Title

High strength, light weight, abrasion resistant, UV stabilized, corrosion and abrasion resistant, anti slip/ anti skid, zero scrap value, less expandable fibre reinforced plastic manhole cover and frame.

Field of Invention

The present invention relates to high strength and relatively light weight, abrasion resistant, UV stabilized, corrosion resistant, anti slip / anti skid, zero scrap value, less expandable and/or air tight/leak proof fibre reinforced plastic manhole cover 8B frame, in the field of manhole cover manufacturing technology.

Background

A manhole cover is a removable plate forming the lid over the opening of a manhole, to prevent anyone from falling in and to keep unauthorized persons out. A manhole cover is generally placed on the road as top opening which provides easy access to undertake maintenance of the underground sewerage system. The said manhole covers are commonly made by the solid steel which withstands heavy loads of vehicles. Therefore, the manhole cover requires greater tensile and impact strength and rigidity to withstand heavy loads. Usually the manhole cover assembly consists of two parts i.e. manhole cover and its frame.

US Patent no.5788406, teaches about a manhole cover which can be lifted by a spring and supported by a bar assembly.

US patent no. D.583067, which teaches about manhole assembly gate valve sealing structure.

Objects of the invention

The primary object of the present invention is complete wrap-up which forms continuous reinforcement all around the polymer concrete thereby imparting excellent tensile strength to the entire product which is highly prone to tensile load and simultaneous/parallel processing of both anti-skid abrasion resistant top part as well as the bottom part of the manhole cover and frame, bonding of top and bottom part during tack free stage ensures excellent bonding between the two parts which is one of the critical aspects for performance of the product due to which the bonding between the two parts is very strong, if the preparation of both the parts (top part & bottom part) is not undertaken simultaneously then there are chances of de-bonding of top and bottom parts due to weak adhesion.

Important object of the present invention is instead of giving flat edge at the interface of the manhole frame and cover, curvature of the bottom of manhole cover is extended till the edge of the cover therefore the sudden change in cross section of the manhole cover is avoided which in turn reduces the stress concentration at the junction of profile due to which the load is divided in two components (one in vertical direction and one in horizontal direction) which divides load thus preventing failure of the cover at the interface of the frame and cover due to concentrated shear stresses as shown in the prior art. This object of invention increases the life of the product considerably and in turn reducing the life time cost of the product.

Very important object of the invention is application of vibration which results in getting very compact and void free polyconcrete mix, ptimized ratio of mesh sizes of fillers in polymer concrete mixture also helps in obtaining void free and compact polymer concrete core resulting in better load bearing capacity of the product and fatigue resistance. Another important object of the invention is addition of gelcoat layer which protects the cover from harmful toxic gases, chemicals, liquids, etc. and thereby increasing the life of the product, gelcoat reinforcement layer imparts strength to the gelcoat layer thereby enhancing its flexibility.

Another important object of the invention is addition of top cast layer which gives abrasion resistance and UV stabilization to the product and addition of reinforcement layer to top part increases the flexibility and impact strength absorption of the product.

Very important object of the invention is addition of special additivesto enhance mechanical and chemical properties of the product significantly adds to the life of the product.

Another important object of the invention is chamfered edge design of moulds helps significantly in reducing chipping of the edges of the product. Pouring of resin on the filler after vibrations helps to fill all the air gaps present after vibration thus enhancing the strength and fatigue rating of the product. Addition of resin putty paste greatly helps in increasing the bonding between the top and bottom parts making a homogenous product after demoulding. Application of resin putty paste at the edges after grinding helps to protect the exposed reinforcement fibres from the external environment thus extending the life of the product.

Description with reference to drawings

Fig. l:- Perspective view of the manhole cover assembly, according to a preferred embodiments of the invention.

Fig.2:- Illustrating the preferred embodiments of the bottom mould Fig.3:- Illustrating the preferred embodiments of the wrapped bottom mould

Fig.4:- Illustrating the manhole cover top mould, in accordance to the preferred embodiments

Fig.5:- Perspective view of the frame assembly, according to a preferred embodiments of the alleged invention.

Fig.6:- Illustrating perspective view of the shapes of the bottom mould of manhole cover

Fig.7a:- Illustrating view of prior art design of manhole cover and frame

Fig; 7b:- Illustrating view of invention of gradient design of the manhole cover and frame assembly

Description The present invention describes about a high strength and relatively light weight, abrasion resistant, UV stabilized, corrosion and abrasion resistant, anti slip/ anti skid, zero scrap value, less expandable fibre reinforced plastic manhole cover and its frame and a method of manufacturing thereof. The present invention is designed to overcome a number of problems associated with prior art manhole cover and frame assemblies, including a specified embodiment. The alleged invention comprising of a bottom mould and top mould as shown in figures 1 to 7b containing base support which facilitates to provide required shapes of mould bottom (1) as shown in figure 1. The said bottom mould having various shapes as shown in figure 6 such as cylinder with convex curvature, cylinder with concave curvature, flat bottom, complete curvature, corrugated bottom, the said bottom base support is detachably associated with mould (2).

