DE2634024B2 - Screw extruder - Google Patents

Description

The invention relates to a screw extruder of the type specified in the preamble of claim 1 Art.

Such a screw extruder is known from DE-AS 1268823. The one there in the screw cylinder Circumferentially distributed grooves serve the purpose, the output power and thus the efficiency to increase the screw or to shorten the dwell time of the plastic in the screw press, to a decomposition of the plastic, in particular a heat-sensitive plastic, in the To prevent screw extruder.

Tests have shown that grooved screw cylinders in the feed zone without additional measures the intake behavior of especially polyamide and polyester granulate and thus also the output rate of the Do not increase the screw extruder significantly. It was even observed that the discharge performance slightly decreased. This can be attributed to the fact that there «! Ciranulate on and off Longitudinal grooving of the cylinder is already compressed into a solid plug in the feed zone, which is The screw is poorly conveyed and can only be digested poorly in the transformation zone. Furthermore, it is described in CH-PS 420580 that guide elements designed as kneading bolts in the feed zone are arranged on the circumference of the housing and protrude into the worm gear to a To prevent the product from rotating at the same time. This one

ι »kneading bolts are corresponding interruptions in assigned to the webs of the screw.

The known arrangement serves the purpose of mixing and kneading the items filled in the feed hopper Intensify plastics and additives.

ii An increase in output is not achieved. Rather, it is pointed out in CH-PS 420580 that in the zones in which a higher The conveying effect of the screw is to be achieved, the guide elements removed and the web interruptions

: »The screw closed by passage closing elements should be.

The object of the invention is now for a single-screw extruder for melting and Extrusion of free-flowing plastics, desen

- '"> the screw cylinder has grooves in the feed zone, indicate constructive measures in order to significantly increase the output of the screw extruder to increase, this screw extruder in particular for the processing of the most common

suitable in spinning materials such as polyamides and polyester should be.

The solution to this problem results from the characterizing part of claim 1.

By using the well-known grooves in the

π feed zone of the extruder cylinder in connection with the known guide elements protruding into the screw flight became more surprising Way, a considerable increase in discharge capacity achieved based on the test results with

w screw extruders, each of which only had the individual features, could not be foreseen in any way. This is so much more so than there was a prejudice in the professional world due to CH-PS 420580, pins protruding into the worm gear with associated pins

; ■) web interruptions to be used if a Output increase should be achieved, since this measure is known to reduce the backflow and this significantly promotes back-mixing of the plastic in the screw channel.

-.ο From G. Schenkel, Kunststoff-Extrudertechnik, 1963, Carl-Hanser-Verlag, Munich, as well as from US-PS 2,765,491 it is finally known per se for Increase in the conveying capacity, the pitch of the screw flight degressively in the extrusion direction

-> ■> educate. This is intended to increase the delivery rate can be achieved. Practice shows, however, that the increase in performance compared to a screw with constant pitch is minimal.

The application of this per se known feature

On the other hand, h »maize fell on the snail according to claim 1 another significant increase in performance. The arrangement of the guide elements or the pins at a small distance behind the grooves, according to claim 3, has the advantage that that still

μ unmelted granules turning into the Snail threads are effectively prevented. This effect is achieved by the measure according to claim 4 still increased.

It is particularly advantageous to design the guide elements in accordance with claim 5 so that they can be heated, as this is the case the introduction of heat to melt the plastic granulate from the cylinder into the interior of the Auger thread significantly increased due to the better thermal conductivity of the material of the pins can be.

Furthermore, the proposal according to claim 6, the grooves in the feed zone of the extruder barrel are thread-like to train, significantly to increase their service life, since this reduces the vcn of the screw forces exerted on the granulate can be applied parallel to the longitudinal extent of the groove.

The geometric dimensions of the grooves ultimately ensure that even hard plastics, for example polyamides and polyesters without starting problems or too high torques at high Output can be processed.

In order to be able to adapt the grooves to the respective material, it is further proposed according to claim 8, to arrange externally adjustable steel strips in these grooves.

Finally, the known cooling of the screw cylinder in the area of the grooves according to claim 9 prevents smearing of the granules in the feed zone and ensures that the granulate as a plug flow into the compression or conversion zone of the screw extruder is promoted.

In the following, the invention is illustrated by means of a purely schematic exemplary embodiment and with reference explained in more detail on reproducible test results.

The single figure shows a cross section through a single-screw extruder with the inventive Design.

The screw 1 is rotated in the screw cylinder 2 by the motor and gear unit 3. in the In the area of the hopper 4, the screw cylinder 2 is grooved, the grooves 5 being uniform Are arranged at a distance from one another on the inner circumference of the screw cylinder 2.

