Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to manhole
assemblies and more particularly a novel method and
apparatus for forming manhole assemblies utilizing
liner sections formed of a suitable material which
is inert to the toxlc influences encountered in
manhole assemblies to provide a manhole assembly
having an interior liner exhibiting superior water-
tight capabilities to protect the cast material.
It is well known to those responsible for
the design, construction, maintenance and use of
waste water handling and treatment systems that the
cumulative effect of toxic materials and/or
chemicals carried by waste water cause interior
corrosion and deterioration of the cast material,
which harmful effects are cumulative and lead to a
significant reduction in the useful operating life
of such systems resulting in premature and costly
repair and/or replacement of such systems and/or
components thereof.
Some of the more significant corrosive
influences experienced by cast manhole assemblies
and solutions and techniques for substantially
reducing such corrosive effects are set forth in
detail in U.S. Patent No. 4,751,799 issued June 21,
1988 and U.S. Patent No. 5,081,802 issued January
21, 1992, both of which are assigned to the assignee
of the present application
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Briefly, the techniques employed therein
to shield the cast material from corrosion and/or
deterioration include the provision of a liner
formed of a plurality of vacuum formed liner
sections joined together to provide a water-tight
protective shield for the cast material.
Although the techniques and apparatus set
forth in the above-mentioned patents have
considerably reduced deterioration of cast members
due to corrosive influences carried by effluent
handled by the cast members, the present inventors
have nevertheless noted a number of disadvantages of
prior art techniques which include, among others,
the following:
1. Liner sectlons produced using vacuum
forming techniques having a high scrap rate.
2. The vacuum forming process limits the
panel size which can be formed making it necessary
to increase the number of panels needed to form a
cylinder.
3. Panels produced using the vacuum
forming process have variations in wall thickness
and require mechanical fasteners which are tedious
and time consuming to mount and assemble.
4. Vacuum formed liners are degraded by
stream curing operations employed during the casting
process and further do not hold up well in
environments experiencing frigid temperatures.
The present invention is characterized by
comprising a method and apparatus for resolving the
disadvantages of present day design including among
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them those discussed hereinabove, as well as
- delivering significant improvements in
manufacturing, assembly and casting as well as field
installation and performance of the entire system.
5The present invention is characterized by
utilizing a rotocasting process for molding panels,
preferably from polyethylene, through the use of a
tool fabricated to resemble an elliptical cylinder
utilized to form two panels simultaneously. In one
10preferred embodiment, each panel represents one-
third of the desired circumference of a cylindrical
shaped cast member.
Tooling requirements are minimized by
utilization of a tool having a standard length
15determined by the diameter of the cast member and
having reenforcing ribs equally spaced along the
height of the tool by a predetermined distance
enabling panels to be cut down to a desired shorter
height.
20The tool utilized to cast the liner
sections and containing the mold material is spun by
suitable drive means to simultaneously form a pair
of rotocast liner members having substantially solid
flanges, reenforcing ribs and joining ribs which act
25to provide curved liner sections having excellent
structural strength to prevent warping and buckling
and which are joined by suitable plastic ties to the
internal wire mesh of the cast member, thereby
providing excellent anchoring of the liner sections
30to the cast material. This arrangement provides an
anchoring arrangement which has a significantly
improved capability of being properly centered and
retaining its curved shape without buckling, bending
or warping as compared with the roto-cast liners
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disclosed in U. S. Patent No. 5,303,518, issued
April 19, 1994.
The liner sections, preparatory to
placement within the casting mold, are joined to one
another by a clip which slides over a pair of
returns or flanges of adjacent liner sections,
locking the returns to one another and squeezing a
resilient compressible foam rubber strip positioned
between adjacent surfaces of the joined returns
which assures a water-tight seam therebetween. The
clip also serves as a fluid barrier over the entire
length of the seam.
The clip member joining vertical returns
of adjacent liner sections may be either a plastic
clip assembly or a stainless clip assembly, the
latter being capable of either being slipped or
snap-fitted into position.
