U.S. patent application number 10/138555 was filed with the patent office on 2003-11-06 for process and apparatus for determination of fiber length in reinforced thermoplastic composites.
Invention is credited to Rannenberg, Chris, Weber, Charles.
Application Number | 20030205508 10/138555 |
Document ID | / |
Family ID | 29269370 |
Filed Date | 2003-11-06 |
United States Patent
Application |
20030205508 |
Kind Code |
A1 |
Weber, Charles ; et
al. |
November 6, 2003 |
Process and apparatus for determination of fiber length in
reinforced thermoplastic composites
Abstract
The present invention comprises a method for determining the
average length of a reinforcing fiber of a composite material
comprising a resin and a plurality of reinforcing fibers
encapsulated therein. In addition, a fiber separating apparatus for
dividing a sample of reinforcing fibers into fractions defined by
the relative lengths of the reinforcing fibers is also
disclosed.
Inventors: |
Weber, Charles; (Onalaska,
WI) ; Rannenberg, Chris; (Winona, MN) |
Correspondence
Address: |
Christopher J. McLaughlin
Moore & Hansen
2900 Wells Fargo Center
90 South Seventh Street
Minneapolis
MN
55402
US
|
Family ID: |
29269370 |
Appl. No.: |
10/138555 |
Filed: |
May 3, 2002 |
Current U.S.
Class: |
209/17 ;
209/728 |
Current CPC
Class: |
B29B 17/02 20130101;
Y02W 30/62 20150501; B29B 2017/0224 20130101; B29K 2105/06
20130101; B07B 1/02 20130101; B07B 2230/01 20130101; Y02W 30/523
20150501; Y02W 30/622 20150501; Y02W 30/52 20150501; B29B 17/0206
20130101; B07B 1/06 20130101 |
Class at
Publication: |
209/17 ;
209/728 |
International
Class: |
B03B 007/00 |
Claims
What is claimed is:
1. A fiber separating mechanism comprising: a top section
comprising a hollow cylinder having a length sufficient to enclose
therein a predetermined volume; a screen section comprising a
hollow cylinder of substantially the same diameter as the top
section, the screen section having a predetermined height and a
membrane of screen cloth stretched entirely across the inner
diameter thereof; and a bottom section comprising a hollow cylinder
having a closed bottom end, the top section, screen section and
bottom section being capable of being coupled to one another so as
to form a single hollow cylinder having a closed bottom end.
2. The fiber separator of claim 1 further comprising a plurality of
screen sections, the plurality of screen sections having
successively finer screen cloth membranes in each successively
lower screen section.
3. The fiber separator of claim 1 wherein each of the sections of
the fiber separator is constructed and arranged to be threadedly
connected to the other sections of the fiber separator.
4. A method of determining an average length of a reinforcing fiber
in a composite material comprising a resin and a plurality of
reinforcing fibers, the method comprising the steps of: obtaining
an appropriately sized sample of the composite material; removing
the resin from the composite material by exposing the sample of
composite material to an elevated temperature for a predetermined
period of time; annealing the reinforcing fibers; weighing the
resulting sample of reinforcing fibers to obtain a sample weight;
placing the sample of reinforcing fibers from the composite
material in a fiber separating mechanism to divide the sample of
reinforcing fiber into a plurality of fractions, each fraction
comprising reinforcing fibers of substantially the same size;
weighing the plurality of fractions; and calculating an average
fiber length from the relative weights of each of the plurality of
fractions and the weight of the total reinforcing fiber sample.
5. A method of claim 4 wherein the ratio of the diameter of the
sample of composite material to the length of the sample of
composite material is at least 1:25.
6. The method of claim 4 wherein the sample of composite material
is gradually heated to remove the resin therefrom starting at a
temperature of between 0.degree. and 30.degree. C. and rising to a
temperature of approximately 350.degree. C. at a rate of no more
than 10 degrees Celsius per minute.
7. The method of claim 6 wherein the sample of composite material
is subsequently exposed to a temperature of approximately
550.degree. C. for approximately two hours.
8. The method of claim 7 wherein the sample of composite material
is subsequently cooled to a final temperature of between 0.degree.
and 30.degree. C. at a rate of no more than 20.degree. C. per
minute.
