AU2015204285B2 - Apparatus and methods for investigating process variables in the production of carbon fiber materials - Google Patents

Abstract

The present invention provides an apparatus for treating a length of carbon fiber precursor, the apparatus comprising: heating means configured to rapidly alter the temperature of a length of carbon fiber precursor, and retaining means configured to retain the length of carbon fiber precursor proximal to the heating means. The apparatus allows for a carbon fiber production process to be simulated in a small scale thereby providing means for optimising production parameters. CO) Cx14 CC-0

Description

ABSTRACT

The present invention provides an apparatus for treating a length of carbon fiber precursor, the apparatus comprising: heating means configured to rapidly alter the temperature of a length of carbon fiber precursor, and retaining means configured to retain the length of carbon fiber precursor proximal to the heating means. The apparatus allows for a carbon fiber production process to be simulated in a small scale thereby providing means for optimising production parameters.

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APPARATUS AND METHODS FOR INVESTIGATING PROCESS VARIABLES IN THE

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PRODUCTION OF CARBON FIBER MATERIALS.

FIELD OF THE INVENTION

The present invention is directed to the field of carbon fiber production. In particular, the invention is directed to apparatus for investigating the effects of process parameters potentially important in methods for producing carbon fiber.

BACKGROUND TO THE INVENTION

The properties of carbon fibers, such as high stiffness, high tensile strength, low weight, high chemical resistance, high temperature tolerance and low thermal expansion, make these 15 materials highly desirable in aerospace, civil engineering, and military applications. However, carbon fiber materials are relatively expensive and more difficult to manufacture when compared to fibers made from other materials such as glass or plastic.

Carbon fiber is produced by pyrolysis of an organic precursor fiber in an inert atmosphere. 10 Steps included in the process are the polymerization and spinning of the precursor into a fiber, oxidation (also referred to as stabilization) of the spun fiber, carbonization of the oxidized fiber, surface treatment and sizing application.

The process begins with a polymeric feedstock, which may be fabricated from a rayon- or 25 pitch-based precursor, but the majority is derived from polyacrylonitrile (PAN), made from acrylonitrile

Converting feedstock into carbon fiber provides significant challenges to the skilled artisan. While the quality of the precursor feedstock is the major determinant of the finished carbon 30 fiber’s properties, the processes of oxidation and carbonization are also significant contributors.

In the oxidation step, bobbins of PAN fiber are loaded into a creel that feeds the fiber through a series of specialized ovens. Before they enter the first oven, the PAN fibers are 35 spread flat into a tow band or sheet referred to as warp. The oxidation oven temperature is relatively low, ranging from 200°C to 300°C. The process combines oxygen molecules from

2015204285 14 Jul 2015 the air with the PAN fibers in the warp and causes the polymer chains to crosslink thereby increasing the fiber density.

Oxidation time varies, driven by specific precursor chemistry. As a guide, a 24K tow may be oxidized at about 13 meters per minute on a large production line with multiple oxidation ovens. An elapsed time of 60 to 120 minutes is typical, as are four to six ovens per production line, with ovens stacked to provide two heating zones that offer 11 to 12 passes of the fiber per oven.

Carbonization occurs in an inert (oxygen-free) atmosphere inside a series of specially designed furnaces that progressively increase the processing temperatures. At the entrance and exit of each furnace, purge chambers prevent oxygen intrusion. In the absence of oxygen, only non-carbon molecules, including hydrogen cyanide elements and other VOCs (generated during stabilization at concentration levels of 40 to 80 ppm) and particulate (such as local build-up of fiber debris), are removed and exhausted from the oven for posttreatment. Carbonization typically begins in a low-temperature furnace that subjects the fiber to 700°C to 800°C, and ends in a high-temperature furnace at 1200°C to 1500°C. Fiber tensioning must be maintained throughout the production process.

Ultimately, crystallization of carbon molecules can be optimized to produce a finished fiber that is more than 90 percent carbon. Although the terms carbon and graphite are often used interchangeably, the former denotes fibers carbonized at about 1315°C and that contain 93 to 95 percent carbon. The latter are graphitized at 1900°C to 2480°C and contain more than 99 percent elemental carbon.

