Seat for a Child's Swing

This invention relates to a seat for a child's swing.

The seat of a child's swing is traditionally made of wood. The main disadvantage of such seats is that they are hard. Thus, as a child's swing can travel at speeds in excess of 30 m.p.h. and even unmanned can impact with a force of many tons, if a child is hit by such a seat, he or she will probably be hurt and may even fracture a bone.

To reduce the severity of accidents, the recent practice has been to replace the wooden seat with a moulded plastics seat, which is considerably lighter than a comparable wooden seat and so less likely to cause severe accidents, or an old car tyre which tends to give during collisions. The main disadvantages of the moulded plastics seat are its hardness, which still results in cuts and bruises in collisions with children, and its susceptibility to vandalism. The disadvantages of swing seats composed of old car tyres are that they are not sufficiently rigid to provide a firm platform on which a child can either sit or stand during swinging, that they require painting to prevent marking of children's clothing, and that they too are prone to vandalism. Moreover, a car tyre tends to give appreciably only if struck at the centre of its tread pattern. Thus, if a child is hit by the sidewall or the buttress of the tread of a swinging tyre, there is still a considerable risk of severe injury to the child.

In another attempt to reduce the severity of accidents, strips of foamed plastics material have been stuck round the edges of wooden and metal seats. Unfortunately, this has not been successful in reducing significantly the impact load of such a swing seat. Moreover, the strips tend to peel off and are very susceptible to vandalism.

The present invention provides a seat for a child's swing, the seat being of composite structure comprising a first member, which is sufficiently rigid to bear the weight of a child, and a second member made of a compressible polymeric material, the first member being of substantially laminar form and the second member covering at least part of the peripheral edge of the first member, wherein the force-deflection characteristic of the second member is such that, on impact with an object, the second member initially deforms to conform with the shape of the impacted object and then deforms further to absorb the main energy of the impact.

Preferably, the second member covers the entire peripheral edge of the first member. Such a seat is, therefore, strong enough to support a child but is cushioned at the edges to minimise the possible injury to a child hit by the seat.

Advantageously, a plurality of blind apertures are provided in the second member, the apertures extending along, and adjacent to, the periphery of the first member and the axes of the apertures being substantially perpendicular to the first member. Preferably, each of the apertures is of circular cross-section.

The first member and the swing seat may be generally of rectangular configuration, the apertures extending in rows along the sides of the seat. Preferably, the apertures extending along any given side of the seat are all of the same diameter.

Advantageously, the apertures extending along both of a first pair of opposite sides of the seat have the same diameter and the apertures extending along both of the second pair of opposite sides of the seat have the same diameter, the apertures extending along the second pair of sides having a greater diameter than the apertures extending along the first pair of sides. Preferably, the parts of the second member forming the first pair of sides are each provided with a respective further row of blind apertures parallel to the corresponding first-mentioned row of apertures. In this case, the apertures in said further rows may be of circular cross-section and have the said diameter, the diameters of the apertures in said further rows being less than the diameters of the apertures in the corresponding first rows of apertures, and their centres being off-set with respect to the centres of the apertures in the corresponding first rows of apertures.

Preferably, the apertures in any row are equispaced.

The distance between the centres of each pair of adjacent apertures in any row is, preferably, not greater than 1.33 times the diameter of the apertures in that row. Also, the distance between the centre of each aperture in any given row and the adjacent edge of the swing seat is, preferably, not greater than 0.75 times the diameter of the apertures in that row.

This arrangement of apertures leaves a plurality of relatively thin columns of polymeric material extending right round the periphery of the seat, each column being at right-angles to the adjacent edge of the seat. These columns act in a very similar way to Euler buckling struts and so permit the second member to absorb quite large impact loads. Thus, the first pair of opposite sides (the front and rear sides of the seat) each have two rows of apertures. As the seat hits an object, such as the head of a child, the initial deformation permits the soft outer "skin" of the compressible material to deform to the contours of the impacted area of the object. This initial deformation includes a deformation of the soft outer "skin" and a buckling of thin columns left between the apertures of the first row of apertures. This is followed by a buckling of the larger columns left between the smaller apertures of the further row, which absorbs the main energy of the impact.