The release agent (3) is a layer applied on the mould surface to prevent adhesion of gelcoat layer to mould surface, which is helpful in demoulding the final product. A gelcoat layer (4) fig. l and fig.2 having characteristics of non porous resin rich layer which prevents product from toxic gases, liquids and toxic chemicals etc, the said gelcoat is also provides the flexibility and abrasion resistance, when it is applied on the release agent, layer on finished smooth side of mould . The gelcoat layer is strengthened with a gelcoat reinforcement layer (5). In the further embodiment of the present invention contemplates producing a manhole cover and frame, according to the figure. 2 which shows bottom part preparation comprising of first resin impregnated extended first reinforcement layer (6) as shown in fig.2 is placed on reinforced gelcoat layer, and the both the ends of this layer are upwardly vertically or horizontally arranged to facilitate complete wrapping of all reinforcement and polyconcrete layers. Multiple reinforcement layers (7) fig 1 and fig 2 are impregnated with resin to provide desired strength to the product which is applied onto the extended first reinforcement layer.

Polyconcrete (8) mixture is poured on the multiple reinforcement layers to form a core which imparts rigidity, strength to the product. The entire assembly allowed to vibrate by vibrating means to release entrapped of air in the polymer concrete core. Further the resin (9) is poured on polyconcrete mixture to fill up the air gaps that remains even after vibration. The said product is allowed to wrap with extended first reinforcement layer to cover all reinforcement and polyconcrete layers. A resin adhesive paste (10) poured on this layer as shown in fig 3 for better adhesion between top and bottom parts. A top mould (11) as shown in figure (4) having a characteristic of abrasion resistant, antf -skid / anti -slip, UV stabilised, decorative and flexible layer having chamfered edges are provided to avoid chipping as shown in fig 4. Release agent (12) is applied on the finished side of the top mould surface and then mixture of quartz silica crystals and resin (13) is poured on the release agent layer._The resin impregnated reinforcement layer (14) is being applied to the top mould to provide tensile strength, better bonding between top and bottom parts of the product. The details of the product including name, logo or device of customer, manufacturer etc., can be casted over the top mould.

Simultaneous/ parallel processing of anti-skid abrasion resistant top part as well as the bottom part of the manhole cover ensures excellent bonding between the two which is one of the critical aspects for performance of the product, due to simultaneous initiation of curing process, the bonding between the two parts is very strong, if the preparation of both the layers (top part 8B bottom part) is not undertaken simultaneously then there are chances of de- bonding due to weak adhesion, good inter-laminar bonding makes the complete system homogenous which results into much better load carrying capacity, Instead of giving flat edge at the interface of the manhole frame and cover (fig.7a), curvature of the bottom of manhole cover is extended till the edge of the cover (fig.7b), the sudden change in cross section of the manhole cover is avoided which in turn reduces the stress concentration at the junction of profile, during the load tests, when the point load is applied at the centre of the cover, it transfers to the frame at the interface of the cover and frame, at the contact point, because of the inclined surface, the load is divided in two components (one in vertical direction and one in horizontal direction), this vertical component of the load is lesser in magnitude than the applied load by Cosine of the angle (as shown in the diagram), this reduced load preventing failure of the cover at the interface of the frame and cover due to concentrated shear stresses in the prior art, ultimately, this invention increases the life of the product considerably and in turn reducing the life time cost of the product,

Addition of special additives like air release agents, bond improvement of filler, to improvise wetting of fillers, UV stabilizers, low shrinkage, etc to enhance mechanical and chemical properties of the product significantly adds to the life of the product,

Chamfered edge design of moulds helps in significantly reducing chipping of the edges of the product, Application of resin putty paste mixed with hardeners at the edges after grinding helps to protect the exposed reinforcement fibres from the external environment for extending the life,

Post curing of the product is undertaken if required to complete the polymerization process,

Manhole cover optionally contains an air tight/ leak proof manhole cover with an arrangement such as a rubber gasket for sealing.

A manhole cover with single frame and single cover or single frame with multiple covers is also additional feature of the present invention.

A manhole cover optionally has a locking arrangement for extra protection.

A manhole cover with frame optionally contains a tray which is provided below the cover for collection of dust, sand or small particles.