The liner and plastic clip are preferably
formed of polyethylene which inert to substantially
all of the toxic materials encountered in sewage
systems yielding excellent protection for the cast
material. In addition, polyethylene prevent
leaching.
Gasketing is provided between vertically
stacked sections of the manhole assembly to provide
a water-tight seal between the manhole base and
riser sections and between the riser section (or
sections) and the top section. Flanges are provided
on the liners at the upper ends thereof to provide
corrosive protection along the interior region of
the joined manhole sections.
Openings are formed in the liner section
at those Locations designated for receipt of a
conduit. A connector mandrel arranged within the
mold preparatory to casting supports a gasket for
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water-tightly sealing a conduit or pipe inserted
into the manhole assembly, the gasket being provided
with a continuous outer flange having a
substantially T-shaped cross-section for anchoring
the gasket in the cast material. The main body
portion of the gasket is provided with a plurality
of continuous annular voids of varying lengths which
are diagonally oriented to control the resiliency
and compression of the gasket during the insertion
of conduit thereby assuring placement of the gasket
material where it is needed most for supporting and
water-tightly sealing a conduit inserted therein.
A top liner member is provided for
protecting the roof of the manhole assembly. The
substantially circular-shaped top liner is provided
with reenforcing ribs and a substantially stepped
cylindrical projection defining an eccentric opening
in the top liner. The reenforcing ribs of the slab
top liner are joined to a wire reenforcement
embedded in the cast member by non-corrosive tie
members. The generally cylindrical-shaped access
opening portion of the liner is integral with the
disk-shaped portion and cooperates with a hollow,
cylindrical-shaped extension member telescopically
received within the stepped, cylindrical-shaped
projection extending upwardly from the top liner.
One or more O-rings are arranged in seating recesses
arranged about the outer periphery of the
cylindrical extension member to provide an
adjustable, water-tight seal between the telescoping
members.
The sealants employed between adjacent
vertically aligned sections of the manhole assembly
may be EPDM which are employed in waste-water
applications and nitrile gaskets for use in
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applications in which oil and fluorocarbon materials
are encountered.
5It is therefore one object of the present
invention to provide precast concrete vertical
placed structures, manhole assemblies or the like
having novel rotocast liner assemblies impervious to
toxic materials for protecting the concrete.
10Still another object of the present
invention is to provide a novel liner assembly for
lining and protecting annular concrete structures
and the like from corrosion, the liner assembly
being formed of liner sections having integral
15returns joined to one another by fastening clips,
eliminating the need for conventional fasteners and
having resilient gasket means arranged between
adjacent surfaces of the returns for providing an
excellent water-tight seal along the clip assembly.
20Another object of the present invention is
to provide novel liner sections joined to one
another with slide-on clip means and having
reenforcing ribs which are anchored to the cast
concrete by means of ties permanently anchoring the
25liners to the wire mesh reenforcement of the cast
member to assure retention of the liner section
curvilinear-shape and to present bulging or warping.
Still another object of the present
lnvention is to provide a liner assembly for lining
30manholes and the like and which is easy to both
manufacture and install.
It i~ a further object of the present
invention to provide a liner assembly formed of
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rotocast liner sections which are ~ecurely and
- permanently anchored to the cast manhole sections.
Still another object of the present
invention is to provide a connector for manhole
assemblies and the like which provides a corrosion
resistant water-tight connection between entry
castings and precast concrete cones and flat-top
sections and enables grade adjustments without the
need for added parts.
In the accompanying drawings:
Fig. 1 is a sectional view of a manhole
assembly embodying the principles of the present
invention.
Fig. la, lb and lc are detailed sectional
views showing the sealants employed between adjacent
manhole sections.
Fig. 2 is a perspective view, partially
sectionalized, showing the interior of the liners in
ne manhole section of Fig. 1.
Fig. 2a is a detailed sectional view of a
portion of Fig. 2 shown encircled.
