Composite tubular rod and method for making same

The present invention is directed to a hollow, flexible rod (20) having a body portion (21), a tip portion (23) and a transition portion (24) between the body and tip portions. A plurality of reinforcing strands (30) of a first material extend longitudinally within the body portion (21) and into the transition portion (24). A plurality of reinforcing strands (31) of a second material extend within the tip portion (23) and into the transition portion (24). The reinforcing strands of the first and second materials overlap one or more integer multiples (N) along the circumference of the rod. The present invention is also directed to the method whereby independent prepreg sheets (26,28) formed of the first and second reinforcing strands (31,30) are cut to a tapered apex (33 or 34) and overlapped to a predetermined, interrelated extent longitudinally (T) and laterally (S). So overlapped, the prepreg sheets (26,28) are simultaneously wound onto a mandrel (29) and cured to produce the aforesaid rod (20).

TECHNICAL FIELD 
The present invention relates to flexible, hollow rods. More particularly, 
the present invention relates to flexible, hollow rods comprising a 
plurality of reinforcing filaments bonded together by a suitable, 
flexible, plastic resin. Specifically, the present invention relates to 
hollow rods having a body portion with preselected bending characteristics 
and a tip portion with preselected, and distinctly different, bending 
characteristics--the said body and tip portions being uniquely 
interconnected through a transition portion located medially of the body 
and tip portions. 
BACKGROUND ART 
Although flexible, high strength, lightweight, tubular rods are desirable 
for a wide variety of usages, such structural configurations are 
particularly suited for fishing rods. 
Over the past three decades numerous materials and designs have been 
employed in the construction of fishing rods, but the use of reinforcing 
filaments embedded in a hard, but flexible, resin have been particularly 
satisfactory. 
Initially, such rods were fabricated with fiberglass strands embedded in 
resin. One of the pioneer patents in this area--U.S. Pat. No. 
2,571,717--taught the use of longitudinally oriented, resin coated, 
fiberglass strands laid over a mandrel and wrapped with a cellophane tape 
until the resin cured. Another approach--as disclosed by U.S. Pat. No. 
2,726,185--was to wrap a resin impregnated fabric comprised of fiberglass 
reinforcing strands onto a mandrel and allow the resin to harden with the 
fabric so wrapped upon the mandrel. Both of these prior art patents 
emphasized the longitudinal orientation of the fiberglass strands to 
impart the necessary flexural strength to the finished rod. 
U.S. Pat. No. 2,749,643 contributed a further advance to the art by 
teaching that the reinforcement achieved by the longitudinally oriented 
fibers would be augmented by the use of a short pitch helical wrap of 
fiberglass strands to impart hoop strength to the arrangement. The 
aforesaid prior art, however, taught that all reinforcing strands in any 
one rod would be of a common material. 
Eventually rods were made which constituted a composite of more than one 
type of reinforcing strand. U.S. Pat. No. 4,061,806 exemplifies the use of 
an intermix of glass fibers and graphite fibers to provide a very 
lightweight, high strength construction. 
Even over and above lightness of weight and high strength, the "action" is 
perhaps one of the most significant characteristics of a fishing rod. 
A typical hollow fishing rod made only of glass strands encapsulated in a 
suitable resin normally would have a modulus of elasticity on the order of 
5.times.10.sup.6 psi. A comparable rod made only of graphite encapsulated 
in a suitable resin would have a modulus of elasticity on the order of 
12.times.10.sup.6 psi. Hence, the graphite rod would be stiffer than its 
fiberglass counterpart. Although each fisherman is somewhat of an 
individualist, a great number appreciate the stiffer response through the 
body portion of the rod but prefer a more flexible tip portion. 
Some initial experiments were made in employing materials of different 
moduli in the body and tip portions, but those attempts effected joinder 
between the different sections of the rod by such means as ferrules or 
adhesive butt-joints. Such joinder techniques effect a sharp demarcation 
between portions of the rod having different flexural characteristics. 
When such a rod is bowed, as when playing a fish, the different flexural 
characteristics on either side of the joinder impart an appearance that 
the rod has some inherent structural flaw which is about to permit the rod 
to break under load. This would be aesthetically unacceptible even if the 
rod were functionally unimpared. 
However, such a joinder is marked by a localized increase in the diameter 
of the rod which not only detracts from the aesthetic appearance thereof 
but also functionally affects stress concentrations across the joinder 
that are highly deleterious to the integrity of the rod. 
DISCLOSURE OF THE INVENTION 
It is, therefore, a primary object of the present invention to provide a 
rod having a tip portion that is relatively more flexible than the body 
portion. 
