AU712910B3 - Impact resistant cover - Google Patents

Description

1

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A PETTY PATENT Name of Applicant: Actual Inventor: Address for Service: Invention Title: MASTERFIBRE PTY LTD JONATHAN RODNEY BARNES CULLEN

CO.,

Patent Trade Mark Attorneys, 240 Queen Street, Brisbane, Qld. 4000, Australia.

IMPACT RESISTANT COVER The following statement is a full description of this invention including the best method of performing it known to us THIS INVENTION relates to an impact resistant cover for a surface and in particular, relates to an impact resistant cover for a playground. The present inrention also relates to a method of installing an impact resistant cover.

The present invention will be described with reference to an impact resistant cover for a playground surface. However, it will be appreciated that the cover and method of the present invention is suitable for any application where an impact resistant surface is desirable and no limitation is intended thereby.

In recent times, playground designers, architects, school authorities and accident prevention authorities have been paying particular attention to the design of playground equipment and the surfaces beneath them. It is now a legal requirement to provide a playground surface which is impact resistant and meets minimum safety requirements.

Generally, playground surfaces are covered with a rubber mat or rubber tiles. Such rubber mats are well known and are generally formed from granulated rubber bound together by a polymeric binder. Typically, the granulated rubber includes recycled tyres. Conventional rubber mats typically have a thickness of about 15 25 mm. This thickness is generally suitable for a play surface to protect children from minor falls. However, in some cases, a cover having a higher impact resistance from than the conventional rubber mat is required. Also, in some jurisdictions, governments are introducing more stringent minimum impact resistant requirements for playground mats.

One method of meeting these more stringent requirements is simply to increase the thickness of the rubber mat or tile. A drawback of providing rubber mats or tiles which are thicker than the conventional mats or tiles is that due to the large volume, a considerably large amount of polymeric binder is required. Whilst the rubber material itself, may be inexpensive, the binders are quite expensive. The result is that the cost of producing thicker than normal rubber mats or tiles can be prohibitively expensive.

Accordingly, it is an object of the present invention to provide an impact resistant cover for a surface which may at least partially overcome the above disadvantage or provide the public with a useful choice.

According to a first broad form of the present invention, there is provided an impact resistant cover, the cover having a retaining structure at least partially filled with a free flowing particulate filler to form a particulate filler layer and an upper layer formed from a rubber mat material, and the air pressure within the retaining structure is substantially atmospheric.

According to a second broad form of the invention, there is provided a method of constructing an impact resistant cover for a surface, the method including the steps of forming or constructing a retaining structure, at least partially filling the retaining structure with a particulate filler material, and covering the particulate filler material with an upper layer of a rubber mat material.

The impact resistant cover of the present invention includes a first layer of a filler material held in place by a retaining structure. The retaining structure can be of any suitable shape or size providing it can hold the particulate filler material together. The retaining structure may be rigid or flexible. Typical rigid retaining structures may be formed from earth, timber, concrete, metal, from clay or concrete, bricks or pavers, either singularly or in combination.

Alternatively, the retaining structure may be in the form of a flexible envelope. In this case, the envelope may be formed from a flexible membrane material having sufficient structural integrity to hold a particulate filter material in place when the cover is in use.

The particulate filler material can be any material in which the particles can move with respect to each other when subjected to a force.

Exemplary materials include sand and in particular sand having a maximum particle size of 5 mm and rubber particles including new or recycled rubber particles which may be made from synthetic rubber, natural rubber, recycled tyre rubber or any combination thereof. Preferred rubber particles have a maximum particle size of 100 mm. Other suitable particulate fillers include bark or tree mulch of any size or shape and gravel or aggregate of any size or shape. Preferably, the gravel or aggregate having a maximum particle size of o 20 mm. Other suitable filler materials include plastic granules either recycled or new. Typically the plastic granules will have a maximum particle size of mm. Still further suitable particulate materials include plastic or rubber balls of any size. The filler material can also include a mixture of any two or more of the preceding materials.

The depth of the filler material layer as used in the cover of the s present invention will typically be selected according to the desired properties of the resultant cover. Where lower impact resistant areas are required, the layer may be of a typical thickness of up to about 100 mm. Where higher impact resistance is required, a thicker layer of filler material may be used, for example, up to about 300 mm.

The cover also includes an upper layer of a rubber mat material.

The rubber mat material suitable for use in the present invention may be any rubber material formed from rubber such as granules, fibres or a combination thereof held together by a polymeric binder. Such rubber materials may include conventional rubber mats and tiles and these are well known in the art. The thickness of the rubber material which may be used in the present invention may of course vary depending upon the desired impact resistance of the cover and also the depth and nature of the particulate filler material layer. Typically, the rubber mat will have a thickness of about 25 mm.

Rubber mat material of greater thickness is undesirable because of the increased cost and would normally be unnecessary due to the inclusion of the particulate filler layer.

In a preferred embodiment of the invention, the particulate filler material layer and the upper rubber mat layer and separated by an intermediate layer which can hold the rubber mat in place and does not allow slippage or movement of the rubber mat across the membrane surface.

Suitable intermediate layers may be formed from woven materials and include woven polyester, or even woven cotton in the form of hessian bags. Where the retaining structure is a rigid structure formed from timber or concrete or the like, this intermediate layer would normally be simply laid across the top of the particulate filler material layer. However, where the retaining structure is a flexible envelope, it is preferred that the envelope is formed from the intermediate layer material.

