Note: Descriptions are shown in the official language in which they were submitted.
335
This invention relates to spring assemblies for mat~
tresses, c~lshions, and the like, and more particularly to con-
nected series of individually-pocketed springs for mattresses
and cushions having the so-called Marshall cons-truction.
In such units, each spring coil is encased within its
own fabric sack, which is usually made in the form of a pocket
defined between two plies of a fabric strip connected together
at intervals by transverse stitching. The two-ply strip is
usually formed by folding a strip of double width upon itself
along its longitudinal midline, leaving the overlapped plies
along the unjoined opposite edge of the strip to be connected to
each other to close the pocket after the spring is inserted.
A variety of techniques have evolved for the manu-
facture of pocketed springs, some contemplating the creation of
the pockets within the fabxic plies prior to insertion of the
wire spring and others the insertion of the coaxially compressed
wire springs between the plies of the strip and the subsequent
creation of the pockets by stitching the two plies to each other
along transverse lines between adjacent springs. In either
technique, the pocket is closed after the insertion of the spring,
usually by stitching the two plies toge~her along a line parallel
to the free edges of the plies.
The present invention rela-tes to a particular form of
such a series of pocketed springs in which the overlaid fabric
plies are secured to each other along the transverse and longi-
tudinal lines of attachment earlier referred to by thermal weld-
ing rather than by the use of stitching, as had conventionally
~ been done. In particular, the invention contemplates a series
- of pocketed springs in which the pocket fabric is thermally weld-
able to itself so that the two plies of fabric of the folded
strip in which the pockets are defined may be secured together
without the necessity for stitching~
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IL33S
A more particular object of the invention is the join-
ing of the overlaid plies in a manner such as to provide a
stronger bond than is achieved in the same fabric material by
production sewing~ and, at the same time, the elimination of any
need for the thread and the sewi.ng apparatus which was heretofore
necessary to the manufacture of upholstery springs of this type.
: The mechanical requirements upon sewing machines for this servi~e
are severe, and the mechanisms required for moving the sewing
machines in relation to the work, particularly in making the
lo transverse stitching which defines the pockets, has of necessity
been complicated in machines of high speed, whose productivity
is limited by the limitations of the sewing machines, including
the problem of thread breakage. In contrast, the utilization of
thermally weldable materials promises substantial simplification :
of the manufacture of superior springs in accordance with this :
invention.
The invention will be read.ily understood from the fol-
lowing description made in reference to the accompanying drawings,
of which: :.
FIGURE 1 is a fragmentary plan view of a series of
- pocketed springs made in accordance with the invention~ and shown
with the springs axially compressed in the position of their
insertion between the fabric plies and before their respective ..
axes have been turned into alignment with the longitudinal axes
of the pockets;
FIGVRE 2 is a top view of such a series of pocketed
springs after the axially compressed springs have been rotated
: ~ through 90 degrees from the Figure 1 position to cause their
axes to coincide with the long axls of the spring pocket. In
the process o~ being turned, the sprinys expand to the extent
permitted by the distended height of the pockets, and the series
of springs becomes shorter as the two overlaid plies in which the
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,: . , .. .. . .. . . . - . .. .
335
pockets are formed are separated by the expanded springs;
FIGURE 3 is an elevational view of the series of poc-
keted springs shown in Figure 2;
FIGURE 4 is an enlarged fragmentary view of the series
of welds which form the line of attachment of the fabric plies
to each other; and
FIGURE 5 is an enlarged sectional view taken on the
: line 5-5 of Figure 4.
As already indicated, the fabric material used in the
practice of the invention must be thermally weldable, either
because of the inherent characteristics of its onstituent fibers
or by reason of the application of a thermoplastic film, layer,
or coating attached to the fabric or otherwise supplied at the
site of the desired attachment of the two plies to each other.
From an operational standpoint, it is far simpler to
employ for this purpose a fabric composed of fibers which are
thermoplastic, and that lS the illustrated and preferred ~orm
of the invention, although it has been practiced also by using
. ~ added materials under certain circumstances later herein de-
scribed.
I have found a very satisfactory fabric for the pre-
: ferred form in a non-woven polypropylene fabric consisting
essentially of a carded web of staple fibers which are bonded
to form a fabric of substantially uniform thickness throughout
and of substantialIy uniform strength in cross directions in the
plane of the fabric.
~ The above-mentioned material in which the staple fibers
:~ are entirely poLypropylene, and which has a basis weight of 2.2
to 4 ounces per s~uare yard, has provided especially satisfactory
results when handled in the manner hereinafter describedO
As illustrated in Figures 1 and ~, the transverse lines
:~ of attachment 10 of the overlaid plies 12 and 14 of the strip 16
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~7~335
to each other to define the spring pockets, as well as the line
18 of attachment which closes the pockets along the side edges
of the plies between which the spring was inserted, are formed
of discrete individual welds 20 rather than as a continuous weld~
It will also be observed that, as illustrated, the individual
welds 20 are spaced apart within the line by a distance approxi-
mately equal to the length of the individual welds along the line,
and, further, that the we]ds at each end of the transverse lines
10 of welds between the pockets do not intercept either the
folded edge ~2 of the fabric strip 16 or its overlaid edges 24
between which the spring was inserted. Both features serve a
particular purpose in achieving the desired result, which can
better be appreciated by particular reference to Figures 4 and 5.
