DE1629711A1 - Plasticizing and ejection unit for plastic masses, preferably for hollow body blow molding machines that process thermoplastics - Google Patents

Description

Plasticizing and ejecting unit for plastic masses, preferably for blow molding machines processing thermoplastics The invention generally refers to screw extrusion presses and plasticizing units combined with them for more special processing methods. In particular, it concerns a discontinuous Working plasticizing unit with a high volume output for the feeding of blow molding machines.

It is known for blowing large hollow bodies made of thermoplastic Substances from a screw extruder and an upstream collecting chamber to use existing plasticizing unit with ejector piston. The mass space of the Screw extruder and the upstream, equipped with the ejector piston The collecting areas are connected to one another by relatively narrow channels, to maintain the fluidity of the mass even over the break times must be sufficiently heated during processing. It follows that thermally sensitive or close to the decomposition temperature to be processed The quality of plastics in the area of these channels, which are temporarily not flushed be influenced in part.- 1) The volume of the upstream collecting space can with many of the known plasticizing units largely arbitrarily dimensioned will. However, complete emptying is due to the constructive conditions usually not possible because the end face of the ejection piston is due to the low speed the mass flowing past it is only insufficiently rinsed. When changing the material or the color are therefore either long for such units Business interruptions for manual cleaning or correspondingly large quantities of material required for flushing. At first the whole volume is filled with a gas, which only displaces when the plasticized material is increasingly filled will. During this time the gas can possibly detrimentally with the liquefied Material react.

To be raised in this regard to an improved plasticizing unit Requirements are therefore the elimination of any narrow cross-sections for the flow of material up to the collecting space, the direct flow impingement of the end face of the Ejection piston as well as the continuous adjustment of the collecting space volume to the in this pressed-in mass.- Another essential requirement concerns the drive the worm spindle.

The drive power of the screw is in each plasticizing unit thanks to the maximum torque that can be transmitted over the smallest screw cross-section certainly. However, the dimensioning of the screw cross-sections should not only be based on the to be transmitted torque take place, but first of the gentlest liquefaction and the greatest possible plasticizing capacity. The invention provides under the axially displaceable spindle provided with worm flights among other things, the torque transmission at the discharge end of the screw before, without to impair the fulfillment of the other requirements.

In another context, there are injection molding machines with axially displaceable ones Known screw piston. With them, the plasticized mass is removed from the collecting space or the mass filling chamber, always in front of the nozzle by moving the screw piston excreted in the same direction as the main flow direction of the mass through the plasticizing chamber is equivalent to. Accordingly, the discharge port is located in such injection molding machines approximately at the extreme end of the traveled by each plasticized mass particle Distance. An application of force for rotational and maximum movements of the screw piston is therefore only possible at its rear cold end. The collection room for the mass to be ejected discontinuously is formed by the plasticizing cylinder. being Volume is given by the screw diameter and the stroke of the screw piston This stroke is determined by reducing the effective screw length at Filling of the collecting space is limited. The usual maximum possible stroke of such machines corresponds to about three times the screw diameter. To with certain processing methods It is therefore possible to eject relatively large volumes of plasticized plastic necessary to enlarge the screw diameter. The corresponding increase achieved in the process however, the plasticizing and conveying capacity cannot be achieved with such a dimensioning be exploited. As a result, such machines are uneconomical.

With many processing methods in which the manufacturing time of a molded body to be produced essentially by the required cooling time is determined, on the other hand, is a relatively high discharge from the plenum only required at times during a certain period of the work cycle. A plasticizing unit with a large screw diameter can therefore be used for such Process either only works in a throttled manner, or it would have to work in every work cycle be switched off temporarily. For the last-mentioned embodiment must so far the drive of the machine can be oversized. All plasticizing units customary up to now therefore need to be improved in various ways.