By way of example only, the present invention will now be

M

described with reference to the following examples.

Impact resistant surfaces for playgrounds are tested under standard testing procedures.

These tests are conducted by dropping an instrumented test head form from various heights onto a surface and recording the resulting acceleration time history of each impact. The recorded impacts are then analysed to determine the fall height at which any one of two safety criteria are exceeded. These criteria are the head injury criterion (HIC) of 1000 or a deceleration of 200 g.

The head injury criterion is an index which measures the severity of the impact of a person's head onto a surface. A severity index of 1000 is used as the threshold for serious head injury based on experimental data. It is calculated as the area under the deceleration/time curve. The critical fall height is the fall height in metres at which head concussion may occur, resulting from a peak deceleration of 200 g or a severity index of at least 1000.

Various impact resistant covers having layers and material thicknesses as indicated in Table 1 were prepared. The covers of the invention were installed by constructing a wooden frame on top of a concrete floor. Sand having a particle size distribution as indicated in Table 2 was placed inside the wooden frame and compacted to the required depth. A grey fabric woven cloth, which is available under the trade name GEOFABRIC, was placed on top of the sand. Finally, a rubber tile was laid on top of the grey fabric cloth.

TABLE 1 Comparative Example 1 Large 25 mm thick crumbed rubber tile laid over concrete. A layer of grey fabric was placed between the tile and the concrete.

Example 1 Large 25 mm thick crumbed rubber tile laid over 50 mm of compacted sand. The sand was placed on top of a concrete base. A layer of grey fabric was placed between the tile and the sand.

txample z Liry L[3 T LHIGA I IUIIUU IUUUU I LIIltU iu uver Iuu mm of compacted sand. The sand was placed on top of a concrete base. A layer of grey fabric was placed between the tile and the sand.

Comparative Example 2 Small 25 mm thick crumbed rubber tile laid over concrete.

A layer of grey fabric was placed between the tile and the concrete.

Example 3 Small 25 mm thick crumbed rubber tile laid over 50 mm of compacted sand. The sand was placed on top of a concrete base. A layer of grey fabric was placed between the tile and the sand.

Example 4 Small 25 mm thick crumbed rubber tile laid over 100 mm of compacted sand. The sand was placed on top of a concrete base. A layer of grey fabric was placed between the tile and the sand.

TABLE 2 4.75 100 2.36 97 1.18 78 0.60 66 0.30 46 0.15 11 0.075 1 The test results are shown in Table 3.

TABLE 3 Comparative 0.9 1 u.0 z 1 1 Ut Examplel 2 0.75 671 162 3 1.0 1035 203 4 1.25 1701 269 Example 1 1.2 1 0.5 180 78 2 1.0 688 156 3 1.5 1388 224 4 2.0 2002 267 Example 2 1.4 1 0.5 153 73 2 1.0 587 142 3 1.5 1074 193 4 2.0 1352 214 Comparative 0.9 1 0.5 253 96 Example 2 2 0.75 628 154 3 1.0 1025 201 4 1.25 1572 252 Example 3 1.2 1 0.5 177 76 2 1.0 640 145 3 1.5 1409 218 4 2.0 2260 282 Example 4 1.5 1 0.5 127 66 2 1.0 455 124 3 1.5 895 173 4 2.0 1538 228 It can be seen that the examples of the invention exhibited a surprisingly superior impact resistance performance over the conventional rubber mat covers.

In Examples 5 and 6, further tests were conducted using loose rubber fill as the particulate filler material. These covers have layers of the thicknesses as given in Table 4.

TABLE 4 1.2 m x 1.2 m x 15 mm shredded rubber tile laid over 50 mm shredded rubber loose fill. Grey Geotech cloth was laid between the tile and shredded rubber.

1.2 m x 1.2 m x 15 mm shredded rubber tile laid over 75 mm shredded rubber loose fill. Gray Geotech cloth was laid between the tile and shredded rubber.

Example 6 These covers were constructed in the same manner as for Examples 1 to 4 in that a wooden frame was constructed on top of a concrete surface. The shredded rubber loose fill was then placed in the wooden frame to the desired level.

The covers prepared according to Examples 5 and 6 were tested and the results are indicated in Table TABLE txample 1.0 m 2 1.0 414 116 3 1.5 881 173 1625 237 Example 2.8 m 1 1.5 300 82 6 2 2.0 510 107 3 2.5 774 133 4 3.0 1087 161 It can be seen from the above results that a cover of the present invention shows very good impact resistant properties whilst using a minimum layer of rubber mat. It will be appreciated that covers of the present invention may be constructed at considerable less cost than rubber mats of a 9 comparable thickness, whilst achieving comparable impact resistant results.

It will be appreciated that various changes or modifications may be made to the invention described and claimed therein without departing from the spirit and scope thereof.

Claims (3)

1. An impact resistant cover, the cover having a retaining structure at least partially filled with a free flowing particulate filler to form a particulate filler layer and an upper layer formed from a rubber mat material, and when the cover is in use the air pressure within the retaining structure is substantially atmospheric.

2. The cover of claim 1 which further includes a further layer intermediate the particulate filler layer and the upper layer, the intermediate layer being adjusted to minimise movement of the rubber not relative to the intermediate layer.

3. The cover of claim I or claim 2, substantially as hereinbefore described with reference to any one of Examples 1 to 6.