The number of furnaces is determined by the modulus desired in the carbon fiber; part of the relatively high cost of high- and ultrahigh-modulus carbon fiber is due to the length of dwell time and temperatures that must be achieved in the high-temperature furnace. While dwell times are proprietary and differ for each grade of carbon fiber, oxidation dwell time is 30 measured in hours, but carbonization is an order of magnitude shorter, measured in minutes.

Surface treatment and sizing follow oxidation. Carbon fibers are then typically combined with other materials to form a composite. When combined with a plastic resin and wound or molded it forms carbon fiber reinforced polymer (often referred to as carbon fiber) which has 35 a very high strength-to-weight ratio, and is extremely rigid although somewhat brittle.

However, carbon fibers are also composed with other materials, such as with graphite to form carbon-carbon composites, which have a very high heat tolerance.

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The efficient production of high quality carbon fiber materials is a challenge. The production process has many process variables, any of which may (alone or in combination with other parameters) dramatically affect the quality or economics of the product. As mentioned 5 specific characteristics of precursor feedstock show inter-lot variability, and so process parameters that provide high quality product for a given precursor stock may not necessarily provide that same result for another. Accordingly, there is a need in the art to constantly investigate process parameters with a view to consistently producing high quality product.

While the prior art provides laboratory scale and pilot scale furnaces capable of investigating process parameters, these furnaces are large and expensive to operate requiring significant energy for heating, and high volumes of inert gas. Apart from cost, prior art apparatus requires significant time to set up and stabilize in order to test the effect of a given process variable on a product characteristic. Given the desirability of testing as many process 15 variables and in as many combinations as possible it will be seen that the use of prior art furnaces are limited in their abilities to provide useful information quickly and inexpensively.

It is an aspect of the present invention to overcome or ameliorate a problem of the prior art by providing an improved laboratory scale furnaces. It is a further aspect to provide a useful 10 alternative to prior art laboratory scale furnaces.

The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or 25 were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a diagrammatic representation of an exemplary laboratory-scale furnace of the present invention.

FIG. 2 shows an enlargement of the area defined by the box marked 44 in FIG.1.

FIG. 3 shows an exemplary temperature profile achievable by the apparatus of FIG. 1 and

FIG. 2. The profile is a simulation of a carbonization step.

SUMMARY OF THE INVENTION

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In a first aspect the present invention provides an apparatus for treating a length of carbon fiber precursor, the apparatus comprising: heating means configured to rapidly alter the temperature of a length of carbon fiber precursor, and retaining means configured to retain the length of carbon fiber precursor proximal to the heating means.

In one embodiment, the apparatus is configured to heat the length of carbon fiber precursor 0 at a rate of at least about 10°C per second.

In one embodiment, the heating means is configured to surround the length of the carbon fiber, and may be substantially conduit-shaped such that the length of carbon fiber precursor is positionable within the conduit. In one embodiment, the heating means comprises a 5 graphite tube.

In one embodiment, the heating means comprises induction means.

In one embodiment, the apparatus comprises temperature control means configured to control the heating means, and in turn the length of carbon fiber precursor. The temperature control means may comprise temperature measuring means configured to measure the temperature of the heating means, which is in turn indicative of the temperature of the length of carbon fiber precursor. In one embodiment, the temperature measuring means is an optical device.

In one embodiment, the apparatus comprises tensioning means configured to maintain tension on the length of carbon fiber precursor, and may further comprise tension measuring means configured to measure the tension of the length of carbon fiber precursor.

In one embodiment, the apparatus comprises atmosphere control means configured to provide a controlled atmosphere about the length of carbon fiber precursor.

In a second aspect the present invention provides a method for treating a length of carbon fiber precursor, the method compromising the steps of: providing a length of carbon fiber 35 precursor, retaining the length of carbon fiber precursor in a fixed position, rapidly altering the temperature of the length of carbon fiber precursor to simulate a temperature alteration experienced by a carbon fiber precursor in a carbon fiber production process.

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In one embodiment, the temperature of the length of carbon fiber precursor is altered at a rate of at least about 10°C per second.

In one embodiment, the method comprising rapidly altering the temperature in two or more steps.

In one embodiment, the method comprises the step of providing the apparatus as described herein and disposing the length of carbon fiber precursor proximal to the heating means.

In one embodiment, the method comprises the step of analyzing the treated length of carbon fiber precursor for a desired property or an undesired property.

