AU2004101072A4 - Improvements In Composite Structures - Google Patents

Description

AUSTRALIA

PATENTS ACT 1990 COMPLETE

SPECIFICATION

FOR AN INNOVATION

PATENT

ORIGINAL

Name of Applicant: Actual Inventor: Agent and Address Hills Industries Limited William Alan Cosgrove tor Service: MADDERNS, 1 s t Floor, 64 Hindmarsh Square, Adelaide, South Australia, Australia Invention Title: Improvements In Composite Structures Details of Associated Provisional Application No: 2003907132 dated 24t December 2003 The following statement is a full description of this invention, including the best method of performing it known to us.

O IMPROVEMENTS IN COMPOSITE

ASSEMBLIES

0 SBACKGROUND OF THE INVENTION This invention relates to a method for producing a composite assembly and a composite assembly so produced. The invention will be particularly discussed with reference to a ladder and a ladder produced by the method but is not so restricted. The invention is particularly directed to ladders with a minimum or 0absence of metallic components and which are formed as stepladders, but is not 10 restricted to either feature.

BACKGROUND OF THE INVENTION Ladders are conventionally formed from wood often with wire reinforcement along opposed stiles and under rungs. A substantial improvement has arisen with the use of aluminium ladders which provide lightweight and strong structures and which may be formed as fixed ladders, extension ladders or stepladders.

These ladders still require production of individual rungs and subsequent insertion between opposed stiles. This requires expensive machinery and can be somewhat labour intensive.

A further consideration in relation to metallic ladders is their electroconductivity especially aluminium ladders. When used around high voltage power lines and by tradesmen such as a electricians, the risk to a worker arising from the chance of contacting live wires is substantial. Numerous fatalities have occurred as a result of current conduction through aluminium ladders which due to their relatively light weight may be of considerable length, thereby more easily and inadvertently striking power lines.

Attempts have been made to produce ladders formed from a plastics material or more accurately small steps formed from a plastics material providing a relatively low total height. A limitation in these devices is the need to use a substantial amount of fabricating material in order to obtain sufficient weight supporting 8 capacity in the small step device. As a result, the size and transportability of such Sladders have been severely restricted.

0 SUMMARY OF THE INVENTION Throughout this specification, unless the context requires otherwise, the word I/comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element or integer or group of elements or integers but not the exclusion of any other element or integer or group of elements or integers.

In a first aspect the invention resides in a method of forming a composite assembly, the method comprising the steps of forming a lightweight core and forming an outer layer of fibre reinforced polymer resin around the lightweight core, wherein the outer layer is formed onto the core using a technique selected from resin transfer moulding, resin transfer moulding light, vacuum assisted resin transfer moulding, resin injection moulding, multiple insert tooling, injection, infusion, pressure moulding, moulding with prepregs, vacuum forming, open moulding and manual moulding.

Preferably the lightweight core is formed from a material selected from the group of materials comprising PVC closed cell foam or urethane foam in a cast form or cut from sheets, end grain balsa, straight grain balsa, light weight timber, plywood, honeycomb in aluminium, paper, fiberglass or plastics, Tricell, Nycell, Duracore or any combination of the above.

The polymer may be a material selected from the group comprising polyester, vinylester, epoxy, phenolic, Metton, LCDP resin, pigmented resin, resins with fillers added and any blending of resins.

The fibre reinforcement for the resin may be selected from the group comprising glass fibre, carbon fibre or aramid fibre in the form of chopped strand, mat, knitted 8 braids, unidirectional rovings and woven rovings, or in the form of biaxial, triaxial C or quadraxial woven fabrics or RovicoreTM.

0 In one embodiment the of method the composite assembly may be a ladder.

SIn a further form the invention comprises a method of forming a ladder, the 0 method comprising the steps of: forming at least a part of the ladder having an outer layer having an internal hollow with an internal wall; forming an insert locatable in the hollow and at least in part in contact with the internal wall of the hollow; and fixing the insert in the internal hollow to engage with at least part of the internal wall; wherein first two steps are not necessarily in the above sequential order and the insert and the outer layer is formed from a reinforced polymer resin material.

Preferably the least a part of the ladder having an outer layer having an internal hollow with an internal wall comprises a substantially U-shaped cross section body having an open side and the insert is received in the open side.

There may also be placed a lightweight material into the hollow to further stabilize the ladder structure.

