FIELD

Embodiments relate to manhole covers and a process for manufacturing manhole covers; and more specifically, to manhole covers containing parts that are manufactured using a pultrusion process.

INTRODUCTION

A manhole (alternatively utility hole, cable chamber, maintenance hole, inspection chamber, access chamber, sewer hole or confined space) is the top opening to an underground utility vault used to house an access point for making connections, inspection, valve adjustments, or performing maintenance on underground and buried public utility and other services including sewers, telephone, electricity, storm drains, district heating and gas.

The top access opening of a manhole is protected by a manhole cover, a flat plug designed to reduce the possibility of and/or prevent accidental or unauthorized access to the manhole. Manhole covers works as a safety device and protects pedestrian/vehicle and any other objects entering into underground passages or confined spaces. Based on size and area of application these manhole covers have to bear high bending load based on criteria prescribed by government standards.

Depending upon the areas of application, the manhole cover has to meet a specific test load and displacement criteria.

Generally, manhole covers are made in circular, square, or rectangular shapes; and most commonly in a circular shape. For example, U.S. Patent No.

3,920,347 discloses a circular manhole cover. A side cross sectional view of a conventional manhole cover and frame design is generally shown in Figure 1 and indicated by reference numeral 10. Figure 1 shows an arrangement of a regular manhole cover with a simple support system such as for example a manhole cover 11 with its end portion resting on a frame 12. The manhole cover 11 is supported by the side frame 12. The manhole cover 11 is placed on the side frame 12 interface. Any load placed on the cover is transferred to side frame 12 through the interface surface of the manhole cover 11.

Conventional manhole covers or plugs are traditionally made of metal, but may be constructed from precast concrete, glass reinforced plastic or other composite material. Typically, the metal used for manhole covers is cast iron or steel. More recently, reinforced cement concrete (RCC) has been replaced by composite materials (e.g., a thermosetting resin and a glass mat reinforcement material). Known composite manhole covers provide the required strength and light weight criteria prescribed by government standards; however, the required manhole properties such as strength and weight are achieved by using a high percentage (e.g., greater than 30 percent by weight) of reinforcement materials and/or fillers. Also, known composite manhole covers are manufactured in 2-3 stages to address glass mat wetting issues, with challenges to maintain the bending strength of the manhole cover consistently.

WO 2012/056381 Al discloses a process that consists of open mold pouring of a mixture of a thermoset resin mixed with reinforcement fibers to manufacture a manhole cover. The above prior art mentions, in general, use of chopped fiber glass as reinforcement for a manhole cover; however, no working example is disclosed in the above reference.

U.S. Patent Publication No. US 2012/0114414 Al discloses a manhole cover and a method for manufacturing the manhole cover, wherein the manhole cover beneficially: (1) maintains strength and weight properties the same as those of conventional manhole covers made of cast iron, (2) eliminates the risk of theft, and (3) achieves improved corrosion resistance and sealing properties. The manhole cover comprises: a base unit made of composite materials having compositions containing 12 wt % to 18 wt % of glass fiber, 17 wt % to 23 wt % of a polyester resin, with the remainder being calcium carbonate (CaC0 ₃ ), wherein the base unit is mounted on the manhole such that an upper portion of the base unit is exposed aboveground; and a metal reinforcement unit which is uniformly distributed within the base unit to reinforce the base unit and increase weight and strength of the base unit. Further, US 2012/0114414 Al describes manufacturing a tightly sealed manhole cover including mainly two embodiments, (1) a base part which is exposed to the ground, and (2) an upper metallic reinforcement part placed over the base part. The base part is made of a composite polyester resin, glass fiber and CaC0 ₃ as filler agent; and optionally a UV resistant agent. The CaC0 ₃ filler agent contributes in increasing weight of the manhole. US 2012/0114414 Al discloses a polyester composite heat cured method of making a manhole cover which includes a wire of steel pipe or solid pipe as a metallic reinforcement part.

CN101906784A discloses a non-metal material reinforced unsaturated polyester resin manhole cover including a surface layer (1), where the bottommost layer of the manhole cover is a glass fiber cloth precast slab layer (5), a resin concrete layer (3) or a short fiber reinforcing layer (2), and the surface layer is orderly arranged from top to bottom. Also disclosed in the above reference is a method for preparing the non-metal material reinforced unsaturated polyester resin manhole cover comprising: (i) coating de-molding agent on the surface of the mold; (ii) orderly coating the surface layer, the short fiber reinforcing layer and the resin concrete layer; (iii) coating and vibrating the mold; (v) after coating, stopping vibrating; (vi) coating the glass fiber cloth precast slab layer on the resin concrete layer; and (vii) preserving and de-molding to fix the form and bonding the glass fiber cloth precast slab layer on the resin concrete layer through the bonding agent layer, where the preserving temperature is 10-40° C and the duration for molding is 20 minutes. The manhole cover is useful on the underground pipes of communication, water, natural gas, rain-dirt split-flow and petrochemical industry. The manhole cover: has high strength compared to the casting iron or cement concrete manhole cover; exhibits stealing resistance; is difficult to crush and is waterproof; resists acid and alkali; and is long standing.

U.S. Patent No. 5,132,069 discloses a method of molding complex composite articles having skin portions containing fibers to be injected with a resin and a core portion includes providing one or more galleries in the core or fiber skin and injecting resin into the gallery or galleries whereby it is rapidly transmitted to all portions of the skin. The galleries overcome the resistance to flow created by the capillary nature of the fibrous layer and enable more rapid mold cycles to be employed and more complex articles therefore to be molded.

All of the aforementioned prior art references disclose certain aspects of a manhole cover, but do not disclose the details of the manhole cover of the embodiments herein. It would be desirable to provide a manhole cover with the properties required by government or regulatory standards; and a process for manufacturing such manhole cover.

SUMMARY

Embodiments may be realized by providing a manhole cover composite article including (a) at least one pultruded elongated reinforcement member in a longitudinal direction forming an inner core skeleton of the manhole cover, and (b) a cured resin integral formed with the pultruded elongated reinforcement member. The thermoset resin encapsulates at least the outer surface of the pultruded elongated reinforcement member. BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the embodiments, the drawings show a form of the present invention. However, it should be understood that the embodiments are not limited to the precise arrangements and instrumentation shown in the drawings. In the drawings, like elements are referenced with like numerals. Therefore, the following drawings illustrate non-limiting embodiments, wherein:

Figure 1 illustrates a side cross-sectional view showing a conventional manhole cover on a support frame.

Figures 2a - 2d illustrate four different perspective views showing an exemplary embodiment of a manhole cover with pultruded parts overmolded in resin. Figure 3 illustrates a perspective view of a manhole cover having an inner core with pultruded parts, according to an exemplary embodiment. Figure 4 illustrates a perspective view of a manhole cover having an inner core with hollow pultruded parts place in both the longitudinal and the traverse directions, according to an exemplary embodiment.

Figure 5 illustrates a schematic box flow diagram showing an exemplary manufacturing process of the manhole cover.

Figure 6a illustrates a perspective view of several pultruded parts arranged parallel to each other and having varying strengths, disposed in the inner core of the manhole cover, according to an exemplary embodiment.

Figure 6b illustrates a perspective view of several pultruded parts arranged parallel to each other and spaced apart by varying distances, disposed in the inner core of the manhole cover, according to an exemplary embodiment.

Figure 7 illustrates a side cross-sectional view of the manhole cover with varying section modulus of the pultruded parts disposed in the inner core of the manhole cover, according to an exemplary embodiment.

Figure 8 illustrates a side cross-sectional view of manhole cover showing irregular pultruded closed section with multiple hollow partitions, as the inner core member overmolded in resin, according to an exemplary embodiment.

Figure 9 illustrates a side cross-sectional view of the inner core member with irregular pultruded closed section with multiple hollow partitions, according to an exemplary embodiment.

