Device and method for deriving viscosity of molten polymer

Abstract

A device (1) for deriving the viscosity of a molten polymer, comprising: a conduit (10) having an inlet (10I) and an outlet (10U) and through which a flow of molten polymer material passes; a sensor system (13) in operative contact with the molten polymer material flowing in the conduit (10) to measure a pressure value and, if desired, a temperature value and generate a measurement signal; a processing unit (14) connected to the sensor system (13) to receive the measurement signal and / or the plurality of measurement signals and programmed to process the measurement signals to derive an estimate of the viscosity of the molten polymer material flowing in the conduit (10). The sensor system (13) comprises an optical fiber defining at least one or more differential pressure sensors located inside the conduit (10) for operable contact with the molten polymer material and, if desired, a temperature sensor.

Description

Technical Field

[0001] This invention relates to apparatus and methods for determining the viscosity of molten polymers. Background Technology

[0002] Viscosity sensors are used to measure or estimate the viscosity of liquids such as molten plastics, inks, sludge, or oil in a variety of industrial environments.

[0003] Typically, especially regarding the processing of plastics, extruders are used to produce a stream of liquid plastic (alternatively, pistons or other devices may be used); downstream of the extruder are processing devices, such as molding machines (typical of beverage lines, used to form caps or preforms) or other machines for performing other processes (e.g., the production of plastic films or sections).

[0004] The use of sensors in the field of plastics processing is known, for example, from the following patent documents: US5197633A, US20190315048A1, US5303141A, US20200324311A1, US10137679B2, and US6492485B1. For example, patent document US5197633A describes the use of a proximity sensor made of optical fiber to measure the flow rate of molten plastic.

[0005] Regarding viscosity measurement, several technical solutions are known, for example, from patent documents US2019250086, US5708197A, US5197633A, US4425790A, CN104568663A, and CN204439494U. For instance, the solution proposed in US4425790A involves measuring the differential pressure in a mold conveying molten plastic. However, this solution implies constructing a dedicated device for viscosity measurement, which is complex and expensive because, for example, it requires the use of branch pipes and a specialized pump.

[0006] Therefore, there is still a need for a reliable and mechanically simple system for deriving the viscosity of fluids (such as liquid plastics) flowing in pipes. Summary of the Invention

[0007] The object of the present invention is to provide an apparatus and method for adjusting the viscosity of a liquid (specifically, but not exclusively, a molten polymer) to overcome the aforementioned disadvantages of the prior art.

[0008] In particular, the object of the present invention is to provide an apparatus and method for extracting the viscosity of a liquid (specifically, but not exclusively, a molten polymer) that is reliable, simple, and therefore inexpensive.

[0009] These objectives are fully achieved by the apparatus and methods of this disclosure as characterized in the appended claims.

[0010] This disclosure relates to an apparatus (or system) for deriving the viscosity of a liquid. The concepts and features described in this disclosure are applicable to deriving the viscosity of any liquid, or liquid or semi-liquid substance made to flow in a pipe, such as ink, oil, sludge, or molten plastic. In particular, the concepts of this disclosure are applicable to deriving the viscosity of Newtonian fluids and non-Newtonian, pseudoplastic fluids. The remainder of this disclosure focuses on applications to molten plastics, that is, applications where the viscosity of the liquid to be derived is that of a molten plastic, but this disclosure does not lose its generality (therefore, it should be understood that terms such as "molten plastic" or "molten polymer material" as used in this disclosure may be replaced by the term "liquid").

[0011] Molten polymer flows in a pipe. In an example embodiment, this is part of a pipe-forming apparatus. The pipe has an inlet and an outlet.

[0012] The device includes a sensor system. The sensor system includes one or more sensors.

[0013] The sensor system is configured to capture a measurement signal representing one or more quantities that depend on the physical state of the molten polymer flowing in the pipe. More specifically, the sensor system measures the pressure of the molten plastic flowing in the pipe (and, if necessary, the temperature).

[0014] In an example implementation, the sensor system is operatively contacted with molten polymer material flowing in the pipe. Therefore, the sensor system is operatively contacted with the molten polymer material flowing in the pipe to capture pressure values ​​(and, if necessary, temperature values), and the measurement signal generated by the sensor system represents the captured pressure values.

[0015] The device also includes a processing unit. For example, the processing unit includes a memory and a processor. The processing unit is connected to the sensor system to receive and process the signals. The processing unit is programmed to derive an estimate of the viscosity of the molten polymer material flowing in the pipe based on the measured signals.

[0016] The sensor system includes an optical fiber sensor. More specifically, the sensor system includes an optical fiber defining a differential pressure sensor. In an example embodiment, the optical fiber defining the differential pressure sensor is located inside the pipe so as to be operatively in contact with the molten polymer material.

[0017] The signal flows inside the optical fiber (i.e., the optical fiber is configured to propagate or transmit signals within the optical fiber itself).

