US20170268135A1

US20170268135A1 - Method of separating fiber tows

Info

Publication number: US20170268135A1
Application number: US15/075,660
Authority: US
Inventors: Haibo Zhao
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2016-03-21
Filing date: 2016-03-21
Publication date: 2017-09-21
Also published as: CN107217321A; DE102017105976A1

Abstract

Methods and systems for separating fiber tows (e.g., carbon tows) are disclosed. The system may include a chamber defining first and second openings and a hollow interior therebetween. The first opening may be configured to receive a fiber tow and the second opening may be wider than the first opening. A vacuum source communicating with the chamber may be configured to reduce an air pressure in the hollow interior and expand the fiber tow. The method may include pulling a fiber tow having an initial width into a first chamber opening, through a hollow chamber interior, and out of a second chamber opening. Air pressure within the hollow chamber interior may be reduced to separate the fiber tow residing in the hollow chamber interior into an expanded fiber tow having a width greater than the initial width. The disclosed methods may separate the tow more gently than mechanical methods.

Description

TECHNICAL FIELD

This disclosure relates to a method of separating fiber tows, for example, carbon fiber tows.

BACKGROUND

Increased fuel economy is an important goal for vehicle manufacturers. The desire for improved fuel economy may be driven by fuel costs, emissions standards (e.g., for carbon dioxide), improved range, or other reasons. One approach to improving fuel economy is using lightweight materials to reduce vehicle weight. Carbon fiber is a low-density material with good mechanical properties. Currently, carbon fiber is generally used in applications such as aerospace, wind energy, sporting goods, and high-end vehicles. These applications are generally lower in volume and higher in price compared to high-volume vehicles. Implementation of carbon fiber into high-volume, non-luxury vehicles in the auto industry poses some challenges.
One of the challenges is developing low-cost processing technology for high-volume production. A sheet molding compound (SMC) process has been used to manufacture glass fiber reinforced parts, such as decklids, hoods, bumpers, and others. However, the same SMC process may not be suitable for carbon fibers due to differences in the physical properties of the two fiber types. Carbon fibers may be smaller in diameter compared with glass fibers (e.g., twice as small), which can make carbon fiber tows difficult to separate. In addition, sizing materials that may be coated on the carbon fiber surface can make carbon fibers tend to agglomerate.

SUMMARY

In at least one embodiment, a fiber tow separating system is provided. The system may include a chamber defining first and second openings and a hollow interior therebetween; the first opening configured to receive a fiber tow; the second opening being wider than the first opening; and a vacuum source communicating with the chamber and configured to reduce an air pressure in the hollow interior and expand the fiber tow.
A sealing member may extend around the first opening and be configured to engage the fiber tow. The sealing member may be made of rubber. A sealing member may extend around the second opening and be configured to engage the expanded fiber tow as it exits the second opening. In one embodiment, the second opening is at least 50% wider than the first opening. In another embodiment, the second opening is at least 200% wider than the first opening. The first opening may have a width of 3 to 20 mm and the second opening may have a width of 5 to 75 mm. In one embodiment, a width of the hollow interior continuously increases from the first opening to the second opening. One or more hoses may be coupled to the chamber and the vacuum source. In one embodiment, the vacuum source is configured to reduce the air pressure in the hollow interior to 1 torr or less.
In at least one embodiment, a method of separating fiber tows is provided. The method may include pulling a fiber tow having an initial width into a first chamber opening, through a hollow chamber interior, and out of a second chamber opening; and reducing an air pressure within the hollow chamber interior to separate the fiber tow residing in the hollow chamber interior into an expanded fiber tow having a width greater than the initial width.
In one embodiment, the second chamber opening may be wider than the first chamber opening and reducing the air pressure within the hollow chamber interior may separate the fiber tow into an expanded fiber tow having a width that is substantially the same as a width of the second chamber opening. A sealing member may extend around a perimeter of the first chamber opening and pulling the fiber tow into the first chamber opening may form at least a partial seal between the fiber tow and the sealing member. A sealing member may extend around a perimeter of the second chamber opening and pulling the fiber tow out of the second chamber opening may form at least a partial seal between the expanded fiber tow and the sealing member.
In one embodiment, the reducing step may include reducing the air pressure within the hollow chamber interior to 1 torr or less. The reducing step may include reducing the air pressure within the hollow chamber interior using a vacuum hose coupled to the hollow chamber interior and to a vacuum source. In one embodiment, the reducing step includes reducing the air pressure within the hollow chamber interior to separate the fiber tow into an expanded fiber tow having a width that is at least 100% greater than the initial width. The method may further include chopping the expanded fiber tow into a plurality of expanded fiber tow segments and incorporating the expanded fiber tow segments into a sheet molding compound material. In one embodiment, the fiber tow is a carbon fiber tow.
In at least one embodiment, a method of separating a carbon fiber tow is provided. The method may include pulling a carbon tow having an initial width into a first chamber opening, through a hollow chamber interior, and out of a second chamber opening; and reducing an air pressure within the hollow chamber interior to 100 torr or less to separate the carbon tow residing in the hollow chamber interior into an expanded carbon tow having a width at least 50% greater than the initial width.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an example of a carbon fiber tow;