From Figures 4 and 5, it can be appreciated that at the
; 15 site of each weld 20, the pocket fabric, which is essentially
opaque, becomes an almost transparent panel or film 26 at the
site of the weld by the fusion of the individual fibers into a
conglomerate whole. This film is quite thin in comparison to
the thickness of the fabric, and is both stiffer and weaker than
the surrounding fabric, and may be fractured more readily than
the rabric itself. A continuous weld, accordingly, is less
satisfactory for the purpose because it creates a line of weak-
ness in the connected series of pockets which can create handling
probLems in the subsequent use of the pocketed springs in the
making of spring assemblies or "constructions" to be incorporated
into mattresses or cushions.
I find it desirable, therefore, for the sake of the
tensile strength of the entire series or belt of pocketed springs,
such ~s illustraked in Figures 2 and 3, to interrupt the line of
the weld, and, for the same reason, to place the first individual
weld at each end of the transverse lines of welds inwardly from
the side edges of the strip so as not to create an initial point
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L33~i
of weakness which might otherwise permit the initiation of a
tear of the entire strip ~y the successive tensile fracture of
each interweld width of fabric along the entire line.
As to the efficacy of the interrupted weld to provide
a secure bond between the two plies of fabric in the preferred
form illustrated, the arrangement of the interrupted welds in my
selected proportion provides bonding strength between the plies
which is at least equivalent to a continuous line of weld. This
will become apparent from examination of Figures 4 and 5, and
fxom the further consideration that although each individual weld
appears as an almost transparent "window" 26 through the two
opaque plies 12 and 14, there is necessarily a transi-tionai area-
28 in a band around the window in which the discrete fibers of
the fabric have not totally los-t their fibrous identity but are
nevertheless fused to one another within each ply and between
the plies. It seems apparent that the strenyth of the weld is
attributable in larger part to that interfiber fusion rather
than from the film which results in the area of the greatest
applied energy. Accordingly, by spacing the individual welds
as far apart as the length of each individual weld and by making
the individual we]d approximately half as wide as it is long,
the fused fiber bands 28 which surround the "window pane" of
each weld provide each pocket with a length of welded fabrlc
equivalent to that which would result from a continuous weld.
Moreover, by preservinq the continuum of the fibrous
strip fabric in the interweld spaces, I maintain the tensile
integrity of the entire band or series of pocketed springs,
while at the same time providing all of the essential bonding
strength between the plies to withstand the tensile forces
created in the plies by the expanded spring and by the ultimate
use to which assemblies of such springs are put.
With an interrupted line of thermal welds as described,
33~;
and using non-woven polypropylene abric earlier referred to,
I have found that a line of interrupted welds each a quarter-
inch long and approximately one-eighth inch wide and separated
from each other by approximately one-quarter inch in the line,
exhibits over forty percent (40%) greater resistance to separa-
tion of the pocket-forming plies than the identical material
sewed on production equipment for the manufacture of pocketed
springs by the conventional stitching method, using thread which
is conventional for the single-thread interpocket stitching, viz.,
Number 30-3 soft cotton.
While thermal welding in the prescribed pattern may
be achieved in a variety of ways, including con~act heating and
high frequency welding, the ultrasonic we]ding technique appears
to be especially suitable in that the internal induction of heat
15 by its mechanical working of the material is faster than contact
heating, and more controllable as well as less dangerous than
high-frequency electrostatic methods. Moreover, within limits,
any desired pattern of welding can be achieved ultrasonically
in this context by suitable modification of the anvil against
which the material to be welded is pressed by the welding horn.
I have also made pocketed springs usin~ other thermo-
plastic fabrics, sueh as a non-woven polyethylene composed of
eontinuous fibers which are laid en masse and subsequently par-
tially fused by heat and other processing into a sheet fabric
material. In economic weights of this material, however, I have
found the control of the weld more difficult than I prefer for
production purposes, but nevertheless controllable independently
of the welding proeess by the inclusion along the line of the
weld of an additional film, layer, or band of thermoplastic
material.
These experiences lead me to conclude as well that
i satisfactory control of the weld in lighter weight thermoplastic
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3~;
fabrics may be accomplished by the inclusion of a non-thermo-
plastic matrix, such as cotton scrim, between the plies along
the line of the weld to provide a non-fusible network to which
the thermoplastic fabric can bond itself, and, conversely, that
similarly satisfactory welding may be achieved between two layers
of woven textile fabrics of natural fibers, such as cotton, etc.,
if a thermoplastic material is included between the plies in
the line of the weld.
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