AT510024A4 - PLASTICIZING UNIT WITH WEAR MEASURING SENSOR - Google Patents

Description

1

The invention relates to a plasticizing unit with a plasticizing cylinder and a plasticizing screw rotatably mounted in the plasticizing cylinder,

Plasticizing screws are used in injection molding machines for transporting and melting plastics. The geometry of this plasticizing screw is an essential factor for the melt quality and thus component quality and plasticizing performance. With increasing use time of such screws occurs at different points by abrasion and corrosion wear and the performance decreases. This means that both the conveying behavior and the melt quality are reduced. If a certain value of the performance falls below, depending on the process requirements, the screw must be replaced.

The power loss will not be linear in practice, since this waste also depends very much on the type of wear protection. In the first phase, when the wear protection is still intact, the power loss will be low. If the wear protection is reduced, the power loss will be greater and a replacement of the screw necessary.

In practice, it is difficult to determine the correct time for a worm exchange because the performance of the worm can only be estimated if the worm is removed and precisely measured. Especially with large machines, this is a very time-consuming process and involves high costs.

Some methods for determining wear are already known from the prior art, wherein WO 2008/071552 A1 relates to a method for condition diagnosis of injection molding machine parts over frequency ranges.

Furthermore, DE 10 2007 021 037 B4 shows a method for determining the wear value in worms and cylinders of a twin-screw extruder. In this case, a selection of relevant parameters is performed, wherein such a parameter may be the duty cycle or the duty cycle of the heating and cooling performance. After that, a measured value is acquired, a function is derived from the measured values and a comparison is made possible by permanently repeating the method steps. 67872 22 / fr * »» «φ * · 4 | »•« «» »* *« · · # + · * «« f · * · 2

Similarly, DE 103 54 273 B4 specifies a method for determining wear in extrusion machines, with the mass throughput being the parameter for the wear.

EP 0 977 658 B1 also relates to a method for monitoring the degree of wear of a screw. It is closed by the pressure of the conveyed by the sealing screw material on the Abnützung.

Although WO 2008/074172 does not show a method for determining wear, a nozzle pressure sensor and also other measuring elements or force sensors are shown in the plasticizing cylinder.

The object of the present invention is therefore to provide a comparison with the prior art improved plasticizing. In particular, it should be possible as simple and accurate as possible to close the worm wear - even during operation.

This is achieved for a plasticizing unit with the features of the preamble of claim 1, characterized in that the distance between the plasticizing cylinder and the plasticizing screw can be measured by a measuring sensor. This pure distance or distance measurement can be deduced depending on the positioning of the at least one measuring sensor on the wear of the screw.

According to a preferred embodiment of the present invention, it can be provided that the measuring sensor measures the distance between the inner wall of the plasticizing cylinder and a screw web of the plasticizing screw, preferably transversely to the longitudinal direction of the plasticizing screw, at at least one measuring point. Of course, several measuring points can be provided. Also, the measurement does not necessarily have to be transverse to the longitudinal direction of the plasticizing screw, but it is certainly advantageous for metrological reasons, if the measurement of the distance or the gap between the screw and cylinder in the radial direction is measured.

The measuring sensor can be designed, for example, as a capacitive sensor, as a Uitraschallsensor or as an electromagnetic sensor. With all these measuring sensors, a measurement of the distance between the worm and the cylinder during operation 3

Plasticizing or without mechanical disassemble the plasticizing unit allows.

Basically, two different positions for the mounting location of the measuring sensor are possible. On the one hand, the measuring sensor can be arranged in the plasticizing cylinder and on the other hand in the plasticizing screw, preferably in each case in a hollow bore. Of course, if a plurality of measuring sensors are provided, they may each be arranged at different locations of the worm and / or the cylinder.

In order to obtain the most optimal and unadulterated measurement result, it may be preferable to arrange the measuring sensor less than 10 mm, preferably less than 5 mm, away from the inner wall of the plasticizing cylinder in the plasticizing cylinder or from the screw surface in the plasticizing screw.

Furthermore, it can preferably be provided that the measuring sensor is connected to a control and / or regulating unit, it being possible to output a corresponding warning signal from the measuring sensor or from the control and / or regulating unit when measuring a specific, stored limit value. This stored limit value can be set once for each screw type by the manufacturer of the screw after various tests. This can be done, for example, by installing a new screw and measuring its distance or the measure of the electrical capacitance between the screw flight and the plating cylinder and subsequently installing an already worn or just no longer usable screw and comparing the test results. From these differences in the test results results in a limit, which is then deposited accordingly in newly installed screws in the controller or in the measuring sensor, which is always possible without removing the screw a conclusion on the wear of the screw.