FIG. 2 is a top view of a fiber tow separation system, according to an embodiment;

FIG. 3 is a top view of a fiber tow entering and being separated by a fiber tow separation system, according to an embodiment;

FIG. 4A is a front end view of a fiber tow separation system form, according to an embodiment;

FIG. 4B is a rear end view of a fiber tow separation system form, according to an embodiment;

FIG. 4C is a side view of a fiber tow separation system form, according to an embodiment;

FIG. 5A is a top view of a fiber tow separation system form, according to an embodiment;

FIG. 5B is a top view of a fiber tow separation system form, according to another embodiment;

FIG. 5C is a top view of a fiber tow separation system form, according to another embodiment; and

FIG. 6 is a schematic of a fiber tow chopping system, according to an embodiment.

DETAILED DESCRIPTION

As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.
As described in the Background, the SMC process used to manufacture glass fiber reinforced parts may not be suitable for producing carbon fiber reinforced parts. The bundling of carbon fibers can cause issues in the SMC process. For example, it may be difficult for resin to wet out (e.g., fully impregnate) the carbon fibers and the fibers may not flow well during molding. These issues may result in relatively low surface contact between the carbon fibers and the resin. Due to these issues, carbon fiber reinforced SMC parts have not yet met the required mechanical performance for some applications. An economical and effective method to improve the carbon fiber separation in the carbon fiber SMC process may improve final part performance.
An example of a partially separated carbon tow 10 is shown in FIG. 1. A carbon tow is a bundle of individual carbon fiber filaments or strands 12 that form a larger strand. Carbon tows may be woven together into cloth or a weave. Carbon tows may be defined or classified by size, such as 3 k, 6 k, 12 k, 24 k, 36 k, 48 k, or higher, where the “k” represents a thousand filaments. For example, a 12 k carbon tow may include 12,000 carbon filaments. Carbon tows may come in a variety of sizes, and the size chosen may depend on the application. The diameter of the filaments may also vary depending on the desired properties or the application. The diameter of the filaments may vary, for example, from 1 to 25 microns, or sub-ranges therein, such as 5 to 15 microns or 5 to 10 microns.
The production of carbon fiber and carbon fiber tows is known in the art, and will not be described in detail. In general, the production of carbon fiber tows includes the steps of polymerization, spinning, oxidation, carbonization, and surface treatment. However, there are multiple methods for producing carbon fiber tows and any method may be compatible with the present disclosure. Polymerization generally includes converting a polymeric feedstock (e.g., precursor) into a material that can be formed into fibers. In general, fibers may be formed from polyacrylonitrile (PAN), made from acrylonitrile, however fiber may also be formed from other precursors such as rayon or pitch-based precursors. The precursor may be in a powder form and may be dissolved in a solvent, such as an organic or aqueous solvent, to form a slurry.
Fibers may be formed by spinning, such as wet spinning. The slurry may be immersed in a coagulant and extruded through holes in a bushing or spinneret having a number of holes that matches the desired filament count of the tow. The wet-spun fiber may be washed, dried, and stretched. While wet spinning is one approach to forming carbon fibers, others known in the art may also be used. After drying, the fibers may be wound, for example, onto bobbins.
The fibers, which may be wound or rolled, may then be inserted or fed through one or more ovens during the oxidation step. The oxidation temperature may range from about 200° C. to 300° C. The process may cause the polymer chains to crosslink and increase in density. The oxidized fibers may contain about 50 to 65 percent carbon molecules after oxidation, with elements such as hydrogen, nitrogen and oxygen forming the balance.
In the carbonization step, the fibers are heated again but in an inert or oxygen-free atmosphere. Without oxygen, non-carbon molecules are removed from the fibers. The carbonization step may include heating at one or more temperatures, for example, a first, lower temperature and a second, higher temperature. The temperatures may range, for example, from 700° C. to 1500° C. The fibers may held in tension throughout the production process. During carbonization, crystallization of the carbon molecules occurs and the finished fiber may be more than 90 percent carbon.
After carbonization, the fibers may receive a surface treatment and/or a coating named sizing. The surface treatment may include pulling the fiber through an electrochemical or electrolytic bath that contains solutions to etch or roughen the surface of each filament. A coating, generally called sizing, may then be applied to the fibers. The sizing is intended to protect the carbon fibers during handling and processing so that the fiber surfaces are not scratched or damaged. After the sizing is applied and has dried, the fiber tows are generally bundled or wound-up for later use (e.g., on bobbins).