[0018] In one example, the optical fiber terminates at an end. In other words, the optical fiber includes an end. The end can be located inside a conduit. Preferably, the end can (operably) contact a molten polymer material. Thus, the signal propagates (travels) to the end of the optical fiber. In particular, the end constitutes the free end of the optical fiber.

[0019] In one embodiment, the optical fiber includes a reflective layer. The reflective layer may be located at an end point. In other words, the reflective layer may be positioned in direct contact with the end point (i.e., the end point may include the reflective layer). The optical fiber may include a reflective coating applied to the optical fiber (specifically, the end point of the optical fiber) (i.e., the reflective coating defines the reflective layer). In another example, the reflective layer is located at a distance spaced from the end point, preferably inside the conduit (i.e., in contact with the molten polymer material).

[0020] Therefore, the signal propagates inside the optical fiber to the end point; the reflective layer reflects the signal back into the optical fiber.

[0021] In one example, the endpoint defines or includes a differential pressure sensor.

[0022] It has been observed that an optical fiber defining (or including) a differential pressure sensor means that the optical fiber includes a waveguide (i.e., a portion of the optical fiber in which a signal travels) and a sensor (where the signal is affected by changes in one or more of its properties). According to one method, the sensor of the optical fiber includes a senseable (or sensorized) portion, particularly disposed within the waveguide (along the waveguide). According to another method, the sensor of the optical fiber includes a senseable portion disposed at an end point. In other words, the end point includes an end (where the end point defines the sensor of the optical fiber). In other words, the optical fiber includes an end point disposed at the end of the optical fiber. This end point may have a reflective layer (or coating). This end point may have a senseable layer (or coating).

[0023] Therefore, the term "differential pressure sensor" can also include examples where the optical fiber has a first end and a second end. Each end is preferably located inside a conduit and in direct contact with the molten polymer material. The optical fiber includes a first waveguide and a second waveguide, such that a signal travels within the first waveguide to the first end and within the second waveguide to the second end. The optical fiber may include a first reflective layer and a second reflective layer. In one example, the reflective layer is spaced apart from the respective end. In another example, the reflective layer is in direct contact with the respective end. In this case, in the first approach, the optical fiber has a first senseable portion and a second senseable portion respectively disposed in the first and second waveguides. In the second approach, the optical fiber has a first senseable layer and a second senseable layer respectively disposed at the first and second ends of the optical fiber; in this approach, the optical fiber may include a first end and a second end respectively disposed at the first and second ends. Each of the first and second ends has a senseable layer (or coating) and a reflective layer (or coating).

[0024] In one example, the sensing layer is made of silicon or titanium dioxide. The sensing layer is configured to change one or more properties in response to changes in the molten polymer material, particularly changes in the pressure (and / or temperature) of the molten polymer material. Therefore, generally, the term "sensing layer" or "sensing portion" refers to a layer or portion configured to change one or more properties in response to changes in the properties of the molten polymer material (e.g., changes in pressure). In one example, the sensing layer may be a deformable layer. Therefore, the sensing layer can change its dimensions in response to changes in pressure or temperature. In one example, the reflective layer is made of gold.

[0025] In one embodiment, the end includes another reflective layer. A sensing layer may be inserted between the reflective layer and the other reflective layer. The end may include an adhesive layer. The end may include another adhesive layer. The adhesive layer may be made of titanium. An adhesive layer may be located between the reflective layer and the sensing layer. An adhesive layer may be located between the reflective layer of the optical fiber and the waveguide (especially, the end). The optical fiber includes portions or segments that define sensors. In fact, in techniques of essentially the type known in the field of optical fiber sensors, these fiber segments or portions are modifications to the fiber structure such that these portions are “sensitive” to predetermined amounts, meaning that their optical fiber transmission properties vary depending on the amount involved. For example, if the fiber portion is pressure-sensitive, thus defining a pressure sensor, then the fiber portion has optical fiber transmission properties that vary depending on the pressure applied to the fiber portion; in another example, if a portion of the fiber has optical fiber transmission properties that vary depending on the temperature applied to that portion of the fiber, then that portion of the fiber defines a temperature sensor. Thus, the fiber has multiple sensorized segments; the fiber may also include non-sensorized segments along which optical signals are transmitted (in a predetermined manner independent of factors or conditions outside the fiber).

[0026] Therefore, in the solution according to this disclosure, the optical fiber has a first (sensorized) portion and a second (sensorized) portion spaced apart from each other and each defining a pressure sensor; thus, the optical fiber defines a differential pressure sensor because it allows the processing unit to derive the pressure difference between the first and second portions of the optical fiber.

[0027] Thanks to the differential pressure sensor, the device knows the difference between two spaced-apart areas of the pipe.

[0028] Starting from this pressure difference, the processing unit uses known mathematical formulas in the field of rheology to derive estimates of the molten polymer material flowing in the pipe (apparent and actual values, or apparent values ​​for all liquids and actual values ​​for Newtonian and pseudoplastic fluids).