It is another object of the present invention to provide a rod, as above, 
wherein the joinder of the tip portion to the body portion is accomplished 
with a smooth joinder which is devoid of bumps, ridges or ferrules and 
which is not, therefore, readily detectable by sight or touch either when 
the rod is at rest or in use. 
It is a further object of the present invention to provide a rod, as above, 
wherein the tip portion is reinforced by fiber strands such that the 
composite modulus of elasticity for said tip portion is less than the 
composite modulus of elasticity for the body portion, which is also 
reinforced by fiber strands. 
It is an additional object of the present invention to provide a rod, as 
above, which is fabricated with the fiber reinforcing strands of the body 
portion overlapping those of the tip portion within a transition portion 
located medially of the body and tip portions. 
It is a still further object of the present invention to provide a rod, as 
above, wherein the overlap of the reinforcing strands within the 
transition portion extends one or more integer multiples along the 
circumference of the transition portion of said rod. 
It is yet another object of the present invention to provide a rod, as 
above, that is particularly suited to be a fishing rod. 
It is an even further object of the present invention to provide a method 
for manufacturing a rod, as above. 
It is a still further object of the present invention to provide a method, 
as above, in which the reinforcing strands of the body and tip portions 
are incorporated in separate, flexible prepreg sheets that are cut to 
tapered apices, longitudinally overlapped to a predetermined extent and 
simultaneously wound onto a mandrel to effect the desired circumferential 
overlap in the completed rod. 
These and other objects, together with the advantages thereof over existing 
and prior art forms which will become apparent from the following 
specification, are accomplished by means hereinafter described and 
claimed. 
In general, a method for making rods in accordance with the concept of the 
present invention comprises the steps of forming prepreg sheets from 
reinforcing strands having the desired physical and structural properties. 
The prepreg sheet used to form the body portion of the rod will employ one 
type of reinforcing material, and the prepreg used to form the tip portion 
will employ another type of reinforcing material. 
With the prepreg sheets for the body and tip portions being appropriately 
selected they will be cut in a generally understood manner to be wrapped 
onto a mandrel, but in addition, the two prepregs will be cut uniquely to 
present tapered apices that can be longitudinally overlapped to a 
predetermined extent and then simultaneously wound onto a mandrel. 
Thereafter, the resin in the prepregs will be suitably hardened, and the 
mandrel preferably removed, to complete the rod. 
The resulting rod, which is particularly suitable for fishing, will have a 
body portion, a tip portion and a transition portion between the body and 
tip portions. A plurality of reinforcing strands fabricated from a first 
material extend longitudinally within the body portion and into the 
transition portion. Similarly, a plurality of reinforcing strands 
fabricated from a second material extend longitudinally within the tip 
portion and into the transition portion. The length of the various strands 
are such that those from the body and tip portions circumferentially 
interlaminate within the transition portion only as an integer multiple of 
the circumferential dimension of the rod at the transition portion. 
One preferred embodiment of a rod incorporating the objects of the present 
invention is shown by way of example in the accompanying drawings and 
described in detail, together with a method by which said rod may be 
fabricated, without attempting to show all of the various forms and 
modifications in which the invention might be embodied; the invention 
being measured by the appended claims and not by the details of the 
specification.

DESCRIPTION OF A PREFERRED EMBODIMENT 
As heretofore explained, the wrapping of a prepreg sheet onto a mandrel, 
and then hardening the resin to form a rod, is well known to the art. 
Although the prior art adequately defines a "prepreg" sheet, a complete 
understanding of the present invention may be enhanced by knowing that a 
prepreg sheet constitutes a cloth formed from the desired reinforcing 
fibers. The reinforcing fibers are coated with a suitable resin that is 
latentably hardenable but which remains flexible until it is intentionally 
hardened. The resin binds the adjacent fibers together into a sheet which, 
like cloth, has sufficient integrity that the adjacent fibers are not 
easily separated and yet affords adequate flexibility for the sheet to be 
readily workable, as required to wind the sheet onto a mandrel in 
accordance with the explanation which follows. In a sense, then, the sheet 
has been preimpregnated with resin--hence, the designation "prepreg" 
sheet. 
Historically, when making a tapered rod the prepreg is cut as truncated 
isosceles triangle or, as shown, a right angled trapezoid--Item 10 in FIG. 
1--with two parallel sides 11 and 12 and two nonparallel sides 13 and 14. 
The reinforcing filaments 15 are normally oriented parallel to side 13, 
and side 13 is aligned with the longitudinal axis 16 of the tapered 
mandrel 18. The mandrel is then rotated to wind the prepreg thereabout. 
The lengths of the two parallel sides 11 and 12 are determined by the 
circumference of the mandrel at the location therealong at which the sides 
are to be wrapped, and the number of times the prepreg shall be wrapped 
about the mandrel. This concept is well known to the prior art. 