In the extrusion direction 6, the guide elements 7 are distributed in two rows on the circumference of the screw cylinder 2 at a distance from the grooves 5. The guide elements 7 can be designed in the shape of a shovel or a boat. They are height-adjustable and rotatable in the screw cylinder 2, and they can be adjusted down to the bottom of the screw channel. For this reason, the corresponding points of the screw flights 8 in the area of the guide elements 7 have interruptions 9. The advantageous combination of the individual features is to be explained in more detail on the basis of the test results listed below. All series of tests were carried out on two different extruders. The following data were available for the first test arrangement:
outer diameter
of the screw: D = 90 mm

Length of the worm: L = 24 D
Arrangement of

Snail: lying

Slope: t = 1 D (constant)

Speed: η = 100 min '

Material: PA 6 (Ultramid) LV = 2.4

Melting pressure: ρ = 100 bar ± 2%

Melt temperature: I, = 265 "C ± 1" C.

First, tests were run in which no further training on the screw 1 and the Screw barrel 2 have been made to be an initial value for the following comparisons to achieve. The extruder achieved a rate of output of 245 kg / h of homogeneously melted extrudate.

In the following series of tests, radial guide elements 7 were arranged in the screw cylinder in the feed area, extending to the bottom of the screw channel were enough. Two lines of two each were distributed around the circumference of the screw cylinder 2 arranged guide elements 7 used. Each guide element 7 had a width of 25 mm. the The first row was at a distance of 180 mm from the feed hopper 4 - viewed in the extrusion direction arranged. The second row was at a distance of 1 D behind (in the direction of extrusion) the first arranged.

The screw 1 did not produce any additional output compared to the first attempt, i.e. the volume output persisted at 245 kg / h of homogeneously melted extrudate.

In the next series of experiments, instead of the Guide elements 7 grooves 5 used in the feed zone of the extruder. The grooves 5 had a total length of 60 mm, a depth of 0.7 mm and a width of 7 mm. There were 16 pieces on the circumference of the Schneckenzyiinders 2 arranged distributed. These grooves 5 were cooled with the hopper 4. Here, too, there was no additional output, rather the volume output even declined slightly and amounted to 240 kg / h.

In the last series of tests, the two structural features described first were combined at the same time applied. This resulted in an increase in volume output to 460 kg / h.

The same series of tests were carried out with an extruder with a different pitch Screw flight 8 carried out. The following data were available for the second test arrangement:

outer diameter
the snail:
Length of the screw:
Arrangement of
Slug:
Pitch:

Rotational speed:
Material:
Melt pressure:
Melt temperature:

D = 90 mm L = 24 D

lying

t = 1.5 to 0.8 D (in the compression zone
evenly decreasing)

η = 120 min '

PA 6 (Ultramid) LV = 2.4

ρ = 100 bar ± 2%

t = 265 "C ± I" C.

Here, too, as in the first example, tests were initially carried out in which no further training was provided on the extruder to be a baseline for the comparisons below

mi to achieve. The extruder produced a quantity output of 288 kg / h.

The following experiment was also carried out with two rows of two each on the circumference of the screw cylinder 2 guide elements 7 arranged in a distributed manner

tv "> carried out. The arrangement and implementation of the Guide elements 7 on or through the screw cylinder 2 were the same as in the first test arrangement. In this attempt a quantity guideline was

Decrease in performance to 230 kg / h was determined.

In the further experiment, grooves 5 were used in the area of the feed zone of the screw 1. Of the Screw barrel 2 was the same as in the first experimental set-up. This resulted in almost the same output as with unslotted screw cylinder 2. The amount of output was 280 kg / h.

In the final series of tests, both characteristics were first applied separately used at the same time. This resulted in a significant increase in volume output to 360 kg / h.

Both experimental set-ups show that only through the proposed combination of some of the siel known features a noteworthy quantity performance increase is to be achieved.

If a different material than the one mentioned above is used, some changes may be made the size and arrangement of both the Leiteleri: duck "and the grooves 5 are required. The Leit Elements 7 are therefore - as already mentioned - height adjustable and pivotable about their axis orderly. The depth of the grooves 5 can be changed by inserting stool strips into the grooves 5 which steel strips can be adjusted from the outside in the grooves.

1 sheet of drawings

Claims (9)

Patent claims: 1. Screw extruder for melting and extruding free-flowing plastics, its Has screw cylinder in the feed zone, characterized in that in Direction of extrusion behind the grooves (5) protrude radially into the worm gear guide elements (7), which corresponding interruptions (9) of the screw flights (8) of the screw (1) are assigned are. 2. Screw extruder according to claim 1, characterized in that the slope of the Screw web (8) runs degressively. 3. Screw extruder according to claims 1 and 2, characterized in that the guide elements (7) at a distance greater than the outer diameter of the worm behind the grooves (5) are arranged. 4. screw extruder according to claims 1 to 3, characterized in that two rows arranged distributed by two guide elements (7) on the circumference of the screw cylinder (2) are. 5. screw extruder according to claims 1 to 4, characterized in that the guide elements (7) are heatable. 6. screw extruder according to claims 1 to 5, characterized in that the grooves (5) run helically. 7. screw extruder according to claims 1 to 6, characterized in that the grooves (5) 0.5 to 1 times as long as the outer diameter of the snail are less than 1 mm deep and less than 10 mm wide. 8. screw extruder according to claims 1 to 7, characterized in that in the grooves (5) externally adjustable steel strips are arranged. 9. screw extruder according to claims 1 to 8, characterized in that the screw cylinder (2) can be cooled in the area of the grooves (5).