In a third aspect, the present invention provides a product produced by the method as 5 described herein.

DETAILED DESCRIPTION OF THE INVENTION

After considering this description it will be apparent to one skilled in the art how the invention is implemented in various alternative embodiments and alternative applications. However, although various embodiments of the present invention will be described herein, it is understood that these embodiments are presented by way of example only, and not limitation. As such, this description of various alternative embodiments should not be 25 construed to limit the scope or breadth of the present invention. Furthermore, statements of advantages or other aspects may apply only to specific exemplary embodiments, and not necessarily to all embodiments covered by the claims.

Throughout the description and the claims of this specification the word “comprise” and 30 variations of the word, such as “comprising” and “comprises” is not intended to exclude other additives, components, integers or steps.

Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment 35 is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may.

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Use of the terms “first” and “second” herein is not intended to infer any aspect of chronology, proximity, position, importance, relevance or the like. The terms are used interchangeably, and are intended only to refer to the separate nature of the so-described features.

The present invention is predicated at least in part on the Applicant’s discovery that a carbon fiber production process (or part thereof) may be simulated in a small scale furnace capable of rapidly altering the temperature of a carbon fiber precursor, the precursor remaining stationary within the furnace. Accordingly, in a first aspect the present invention provides 0 apparatus for treating a length of carbon fiber precursor, the apparatus comprising: heating means configured to rapidly alter the temperature of a length of carbon fiber precursor, and retaining means configured to retain the length of carbon fiber precursor proximal to the heating means.

The present invention is a significant departure from prior art laboratory scale furnaces commonly used to assess the effect of altering temperature-related parameters on a carbon fiber production process. Such furnaces attempt to simulate the production process by simply scaling down the production scale process. Thus, the carbon fiber precursor is moved through one or more furnaces, with each furnace set to a given temperature. For ?0 example, the precursor may be PAN fiber which, (after an oxidation step) is subject to a carbonization process which begins in a low-temperature furnace that subjects the fiber to 700°C to 800°C, and ends in a high-temperature furnace at 1200°C to 1500°C. A prior art laboratory scale furnace for simulating a production scale carbonization typically has a low temperature furnace and high temperature furnace, with the precursor being fed sequentially 25 through the low temperature and then the high temperature furnace.

By contrast, the present invention is operable as a single furnace capable of rapidly altering the temperature of a stationary precursor to simulate feeding a precursor fiber into and out of a furnace heating chamber. The apparatus may be used to simulate the sequential 30 movement of a carbon fiber precursor through firstly a low temperature furnace, and then a high temperature furnace. Other parameters such as fibre tension and/or inert gas temperature and/or inert gas velocity over the fibre surface, and/or the effect of inert gas turbulence about the fibre precursor may also be concurrently investigated as will be further described infra.

As used herein, the term “rapidly altering the temperature” is intended to mean that the rate of temperature increase or decrease is as rapid as required to simulate a temperature

2015204285 14 Jul 2015 transition of a product scale carbon fiber production process step. The step may, for example, be the transition from ambient temperature to the highest temperature encountered in a low temperature furnace used in carbonization, or the transition from the highest temperature encountered in a low temperature furnace used in carbonization to ambient 5 temperature, the transition from ambient temperature to the highest temperature encountered in a high temperature furnace used in carbonization, or the transition from the highest temperature encountered in a high temperature furnace used in carbonization to ambient temperature.

In one embodiment, the heating means of the present apparatus may be capable of heating the precursor from ambient temperature to 1600 °C in less than two minutes, one minute, 50 seconds, 40 seconds, 30 seconds, 20 seconds or 10 seconds. Expressed differently, the heating means may be capable of heating the precursor at a rate of at least about 5, 10,15, 20, 25, 30, 35, 40, 45, 50, 55 or 60 °C per second.

Such rapidity in heating is achievable for carbon fiber precursor (such a flat carbon fiber tow band) which has very low thermal mass and therefore able to heat quickly. The surface area to volume ratio of the precursor is high, the emissivity is high and the mass of the product very low. Accordingly, the fiber is able to absorb the radiant heat rapidly and closely follow 10 the heat up rate of the heating means .

