Classifications

• • E—FIXED CONSTRUCTIONS
  • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
  • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
  • E02D29/00—Independent underground or underwater structures; Retaining walls
  • E02D29/12—Manhole shafts; Other inspection or access chambers; Accessories therefor
  • E02D29/14—Covers for manholes or the like; Frames for covers
• • E—FIXED CONSTRUCTIONS
  • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
  • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
  • E02D29/00—Independent underground or underwater structures; Retaining walls
  • E02D29/12—Manhole shafts; Other inspection or access chambers; Accessories therefor
  • E02D29/124—Shaft entirely made of synthetic material
• • E—FIXED CONSTRUCTIONS
  • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
  • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
  • E02D29/00—Independent underground or underwater structures; Retaining walls
  • E02D29/12—Manhole shafts; Other inspection or access chambers; Accessories therefor
  • E02D29/14—Covers for manholes or the like; Frames for covers
  • E02D29/1454—Non-circular covers, e.g. hexagonal, elliptic
• • E—FIXED CONSTRUCTIONS
  • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
  • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
  • E02D29/00—Independent underground or underwater structures; Retaining walls
  • E02D29/12—Manhole shafts; Other inspection or access chambers; Accessories therefor
  • E02D29/14—Covers for manholes or the like; Frames for covers
  • E02D29/1472—Cover entirely made of synthetic material

Definitions

• the present invention relates to a manhole cover having a minimum thickness of 10 mm, in particular a manhole cover able to be subjected to bending loads, even high loads, in particular a manhole cover for pits, such as drain shafts, manholes, and suchlike, able to close an access opening, which may be located, for example, in the ground or a floor, and able to bear heavy loads, such as those transmitted by the wheel
• the invention also concerns a process for the production of the said manhole cover.
• Manhole covers have long been made of metallic materials, such as steel or cast iron. Because of the ensuing great weight, as well as for corrosion resistance reasons, attempts have been made to replace the metallic material with lighter, cheaper materials, such as thermosetting plastics, particularly polyurethane. Among other things, these materials offer the advantage of allowing the manufacturing of pieces that are less noisy when installed and subjected to the passage of vehicle wheels. To ensure high mechanical resistance, particularly during bending, it has always been necessary to provide reinforcement structures to embed in the plastic material during moulding of the article. For example, structures have been proposed such as a suitable intertwined pultruded fibreglass rods to insert into a mould prior to the injection of a plastic material. The fibreglass can be rendered compatible with the plastic material utilised by means of coatings with appropriate chemical agents. Plastic materials utilised include polyester and polyurethane, the latter being preferable, due to its resistance to
• the invention also relates to a manhole cover made of a thermosetting plastic material, having a thickness of at least 10 mm, comprising a plurality of reinforcement fibres (meaning that a layer with a different fibre concentration may be envisaged, as may be a substantially fibre-free layer), which is uniformly dispersed in the volume of the 5 thermosetting material, in particular a manhole cover obtainable by means of the aforesaid process.
• the manhole cover is, in particular, a manhole cover able to withstand the application of a load of at least 100 kN, applied - in accordance with the testing procedures envisaged by standard EN 124 - to the upper face, with the manhole cover laid and the 10 border (measuring a minimum of 5 mm) around the edge of the lower face resting in position.
• thermosetting plastic material is a two-component material, usually comprised of two different monomers.
• polyester or epoxy resins Particularly preferred is polyurethane, with the mixture of reagents preferably
• both components have a viscosity of no more than 5000 mPa*s, and more preferably no more than 3000 mPa*s, in the absence of mineral fillers. If mineral fillers (e.g. calcium carbonate) are employed, the viscosity of the components after addition is preferably no more than 50000 mPa*s, and more preferably no more than 20000 mPa*s.