[0029] The sensor system also includes devices for generating optical signals that travel along the fiber. The sensor system is also configured to detect and analyze distortions or alterations in the optical signals delivered to the fiber, caused by the sensorized portion of the fiber according to the amount to which the sensorized portion is sensitive.

[0030] This method can estimate the viscosity of molten polymer materials flowing in a pipe in a particularly simple and inexpensive way. It can also measure pressure differentials (in the millibar range) with exceptionally good accuracy.

[0031] In an example implementation, the optical fiber has a first end outside the conduit (connected to an optical signal generator) and another end inside the conduit. Therefore, in this example implementation, the optical fiber has an effective segment (including a sensorized portion) inside the conduit and in contact with the molten plastic, and an initial segment upstream of the effective segment, outside the conduit, and therefore not in contact with the molten plastic. In this example, the fiber defines an "interrupted" optical loop in which a portion of the optical signal is reflected back for reception and processing by the sensor system.

[0032] In possible examples, the effective portion of the optical fiber is fabricated using a Bragg grating for measuring pressure and / or temperature. "Parallel" fiber bundles, preferably held together in a single sheath, can also be used.

[0033] The sensor system may also include a temperature sensor for measuring the temperature of the molten polymer material flowing in the pipe. The temperature sensor may also include an optical fiber sensor. Preferably, the same optical fiber defining the differential pressure sensor also defines the temperature sensor. For example, the optical fiber may include a temperature-sensitive third portion. For example, the third (temperature-sensitive) portion may be inserted along the length of the optical fiber between the first (pressure-sensitive) portion and the second (pressure-sensitive) portion. Thus, the temperature sensor is also located inside the pipe to be operatively in contact with the molten polymer material. The presence of the temperature sensor in the same optical fiber defining the pressure sensor has the advantage of making the device simpler and less conspicuous.

[0034] In a possible example implementation, the effective segment of the optical fiber (the segment located inside the pipe) may include multiple sensorized regions to define corresponding multiple temperature sensors. Preferably, the temperature sensors are positioned at different distances along the longitudinal axis of the pipe. This feature advantageously allows for the derivation of information representing the temperature distribution inside the pipe.

[0035] Therefore, the processing unit is programmed to derive the apparent viscosity value of the molten polymer material flowing in the pipe based on the measurement signal. Preferably, the processing unit is also programmed to apply Rabinowitsch or Weissenberg-Rabinowitsch corrections to the apparent viscosity value to derive the corresponding actual viscosity value. These corrections are implemented using formulas of essentially known types in the field of rheology. The processing unit is also programmed to derive the value of the shear rate of the molten polymer flowing in the pipe. This feature allows for even more precise estimation of viscosity.

[0036] Therefore, the first and second fiber segments defining the first and second temperature sensors are spaced apart from each other and located at two different points in the pipe; preferably, they are spaced apart along the longitudinal direction of the pipe, which corresponds to the flow direction of the molten plastic along the pipe.

[0037] In the example implementation, the pipe has two sections with different cross-sectional dimensions; that is, it has a first section and a second section, the first section having a first cross-sectional dimension (for the flow of plastic material) and the second section having a second cross-sectional dimension (for the flow of plastic material), the second cross-sectional dimension being smaller than the first cross-sectional dimension.

[0038] In this scenario, as an example, the first sensorized segment of the optical fiber is located in the first segment of the pipe, and the second sensorized segment of the optical fiber is located in the second segment of the pipe. Thus, the fiber defines a first differential sensor and a second differential sensor, wherein the first differential sensor (defined by the first sensorized segment of the optical fiber) is located in the first segment of the pipe, and the second differential sensor (defined by the second sensorized segment of the optical fiber) is located in the second segment of the pipe. In this case, the optical fiber defines two distinct differential sensors located in two pipe segments with different cross-sectional dimensions. The cross-sectional dimensions and the pipe are known to the sensor system.

[0039] The presence of pressure sensors located in pipe sections with varying cross-sectional dimensions allows for the derivation of parameters needed to estimate viscosity (known as the "power-law exponent," n) without altering the flow rate of the molten plastic within the pipe. This is particularly useful when the device is applied directly to equipment where the flow rate of the plastic cannot be arbitrarily changed, for example, as it is controlled by an extruder based on the production requirements of industrial equipment.

[0040] In an example embodiment, the conduit has a longitudinal segment oriented along a longitudinal axis, and the effective segment of the optical fiber (or at least a portion thereof, particularly its end) is oriented parallel to the longitudinal axis; preferably, the effective segment (or a portion thereof) is aligned with the longitudinal axis of the conduit.