The present apparatus allows for the rapid testing of a range of process variables such as temperature, and temperature transition profile. Thus, a length of precursor is retained within the apparatus, and then heated to various temperatures, and also allowed to cool (or 25 may be actively cooled in some embodiments) to a various temperatures. The treated fiber is removed from the apparatus, and then a second precursor (which is typically identical to the first precursor) is retained in the apparatus. The second fiber precursor is then subjected to a different temperature profile to the first, and the treated fiber removed from the apparatus. All carbonized fibers are then subsequently assessed (typically batch-wise) for a 30 desired or undesired characteristic. A direct comparison between the temperature profiles can then be assessed.

Prior art laboratory scale furnaces take a significant amount of time to set up for a given high temperature and low temperature treatment. The temperatures must be adjusted carefully 35 and allowed to stabilize to give a desired temperature in the fiber. Production size lines are expensive to run and it is difficult and time consuming to make changes to process parameters. Smaller scaled-down lines have the same problems but just to a lesser degree.

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Laboratory scale furnaces are typically configured to operate at a set temperature, and so are not easily used to investigate the effects of temperature variations. Thus, prior art furnaces must be set up and stabilized for each small change in temperature and/or transition profile to be tested. The significant amount of work involved is one of the reasons 5 that systematic investigation of process parameters in carbon fiber production is not routinely carried out.

In order to accurately simulate the temperature transition of a carbon fiber precursor from a low temperature (such as ambient temperature) to a higher temperature (such as that 0 provided by a carbonization furnace) the present apparatus must be capable of rapidly altering the temperature of a carbon fiber precursor. In a production process, feeding of a precursor into a furnace reaction chamber causes rapid heating of the precursor, with this rapid heating being emulated in the present apparatus. Rapid heating is in the present apparatus is achieved by the use of heating means capable of rapidly and accurately altering 15 temperature of the heating means, and therefore in turn the stationary length or carbon fiber.

Preferably, the precursor is heated from all directions to simulate process scale. In one embodiment, the heating means is configured to heat in all directions orthogonal to the longitudinal axis of the precursor. This may be achieved by the use of a conduit-shaped 10 heated element which surrounds the precursor, the heated element being part of the heating means. The precursor is retained within the lumen of the conduit-shaped heated element.

In one embodiment, the heating means operates by induction whereby a power supply converts AC line power to a higher frequency alternating current, and delivers the current to 25 a work coil thereby creating an electromagnetic field within the coil. The conductor of the induction means may be a graphite tube, with the work coil wound thereabout.

The skilled artisan is entirely familiar with induction heating system design, and also the construction and operation of such systems, as outlined in Davis et al; Induction Heating 30 Handbook, 1979 (McGraw-Hill); the contents of which is herein incorporated herein by reference.

The size of the tube and the specific application dictates the operating frequency of the induction system. Generally the larger the tube the lower the frequency. The operating 35 frequency is determined by the capacitance of the tank circuit, the inductance of the coil and the material properties of the tube.

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The relationship of the current flow in the tube and the distance between the tube and the coil may be optimized. It is understood by the skilled person that the closer the coil, the more current in the graphite tube. However, the distance between the coil and the tube may first be optimized for the heating required. Many factors in the induction system can be 5 adjusted to match to the coil and optimize the coupling efficiency.

The skilled person further understands that the power required to heat the graphite tube depends on: the mass of the tube, the material properties of the tube, the temperature required, the rapidity of heating required, the effectiveness of the field owing to the coil 0 design, and any heat losses during the heating process.

The heated element may have a wall thickness of at least about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15 or 20 mm. In one embodiment, where the heated element is a graphite tube the wall thickness of the tube is about 3 mm.

Where the heated element is circular in cross-section, the internal diameter may be at least about 5, 10, 15, 20, 25, 30, 35, 40, 45 or 50 mm. Where the heated element has a cross section which is non-circular, a cross-sectional area equivalent to those of the aforementioned diameters may be applicable.

As will be understood, the retaining means of the apparatus is capable of maintaining the precursor in position relative to the heating means. Typically, the precursor is retained less than about 5, 10, 20, 30, 40 or 50 mm from a heated surface of the heating means (such as the internal luminal face of a graphite tube). The retaining means may be a clamping 25 means. Given that the precursor is stationary and does not move through the retaining means, there is no requirement for the retaining means to be particularly gentle, at least where a plurality of fibres is being treated. It is the central area of the carbon fiber precursor which is treated and analysed, and so any damage to the termini of the precursor fiber by clamping or similar mechanical force may be ignored. Where the length of carbon fiber 30 precursor is disposed substantially horizontally, two retaining means are typically used - one toward each terminus.