In order to form a carbon fiber reinforced SMC component, it may be beneficial to separate or split the carbon fiber tow (e.g., the finished tow) into individual filaments. This may improve wet-out of the filaments and increase the surface area contact between the fibers and the resin, leading to improved properties of the SMC component (e.g., load transfer). Previous approaches to splitting the tows have included mechanical methods to physically separate the fiber filaments. These methods can damage the fiber surface during the process and generally only split large fiber tows into relatively smaller fiber tows.
With reference to FIGS. 2-5C, embodiments of a method for separating or splitting fiber tows are shown. In addition, embodiments of a system for splitting fiber tows are shown and described. While the embodiments may be described using carbon tows as an example, other types of fiber tows may be used in the methods, systems, and components and such use is contemplated herein. For example, glass fiber tows, ceramic fiber tows, polymer fiber tows, or others may be used.
An alternative to mechanically separating the filaments of a tow, for example, by using rollers with projections extending therefrom or applying high pressure fluid to the tow has been discovered. It has been found that reduced or low pressure may be used to separate the filaments in a more gentle fashion, without causing as much surface damage or breakage to the filaments. With reference to FIG. 2, a system 20 is shown for separating the filaments of a fiber two to increase the width of the tow and the spacing between the filaments of the tow. Accordingly, the total surface area of the tow may be increased, which may allow better resin wet-out and improved surface contact between the carbon fibers and the resin during the production of a composite.
In at least one embodiment, the system 20 may include a chamber (e.g., vacuum chamber) or form 22. The form 22 may be referred to as a tow expander or separator. The form 22 may have a body 24, which may define a hollow interior 26. The body may be formed of a rigid material that is able to withstand a substantial pressure difference (e.g., as described below) between the hollow interior 26 and the exterior of the form 22 (e.g., the atmosphere). For example, the body 24 may be formed of a metal or a rigid plastic. The walls of the body 24 defining the hollow interior 26 may be smooth (e.g., low surface roughness) in order to prevent damage to the fiber tow as it passes through. For example, if the body 24 is metal, it may be polished. The form 22 may have a first end 28 and a second end 30. The first end 28 may be a tow receiving or entering end, while the second end 30 may be a tow exiting end. The first end 28 may define a first opening 32 that is configured to receive a tow. The tow may be received by the first opening 32, pass or extend through the body 24 and exit from a second opening 34 defined by the second end 30.
The first end 28 may include a sealing member 36 extending around at least a portion of the first opening 32. In one embodiment, the sealing member 36 extends around an entire perimeter of the first opening 32. The sealing member 36 may be flexible such that it may conform to the shape of the tow when the tow passes through the first opening 32. The sealing member may be formed of a rubber or other elastomeric material. In at least one embodiment, the first opening 32 may be sized to have a same or similar shape as the cross-section of a fiber tow. Fiber tows may generally have a rectangular or roughly rectangular cross-section, having a relatively large width and a relatively small height. Accordingly, the first opening 32 may also have a rectangular or roughly rectangular cross-section, having a relatively large width (W1) and a relatively small height (H1) with dimensions that are the same or substantially the same as a fiber tow. For example, the tow width may occupy from 95 to 100% of the width (W1), such as 97 to 100% or 99 to 100%. Therefore, the dimensions of the first opening 32 may vary depending on the size of the tow. For example, a 12 k tow may have a smaller width than a 48 k tow, therefore, a form 22 for a 12 k tow may have a first opening 32 that is smaller than a form 22 for a 48 k tow.
Accordingly, when a tow enters and extends through the first opening 32 having dimensions the same or very similar to the tow, the sealing member 36 may conform to the tow to form at least a partial seal with the tow. As used herein, a partial seal may refer to a seal that allows some airflow and/or balancing of pressure but that still allows a significant differential in pressure on either side of the seal to be generated and maintained. For example, if the pressure outside of the form 22 is at ambient pressure (e.g., 1 atm or 760 torr) then the partial seal may allow for an internal pressure within the body 24 of significantly less than ambient pressure (e.g., less than 0.5 atm or 380 torr). In contrast, if the first opening 32 was larger than the tow by a substantial amount, then there may be no seal formed and no significant pressure differential may be maintained. In other embodiments, a complete seal or a nearly complete seal may be formed between the tow and the first opening 32.