Preferably the step of fixing is selected from applying an adhesive between the insert and the outer layer, frictional engagement, plastic welding or riveting or other suitable means. Alternatively the step of fixing the insert in position comprises the steps of wrapping a fibre glass outer layer around the insert and impregnating it with the polymer resin material.

The ladder member may be formed with stiles and steps integrally formed therein.

The step of fixing the insert in position may be achieved by resin transfer (N moulding, resin transfer moulding light, vacuum assisted resin transfer moulding, resin injection moulding, multiple insert tooling, injection, infusion, pressure moulding, moulding with prepregs, vacuum forming, open moulding and manual moulding.

(-i Preferably forming the internal hollow may comprise the step of forming a slotted hollow, said slotted hollow communicating externally of the outer layer. The ,method may further include the step of forming the insert for location in the 0 10 hollow and locating it in frictional engagement with the wall of the hollow.

Alternatively fixing the insert in position may include the step of forming the outer layer around the insert.

Additionally and alternatively, the step may include the step of bonding the insert to the outer layer. Bonding the insert to the outer layer may include the step of applying an adhesive between the insert and the outer layer and allowing it to cure. Alternatively, the method may include the step of welding or otherwise fixing the insert to the outer layer. Further, alternatively, the method may include the step or wrapping a fibre glass outer layer around the blank and impregnating it with a settable resin.

In a further form the invention comprises a ladder comprising an integral outer layer defining stiles and steps, the outer layer having an internal hollow, an insert positioned within the internal hollow and adapted to reinforce the strength of the outer layer and the insert being fixed to the outer layer, wherein the outer layer is be formed from a fibre reinforced polymer resin material and the insert is formed from a lightweight material.

The insert may be formed as a U shaped channel. Alternatively, the insert may be formed to substantially occlude the cavity of the hollow. The insert may substantially fill the hollow. The insert may be formed of a foam.

0 Preferably the internal cavity extends externally of the outer layer.

Preferably the ladder comprises a step ladder and further comprises a stabilizing Smember hingedly connected to the stiles and steps.

SPreferably the stabilizing member comprises a bracing frame hingedly connected Sto the ladder through pivot pins located around a moulded head piece of the ladder member of the step ladder and the bracing frame is rotatable between an opened and closed position.

Preferably the lightweight material is selected from PVC closed cell foam or urethane foam in a cast form or cut from sheets, end grain balsa, straight grain balsa, light weight timber, plywood, honeycomb in aluminium, paper, fiberglass or plastics, Tricell, Nycell, Duracore or any combination of the above, the polymer is a material selected from the group comprising polyester, vinylester, epoxy, phenolic, Metton, LCDP resin, pigmented resin, resins with fillers added and any blending of resins and the fibre reinforcement for the resin is selected from the group comprising glass fibre, carbon fibre or aramid fibre in the form of chopped strand, mat, knitted braids, unidirectional rovings and woven rovings, or in the form of biaxial, triaxial or quadraxial woven fabrics or RovicoreTM.

At least one of the components of the ladder may be formed from fibre glass by the method discussed above. The ladder is a step ladder having a step section and a bracing section each hingedly connected to the other. In a platform ladder the ladder and bracing sections may be formed from conventional materials and the platform may be formed according to the present invention.

Both the step section and the bracing section may be formed with an outer layer and an insert.

(N The insert may be formed from foam, plastic or any other suitable material.

SPreferably, the outer layer of the ladder member is formed with stiles and steps integrally formed and preferably, at least in part, of fibre glass.

In a further aspect, the invention resides in a ladder comprising: 0an integral outer layer defining stiles and steps, the outer layer having an internal Scavity; and a reinforcing member positioned within the cavity and adapted to reinforce the strength of the outer layer.

The outer layer may have an internal cavity which communicates externally of the outer layer.

The ladder is preferably a step ladder and further comprises a stabilizing or bracing member hingedly connected to the stiles and steps.

The outer layer and/or the reinforcing member may be formed from fibre glass.

Preferably the outer layer describes curves at the junction of the stiles and steps.

The reinforcing member may be formed from a plastic compound.

The reinforcing member may be a U shaped channel member. Alternatively the reinforcing member may be adapted to substantially occupy the internal cavity.

The stabilizing member is preferably a bracing frame hingedly connected to the ladder and rotatable between an opened and closed position. The bracing frame may be hingedly connected to the ladder through paired pivot pins located around a head piece of a ladder member of the step ladder. The paired pivot pins may be formed from high density nylon. The ladder may include a moulded head O piece.