In one embodiment, the apparatus comprises tensioning means capable of maintaining tension of the length of carbon fiber precursor under treatment. In one embodiment there 35 may be a single retaining means whereby the precursor is disposed substantially vertically and the weight of the precursor itself provides the tension. More typically, a dedicated tensioning means is used. The tensioning means may be a simple weight clamped to via

2015204285 14 Jul 2015 vertically disposed precursor, with the tension applied being alterable by changing the weight.

In other embodiments, the tensioning means is configured to provide an adjustable tension to a substantially horizontally disposed precursor. As an example, the precursor may be retained at each terminus, with the precursor disposed upon a small roller disposed between the termini. A weight is hung between the roller and the terminus to apply a tension.

Alternatively, the tensioning means may be a second retaining means (which may be a 0 clamp), with the precursor stretched and then clamped at a desired tension.

The skilled person is enabled to devise other means of applying a tension to a precursor such as the used of springs and other contrivances.

Where a plurality of fibres is being tested, the skilled person understands that some attention may be given to ensuring (as far as possible) that each individual fibre is under substantially the same tension. Even where it is not possible to apply the same tension to all fibres, the comparative data provided by the present apparatus and methods will nonetheless provide useful information in the investigation of carbon fibre production process parameters.

Tension may be an important process variable in some steps of the carbon fiber production process, with the ability to vary that parameter adding further advantage to the present apparatus. Indeed, tension may be altered across a series of tests with all other variables (such as temperature) being fixed such that information on the effect of tension on product 25 characteristics may be ascertained.

In some embodiments, the apparatus comprises programmable temperature control means, providing for the precursor to be heated (and optionally cooled) according to a particular profile. For example, the program may be configured to define a first temperature and a 30 second temperature. In addition the program may be configured to define a rate of temperature change between the first and second temperatures.

The program may be configured to define a specific profile between a first and second temperature. Thus, the profile may be linear, logarithmic, sigmoidal, or any other. For 35 example, it may be found that a sigmoidal profile is preferred whereby the fiber is heated firstly at a slow rate, and then at a rapid rate, and then to more slowly increase to arrive at

2015204285 14 Jul 2015 the second temperature. Prior artisans have never before been able to easily ascertain the effects of subtle changes in heating of a carbon fiber precursor.

Such programmable temperature transitions will typically be achieved by the use of a 5 processor (typically in the form of a personal computer) under instruction from appropriate software.

In one embodiment, the apparatus comprises means for measuring the temperature of the precursor. The temperature measuring means may provide data input into the temperature 0 control means of the heating means such that the heating means stops heating the precursor once the precursor is at the programmed target temperature.

In one embodiment, temperature of the heating means within the apparatus is measured by optical means. Given the substantially complete and rapid absorption of heat energy by the 15 carbon fibre precursor it is proposed that the temperature of the fibre may very closely mirror that of the heating means.

Given the rapid alteration in temperature of the precursor when heated by the present apparatus, and to achieve useful control of temperature it is necessary for alteration in 10 temperature to be rapidly detected. While thermocouples (and similar devices) can accurately measure temperature, their response times lag given the need to heat the device itself. It is proposed that non contact means (such as optical means) are preferred given the instantaneous detection of a change in temperature. For example, infrared (IR) means may be used to measure temperatures of up to 3000 °C and will be suitable in the context of the 25 present apparatus.

Advantageously, the use of an optical temperature measuring device trained on the heating means provides for a more accurate measurement of the temperature of the heating means and therefore also the length of carbon fiber precursor as compared with the temperature 30 measuring means in pilot and production scale furnaces. Prior art apparatus typically dispose several thermocouples at strategic points which provide an indicative average temperature within, which may not be an accurate indication of the actual temperature of the carbon fibre precursor. The more accurate temperature data provided by the present apparatus provides the opportunity to more properly investigate the effect of temperature on 35 carbon fiber production.

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A suitable pyrometer may be the FA2B series fiber optic non-contact thermometer of Raytek

Corporation (Santa Cruz, CA). ...