9. The method of claim 4 wherein the fiber separator comprises: a
top section comprising a hollow cylinder having a length sufficient
to enclose therein a predetermined volume; a screen section
comprising a hollow cylinder of substantially the same diameter as
the top section, the screen section having a predetermined height
and a membrane of screen cloth stretched entirely across the inner
diameter thereof; and a bottom section comprising a hollow cylinder
having a closed bottom end, the top section, screen section and
bottom section being capable of being coupled to one another so as
to form a single hollow cylinder having a closed bottom end.
10. The method of claim 9 wherein the fiber separator is filled
with water and the sample of reinforcing fibers is placed in the
water in the fiber separator.
11. The method of claim 10 wherein the water within the fiber
separator is generally stirred for 10 seconds after which the water
is allowed to settle for 15 seconds, this cycle being repeated a
predetermined number of times.
12. The method of claim 11 wherein the stir/rest cycle is repeated
at least three times.
13. The method of claim 9 wherein the bottom portion is removed
from the fiber separator so as to allow the water within the fiber
separator to drain out.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] NONE
FIELD OF THE INVENTION
[0002] The present invention relates to the assessment of fiber
lengths in reinforced thermoplastic composites. More specifically,
the present invention relates to a method whereby fibers are
extracted from a fiber reinforced thermoplastic composite and
separated according to length to determine an average fiber length
in the sample of the reinforced thermoplastic composite.
BACKGROUND OF THE INVENTION
[0003] In ensuring the uniformity of the physical properties of a
given fiber reinforced thermoplastic composite, it is necessary to
determine whether a given sample of composite material does indeed
contain fibers of a specified length. In the past, this was
accomplished by burning off the thermoplastic resin portion of the
composite, leaving behind the reinforcing fibers. The reinforcing
fibers would then be picked up using an electrostatically charged
brush, typically fashioned of camel hair, and placed on a sampling
surface such as a Petri dish. Those fibers deposited upon a
predetermined portion of the Petri dish would then be counted and
their sizes measured. This process would be repeated until a
predetermined number of fibers had been counted and measured,
thereby permitting the calculation of an average fiber length.
[0004] As can be appreciated, this statistical sampling method is
time consuming and yields only approximate results at best. More
often, the results yielded by this sampling method skew the test
results such that the average fiber lengths are reported as being
shorter than what actually exists in the sample of composite
material. Typically, this is due to breakage of the reinforcing
fibers that had been embrittled in the burn-off process in which
the fibers were removed from the thermoplastic resin. In addition,
because the electrostatic charges present within a camel hair brush
commonly used in this process can vary from moment to moment and
day to day depending on many environmental factors including
humidity, the size and number of reinforcing fibers that may be
picked up in a given sampling would not be uniform. As can be
appreciated, when the electrostatic forces on the camel hair brush
are relatively strong, longer fibers would be picked up by the
brush. Conversely, where the electrostatic charge on the brush was
relatively low, only shorter fibers would be picked up. Therefore,
the results of this prior art type of statistical sampling are
variable and tend to report smaller average fiber lengths than what
exist in reality.
[0005] In order to overcome these problems, the present invention
comprises a burn-off procedure in which the reinforcing fibers are
annealed, thereby preventing fiber embrittlement that might
otherwise increase breakage during the testing process. In
addition, the present invention comprises a fractionation process
and apparatus that accounts for all of the fibers in a given sample
of composite material. In this manner, more accurate results may be
obtained. In addition, the process and apparatus of the present
invention is faster and easier to use.
SUMMARY OF THE INVENTION
[0006] The present invention comprises a method of determining an
average length of a reinforcing fiber in a composite material. The
method begins with the step of calculating an appropriate size for
the sample of composite material. Once this has been completed a
sample of the composite material having approximately the
calculated sample size is then obtained. Preferably the ratio of
the diameter of the sample of composite material to its length is
at least 1:25. This ration limits the number of fibers in the
sample that are cut in obtaining the sample. Now that the sample
has been obtained the resin is removed from the composite material
by exposing the sample of composite material to an elevated
temperature for a predetermined period of time, after which the
reinforcing fibers are annealed to minimize or eliminate breakage
of the reinforcing fibers. This process is referred to as
"burning-off" the resin. The reinforcing fibers are then weighed to
obtain a sample weight.
[0007] Preferably the resin is removed from the reinforcing fibers
of the composite material by gradually heating the composite to
predetermined temperature, holding the composite material at that
predetermined temperature for a chosen length of time, and then
gradually cooling the remaining reinforcing fibers, The first part
of this process, i.e. gradually heating the composite material and
holding it at a predetermined temperature, removes the resin by
burning and melting it away. A suitable heating regimen has been
found to start at a temperature of between approximately 0.degree.