Fig. 2b is a perspective view, partially
sectionalized, showing the arrangement of two liner
section and a reinforcing mesh cage surrounding the
liner sections and the members anchoring the liners
of the cage.
Fig. 2c is a detailed sectional view of
Fig. 2b showing the portion of Fig. 2b encircled.
- Fig. 3 shows simplified top plan vlew of
liner sections joined together.
Fig. 3a is a top view showing one of the
clamping assemblies of Fig. 3 in grater detail.
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Fig. 3b is a top view similar to that
shown in Fig. 3a showing an alternative fastening
clip .
Fig. 4 shows a top plan view of a liner
for use with the slab top section of a type shown in
Fig. 1.
Fig. 4a is a sectional view of Fig. 4
looking in the direction of arrows 4a-4a of Fig. 4.
Fig. 4b is a sectional view looking in the
direction of arrows 4b-4b of Fig. 4c;
Fig. 4c is an elevational view of Fig. 4
with a number of the reinforcing ribs removed to
simplify the figure.
Fig. 5 is a detailed view showing the
manner in which a manhole gasket is assembled with
a liner in a mold for casting a manhole section.
Fig. 5a is an exploded sectional view of
the mandrel assembly.
Fig. 5b is an enlarged and detailed cross-
section of the gasket of Fig. 5.
Fig. 6a shows a top view of a molding tool
used in rotocasting liner sections.
Fig. 6b shows one of the end caps secured
to top and bottom ends of the molding tool.
Fig. 6c is an interior side view of one of
the panel forming sections employed in the mold tool
of Fig. 6a.
Fig. 1 shows one typical manhole assembly
10 comprising a manhole base 20, riser section 30
and top section 40, each being of a cylindrical-
shape. Top section 40 is typically shorter than
sections 20 and 30 and provides a top opening which
21 62357
g
is eccentrically aligned for receiving a cast iron
frame 50 and sewer lid cover 52, which opening is
aligned with the ladder steps to enable service
personnel to gain access to the interior thereof.
Although the assembly 10 utilizes a slab top 45, a
cone-shaped top may be employed.
Members 20, 30 ahd 40 are formed of
concrete and each has a metal reenforcing framework
or cage comprised of a grid work of mutually
perpendicularly aligned rods. For example, note the
rods 21 and 22 shown in section 20 of Fig. 1. It
should be understood that a number of vertical rods
21 are arranged at a substantially equispaced
intervals about the circumference of section 20 to
make up the wire mesh cage.
Base 20 is typically provided with two
openings only one of which is shown at 25, each
opening receiving one end of a pipe section,
inserted into the base section from the exterior
thereof. Resilient rubber-like seal 26 is
preferably integrally cast into the base member
although it can be hydraulically placed after the
opening is either cast or cored to provide a water-
tight seal between the pipe section (not shown) and
base section 25. An interior shoulder 27 is
provided along the top edge of base 20 and has an
outer projection 28 surrounding shoulder 27.
Riser section 30 has a like reenforcement
cage structure comprised of mutually perpendicularly
aligned steel rods 31 and 32. An outer shoulder 33
at the bottom of section 30 rests upon projection 28
and an inner projection 34 rests upon shoulder 27.
The top end of riser section 30 is
provided with an inner shoulder 35 have a projection
43 provided that the bottom of section 40 resting
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thereon. An outer projection 36 at the top of
section 30 has an outer shoulder 44 of section 40
resting thereon. The inner shoulder 35 supports an
inner projection 43 of top section 40.
Similar to sections 20 and 30, top section
40 is likewise provided with a wire reinforcement
comprised of mutually perpendicular wires or rods 41
or 42.
A water lock entry sleeve 47, to be more
fully described is provided to protect the cast
material forming opening 46.
A circular shaped protective liner 49 has
a portion 49a extending into a lower portion of
opening 46 and cooperates with sleeve 47, which is
telescopingly received within portion 49a, to
provide water tight corrosion protection. The water
tight seal is obtained through the use of O-rings
which will be described hereinbelow.