The second end 30 may also include a sealing member 38 extending around at least a portion of the second opening 34. The sealing member 38 may be formed of the same or similar materials to the sealing member 36 (e.g., rubber or elastomer). In one embodiment, the sealing member 38 extends around an entire perimeter of the second opening 34. The sealing member 38 may be flexible such that it may conform to the shape of the expanded or separated tow when the tow passes through the second opening 34 and exits the form 22. When a tow exits through the second opening 34, the sealing member 38 may conform to the expanded/separated tow to form at least a partial seal with the expanded/separated tow. The term partial seal may have a similar meaning to that described above. In other embodiments, a complete seal or a nearly complete seal may be formed between the expanded/separated tow and the second opening 34.
As described above, fiber tows may generally have a rectangular or roughly rectangular cross-section, having a relatively large width and a relatively small height. The second opening 34 may also have a rectangular or roughly rectangular cross-section, having a relatively large width and a relatively small height. However, the dimensions of the second opening 34 may be different than the tow's original dimensions (e.g., just prior to entering the first opening 32). As described in greater detail below, the tow may be expanded or separated within the form 22 such that it has a greater width when it exits the form 22 through the second opening 34. Therefore, the dimensions of the second opening 34 may be configured to have a larger width (W2) than the original tow. The expanded tow may have a width that is the same or substantially the same as the width (W2) of the second opening 34 when it exits the second opening 34. For example, the expanded tow width may occupy from 95 to 100% of the width (W2), such as 97 to 100% or 99 to 100%.
The width of the second opening 34 may correspond to a desired expanded tow width. The expansion or separation of the tow may be defined in terms of percent expansion or separation. For example, the separated tow may have a width that is at least 25% larger than the original tow width (e.g., 1.25× the original width). In one embodiment, the separated tow may have a width that is at least 50%, 100%, 150%, 200%, 250%, or 300% larger than the original tow (e.g., 1.5×, 2×, 2.5×, 3×, 3.5×, or 4× the original width). Even greater expansion may be possible, however, may not be required for sufficient improvement in resin wet-out.
In addition to the second opening 34 being wider than the original tow, it may also have a height (H2) that is smaller than the original tow. As the separated tow becomes separated or expanded in the width direction, it may become shorter in height. Accordingly, the second opening 34 may have a height that is smaller than the original tow. The reduction is height may or may not match the increase in width. For example, if the second opening 34 is 100% larger in width (2×), it may be 50% of the original height (½×). However, a 1:1 ratio in change is not necessary. In some embodiments, the reduction in height may be less than the increase in width (e.g., 2×width, ¾× height).
A fiber tow, for example a carbon fiber tow, may have a range of widths depending on the tow and/or filament size. In one embodiment, the tow may have a width of 3 to 25 mm, or any sub-range therein, such as 3 to 20 mm, 3 to 15 mm, 5 to 15 mm, 5 to 10 mm, 10 to 15 mm, 7 to 13 mm, or others. Accordingly, the first opening 32 may have a width that is the same or similar to the tow width (e.g., same ranges as above). Similarly, a fiber tow may have a range of heights depending on the tow and/or filament size. In one embodiment, the tow may have a height or thickness of 10 to 250 μm, or any sub-range therein, such as 25 to 250 μm, 25 to 200 μm, 25 to 150 μm, 50 to 250 μm, 50 to 200 μm, 50 to 150 μm, 50 to 100 μm, 25 to 75 μm, or others. Accordingly, the first opening 32 may have a height that is the same or similar to the tow height (e.g., same ranges as above).
As described above, the second opening 34 may have a width that is larger than the first opening 32 and larger than the original tow width. For example, it may be 50%, 100%, 150%, 200%, 250%, or 300% larger than the original tow. Accordingly, the width of the second opening 34 may be 50%, 100%, 150%, 200%, 250%, or 300% larger than the values described above for the width of the first opening 32. In one embodiment, the width of the second opening may be from 5 to 100 mm, or any sub-range therein, such as 5 to 75 mm, 10 to 100 mm, 10 to 75 mm, 10 to 50 mm, 15 to 75 mm, 15 to 50 mm, 10 to 30 mm, 15 to 30 mm, or others. As described above, the second opening 34 may have a height that is the same or smaller than the first opening 32. Accordingly, the second opening 34 may have a height that is the same or smaller than the values described above for the first opening.