A preferred embodiment of the present invention can provide that the screw web is movable relative to the plasticizing cylinder, wherein the electrical capacitance which changes as the screw web moves past the measuring sensor can be measured by the capacitive sensor arranged in the plasticizing cylinder and the (corresponding to the measured capacitance change) Time and wear changing) distance between plasticizing and plasticizing cylinder can be determined. In other words, it is possible for the capacitive sensor arranged in the plasticizing cylinder, which changes when the worm web moves past the measuring sensor, to move • ♦ * * * * * * * * * * * * * * * ·

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· «« «I < I 4 electrical capacitance and on the distance between plasticizing screw and plasticizing closes. In particular, this measurement is carried out by the fact that the passing of the bridge on the sensor mounted in the cylinder, a frequency peak (peak) is given, which is filtered out by the sensor. If this amplitude level changes with time, it is possible to deduce the change in distance and thus the wear because the frequency behavior changes as the gap size increases. In order to obtain a particularly meaningful measurement result, the sensor should be arranged at a measuring point with the highest wear (for example in a screw flight in the front area of the screw). Especially when the screw is used not only as an extruder screw, but also as an injection screw, it is important that always the same point of the screw flight is measured. For this purpose, it can preferably be provided that the position of the screw in the plasticizing cylinder can be fed to the measuring sensor or to a downstream evaluation unit (control and / or regulating unit). Thus, the distance measurement is always carried out only at a certain longitudinal position of the worm, whereby always the same area of the worm web as a reference point - and not spaced apart, different points of the web is used for the wear measurement. However, it should not be ruled out that several reference points are either measured independently or that an average value for the entire screw wear is calculated from several reference points.

In the same way, this applies when the screw flight is movable relative to the plasticizing cylinder, wherein a change in the measured electrical capacitance can be measured by the capacitive sensor arranged in the plasticizing screw and, depending on the measured capacitance change, the distance between the screw surface and the inner wall of the plasticizing cylinder is determinable. Thus, in this embodiment, too, the capacity slowly changing as a result of wear can be deduced from the change in distance. In order to enable an indirect measurement of wear it can be provided that the worm web has a wear-inhibiting coating or web armor and the measuring sensor is arranged in the plasticizing screw, wherein the distance between the plasticizing screw and the plasticizing cylinder can be calculated as a function of the thickness of the coating measured by the measuring sensor. Thus, the thickness of the coating on the distance or the distance between the screw and cylinder is inferred. The measuring sensor is thereby incorporated into the surface so that it is installed as far as possible outside in the screw and only a distance between 2 and 5 mm to the cavity (gap) between the screw and the fifth

Cylinder has. There is always some play between the worm and the cylinder, which means that the worm always oscillates easily in the cylinder. The newer and unused the snail is, the smaller is this commuter. The greater the wear becomes, the closer the sensor located in the screw flight reaches the cylinder wall during oscillation, as a result of which this decreasing distance (distance) makes the wear inferred. That is, the greater the wear, the larger the commuter and the closer the sensor gets to the cylinder wall.

Especially when the measuring sensor is mounted in the screw, it is a problem how the measured data can be taken out of the rotating screw, for example to a control unit. This is done according to a preferred embodiment of the present invention in that detected Measuring parameters of arranged in the plasticizing measuring sensor either via a signal line with contact point, preferably slip ring, at the end of the plasticizing screw or a telemetry device to the control and / or regulating unit are transferable.

Particularly preferably, it can be provided that the signal line from the measuring sensor to a coupling point on the plasticizing screw or on a

Screw take-up shaft leads, wherein at the coupling point an evaluation unit connected, preferably attachable, and to this evaluation unit the

Measurement parameters are transferable. This data transmission should take place with the screw stopped, via the coupling point. Thus, no complicated transmission mechanism from the rotating to a non-rotating part must be done. Rather, during measurement pauses of the discontinuously operating screw, measurement parameters collected or stored during operation may be cyclically read out or forwarded cyclically. If an evaluation unit is provided, the measurement parameters do not have to be forwarded to a control and / or regulating unit. Rather, by the evaluation unit itself immediately a signal or a display, whether the wear has already reached the previously definable limit. It is also possible that the

The evaluation unit (or also the control and / or regulating unit) shows to what percentage the worm is already worn. It can also be displayed on the basis of the regularly measured distance values, a wear curve from which can be derived or calculated how many injection cycles until the screw exchange can probably be driven. • * t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t 6 6

In this context, it should also be noted that the measuring sensor does not have to be constantly in the plasticizing unit. Especially when a corresponding recess for receiving a measuring sensor is formed in the plasticizing cylinder, it can also be provided that the measuring sensor is introduced into the recess only during a pause in operation {z. B. inserted or screwed) is and performs the distance measurement. However, in order to ensure constant monitoring of the wear, it is preferably provided that the measuring sensor is also arranged in operation of the plasticizing screw in the plasticizing cylinder.