[0041] In an example embodiment, the device includes a guiding element for guiding fibers into a conduit. The guiding element has an outer portion located outside the conduit and an inner portion extending into the interior of the conduit. The guiding element internally defines a channel having an inlet formed in the outer portion and an outlet formed in the inner portion. An initial segment of the optical fiber is housed within the channel and located upstream of the effective segment (in the flow direction of the molten plastic within the conduit); the effective segment is positioned downstream of the channel outlet. In a possible example, the channel in the inner portion of the guiding element defines a bend such that the channel outlet is oriented parallel to the longitudinal axis; preferably, the channel outlet is aligned with the longitudinal axis.

[0042] Optical fibers have a core and a sheath. The core can be made of, for example, glass, and the sheath can be made of stainless steel (which allows the fiber to withstand medium to high temperatures). The sheath may include a ceramic layer that is inserted between the (stainless steel) outer layer and the (glass) core to prevent potential mechanical problems or damage due to the different thermal properties of steel and glass.

[0043] This disclosure also provides a method for deriving the viscosity of molten polymers (or generally liquids).

[0044] The method includes the step of conveying molten polymer material through a pipe having an inlet and an outlet.

[0045] The method also includes the step of generating a measurement signal representing a pressure value via a sensor system. Preferably, the sensor system is operatively in contact with molten polymer material flowing in the pipe.

[0046] The method includes the step of processing measurement signals to derive an estimate of the viscosity of a molten polymer material flowing in a pipe.

[0047] The method involves capturing measurement signals via a sensorized optical fiber that defines a differential pressure sensor located inside the pipe, thus bringing it into contact with the molten polymer material.

[0048] The signal flows inside the optical fiber (i.e., the optical fiber is configured to propagate or transmit signals within the optical fiber itself).

[0049] In one example, the optical fiber terminates at an end point, which is preferably located inside the conduit. Preferably, the end point can (operably) contact the molten polymer material.

[0050] The method may include the step of propagating a signal to an endpoint by an optical fiber. In one embodiment, the optical fiber includes a reflective layer. The reflective layer may be located at the endpoint (in direct contact with the endpoint) or spaced apart from the endpoint, preferably inside the conduit (i.e., in contact with the molten polymer material). The method may include the step of reflecting the signal back into the optical fiber by the reflective layer.

[0051] In one example, the endpoint defines the differential pressure sensor (i.e., the endpoint includes the differential pressure sensor).

[0052] According to one method, the sensor of the optical fiber includes a senseable (sensitized) portion, particularly disposed within the waveguide of the optical fiber. According to another method, the optical fiber, particularly its endpoint, includes an end (wherein the end defines the sensor of the optical fiber). In other words, the optical fiber includes an end disposed at the endpoint of the optical fiber. The end may have a reflective layer (or coating). The end may have a senseable layer (or coating).

[0053] In one example, the sensing layer is made of silicon or titanium dioxide. The sensing layer is configured to change one or more properties in response to changes in pressure (and / or temperature) of the molten polymer material. Therefore, the method may include the step of changing the properties of the sensing layer by means of the molten polymer material. For example, the method may include, for instance, the step of deforming the sensing layer in response to changes in pressure or temperature of the molten polymer material.

[0054] In one example, the reflective layer is made of gold. In one implementation, the end includes another reflective layer. A sensing layer may be inserted between the reflective layer and the other reflective layer. The end may include an adhesive layer. The end may include another adhesive layer. The adhesive layer may be made of titanium. An adhesive layer may be located between the reflective layer and the sensing layer. An adhesive layer may be located between the reflective layer of the optical fiber and the waveguide (particularly the end).

[0055] The process involves applying Rabinowitsch or Weissenberg-Rabinowitsch corrections to the apparent viscosity values ​​of the molten polymer material flowing in the pipe in order to derive the corresponding actual viscosity values.

[0056] It also measures the temperature of the molten plastic flowing in the pipe; preferably, the captured measurement signal also represents temperature, since the optical fiber also defines one or more temperature sensors.

[0057] The optical fiber has a (free) end located inside the pipe and immersed in the molten plastic flow; preferably, the molten plastic flow has the effect of arranging the optical fiber segment located inside the pipe in contact with the molten plastic in a direction parallel to the longitudinal direction of the molten plastic flow itself.

[0058] In one example, two sensorized fiber segments are located in a pipe section with different cross-sectional dimensions for the molten plastic, thus defining corresponding differential pressure sensors; the purpose is to calculate the "power-law exponent" during processing even when the molten plastic is flowing at a constant rate (static). Each sensorized fiber segment can define a differential sensor, that is, each sensorized segment can further include a pair of sensors defining a differential sensor for measuring the differential pressure; the two sensorized fiber segments can be located in a pipe section with different cross-sectional dimensions for the plastic flow. Therefore, in this example, there are four sensors, that is, two pairs of sensorized fiber segments corresponding to two differential sensors.

[0059] According to one aspect, this disclosure provides an apparatus for the continuous processing of plastic materials. This apparatus represents one possible implementation of the device according to this disclosure.