As will be appreciated by the skilled person, the pyrometer will require calibration before use, 5 with suitable methods for calibration being well known in the art.

In one embodiment, the apparatus comprises atmosphere control means. Typically, such means are included where a carbonization process is simulated and where oxygen is excluded as far as possible from the apparatus. Typically, the atmosphere control means 0 comprises means for injecting an inert gas (such as nitrogen) about the precursor with such means being well known to the skilled artisan. Means for containing the injected gas is typically included, such as a housing or other type of enclosure to retain inert gas about the precursor and exclude atmospheric gases.

The present apparatus provides further advantage in that the effects of inert gas parameters such as temperature and velocity may be investigated. Furthermore, given the relatively small scale of the present apparatus, a more complete purge of atmospheric gases is achievable. Whether or not more complete purging at production scales leads to any significant improvement in fibre quality may therefore be assessed. If significant improvement is noted more complete purging can be effected at production scale if economically warranted.

In one embodiment the apparatus comprises cooling means configured to actively cool the precursor. The cooling means may be provided by the injection of a gas (and optionally a 25 refrigerated gas). The gas may be injected also for the purpose of atmosphere control as discussed supra.

In a second aspect the present invention provides a method for treating a length of carbon fiber precursor, the method compromising the steps of: providing a length of carbon fiber 30 precursor, retaining the length of carbon fiber precursor in a fixed position, rapidly altering the temperature of the length of carbon fiber precursor to simulate a temperature alteration experienced by a carbon fiber precursor in a carbon fiber production process.

The length of carbon fiber precursor can be any minimum length capable of being 35 adequately retained in the apparatus and sufficient material for any testing after treatment.

Typically, the graphite tube is around 20 cm long, and therefore the precursor will be

2015204285 14 Jul 2015 somewhat longer to extend beyond the lumen of the tube to be engagable by the retaining means.

The carbon fiber precursor subject the present method may be a spun fiber made from a rayon- or pitch-based precursor, or more typically polyacrylnitrile (PAN). Such precursor is first typically subject to an oxidation step in carbon fiber production. The precursor product of the oxidation step may be subject the present method, in which case the apparatus is programmed to simulate passage through the low and high temperature furnaces of the carbonization step in carbon fiber production.

While the length of carbon fiber typically consists of a plurality of individual fibres, it is contemplated that the present apparatus and methods are applicable to a single fiber. This will allow very precise research into the effects of temperature and other parameters on single carbon fibers, and without the potential for confounding effects caused neighbouring 15 fibers. Of course, a single carbon fiber is fragile and so suitable retaining means is used to prevent breakage of the fiber. Means for retaining and testing single carbon fibres is disclosed by Kumar et al, Arch. Meeh., 65, 1, pp.27-43, Waszawa 2013; the content of which is incorporated herein by reference.

As discussed, the quality of the finished fiber is directly dependent on that of the precursor. Specifically, attention to precursor quality minimizes variation in the yield, or length per unit of fiber weight. It will be appreciated that the present apparatus and methods allow for the rapid trialling of different types of precursor, and also allows for rapid assessment of changes to process variables on the fiber product.

Furthermore, the present apparatus and methods may be used to investigate, for example, the relationship between residence time, temperature and fiber properties in each of a low temperature and high temperature furnace, upper and/or lower limits for heat up rate at each stage of a heat up curve, the effect of reducing atmosphere dilution in the low temperature or 30 high temperature furnace, the effect on fiber properties of a temperature variation across the tow band, the maximum impingement velocity of a gas at which fiber deterioration is observed, the effect of very rapid cool down profiles in the high temperature and low temperature furnaces, temperature variation limits that cause a noticeable change in fiber characteristic.

A fiber produced by the present methods may be analyzed for any desired or undersized characteristic, or any parameter such as Young’s modulus, in plane shear modulus, Major

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Poisson’s ratio, tensile strength, comp, strength, in plane shear strength, tensile strain, comp, strain, thermal expansion coefficient, moisture expansion coefficient, density, and the like.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Turning to Fig. 1 there is generally shown schematically a research-scale furnace apparatus according to the present invention. The carbon fiber precursor 10 is clamped between a first clamping mechanism 12 and a second clamping mechanism 13. Tension is maintained on 0 the precursor by a system of rollers 14, 16, 18, with roller 16 having a weight 20 attached thereto. The weight 20 is alterable according to the amount of tension required. The heating means comprises an inner graphite tube 22, with the precursor 10 running substantially along the central axis of the graphite tube 22..

