen in the drawings, the The depth of the groove 8 is the same as that of the thread 2 on the valley side The groove defined at the end of the loading zone, while the depth of the groove 9 is greater. The entire passage cross-section in the plasticizing ζ one thus increases progressively from a value that is practically the same as that given at the end of the supply zone on the valley side is up to a value equal to that at the mountain end of the decompression zone corresponds to where the core of the screw has the same diameter as at the bottom of the groove 9. At the valley end of the decompression zone the core of the screw has a frustoconical part 10 in such a way that at this point the passage cross-section of plastic material experiences a reduction.

The screw 3 has on its axis a line 11 on its mountain side opens and is closed on the valley side, this channel being connected to the outer surface of the screw by outlet channels 12, which radially are drilled in the plasticizing zone. As can be seen in the drawing, these channels open into the groove 9 with increasing cross-section, and

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although directly above the through thread. On the other hand in the decompression area, i.e. in the part where the core of the screw has the same diameter as in the rising groove 9, a Drain line 13 is provided, which is mounted in the cylinder 1. The channel and the line 13 are connected to pipes leading into the outside air flow out. If necessary, these pipelines could be connected to suction devices.

The lines 11, 12 and 13 and the special arrangement of the groove 9 secure the degassing. It is in fact known to be that of the screw Backed-up material experiences a compression in the course of the shift to the right as soon as it has entered the groove 8, so that it tends to above the passage thread via the play between this thread and to be backed up to the cylinder in order to get into the recess 9. So it's the most fluid parts of the mixed material in of the screw that run over this thread. Now these most fluid parts not only have the plastic material that has already been liquefied, which is through Heating up was made liquid, but also the trapped gases. The material passes between the continuous thread and the cylinder in the form of a thin film and has been found to be in this condition of the material facilitated degassing. Since the groove 9 is deeper is than the groove 8, the material backed up via the thread experiences a decompression, after more volume is in this groove Available. Because liquid material has a tendency towards the valley side of the thread 2 to accumulate, under the action of friction against the cylinder wall, is created on the mountain side of the passage gain of 7 one of the gas occupied zone, which is why the gas can escape via the channels 12 and the collector 11. The line 13 allows the venting of the gas to be completed that is located in the plasticizing and decompression zones has released. In fact, the fully plasticized ma-

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material when passing through the frustoconical part 10 of the screw a compression that shifts the gas that is still present uphill and promotes its discharge through line 13.

Optionally and in other embodiments, the lines 12 and the collector 11 can be omitted, in which case the discharge of the gases only takes place through lines in the cylinder corresponding to the decompression zone are arranged. On the other hand, the screw 3 shown in the drawing could also be used in an Extrudiermas chine the cylinder of which does not have a discharge passage, the entirety of the enclosed gases being discharged through the collector 11.

The screw described above could also be in other forms with the same Advantages are created. Instead of a depth difference between the groove with increasing cross-section and the groove with decreasing Cross-section could also be provided to give the backwater thread in the plasticizing zone a progressively increasing step. These Measure would also cause a progressive increase in the total flow area for the plastic material and the degassing in the course of the Enable plasticization by decompression of the plasticized material. In the same way, the diameter of the thread and of the core of the screw in the plasticizing zone, keeping the step and depth of the grooves constant. The reduction of the cut of the groove in the decompression area could then be achieved, for example, by changing the thread.

In the case of the screw with an overall cylindrical shape, as in the drawing shown, the thread pitch of the through-going thread could of course also be smaller than or equal to that of the backwater thread. On the other hand, it was found that it was not imperative to find a difference between to have the play of the backflow or through-flow threads. Even if this

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Games are the same, the desired effect is achieved.

Patent claims :

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Claims (10)

29.978 9350674 • Patent a η s ρ r ü c h e: 1. j screw for extrusion machine of thermoplastic or V J - - '■' ■ - '-ι "■■■■' ■■ elastomeric materials that run along their entire length. a backwater thread which is intended to interact with the cylinder of the Extrudierm as chine to move the material to be extruded downhill and which is divided into a loading zone, a plasticizing zone, a decompression zone and a pumping zone, the plasticizing zone being determined by the presence of a pass-through thread, which forms an entrance and an exit groove between the turns of the backwater thread, these grooves being arranged in the manner are that the material to be extruded progressively moves from the inlet channel to the outlet channel above the throughfeed and passes through the plasticizing zone, marked by it e t that the entrance groove has a flow cross-section at most has equal to the total flow cross-section at the entrance of the plasticizing zone, and in that the profile of the exit saus groove is such that the entire flow cross-section, regardless of the point at which it is mentioned The plasticizing zone is larger than at the entrance to the aforementioned zone. 2. Screw according to claim 1, characterized in that the passage thread de has a different step than the backwater thread and thereby, that the entrance and exit grooves each have a decreasing or increasing cross-section. 3. 'Screw according to claim 2, characterized in that the entire flow cross-section in the plasticizing zone progressively from the mountain side to the valley side of the zone increases. 409816/0900
ORJGlMAi INSPECTED - * " ^v 7350-674 4. Screw according to claim 2, the back pressure thread of which has the same outer diameter over its entire length and also a constant one Step, characterized in that the throat with decreasing Cross-section has the same depth as that of the backwater thread in the loading zone is formed, while the groove with increasing Cross-section has a greater depth. 5. Screw according to claim 2, characterized in that at least in the plasticizing zone the outer diameter of the thread is variable. 6. Screw according to claim 2, characterized in that the Step at least one of the "two threads" along the plasticizing zone changes. 7. Screw according to claim 2, characterized in that it has gas discharge channels which are drilled radially in its core and with connected to a collector drilled according to the axis of the core. 8. A screw according to claim 7, characterized in that the discharge channels open into said groove with an increasing cross-section. 9. '"screw according to claim 8, characterized in that the *' Drainage channels open directly above the through-going thread. '' '■ .. ".- 10. Screw nach.Anspruch 8, characterized in that the Axial collector is open at the mountain end of the screw. 409816/0900 Γ ^ ⁰ ·· Blank page