[0060] The equipment includes: an extruder configured to receive raw plastic as input and produce a stream of molten plastic material as output; a processing machine configured to perform processing on the plastic in a continuous cycle (e.g., a compression or injection molding machine, which may be a rotary or reciprocating machine); and a connecting pipe for conveying the molten plastic from the extruder to the processing machine.

[0061] The device also includes means for deriving the viscosity of the molten polymer and including one or more features described in this document. In an example embodiment, the conduit of the device (with the sensorized optical fiber located therein) is a connecting conduit (or formed by a portion thereof).

[0062] In one example, the device includes a controller configured to adjust one or more process parameters related to the activity of the extruder. The controller may be connected to the processing unit to receive an estimate of the viscosity of the molten polymer material and may be programmed to adjust one or more process parameters based on the estimated viscosity of the molten polymer material.

[0063] Process parameters may include one or more parameters selected from the following: temperature, mixture of input materials (new and / or recycled), additives, and screw speed.

[0064] The purpose of this feedback to process parameters (such as temperature, mixture of input materials (new and / or recycled), additives, screw speed) is to maintain and / or achieve the set value of the measured variable (i.e., viscosity). Therefore, the controller can adjust one or more process parameters to maintain and / or achieve a specific value for the measured viscosity.

[0065] According to another aspect, this disclosure provides a method for continuous processing of plastic materials.

[0066] The method includes the step of extruding raw plastic to produce a stream of molten plastic material.

[0067] The method also includes the step of continuously processing the molten plastic material from the extruder (in a processing machine).

[0068] The method also includes the step of deriving the viscosity of the molten polymer using one or more features as set forth in this specification.

[0069] Preferably, the conduit containing the optical fiber is part of a connecting conduit used to deliver molten plastic from the extruder to the processing machine.

[0070] In one embodiment, the method includes the step of performing feedback control on one or more process parameters based on an estimated value of the viscosity of the molten polymer material, wherein the process parameters may be related to the activity of the extruder. Attached Figure Description

[0071] These and other features will become more apparent from the following description of preferred embodiments illustrated by way of non-limiting example in the accompanying drawings:

[0072] - Figure 1 A processing apparatus according to one or more aspects of this disclosure is shown;

[0073] - Figure 2A and Figure 2B A cross-section of an optical fiber according to one or more aspects of this disclosure is shown;

[0074] - Figure 3A , Figure 3B An apparatus according to one or more aspects of this disclosure is shown;

[0075] - Figures 4A to 4C A portion of an optical fiber according to one or more aspects of this disclosure is illustrated schematically. Detailed Implementation

[0076] The number 1 in the attached figure indicates a device used to derive the viscosity of the molten polymer.

[0077] The device 1 includes a conduit 10 having an inlet 10I and an outlet 10U. Molten polymer material flows through the conduit 10 from the inlet 10I to the outlet 10U. The conduit 10 includes an inner wall 10A; the inner wall 10A defines an interior I of the conduit 10 in which the molten polymer material flows. The conduit 10 (specifically, the interior I of the conduit 10) has a longitudinal section oriented along a longitudinal axis X.

[0078] The pipe 10 has an inlet portion 110 defining an inlet 10I. At the inlet portion 10I, the interior I of the pipe 10 has a first diameter or cross-sectional dimension D1 defined perpendicular to the longitudinal direction. The pipe 10 has a first portion 111; at the first portion 111, the interior I of the pipe 10 has a first length L1 in the longitudinal direction, and preferably has a diameter or cross-sectional dimension equal to D1. The device 1 includes a guide element 12 located in the first portion 111 of the pipe 10. In one example, the guide element 12 has an outer portion 12A located outside the pipe 10 (i.e., outside relative to the interior I of the pipe 10), and an inner portion 12B extending into the interior I of the pipe 10. In another example, the guide element 12 includes only the outer portion 12A.

[0079] The pipe 10 includes a second portion 112, in which the interior I of the pipe 10 has a length L2 in the longitudinal direction. The pipe 10 includes a third portion 113, in which the interior I of the pipe 10 has a length L3 in the longitudinal direction and a diameter or cross-sectional dimension D2 defined perpendicular to the longitudinal direction. In one example, the diameter D2 is between 5 mm and 100 mm. In one example, L3 is greater than 10 mm.

[0080] The pipe 10 includes a fourth portion 114 in which the interior I of the pipe 10 has a length L4 in the longitudinal direction. The pipe 10 includes a fifth portion 115 in which the interior I of the pipe 10 has a length L5 in the longitudinal direction and a diameter or cross-sectional dimension D3 defined perpendicular to the longitudinal direction. Preferably, L5 is greater than 10 mm. The fourth portion 114 defines a portion of the pipe 10 (specifically, the interior I of the pipe 10) that is tapered (i.e., conical in shape), meaning that at the fourth portion 114, the cross-section of the pipe 10 narrows along the longitudinal axis X toward the fifth portion 115 to form an angle A2.