Figure 10 illustrates a side cross-sectional view of the manhole cover showing rectangular pultruded closed sections with multiple hollow partitions as the inner core member overmolded in resin, according to an exemplary embodiment.

Figures 11a - lid illustrate four perspective views showing exemplary embodiments of a manhole cover with pultruded parts overmolded in resin.

Figures 12a - 12c illustrate three side cross-sectional views showing an exemplary embodiment of a manhole cover with pultruded parts overmolded in resin. Figures 13a and 13b illustrate two perspective views showing an exemplary embodiment of a manhole cover with pultruded parts overmolded in resin and showing the manhole cover undergoing testing of application of a load.

Figure 14a and 14b illustrate the displacement and stress contour of exemplary manhole covers after undergoing displacement testing in the Examples.

DETAILED DESCRIPTION

Definitions

"Overmolded" or "overmolding" herein means molding of an article carried out in multiple steps, wherein one part is molded/pultruded separately such that the one part is placed inside a final article mold for embedding within a thermoset resin component, such that the resultant overmolded article includes the one part embedded within thermoset resin component.

"External load application" herein means load experienced by the manhole cover when subjected to either testing or due to service (such as movement of humans, animals, machines, and/or vehicles during service). " Bending load" herein means external load applied over the manhole cover either in test or load experienced during service. Bending load is applied perpendicular to the manhole cover top surface. "Stiffness" or "bending stiffness" or "geometric stiffness" or "rigidity" herein means resistance to bending, provided by the material and/or the geometry of the article. "Load carrying strength" herein means load bearing capacity of the manhole cover without visually observable failure of the manhole cover at targeted displacement correspond to applied load. Visually observable failure includes significant cracking and breaking of the manhole cover. "Section modulus" herein means geometric property for a given cross-section of pultruded parts used in the design of the manhole cover.

"Longitudinal direction" herein refers to the elongated ("length") direction of the pultruded parts. The length direction is differentiated from the "width" direction of the pultruded parts, which width direction is typically shorter than the length direction. The longitudinal direction encompasses forming the short side or a long side of a multi-sided manhole cover. For example, for a rectangular manhole cover having a short side and a long side, the pultraded parts in the longitudinal direction may define the short side (e.g., such that the pultruded parts are arranged in parallel to the long side) of the manliole cover; or the pultruded parts in the longitudinal direction may define the long side (e.g., such that the pultruded parts are arranged in parallel to the short side) of the manhole cover. "Traverse direction" herein refers to a direction crossing or intersecting the longitudinal direction in a plan view. For example, the traverse direction may form a right angle with the longitudinal direction in a plan view. "Parallel" herein refers to adjacent pultruded parts that are arranged side by side, optionally with a space therebetween. The adjacent pultruded parts may be arranged to have a substantially same distance continuously therebetween.

I. THE MANHOLE COVER CONFIGURATION

In its broadest scope, the embodiments encompass a manhole cover for the top opening to an underground utility vault, and a process for manufacturing the manhole cover composite article. In one aspect, for example, the manhole cover may include (a) at least one pultruded elongated reinforcement member in a longitudinal direction and optionally in a traverse direction forming an inner core skeleton of the manhole cover; and (b) a cured thermoset resin integral with the pultruded elongated reinforcement member. The cured thermoset resin envelopes or encapsulates the outer surface of the pultruded elongated reinforcement member.

In an exemplary embodiment, the manhole cover is made of a composite material and the at least one pultruded elongated reinforcement member, component (a), includes a plurality of separate (for example separately provided) pultruded elongated reinforcement members extending in the longitudinal direction and spaced apart from each other, and optionally extending in the traverse direction, that form an inner core skeleton of the manhole cover. The plurality of separate pultruded elongated reinforcement members may be in parallel configuration with varying distances between members such that a shorter pitch space is realized for the members near a center of inner core skeleton (or manhole cover) relative to the members further away from the center and/or near the lateral ends of the inner core skeleton (or manhole cover).

The Pultruded Elongated Reinforcement Member or Part

The pultruded elongated reinforcement members may be produced in sections of various profiles, for example, open sections such as I-shaped, C-shaped, H-shaped and the like; beams; angles; tubes; hollow squares/rectangles/polygons; and solid rods also of various profiles. Various combinations of different profiles for pultruded elongated reinforcement members may be used to form the manhole cover. The pultruded elongated reinforcement member can include, for example, a closed box sectional profile. When the pultruded member is an open hollow square, for example, the open ends of the pultruded part may include a closing member or any component which can be snapped onto each of the open sides of the pultruded part to make it a closed hollow member. In another embodiment, the hollow section of pultruded part can be closed by some means such as POP (plaster of paris) or some other ways like end caps, tape which can seal the hollow section and restrict flow of PU resin into the interior cavity of the hollow section of the pultruded part.

The manhole cover may include (a) at least one pultruded elongated reinforcement member in a longitudinal direction forming an inner core skeleton of the manhole cover; wherein the pultruded elongated reinforcement member is embedded, enveloped or encapsulated by (b) a cured resin (for example a thermoset resin) integral with the pultruded elongated reinforcement member. The manhole cover may optionally include at least one pultruded elongated reinforcement member in the traversing direction relative to the at least one pultruded elongated reinforcement member in the longitudinal direction. For example, the at least one pultruded elongated reinforcement member in the traversing direction may be located above and/or below the at least one pultruded elongated reinforcement member in the longitudinal direction.

The Inner Core

According to embodiments, the inner core includes at least one least one pultruded elongated reinforcement member elongated in a longitudinal direction. The pultruded elongated reinforcement member may have a circular or polygonal (including square and rectangular) cross-sectional shape (as viewed in a cross section taken along a direction traversing the longitudinal direction). The inner core may have a shape, e.g., a polygonal shape such as rectangular shape, corresponding to the polygonal shape of the desired manhole cover. The inner core may have a shape extending in any direction, e.g., a circular shape, corresponding to the circular shape of the desired manhole cover. The inner core may be formed using a combination of materials, such as for example using a pultruded member as a bottom portion of the inner core and optional a top portion having another pultruded member, chopped glass mat, and/or a steel grill.

The pultruded elongated reinforcement member can be made with any one or more of fiber reinforcements (such as glass, carbon, aramid, jute, and basalt) in combination with one or more resins (such as polyester, vinyl ester, polyurethane, cyanate ester, poly amide and epoxy). The pultruded elongated reinforcement member can be made with any one or more of the fiber reinforcements with one or more thermoplastic resins.

The inner core of pultruded parts can be prepared using various fabrication techniques. For example, longitudinally laid pultruded parts can be joined by connecting members that are transversely laid pultruded parts, which can optionally be interlocked together with longitudinal parts to make a complete core. Then, the fabricated inner core skeleton reinforcement can be overmolded with resin. The above fabricated inner skeleton can also include steel wire mesh, and pultruded strips. The inner core of pultruded parts can be fabricated by orienting pultruded bars in parallel (an optionally in a traversing direction) or the pultruded parts can be randomly laid at any suitable angle to form the inner core skeleton.

In an exemplary embodiment, the at least one pultruded elongated reinforcement member, component (a), includes a plurality of separate pultruded elongated reinforcement members spaced apart from each other and in parallel formation [configuration] forming an inner core skeleton of the manhole cover; and component (b) includes a cured resin (such as thermoset polyurethane resin) integral with the plurality of pultruded elongated reinforcement members. The cured resin envelops or encapsulates the outer surface of the plurality of pultruded elongated reinforcement members. For example, the cured resin completely encapsulates upper surfaces of the plurality of pultruded elongated reinforcement members, and optionally completely encapsulates both side and lower surfaces of the plurality of pultruded elongated reinforcement members.

