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This invention relates generally to hot tubs or spas, and more particularly
to a low-cost, light-weight, insulated, semi-rigid plastic spa, which is
esily portable, and hot water supply means therefor.
Conventional hot tubs are heavy, non-portable, and expensive in their
construction; also, excessive electrical and heat energy is required for
their operation. There is need for a greatly improved spa structure with
the unusual advantages in construction, modes of operation, use and
transport, and results, as are now made possible by the present invention,
as will appear.
SUMMARY OF THE INVENTION
It is a major object of the invention to provide a hot tub or spa meeting
the above needs. Basically, the inexpensive, light-weight tub apparatus
comprises:
(a) a foamed plastic wall having an inner side and an outer side, the tub
having an interior to receive liquid,
(b) a tensile liner adjacent the wall side, the liner comprising interwoven
strips of pre-stretched plastic material characterized in that the liner
resists outward expansion in response to loading exerted by liquid filled
into the tub interior.
It is a further object to provide a non-stretchable flexible liner that
includes a plastic foam layer bonded to the interwoven strips and also to
the wall inner side. As will be seen the plastic strips may consist of
pre-stretched polyethylene, and the mesh formed by the interwoven strips
is typically embedded with a plastic coating to prevent leakage of liquid
through the liner.
If the liner is applied to the inner side of the tub wall, a similar liner
may also be applied to the outer surface of the wall defined by the spiral
wound layers, to resist wall expansion, and a plastic jacket may be
applied over the composite wall, as thus formed.
The method of constructing the tub apparatus basically includes:
(a) winding said sheet in a spiral to form spiral convolutions and
progressively bonding together the spiral convolutions during said
winding, thereby to form an upstanding tub wall having an inner side and
an outer side, and a tub interior,
(b) and bonding said liner to said wall inner side to resist outward
expansion toward said wall in response to loading exerted by liquid filled
into the tub interior.
Bonding is typically affected by heating the side of the liner to tacky
state, and pressing the heated side of the liner against the side of the
tub wall; the liner also typically includes a plastic foam layer bonded to
said interwoven strips, and said heating heats a surface of the plastic
foam layer to tacky state; and a roller is typically employed to
progressively press the liner toward said wall, and the liner is fed about
the roller to present said surface of foam layer away from the roller, for
heating.
These and other objects and advantages of the invention, as well as the
details of an illustrative embodiment, will be more fully understood from
the following specification and drawings, in which:
DRAWING DESCRIPTION
FIG. 1 is a perspective view of spa equipment embodying the invention:
FIG. 2 is an enlarged section on lines 2--2 of FIG. 1;
FIG. 3 is an enlarged section showing construction of the spa side wall and
bottom wall;
FIG. 4 is an enlarged section showing interior construction of the spa unit
cover;
FIG. 5 is a wiring diagram;
FIGS. 6 and 6a are enlarged views showing tub wall structure;
FIGS. 7a and 7b show plastic strips;
FIG. 8 shows a mesh formed by interwoven strips, and coated with plastic;
FIG. 9 shows a completed liner;
FIG. 10 shows bonding of a liner to the tub wall;
FIG. 11 shows a completed tub with lining or linings applied; and
FIG. 11a is a fragmentary view showing a jacket applied.
DETAILED DESCRIPTION
Referring first to FIG. 3, the apparatus 10 includes a tub 11 having an
insulative, annular side wall 12, and a bottom wall 13 attached to side
wall. The side wall comprises a foamed plastic sheet or sheets 14 wound in
a spiral about the tub axis 15, to form multiple layers. The latter are
better indicated at 16 in FIG. 6, with glass fiber reinforcement screen
material 17 between the foamed plastic layers 16. Such layers may
typically consist of polyethylene foam of between 1/8 and 3/8 inch
thickness, as for example, about 1/4 inch thickness; and the glass fiber
screen may define about 1/2 inch square open spaces between woof strands,
and between warp strands. The polyethylene layers are rapidly joined
together as by engagement of the outermost layer, during spiral winding,
with a heating flame 18 and a roller 19, as seen in FIG. 6a. The pressure
roller presses the heated inner surface of the outermost layer 17' against
the flame heated outer surface of the next inner layer 17" to establish
fusion contact, as for example through the spaces between warp strands 20,
and also between woof strands extending at 90.degree. to strands 20. Thus,
an integral relatively stiff and very sturdy spiral fusion laminated
light-weight side wall 12 is gradually formed during the spiral winding
process; and a person may sit comfortably on the top edge or rim 12a of
the wall 12 without damaging it or the tub construction.