Method of manufacturing;

A method of manufacturing high strength, UV stabilised, less expandable, low weight, corrosion and abrasion resistance, zero-scrap value manhole cover and frame, and its method of manufacturing thereof, the ^"" said method comprising the following steps, the moulding is carried out in two parts i.e. bottom part preparation and top part preparation. The purpose of bottom part is to impart required strength and rigidity to manhole cover and top part is to provide abrasion resistance, UV stability and anti- skid/ an ti- slip surface to the product.

A. The process of bottom part preparation begins with thorough cleaning of the mould and then release agent layer is applied on its surface layer. Thenafter, application of gelcoat along with desired pigments and additives is undertaken. Layers of reinforcement impregnated with resin are then applied onto this layer to build up the required thickness according to load bearing capacity. Polyconcrete is then poured onto the reinforcement layers to impart rigidity to the cover. Polyconcrete is a proportionate mixture of silica and quartz sand and resin.

B. The process of bottom core/part preparation comprises of the following: -

1. The process begins with cleaning of the mould and application of release agent on the entire mould surface which is crucial for demoulding the product and better mould life. 2. Thenafter, application of gelcoat layer mixed with hardeners onto the mould surface is undertaken. Gelcoat is made of resin added with fillers and special additives for better performance. This provides non-porous resin rich layer which protects the cover from various toxic gases emitted from the drains by acting as a shield over the surface.

3. This gelcoat layer is then allowed to cure till the tack free state is achieved. This is one of the most crucial parts of the manufacturing process.

4. Application of reinforcement layer impregnated with resin mixed with hardeners is applied onto the gelcoat layer to provide sufficient strength which is known as gelcoat reinforcement layer.

5. Depending on the load rating, layers of reinforcement are applied onto the gelcoat reinforcement layer impregnated with resin mixed with hardeners which imparts the necessary strength to the cover and are crucial in imparting tensile and impact strength to the product. First layer out of them is cut in such a way that it is sufficient to wrap cover more than two layers. 6. Polyconcrete is used as rigid core of manhole cover and is critical element in imparting the required rigidity to the product. Polyconcrete is mixture of fillers of various mesh sizes, resin, hardeners and additives in optimised proportions wherein the interlocking of fillers along with optimum quantity of resin mixed with hardeners makes the polymer concrete rigid and stronger. Voids between the bigger particles are filled up with finer particles and resin thus resulting in more compact void free polymer concrete core. Therefore, optimum proportion of fillers of different sizes is vital. This polyconcrete mix is then poured into the mould which is already having a gelcoated surface and reinforcement layers.

7. This mix is then subjected to mechanical vibrations which helps to release voids from the mixture which otherwise would have formed weaker section. This is one of the most critical steps in ensuring proper compaction of the polyconcrete mix.

8. Once the vibration process is completed, resin is poured to fill up the gaps that remain even after vibration and the excess length of first layers is wrapped up to completely cover the polyconcrete mix from all sides and resin bonding paste is applied to itfor better bonding between top and bottom parts of the product. C) Top part preparation: -

Preparation for top part begins with thorough cleaning of moulds and application of release agent as in case of bottom part preparation. A mixture of coloured silica quartz particles and resin mixed with hardeners is then poured onto the mould surface. Application of reinforcement layer is undertaken to provide strength to the top part. Then this assembly is kept till tack free state is achieved.

The purpose of this layer is to provide abrasion resistant and is UV stabilised which is critical for the life of the product. Apart from this add single or multicolour quartz silica crsytals to give desired finish which adds the aesthetic value to the cover. The top part process is undertaken simultaneously alongwith the bottom part preparation. Both these parts are bonded together and application of pressure is undertaken for sometime. It is very much essential that both these parts are bonded together during tack free state. Tack free state is the transition phase of polyester resin matrix from liquid to solid state. To ensure this, it is necessary to have simultaneous preparation of both these parts. This ensures a much superior mechanical bonding between the two layers. Weak bonding would result into air entrapment between the two layers which would drastically affect the strength and performance of the product. 1. The process begins with ^" thorough cleaning of the mould and application of release agent on the entire mould surface which is crucial for demoulding the product and better mould life.

2. A mixture of coloured silica particles along with quartz crystals is prepared along with the resin, hardeners and additives as per the surface finish required.

3. This mixture is then poured into the mould surface and the mould is subject to mechanical vibrations for proper compaction and air release.

4. Thenafter one reinforcement layer is applied onto this layer. This layer imparts strength to the top surface and plays an important role in adhesion with bottom part of the mould.