C. and 30.degree. C., rising to a temperature of approximately
350.degree. C. at a rate of no more than 10.degree. C. per minute.
Once the composite material has reached approximately 350.degree.
C., the temperature may be raised relatively quickly to 550.degree.
C., where it is held for approximately two hours. Once the resin of
the composite material has been burned away, the remaining
reinforcing fibers are annealed by gradually cooling the fibers at
a rate of no more than 20.degree. C. per minute. The second part of
the burning-off process comprises an annealing step that reduces
internal stresses in the reinforcing fibers, thereby resulting in a
sample of reinforcing fibers that are relatively strong and
flexible. This annealing step helps prevent breakage of the fibers
that might skew the results of the testing process.
[0008] The sample of annealed reinforcing fibers is next placed in
a fiber separating mechanism to divide the sample of reinforcing
fiber into a plurality of fractions wherein each fraction comprises
reinforcing fibers of substantially the same size. Each of the
fractions is then weighed and an average fiber length is calculated
from the total weight of the reinforcing fibers and the weights of
each of the plurality of fractions.
[0009] A suitable fiber separator comprises a top section that
preferably takes the shape of a hollow cylinder having a length
sufficient to enclose therein a predetermined volume, a screen
section that also preferably takes the shape of a hollow cylinder
of substantially the same diameter as the top section, and a bottom
section also preferably taking the shape of a hollow cylinder but
having a closed bottom end. The screen section has a predetermined
height and a membrane of screen cloth stretched entirely across its
inner diameter. The top section, screen section and bottom section
of the fiber separator are capable of being coupled to one another
so as to form a single hollow cylinder having a closed bottom
end.
[0010] In use the fiber separator is filled with water and the
sample of reinforcing fibers is placed in the water in the top
section of the fiber separator. Preferably the water within the
fiber separator will be gently stirred for 10 seconds after which
the water is allowed to settle for 15 seconds, this cycle being
repeated a predetermined number of times and preferably at least
three times. Once the reinforcing fibers have been allowed to
settle, the bottom portion of the fiber separator is removed and
the water is drained out of the separator. The fiber separator is
then disassembled and the respective screen portions are dried and
then weighed to obtain the weight of the fractions of the fiber
material. The method and apparatus of the present invention permit
the simple, accurate and rapid assessment of reinforcing fiber size
in fiber reinforced thermoplastic composite materials.
[0011] These and other objectives and advantages of the invention
will appear more fully from the following description, made in
conjunction with the accompanying drawings wherein like reference
characters refer to the same or similar parts throughout the
several views.
DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is an exploded view of a fiber separator.
[0013] FIGS. 2-6 are top plan views of portions of the fiber
separator of FIG. 1 taken along the respective view lines 2-2 to
6-6 respectively.
[0014] FIG. 7 is an elevational view of the fiber sorter of FIG. 1
as assembled.
DETAILED DESCRIPTION OF THE INVENTION
[0015] Although the disclosure hereof is detailed and exact to
enable those skilled in the art to practice the invention, the
physical embodiments herein disclosed merely exemplify the
invention which may be embodied in other specific structure. While
the preferred embodiment has been described, the details may be
changed without departing from the invention, which is defined by
the claims.
[0016] The present invention comprises a method for extracting
reinforcing fibers from a composite material and analyzing those
reinforcing fibers to determine an average length. A fiber
separator 10 is utilized to separate the reinforcing fibers into
groups of substantially identical length. Typically, the method of
the present invention will be used to analyze composite molding
materials made from a thermoplastic resin and a reinforcing fiber
such as fiberglass. It is to be understood that other types of
composite materials may be analyzed using the method of the present
invention. NAME OTHER TYPES OF COMPOSITE MATERIALS AND REINFORCING
FIBERS HERE.
[0017] The first step of the method of the present invention is to
obtain a suitable sample of a fiber reinforced composite material
for examination. Because the point of the method of the present
invention is to determine the actual average length of fibers
within a particular sample of composite material, it is important
to obtain a sample of the composite material in such a manner that
minimizes the number of reinforcing fibers that would be cut or
otherwise broken in obtaining the sample. Therefore, the
cross-sectional area of the sample of composite material that is to
be cut is to be minimized in comparison with the overall volume of
the desired sample. For example, where the composite material is
being extruded in a simple cylinder form, it is preferred to obtain
a sample that has a length that is at least 25 times the diameter
of the extruded shape. WHAT ARE THE RANGES ON THIS RATIO?