The present invention expands upon the knowledge imparted by the prior art 
in a most novel and unique manner. Specifically, the knowledge imparted by 
the prior art teaches one how to determine the metes and bounds of the 
perimeter to which the prepreg must conform in order to achieve the 
desired wrap of the prepreg with respect to the body and tip portions per 
se. Hence, the prior art teaches that the dimensions of the parallel sides 
11 and 12 of the prepreg sheet depicted in FIG. 1 must be of sufficient 
magnitude overlappingly to embrace the circumference of the mandrel 18 at 
the location therealong about which the parallel sides would be wrapped. 
A rod 20 (as best seen in FIGS. 4 and 5) embodying the concept of the 
present invention and employed as a fishing rod has a body portion 21 to 
one end of which the handle 22 is secured. A tip portion 23 is presented 
at the end of the rod distal with respect to the handle 22. Medially of 
the body and the tip portions 20 and 23, respectively, is a transition 
portion 24. 
As schematically depicted in FIG. 5, when the fishing rod 20 is in use it 
is generally desired that the body portion 21 will have more spine--i.e., 
the body portion will be relatively stiffer than the remainder of the 
rod--and the tip portion 23 will have considerably greater flexibility. 
The relative stiffness of the body and tip portions of a fishing rod is, 
in the composite, designated as the "action" of the rod. 
The action of the fishing rod is just as important in casting the lure as 
it is to the response of the rod when the fisherman sets the hook or 
subsequently plays the hooked fish. Rod makers fully recognize the 
importance not only of the relative spine, or stiffness, of the body and 
tip portions, but each rod maker also has his own preference as to the 
relative length of the body and tip portions. The present invention is not 
intended to encroach upon the parameters the various rod makers have 
individually established for the relative spine, or the relative lengths, 
of the body and tip portions. Rather, the present invention is directed to 
the means by which the body and tip portions can be joined together to 
assure that flexure consistent with the desired action will be provided 
across the joinder irrespective of the circumferential location on the rod 
along which one might choose to mount the line guides. In addition, the 
present invention affords a smooth transition between the body and tip 
portions--the length of the transition being capable of preselection, 
within a reasonable range, by the rod designer to accommodate his personal 
idiosyncrasies. 
The rod 20 can, according to the concept of the present invention and as 
best seen in FIGS. 2 and 3, be formed from two prepreg sheets 26 and 28 
that are overlapped, as hereinafter more fully explained, and wrapped 
about a mandrel 29. 
The prepreg sheet 26 will form the tip portion 23 of the finished rod 20, 
and as such comprises a fabric made from a reinforcing strands 31 selected 
such that the composite modulus of elasticity for the tip portion 23 will 
provide the degree of flexibility desired by the rod designer for that 
portion of the rod 20. 
Any number of materials may be selected to reinforce the tip portion 23, 
but fibers of glass or Kevlar would be quite suitable. Fiberglass 
reinforced sections may readily be fabricated to provide a composite 
modulus of elasticity in the range of from approximately 4.times.10.sup.6 
psi to approximately 7.times.10.sup.6 psi. Kevlar reinforced sections can 
similarly be fabricated to provide a composite modulus from about 
8.times.10.sup.6 to approximately 11.times.10.sup.6 psi. 
Similarly, the prepreg sheet 28 will form the body portion 21 of the 
finished rod 20, and as such comprises a fabric made from a reinforcing 
material selected such that the composite modulus of elasticity for the 
body portion will provide the stiffness desired by the rod designer for 
the body portion. 
Here, too, any number of materials may be selected for use as the 
reinforcing strands 30. When the rod is to be fabricated so that the body 
portion 21 is stiffer than the tip portion 23, as is generally preferred 
for fishing rods, one might consider using graphite fibers for the 
reinforcing material. It is well within the capability of one skilled in 
the art to fabricate a graphite reinforced body portion having a composite 
modulus of elasticity in the range of from approximately 12.times.10.sup.6 
psi to approximately 25.times.10.sup.6 psi. One might also employ boron 
fibers, which permit a rage of approximately 20.times.10.sup.6 to 
35.times.10.sup.6 psi for the composite modulus of elasticity for such a 
structural section. 
The foregoing examples are, of course, merely exemplary. As time goes by, 
more and more sophisticated materials may become available, and they, too, 
could well be employed within the concept of the present invention. Those 
skilled in the art may also employ more than one type of reinforcing fiber 
within each portion of the rod, as required to achieve the desired modulus 
for a given size of rod section. In fact, for some applications it may 
well be desirable to have thetip portion stiffer than the body portion, or 
perhaps have a tip portion on either end of the body portion. Once the 
basic concept of the present invention is understood, many variations are 
well within the realm of possibility. 