Sections 20 and 30 have corrosion
protecting liner assemblies 60 and 70, each of which
lines the interior surface of its associated
manhole, and thereby protects the surface from
corrosion and deterioration.
Figs. la, lb and lc show three different
techniques for providing a water tight seal between
adjacent manhole sections which are stacked one upon
the other. In Fig. la, a substantially toroidal
shaped rubber gasket 90 having an annular cross-
section is arranged upon a small shoulder as shown.
A strip of butyl material 92 is arranged upon
projection 28. Gasket 90 is lubricated preparatory
to its placement. The butyl strip has its right-
hand end set back approximately one-quarter inch
from the outer diameter of the manhole section 20.
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11
Fig. lb shows an arrangement in which a
- "spigot up" joint receives a butyl strip over the
top of projection 28, and extending downwardly along
the tapered surface 28a. This arrangement is used
in manhole assemblies having 48-60 inch diameters.
Fig. lc shows the arrangement utilized in
manhole assemblies having 72-144 inch diameters
wherein the first butyl strip 92 is placed upon the
surface of projection 28 so that its right-hand end
is set back approximately three-quarters of an inch.
A second butyl strip 94 has a portion thereof
resting upon inner shoulder 27 and extending
upwardly along the tapered surface 28a.
The liner assemblies are comprised of a
plurality of liner sections, three such liner
sections being provided in one of the preferred
embodiments described herein. Two such liner
sections 100' and 100" are shown in Fig. 2. The
liner sections have outwardly directed flanges 102',
102" and 103', 103" at the upper and lower ends
thereof said flanges engaging flanges of adjacent
liner assemblies as will be more fully described
hereinbelow.
A suitable sealant is provided between
adjacent flanges to assure a water tight corrosion
seal in the region of mating flanges. Figs. 4a, 4b
and 4c show the manner in which sealing material is
arranged along the mating surfaces to provide the
desired water tight seal.
Figs. 2, 2a and 2b show details of the
manner in which the liner sections which are joined
along vertical flanges or returns, are anchored to
the wire mesh reinforcement, and are thereby
securely fixed within the cast member.
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Sections 100', 100", which are roto-cast
in a manner to be more fully described, are joined
by joining clips 110 and are arranged within mold
members, not shown for purposes of simplicity,
preparatory to a casting operation. A wire mesh
reinforcement cage comprised of the plurality of
vertically aligned spaced parallel wire members 21
which are joined to a plurality of horizontally
aligned spaced parallel wires 22 which form closed
circular members that are affixed to, welded to or
otherwise joined to the vertical members 21. Each
of the liner sections 100', 100" is provided with a
plurality of arcuate-shaped reinforcement ribs which
are substantially horizontally aligned, and arranged
in spaced parallel fashion to one another, the ribs
being provided with holes or openings 106a" shown in
Figs. 2b and 2c. Plastic wrap-it ties typically
referred to as nylon ties, have a female locking
member at one end for receiving an opposite end of
the tie member which, once inserted, cannot be
pulled out. The tie members are threaded through
the openings 106a" and wrapped about either the
horizontal wires 22 or the vertical wires 21 or both
thereby anchoring the liner sections and centering
the liner sections within the casting mold. The
ties 108 have a 100 pound pull strength capability.
The number of ties utilized may vary over a wide
range. In the preferred embodiment, two ties are
typically arranged at approximately six (6) inch
inwardly spaced horizontal intervals from the
vertical sides of each liner with a third tie
arranged at the center of the rib. Every other rib
is anchored in this manner. The "intervening" ribs
have only two ties equi-distant from the center
position and six (6) inches in from the ends of the
2 1 62357
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ribs. The top rib overlies the top lip of the cast
- member.
The ties are tightened to form four (4)
inch circles.