The inner core skeleton may include a plurality of pultruded parts that can be of a hollow polygonal shape or circular shape, for example a rectangular section with shorter side (width) in the plane of manhole cover. The inner core section can also be of hat section or honeycomb section. The two hat section joined together can make a closed section. Pultruded parts can be of solid section with polygonal or circular section or I-section or L-section (for example two L-section pultruded parts can be combined to make rectangular or square hollow section). The section size and material of the pultruded parts can be determined based on a manhole cover size and/or a load carrying strength required for such manhole cover size.

An exemplary embodiment includes an inner core made from a plurality of pultruded reinforcement parts or members extending in the longitudinal direction, and optionally in the traverse direction, overmolded with a thermosetting polyurethane (PU) resin composition. The cured thermosetting polyurethane resin is cured with the plurality of pultruded reinforcement members (forming the inner core skeleton) embedded in the cured thermoset resin to form the manhole cover. The pultruded reinforcement members may be manufactured separately by a pultrusion process. The reinforcement members may have multiple partitions that could be of regular cross section or irregular cross section. The reinforcement members may be elongated members with a desired predetermined interior hollow section (for example having a regular/symmetrical cross section along an entire length of the reinforcement member). The elongated hollow members can then be laid up and integrated to prepare an inner core skeleton, which is then overmolded in the thermoset polyurethane (PU) resin.

The novel design of the inner core of the manhole cover provides several benefits such as (a) the flexibility to choose reinforcement type and resin to suit the desired load carrying capacity and/or deflection (b) flexibility to tune the load carrying capacity by increasing or decreasing the number of pultruded members in single mold; and/or (c) control overload and/or deflection of the manhole cover depending upon a pultrusion profile and/or material strength of the chosen pultruded parts.

An exemplary method of manufacturing the inner core of the manhole includes arranging a plurality of pultruded reinforcement members as the core. The pultruded reinforcement members can include, for example, pultruded hollow section parts, and extruded glass or carbon fiber strips, wooden and steel wire mesh, and/or chopped glass mat. In an exemplary embodiment, the skeleton of the reinforcement member can be made by combining hollow pultruded or solid pipes to form an inner core, for example, arranged in parallel or over top of each other placing in any direction, as per design load carrying strength requirements. Then, the inner core is placed in a mold for forming a manhole cover and the resin is injected or poured into the mold to make the manhole cover.

Exemplary embodiments of manufacturing the manhole cover include arranging a plurality of hollow section elongated pultruded bars as the reinforcement members, which are then overmolded with thermosetting PU resin. The pultruded bars may act as reinforcement to withstand the external load application. The bending stiffness of manhole cover may be mainly achieved by placing hollow pultruded parts that act as an inner core for sandwich design construction. For any given size and material, higher strength with lower mass may be attained with the hollow pultruded bars due its geometric stiffness. The pultruded parts offer high strength and light weight properties. The pultruded bars may be made up of resins such as unsaturated polyester or polyurethane with 5%-90% (by volume) of glass or carbon fiber content. The required hollow inner core shape can be readily achieved by using a pultrusion process. Exceptional strength along draw direction and with sufficient strength in transverse direction along with ease of manufacturing makes a pultruded part usable as an inner core for manhole cover. Optionally, rectangular pultruded strips may be placed transversely over the pultruded hollow section bars as shown in Figure 3. The rectangular pultruded strips may have a solid interior (for example, so as to exclude a hollow section). Arrangement of multiple pultruded parts with specific pitch (that may vary according to design) gives flexibility in design to increase load carrying capacity for a given pultruded part size and manhole cover size. The Pultruded Part Materials and Properties

The pultruded parts are made by either thermosetting or thermoplastic resin systems. The parts made with thermoplastic resins are also called extruded or coextruded parts. These resin systems can include for example, polyester, vinyl ester, polyurethane, epoxy, methacrylate, phenol resins, and mixtures thereof. As would be understood by a person of ordinary skill in the art, these resins should be of pultruded grades.

In one embodiment, the fiber content in the pultruded parts can range for example from 5 % by volume to 90 % by volume or from 5 % by weight to 90 % by weight. In another embodiment, the inner reinforcement core skeleton made up of the plurality of elongated members can contain from 10 percent (%) to 80 % glass fibers built up by the pultrusion process.

The fiber can be for example, glass, carbon, aramid (e.g., Kevlar), any other organic fiber, or mixtures thereof. Exemplary useful glass fiber or filament include, for example, E, C or S class with rovings weight between 600 to 9600 tex to form unidirectional rovings. Types of glass filament used for pultrusion can include for example (1) smooth roving, (2) textured roving, (3) monofilament roving, and mixtures thereof. Significant transverse strength can be achieved with the latter type of glass filament despite being in a unidirectional arrangement. Another type of useful fiber may include for example, continuous filament mats (CFM) with a multi-axial arrangement. Woven fabrics or non woven fabrics can be also be used in pultruded parts to increase transverse strength significantly.

The wall thickness of the pultruded part can be, for example, from a minimum of 1.5 mm to a maximum of 60 mm; from 2 mm to 50 mm; from 3 mm to 10 mm; and/or from 3 mm to 5 mm. The pultruded part, for example as shown in Figures 6 a-b and Figure 7, can be made of different wall thicknesses and different pitch between adjacent walls. The pultruded part may have a rounded fillet of from 0.5 mm radii to 5 mm radii. The density of the pultruded part may be, for example, within the range of from 1.2 g/cc to 3.0 gm/cc, and/or from 1.6 g/cc to 2.2 g/cc. Holes of various shapes and sizes can be machined in a post-pultrusion operation to aid arrangement of pultruded members in multiple directions. The tensile modulus of elasticity in the longitudinal direction of the pultruded part may be, for example, within the range from 1 GPa to 250 GPa, from 5 GPa to 150 GPa, from 8 GPa to 50 GPa, from 7 GPa to 40 GPa, and/or from 15 to 35 GPa. The flexural modulus of elasticity in the transverse direction of the pultruded part may be, for example, within the range of from 1 GPa to 250 GPa, from 5 GPa to 150 GPa, from 3 to 35 GPa, from 7 GPa to 40 GPa, and/or from 7 to 25 GPa. In an exemplary embodiment of circular or square manhole cover the pultruded members in longitudinal (and the optional pultruded members in transverse direction) may have equal or close range of material strength. In another exemplary embodiment of rectangular manhole cover, pultruded members placed along the longitudinal direction of manhole cover may have higher tensile modulus compared to pultruded members in the transverse direction, the strength ratio in longitudinal to transverse directionally placed pultruded members for a rectangular manhole cover can range anything between 1.0-20.0, the most optimum ratio is 1.1-3.0.

Discussion of the Other Figures

With reference to Figures 2a - 2d, there is shown one embodiment of a novel design of a manhole cover for a rectangular-shaped manhole cover, which includes the plurality of separate pultruded elongated reinforcement members spaced apart from each other and in parallel formation, shown in Figure 2d. In this embodiment, the manhole cover is rectangular shaped as shown in the top view. Figure 2a, of the manhole cover, shows the cured resin on top of the pultruded elongated reinforcement members. Figure 2b shows the cured resin all around and enclosing the pultruded parts and includes a chopped glass mat laid on top of the pultruded parts before the resin contacts the pultruded parts and cured in place on top of the pultruded parts. In the bottom view of the pultruded part, Figure 2c, there is shown cross ribs in the manhole cover used for adding strength to the manhole cover. In one embodiment, the manhole cover incorporates a chopped glass mat as additional reinforcement to the manhole cover, wherein the resin readily and substantially completely wets the glass mat and substantially completely fills the mold to complete the manhole cover article. Figure 2d, further shows the pultruded parts may be spaced apart by a relatively shorter distance along the traverse direction near the center of the manhole cover and spaced apart by a relatively longer distance further away from the center.

