U.S. patent number 3,738,096 [Application Number 05/087,970] was granted by the patent office on 1973-06-12 for manufacture and construction of strings.
This patent grant is currently assigned to Ashaway Line & Twine Mfg. Co.. Invention is credited to Julian T. Crandall.
United States Patent |
3,738,096 |
Crandall |
June 12, 1973 |
MANUFACTURE AND CONSTRUCTION OF STRINGS
Abstract
An integrated string of the type used for tennis rackets of the
type comprising a plurality of individual thermoplastic strands,
each of which is individually twisted in a first hand, the strands
then being twisted together in an opposite hand, the resultant
string then being coated in a thermoplastic formulation and then
passed through a heating chamber to become dried, said coating and
drying steps being repeated a plurality of times, after which the
string is stretched under heat and then again coated and dried.
Inventors: |
Crandall; Julian T. (Ashaway,
RI) |
Assignee: |
Ashaway Line & Twine Mfg.
Co. (Ashaway, RI)
|
Family
ID: |
22208344 |
Appl.
No.: |
05/087,970 |
Filed: |
November 9, 1970 |
Current U.S.
Class: |
57/242 |
Current CPC
Class: |
D02G
3/444 (20130101); A63B 51/02 (20130101); D02G
3/404 (20130101); A63B 51/026 (20200801) |
Current International
Class: |
D02G
3/40 (20060101); D02G 3/44 (20060101); A63B
51/00 (20060101); A63B 51/02 (20060101); D02G
3/22 (20060101); D02g 003/36 () |
Field of
Search: |
;57/14C,14R,139,149,153,162,164 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Watkins; Donald E.
Claims
What is claimed is:
1. An integrated string comprising a plurality of thermoplastic
strands, each of which has an identical twist in a first direction,
said strands being twisted together in the opposite direction to
form the core of said string, and a coating of plastic material
penetrating between said strands and covering same to integrate
said string, the outer surface of said string being gently
undulated.
2. In the string of claim 1, said first twist being approximately
twelve turns per inch, and said second opposite twist being
approximately five turns per inch.
3. In the string of claim 1, said strands and coating both being
nylon.
4. In the string of claim 1, there being a total of three
individual strands.
Description
BACKGROUND OF THE INVENTION
Integrated plastic strings for use in tennis rackets and the like
are broadly old and well known in the art as evidenced, for
example, by U. S. Pat. Nos. 2,649,833; 2,712,263; 2,735,258;
2,861,417; and 3,050,431, all previously issued to the present
inventor. In all of these prior patents, however, the integrated
plastic string comprised a core with some sort of a sheath
positioned therearound, said core and sheath then being integrated
by use of a compatible plastic coating. The resultant string in all
of these cases embodied a substantially smooth cylindrical
configuration on their outer surface; and, while eminently
satisfactory for their intended purposes, it has been found that
these prior art string constructions, when used for tennis
purposes, did not permit the player to impart maximum spin to the
ball. Expressed differently, the perfectly smooth, flat outer
surface of these prior art strings did not permit maximum bite when
the string engaged the ball, since the flat, smooth outer surface
tended to minimize friction between the string and the ball during
contact.
SUMMARY OF THE INVENTION
It is therefore a primary object of the present invention to
provide an integrated plastic string wherein the outer surface of
same, while smooth and continuous, nevertheless has gentle
undulations therein which permit the string to impart maximum bite
upon contact with a tennis ball, thus permitting the player to
impart a more effective and pronounced spin upon the ball during
the striking thereof.
In addition, it is the object of the present invention to provide
an integrated plastic string which, when used for tennis purposes,
will cushion the shock which results when the ball is struck and
which, at the same time, is durable and wear resistant during use,
thus resulting in relatively long and effective life.
In carrying out the above objectives, it has been found that an
outer sheath is not required. Quite to the contrary, the string of
the present invention comprises a plurality of individual strands,
preferably three in number, each of which is individually twisted
in a first hand. The strands are then twisted together in the
opposite hand, after which the string is coated with a plastic
formulation and then passed through a heating chamber for drying.
The coating and drying processes are sequentially performed a
plurality of times, after which the string is stretched under heat
to a predetermined elongation. The coating and drying steps are
then sequentially repeated to arrive at the finished string which,
while thoroughly coated and integrated, nevertheless maintains on
its outer surface the gentle undulations resulting from the
twisting together of the individual strands.