Further details and advantages of the present invention will be explained in more detail below with reference to the description of the figures with reference to the exemplary embodiments illustrated in the drawings. Show in it

1 is a plasticizing in cross section,

2 a plasticizing unit in cross-section with two measuring sensors,

Fig. 3 is a measuring sensor in the screw land with two detail cutouts and

4, a measuring sensor in the hollow bore of the screw with detail.

1 shows a plasticizing unit 1 with a plasticizing screw 3 which is rotatably or movably mounted in the plasticizing cylinder 2. The illustrated plasticating screw 3 is catchy and thus has a continuous screw web 6. In the front region of the screw 3, a measuring sensor 4 is mounted in the plasticizing cylinder 2, which measures the distance D between the inner wall 5 of the plasticizing cylinder and the screw web 6 or the screw surface 8. In addition, a further measuring sensor 4 is mounted in the plasticizing screw 3, which is connected via a signal line 11 not shown here in def hollow bore 7 with contact points 12 at the end of the plasticizing screw 3. From this contact point 12 (sliding contacts) a further signal line 11 is shown schematically, the measurement parameter P to the control and Regeieinheit 9 passes. Measuring parameters P are also fed to the control and / or regulating unit 9 via the signal sensor 4 shown above. In particular, if the measuring sensor 4 is arranged in the plasticizing screw 3, it can be advantageous for the signal transmission if, for example, a radio transmitter of a telemetry device 13 is arranged in the rear area of the plasticizing screw 3 and sends the measuring parameters P to a receiver in the control unit. and / or control unit 9 transmits or transmits. • I f · «« «· · · · · · * I * ·« «* * * * * * *« «· 7

Since the plasticizing screw 3-when it is used in an injection molding machine and not in an extruder-runs in discontinuous or interrupted operation, a more favorable embodiment variant can also provide for an evaluation unit 50 to be connected to the plasticizing screw 3 or to a screw receiving shaft 3b. so that the measurement parameters P are read from this (see detail C). For example, a reader (automatic or manually operable) can be connected to the coupling point 48 of the signal line 11 in the plasticizing screw 3 (or in the screw receiving shaft 3b) via a plug connection 49, thereby cyclically (eg after 1,000 injections or after 24 hours). the current measuring parameters P can be transmitted from the measuring sensor 4 to the evaluation unit 50 or from the latter to the control and / or regulating unit 9. The connection of the signal line 11 between the screw 3 and screw receiving shaft 3b can be made via a plug connection, not shown, or via contact pins.

Furthermore, it can be seen in FIG. 1 that the plasticizing cylinder 2 is surrounded by a tempering device 15. In the front region of the screw 3, the plasticizing cylinder 2 has an injection nozzle 16. In addition, the necessary for a backflow preventer parts screw tip 25, locking ring 14 and pressure ring 19 are shown in this area. In the rear region of the plasticizing cylinder 2, the filling opening 17 is shown for einzufüllendes granules.

Fig. 2 shows in detail the front portion of the plasticizing unit 1, wherein the worm 3 along the longitudinal direction L (for injection) or about the axis L (for plasticizing) is movable. According to this representation, in the plasticizing cylinder 2, a capacitive sensor 4a is arranged at a small distance (between 1 and 10 mm) from the inner wall 5. From the sensor 4a leads a signal line 11 away. From the measuring sensor 4 a can be inferred about the change in capacitance when passing the web 6 to the distance D between the screw 3 and cylinder 2.

FIG. 3 shows a further variant of a measuring sensor 4, wherein this measuring sensor 4 is arranged in the region of a screw land 6 and is covered or protected by a coating 10 (for example made of ceramic, tungsten carbide, chromium carbide or cobalt-chromium-based stellite) , However, the coating 10 may also be formed as a web armor, which is formed for example by welding or applying cobalt-base alloys or iron-based alloys on the screw 3. As can be seen from detail A is in a still little used 8

Screw 3, the thickness C of the coating 10 is still much larger and thus the distance or the distance D between screw land 6 and inner wall 5 of the plasticizing 2 small. If, as can be seen in detail B, the worm 3 continues to wear, the thickness C of the coating 10 also decreases, so that the distance D becomes greater. As already stated, the screw 3 is not completely clamped in the plasticizing cylinder 2, but has a slight gap dimension D. The greater the wear, the more this gap dimension D increases, as a result of which the screw 3 in the plasticizing cylinder 2 "oscillates" ever more steadily. As can be seen from detail B, the measuring sensor 4 could thereby come substantially closer to the inner wall 5 of the plasticizing cylinder 2, whereby a different electrical capacitance is measured by the measuring sensor 4, since the measuring sensor 4 can get much closer to the plasticizing cylinder 2 than in the detail A. Depending on which limit value G is preset, a warning signal or a corresponding message is output from a certain capacity (hence a certain thickness C) that the plasticizing screw 3 is to be exchanged.