With reference to Figure 3, a further modification of Figures 2a- 2b includes a plurality of hollow separate pultruded elongated reinforcement members spaced apart from each other and in parallel formation in the longitudinal direction. Figure 3 further illustrates, pultruded elongated strip members (for example having a solid interior) spaced apart from each other and in parallel formation in the transverse direction (for example, perpendicular to the direction of the hollow plurality of separate pultruded elongated reinforcement members). With reference to Figure 4, there is shown another embodiment including a first set of a plurality of hollow separate pultruded elongated reinforcement members spaced apart from each other and in parallel formation in the longitudinal direction and a second set of a plurality of hollow separate pultruded elongated reinforcement members spaced apart from each other and in parallel formation in the transverse direction.

As aforementioned, a range of manhole cover sizes and shapes can be produced for different load carrying capacity by overmolding hollow section pultruded parts (laying it either longitudinally or transversely) and further strengthening its perpendicular direction by adding pultruded strips (carbon/PU/polyester) or with another set of hollow pultruded parts. In addition to hollow section/ rectangular strips of pultruded parts, mild steel wire mesh (gauge size 2-50 mm) can be added as additional reinforcement. The rectangular strips can also be replaced by steel strips. Steel wire mesh or strips can be used as an additional reinforcement, e.g., if the desired manhole cover does not have burglar proof requirements and/or restrictions on use of conducting material. The inner core member can also be built using hollow pultruded parts laid up either in longitudinal as well as transverse direction or combination of both as shown in Figure 4. This cross arrangement can be achieved either by simply placing pultruded parts laid up on top of each other or can be integrated before placing in mold by means adhesively or any other joining method.

With reference to Figure 5, an exemplary process for forming the manhole cover is provided. Step 51 includes manufacture of pultrusion parts

(pultruded parts). Step 52 includes positioning pultruded parts in an open mold to fabricate an inner core of the manhole cover. Step 53 includes providing/placing a chopped glass mat on the pultruded parts, for example, the chopped glass mat may be placed directly on the pultruded parts. Step 54 includes a step of providing a resin composition, such by polyurethane injection, in an overmolding process. Step 55 includes curing the overmolded polyurethane to form a manhole cover. The resultant manhole cover includes coated pultrusion parts that are embedded within the cured overmolded polyurethane. Once cured, the manhole cover article is removed from the mold and then may be used as a manhole cover.

Figures 6 -11 show other embodiments of the manhole cover. For example, with reference to Figure 6a, there is shown a plurality of hollow separate pultruded elongated reinforcement members spaced apart from each other and in parallel formation in the longitudinal direction. In this exemplary embodiment, the hollow members are elongated tubes rectangular in shape. The various hollow members can be made to have a different strength, i.e., a tensile modulus, depending on the positioning of the members, as indicated in Figure 6a.

For example, at least two members near the center of the inner core, indicated by numeral 1, can have the highest modulus say 100%. Further, at least the four members 2, near of the center members 1, can have a relatively lower modulus from about 50-80% of the highest modulus of numeral 1. Also, at least two members indicated by numeral 3, on each end of the array of members can have the lowest modulus of from about 30-50% of the highest modulus of numeral 1. While arranging the pultruded parts as per material modulus strength, the modulus of the pultruded parts can range from 2-300 GPa. The pultruded member numerals 1-3 can be placed as per their varying material modulus strength with highest modulus members near the center of the inner core with adjacent side member's strength can be chosen to have an arrangement with proportionally lower modulus towards outer members of the inner core. In one of the exemplary embodiments of inner core, as shown in Figure 6, two members in the center have 35 GPa (100%), then the four adjacent members next to center members have material modulus 20 GPa, approximately 57% of center members material modulus while the two members indicated numeral 3 have material modulus 15 GPa, approximately 43% of center members. While arranging pultruded parts their proportional material modulus strength can vary anything between 0-90 %, of the material strength of pultruded members.

Figure 6b, there is shown a plurality of hollow separate pultruded elongated reinforcement members in parallel formation in the longitudinal direction and spaced apart from each other in varying distances (so as to have a varying pitch). For example, moving away further from the center of the arrangement, the distance between the pultruded elongated reinforcement members can increase from a pitch ratio of 1.1 to 5.0 (from example of, 1.1 to 3.0, 1.1 to 2.5, or 1.1 to 1.8) from near the center of the inner core to the lateral ends of the inner core. The distance may increase as pattern, for example for each successive member or for a fixed multiple of successive members, when the members are arranged in a parallel formation.

For example, in an exemplary instance (for explanatory purposes only) where there are a total of eight members, there are two members near the center of the inner core, indicated by numeral 1, that can be spaced apart by a distance "d". Further, a member indicated by number 2 next to one of the members 1, can be spaced apart by a first distance from the member 1 such that the first distance is equal to a first ratio (within the range 1.1 to5.0) multiplied by "d" (dl=d* (one selected from 1.1 to 5.0). Further, a member indicated by number 3 next to the member 2, can be spaced apart by a second distance from the member 2 such that the second distance is equal to a second ratio (within the range 1.1 to 10.0) multiplied by "dl" (d2=dl* (one selected from 1.1 to 5.0). Further, a member indicated by number 4 next to the member 3, can be spaced apart by a third distance from the member 3 such that the third distance is equal to a third ratio (within the range 1.1 to 5.0) multiplied by "d2" (d3=d2* (one selected from 1.1 to 5.0)). In exemplary embodiments, d3 is greater than d2, d2 is greater than dl, and dl is greater than d, such that the distance between adjacent members increases in a direction from near the center of the inner core to the ends of the inner core. The first, second, and third ratios may be the same or different.

With reference to Figure 7, there is shown a cross-sectional view of one embodiment of the manhole cover having hollow members embedded therein. In this embodiment, the hollow members are rectangular in shape and vary in size in height and/or width. For example, from the center members 1 to the outside members 3, the height decreases and the width may also decrease or increase. The size of each of the hollow members can be varied to achieve a desired higher bending stiffness of the manhole cover. Pultruded parts with a greater size with higher section modulus can be placed centrally and pultruded parts with a reduced size with lower section modulus can be placed towards edge as shown in Figure 7. For example, the size of each of the hollow members can be from 20 mm to 500 mm. The thickness of the pultruded members can vary, e.g., from 0.5 to 50.0 mm. and/or 1.0-10.0 mm.

The arrangement shown in Figures 6a and 7 provides a significant load carrying strength to the manhole cover. The combination of both high material strength and increased section size of pultruded parts placed centrally can be effectively combined both at a longitudinal and a transverse direction. The material strength and section size of pultruded parts can be varied for its effectiveness to make any circular or polygonal mesh as an inner core. For example, the load carrying strength can be from about 500 kg to about 40,000 kg.

With reference to Figure 8, there is shown a cross-sectional view of still another embodiment of the manhole cover. In this exemplary embodiment, the reinforcement member making up the inner core is a one-piece truss-like shaped pultruded elongated reinforcement member having hollow sections defined within the one-piece part. Alternatively, the reinforcement member may have a solid interior defined with the one-piece part. The entirety of the one-piece part may be surrounded (e.g., completely surrounded) by the resin. The pultruded elongated reinforcement member making up the inner core member may be a plurality of irregular- shaped members and can be overmolded with resin (such as thermoset polyurethane resin) to make a manhole cover as illustrated in Figure 8.

With reference to Figure 9, there is shown a cross-sectional view of yet another embodiment of the hollow member. In this exemplary embodiment, the reinforcement member is a plurality of separate various shaped pultruded reinforcement members positioned in the mold as a truss-like shaped pultruded elongated

reinforcement member having hollow sections. The plurality of separate reinforcement members are surrounded (e.g., each member is entirely enclosed by) the resin. The irregular section, as shown in Figure 9, can be pultruded with different wall thickness and different percentages of fiber reinforcement to provide the desired or

predetermined load carrying capacity.

With reference to Figure 10, there is shown a cross-sectional view of still another embodiment of the manhole cover. In this exemplary embodiment, the reinforcement is a one-piece truss-like shaped pultruded elongated reinforcement member having hollow sections generally in a rectangular shape. Figure 10 shows an embodiment of a pultruded inner core with straight rectangular section with straight webs overmolded in resin. The spacing between webs, the height of the spacing and the thickness of the spacing can be changed to tune the load carrying capacity for a specific manhole cover size. The number of webs in the pultruded inner core is can be increased or decreased to suit the manhole cover size and load carrying capacity.

