STORMWATER FILTRATION GRATE

FIELD OF THE INVENTION The present invention relates to filtering stormwater. More particularly, but not exclusively, the invention relates to a stormwater filtration grate and methods of forming same.

BACKGROUND OF THE INVENTION

Sediment and other contaminants in stormwater runoff can clog collection systems and pollute waterways in which the runoff flows into. It is desirable to filter stormwater runoff to reduce the chances of collection systems becoming clogged and to improve the quality of water flowing into waterways. It is also desirable to provide such filtration systems that are simple and cheap to manufacture and can be easily serviced.

Stormwater filtration grates can provide a practical method of filtering stormwater runoff before it enters collection systems. However, previous stormwater filtration grates can be expensive to manufacture.

Examples of the invention seek to solve, or at least ameliorate, one or more disadvantages of previous stormwater filtration grates.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a stormwater filtration grate comprising a frame having a support base, and a filtration medium through which. the stormwater can flow, the filtration medium being supported by the support base and the support base being of unitary construction.

Preferably, the support base is pressed from a metal sheet. According to the present invention, there is also provided a stormwater filtration grate comprising a frame having a support base, and a filtration medium through which the stormwater can flow, the filtration medium being supported by the support base and the support base being pressed from a metal sheet.

Preferably, the support base is formed from a single sheet of material.

According to preferred embodiments, the support base includes outer support members which define a space through which liquid can flow, wherein a portion of the outer support members which is lowermost in use extends inwardly so that the space constricts along a flow path of the liquid to support the filtration medium. Preferably, the support base further includes inner support members extending laterally across the grate, a lower surface of the inner support members extending inwardly to support the filtration medium.

Preferably, the filtration medium comprises aggregate set in an epoxy resin matrix. Preferably, the aggregate includes basalt. Preferably, the filtration medium is formed in situ. According to the present invention, there is also provided a method of manufacturing a stormwater filtration grate, comprising the steps of: forming a support base, the support base being of unitary construction and at least partially defining a space through which liquid can flow; and applying a filtration medium to the support base to filter liquid flowing through the space.

Preferably, the support base is formed using a pressing operation. Preferably, the support base is formed by pressing a metal sheet.

According to the present invention, there is also provided a method of manufacturing a stormwater filtration grate, comprising the steps of: forming a support base by pressing a metal sheet, the support base at least partially defining a space through which liquid can flow; and applying a filtration medium to the support base to filter liquid flowing through the space.

Preferably, the support base is pressed from a single sheet. The pressing operation can include a trimming operation.

Preferably, the filtration medium comprises aggregate set in an epoxy resin matrix, the filtration medium being cast in situ by casting within the support base. BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will be further described, by way of non-limiting example only, with reference to the accompanying drawings in which:

Figure 1 is an upper perspective view of a stormwater grate of one embodiment of the invention;

Figure 2 is an underneath view of a support pan of the stormwater grate; and Figure 3 is a sectional side view of the stormwater grate.

DETAILED DESCRIPTION

A stormwater filtration grate 10 according to a preferred embodiment of the present invention is shown in Figure 1. The stormwater filtration grate 10 is configured to cover a stormwater pit and to filter stormwater runoff flowing into the pit. The stormwater filtration grate 11 includes a frame 12 having a support base 14, which is shown in Figure 2, and a filtration medium (not shown) through which the stormwater can flow. The filtration medium is supported by the support base 14 and the support base 14 is of unitary construction. As illustrated in Figure 2, the support base 14 includes outer support members 16 which define a space 18 through which liquid can flow. As can be seen in Figure 3, a portion of the outer support members 16 which is lowermost in use extends inwardly so that the space 18 constricts along a flow path of the liquid to support the filtration medium. As liquid flows through the filtration medium, a force which acts in a direction of the liquid flow will be exerted on the filtration medium. Because the space 18 constricts along the flow path, the filtration medium can be held in position by an interference fit caused by the outer support members which act on a lower surface of the filtration medium.