0 The ladder member and bracing frame may be formed from resin transfer moulding procedures.

In a further aspect, the invention resides in a ladder with at least some of its components formed from a foam cored reinforced polymer composite. The preferred components are load bearing members such as rungs, treads and stiles.

In a preferred embodiment, the whole ladder is formed from a foam cored reinforced polymer composite.

It is also possible to form ladders in combination with other materials such as aluminium. For example, aluminium rungs may be cast into RTM stiles. The foam core may be cut from a sheet or sheets or moulded to shape. A range of densities may be recruited and used as indications require. Reinforcement for the polymer may include glass rovings, glass mats, surface veil, aramid fibre, carbon fibre and any other suitable fibre, natural or synthetic, alone or in combination. The polymer may be thermoset or thermoplastic.

In this aspect, the invention therefore extends to foam cored reinforced polymers for use in ladders, particularly in load bearing components, such as stiles, rungs and treads. The invention also extends to the use of Resin Transfer Moulding techniques for ladders and variations thereof, such as vacuum assisted resin transfer moulding ("VARTM").

In a further form the invention is said to reside in a ladder structure including a core portion and a skin portion, the core portion having stiles and integral rungs and being formed from a foamed material, the skin portion enveloping and adhering to the core portion, the skin portion being a fibre reinforced polymeric resin, and the skin portion being applied to the core portion by resin transfer O moulding techniques.

0 Preferably the ladder structure includes integral fixing locations.

The ladder structure may include anti-slip patterning on an upper surface of the C rungs.

0 In one form the invention comprises a step ladder having a ladder structure as defined above and a bracing frame pivotally mounted to the ladder structure and S 10 collapsible struts between the ladder structure and the bracing frame.

In a further form the invention comprises an extension ladder having two ladder structures with one ladder structure sliding in brackets associated with the other ladder structure and a locking arrangement between the ladder structures.

In yet a further aspect the invention extends to foam cored, reinforced polymer construction members for use in suitable applications. Preferably the reinforced polymer is formed with RTM techniques or variations thereof. As a further aspect, the invention extends to a method of forming a construction member, the method comprising the steps of forming a foam core and forming an outer layer of reinforced polymer around the foam core. The outer layer is preferably formed using resin transfer moulding techniques.

In preferred embodiments a ladder according to the present invention may be constructed from the following materials.

In a preferred embodiment the quantity of resin to total mass of resin and fibre reinforcement may be in the range of 30 to 50% by weight.

BRIEF DESCRIPTION OF THE DRAWINGS This then generally describes the invention but to assist with understanding 8 reference will now be made to the accompany drawings which show preferred embodiments of the invention.

0 In the drawings: Figure 1 is a front perspective view of a step ladder formed according to the present invention; Figure 2 is a perspective section of a portion of the ladder of Figure 1; Figure 3 is a rearward perspective view of a variation of the portion of Figure 2; Figure 4 is a cross section of a stile of the ladder of Figure 1; Figure 5 is a side view of a top portion of the ladder of Figure 1; Figure 6 is a front view of the ladder of Figure 1; Figure 7 is a perspective view of a stile and tread intersection formed according to an alternative embodiment of the invention; Figure 8 is a top sectional view of a mould suitable for forming the embodiment of Figure 7; Figure 9 is a series of views of an extension ladder according to the present invention; Figure 10 is a series of views of a step ladder with rail; and Figure 11 shows a platform ladder according to an alternative embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS Referring to Figure 1 there is seen a ladder 10 formed as a step ladder having a ladder or step section 11 and a bracing section 12 formed as two frame members 13, 14 which are interconnected and pivotally attached to the ladder section 11.

Collapsible struts 15, 16 are provided to limit rotation of the bracing section 12 relative to the ladder section 11. The ladder section 11 is formed of spaced stiles 17,18 which are formed integrally with rungs 19. A head piece 20 is also provided and is preferably formed integrally with the ladder section 11.

It is preferred if the ladder is devoid of metallic components to minimise the chance of electrical conduction and also corrosion in hostile environments.

Figure 2 shows the relationship of a sectioned stile 18 and rung 19 which are formed preferably integrally with a curve 21 described by the transition from stile 18 to tread or rung 19. This curve may be of advantage in providing extra bracing of the treads or steps. The ladder 10 is formed as an outer layer 21 describing an 0 internal cavity 22 which when moulded communicates with the exterior. The internal cavity 22 and the present embodiment is shaped substantially as an elongate U.