From the German patent 845 855 an injection molding machine is also known, in the case of a sleeve-like sleeve provided with an axial bore in the cylinder Injection piston is arranged axially displaceable. The plasticization of the plastic takes place by means of an injection plunger that is similar to the inside of the sleeve and can be rotated mounted screw, which is continuously located in front of the face of the injection piston Collecting space fills. During the emptying of this mass filling space, the nozzle-like Bore closed by a non-return valve. In this machine, the The diameter of the collecting space is larger than the diameter of the screw diameter. It is of the type however, the disadvantage that it is particularly suitable for low-viscosity plastic melts no perfect seal between the sleeve-like injection plunger and the Spritzzylin can be achieved. The one pressed between these functionally essential parts Plastic soon leads to a significantly reduced heat transfer, so that the heat required for plasticization is insufficient for the fabric can be fed. Finally, machines designed in this way still have the shortcoming that the relatively large heat conduction distances only a very sluggish temperature control allow the whole system, therefore leave it thermally particularly sensitive For this reason, plastics cannot be processed with such units.

An uneconomical dimensioning of the ratio of the volume of the collecting space to avoid the filling volume of the screw threads or the diameter of the screw, is in the collecting chamber of another known screw machine for discontinuous Processing of the plasticized material a much larger screw head Diameter than that of the worm spindle can be axially displaced. Snail and snail head form here a component and it is over the screw shaft from the rear At the end both the rotational movement and the axial movement are initiated. The screw plasticizes the plastic either in a manner corresponding to the axial one Cut of the screw with head-shaped cylinder or in a sleeve, which because of the necessary axial displacement is positively connected to the worm and is secured against twisting in the machine housing. Also in these embodiments of a plasticizing unit, the plastic is fed through narrow channels in the son's corner head conveyed from the plasticizing area to the collecting area. The plastic to be pushed out Material is transported in the conveying direction by the extension of the screw axis in the outermost end of the collecting space arranged nozzle pushed out. To close a non-return valve is required during the pushing-out of the channels The construction allows the excavation of a relatively large volume of plastic-fixed material with only small snail diameter. The necessary torque for the drive the snail and also the force generating the push-out pressure must, however, be transmitted over the smallest screw cross-section.

This combined load consequently determines the size of the screw. There are only relatively long worm spindles with a given buckling strength small forces can be transferred. Even with tight tolerances between the cylinder or 0 the sleeve on the one hand and the screw on the other hand occur in the unavoidable high load radial forces, which result in undesirable wear on the screw or the surrounding cylinder.

In the case of the above known construction, the rest of the time Operation still has the following disadvantages: Plasticizes the screw with the screw piston Much larger diameter the plastic directly in the-accordingly the axial section shaped cylinder; so when ejecting occurs between the screw-side Flat of the head and the cylinder a space into which during the extension the plasticized material continues to be conveyed. A filling of the collecting space between the end face of the head and the discharge opening does not occur until that screw-side space is filled and an overflow through the into the screw piston provided channels. If the screw should run back axially in this phase, so the mass accumulated behind the screw head must also be displaced. further can a return of the screw piston can only be achieved if the area difference of the screw piston is dimensioned accordingly large. The pulling force is therefore exclusively dependent on the dimensioning of the plasticizing screw. she can consequently not without considering other conditions according to the to be applied Plasticizing capacity can be selected.- Finally, the screw works up to Filling of the space on the side of the snail behind the head with practically no back pressure. Of the Plastic conveyed into this space may therefore not be sufficient under certain circumstances homogeneously plasticized.

The invention is therefore based on the object of a discontinuous Working plasticizing unit with an output volume that can be varied over a wide range in which the plasticizing capacity of the screw is taken into account of the work cycle can be fully utilized without the homogenization .des to be processed Affect the substance and the uniform introduction of additives. - In line with this requirement, such an improved unit in the B / D ratio is intended the plasticizing screw by the attacking driving forces no restrictions and there are bottlenecks between the plasticizing area and the collecting area to avoid.