The filtration medium is fixed within the stormwater filtration grate on its upper surface by grid members 22, 24 of the frame 12. Grid members 22, 24 extend transversely across the frame 12 and provide structural support to the stormwater filtration grate 10 so that it can support the weight of vehicles and pedestrians so that it is suitable for use in trafficable areas. When installed, an upper surface of the filtration medium will be at a level which is below an upper surface of the grid members 24 so that the weight of traffic and pedestrians passing over the stormwater filtration grate 10 will bear upon the grid members 24. Advantageously, the weight of vehicles and pedestrians is not required to be supported by the filtration medium, thereby increasing the load limit of the stormwater filtration grate 10.

The support base 14 further includes inner support members 20 which extending laterally across the grate to form a cross-shaped brace. Similar to the outer support members 16, a lower surface of each of the inner support members 20 also extends inwardly to support a lower surface of the filtration medium.

The support base 14 is formed from a single sheet of material. In the described embodiment the support base is pressed from a metal sheet, such as galvanised mild steel. In other embodiments, the support base is pressed from a metal sheet, which may or may not be a single sheet of material. Present stormwater filtration grates are constructed by welding pre-formed sections of metal together. Such processes can be expensive and time consuming. Because the support base 14 is formed using a more economical pressing operation, it can be more easily and cheaply formed. The support base 14 is configured so as to have sufficient strength to support the filtration medium. As the filtration medium is not required to be load bearing, the required strength of the support base 14 can be reduced. Although the described support base 14 is formed from metal, a person skilled in the art will appreciate that the support base 14 may be formed of other materials, such as plastics, and formed using conventional forming processes such as vacuum, injection, blow or rotational moulding. The filtration medium (not shown) comprises aggregate set in an epoxy resin matrix. The aggregate is a blue stone material, such as that which includes basalt. It will be appreciated that the aggregate can be formed of other materials and that other resins or binding agents may similarly be used to form a filtration medium. In the described embodiment, the filtration medium is formed or cast in situ in the support base 14. Dimensional variance of previous support bases can make it difficult to secure a filtration medium within a stormwater filtration grate. Forming the filtration medium in situ allows the filtration medium to accommodate such dimensional variances. Furthermore, forming the filtration medium in situ avoids the need to have a number of separate moulds for forming the filtration medium, thereby reducing tooling costs for manufacturing.

The stormwater filtration grate 10 is manufactured by forming a support base 14 which is of unitary construction. The support base 14 is formed so as to least partially define a space through which liquid can flow. A filtration medium is then applied to the support base 14 to filter liquid flowing through the space.

As previously discussed, the support base 14 is formed using a pressing operation and is pressed from a metal sheet. In other embodiments, the support base is formed by pressing a metal sheet, which may or may not be a single sheet. The pressing operation is a general metal forming operation which may include one or steps and may be in the form of stamping, coining or other known forming operations. The pressing operation can include a trimming operation in which an outline of the support base 14 is formed at the same time as it is pressed.

The filtration medium is cast in situ by casting within the support base 14. The support base 14 is formed and then the frame 12 is fixed to the support base 14 using a welding process, for example. The frame 12 may be generally in accordance with conventional grates used to cover stormwater drainage pits and incorporate conventional lock-down and lifting points. The frame 12 may be formed using conventional welding processes.

The support base 14 and frame are then secured to a casting bed or casting surface so that the support base 14, the frame 12 and the casting surface define a mould in which the filtration medium is cast. The aggregate is mixed with the epoxy resin and the mixture is poured into the mould and allowed to cure. After the mixture is poured, a vibration settling process may be used to settle the mixture. The mixture is poured to a level just below an uppermost surface of the frame 12 so that the weight of traffic or pedestrians passing over the stormwater filtration grate 10 will bear upon the frame. Advantageously, the stormwater filtration grate 10 has good stormwater filtration properties without being limited to low weight bearing applications because the strength of the stormwater filtration grate 10 is not dictated by the strength of the filtration medium.

The filtration medium is formed as a single block, though it will be appreciated that the inner support members 20 may be configured so as to divide the mould so that four discrete filtration mediums are formed.

Once the filtration medium has set, the stormwater filtration grate 10 can be installed as an assembly and also removed for cleaning as an assembly. The embodiments have been described by way of example only and modifications are possible within the scope of the invention disclosed.