With reference to Figures 11a - l id, there is shown other embodiments of a rectangular- shaped manhole cover with transversely placed solid strips [(Figure lid) on the top of the hollow members positioned in the longitudinal direction before the strips and hollow members are contacted with the resin. The hollow members are illustrated as having a square cross-section, and other cross-sections are possible such as circular and rectangular. Figure 11a illustrates a top view Figure lib illustrates a cross-section view, and Figure 11c illustrates a bottom view, of after the hollow members have being contacted with the resin.

With reference to Figures 12a - 12c, there is shown variously arrangements of the inner core of a manhole cover with pultruded members embedded in PU resin. The parts dimensions are related to a design for 1.5 Tonne (15 kN) load carrying capacity. Figure 12a, there is shown a part having a total weight of 500 nm and having shorter spaced distances near the center and higher spaced distances near the lateral edges. Figure 12b, there is shown a part having varying widths of the PU resin as coated on the pultruded members. Figure 12c, there is shown with shorter spaced distance near the center and higher spaced distance between adjacent edge pultruded members.

With reference to Figures 13a and 13b, there is shown a manhole cover article design being subjected to an exemplary testing of a loading force of 1.5 Tonne (Figure 13a). In particular, Figure 13a illustrates a top view of the manhole cover and Figure 13b illustrates a bottom view of the manhole cover.

With respect to Figure 14a and 14b, there are shown representations of a manhole cover and the varying displacement/deformation and stress/strain contours, respectively, after undergoing displacement testing in a simulation example. The different shades provide a measure of the different displacements or stress contours. The displacement is measured in mm units. The stress/strain is reported as a percentage. Figures 14a and 14b are discussed further in the Examples.

The novel design of the manhole cover of the present invention and the method of manufacturing the manhole cover includes manufacturing the manhole cover by an overmolding resin process (for example a polyester/PU/epoxy resin) using pultruded reinforcement as core member. The present invention includes overmolding of pultruded hollow section part and strips in PU resin as outer skin. The reinforcement skeleton made of combining hollow pultruded or solid pipes to form an inner core. The inner core is placed in the mold and resin is poured to make a manhole cover.

II. THE PROCESS FOR MANUFACTURING THE MANHOLE COVER

With reference to Figure 5, there is shown a manufacturing process of the novel manhole cover of the present invention. The inner core is fabricated or simply placed inside the mold as per design size and strength chosen. Then the inner core is overmolded in PU resin. Referring to Figure 5, the manhole cover composite article of the present invention may be manufactured by the following steps:

(I) providing at least one pultruded elongated reinforcement member forming an inner core skeleton of the manhole cover, for example, this step includes providing a plurality of separate pultruded elongated reinforcement members spaced apart from each other and in parallel formation [configuration] forming an inner core skeleton of the manhole cover;

(II) providing a polymer resin composition such as thermosetting resin composition;

(III) placing the pultruded elongated reinforcement member in a manhole cover mold, for example, this step includes placing the plurality of separate pultruded elongated reinforcement members spaced apart from each other and in parallel formation in a manhole cover mold;

(IV) injecting or pouring the thermosetting resin composition over and about the pultruded elongated reinforcement member such that the thermosetting resin envelops the outer surface of the pultruded elongated reinforcement member, for example, this step includes injecting or pouring the thermosetting resin composition over and about the plurality of pultruded elongated reinforcement members such that the thermosetting resin envelops the outer surface of the plurality of pultruded elongated reinforcement members; and

(V) curing the thermosetting resin such that the thermosetting resin cures and envelopes the outer surface of the pultruded elongated reinforcement member (for example the plurality of pultruded elongated reinforcement members) in a cured state; and wherein the pultruded elongated reinforcement member (for example the plurality of pultruded elongated reinforcement members) forms the inner core of the manhole cover

Using the above novel method of making manhole covers, the manhole cover can be manufactured with a reduced development cycle time including making manhole covers of different load carrying capacity with single mold (e.g., from 0.5 Tonne to 40 Tonne) with uniform or varying thicknesses. Also, the novel manhole covers could be of different shapes such as rectangular shapes, polygonal shapes or circular shapes.

Step (I) - Providing the Elongated Reinforcement Members

The inner core of the manhole cover can be made up of one or more pultruded elongated reinforcement member(s). As would be understood by a person of ordinary skill in the art, pultrusion is a known method for fabricating reinforcement parts. An exemplary method of manufacturing the manhole cover includes the step of providing a plurality of separate pultruded elongated reinforcement members spaced apart from each other and in parallel formation [configuration] forming an inner core skeleton of the manhole cover. In one exemplary embodiment of the first step, the pultruded reinforcement members can be manufactured separately as elongated members with a desired predetermined interior hollow section. Regular standard cross section hollow pultruded members can be procured from other pultruded part manufacturer. Optionally, a chopped glass mat can be positioned on the top of the pultruded elongated reinforcement members and embedded in the resin along with the pultruded parts as additional reinforcement, wherein the resin readily and substantially completely wets the glass mat and substantially completely fills the mold to complete the manhole cover article.

Exemplary General Procedure of a Pultrusion Process

Pultrusion is the process of "pulling" raw material, such as fiberglass and resin, through a heated shaped die creating a continuous composite profile. An exemplary pultrusion process includes a series of steps that are geared toward creating a quality cured pultruded Fiber Reinforced Polymer (FRP) composite product. The pultrusion process includes the use of, for example, continuous fiberglass

reinforcement, pre-forming guides, an impregnation or resin bath, a heat source, a pull mechanism, and a cutting saw.

The exemplary pultrusion process starts with racks or creels holding rolls of fiber mat or doffs of fiber roving. Rolls of filament or fabric work are used to keep strength across the profile of the product. Most often the reinforcement is fiberglass, but the reinforcement may be carbon, aramid, or a mixture thereof. The machinery used in the pultrusion process includes a tension roller. The material spools and reinforcements are threaded into the tension roller. The roller will help to shape the pultrusion into what will soon become the finished product. The glass fibers are then contacted with a resin mixture using an impregnation means or a resin bath.

The exemplary pultrusion process involves pulling or drawing fiberglass (in the form of continuous roving filaments, or fiber bundles) off the racks and guided through a liquid resin bath or liquid resin impregnation system. The impregnating stage of the pultrusion may utilize different types of resin, such as polyester, vinyl ester, polyurethane, and epoxy resin. The raw liquid resin is typically a thermosetting resin, and the resin may sometimes be combined with fillers, catalysts, and/or pigments. Pigments may be used to add color and enhance the product' s appearance. Catalysts can be added to the resin to assist in curing or solidifying the profile. Other additives can be used in the resin mixture such that the final product can be protected from corrosion, UV rays, and other impact issues.

The liquid resin may saturate the fiberglass reinforcement. This saturation with the resin mixture (called "wet-out") allows for multidirectional reinforcement, which is why pultrusion results in a strong material. The fiber reinforcement becomes fully impregnated (wetted-out) with the resin such that all the fiber filaments are thoroughly saturated with the resin mixture. The resin, sometime referred to as "wet-out," will soak and permeate the unfinished product. As the resin- rich fiber exits the resin impregnation system, the un-cured composite material is guided through a series of tooling to arrange and organize the fiber into the correct shape, while excess resin is squeezed out, also known as "debulking." This tooling is known as a "pre-former." A surface veil may also be added to the fiberglass reinforcement to protect the product against erosion or "fiber bloom" and/or provide corrosion resistance and ultraviolent resistance. Often continuous strand mat and surface veils are added in this step to increase structure and surface finish of the composite.

