DE2230771A1 - Pyrometer for plastic material inside an extruder - situated just before the nozzle and located inside the screw - Google Patents

Abstract

A single screw is bored to take an inner tube with cooling water channels. A thermal sensor lies in a hollow cone which is surrounded with thermal insulation, this fits inside a tubular end which screws on to the end of the extruder screw. Wires from the sensor pass down the central tube. The sensor is thus located at the very end of the screw and accurately measures the temp. of the plastic mass just before it passes out through the nozzle, without inhibiting the flow of material.

Description

Temperature Measuring Device The invention relates to a temperature measuring device for measuring the temperature of the melted plastic in an extruder, preferably a single screw extruder.

Extruders are used for the continuous processing of plastic masses, one or more screws running in a corresponding housing, so that the raw material fed in as powder, agglomerate or granulate is continuously conveyed, compressed, vented and degassed, melted, mixed and finally to Shaping can be printed by an ixise. Here, the extruder can be a have external cylinder heating or the speed of the extruder screw can are so high that the frictional heat generated provides sufficient heating of the cylinder content takes place.

In any case, the temperature of the plasticized Eunstætoff mass, in order to obtain optimal processing conditions, with a very specific value which may fluctuate by a maximum of ## 1 + ~ 1 ° ~.

The temperature must not only be monitored continuously, but also be kept at the same level through appropriate measures.

The first prerequisite for this is a measurement that is at least one order of magnitude is more precise than the desired tolerance. The measurement inaccuracy is likely to be at most + 0.10 C.

As mentioned, the temperature of the plasticized plastic must be measured , the plastic mass that is located at the entrance of the extruder nozzle. At this point, however, the plastic melt has temperatures of 1500 ... 4000 a and is under a pressure of 80 ... 600 atm. This high pressure requires extraordinary measures for attaching a thermal sensor.

So it belongs to the known state of the art including a thermal sensor its supply line can be screwed into a cylinder wall of the extruder Insert threaded bolts, using electrically non-conductive as connecting material materials are used that also have a largely heat-insulating effect.

Here, the thermocouple comes with the plastic compound on the inner wall of the cylinder in contact, so it measures their temperature.

At the same time, however, the thermocouple also only measure very slowly changing temperature of the cylinder wall, so that the temperature changes the melted plastic mass completely due to this constant wall temperature is covered. The consequence of this is the pretense of an almost constant temperature of the plastic compound or measurement inaccuracies in verifiable examples via + igOC lie. Such measurement inaccuracies naturally lead to corresponding bad end products or rejects.

An improved measuring device was indicated that, again starting from a threaded bolt that can be screwed into the wall, a thermal sensor attached to a boom immersed in the plasticizing plastic compound is, with the actual Tilermo sensor in the longitudinal direction of the worm against the Plastic stream is directed. This will be largely the The influence of the thick, heat-storing cylinder wall is eliminated, however as a result, the continuous flow of plastic is disturbed and behind the thermocouple so swirled that again: no optimal processing conditions set. In addition, such a thermal sensor is also very prone to failure. On the other hand, falsify with this upstream temperature sensor, relatively high flow resistances the plastic melt the results of the temperature display.

Whether the thermal sensor is in the cylinder wall or on one of the Cylinder wall inwardly protruding boom is attached, it always does not show exactly the plastic compound temperature, since the display is still covered by the heat storage on the one hand from the cylinder wall and on the other hand from the hermo sensor surrounding metal. With the arrangement of the temperature sensor in one after the cylinder interior pointing boom, there is also that at the point of contact of the boom Significant frictional heat is generated with the plastic compound, which, depending on the processing temperature, Mass and processing speed is different. These influences are However, it can hardly be grasped, so that this creates further uncertainty.

In order to eliminate these influences, the general procedure is as follows: that the extruder is heated to a certain temperature at which good Set the results and then record this temperature as precisely as possible. Due to the memory effect, however, temperature control can only be achieved carry out with very long delays, so that even with this empirical measure corresponding committee must be accepted.

for the exact determination of the temperature of the melted plastic mass should be the temperature in the enamel center, i.e. immediately before entering the Nozzle, measured in such a way that the continuous flow of plastic does not is hindered, and that the heat capacity of the surrounding area or the thermal sensor covering Components not or as little as possible.

This is done in the manner according to the invention in the case of a temperature measuring device achieved at an extruder in that the extruder screw pierces and anal the thermocouple is placed in the screw tip.