Continuing with the exemplary disclosure of the present invention as it 
relates to the manufacture of a fishing rod having the design parameter 
that the tip portion be relatively more flexible than the body portion, it 
has been noted that for such purpose the composite modulus of the tip 
portion 23 should be at least 2.times.10.sup.6 psi less than the composite 
modulus for the body portion 21. 
The rod designer will next determine the longitudinal dimension "T" he 
desires for the transition portion of the particular rod 20, and with that 
information he can calculate the apex angle .theta. to which the apices 33 
and 34 of the two prepreg sheets 26 and 28, respectively, are to be cut by 
the following formula: 
EQU arc contangent .theta.=T/.pi.ND 
wherein 
T=the longitudinal dimension of the transition portion 24 
N=an integer (preferably an even integer) 
N=the diameter of the mandrel at the location along the mandrel about which 
the sheets are to wrap the even integer number of times designated by N 
In practice it has been found that .theta. should preferably fall within 
the range of from about 40.degree. to approximately 75.degree.. Larger 
angles tend to make the transition portion 24 too short to be most 
effective, and smaller angles similarly tend to make the transition 
portion too long. 
It should also be understood that N is selected to be an even integer so 
that the overlap of the prepreg sheets will span the circumference of the 
mandrel a predetermined number of times. In essence, it is essential that 
the overlapped portions of the sheets wrap around the mandrel an exact 
number of turns. Thus, the span "S" from the coincident edge 27 of the 
overlapped sheets 26 and 28 to the crossover point 32 must be such that as 
the overlapped portions have been wrapped about the mandrel 29 the 
crossover point 32 will be radially superposed with respect to the 
coincident edge 27. This distance "S" must, therefore, constitute an 
integer multiple "n" of the circumference of the mandrel 29. 
Balanced bending strength in the rod is further assured by having the 
crossover point 32 lie halfway between the coincident edge 27 and the 
preferably aligned edges 37 and 38 of the prepreg sheets 26 and 28, 
respectively. Thus, when the prepreg sheets have been fully wrapped onto 
the mandrel the edges 37 and 38 will also be radially superposed with 
respect to the coincident edge 27. As such, the total number of wraps from 
edge 27 to edges 37 and 38 must be an even integer "N", irrespective of 
the integer number "n" of wraps from edge 27 to the crossover point 32. 
The span, therefore, from edge 27 to edges 37 and 38 must constitute an 
even integer multiple "N" of the circumference of the mandrel 29. Were the 
overlapping wraps to constitute a fractional number of turns, the 
resulting rod would not possess uniform bending strength in all 
directions. 
Were one arbitrarily to select an apex angle .theta. and then wish to 
determine the dimension "F" to which the apex of the prepreg sheet should 
extend beyond the crossover point 32, for a given number of wraps the 
following formula would be used to calculate that dimension: 
EQU F=n.pi.D cotangent .theta. 
wherein the variables are those hereinbefore identified and explained. 
When the apices of the two prepreg sheets are cut to the same angle, the 
total overlap would be equal to twice the dimension F, but, as depicted in 
FIG. 6, where the apices 33A and 34A are cut to different angles--.theta. 
and .PHI.--one would solve for dimension F.sup.1 with respect to angle 
.theta. and F.sup.2 with respect to angle .PHI. and the total overlap 
would be equal to F.sup.1 plus F.sup.2. 
With the apices of the two prepreg sheets cut according to the desired 
angle, and with the apices overlapped as depicted in FIG. 2, they would 
then be simultaneously wound onto the mandrel 29 and the resin cured to 
its final stage. So wound onto the mandrel the sheets 26 and 28 forming 
the tip and body portions are disposed in cylindrical coils with the 
reinforcing strands in each coil extending substantially longitudinally of 
the coils--i.e., substantially parallel to the longitudinal axis 36 of the 
mandrel 29 onto which the prepreg sheets are wound. By having been 
overlappingly disposed, as the prepreg sheets are wound onto the mandrel 
the coil forming the body portion 21 will be disposed interlaminate the 
coil forming the tip portion 23 within the transition portion 24. 
The resins to be used with the prepregs should be selected to be each 
compatible with the other and each to be compatible with the reinforcing 
strands in both prepregs. The making of the prepregs, the general type 
resins to be employed and the hardening stages desired for the resins are 
well known to the art and are fully explained in U.S. Pat. No. 2,726,185 
to which reference is specifically made. 
In view of the foregoing disclosure it should be apparent to one skilled in 
the art that the subject invention discloses a novel and unique 
construction, as well as a method, by which to conjoin body and tip 
portions of differing moduli into a unitary fishing rod and otherwise 
accomplish the objects of the invention.