[0018] The quantity of reinforcing fibers in a sample of a
composite material that is to be analyzed must also be taken into
account. It has been found that placing too large a quantity of
reinforcing fibers in a fiber separator 10 (described in detail
hereinbelow) has a tendency to clog the fiber separator 10. This
can, in turn, result in inaccurate results. Therefore, using the
known nominal weight percentage of reinforcing fiber in a composite
material sample, an ideal reinforcing fiber sample size may be
calculated. The magnitude of the ideal reinforcing fiber sample
mass is related to the physical characteristics of the fiber
separator 10, and therefore the exact value may vary. However, in a
preferred embodiment of the present invention it has been
determined that a sample weight of reinforcing fibers of between
0.9 and 1.2 grams of reinforcing fiber provides a statistically
significant quantity of fibers that pass easily through the
respective filters of the fiber separator. NOTE HERE ANY KNOWN
RELATIONSHIPS BETWEEN SORTING MESH SIZE AND IDEAL SAMPLE WEIGHT OF
FIBERS. Given the nominal weight percent of reinforcing fibers in a
given composite material and the desired dimensional ratios as set
forth above, one can easily calculate the dimensions of a suitable
sample of fiber reinforced composite material.
[0019] Once a suitable sample or samples of the composite material
have been secured, the reinforcing fibers of the composite material
must be removed from the resin in which they are embedded.
Typically, this is done by "burning-off" the resins in an oven. The
relatively high temperatures of the oven melt and burn the resin,
leaving behind only the reinforcing fibers of the composite
material. It will be noted that the preferred material of the fiber
reinforced composite material is a glass fiber commonly known as
fiberglass. This type of reinforcing fiber easily withstands the
temperatures necessary to burn off the resins of the composite
material. However, exposure to the high temperatures and the large
temperature gradients present when the sample is first placed in an
oven, and when the sample is removed from the oven, can severely
embrittle the glass reinforcing fibers. Therefore, in a preferred
embodiment of the method of the present invention, the resins of
the composite material are burned off using a gradual temperature
cycle that starts at approximately 0.degree. C., rises gradually
(at approximately 10.degree. C. per minute) to 350.degree. C.,
where it is held for approximately one hour, and then ramped up to
approximately 550.degree. C. at any desirable rate. The sample is
held at approximately 550.degree. C. for approximately two hours.
Immediately thereafter, the temperature in the oven is gradually
reduced down to the initial 0.degree. C. at a rate of approximately
20.degree. C. per minute. The gradual rise and fall of the
aforementioned temperature cycle reduces or eliminates temperature
shocks that would otherwise needlessly embrittle the glass
reinforcing fibers. Consequently, the glass reinforcing fibers of
the sample of composite material are relatively stronger than those
glass reinforcing fibers obtained using prior art methods of
burning off the resins.
[0020] Note that the burn-off temperature cycle given above may
vary in the exact temperatures used and in the time and warming and
cooling rates employed. What is important is to avoid embrittlement
or breakage of the reinforcing fibers that might occur due to
thermal shock. In addition, the physical properties of the
reinforcing fibers themselves may require different burn-off
temperature cycles to properly anneal the fibers.
[0021] Once the glass reinforcing fibers have been fully cooled, it
is necessary to sort all of the fibers into groups based on their
length. This is done using a fiber separator 10 illustrated in
FIGS. 1-7. Referring first to FIG. 1, the fiber separator 10 can be
seen to comprise a top section 12, a plurality of screened sections
14, and an end cup 16. FIG. 1 illustrates the fiber separator 10
prior to assembly while FIG. 7 illustrates the fiber separator 10
as it appears when assembled. The various portions of the fiber
separator 10 comprise means for interchangeably securing the
various portions of the fiber separator 10 to one another in a
watertight manner. Preferably, top section 12 and screen sections
14 comprise a male threaded portion 13, 15, respectively. Note that
these threaded portions 13, 15 extend from the lower edge of the
respective fiber separator portions and meet with a complementary
female threaded portion (not shown) at the top edge of each of the
respective fiber separator portions. In this manner, the respective
portions of the fiber separator 10 may be rapidly assembled or
disassembled and may also maintain a watertight seal therebetween.