[0081] At inlet portion 110, first portion 111, second portion 112, and third portion 113, pipe 10 defines a first section of interior I of pipe 10, which has a first cross-sectional dimension equal to the diameter or cross-sectional dimension D2 for the flow of plastic material. At fifth portion 115, pipe 10 defines a second section of interior I of pipe 10, which has a second cross-sectional dimension equal to the diameter or cross-sectional dimension D3 for the flow of plastic material. More specifically, the cross-sectional dimension of the first section is larger than the cross-sectional dimension of the second section.

[0082] The pipe 10 includes a sixth section 116 in which the interior I of the pipe 10 has a length L6 defined in the longitudinal direction.

[0083] The conduit 10 (specifically, the interior I of the conduit 10) has a transverse segment oriented along the transverse axis Y. The conduit 10 includes a seventh portion 117 in which the interior I of the conduit 10 has a length L7 defined in the transverse direction. The seventh portion 117 includes an outlet portion 118 defining an outlet 10U of the conduit 10. At the outlet portion 10U, the interior I of the conduit 10 has a fourth diameter or cross-sectional dimension D4 defined perpendicular to the transverse direction.

[0084] Device 1 includes a sensor system 13. Sensor system 13 includes an optical fiber comprising a core 13A, a cladding 13B, and an outer sheath 13C. For temperatures between 5°C and 150°C, the core 13A and cladding 13B may be made of glass (e.g., silica) or plastic (e.g., PMMA), and the outer sheath 13C may be made of plastic (e.g., PE, PVCF for greater flexibility, or fluoropolymer for greater chemical resistance) or stainless steel (to facilitate heat transfer to the optical fiber without affecting its sensing characteristics and to protect the optical fiber from handling, impact, and bending). For temperatures between 150°C and 700°C, the core 13A and cladding 13B may be made of glass (e.g., silica) or plastic (e.g., PMMA), and the outer sheath 13C may be made of stainless steel. For temperatures of approximately 700°C and higher, the core 13A can be made from a single sapphire crystal (glass transition temperature Tg of 2030°C), and the outer sheath 13C can be made of metal (stainless steel for temperatures up to 900°C, or a special high-temperature resistant alloy for temperatures above 900°C). The optical fiber may include an intermediate sheath 13C' between the outer sheath 13C and the cladding 13B, which is made of, for example, a ceramic material, to harmonize the thermal properties of the outer sheath 13C with the glass of the core 13A.

[0085] An optical fiber is partially located within the interior I of the conduit 10. More specifically, the optical fiber has a first portion (or first segment) sensorized and defining a first sensor 131 and a second portion (or second segment) sensorized and defining a second sensor 132; the first and second portions together define an optical fiber sensor. The first sensor 131 and the second sensor 132 are operatively in contact with molten polymer material flowing within the interior I of the conduit 10 to measure pressure values.

[0086] The first sensor 131 and the second sensor 132 each define a differential sensor; therefore, each sensor includes a pair of sensors for measuring the differential value. The first sensor 131 and the second sensor 132 are positioned along the effective section of the optical fiber, wherein the effective section is located inside the conduit 10, in contact with the molten plastic. The optical fiber includes an initial section located upstream of the effective section, outside the conduit 10, and not in contact with the molten plastic.

[0087] In one embodiment, the guiding element 12 internally defines a channel having an inlet formed in an outer portion 12A of the guiding element and an outlet formed in an inner portion 12B of the guiding element 12; an initial segment of the optical fiber is accommodated in the channel and located upstream of the effective segment, while the effective segment of the optical fiber is located downstream of the outlet of the channel in the guiding element 12. The effective segment of the optical fiber is at least 10 mm long.

[0088] The first sensor portion or sensor segment is located in the first section of the interior I of the pipe 10, and the second sensor portion or sensor segment is located in the second section of the interior I of the pipe 10. Therefore, the first sensor 131 and the second sensor 132 are located in sections of the pipe 10 with different cross-sectional dimensions, namely the first section of the pipe 10 and the second section of the pipe 10.

[0089] In one example, a channel in the inner portion 12B of the guide element 12 defines a bend such that the outlet of the channel is oriented parallel to the longitudinal axis X.

[0090] The first sensor 131 and the second sensor 132 each define a differential pressure sensor; therefore, the first sensor 131 measures the differential pressure value in the first section of the interior I of the pipe 10, and the second sensor 132 measures the differential pressure value in the second section of the interior I of the pipe 10.

[0091] In a possible implementation, the first sensor portion (first sensor 131) and the second sensor portion (second sensor 132) can be configured to measure the temperature of the molten polymer material flowing in the pipe 10.

[0092] Each sensor is made in the form of a fiber Bragg grating (FBG), that is, strips of material with different refractive indices alternating with each other. Sensor system 13 (or each of sensors 131 and 132) measures the pressure value and generates a measurement signal. Device 1 includes a processing unit 14 connected to sensor system 13 to receive the measurement signal and programmed to process the measurement signal to derive an estimate of the viscosity of the molten polymer material flowing in pipe 10 (i.e., in interior I).