The tub bottom wall 13 has a similar construction except that parallel
sheets 13a (5/8 inch thick) of cross linked polyethylene foam, with or
without glass fiber layers 12 therebetween, are heat fusion welded to form
an integral bottom wall. The latter is then peripherally fusion welded as
at 22 to the bottom of the side wall. A plastic jacket 23 may be fitted
about both the side wall and bottom wall. Jacket 23 sheets may consist of
foamed, reinforced, marine vinyl resin; and include inner sheet 23a, outer
sheet, 23b, crest sheet 23c, and bottom sheet 23d, all joined together to
form an internal waterproof decorative jacket, as shown. Jacket lower edge
extent may be looped as at 23e, and a draw string fitted in the loop to be
drawn tight and attach the jacket to the wall 12. A welded seam is
indicated at 23f. The vinyl jacket may have selected weatherable color.
A pool cover is shown at 25 in FIG. 4, with generally the same spiral
polyethylene layer construction, as does wall 12. Thus, spiral
polyethylene layer or layers 26 extending about vertical axis 27 can be
fusion welded together, similar to the wall section but typically without
the fibers. Additional structure and stiffness is imparted to the cover by
creating thermally densified layers on each face, 26 and 28. These are
created by compressing the spiral wound structure between two hot
plattens. A vinyl jacket 29 is fitted about the polyethylene windings, and
is held in place by a draw string in loop 29a.
FIG. 2 shows upper and lower ports formed through the tub wall as by
tubular plastic fittings 30 and 31. Water circulating means 32 is
connected with those ports, and includes a pump 33, for circulating water
into the tub interior 34 via upper port 30a, and for withdrawing water
from the tub interior 34 as via lower port 31a. A filter 35 is located
within the tub to filter the water being withdrawn through port 31a, so
that dirt and small objects are not fed to the pump lower inlet 33a. The
filter is easily withdrawn upwardly at the tub interior, for cleaning or
replacement. The pump discharges sidewardly at outlet 33b, and plastic
piping extends upwardly at 36 to deliver pressurized and heated water to
port 30a.
In accordance with an important aspect of the invention, the water
circulating means includes an electric motor connected in driving relation
with said pump, and includes a shunt duct connected with the water
circulating means and located to receive heat generated by operation of
the motor to heat a side stream of the water passing through the shunt
duct. The illustrated shunt duct includes metallic tube 40 wound about the
pump drive motor 45 to receive heat from same, for heating the tub water,
whereby extreme simplicity and energy savings are realized. The duct 40
has an end connected at 40a into the water circulating system proximate
pump outlet i.e. into piping upper branch 36; its opposite end connected
as at 40b into the water circulation system proximate pump inlet 33a, i.e.
in lower piping branch 43 extending from port 31a to inlet 33a.
Accordingly, water flows in the shunt duct from a higher (pressurized)
level to a lower level; and a portion of the water flowing through the
pump is heated and re-heated, for highly efficient heating action. Thus,
no external source of heat for the hot-tub water is required, and motor 45
serves multiple functions, its waste heat being efficiently utilized. The
height of the inlet and outlet of the shunt duct are approximately the
same to minimize thermosyphon action when the motor is off. The
thermosyphon action can cause a momentary surge of extra hot water to trip
the high limit switch 49.
In the schematic of FIG. 5, the motor coil 45a is supplied with electrical
energy from a plug 46, such as is insertible into a household 120 volt
outlet receptacle. The wiring interconnecting the plug and coil includes
line 47 with which thermostat switch 48, and high limit switch 49 are
connected in series. Switch 48 is operated by a thermostat sensor 49
applied to inlet port 30a, whereby if the water is too hot, the motor is
shut down. Limit switch 49 is also controlled by temperature sensor 50
located adjacent the tub to shut the motor down if the tub becomes
overheated. Line 47 and return line 47a pass through cord 52, and through
a ground fault interruptor 53, as shown.
A plastic shell enclosure or housing for the pump and motor is indicated at
60. It is well insulated to keep the heat generated by the motor inside
where it can be transmitted to the water, and to minimize sound from the
motor and pump inside for the comfort of the users. It is a compact
package which facilitates ease of transport and set-up of same.
In FIG. 11 the tub apparatus 111 includes an insulative, bottom wall 113
supporting the side wall, as by attachment to the lowermost extent
thereof, at 113a. The side wall comprises a foamed plastic sheet or sheets
114 wound in a spiral about tub axis 115, to form multiple layers. Such
layers may typically consist of polyethylene foam of between 1/8 and 3/8
inch thickness, as for example about 1/4 inch thickness. The layers are
rapidly joined together as by engagement of the outermost layer, during
spiral winding, with a heating flame, as described above in connection
with FIG. 6a; however, no glass fiber screen is employed.
Instead, an inner liner 117 is provided adjacent the wall inner side 112a.
As indicated in FIG. 9, that liner comprises interwoven strips 118a and
119a of pre-stretchable plastic material characterized in that the liner
resists outward expansion toward wall 112 in response to loading exerted
by liquid such as water 121 in the tub interior. See FIG. 11. Therefore,
the tub wall 112 is not deflected or stretched radially outward, as it
would be in the absence of the liner.