Advantageously, the second member is made of a material having a hardness lying within the range of from 40 to 50 I.R.H.D., and preferably the second member is based on a mixture of ethylene-propylene terpolymer and polychloroprene, the polychloroprene being present to at least 10% of the total polymer content. The unit I.R.H.D. is the standard unit for measuring the hardness of rubber and rubber-like materials, the letters standing for "International Rubber Hardness Degrees."

Preferably, the first member is made of a sheet of mild steel 1/16 of an inch thick. This helps to keep down the weight of the swing seat which is very important as the proposed British Standards Institute maximum allowed weight for such a seat is 3 kg. This reduction of mass is also important as it results in lower kinetic energies during use which in turn means lower impact energies. In order to improve the rigidity of such a thin sheet, it may be formed with strengthening means constituted by an integral flange formed along, and substantially at right-angles to, each edge of the first member. Even these flanges may not prevent distortion of the seat by vandals and so it is preferable for each flange formed along one of the longer sides of the first members to be provided with a reinforcing strip of 1/8 inch thick mild steel spot welded thereto. A further form of increasing the rigidity of the steel sheet is to provide it with a number of corrugations.

A thin layer of the material from which the second member is made may cover both faces of the laminar first member. Preferably, the layer of material covering that side of the first member which, in use, is uppermost, is provided with a non-slip finish. This tends to prevent a child slipping off the swing seat.

Advantageously, the second member is compression moulded to the first member. Not only is this a cheap and easy manufacturing process, but also with the preferred materials helps to provide a firm bond between the first and second members.

Two forms of swing seat constructed in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a plan view of the first form of seat;

FIG. 2 is a cross-section taken on the line II--II of FIG. 1;

FIG. 3 is a cross-section taken on the line III--III of FIG. 1;

FIG. 4 is a plan view of the second form of seat;

FIG. 5 is an underneath view of the seat of FIG. 4;

FIG. 6 is a cross-section taken on the line VI--VI of FIG. 5; and

FIG. 7 is a cross-section taken on the line VII--VII of FIG. 5.

Referring to the drawings, FIGS. 1 to 3 show a seat for a child's swing which comprises a generally rectangular mild steel member 1 and a cushioning member 2 made out of a compressible polymeric material. The seat is 171/2 inches long, 91/2 inches wide and has rounded corners. The steel member 1 is made from a sheet 1/16 inch thick and is provided with an integral flange 1a which depends at right-angles from its peripheral edge. This flange 1a increases the rigidity of the member 1 so that it can take a weight of 125 kg. Those parts of the flange 1a depending from the longer sides of the sheet 1 are provided with a reinforcing strip 1b of 1/8 inch thick mild steel spot welded thereto. A pair of longitudinally extending corrugations 1c and a pair of transversely extending corrugations 1d are provided to increase further the rigidity of the member 1.

The cushioning member 2 is arranged to cover the entire surface of the steel member 1. The upper part 2a of the cushioning member 2 is provided with five upstanding ribs 2b, each of which has a knurled upper surface. The ribs 2b and their knurled surfaces help to prevent a child from slipping off the seat when the swing is being used.

The cushioning member 2 is made of a polymeric material based on a mixture of an ethylene-propylene terpolymer and polychloroprene. One suitable example is constituted by 57.91% ethylene-propylene terpolymer, 8.58% polychloroprene, 3.43% zinc oxide, 0.43% stearic acid, 1.58% accelerators, 0.64% sulphur, 0.86% sun-checking wax, 3.04% dyestuff, 6.40% silica, 6.40% aluminium silicate, 2.15% titanium dioxide and 8.58% paraffinic oil.