• mineral fillers e.g. calcium carbonate
• the manhole cover is plate-like in appearance and has any appropriate form, for example, rectangular, square, or round. It has two substantially parallel faces, usually an upper face destined to be facing towards the exterior, especially if it is a manhole cover for pits, and a lower face able to rest on a relative seat, generally around the edge thereof, the said seat being part of a frame which is appropriately5 positioned in correspondence with the opening to be closed.
• projections may be provided to render the surface less slippery
• the lower face there may be reinforcement, or depressions to reduce the thickness in areas subjected to less stress.
• the lower face may have projections in 5 correspondence with the area of the edge intended to rest on the corresponding frame of the seat made in the pit or similar structure, in order to properly distribute the load on the frame and ensure proper closure around the entire perimeter.
• the fibres may be of the carbon, aramid, or, more preferably, glass variety, and the polymerized mass of
• the finished manhole cover may have a concentration by weight of between 20 and 70%.
• the length of the fibres should preferably be between 10 and 120 mm, and more preferably between 20 and 80 mm.
• the length may be chosen in consideration of the thickness of the manhole cover, in particular to prevent agglomerates, inhomogeneity, or undesired preferential orientations occurring due to the shifting of the mass of reagents
• Figures 1, 2, and 3 represent schematic views, showing respectively, a plan, a cross section cut along plane II-II of figure 1, and a bottom-up view of a manhole cover obtainable according to the present invention
• Figure 4 represents a schematic view of the production process in accordance with the present invention.
• Figure 5 represents a schematic view of the production process in accordance with a different aspect of the present invention.
• Figures 1 and 2 show a manhole cover for pits, according to a particular aspect of the present invention.
• the manhole cover is plate-like and appropriately shaped, as mentioned.
• the said cover is square-shaped, which represents the most common type.
• the manhole cover 1 has an upper face and a lower face 2, which are substantially mutually parallel, and their distance apart is the thickness, which is over 10 mm.
• the process according to the invention allows the manufacture of the manhole covers with excellent results as regards homogeneity, mechanical characteristics, and reproducibility of results, even with the thicknesses stated above, which are necessary for parts of that type; it has been found that these results can also be obtained in the construction of manhole covers with thicknesses of over 10 mm, and even with thicknesses up to 80 mm, which constitutes a particular aspect of the present invention.
• These thickness values should concern at least 1/3 of the surface of the faces, and preferably at least 40% of the said surface.
• the thickness of substantially all of the said areas is, however, at least 10 mm.
• holes for example, holes that run through the thickness of the manhole covers, designed for the application of extractors, as already commonly occurs in the case of manhole covers according to the commonly known technique.
• reliefs or channelling on the faces for example on the upper face, there may be writing or formations in relief 3 and 4 designed to foster friction with feet or soles to prevent slipping, the said writing or formations being similar in size to those which are customary for these structures.
• Lighter areas may be provided, with reduced thickness with respect to the rest of the article, such as, for example, the appropriately shaped indentation 5 made on the lower face.
• the manhole cover resting area on the lower face is constituted of a border 6 with a minimum width of 5 mm, which can be in relief. It can be continuous or discontinuous around the edge of the lower face, depending on requirements, and can have an appropriate section, for example, a semi-circular section, as shown in Figure 3, to allow adequate deformation and appropriate load distribution, preventing undistributed stress caused by irregular deformation of the manhole cover under load, and improving the seal.
• teeth 7 may be teeth 7 present, designed to engage with the indentations in the frame of the pit and act as a hinge point during the early stages of manhole cover lifting, or simply as a guide for correct placement of the manhole cover, and any other type of known structure, commonly used in this field.
• the manhole cover is suitable for pit structures of a commonly known type, with frames made of commonly used materials, such as metal, reinforced or non-reinforced plastics, including the types used in the manufacturing of the manhole cover.
• the frame may, if desired, also be manufactured in different colours.
• the frame is plastic, it can be appropriately coloured through the introduction of pigments into the mixture to be sent to the mould.
• the colour may perform the function of identifying different characteristics, such as the intended use of the pit, the manufacturer, or otherwise.