Furthermore, by using interchangeable thread sizes, it is possible
to assemble virtually any configuration of portions of the fiber
separator 10. It is to be understood that other structures aside
from a male-female thread structure may be utilized to connect the
portions of the fiber separator 10 to one another without exceeding
the scope of the prevention invention.
[0022] Top section 12 of fiber separator 10 comprises a hollow
cylinder having an uninterrupted bore formed therethrough. See FIG.
2. Screen sections 14 also comprise hollow cylindrical members but
differ from top section 12 in that each screened section 14 has a
section of screen cloth 20 disposed across its entire cross
section. See FIGS. 3-5. The screen cloth 20 of each screen section
14 is constructed and arranged to retain thereon fibers of a
predetermined length and to pass fibers smaller than that
predetermined length therethrough. As will readily be understood,
it is preferred that the uppermost screen section 14 have the
coarsest screen cloth 20, with each successively lower screen
section 14 having a finer screen cloth 20. In this manner, longer
reinforcing fibers will be trapped by the uppermost coarse screen
cloth 20, while successively shorter reinforcing fibers will be
captured by the successively finer screen cloths 20. While only
three screen sections 14 are illustrated, it is to be understood
that more or fewer screen sections 14 may be utilized in various
configurations of fiber separator 10.
[0023] In operation, the respective portions of the fiber separator
10 are connected as illustrated in FIG. 7. The fiber separator 10
is then filled with water and, after the water has settled, a
sample of reinforcing fibers is placed into the top section 12.
Prior to placing the sample of reinforcing fibers in the fiber
separator 10 however, the sample is weighed and the weight
recorded.
[0024] While it is unlikely that the reinforcing fibers may float,
it is possible that the reinforcing fibers may clump together or
otherwise be suspended at the surface of the water in the top
section 12 due to the surface tension of the water. Therefore, it
is preferred to use a small quantity of a dispersal agent such as a
mild dish detergent to break the surface tension in the top section
12 of the fiber separator 10.
[0025] It is preferred to impart a rotational velocity to the water
within the fiber separator 10 so that the reinforcing fibers will
be oriented in a plane that is substantially parallel to that of
the screen cloth 20 of the various screen sections 14. In this
manner the reinforcing fibers will not address the screen cloth 20
longitudinally. While numerous structures and mechanisms may be
utilized to impart a rotary motion to the water within the fiber
separator 10, it is preferred to manually stir the water in a
gentle manner such that no reinforcing fibers are extracted from
the water and any breakage of the fibers is minimized or
eliminated. Preferably, the water in the top section 12 of the
fiber separator 10 is stirred for approximately 10 seconds followed
by a rest period of approximately 15 seconds. This cycle of
stirring and rest is repeated approximately three times. After the
third cycle of stirring and rest has been completed, the end cup
portion 16 of fiber separator 10 is removed. This allows the water
within the fiber separator 10 to drain and also brings any
reinforcing fiber suspended within the water into contact with the
screen cloth 20 of the respective screen sections 14 so as to
categorize the reinforcing fibers according to length.
[0026] Once all the water has drained from the fiber separator 10,
the various portions of the fiber separator 10, 14 are disassembled
and dried to remove any trace of water. Preferably, the screen
sections 14 will be dried using an oven though any suitable drying
mechanism or process may be used. When dry, each screen section 14
is weighed to determine a total weight of the screen section 14
plus the reinforcing fiber fraction disposed on the screen cloth 20
thereof. Next, the tare weight of the screen section 14 is
subtracted from the gross weight of the screen section 14 and
reinforcing fiber sample to obtain the net weight of the fraction
of the reinforcing fiber sample that is deposited on the screen
cloth 20 of the screen section 14. Using the net weights of the
respective fractions of the reinforcing fiber sample that were
deposited upon the respective screen portions 14 of the fiber
separator 10, an average reinforcing fiber length as well as a
distribution of the lengths can accurately and easily be
calculated.
[0027] The foregoing is considered as illustrative only of the
principles of the invention. Furthermore, since numerous
modifications and changes will readily occur to those skilled in
the art, it is not desired to limit the invention to the exact
construction and operation shown and described. While the preferred
embodiment has been described, the details may be changed without
departing from the invention, which is defined by the claims.
* * * * *