5. The complete system is then left for some time until it reaches tack free state.

D) The top part is placed over the bottom part with proper alignment with resin adhesive paste in between the two parts. This complete assembly is then subjected to mechanical pressure for some time to bond the two layers together. Once curing is completed, the applied pressure is released and carefully demoulding is undertaken to separate the product from its mould.

The entire process of manufacturing manhole cover is split into two moulding process or rather split moulding. It means that two moulding process are carried out simultaneously. Moulding time difference between the two processes should not be more than 3 hours i.e. one for bottom part and one for the top part. This unique process is completely optimized and fine tuned to get the desired load bearing capacity and stronger product.

1 Assembling both the moulds i.e. the bottom part and the top part are then placed together on each other when they are still in the tack free state and application of resin putty paste mixed with hardeners in between them which gives superior inter-laminar adhesion.

2 The complete system is then subjected to pressure for sometime so as to allow cross linking of polymers which is called curing.

3 The demoulding process then carried out carefully to separate the actual product from its mould.

4 Finally the process of manufacturing is completed and the cover is then taken for trimming, grinding and finishing. 5 Resin layer is applied on the grinded edges to prevent exposure of reinforcement to the atmosphere.

The process of manufacturing the fibre reinforced plastic frame is exactly same as that of the manhole cover as shown in Fig. 5

Advantages of Inventions:

1. Complete Wrap-up forms continuous reinforcement all around the polymer concrete thereby imparting excellent tensile strength to the entire product which is highly prone to tensile load.

2. Simultaneous/ parallel processing of anti-skid abrasion resistant top part as well as the bottom part of the manhole cover ensures excellent bonding between the two which is one of the critical aspects for performance of the product. Due to simultaneous initiation of curing process, the bonding between the two parts is very strong.

If the preparation of both the layers (top part 8s bottom part) is not undertaken simultaneously then there are chances of de-bonding due to weak adhesion.

Good inter-laminar bonding makes the complete .system homogenous which results into much better load carrying capacity. 3. Instead of giving flat edge at the interface of the manhole frame and cover (fig.7a), curvature of the bottom of manhole cover is extended till the edge of the cover (fig.7b). The sudden change in cross section of the manhole cover is avoided which in turn reduces the stress concentration at the junction of profile.

During the load tests, when the point load is applied at the centre of the cover, it transfers to the frame at the interface of the cover and frame. At the contact point, because of the inclined surface, the load is divided in two components (one in vertical direction and one in horizontal direction). This vertical component of the load is lesser in magnitude than the applied load by Cosine of the angle (as shown in the diagram). This reduced load preventing failure of the cover at the interface of the frame and cover due to concentrated shear stresses in the prior art. Ultimately, this invention increases the life of the product considerably and in turn reducing the life time cost of the product.

4. Application of vibration results in getting very compact and void free polyconcrete mix. 5. Optimized ratio of different mesh sizes of fillers in polymer concrete mixture helps in the interlocking of fillers along with optimum quantity of resin mixed with hardeners makes the polymer concrete rigid and stronger. Voids between the bigger particles are filled up with finer particles and resin thus resulting in more compact void free polymer concrete core. Therefore, optimum proportion of fillers of different sizes is vital .

6. Once the simultaneous/parallel process of preparation of both top part and bottom part is completed, both these parts are joined together and application of pressure is undertaken for more than 15 minutes. It is very much essential that both these parts are bonded together during "tack free state".

Tack free state is the transition phase of resin from liquid to solid state. To ensure this, it is necessary to have simultaneous/ parallel preparation of both these parts. This ensures a much superior mechanical bonding between the two layers.

7. Addition of gelcoat layer protects the cover from harmful toxic gases/ chemicals/ liquids and thereby increasing the life of the product. 8. Gelcoat reinforcement layer imparts flexibility and strength to gelcoat layer thereby enhancing its impact load absorbing capacity.

9. Addition of special additives like air release agents, bond improvement of filler, to improvise wetting of fillers, UV stabilizers, low shrinkage, etc to enhance mechanical and chemical properties of the product significantly adds to the life of the product.

10. Chamfered edge design of moulds helps in significantly reducing chipping of the edges of the product.

11. Pouring of resin on the filler after vibrations helps to fill all the voids that remain after vibration thus enhancing the strength and fatigue rating of the product.

12. Addition of resin putty paste mixed with hardeners greatly helps is increasing the bonding between the top and bottom casting layer making a homogenous product.

13. Application of resin putty paste mixed with hardeners at the edges after grinding helps to protect the exposed reinforcement fibres from the external environment thus extending the life.

14. Post curing of the product is undertaken if required to complete the polymerization process.