DESCRIPTION OF THE DRAWING
In the drawing which illustrates the best mode presently
contemplated for carrying out the present invention,
FIG. 1 is a perspective view of a portion of one of the individual
strands used in the instant invention;
FIG. 2 illustrates a plurality of the strands shown in FIG. 1
twisted together;
FIG. 3 schematically illustrates the coating and drying means used
in the instant invention;
FIG. 4 is an elevational view, on an enlarged scale, and partly in
section, showing the completed string; and
FIG. 5 is a section taken on line 5--5 of FIG. 4.
DESCRIPTION OF THE INVENTION
Referring now to the drawings, there is shown at 10 in FIG. 1 an
individual strand that is used in the manufacture of the present
invention. The strand 10 is of thermoplastic construction, and
nylon has been found to be highly preferable because of its
strength. Where a tennis racket string is being manufactured, it
has been found that the strand 10 may be of 3,360 deniers,
although, obviously, the size of the finished string may be
controlled by using individual strands of lesser or greater
deniers. A plurality of individual strands 10 are provided, and
preferably, three such strands are utilized in the manufacture of a
tennis string in accordance with the present invention. Each of the
strands 10 is individually twisted, and, preferably, it has been
found that an "S" twist of 12.4 turns per inch has proven to be
particularly desirable. After the individual strands 10 have been
so twisted, they are laid together and then twisted in the opposite
hand, as illustrated in FIG. 2. More specifically, where the
individual strands have been "S" twisted, the bundle of strands, as
illustrated in FIG. 2, are twisted together in a "Z" twist,
preferably at the rate of 5.3 turns per inch.
The resultant string 12 is then dipped in a thermoplastic
formulation 14, as illustrated in FIG. 3, it being noted that
suitable pulleys 16, 18 and 20 are provided for continuously
passing through the formulation 14, it being understood that any
other suitable mechanical means may be employed for effectively
coating the string 12. The formulation 14 is a nylon solution,
preferably comprising by weight approximately 14.4 per cent nylon;
61.1 per cent Methanol; 4.9 per cent tetrahydrofurfyl alcohol; and
19.6 per cent water. The above proportions are not critical but
have been found to be desirable for providing a nylon solution of
suitable consistency.
After the string 12 has been coated with the solution 14, it passes
through a heating chamber 22 where the string is dried.
Specifically, it has been found that proper drying is effected
where the chamber 22 is approximately 100 feet long, where the
string passes therethrough at a speed of approximately 33 yards per
minute, and where the temperature within the chamber is maintained
at approximately 220.degree. F. The coating and drying of the
string, as just described, is repeated a plurality of times, since
it has been found desirable to apply several thin layers of coating
rather than a single heavier layer. With the particular formulation
hereinbefore described, it has been found that the coating and
drying operation should be performed approximately twenty times in
order to achieve the desired coating and integration of the
string.
After the string has been coated and dried as above described, it
is stretched under heat to properly orient the string and draw it
down to the desired diameter. Specifically, it has been found that
placing the string under 75 pounds tension in a chamber maintained
at approximately 450.degree. F. will result in approximately 17 per
cent elongation of the string, which has been found to be
desirable. After the heat stretching operation, it has been found
that minute pockets or voids sometimes exist in the string coating;
and hence, in order to fill in these pockets or voids and provide a
string having a smooth and uninterrupted outer surface, the
aforesaid dipping and drying steps are again repeated, preferably
two times.
As will be seen most clearly in FIGS. 4 and 5, the resultant string
24 is coated and integrated by the plastic 14, it being noted that
the coating 14 not only surrounds the twisted strands 10, but also
penetrates therebetween to effectively bond the string. Actually,
the repeated dipping and drying operations performed on the string
12 will result in substantial integration of the plastic 14 with
the strands 10, although, for purposes of illustration, the coating
14 has been shown in FIGS. 4 and 5 as being distinct from said
strands. Also note that the coating 14 conforms to the indentations
which exist between adjacent strands 10, thus resulting in
indentations 26 on the outer surface of string 24, said
indentations imparting a gentle undulation to the finished string,
which undulation enhances the bite that the string may impart to a
tennis ball, whereby a more effective spin may be imparted to the
ball when it is struck. In addition, it has been found that a
string manufactured in accordance with the instant invention is
long wearing and durable, and, at the same time, cushions the shock
that results when the string strikes a tennis ball.
* * * * *