The tip of the snail is right there, or can be placed right there where the temperature is to be measured, namely in the melting center, directly before entering the nozzle. So the plastic temperature is measured there, where it is of interest, not in a place remote from the melting center like with the previously known measuring devices. In addition, this point is different from the surrounding area The cylinder wall is the same distance everywhere, so that influences from the storage capacity of the surrounding aterials cannot occur or is negligible stay small. It should also be noted that the screw tip is the continuous one Plastic flow is not hindered, so that turbulence of the conveyed plastic mass need not be feared. At the same time it is also ensured that the frictional heat does not falsify the measurement, as the screw tip moves in the direction of of the plastic flow is tapered and overall the geometry in this space, the so-called Calming zone, is or can be adjusted. Thereby are but also all sources of interference that previously had an impact on the temperature result eliminated: The storage effect of the thick cylinder wall is switched off; the The influence of frictional heat is eliminated or reduced in such a way that the Measurement result is no longer influenced; a swirling of the Kunstetoffinasse no longer takes place.

This results in perfect measurement results, the errors of which are within of the error limits listed above, + 0.10 C, lie and the unambiguous temperature control allow the plastic mass before the inlet to the nozzle.

The thermal sensor can be inserted into the screw tip, advantageously again with a connecting material that does not conduct electricity and against heat transfer isolated.

When using an electrical thermal sensor, the thermal voltage removed from the far end of the worm by slip rings or similar means and fed to the display or control device.

According to the invention, however, the procedure is advantageously that the screw tip is inserted into the screw by means of a heat-insulating adhesive or through a heat-insulating layer inserted hollow cone in which the thermal sensor is appropriate.

With this design there is a heat supply from the screw material Much better avoided than when inserting the thermal sensor directly into the Snail material, albeit with a heat-insulating layer. This now the Hollow bodies forming the screw tip can be much more precise and pressure-resistant in the snail should be inserted as the dorch against mechanical damage right sensitive thermocouples. Is still according to the invention in the axial bore A fixed tube is inserted into the screw, which is supported by the screw tip, and the derivation of the thermocouple arranged in the screw tip by the Pipe passed through, so the thermocouple can be held, so it does not have to join in the rotation of the worm.

This also eliminates the need for transmission links such as slip rings etc., which can definitely falsify the measurement result. Since that turns out to be a snail tip If the intended hollow cone rotates, but the thermocouple is stationary, a relative movement occurs between these two elements. The resulting frictional heat is, however, due to the small diameter of the thermocouple and the relative slow rotation of the screw is very slight and is of the order of magnitude of 0.02% 0 of the full scale value. This error is therefore negligibly small.

The relatively small dimensions of the hollow cone as well as the Thermal sensors result in rapid heat conduction or, as there is hardly any heat capacity is present, a quick one transmission of the respective measured values. To promote this transfer, the hollow cone can also be coated with a thermal paste be filled.

In order to keep the initial conditions largely constant, we recommend # it is that the tube is closed on the end face lying at the screw tip and the tube near the screw tip, directly at the bearing point of the Pipe, is provided with cooling water through holes. It can now cool water by the circular cross-section between the outer wall of the tube and run into the inner wall of the screw axial bore through the cooling water bores pass through the end of the pipe and run off again through the pipe. This results in constant values in the vicinity of the measuring point in the screw material Temperature conditions, so that an influence on the measuring temperature is excluded is.

In order to check the pipe storage or to be able to maintain how It is also recommended for testing the thermocouple and for easier manufacture that the screw front part working in the discharge zone (metering zone) of the extruder an approximately cylindrical screw shaft that can be placed on the screw shaft that is offset at this point Hollow body, is. The screw front part can therefore be removed for the work mentioned and screwed on again after the work has been carried out. Also results by the fact that now the front of the screw can also be machined from the front can, a significant manufacturing savings.

The subject of the invention is shown in one embodiment on the drawing example shown schematically.

A screw 2 rotates and presses in the cylinder 1 of an extruder a plasticized plastic mass through a nozzle 3.

In the longitudinal direction, the cylinder is divided into a compression zone 4, a subsequent discharge zone (metering zone) 5 and a calming zone 6. The worm 2 is pierced axially (7). A tube 8 is inserted into the bore 7, that at his front face cooling water through-holes 9 has.

The tube 8 is on the screw front side via a bearing shaft 10 stored (11); the bearing 11 is protected by seals 12 against the passage of the cooling water 13 sealed. Passed through the tube 8 and sealed (20) in the bearing axis 10 inserted, the derivation 14 of a thermal sensor 15 is the screw tip in one representing hollow cone 16 is arranged. The hollow cone 16 is thermally insulating Mass 17 in an approximately cylindrical screw that can be screwed onto the shaft of the worm 2 Hollow body 18 inserted. To ensure a secure connection between the hollow cone 16 and the hollow body 18 via the insulating mass 17 are the parts at the point of insertion provided with back turns or bevels even with strong Pressure on the screw tip yields the hollow cone 16 or the Do not allow insulating mass 17.