As was set forth hereinabove, each of the
liner sections is provided with a pair of returns or
flanges which are substantially vertically aligned
when cast into the manhole sections. Fig. 3 shows
a top plan view of three liner sections 100, 100'
and 100" joined together to form a circular liner
a~sembly, e.g. the liner assemblies 60 and 70, by
means of an elongated polyethylene clip 109. Each
of the liner sections is provided with returns 105
along opposite vertical sides. An elongated
resilient, compressible foam rubber strip preferably
formed of a EPDM compound is placed between the
confronting surfaces of the returns 105, as shown in
Fig. 3a. The returns are pressed together and the
elongated polyethylene clip is aligned with returns
105 and is slid onto the returns to provide the
locking assembly shown in Fig. 3a. Clip 109 is
substantially C-shaped, and embraces and holds the
bulging portions 105a of the returns 105 being
joined. Strip 110 is compressed therebetween aiding
clip 109 in ret~;n;ng a superior locking grip on the
returns while at the same time providing a water
tight seal along the vertical seam between adjacent
panels.
In addition thereto, the substantially T-
shaped configuration further acts as a further means
to anchor the liner sections within the cast member
at the three locations shown in Fig. 3 spaced at
120 intervals.
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The ends of the reinforcing ribs 106 have
tapered portions 106b to provide adequate clearance
for clip 109.
Fig. 3b shows an alternative embodiment
wherein a stainless steel clip 112 may be
substituted for polyethylene clip 109 shown in Fig.
3a. Clip 112 may either be slid into position in
the same manner as was described hereinabove with
regard to clip 109 or alternatively may be snapped
into position, for example, by orienting the clip so
that its right-hand end embraces the right-hand
return 105 and then snapping the clip over the bulge
105a of the left-hand return 105. As a further
alternative, although it is preferred that the
plastic clip 109 be a continuous one-piece member
extending the height of the liner sections, shorter
clip lengths may be utilized. It is nevertheless
preferred that adjacent edges of clip lengths be in
engagement since a liquid tight seal is desired over
the entire length of the seam. The stainless steel
clip assembly may likewise be a plurality of shorter
length clip sections also preferably arranged so
that adjacent edges of the shorter clip lengths are
in engagement.
Fig. 4 shows a top plan view of the liner
49 employed to protect the slab top 45.
The liner 49 has a substantially circular
shape and the major portion thereof is substantially
flat and is provided with a plurality of reinforcing
ribs 49b. A profile of the liner, with most of the
ribs removed for simplicity, is shown in Fig. 4c
looking in the direction of arrows 4c-4c in Fig. 4.
The slab top liner 49 has an eccentric
opening, and surrounding the opening there is
provided a stepped cylindrical extension 49c whose
21 62357 `
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bottom portion is integrally formed and joined with
the flat, circular portion of the liner as is shown
in Figs. 4a and 4c. The cylinder has a first
diameter portion 49d, which tapers at 49e to define
a smaller diameter portion 49f, the top end of which
terminates in an outwardly directed flange 49g. A
hollow cylindrical extension 47 having an outer
diameter which is slightly less than the inner
diameter of the cylindrical portion 49f, is
telescopingly received within the stepped
cylindrical projection 49. The upper end of the
cylindrical extension 47 has an outwardly directed
annular flange 47a, which is arranged to be secured
between a top one of a plurality of grade rings and
a cover frame 50, which, as is conventional, is
provided with a supporting flange 5Oa resting upon
flange 47a and a flange 50b for positioning and
supporting a manhole cover member, not shown for
purposes of simplicity.
The number of grade rings 120 employed is
dependent upon the spacing required between the
cover frame 50 and the top surface of slab 45. It
should further be understood that additional grade
rings may be inserted or one or more grade rings may
be removed or grade rings of different thickness may
be substituted to accommodate any changes in the
spacing between the top surface of top slab 45 and
grade level.