The combination of resin and fiberglass is then pulled through a special heated and shaped die (in a process called polymerization) using a continuous pulling device. The resin can also be injected directly into the die in some pultrusion systems. The resin/fibers are exposed to a heat source. With the resin base now attached to the fibers, the product enters a hot, steel-forming die. This hot die is pivotal to the pultrusion process as the hot die creates the hard shape of the material. Once the resin impregnated fiber is organized and removed of excess resin, the composite is passed through a heated steel die. Precisely machined and often chromed, the die is heated to a constant temperature, and may have several zones of temperature through-out its length, which will cure the thermosetting resin.

Next, the mass of reinforcement material hardens to conform to the shape of the die and is heat-set into a permanent and rigid structurally reinforced shape. The profile that exits the die is now a cured pultruded Fiber Reinforced Polymer (FRP) composite. This cured FRP profile is now advanced along a pull mechanism. For example, the FRP profile can be pinched and pulled by a "gripper" system. Either caterpillar tracks or hydraulic clamps are used to pull the composite through the pultrusion die on a continuous basis.

The final step of the process may be when the profile meets the cutting saw, where resulting high-strength profile is cut into appropriate or predetermined lengths. At the end of the pultrusion process the cut-off saw is used to cut the pultruded profiles to a desired or predetermined length and the cut profiles are stacked for delivery or for further processing. This completes the pultrusion process and a finished fiberglass reinforced polymer may be the final result; and may be ready for use when it leaves the pultrusion machine.

Forming Inner Core

The pultruded parts are manufactured separately with desired hollow section and size and laid up and integrated to prepare an inner core skeleton, which is then overmolded in thermoset PU resin. In its broadest scope, a first step of the process of the present invention involves building an inner core structure comprising pultruded parts placed in longitudinal and optionally in a transverse direction followed by placing the inner core structure into a mold and then overmolding with resin as an outer skin.

An exemplary process of fabricating the inner core includes placing one, two or more, relatively high material strength pultruded bars as shown in Figure 6a located near the center of the manhole cover article as shown in Figure 7, and one, two or more, relatively lower strength pultruded bars toward outer sides of the manhole cover. This specific arrangement can made in the longitudinal and optionally in the transverse direction for cross layup configurations of the bars. This arrangement of having higher strength pultruded parts located near the center for a given section size provides higher bending stiffness for a given section size.

An exemplary process of fabricating the inner core, includes placing one, two or more, pultruded bars at varying spaces as shown in Figure 6b. This configuration may optionally be combined with the relatively high material strength pultruded bars as shown in Figure 6a. An exemplary method of manufacturing a manhole cover article includes the step of providing a plurality of separate pultruded elongated reinforcement members spaced apart from each other and in parallel formation [configuration] forming an inner core skeleton of the manhole cover. In one exemplary embodiment of the first step, the pultruded reinforcement members can be manufactured separately as elongated members with a desired predetermined interior hollow section. Optionally, a chopped glass mat can be positioned on the top of the pultruded elongated

reinforcement members and embedded in the resin along with the pultruded parts as additional reinforcement, wherein the resin readily and substantially completely wets the glass mat and substantially completely fills the mold to complete the manhole cover article.

Step (II) - Providing the Polymer Resin Composition for Overmolding

The final manhole cover is manufactured by overmolding of pultruded inner core skeleton reinforcement through overmolding process using a polymeric resin matrix. By using the overmolding process, the manhole cover can attain a specified shape and size, a required strength, and protection from impact and the environment.

The method of manufacturing a manhole cover article includes the second step of providing a polymeric resin composition comprising at least one polymeric resin. The resin composition used for overmolding may include either a thermoset or thermoplastic. Exemplary thermoset resins include polyurethane resins, epoxy resins, polyamide resins, and mixtures thereof. Exemplary thermoplastic resins included polyolefins (for example, polyethylene, polypropylene, C ₄ to C ₂₀ alpha- olefins, and any combinations thereof), polystyrene, thermoplastic polyesters (PET, PBT), and mixtures thereof.

Other optional components can be added to the polymeric resin composition components such as a curing agent for curing the thermosetting polymer resin. Other exemplary optional additives for the polymeric resin composition include particulate filler materials, catalysts, cure accelerators, dispersing aids, demolding agents, antioxidants, pigments, UV stabilizers, infrared absorbing materials, polyurethane based powders, silica (such as hollow silica nanoparticles), fire retardants, and/or adhesion promoters. Fillers for Weight Increase

It may be desirable to increase the weight of the manhole cover to reduce the possibility of dislocation or floating due to high fluid pressure, and fillers for this purpose can be used. For example, fillers such as saw dust, wood flour, and others can be used either for filling hollow section of the pultruded part or by placing the fillers in any form inside the mold. Fillers, such as gypsum, kaolin (clay) and alumina trihydrate may be used in composites to enhance performance and reduce costs as such fillers, compared to resins are currently inexpensive.

In some applications, it may be required to increase dead weight of the manhole cover to avoid its dislocation due to the underneath fluid pressure or some other reasons. To increase the manhole cover's dead weight, fillers can be added into the hollow portion of the pultruded parts. Filler materials such as sand, quartz, expandable foams, or combination of all these can be effectively used without compromising quality of pultruded inner core skeleton. In exemplary embodiments, the hollow sections of the pultruded parts may be filled with the filler materials before arranging the parts in the mold for the overmolding process.

Using a Polymeric Resin Composition for Overmolding

In an exemplary embodiment, overmolding process may include admixing components to make a curable resin composition for overmolding hollow pultruded elongated reinforcement members. For example, a thermoset polymer resin such as (i) an epoxy resin, (ii) a PU resin, (iii) a polyester resin; and (iv) mixtures thereof.

Then polymer resin mixture can be processed under conditions for forming a curable composition including heating the above mixture at a predetermined temperature and time to form an effective curable composition. The temperature of heating can generally be in the range of from 10 °C to 300 °C, from 30 °C to 200 °C, and/or from 50 °C to 160 °C. As would be understood by a person of ordinary skill in the art, the predetermined temperature may depend on the melting temperature of the components used in the polymer resin mixture. The heating time to form the curable composition may be, for example, generally from 6 minutes (0.1 hours) to 6 hours in one embodiment, from 15 minutes (0.25 hours) to 2 hours in another embodiment, and/or from 15 minutes (0.25 hours) to 1 hour in still another embodiment. As would be understood by a person of ordinary skill in the art, the heating time may depend on the melting temperature of the components used in the polymer resin mixture

Using PU Resin Composition for Overmolding

In another exemplary embodiment, the polymeric resin composition, formulation, or system used for manufacturing the manhole cover article includes, for example, includes polyurethane (PU) resin. The cured PU resin may be formed through use of a one component system or a two component system. The PU resin system may be selected based on properties like low density and ambient temperature curing. The PU resin system may optional be combined with other resins.

(i) The PU Resin

For a one component system, a PU resin or an isocyanate-terminated prepolymer component (including one or more isocyanate-terminated prepolymers) may be provided with a curing agent or in the presence of a curing agent (such as moisture for moisture-cured one component systems) to form the thermosetting resin composition. For a two component system, a PU resin may be formed as the reaction product of a polyurethane forming formulation that includes an isocyanate component and an isocyanate-reactive component. The isocyanate component may include one or more polyisocyanates, one or more isocyanate-terminated prepolymers, and/or a combination thereof. The isocyanate-reactive component may include one or more polyols and/or polyamines. An isocyanate index with respect to preparing the PU resin may be from 80 to 200. The isocyanate index is defined as the molar stoichiometric excess of isocyanate moieties in a reaction mixture with respect to the number of moles of isocyanate-reactive units (active hydrogens available for reaction with the isocyanate moiety), multiplied by 100. An isocyanate index of 100 means that there is no stoichiometric excess, such that there is 1.0 mole of isocyanate groups per 1.0 mole of isocyanate-reactive groups, multiplied by 100. The isocyanate-terminated prepolymer component, the isocyanate- reactive component and/or the isocyanate-component may further include at least one additive. Exemplary additives for both the one component and two component systems include catalysts, surfactants, blowing agents, and other additives for forming polyurethane polymers, as would be known to a person of ordinary skill in the art.