As described above, the disclosed system may use low or below ambient pressure to expand and/or separate the fiber tow. In at least one embodiment, the system may include one or more (e.g., a plurality) of vacuum hoses or tubes 40 connected or coupled to one or more vacuum sources 42, such as vacuum pump(s). The vacuum hoses may attach to the form 22 at ports 44. For example, there may be a port 44 for each vacuum hose 40. The vacuum hoses 40 may couple or attach to the ports 44 in any suitable manner, such as through a threaded coupling, a snap-on coupling, adhesive, fasteners, interference/friction fit, or other methods. The attachment may be permanent or detachable/releasable. In one embodiment, there may be one or more vacuum hoses 40 connected to each of the top and bottom of the form 22 (e.g., the larger sides, or trapezoidal sides).
In operation, the vacuum source 42 may lower the pressure within the hollow interior 26 of the body 24 of the form 22 by removing air via the vacuum hoses 40 and ports 44. The pressure may be reduced while a fiber tow is being pulled into the first opening 32, through the body 24, and exiting from the second opening 34. Accordingly, the fiber tow may be at a relatively high air/atmospheric pressure just prior to entering the form 22 (e.g., standard atmospheric pressure—1 atm or 760 torr). When the tow enters the hollow interior 26 of the form 22, which is at a lower pressure, the filaments of the fiber tow may be urged or driven to expand or separate by the reduced pressure. The filaments of the tow may expand to the size/width of the cross-sectional area of the body 24 as a result of the reduced pressure. Accordingly, when the tow exists through the wider second opening 34, the tow may have expanded to the width of the second opening 34, or close thereto.
The strength of the vacuum may be any reduced pressure sufficient to separate and expand the fiber tow (e.g., to the size of the hollow interior and/or second opening 34). The magnitude of the pressure reduction required may depend on factors such as the size of the tow (width and/or number of filaments), the size of the second opening (e.g., amount of desired expansion), the length of the body 24 of the form 22, the speed of the fiber tow, or others. In at least one embodiment, the pressure within the body 24 may be reduced to half or less than the ambient or exterior pressure. For example, if the exterior of the form 22 is at standard atmospheric pressure of 1 atm or 760 torr, the pressure within the body 24 may be reduced to 0.5 atm (380 torr) or less. In one embodiment, the pressure within the body 24 may be reduced to 100 torr or less, such as 10 torr or less, 1 torr or less, 10⁻¹torr or less, or 10⁻²torr or less. Even lower pressures may also be used, however, they may be unnecessary to expand the tow to the extend necessary.
With reference to FIG. 3, a schematic of a fiber tow 50 being expanded by a form 52 is shown. The fiber tow 50 has an initial width 54 prior to entering the form 52. Within the form 52, the reduced pressure may cause the tow 50 to expand and/or separate. The tow may expand to the size of the form 52. Accordingly, the width of the form 52 may increase from the side where the tow enters to the side where the tow exits, which may allow the tow to expand as it extends through the form 52.
In the embodiment shown, the width of the form 52 continuously increases from one side to the other, which may allow the tow to similarly continuously increase in width. However, the form need not continuously increase in width, as long as the exit is larger than the entrance. For example, the width of the form 52 may increase in steps, wherein the width is constant for a certain length and then increases, then is constant for a certain length, and increases again, etc. The width of the form 52 may increase linearly (e.g., at a constant rate), as shown, or it may increase at a changing rate, such as parabolic, exponential, or other rates. The tow 50 may expand or separate to fill or substantially fill the width of the form 52 along its length, regardless of the shape of the form 52. When the tow 50 exits the form 52, it may have an expanded or separated width 56 that is larger than the initial width 54. The magnitude of the increase may depend on the geometry of the entrance and exit, as described above.
To initiate the process shown in FIG. 3, the tow 50 may be initially manually, mechanically, or otherwise spread to the separated width 56. This may cause the tow to fill or substantially fill the opening in the second end, which may allow the sealing member around the second opening to form at least a partial seal with the separated tow. Once the at least partial seal is formed, the vacuum source and hoses may reduce the pressure within the form 52. The reduced pressure may then separate or expand the tow without further manual or mechanical separation as the tow is pulled through the form 52.
With reference to FIGS. 4A-4C, example end views and a side view of a form 60 are shown, according to an embodiment. FIG. 4A shows a front end view showing a first end 62 of the form 60 including a first opening 64 and a sealing member 66 surrounding the first opening 64. FIG. 4B shows a back end view showing a second end 68 of the form 60 including a second opening 70 and a sealing member 72 surround the second opening 70. As shown, the first opening 64 has a smaller width than the second opening 70, which may allow the tow to expand from when it enters the first opening 64 to when it exits the second opening 70. The first opening 64 may have a larger height than the second opening 70, as shown, however, it is not required. FIG. 4C shows a side view with the first end 62 on the left and the second end 68 on the right. One of two opposing side walls 74 is shown. If the height of the second opening 70 is smaller than the first opening 64, then the side walls 74 may have a decreasing height from the first end 62 to the second end 68.