The cushioning member 2 is compression moulded to the steel member 1. In order to bond the two members together, the steel member 1 is provided, prior to the moulding process, with several coats of a bonding agent such as Chemlok.RTM. or Thixon.RTM.. In order to ensure that the cushioning member 2 is firmly bonded to the steel member 1, the polychloroprene content of the polymeric material should be at least 10% of the total polymer content of the material. That part of the cushioning member 2 surrounding the flange 1a of the steel member 1 is provided with three sets of blind apertures 2c, 2d and 2e these holes being formed during the compression moulding of the cushioning member. The apertures 2c are each of a diameter of 3/4 of an inch and are provided in two rows, one adjacent each of the shorter edges of the seat. The apertures 2d are each of a diameter of 9/16 of an inch and are provided in two rows, one adjacent each of the longer edges of the seat. The apertures 2e are each of a diameter of 1/2 of an inch and are provided in two rows, one situated between each of the rows of apertures 2d and the corresponding flange 1a. The apertures in each of the rows are equispaced, the centres of adjacent apertures 2c being 7/8 of an inch apart, the centres of adjacent apertures 2dbeing 5/8 of an inch apart and the centres of adjacent apertures 2e being 5/8 of an inch apart. The apertures of rows 2e are staggered with respect to the apertures of rows 2d. Each of the centres of the apertures 2c is spaced from the adjacent edge of the seat by a distance of 1/8 of an inch and each of the centres of the apertures 2d is spaced from the adjacent edge of the seat by a distance of 11/32 of an inch. The apertures 2c formed in a portion 2f of the cushioning member 2 which is 13/16 of an inch thick and which extends well below the bottom surface of the steel sheet 1. Similarly, the apertures 2d are formed in a portion 2g of the cushioning member 2 which is 11/16 of an inch thick and which extends as far below the bottom surface of the steel sheet 1 as does the portion 2f. The apertures 2e are formed in a portion 2h of the cushioning member 2 which is 7/8 of an inch thick but which extends below the bottom surface of the steel sheet 1 only about half the distance to which the portions 2f and 2g extend.

The spacing and size of each set of apertures 2c, 2d and 2e in relation to the thickness of the portions 2f, 2g and 2h results in an arrangement wherein each set of apertures leaves a plurality of relatively thin columns of polymeric material extending right round the periphery of the seat, each column being at right-angles to the adjacent edge of the seat. These columns act as Euler buckling struts so that the cushioning member 2 can absorb quite large impact loads. Strictly speaking, Euler buckling strut theory only applies to columns of uniform cross-section, but it is clear that the columns left between these circular apertures act in a very similar fashion. An arrangement of elliptical apertures (major axes at right-angles to adjacent seat periphery) would give a better agreement with theory, but this would cause difficulties in the moulding of the cushioning member.

The front and rear edges of the seat are provided with two rows of apertures 2d and 2e. As the swinging seat hits an object, such as the head of a child, the initial deformation is taken by the outer "skin" and on the thin columns left between the apertures 2d. This permits the soft outer "skin" of the cushioning member 2 to deform to the contours of the impacted area of the object. This is followed by a buckling of the larger columns left between the apertures 2e which absorbs the main energy of the impact. The extra row of blind apertures 2e provided at the front and rear of the seat ensure increased compressibility at those places most likely to hit a child.

The rows of apertures 2c at the sides of the seat act in a similar way to cushion impacts in these regions. Here, although there is only one row of apertures 2c, the cushioning effect is almost as good as at the front and rear of the seat. The initial deformation is taken up by the buckling of the columns left between the apertures 2c and the main energy of the impact is taken up by the deformation of the portion 2f of the cushioning member 2.

The blind apertures 2c, 2d and 2e also help to reduce the weight of the seat so as to conform with B.S.I. requirements. Indeed the weight of this seat is approximately 2.5 kg which is well within the B.S.I. limit of 3 kg. Consequently, if this seat hits a child it is less likely to injure that child than a conventional swing seat.

Adjacent each lateral edge of the seat are provided a pair of holes 3 for receiving the bolts (not shown) by means of which the seat is fastened to the chains of the swing.

The seat described above is intended primarily for use in parks, children's playgrounds and other public places. Thus, it needs to be resistant to attacks by vandals and so needs strengthening features such as the corrugations 1c and 1d and the reinforcing strips 1b. The embodiment of FIGS. 4 to 7 is for domestic use, that is to say for use in the gardens of domestic houses or in other private surroundings. This embodiment is much less susceptible to vandalism and so does not incorporate these additional strengthening features. In most other respects, this domestic seat is identical with the seat of FIGS. 1 to 3. Thus, this seat comprises a generally rectangular mild steel member 11 and a cushioning member 12. The seat is 17 inches long, 61/4 inches wide and has rounded corners. The steel member 1 is made from a sheet 1/16 of an inch thick and is provided with an integral flange 11a which depends from its peripheral edge. This flange 11a increases the rigidity of the steel member 11 so that it can resist the forces exerted by a load of up to 125 kg.