[0093] Using formulas of essentially known types in the field of rheology, processing unit 14 derives the apparent viscosity and apparent shear rate values ​​of the molten polymer material flowing in pipe 10 from the measurement signals of first sensor 131 and second sensor 132 (and thus from the pressure difference values ​​captured by first sensor 131 and second sensor 132); the processing unit applies Rabinowitsch or Weissenberg-Rabinowitsch corrections to obtain the actual values ​​of the viscosity and / or shear rate of the molten polymer. The data processed by processing unit 14 can be used to change the parameters (e.g., temperature) of extruder 2 located upstream of device 1 and / or change the type of material fed to extruder 2.

[0094] The apparatus 1 is preferably part of a processing equipment L for continuous processing of plastic materials. The equipment L includes an extruder 2. The extruder 2 includes an inlet or hopper 21 for receiving raw plastic material as input, and an outlet 22 for discharging a stream of molten plastic material. The equipment L includes a connecting pipe that connects the outlet 22 of the extruder 2 to a processing machine 3, which is also part of the equipment L. The connecting pipe conveys the molten plastic discharged from the extruder 2 to the processing machine 3.

[0095] Device 1 is inserted between extruder 2 and processing machine 3; more specifically, pipe 10 of device 1 defines a connecting pipe such that inlet 10I of pipe 10 is connected to outlet 22 of extruder 2 to receive molten plastic. Outlet 10U of pipe 10 is also connected to processing machine 3.

[0096] The optical fiber terminates at an end 133 located inside the conduit 10 for contact with the molten polymer material. The optical fiber includes a reflective layer 136, which can be positioned to be in direct contact with the end 133 or spaced apart from the end 133.

[0097] In one example, the optical fiber includes a waveguide 134 and an end cap 135 disposed at an end point 133 of the optical fiber. The end cap 135 has a reflective layer (or coating) 136 and a sensing layer (or coating) 137. The sensing layer 137 is configured to change its dimensions in response to changes in pressure and / or temperature of the molten polymer material. Specifically, the sensing layer 137 (and the reflective layer 136) are in direct contact with the molten polymer material. The sensing layer 137 and the reflective layer 136 serve as coatings for the end point of the optical fiber.

[0098] In one embodiment, the end 135 includes another reflective layer 136', such that the sensing layer 137 is located between the reflective layer 136 and the other reflective layer 136'. The end 135 may include an adhesive layer 138 and another adhesive layer 138'. The adhesive layers 138 and 138' are configured to bond the reflective layer 136 and the other reflective layer 136'. Specifically, the adhesive layer 138 is located between the reflective layer 136 and the sensing layer 137, and the other adhesive layer 138' is located between the other reflective layer 136' and the end point 133 of the optical fiber.

Claims

1. An apparatus (1) for adjusting the viscosity of a molten polymer, comprising: - A pipe (10) having an inlet (10I) and an outlet (10U) through which a flow of molten polymer material passes; - A sensor system (13) operable to contact the molten polymer material flowing in the pipe (10) to measure pressure values ​​and generate measurement signals; - A processing unit (14), which is connected to the sensor system (13) to receive the measurement signal, and is programmed to process the measurement signal to derive an estimate of the viscosity of the molten polymer material flowing in the pipe (10). The sensor system (13) is characterized in that it includes an optical fiber defining a differential pressure sensor located inside the conduit (10) to be operatively in contact with the molten polymer material.

2. The apparatus (1) according to claim 1, wherein the optical fiber terminates at an end point (133) located inside the conduit (10) to contact the molten polymer material.

3. The apparatus (1) according to claim 2, wherein the optical fiber includes a reflective layer (136) in direct contact with the endpoint (133).

4. The device (1) according to one or more of the preceding claims, wherein the endpoint (133) defines the differential pressure sensor.

5. The apparatus (1) according to one or more of the preceding claims, wherein the optical fiber further defines a temperature sensor located inside (I) of the conduit (10) to be operatively in contact with the molten polymer material.

6. The apparatus (1) according to one or more of the preceding claims, wherein the processing unit (14) is programmed to derive the apparent viscosity value of the molten polymer material flowing in the pipe (10) based on the measurement signal, and is further programmed to apply Rabinowitsch or Weissenberg-Rabinowitsch correction to the apparent viscosity value in order to derive the corresponding actual viscosity value.

7. The apparatus (1) according to claim 6, wherein the processing unit (14) is programmed to also derive the shear rate value of the molten polymer flowing in the conduit (10).