With reference to FIGS. 5A-5C, example top and/or bottom views of the form 60 are shown, according to several embodiments. FIG. 5A shows a form 60 where the width increases at a constant rate from the first end 62 to the second end 68. The top/bottom of form 60 may have a trapezoidal or truncated triangle shape. FIG. 5B shows a form 60 where the width increases for a certain length, then remains constant for a length, and then repeats. While two regions of increasing width are shown, there may be more. FIG. 5C shows a form 60 where the width increases at a changing rate from the first end 62 to the second end 68 (e.g., curved or parabolic). The top/bottom of the form in FIG. 5C may be referred to as bell-shaped. The length of the form 60 from the first end (entrance) to the second end (exit) may vary depending on the shape of the form and the rate of change in the width of the form. A form with a more gradual width increase may be longer and a form with a more sharp width increase may be shorter to achieve the same total change in width. In one embodiment, the form 60 may have a length of 0.5 to 10 inches, or any sub-range therein, such as 1 to 10 inches, 1 to 8 inches, 1 to 5 inches, 2 to 8 inches, 2 to 5 inches, or others.
With reference to FIG. 6, a system 100 is shown for splitting fiber tows 102. The system 100 may receive a tow 102, or multiple such tows 10. The tow(s) 102 may be expanded tows that have been separated using the disclosed methods and systems, above. The tow 102 may be received by the system 100 in any suitable way. FIG. 6 shows the tow 102 received via rollers 104, however, others methods may be used, such as a conveyor. The system 100 may include a cutter or chopper 106 to chop the tow 102 into shorter tows or segments 108. The shorter segments 108 may have any length suitable for use in a composite component. In one embodiment, the segments 108 may have a length of 1 to 100 mm, or any sub-range therein. For example, the segments may have a length of 1 to 75 mm, 5 to 75 mm, 1 to 50 mm, 5 to 75 mm, 10 to 75 mm, 20 to 60 mm, 25 to 55 mm, 1 to 2 inches, or other sub-ranges. The chopper 106 may be a separate component, or may be incorporated into the rollers 104. The chopper 106 may be any device capable of cutting the tow 102. The chopper 106 or chopper materials may vary depending on the type of fiber in the tow, such as carbon fiber, glass fiber, polymer fiber, etc.
After the tow 102 is chopped into shorter segments 108, the segments 108 may fall to a receiving surface 110, below. The receiving surface 110 may be stationary or it may be moving. For example, the surface 110 may be a conveyor belt. As a result of falling from the chopper 106 to the receiving surface 110, the segments 108 may be randomly oriented when they land on the receiving surface 110. These segments may be transferred to another system for incorporating the segments into a composite component, for example, a fiber reinforced SMC component (e.g., carbon fiber). In another embodiment, the receiving surface 110 may form part of a SMC process. For example, the receiving surface 110 may be a carrier film (e.g., polymer film) having a resin applied thereon. Therefore, the segments 108 may fall directly onto the resin-carrying film and a second carrier film having a resin applied thereon may be applied on top of the segments to form a fiber reinforced SMC material (e.g., carbon fiber). The SMC material may be compacted (e.g., by rollers) and stored for later use, such as on a take-up roll. Alternatively, the SMC material may be transported for immediate or semi-immediate further processing, such as a molding operation.
Accordingly, embodiments of a system and method for separating a fiber tow are disclosed. The fiber tow may be separated or split into a wider and more spread-out tow without mechanically separating the filaments. This may reduce the amount of damage to the filaments during the splitting process, resulting in higher quality filaments. The fiber tow may be a carbon fiber tow, however, other types of fiber tows may be split using the disclosed system and method. The disclosed system and method may allow carbon tows to be more completely separated than mechanical methods and may address some of the challenges specific to carbon tows, such as their generally smaller diameter compared with glass fibers and sizing materials that may be coated on the carbon fiber surface. The disclosed system and method may be used to produce any type of fiber reinforced component, such as fiber reinforced SMC components. In one embodiment, the system and method may be used to form vehicle components. For example, the system and method may be used to form decklids, hoods, bumpers, or other parts.
While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.