The cushioning member 12, which is made of the same polymeric material as the cushioning member 2 of the seat of FIGS. 1 to 3, is arranged to cover the entire surface of the steel member 11. The upper part 12a of the cushioning member 12 is provided with three upstanding ribs 12b and the whole of the upper surface 12a and the ribs 12b are provided with a grained finish. The ribs 12b and the grained finish help to prevent a child from slipping off the seat when the swing is being used.

The cushioning member 12 is compression moulded to the steel member 11, the grained finish on the surface 12a and the ribs 12b being formed during the moulding. That part of the cushioning member 12 surrounding the flange 11a of the steel member 11 is provided with three sets of blind apertures 12c, 12d and 12e. The apertures 12c are each of a diameter of 3/4 of an inch and their centres are 7/8 of an inch apart. They are formed in two portions 12f of the cushioning member 12 which are 1 inch thick. The centres of the apertures 12c lie 1/2 of an inch from the adjacent edge of the seat. The apertures 12d and 12e are all of a diameter of 7/16 of an inch and their centres are 9/16 of an inch apart. The apertures 12d and 12e are formed in portions 12g of the cushioning member 12 which are 11/4 of an inch wide, the apertures 12e being staggered with respect to the apertures 12d. The centres of the apertures 12d lie 11/32 of an inch from the adjacent side of the seat and the centres of the apertures 12e lie 13/16 of an inch from the adjacent side of the seat. The apertures 12c, 12d and 12e thus provide a plurality of columns which, in a similar manner to that described above with respect to the seat of FIGS. 1 to 3, act as Euler buckling struts and so minimise the injury risk to a child hit by the seat.

Adjacent each lateral edge of the seat are provided a pair of holes 13 for receiving the support bracket (not shown) by means of which the seat is fastened to the chains of the swing. A further hole 14 is provided between each pair of holes 13. These holes 14 are used in conjunction with pairs of ribs 15, provided on the underneath of the seat, for receiving an alternative form of support bracket (not shown).

It will be apparent that a number of modifications could be made to the swing seat described above. Thus, the cushioning member 2 or 12 could be made of other materials than that specified, for example it could be made from rubber or foamed polyvinyl chloride. It would also be possible, particularly for the domestic seat, to use reinforced fibre glass instead of steel for the member 11. Furthermore, the cushioning member 2 or 12 need not be compression moulded to the member 1 or 11, it being possible to use an injection moulding or a transfer moulding process. It is also possible to bond these members together using only an adhesive. Also it is possible to bond by mechanical means, in which case the member 1 or 11 is provided with a plurality of apertures through which the two parts of the cushioning member can be bonded. A plurality of such apertures may, in any case, be provided in the steel member 1 or 11 for further reducing the weight of the finished seat.

It will be apparent that each of the swing seats described above is much safer than any known type of swing seat. Thus, tests have shown that the impact forces of the various types of prior art swing seat are:

a. for a moulded polypropylene seat -- 4.5 times greater than the swing seats of FIGS. 1 to 3;

b. for a cross-ply tyre on its sidewall -- 6.4 times greater than the swing seats of FIGS. 1 to 3;

c. for a standard hardwood seat -- 25.0 times greater than the swing seats of FIGS. 1 to 3.

No tests have been carried out on the swing seat of FIGS. 4 to 7 but as this seat is lighter than that of FIGS. 1 to 3, the impact force should be even less than that of FIGS. 1 to 3. Moreover, the swing seats described above are resistant to both vandals and the effects of the weather.

Although swing seats have been referred to throughout this specification as for children, it will be apparent that, as the swing seat described above is capable of resisting the force exerted by a swinging load of up to 125 kg, it is also suitable for use by adults.