Exemplary isocyanate-terminated prepolymers include ones derived from at least one selected from the group of aromatic, cycloaliphatic, and aliphatic isocyanates. With respect to the isocyanate component, exemplary isocyanates include aromatic, cycloaliphatic, and aliphatic isocyanates. Exemplary isocyanates include m- phenylene diisocyanate, toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,4'-diisocyanate, and/or polymethylene polyphenylisocyanate (PMDI, also referred to as polymeric MDI).

Exemplary polyols include polyether polyols and polyester polyols. Exemplary polyether polyols may be prepared by polymerizing propylene oxide, ethylene oxide, and/or butylene oxide in the presence of an initiator compound or mixture of initiator compounds. The polyether polyols may have a number average molecular weight from 100 g/mol to 6000 g/mol and a nominal hydroxyl functionality from 2 to 8.

In an exemplary embodiment, a formulated polyol system that consists of base polyol(s), surfactant(s), catalyst(s), blowing agents (for example both chemical and physical blowing agents) is provided. Further an isocyanate component that includes PMDI is provided. The formulated polyol system may include from 80.0 wt% to 98.7 wt% of one or more polyols (e.g., polyether polyols), from 0.1 wt% to 5.0 wt% of one or more catalysts, from 1.0 wt% to 5.0 wt% of one or more surfactants, from 0.2 wt% to 1.0 wt% of one or more chemical blowing agents, and optional from 0 to 10.0 wt% of one or more physical blowing agents. (ii) Optional Reinforcement

Material

. Fiber mats can be made of various materials such as glass, carbon, aramid. Fiber source can also be naturally occurring materials like Jute, hemp, bamboo, etc., mats can be of various types such as chopped fiber mats, woven or non- woven mats, uniaxial or multiaxial mats, etc. (iii) Optional manufacturing step(s)

Additional optional manufacturing step(s) may be incorporated into the process of manufacturing the manhole cover. For example, In mold coating or painting can be used to provide additional protection as well as aesthetic appeal. Various colours can be used for color coding based on load capacities of manhole cover, which can also add to the aesthetic appeal. The additional coating (e.g., based on materials such as aliphatic polyurethane, epoxy, acrylate, polyurea, polyester, silicone, and/or hybrids of one or more materials) can be used to provide protection against UV, water absorption, abrasion, and/or various other enhanced properties. Another option for enhanced surface protection may include in mold or after molding pasting of a rubber or plastic pre-molded sheet for similar protection and/or aesthetic purposes.

Step (III) - Placing the Pultruded Members in a Manhole Cover Mold

The pultruded members may be placed in the manhole cover mold in any direction as desired to maximize the strength of the final manhole cover. In an exemplary method high material strength and high section modulus pultruded members are centrally placed and lesser section modulus and material strength pultruded parts are towards edge in descending order to increase the load carrying capacity of the manhole cover. The manhole cover load carrying capacity may be effectively designed and optimized in terms of number of pultruded members used, their material strength, section modulus (section size/thickness), direction of placement, and/or number of layers of pultruded parts on one another. Arrangement of the pultruded parts inside the mold may be carried out to hold the inner core pultruded members in one desired location by temporary supports, while resin pouring and solidification occurs.

Step (IV) - In jecting or Pouring the Resin on the Pultruded Members in the Manhole Cover Mold

Once the pultruded members are placed in the manhole cover mold, the polymeric resin is injected or poured over the pultruded members to fill the manhole cover mold. Providing of the resin can be include, for example, (i) manual mixing and pouring the resin in to the mold (ii) machine mixing and pouring the resin into the mold, or (iii) machine mixing and machine injecting the resin into the mold . The machine injecting method may help remove manual intervention and/or may result in better mold filling when glass fiber mats is present.. The mixing and injection pressure can be in the range of 150-200 bars. Any chosen method of thermosetting resin pouring should ensure encapsulation of inner core pultruded member without dislocation of inner core pultruded members.

The mold containing the pultruded members of the inner core and resin may be held in a compression press or by using heavy clamping mechanism. The clamping tonnage may ensure that the mold does not open during or after resin injection and blowing until curing is complete. The clamping force can be anywhere between 500 kg - 300 MT or 5 MT - 1000 MT, this varies with type of resin and size of manhole cover article.

Once the polymeric resin is injected or poured over the inner core and fills the manhole cover mold, the next step (V) is to cure the thermosetting resin composition to form a thermoset or cured composite manhole cover article. For example, the curing of the curable composition (a thermosettable composition or curable resin formulation) may be carried out at a predetermined temperature and for a predetermined period of time sufficient to cure the curable resin composition to form a cured composite manhole cover.

Step (V) - Curing the Thermosetting Resin

The ideal mould temperature/ curing temperature for PU resin system used is between 50 C - 70 C. However, it can vary anywhere between 10 C - 300 C depending upon the resin system & curing time used. The curing time used may very anywhere between 1 min to even several hours depending upon the resin system reactivity. Some ambient cured resin systems can take days for curing to certain degree and attain usable performance. Curing temperature of 55 C and curing time of 20 minutes was used for the preparation of the cured composite manhole cover of the present invention

Once the polymeric resin is poured over the pultruded members and fills the manhole cover mold, the next step (V) is to cure the thermosetting resin composition to form a thermoset or cured composite manhole cover article. For example, the curing of the curable composition (a thermosettable composition or curable resin formulation) may be carried out at a predetermined temperature and for a predetermined period of time sufficient to cure the curable resin composition to form a cured composite manhole cover.

In general, the curing step (V) for producing the cured composite manhole cover article of the present invention includes carrying out the curing step at process conditions to enable the preparation of a fully cured composite manhole cover product having the desired balance of properties for the manhole cover can be used in such particular application. For example, the curing temperature to carry out the curing step for preparing the cured composite manhole cover can be in the range of from about -10 °C to about 300 °C in one embodiment, from about 10 °C to about 280 °C in another embodiment, and from about 0 °C to about 260 °C in still another embodiment.

For example, the curing pressure to carry out the curing step for preparing the cured composite manhole cover can be in the range of from about 1 psig (6.9 kPa) to about 150 psig (1,034.2 kPa) in one embodiment; from about 5 psig (34.5 kPa) to about 80 psig (551,6 kPa) in another embodiment; and from about 10 psig (68.9 kPa) to about 20 psig (137.9 kPa) in still another embodiment.

For example, the curing time to carry out the curing step for preparing the cured composite manhole cover may be generally from about 2 minutes to about 90 days in one embodiment, from about 2 minutes to about 7 days in another embodiment, from about 3 minutes to about 1 day in still another embodiment, from about 5 minutes to about 8 hours in yet another embodiment, from about 7 minutes to about 4 hours in even still another embodiment, and from about 10 minutes to about 2 hours in even yet another embodiment. In other embodiments, the time of curing can include for example from about 1 minute or greater in one embodiment, from about 2 minutes or greater in another embodiment, from about 3 minutes or greater in still another embodiment, from about 5 minutes or greater in yet another embodiment, from about 7 minutes or greater in even still another embodiment, and from about 10 minutes or greater in even yet another embodiment. In other embodiments, the time of curing can include for example from about 90 days or lower in one embodiment, from about 7 days or lower in another embodiment, from about 1 day or lower in still another embodiment, from about 8 hours or lower in yet another embodiment, from about 4 hours or lower in even still another embodiment, or from about 2 hours or lower in even yet another embodiment.

The preparation of the cured composite manhole cover of the present invention, and/or any of the steps thereof, may be a batch or a continuous process. The equipment employed to carry out the curing step includes equipment known to those skilled in the art.