This object is achieved according to the invention by a screw spindle receiving plasticizing or kneading and mixing cylinder of smaller diameter without Intermediate constrictions, nozzles that reduce the cross-section or connecting channels connected, the ejection piston containing cylindrical plenum essential larger diameter of variable filling volume from which the collected mass against the conveying direction of the worm spindle through one or more between lateral channels provided in both cylindrical spaces can be pushed out.

According to a further feature of the invention, the plasticizing, mixing and kneading screw spindle with the screw piston in the collecting chamber jointly rotating and axially displaceable unit.

According to the invention, the plasticizing screw spindle can be smaller in the cylinder Diameter and the screw piston in the collecting chamber of larger diameter also pushed one above the other and be drivable at different speeds. Preferably here is only the screw piston is axially displaceable in the collecting space.

Another essential feature of the invention is toe, that the drive for the rotating and the axial displacement the Movement unit formed from worm spindle and ejector piston on an extension attacks the ejector piston.

Further features emerge from the detailed below Description in conjunction with the drawings.

1a and 1b show schematic longitudinal sections of an embodiment in two different operating states.-The drive 1 transfers this to the Worm spindle 2 in cylinder 3 to be introduced via the torque in the collecting chamber 4 co-rotating and axially displaceable ejector pistons together with the worm spindle 5. The worm spindle and the ejector piston thus form a single movement unit. The cylindrical one The collecting space 4 has a considerably larger one compared to the plasticizing cylinder 3 Diameter and a multiple of the volume of the plasticizing chamber. In the usual way the plastic is thereby introduced into the hopper 6 in the cylinder 3 and forms a practically solid plug in the filling area of this cylinder, which Backflow of the increasingly liquefied cylinder 3 as a result on the further way Mass prevented when the emptying stroke of the ejector piston 5 is carried out in opposite directions. The mass conveyed into the collecting space 4 moves the ejector piston 5 in the sense increasing collection space volume, where the cross-sectional Flow resistance of the outlet channel 8 in this movement phase, the premature outflow into a attached form or processing device of the ejection piston 5 can be completely or partially provided with a screw cut which is opposite to that of the plasticizing screw spindle 2. Further the front cross section of the ejection piston 5 is poor under avoidance inflow dead spaces selected shape of the collecting chamber housing 4a geometrically similar.-Is there a sufficient volume of the finished part to be produced in the collecting space 4 Contain the amount of plastic to be determined, the rotary drive of the screw 2 and the ejection piston 5 rigidly connected therewith are temporarily stopped.

If the collecting space 4 is filled, eo is over the hydraulically loadable Piston 7, preferably with continued Rotationsw movement from the ejection piston 5 and the screw spindle 2 existing movement unit, their axial movement initiated against the conveying direction of the worm spindle and the collected in space 4 Ground through the laterally branching channel 8 into the connected processing device or a mold cavity pushed out (Fig. Lb). During the pushing out of the mass every point of the collecting area is at least once by an aisle or footbridge of the Snail cut on the Nantelfläche- the 'ejector piston 5 touches and thereby practically complete emptying and cleaning of the collecting space achieved. Instead of just one channel 8 can be used to feed several processing devices several canals branched off to the side.

In Fig. 2 is another embodiment of the plasticizing unit reproduced in longitudinal section. Here, the plasticizing screw spindle 2 and the ejection piston 5 do not have a movement unit, but rotate independently of one another9 for which they are connected to the two drives 1 and 2a.

It follows from this that the worm spindle 2 and the ejection piston 5 can also rotate at different speeds or circumferential speeds. Furthermore, in this embodiment, the worm spindle 2 does not lead in the cylinder 3 axial movement. It ends roughly in the area of the laterally branching canal 8. The structural features of the collecting space, the drive and the axial displacement of the ejection piston 5 and the operation of the device otherwise correspond to Execution according to FIG. 1a.-Another characteristic of this construction and drive arrangement of the plasticizing unit is in the use of a co-rotating or counter-rotating one Double screw can be seen in cylinder 3, with the due to different delivery and pressure conditions the intermeshing screw profiles in certain cases additional advantages can be achieved.