An insert 23 is dimensioned to sit within the cavity 22 and contact the outer layer 21 on its internal walls 24, 25. The insert 23 may be made of any suitable material with sufficient strength to maintain opposed walls 24, 25 of the outer layer 21 substantially in their same relative position. The insert 23 may be formed as a U channel member as shown here and may suitably be made of a plastic or other polymeric material. Although it is preferred that the ladder does not include metallic components, it is clearly possible to provide a ladder made, at least in part, from metal according to the configurations described herein.

Figure 3 shows a rear view of a variation of the arrangement of Figure 2. The curve 26 below the tread 19 is apparent in this view as is the insert 23. The insert may be fixed in position by any suitable means such as frictional engagement, gluing, plastic welding or even riveting or other suitable means. In this embodiment the outer layer 21 and insert 23 envelope a foam core 26. The external features may be assembled around the core, or alternatively, moulded around the core.

The cavity 22 may be further filled by an auxiliary insert such as a form core 26 which is light, insulating and further stabilizing of the structure.

Figure 4 is a cross section of a stile or tread of the embodiment of Figure 1 showing the cavity filled by a foam core 26, the outer layer 21 and insert 23. While a preferred shape of the component is demonstrated, it is possible to have other suitable configurations of the ladder stiles and treads, such as box sections.

Figure 5 shows the pivoting of the bracing section 12 relative to the ladder or step section 11. A pivot 27 is provided on both sides of the step ladder to provide a pair Oof aligned rotation points for the bracing section 12 relative to the ladder or step section 11. The head piece 20 shown in this view is formed by a section 28 in the bracing section 12 and a cooperating section 29 in the ladder section 11. In use, the bracing section 12 may be rotated into proximity with the ladder section 11 for stowage and carrying and may be deployed in an extended position when required for supporting the weight of an operator.

Figure 6 shows an alternative embodiment of a ladder 10 having stiles 117, 118 and treads 119 along with a head piece 120. Feet 130, 131 are provided to enhance the stability of the device and operation. In this embodiment, the same technique and process for production has been used to provide a straight ladder rather than a step ladder. This highlights the utility of the present inventive method. It is clear that its application goes beyond mere step ladders. Non-limiting examples of applications of the present construction technique include the production of steps, ladders, roof racks, chairs and tables, trolleys, trailers, wheelbarrows and carts.

Figure 7 shows an alternative embodiment of a tread and stile intersection 60. In this ladder a foam core 61 is produced which has integral stiles 63 and rungs 64.

An outer layer 62 of a fibre glass material is formed around the foam core 61 and then a settable resin is placed over the fibre glass material so that the resin impregnated the fibre glass material and adheres to the foam core. In production the foam insert is wrapped in an outer layer of fibre glass which is then impregnated with a settable polymeric resin in a resin transfer mould. Once cured, the insert 61 and set outer layer 62 form a lightweight, strong, durable structure.

It will be noted that the foam core of the rung 64 has on its upper surface a patterning in the form of ridges which when the fibre glass is laid onto it and the polymeric resin impregnated into it forms an anti-slip pattern on the rung.

Various forms of patterning can be provided.

Figure 8 shows a mould 70 which is suitable for producing the structure of Figure 7. A mould top 71 is adapted to engage a mould bottom 72 thereby positioning the Sfibre glass material 62 in close proximity to a foam core insert 61. Resin transfer moulding procedures may then be completed to place a settable polymeric resin 73 into the fibre glass material 62 to produce a hard set outer layer on the ladder member. The mould may then be split to allow removal of the formed device. The mould is formed so that stiles and treads are integral.

Figure 9 shows an extension ladder 79 formed from a base ladder 80 and a sliding secondary ladder 81, the two joined by suitable brackets 82, 83. The brackets may be formed as sleeves. The ladder may use a clutch or hooks (not shown) or any other device to allow locking the ladder at different lengths. The locking device itself may be formed according to RTM techniques.

A step ladder with handrail according to one embodiment of the present invention is shown in Figure 10. The step ladder 85 is formed from a ladder portion 86 is formed with the stiles integral with a hand rail 87. Two rungs 88 are provided to give access to a platform 89. A bracing frame 90 is pivotally hinged to the ladder portion adjacent to the handrail 87. In operation, supporting pins 91, 92 of the platform 89 are positioned in slots 93 on the bracing frame (only one is shown) to allow sliding of the platform relative to the bracing frame during folding.