8. The apparatus (1) according to one or more of the preceding claims, wherein the conduit (10) has a first segment and a second segment, the first segment having a first cross-sectional dimension (D2) for the flow of plastic material, the second segment having a second cross-sectional dimension (D3) for the flow of plastic material, the second cross-sectional dimension (D3) being smaller than the first cross-sectional dimension (D2), and wherein the optical fiber includes a first sensorized segment located in the first segment of the conduit (10) and a second sensorized segment located in the second segment of the conduit (10).

9. The apparatus (1) according to one or more of the preceding claims, wherein the conduit (10) has a longitudinal segment oriented along a longitudinal axis (X), and wherein the optical fiber has an effective segment located inside the conduit (10) and oriented parallel to the longitudinal axis (X).

10. The apparatus (1) according to claim 9, comprising a guiding element (12) having an outer portion (12A) located outside the conduit (10) and an inner portion (12B) extending into the interior of the conduit (10), the guiding element (12) defining a channel within the channel having an inlet formed in the outer portion (12A) of the guiding element (12) and an outlet formed in the inner portion (12B) of the guiding element (12), wherein the optical fiber has an initial segment accommodated in the channel and located upstream of the effective segment, the effective segment being located downstream of the outlet of the channel.

11. The device (1) of claim 10, wherein the channel in the inner portion (12B) of the guide element (12) defines a bend such that the outlet of the channel is oriented parallel to the longitudinal axis (X).

12. The apparatus (1) according to one or more of claims 9 to 11, wherein the effective segment of the optical fiber is at least 10 mm long.

13. The device (1) according to one or more of the preceding claims, wherein the optical fiber has a core (13A) made of glass and an outer sheath (13C) made of stainless steel.

14. The device (1) according to claim 13, wherein the optical fiber further comprises an intermediate sheath (13C') made of ceramic material.

15. An apparatus (L) for continuous processing of plastic materials, comprising: - An extruder (2) is configured to receive raw plastic material as input and produce a stream of molten plastic material as output; - A processing machine (3) configured to perform processing on the plastic in a continuous cycle; - A connecting pipe for conveying molten plastic from the extruder (2) to the processing machine (3); - An apparatus (1) for exporting the viscosity of a molten polymer according to one or more of the preceding claims, wherein the conduit (10) of the apparatus (1) is formed from a portion of the connecting conduit.

16. The apparatus (L) of claim 15, comprising a controller configured to adjust one or more process parameters relating to the activity of the extruder (2), wherein the controller is connected to the processing unit (14) to receive an estimate of the viscosity of the molten polymer material and is programmed to adjust the one or more process parameters based on the estimate of the viscosity of the molten polymer material.

17. A method for deriving the viscosity of a molten polymer, comprising the following steps: - Molten polymer material is conveyed through a pipe (10) having an inlet (10I) and an outlet (10U); - A measurement signal representing a pressure value is generated via a sensor system (13) that is operatively in contact with the molten polymer material flowing in the pipe (10); - The measurement signal is processed to derive an estimate of the viscosity of the molten polymer material flowing in the pipe (10). The sensor system (13) is characterized in that it includes an optical fiber that defines a differential pressure sensor located inside (I) of the conduit (10) to contact the molten polymer material.

18. The method of claim 17, wherein the optical fiber terminates at an end point (133) located inside the conduit (10) to contact the molten polymer material.

19. The apparatus (1) of claim 18, wherein the optical fiber includes a reflective layer (136) in direct contact with the endpoint.

20. The device (1) according to one or more of claims 17 to 19, wherein the endpoint (133) defines the differential pressure sensor.

21. The method according to one or more of claims 17 to 20, wherein, First, the processing step derives the apparent viscosity value of the molten polymer material flowing in the pipe (10) based on the measurement signal, and then applies Rabinowitsch or Weissenberg-Rabinowitsch correction to the apparent viscosity value in order to derive the corresponding actual viscosity value.

22. The method according to one or more of claims 17 to 21, wherein the conduit (10) has a first segment and a second segment, the first segment having a first cross-sectional dimension (D2) for a flow of plastic material, the second segment having a second cross-sectional dimension (D3) for a flow of plastic material, the second cross-sectional dimension (D3) being smaller than the first cross-sectional dimension (D2), and wherein the optical fiber includes a first sensorized segment located in the first segment of the conduit (10) to capture the measurement signal and a second sensorized segment located in the second segment of the conduit (10) to capture another measurement signal, the other measurement signal being processed together with the measurement signal.

23. A method for continuously processing plastic materials, comprising the following steps: - In the extruder (2), the raw plastic material is extruded to produce a stream of molten plastic material; - In the processing machine (3), the molten plastic material from the extruder is continuously processed; - The viscosity of the molten polymer is derived using one or more of the methods according to claims 17 to 22, wherein the conduit (10) containing the optical fiber is part of a connecting conduit for conveying the molten plastic from the extruder (2) to the processing machine (3).

24. The method of claim 23, further comprising the step of performing feedback control on one or more process parameters related to the activity of the extruder (2) based on an estimated value of the viscosity of the molten polymer material.

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