External to the graphite tube 22 is a non-suscepting silicon carbide tube 24, about which an induction heating coil 26 is wound. The function of external tube 24 is to provide support for the heating coil 26, and to also contain an inert gas about the graphite tube 22, thereby protecting the graphite tube 22 from uncontrolled combustion. The external tube 24 is fabricated from a material capable which is substantially resistant to very high temperatures, ?0 and also rapid heating and cooling. The skilled person is enabled to investigate the use of materials other than silicon carbide.

The heating coil 26 is in electrical connection with a work head 28, which is in turn in electrical connection with a power inverter 30.

An optical pyrometer probe 32 is inserted through the walls of the boron nitride tube 24 and the graphite tube 22 such that the probe 32 is in optical communication with the graphite tube 24. The probe is in data connection with a microprocessor 34 configured to control the temperature of the precursor 10. Temperature control is achieved by modulating the output 30 of the power inverter 30, which in turn modulates the heat output of the heating coil 26.

Temperature control may be assisted by the modulating the flow of nitrogen gas (which may be heated or refrigerated, the means for which is not shown in this drawing).

The nitrogen gas supply 36 is in gaseous connection with the lumen of the graphite tube 22, 35 and also the concentric space between the graphite tube 22 and the external tube 24.

Surrounding the graphite tube with nitrogen substantially excludes oxygen thereby preventing combustion of the graphite.

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Delivery of nitrogen is controllable differentially to the lumen and the space by way of solenoids 36 and 38, both controlled by the microprocessor 34. Flow rate of the nitrogen gas is further differentially controllable by way of flow controllers 40 and 42. The differential 5 nitrogen supply conduits are shown as 44 and 46 the former injecting gas into the space between the graphite tube 22 and the external tube 24, with the latter injecting gas into the lumen of the graphite tube 22.

Differential injection of gas is provided in this preferred apparatus given the disparate tasks 0 of the injected gases. The gas injected into the lumen of the graphite tube 22 directly contacts the length of carbon fibre precursor 10, and is responsible for ensuring the virtually complete exclusion of molecular oxygen from the surface of the precursor 10, and also the removal of pyrolysis products emitted from the precursor 10. By contrast, the gas injected into the space between the graphite tube 22 and the external tube 24 is only for the purpose 5 of protecting the graphite tube 22 from uncontrolled combustion.

Thus, the gas injected into the lumen of the graphite tube 22 is an actual process parameter (and therefore preferably precisely controlled), with the velocity and temperature of the gas capable of directly impacting on the quality of the carbon fibre produced. The gas injected ?0 into the space between the graphite tube 22 and the external tube 24 is not a process parameter, does not affect the quality of the carbon fibre produced and is therefore not required to be precisely controlled by the microprocessor 34.

Not shown in the drawings is the housing which facilitates control of the atmosphere about 25 the precursor 10 and the graphite tube 22. The skilled person is fully enabled to design a housing allowing for the introduction and removal of a carbon fibre precursor and product while still ensuring the substantial exclusion of oxygen from the interior. Indeed, the lack of any need to continuously feed the present apparatus with a carbon fibre precursor may simplify housing design allowing for a substantially sealed housing to be used. 30 Advantageously, it may not be necessary for the housing to provide appropriately dimensioned entry and exit ports with inert gas curtains for the purpose exclude oxygen from the reaction chamber.

Turning to Fig. 3 there is shown a graphical representation of the temperature of a length of 35 stationary carbon fiber precursor retained within the apparatus described supra and subjected to a pre-programmed temperature profile. The profile is intended to simulate the temperatures to which a single point on a length of precursor experiences as it is feed

2015204285 14 Jul 2015 through a high temperature and low temperature carbon fiber production furnace in the carbonization process.

The induction heating coil is activated at point A to heat the precursor, to commence heating 5 of the tube and in turn the fiber. The program is set to achieve a maximum temperature of

1000°C, and the heating coil remains activated until the pyrometer detects that 1000 °C has been reached. The microprocessor deactivates the heating coil at point B, and the precursor allowed to cool passively at first. This first section of the profile is intended to simulate the precursor entering into and exiting the hot zone of a low temperature production 0 scale furnace.