As can be seen in FIG. 4, the distance D between worm 3 and cylinder 2 can be measured in a similar manner via a measuring sensor 4, which is fastened in a hollow bore 7 on a co-rotating guide rod 18. This rod 18 may itself have a bore for a signal cable 11 and at its end a telemetry transmitter, not shown (for example, with battery) for data transmission. It is also possible and is especially useful in discontinuous operation of the screw 3, if at the end of the signal line 11, an evaluation unit 50 via a coupling point 48 at standstill of the screw 3 can be plugged, whereby the measurement parameters P are readable.

Innsbruck, 15 July 2010

Claims (12)

1. Plasticizing unit (1) with a plasticizing cylinder (2) and a plasticizing (2) rotatably mounted plasticizing screw (3), characterized in that by a measuring sensor (4) the distance (D) between plasticizing (2) and plasticizing screw (3) is measurable. 2. Plasticizing unit according to claim 1, characterized in that the measuring sensor (4) at at least one measuring point, the distance between the inner wall (5) of the plasticizing cylinder (2) and a screw web (6) of the plasticizing screw (3), preferably transversely to the longitudinal direction ( L) of the plasticizing screw (3). 3. plasticizing unit according to claim 1 or 2, characterized in that the measuring sensor (4) is designed as a capacitive sensor (4a), as an ultrasonic sensor or as an electromagnetic sensor. 4. plasticizing unit according to one of claims 1 to 3, characterized in that the measuring sensor (4) in the plasticizing cylinder (2) or in the plasticizing screw (3), preferably in a hollow bore (7) is arranged. 5. Plasticizing unit according to claim 4, characterized in that the measuring sensor (4) is less than 10 mm, preferably less than 5 mm, away from the inner wall (5) of the plasticizing cylinder (2) in the plasticizing cylinder (2) or from the screw surface (8 ) is arranged in the plasticizing screw (3). 6. plasticizing unit according to claim 4, characterized in that the screw web (6) relative to the plasticizing cylinder (2) is movable, wherein by the plasticizing cylinder (2) arranged capacitive sensor (4a) which moves past the Schneckenstegs (6) on the measuring sensor (4) changing electrical capacitance is measurable and depending on the measured capacitance change, the distance (D) between the plasticizing screw (3) and plasticizing cylinder (2) can be determined. 7. plastifying unit according to claim 4, characterized in that the screw web (6) relative to the plasticizing cylinder (2) is movable, whereby by 67872 22Jeh »« «*» · * · · »« · 1 ** «« · «· · ·· 2 * ..... in the plasticizing screw (3) arranged capacitive sensor (4a) a change in the measured electrical capacitance is measurable and depending on the measured capacitance change the distance (D) between the screw surface (8) and inner wall ( 5) of the plasticizing cylinder (2) can be determined. 8. plastifying unit according to claim 4, characterized in that the screw web (6) has a wear-resistant coating (10) and the measuring sensor (4) in the plasticizing screw (3) is arranged, wherein in dependence of the measuring sensor (4) measured thickness ( C) the coating (10) the distance (D) between the plasticizing screw (3) and plasticizing cylinder (2) is calculated. 9. plasticizing unit according to one of claims 1 to 8, characterized in that the signal line (11) from the measuring sensor (4, 4a) leads to a coupling point (48) on the plasticizing screw (3) or on a worm shaft (3b), wherein the coupling point (48) can be connected, preferably connected, to an evaluation unit (50) and the measurement parameters (P) can be transmitted to this evaluation unit (50). 10. Plasticizing unit according to one of claims 1 to 8, characterized in that the measuring sensor (4) is connected to a control and / or regulating unit (9), wherein when measuring a certain, stored limit value (G), a corresponding warning signal from the measuring sensor (4) or by the control and / or regulating unit (9) can be output. 11. Plasticizing unit according to claim 9, characterized in that detected measuring parameters (P) of the plasticizing screw (3) arranged measuring sensor (4) either via a signal line (11) with contact point (12), preferably slip ring, at the end of the plasticizing screw (3 ) or via a telemetry device (13) to the control and / or regulating unit (9) are transferable, 12. Injection molding machine with a plasticizing unit (1) according to one of claims 1 to 11. Innsbruck, 15 July 2010