The telescoping cylindrical section 47, in
one preferred embodiment, is provided with a
substantially corrugated cross-section taken in the
vertical direction so as to form a plurality of
spaced annular recesses arranged at spaced intervals
along the outer periphery, any one or more of the
recesses being adapted to receive and support an 0-
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ring 53. One or more O-rings may be provided as
shown in Fig. 4a. The three O-rings 53 shown in
Fig. 4a are formed of a suitable resilient,
compressible rubber or rubber-like material, which
is compressed between the cylindrical section 47 and
the inner periphery of smaller diameter portion 49f.
The stepped cylindrical projection 49
protects the top slab 45 from corrosion. The water
tight seal provided by the O-rings in cooperation
with the stepped cylindrical projection 49 and the
telescoping cylindrical section 47 protects grade
rings from corrosion.
The opening 25 for receiving a pipe or
conduit is preferably formed during the casting
operation, and as was mentioned hereinabove, a
gasket 26 is anchored in the cast material by
holding gasket 26 with a mandrel assembly 130 as
shown in Figs. 5 and 5a, and comprised of outer and
inner mandrel members 132 and 134 shown in exploded
fashion in Fig. 5a. Interior mandril member 134 has
a central section 134a and a truncated conical
shaped portion 134b integrally joined thereto.
Outer mandrel section 132 has a central portion
132a, a first truncated conical portion 132b joined
thereto and a second truncated conical portion 132c
integrally joined to truncated portion 132b, as
shown. A threaded member 135 having a head 135a and
threaded portion 135b is secured to the central
portion 134a. A thick reinforcing member 136 is
secured to the central portion 132a so that openings
132c and 136a are concentric and are axially
aligned.
A resilient compressible gasket formed o~
a suitable rubber or rubber-like material
for example, polyisoprene, and which is extruded,
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cut to length and formed into an annular shape has
its free ends joined together by a suitable solvent,
epoxy, vulcanization, or other suitable techniques
to form a continuous annular gasket. A cross-
section of gasket 140 is shown in Fig. 5b and is
comprised of a substantially T-shaped portion
defined by a head portion 140a and a tapered portion
140b joining the head portion to the main body
portion of 140c of the gasket. The main body
portion has a triangular shaped cross-section. A
diagonally aligned flange 140d is integral with the
left-hand end of the gasket, as shown in Fig. 5b.
A plurality of hollow, continuous, annular cavities
140e-140h are provided in the main body portion of
the gasket and function in the manner to be more
fully described.
Preparatory to the introduction of the
cast material (i.e. concrete) into the mold,
openings are cut or otherwise formed in the wire
mesh reinforcement 21, 22 and in the appropriate
liner section or sections.
The ann~ular gasket 140 is fitted into the
opening in the liner section 100 as shown in Fig. 5
so that the flange 140d overlies a marginal portion
of the interior periphery of liner section 100 to
provide a liquid seal therealong. The internal and
external mandrel members are then positioned in the
manner shown in Fig. 5 and are secured to one
another by fastener F to embrace the surfaces 140j,
140k, which surfaces extend generally inwardly
toward the center line extending substantially
through the axis of threaded member 135b. The cast
material is poured into the mold and forms about the
exterior mandrel 132, which serves to define the
opening through the cast member which is aligned
2 1 62357
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with the openings in the gasket and the liner
section.
- When the cast material is set, fastener F
is loosened and removed, and the mandrel sections
132 and 134 are withdrawn respectively in the inward
and outward direction.
The T-shaped portion of the gasket is
embraced by the cast material assuring that the
gasket is properly anchored in and fixedly secured
to the cast member.
When a manhole section having an opening
therein is installed at a field site, a pipe or
conduit is inserted into the cast member in the
direction shown by arrow A in Fig. 5. The pipe
being inserted and the gasket are selected so that
the outer diameter of the pipe is greater than the
inner diameter D of the gasket. The tapered surface
140j serves the dual functions of guiding the pipe
into the manhole section, and further collapsing
and/or compressing as the pipe is inserted beyond
the apex 140m of the gasket (see Fig. 5b), the apex
140m thus moves closer toward flange 140d. Cavities
140e-140h begin to collapse in a controlled manner
to provide different amounts of compression which
assures better centering of the pipe within gasket
140, further placing the resilient compressible
material at that portion of the gasket where it is
most needed.