From the embodiments of the plasticizing unit to the Pig. 1 and 2, the construction according to FIG. 3 also differs in the arrangement the rotation of the worm spindle 2 and the ejection piston 5 and its axial Movement causing components for power transmission. The extension 2b the worm spindle 2 through the collecting space 4 4 passes through a central bore of the ejector piston 5 through and ends in the transmission 1, which is the same time the torque for the ejector piston 5 supplies for the transmission of this torque as well as the from Piston 7 her exerted axial displacement force is a hollow shaft 9, which is coaxial is pushed over the extension of the worm spindle 2b. With this arrangement the ejection piston 5 and the worm spindle can be from a single gear 2 also with any different angular speeds or circumferential speeds are driven.

Claims (12)

Claims 1. Plasticizing and ejection unit for plastic Wet, preferably for blow molding machines, consisting of a multi-part, surrounding the plasticizing and collecting space, with inlet, degassing and discharge openings These housings have different sections or zones rotatably mounted therein Diameter having worm shaft and an ejection piston and one or two drive units on one or both screw shaft ends, marked by a plasticizing or kneading device attached to the screw spindle (2) and mixing cylinders of smaller diameter without interposed constrictions, cross-section reducing Nozzles or connecting channels connected, containing the ejection piston (5) cylindrical collecting space (4) of significantly larger diameter of variable height Filling volume from which the collected mass is opposite to the conveying direction of the screw spindle by one or more temporally provided between the two cylindrical spaces branching channels (8) can be pushed out. 2. Plasticizing and ejection unit according to claim 1, characterized in that that the ejection piston (5) in the collecting space (4) is designed as a screw piston. 3. Plasticizing and ejection unit according to claim 2, characterized in that that the ejection piston (5) is opposite to the plasticizing screw spindle (2) with a slope in opposite directions or with an oppositely directed taste cut having. 4. plasticizing and expulsion unit according to claims 1 to 3, thereby characterized in that the plasticizing, mixing and kneading screw spindle (2) in the smaller diameter cylinder (3) with the larger diameter ejector piston (5) in the collecting space (4) a jointly rotating and jointly axially displaceable unit form. 5. plasticizing and ejection unit according to claims 1 to 3, characterized characterized in that the plasticizing, mixing and kneading screw spindle (2) in the cylinder (3) of smaller diameter and the ejection piston (5) in the cylindrical Collecting space (4) pushed one on top of the other and drivable at different speeds are, with only the ejection piston axially displaceable in the cylindrical collecting space is. 6. plasticizing and ejecting unit according to claims 1 to 3, characterized characterized in that the worm spindle (2) and the ejector piston (5) in the area of the exhaust channel (8) are driven separately and independently of each other0 7th Plasticizing and ejecting unit according to claims 1 to 4, with as a movement unit executed screw spindle and ejection piston, characterized in that the Drive for the rotating and the axial displacement of the movement unit on one Extension of the ejection piston (5) engages. 8. plasticizing and ejection unit according to claim 1 to 4, characterized characterized in that the force for the axial displacement of the ejection piston (5) on an extension of the plasticizing screw spindle (2) engages. 9. plasticizing and ejection unit according to claim 1 to 8, characterized characterized in that the ejection piston (5) has an end face towards the collecting space (4) Has conical surface. 10. plasticizing and ejection unit according to claims 1 to 9, characterized characterized in that the contour of the collecting space (4) corresponds to the front cross section of the ejection piston (5) is adapted. 11. plasticizing and ejection unit according to claims 1 to 4, characterized characterized in that the lateral discharge channel (8) approximately in that through the outermost Displacement position of the ejection piston (5) certain plane, preferably perpendicular is guided to the screw and piston axis. 12. Plasticizing and ejection unit make claim 11, characterized in that that the discharge channel (8) the cylindrical collecting space (4) radially or tangentially cuts.