III. THE MANHOLE COVER PRODUCED BY THE PROCESS

After the curable resin composition is cured in the manhole cover mold, the cured product, which is the manhole cover, is removed from the mold. One exemplary embodiment of the manhole cover is shown in Figure 1 la - 1 lc.

The Inner Core

One of the beneficial properties of the core is to provide geometric stiffness to the manhole cover along with providing flexibility in design manhole cover for different load capacity using the same mold. The core of the manhole cover article may be made of pultruded parts either with hollow section or solid section. The number of reinforcement members may vary depending on size and configuration. For example, the number can be from 1 to 200 (for example, from 5 to 100 and/or from 4 to 16). The pultruded parts are made either by thermosetting or thermoplastic resin systems. The thermosetting resins may consist of any one or more of polyester, vinylester, polyurethane, epoxy, methacyclate, and/or phenolic resins. These resins grade should be suitable for use in pultrusion processes. The fiber content in pultruded parts is in the range 5-90% by volume or 5-90% by weight. The fiber could be glass (such as E glass), carbon, aramid (such as Kevlar), and/or any other organic or inorganic fiber.

The Cured Resin

One of the beneficial properties of cured resin is encapsulation of inner core pultruded members and optional distribution of the load uniformly across the manhole cover. The thickness of the cured resin can be generally from 2mm to 700 mm (for example, from 10 mm to 400 mm and/or from 20mm to 100 mm). The thickness of the resin may vary over different regions of the manhole cover.

Optionally, The Strips

One of the beneficial properties of the strips is increased structural support. The strips with rectangular section added to the manhole cover may be made of pultruded parts. The strips may include, for example, carbon, glass, polyurethane, polyester, epoxy, and/or vinylester. The thickness of strips may be in the range of 1 mm to 100 mm (e.g., 2 to 50 mm, 2 to 20 mm, etc.) and width may in the range of 5 mm to 1000 mm. The reinforcement glass content may range from 5-90% by volume.

The Overall Manhole Cover

The thickness of the core of the manhole cover article structure may depend on the intended use. For example, the thickness can be from about 5mm to about 700 mm (for example from 10 to 500 and/or from 20 to 200). In an embodiment where the manhole cover is rectangular, square, or polygon shaped, the overall size in length or width or side length in case of polygon shaped, may be from 50 mm to 2000 mm (for example, 100 mm to 1000 mm and/or 200 mm to 700 mm). For example, the length of the pultruded parts that form the inner core of the manhole cover may be from 50 mm to 2000 mm along the longitudinal direction. In the embodiment where the manhole cover is circular, the overall diameter of the manhole cover may be from 50 mm to 2000 mm (for example, from 100 mm to 1000 mm and/or from 150 mm to 600 mm).

IV. PROPERTIES OF THE MANHOLE COVER ARTICLE

The manhole cover according to embodiments may exhibit a load carrying strength from 1 kN and 400 kN (for example, from 2 kN to 400 kN and/or from 5 kN to 100 kN). The manhole cover exhibits a relatively light weight design, and the overall weight depends upon the size and load carrying capacity. V. END USE APPLICATIONS FOR THE MANHOLE COVER ARTICLE

The manhole cover is used to cover manholes. Other non-limiting examples of enduse applications for the manhole cover of present invention may include, for example, storage tank covers, electric conduit covers, telephone or data cable conduit covers any load floors and platforms to carry specific loads may be designed with above described pultruded member inner core molding method to achieve high strength and light weight goals.

EXAMPLES

Working Example 1

The novel manhole cover construction is as shown in Figures 1 la - 1 Id. The manhole cover is designed for an opening clearance size of 600 mm x 450 mm and a load strength of 1.5 tons (15 kN). The inner core is prepared by placing pultruded hollow square section of pultruded parts 40mm x 30mm with a thickness of 3.5 mm along the length of the resultant manhole cover and rectangular solid section pultruded strips placed over hollow pultruded parts in transverse direction as shown in Figure lid. Both hollow section pultruded parts and solid section strips have tensile modulus of 16 GPa in pultruded direction and 4 GPa in transverse direction are arranged in parallel along the longitudinal direction and second strips pultruded members are arranged in the transverse direction relative to the first pultruding members. The first and second pultruded members are chosen to place inside a mold so as to form an inner core.

Then, the inner core is overmolded with polyurethane resin having a density of 400 kg/m ³ and a modulus of 800 N/mm ² . The detailed design of innovative manhole cover for size 600 x 500 mm is as shown Figures 12a - 12c. The performance of the manhole cover design is simulated by applying 1.5 tons at the center through the rigid plate. The manhole cover size 650 mm x 500 mm is placed on a supporting frame with an opening clearance of 600 mm x 450 mm. The support frame, for simplicity, has been represented as rigid surface with overall size equal to manhole cover 650 mm x 500mm, with center opening equal to opening clearance. The rigid frame has width of 25 mm providing the interface support to manhole cover. The simulation has been carried out in commercial finite element analysis software AB AQUS 6.11. The simulation set up for Finite Element analysis model includes implicit with contact definition. The sliding contact is defined as surface to surface contact at interface between frame and manhole cover.

The pitch (spacing distance) between two adjacent pultruded hollow square sections affects the design performance of the cover. Thus, pitch is varied across the width/length of the cover to increase the strength of the manhole cover under the application of the load, the pitch ratio of 1.25 factor is used in this Example as shown Figures 12a - 12c providing shorter spaced distance 25 mm for centrally disposed pultruded members, adjacent members are at 30 mm considering ratio factor -1.25, and next adjacent pultruded members are at 38 mm as shown in Figure 12c. Similarly the pitch of transversely placed pultruded rectangular solid section stripes is varied to increase the strength of the cover (as shown in Figure lid). The stripes size is 494 mm x 24 mm x 3.5 mm with 16 GPa tensile modulus in pultruded direction and 4 GPa in the width direct. Additional rigid polyurethane based ribs are provided in transverse direction with short pitch distance between ribs at center and increased pitch distance along the outer members. The strength performance of the manhole cover of this Example is evaluated by finite element analysis. Figure 13 shows the finite element model set up representing the test method by application of the 1.5 tons (15 kN) load on the cover. This simulation finite element model is built in millimeter (mm), Newton (N), Tons (T) unit system.

The vertical load of 15000 Newton (1.5 tons) is applied through the rigid circular plate (100 mm diameter) placed at the center. The outer width of 25 mm on each side of cover is being rested on bottom side resting frame as shown in Figures 13a andl3b. The finite element analysis evaluation provided the strength performance of the cover.

The maximum deflection of a manhole cover under 15 kN load is 4.9 mm at the center as shown in Figure 14a and maximum principal stress on inner pultruded part is 73 N/mm ² at the bottom face of the part as shown in Figure 14b, it observed as tensile in nature along longitudinal direction and it is well below the failure stress of 400 N/mm ² . The strength of this cover design is adequate to sustain 15 kN (1.5 Tons) load without material failure, with maximum displacement less that 5 mm showing robustness and durability. Using this present novel method, the load bearing strength of the illustrated manhole cover design can be easily increased by increasing use of number of pultruded members or increasing the tensile and flexural strength of the pultruded part or both. The manhole cover design modifications in terms of use of number of pultruded parts and its strength to increase the load carrying capacity by utilizing same mold.

In addition to use of number of pultruded parts and strength of pultruded parts, adopting more number of rectangular solid section stripes with higher strength placed in transverse direction to pultruded members is also readily used in existing mold tool to increase load carrying strength. Use of chopped glass mat (as

reinforcement material) is another option of increasing load carrying strength of the manhole cover for a given size by using the same mold. Thus, this present invention provides flexibility in terms reuse of molds to cater different load carrying manhole cover for a given size. Another option of increasing the manhole cover load carrying strength is to increase the section modulus of pultruded members and using high strength of the pultruded members. If use of steel is restricted for burglar proofing then use of carbon pultruded stripes along with modifying class/type of glass is an optional for increasing the load bearing strength of given size without altering existing design and molding tool.