The cylindrical hollow body 18 extends approximately over the length the discharge zone and is on a front threaded shaft as shown 19 of the screw 2 is screwed on. After unscrewing the hollow body 18, this is in the end face of the screw 2 or the shaft 19 embedded bearings 11 accessible for maintenance. The rolling bearing in this camp 11 axis 10 is firmly connected to the pipe 8, so stands still.

Through an axial bore in the bearing axis 10, the derivatives for the thermal sensor 15 passed through and sealed with a special seal 20 and held.

The plastic compound is transported to the nozzle 3 by the screw 2 and injected through this nozzle 3. This is where the melting center is located the plasticized plastic mass approximately in the middle of the leading to the nozzle 3 funnel-shaped narrowing. The tip of the hollow cone protrudes exactly into this melting center 16 so that the temperature at that point is accurately detected. The temperature is about the material of the hollow cone 16, which is preferably a high specific Has thermal conductivity, forwarded to the thermal sensor 15 of this value as Current or voltage value to the measuring system passes on. Due to the low heat capacity of the hollow cone 16, relatively fast Temperature fluctuations are passed on to the thermocouple 15 immediately. Because the hollow cone 16 of the material of the screw 2 or of the hollow body 18 through the heat insulating mass 17 is separated, is also a repression of the temperature from the aterial of the screw 2 prevented. In addition, the cooling water 13 reaching almost to the front seats of the screw is cooled, so that the snail itself does not reach temperatures as high as it does surrounding plastic mass. In addition, the cooling water 13 also the bearing axis 10 so cooled that heat is radiated from this bearing axis 10 to the thermal sensor 15 is excluded.

As FIG. 2 shows, the screw shaft 21 ends in a flange 24 which in turn is connected to a drive flange 25.

The screw shaft 21 is not provided with a spring as usual, but only has an axially parallel flattening.

This makes it possible to move the screw 2 in its longitudinal direction and thus also to precisely adjust the screw tip carrying the thermocouple so that it lies exactly in the melting center of the melted plastic. Around always a perfect fit of the screw 2 or the screw shaft 21 to achieve in the flange 24, a threaded sleeve 22 is provided in the Drive flange 25 is screwed in and secured by a counter ring 23. the The end face of the screw shaft 21 strikes this threaded sleeve 22 so that the correct position of the screw 2 always results. The pipe 8 goes through here the threaded sleeve 22 through it, as well as the thermocouple discharge line 14. To the supply line the cooling water is a coaxially the pipe 8 surrounding the cooling water pipe 26, the sealing is inserted into the end face of the screw shaft 21.

Overall, this results in an exactly working and also The measuring device following rapid temperature fluctuations is a perfect one Temperature control of the supplied plastic mass allows.

Claims (10)

Claims W Temperature measuring device for measuring the temperature of the melted Plastic in an extruder, preferably a single screw extruder, thereby characterized in that the screw (2) pierces axially (7) and in the screw tip a thermal sensor (15) is arranged. 2. Measuring device according to claim 1, characterized in that the Screw tip is inserted into the screw (2) by means of a heat-insulating clasp Is hollow cone (16). 3. Measuring device according to claim 1, characterized in that the Screw tip into the screw (2) via a heat-insulating layer (17) inserted hollow cone (16) is. 4. Measuring device according to one of claims 2 or 3, characterized in that that the hollow cone (16) made of a material with a high specific: thermal conductivity is made. 5. Measuring device according to one or more of the preceding claims, characterized in that the hollow cone (16) is filled with thermal paste. 6. Measuring device according to one or more of the preceding claims, characterized in that in the discharge zone (metering zone) (5) of the extruder working screw front part on the screw shaft offset at this point (19) attachable, approximately cylindrical hollow body (18). 7. Measuring device according to claim 6, characterized in that the Hollow body (18) can be screwed on. 8. Measuring device according to claim 1, characterized in that in the axial bore (7) of the screw (2) is a fixed one at the screw tip mounted tube (8) is inserted, and that the discharges (14) of the in the screw tip arranged thermocouple (15) are passed through the tube (8). 9. Measuring device according to claim 8, characterized in that the The tube (8) is closed on the end face at the screw tip and in close to the screw tip directly at the bearing point (11) of the pipe (8) is provided with Khlwasser passage bores (9). 10.Meseinrichtung according to claim 1, characterized in that the Screw (2) is arranged adjustable in the axial direction in the extruder. L e r s e i t e