After some passive cooling, (and at a temperature defined in the program) the stationary length of precursor is actively cooled by purging the apparatus with nitrogen gas (at ambient temperature), as defined by point C of the profile. More rapid cooling ensues, this simulating 5 the precursor passing into a cooling zone of a production scale process. The nitrogen purge ceases at point D of the profile, when the pyrometer detects the precursor has cooled to a defined temperature.

At point E of the profile, the heating coil is again activated, however on this occasion remains 10 activated until the pyrometer detects the precursor has reached a temperature of 1600°C, at which point (marked as F on the profile) the heating coil is deactivated. This simulates the precursor entering and exiting a high temperature production scale furnace. The precursor cools passively at first, and the actively by the purging of nitrogen gas at point G. The gas purge ceases at point H of the profile and the precursor returns to ambient temperature.

Finally, it is to be understood that the inventive concept in any of its aspects can be incorporated in many different constructions so that the generality of the preceding description is not to be superseded by the particularity of the attached drawings. Various alterations, modifications and/or additions may be incorporated into the various constructions 30 and arrangements of parts without departing from the spirit or ambit of the invention.

Claims (18)

1. 2015204285 29 Apr 2019

   THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

   1. Apparatus for treating a length of carbon fiber precursor, the apparatus comprising:

   heating means configured to rapidly alter the temperature of a length of carbon fiber precursor, and retaining means configured to retain the length of carbon fiber precursor proximal to the heating means, wherein in use, proximity of the heating means to the carbon fibre precursor is such that the length of carbon fibre is heated at a rate of at least about 5°C per second.
2. 2. The apparatus of claim 1, wherein, in use proximity of the heating means to the carbon fibre precursor is such that the length of carbon fibre is heated at a rate of at least about10°C per second.
3. 3. The apparatus of claim 1 or claim 2 wherein the heating means is configured to surround the length of the carbon fiber.
4. 4. The apparatus of any one of claims 1 to 3 wherein the heating means is substantially conduit-shaped such that the length of carbon fiber precursor is positionable within the conduit.
5. 5. The apparatus of claims 1 to 4 wherein the heating means comprises a graphite tube.
6. 6. The apparatus of one of claims 1 to 5 wherein the heating means comprises induction means.
7. 7. The apparatus of any one of claims 1 to 6 comprising temperature control means configured to control the temperature of the heating means.
8. 8. The apparatus of claim 7 wherein the temperature control means comprises temperature measuring means configured to measure the temperature of the heating means

   2015204285 29 Apr 2019
9. 9. The apparatus of claim 8 wherein the temperature measuring means is an optical device.
10. 10. The apparatus of any one of claims 1 to 9 comprising tensioning means configured to maintain tension on the length of carbon fiber precursor.
11. 11. The apparatus of any one of claims 1 to 10 comprising tension measuring means configured to measure the tension of the length of carbon fiber precursor.
12. 12. The apparatus of any one of claims 1 to 11 comprising atmosphere control means configured to provide a controlled atmosphere about the length of carbon fiber precursor.
13. 13. A method for treating a length of carbon fiber precursor, the method compromising the steps of:

    providing a length of carbon fiber precursor, retaining the length of carbon fiber precursor in a fixed position, rapidly altering the temperature of the length of carbon fiber precursor a rate of at least about 5°C per second to simulate a temperature alteration experienced by a carbon fiber precursor in a carbon fiber production process.
14. 14. The method of claim 13 wherein the temperature of the length of carbon fiber precursor is altered at a rate of at least about 10°C per second.
15. 15. The method of claim 13 or claim 14 comprising rapidly altering the temperature in two or more steps.
16. 16. The method of any one of claims 13 to 15 comprising the step of providing the apparatus of any one of claims 1 to 12 and disposing the length of carbon fiber precursor proximal to the heating means.
17. 17. The method of any one of claims 13 to 16 comprising the step of analyzing the treat length of carbon fiber precursor for a desired property or an undesired property.
18. 18. A product produced by the method of any one of claims 13 to 17.

    2015204285 14 Jul 2015