Claims

What is claimed is:

1. A system, comprising:

a chamber defining first and second openings and a hollow interior therebetween;

the first opening configured to receive a fiber tow;

the second opening being wider than the first opening; and

a vacuum source communicating with the chamber and configured to reduce an air pressure in the hollow interior and expand the fiber tow.

2. The system of claim 1, further comprising a sealing member extending around the first opening and configured to engage the fiber tow.

3. The system of claim 2, wherein the sealing member is made of rubber.

4. The system of claim 1, further comprising a sealing member extending around the second opening and configured to engage the expanded fiber tow as it exits the second opening.

5. The system of claim 1, wherein the second opening is at least 50% wider than the first opening.

6. The system of claim 1, wherein the second opening is at least 200% wider than the first opening.

7. The system of claim 1, wherein the first opening has a width of 3 to 20 mm and the second opening has a width of 5 to 75 mm.

8. The system of claim 1, wherein a width of the hollow interior continuously increases from the first opening to the second opening.

9. The system of claim 1, further comprising one or more hoses coupled to the chamber and the vacuum source.

10. The system of claim 1, wherein the vacuum source is configured to reduce the air pressure in the hollow interior to 1 torr or less.

11. A method, comprising:

pulling a fiber tow having an initial width into a first chamber opening, through a hollow chamber interior, and out of a second chamber opening; and

reducing an air pressure within the hollow chamber interior to separate the fiber tow residing in the hollow chamber interior into an expanded fiber tow having a width greater than the initial width.

12. The method of claim 11, wherein the second chamber opening is wider than the first chamber opening and reducing the air pressure within the hollow chamber interior separates the fiber tow into an expanded fiber tow having a width that is substantially the same as a width of the second chamber opening.

13. The method of claim 11, wherein a sealing member extends around a perimeter of the first chamber opening and pulling the fiber tow into the first chamber opening forms at least a partial seal between the fiber tow and the sealing member.

14. The method of claim 11, wherein a sealing member extends around a perimeter of the second chamber opening and pulling the fiber tow out of the second chamber opening forms at least a partial seal between the expanded fiber tow and the sealing member.

15. The method of claim 11, wherein the reducing step includes reducing the air pressure within the hollow chamber interior to 1 torr or less.

16. The method of claim 11, wherein the reducing step includes reducing the air pressure within the hollow chamber interior using a vacuum hose coupled to the hollow chamber interior and to a vacuum source.

17. The method of claim 11, wherein the reducing step includes reducing the air pressure within the hollow chamber interior to separate the fiber tow into an expanded fiber tow having a width that is at least 100% greater than the initial width.

18. The method of claim 11, further comprising chopping the expanded fiber tow into a plurality of expanded fiber tow segments and incorporating the expanded fiber tow segments into a sheet molding compound material.

19. The method of claim 11, wherein the fiber tow is a carbon fiber tow.

20. A method, comprising:

pulling a carbon tow having an initial width into a first chamber opening, through a hollow chamber interior, and out of a second chamber opening; and

reducing an air pressure within the hollow chamber interior to 100 torr or less to separate the carbon tow residing in the hollow chamber interior into an expanded carbon tow having a width at least 50% greater than the initial width.