• the manhole cover manufacturing process may include manufacturing of the mixture, introduction of the fibre, and injection into the mould using technology known as LFI (i.e. "long fibre injection") or InterWet.
• This technology involves measuring out and sending the reagents (preferably polyurethane reagents) to a suitable mixing head and sending the reinforcement fibre, in the form of one or more continuous filaments (called roving), to a cutter that continuously produces fibre flakes cut to a predetermined length.
• reagents preferably polyurethane reagents
• roving continuous filaments
• the cut fibre which is extracted by a Venturi system inside the mixing head, encounters the mixed reagents and is impregnated therewith.
• a homogeneous mixture of fibre and resin is issued from the mixing head and distributed over the surface of the mould, following an optimised path.
• the fibre/resin weight ratio is set according to the desired mechanical properties.
• a system of air jets diverts the path of the mixture, in flight, thereby allowing modulation of the distribution, to create large, thin or narrow, thick layers of fibre and resin.
• the length of the cut and the instantaneous flow rate of the fibre can be varied in real time to create zones of the article with different mechanical properties.
• the fibre if necessary, with the surface thereof treated with appropriate finishes to render it compatible with the resin, comes in the form of reels.
• the continuous roving is conveyed, if necessary with the help of air jets, to the cutter via rigid pipes and flexible springs to follow the movement of the spray head.
• Appropriate sensors monitor the presence of the roving, correct unwinding of the reels and any clogging of the cutter.
• This technology is of a kind used commonly in the production of vehicle parts, such as dashboards, bumpers, rear window shelves, exterior panelling for bodywork on industrial and earth-moving vehicles and impact-resistant panels.
• the articles in whose production this technology is used generally have limited thicknesses and are not made to withstand high bending loads; to increase resistance to these types of stress, they are made with ribbing, whose extension is such that they are not possible in a product as compact as a manhole cover.
• the bending resistance in these cases is not comparable to that required by legislation on manhole covers. It has now been found that it is possible, with this type of technology, to manufacture manhole covers which have necessarily higher thicknesses without generating fibre distribution problems, even with
• a process according to the present invention shall now be outlined with reference to Figure 4, in which this technology is applied.
• Appropriate sources 8 and 9, respectively, supply the polyol and isocyanate, i.e. the two components of the polyurethane matrix, through lines 12 and 13, to the mixing head 11, which homogenises the two components; the reinforcing fibre, coming from one or more reels 14, is fed to the cutter 19, where it
• [ 5 is cut and extracted continuously by the device 10 inside the mixing head, where it encounters the polyurethane mixture and is impregnated therewith.
• the fibre reel especially if a polyurethane material is used, can be appropriately finished; this pre- treatment renders it compatible the fibre with the polymer.
• the fibre is usually available on the market already finished.
• Other components such as initiators or catalysts or to mineral fillers, such as calcium carbonate, for example, may be pre-mixed with one of the reagents or be appropriately introduced.
• the mixing head 11, which may or may not be in correspondence with the extraction device, is also capable of spraying the mixture into the mould 17, designed to be closed by an appropriate counter-mould. According to a possible aspect of the invention, the mixing/spraying head can be fixed. According to a possible aspect of the invention, the mixing/spraying head can be fixed. According to a possible aspect of the invention
• '.5 another aspect of the invention, it can be movable, for example mounted on a robotic arm 16, so as to achieve a pre-distribution of the material within the mould before closing the counter-mould.
• the fibre can also be mixed with the reagents (preferably polyurethane reagents) immediately downstream of the mixing head, for example, according to a technology known as CMS PUR (Composite Spray Moulding) or Outerwet.
• CMS PUR Composite Spray Moulding
• these technologies involve measuring out and sending the polyurethane reagents (polyol and isocyanate) to a suitable mixing head 11 and sending the reinforcement fibreglass from the reels (always in the form of one or more continuous filaments, a.k.a. roving), to a cutter 19 which produces continuous fibre flakes cut to a predetermined to length.