FIG. 7a shows a typical thermoplastic (such as polyethylen) strip 118 or
119 prior to pre-stretching, endwise, in the direction of arrows 123 and
124. FIG. 7b shows the same strip 118a or 119a after such stretching, with
a correspondingly reduced width, to provide high tensile strength. FIG. 8
shows the strips 118a and 119a closely interwoven with warp 118a and woof
119a strand or strip layer or mesh pattern 125. The woven strips are then
embedded in or coated with a plastic coating 125a to prevent leakage of
liquid therethrough and to provide load spreading. The plastic coating may
also consist of polyethylene. Such a mesh is a product of Chave and Early,
New York, N.Y., and sold under the name "CE-TEX".
FIG. 9 shows the completed liner 117, which includes a plastic foam layer
126 bonded in face-to-face relation with one side of the coating layer
125a. The layer 126 may for example consist of polyethylene foam. The bond
interface is indicated at 128, and may be formed by heat fusion.
As a result, the composite liner 117 may be fusion bonded to the inner side
112a of the spiral layer wall 112. FIG. 10 shows that process. Bonding is
carried out by heating the outer side 126a of the layer and/or the side
112a, to tacky state, and then pressing the hot tacky side 126a against
the side 112a of spiral layer wall 112. Liner 117 extends more than
360.degree. around the tub, to provide overlap. Heating is effected by
directing flame 130 or other heat source heat against sides 126a and/or
side 112a, as seen in FIG. 10, and as the liner is progressively fed in
direction 131, a pressure roller 132 rolling against the applied liner to
press side 126a against side 112a.
FIG. 11 also shows a like liner 117' applied against the outer side 112a'
of the wall 112, to also resist outward stretching of the wall 112 and
also to add toughness. Finally, a jacket 133 like jacket 123 may be
applied or attached to the inner surface 135 of the completed tub wall and
to tub bottom wall 113, or to the liner 117. See FIG. 11a, the jacket
applied in the same manner as in FIG. 3. A tub wall upper rim appears at
137, in FIG. 11. Jackets 123 and 133 may have the same construction as
tensile liner 117.
In the above FIGS. 10, 11 and 11a, the lined tub wall indicated by layers
114 may instead be a single layer of foam.
From the foregoing it will be understood that the primary purpose of the
tensile band or liner 117 is to absorb the hoop stress caused by the
pressure resulting from the column of water in the tub. Without such
tensile band, the water pressure places continuous compression and tensile
stresses on the inner side of the tub wall. The polyethylene foam walls or
layers 114 expand, especially at the bottom, in the absence of tensile
band 117. That band also provides improved wall toughness and reduced
communication of fluids between tub walls and outside environment.
A like tensile band in the wall between the inner and outer sides of the
wall may be employed to absorb hoop stress while allowing some compression
and compliance of foam inside tensile band. One such layer as seen in FIG.
11 may be considered to represent such an intermediate band.
An O.D. tensile band as at 117, is usable to absorb loads from people
sitting on the tub wall, improve O.D. toughness, improve aesthetics, and
reduce communication of fluids between tub walls and environment.
Liner materials or composites may be constructed to have enough tensile
strength to act as tensile band. Typical materials include vinyl film or
films laminated to polyester fabrics and polyester fabrics coated with
vinyls. Unattached and/or attached tensile band materials include metal
foil, glass fibre reinforced polymers, aluminum sheet, coated and uncoated
polyester fabrics, films laminated to polyester fabrics, spun bonded
polyester fibres, tensilized polyester films, and tensilized polyethylene
films slit to thin strips and woven in two axes and coated with
polyethylene as described herein. Thin layers of PE/EVA, PE, EVA, XLPE
and/or PVC foam may be attached to the inside of the tensile band to
reduce water transport, improve aesthetics and/or feel, from inside the
tub, to act as a tie layer, and to act as a compression element for
plumbing seals.
Fibre or filament molecular orientation is preferably generally
circumferential, however, biaxial and random orientation are also
possible.
Tensile band or bands may be attached to a liner for a tub wall inner
surface, as via adhesive, solvents, and/or thermal fusion techniques
including radio frequency heat sealing and ultrasonic welding. Tie layers
may be used to make material attachment easier, via improved bonding
compatability, to add stiffness, to reduce leakage, and/or improve
aesthetics and feel.
Intermediate tensile bands (between I.D. and O.D.) may use the above
described materials, or glass fibres and polymer fibres in loose,
unidirectional and bidirectional fabrics, fused between layers of
polyethylene foam during wall construction. Outer side tensile bands may
be fastened using above methods, or by shrinking on the tub outer wall.
Tensile band material candidates are typically available as rolls and must
be overlapped to create a circumferential tensile band. Although tensile
bands spirally wound into the tub wall may be overlapped without direct
connection, I.D. and O.D. tensile bands typically require joining as via
solvents, adhesives, mechanical fasteners and/or thermal fusion
techniques.
Tensile band acting as liner, or attached to a liner, may be provided to
add stiffness to the liner and thereby ease fitting to the inside of the
tub. Additionally, this configuration toughens the liner and may be used
along with a foam layer as a mechanical plumbing seal.
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