As was mentioned hereinabove, the liner
sections of the present invention are produced using
a rotocast assembly method. Figs. 6, 6a and 6b show
one suitable mold for casting the curved liner
sections 100, the mold assembly 160, which is
fabricated to substantially resemble an elliptical
cylinder comprised of curved mold sections 1162, 162
2 1 62357
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which are substantially mirror images of one
another. Fig. 6c shows one mold section 162 looking
in the direction of arrows 6c, 6c shown in Fig. 6a.
A plurality of spaced, parallel recesses 162a are
provided within the mold section to define the
curved reinforcing ribs. The sides 162b, 162c of
each mold section are secured by fasteners F to
elongated joining members 163 in the manner shown in
Fig. 6a. The top and bottom surfaces of each mold
section 162 are provided with a plurality of
openings 162e, which receive fastening members (not
shown) for securely but releaseably mounting top and
bottom mold caps, one such mold cap 164 being shown
in Fig. 6b. Each mold cap is provided with a
lS plurality of openings 164a for receiving the
aforementioned fastening members to secure the mold
cap to the top 162d and bottom 162c ends of the mold
sections 162. Additional openings are similar to
openings 164a are provided at the top and bottom
ends thereof for securing the end caps to the top
and bottom sections 163. Openings 164a are aligned
with the openings 162e.
The mold material, which is preferably
polyethylene, is inserted into the rotor casting
mold assembly 160, which is mounted upon a suitable
turntable, and rotated, typically at an angular
velocity suitable to drive the mold material into
the mold sections, thereby forming a pair of panels.
More particularly, polyethylene in
powdered form is inserted into the tool. When the
cover caps are securely fastened to the mold tool,
the assembly is mounted upon a platform capable of
rotating in three (3) mutually perpendicular
directions.
21 62357
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The mold assembly is heated as it is spun.
- When a proper temperature is obtained for a suitable
time period, the mold assembly is transferred to a
cooling station where it is cooled as the mold
continues to spin. When the mold is cooled for a
sufficient period, it is sent to a stripping station
where the liner sections are removed. The process
is the same for each of the liner members of the
manhole sections with the only exception being that
the mold obviously differ for different sections.
In addition, although Fig. 1 discloses a manhole
assembly with a slab top and a liner therefor when
desired, a cone-shaped top can be substituted
therefor and liner sections to line the interior of
a cone-shaped top may also be produced using the
rotocast method.
Each panel represents one-third of the
circumference of a manhole section to be cast. The
mold sections 162 are of a suitable height. The
ribs or returns are spaced at six inch centers
enabling the panels to be cut down to the desired
height.
As was described hereinabove, the returns
along the vertical sides of the liner sections
cooperate to form a substantially T-shaped
configuration when the panels are positioned side-
by-side, enabling the C-shaped clip to be driven
over the top of the T-shaped arrangement, to provide
an effective seal.
The non-corrosive ties, preferably nylon
tie members, which are looped through the
reinforcing ribs at about the wire reinforcement
significantly increase the liner's ability to
withstand pull-out or loss of shape due to
hydrostatic pressure, the anchoring strength
21 62357
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resulting from the solid cross-section of the rotor
cast ribs.
The employment of low density liner
polyethylene as the molding material provides the
Sliners with excellent abrasion and chemical
resistance, high impact resistance, and the ability
- to withstand a multitude of welding methods to
fabricate custom designs, fasten appurtenances
thereto and/or facilitate field repairs.
10The uniform size liner sections, which
require separate molding means for manhole sections
of each standard diameter may be mass produced, and
conveniently stored in a compact manner for use
either in-situ casting in new construction or
15rehabilitation of existing underground structures,
the design herein elim;n~ting the need for custom
fabrication on a job site.