• a spraying process is used to cast the fibre-enriched mixture.
• the polyurethane mixture is sprayed directly into the open mould and, by means of an appropriate introduction device 10, the pre-cut fibreglass encounters the jet of reagents mixed at the mixing and spraying head output and is impregnated therewith in mid air, before reaching the surface of the mould.
• the polyurethane and fibreglass mixture thus formed is distributed over the surface of the open mould, following an optimised path, as per the technology solution described earlier.
• the measuring and spraying system allows maximum production flexibility by allowing the casting of different layers.
• Combinations of layers with different formulations can be adapted to the specific needs of the finished product.
• the mixture is introduced into a mould 17, shaped in correspondence with the upper face of the manhole cover and the mould is then closed by a counter-mould shaped in correspondence with the lower face.
• This allows better distribution, especially with manhole cover forms such as those exemplified, and evacuation of the air from the mould when it is closed, especially in the presence of projections on the upper face and the indentation on the lower face.
• a first layer devoid of fibre or with a lower concentration of fibre, preferably of a thickness of between 0.5 and 2 mm, into the mould with the shape corresponding to the upper face and then supply the rest of the material with fibre.
• a manhole cover is manufactured with the upper face devoid of fibre, which is desirable for aesthetic reasons and for the material's surface abrasion resistance. In this way, the need for coatings or other surface treatments is eliminated.
• the viscosity of the mixture and the setting time are parameters that can be adjusted by choosing different reagents types, which should be chosen taking into account factors such as the need to avoid creating preferential orientations in the fibres, and the need to avoid entrapment of bubbles in the mould
• the mould and the counter-mould can have appropriate gas flow release systems, such as appropriately positioned holes in the counter-mould.
• the moulding time was 7 min, after which the mould was opened and the piece extracted. After removal of the sprue, the final weight of the piece amounted to 3076 g.
• the fibreglass content measured at several points of the finished piece, averaged 40%.
• the final weight of the piece amounted to 3185 g.
• the fibreglass content measured at several points of the finished piece, averaged 40%.
• the load values shown in the above tests are those envisaged by the aforesaid legislation. It should be noted that the aforesaid pieces withstood, without presenting detectable cracks or defects, even when subjected to loads of 180 kN.
• a layer of polyurethane without fibre is distributed for about 2 seconds.
• the polyurethane is sprayed on so as to cover a large area.
• the mixing head moves horizontally at 250 mm/s along a square path which is concentric to the mould; the path is sufficiently sized and of sufficient height to allow complete coverage of the mould bottom.
• the head moves up to a higher level and activates the fibreglass supply.
• the head completes a further two laps around the casting path at a speed of 80-85 mm/s, for a duration of 15-16 seconds.
• the head stops the supply of fibre and polyurethane.
• Distribution of the polyurethane and fibreglass in two laps completed quickly is more homogeneous than distribution in a single lap at half speed.

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• Engineering & Computer Science (AREA)
• Environmental & Geological Engineering (AREA)
• Life Sciences & Earth Sciences (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Mining & Mineral Resources (AREA)
• Paleontology (AREA)
• Civil Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Structural Engineering (AREA)
• Moulding By Coating Moulds (AREA)
• Underground Structures, Protecting, Testing And Restoring Foundations (AREA)

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• 2011
  • 2011-10-20 BR BR112013008978A patent/BR112013008978A2/pt not_active IP Right Cessation
  • 2011-10-20 CN CN201180046561XA patent/CN103124819A/zh active Pending
  • 2011-10-20 US US13/814,819 patent/US20130136537A1/en not_active Abandoned
  • 2011-10-20 EP EP11799308.9A patent/EP2633127A1/de not_active Withdrawn
  • 2011-10-20 RU RU2013119616/05A patent/RU2582396C2/ru active
  • 2011-10-20 WO PCT/IB2011/054692 patent/WO2012056381A1/en active Application Filing

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