An alternative embodiment of ladder being a platform ladder is shown in Figure 11. In this embodiment the platform ladder 100 has a ladder portion 101 and a bracing portion 102 with a platform 104 extending between them.

The ladder portion 101 is formed from a pair of stiles 106 and 108 which extend up to a separately moulded hand rail 110 with an integral tray 112. The tops of the stiles 106 and 108 fit into sockets 107 in the hand rail 110 and are fastened to the hand rail by known fastening methods such as rivets or by adhesive. Steps 109 extend between the stiles. The bracing portion 102 has two legs 122 and 124 which are hingedly connected to the respective stiles. Cross bracing 116 and 123 is provided between the legs 122 and 124. In this embodiment the stiles 106 and 108, the steps 109 and all of the bracing portion 102 are formed from conventional materials such as aluminium extrusions but in other embodiments all of these portions may be formed by the resin transfer techniques of the present invention.

The platform 104 is formed using the resin transfer moulding techniques of the present invention and includes a core of the type discussed earlier and a fibre reinforced resin coating and has a textured anti-slip finish 114 on its upper surface so that a user will not slip when using the step ladder. The core may have a core thickness of 20 mm and a nominal fibre glass coating of 2.5 mm. The platform 104 pivots on an axle 105 mounted onto the stiles and rests on a support 116 on the bracing portion 102.

The platform ladder 100 has two pairs of spring loaded wheels 118 and 120 so that when there is no load on the ladder the springs raise the bottom of the stiles and legs of the bracing portion so that the platform ladder can be moved about. When a person steps onto the ladder the springs are compressed and the stiles and legs take the load so that the ladder will not move with a user on it.

The particular advantage in producing a ladder according to the present invention is the absence of metal in some embodiments. The pivot pins of a stepladder may be formed from nylon thus providing a light weight non-corrosive ladder which is suitable for use in electrical, mining and construction environments. Further the ladder may be easily sterilized and used in areas where hygiene is critical such as in food preparation lines, abattoirs and similar. The insert may be formed as a one piece continuous moulding. The ladder material may be of high resistance and durability which is long lasting and has low maintenance requirements. The applications of the present techniques provides a lightweight, resilient and strong stepping device which may be of great assistance in many applications.

c While the disclosure has primarily been used in ladders and ladder like devices, Othe present method is not necessarily restricted to such applications. The method of forming a foam core with an outer reinforced polymer layer, particularly reinforced fibre glass may be applied to a crude range of construction members.

O

S 10 The outer layer is preferably formed according to RTM techniques. Without in any way restricting the range of applications, the present invention may be used to form, in whole or in part, tables and chairs, composite rudder blades and shafts for marine applications, boarding ladders and steps for marine applications, roof racks and cradles for vehicle tops, trailers and boot extenders for vehicles, food handling equipment such as trolleys, trays, racks and benches and equipment in the health industry. The technology lends itself also to use in camping and outdoor equipment such as stools, tables, chairs, recliners, folding shower cubicles and demountable shelters.

Throughout the specification the aim has been to describe the preferred embodiments of the invention without limiting the invention to any one embodiment or specific collection of features. Those of skill in the art will therefore appreciate that, in light of the instant disclosure, various modifications and changes can be made in the particular embodiments exemplified without departing from the scope of the present invention. All such modifications and changes are intended to be included within the scope of the disclosure.

Claims (5)

1. A method of forming a composite assembly, the method comprising the steps of forming a lightweight core and forming an outer layer of fibre reinforced polymer resin around the lightweight core, wherein the outer layer is formed onto the core using a technique selected from resin transfer moulding, resin transfer moulding light, vacuum assisted resin transfer moulding, resin injection moulding, multiple insert tooling, injection, infusion, pressure moulding, moulding with prepregs, vacuum forming, open moulding and manual moulding.

2. A method as in Claim 1 wherein the lightweight core is formed from a material selected from the group of materials comprising PVC closed cell foam or urethane foam in a cast form or cut from sheets, end grain balsa, straight grain balsa, light weight timber, plywood, honeycomb in aluminium, paper, fiberglass or plastics, Tricell, Nycell, Duracore or any combination of the above.

3. A method as in Claim 1 wherein the polymer is a material selected from the group comprising polyester, vinylester, epoxy, phenolic, Metton, LCDP resin, pigmented resin, resins with fillers added and any blending of resins.

4. A method as in Claim 1 wherein the fibre reinforcement for the resin is selected from the group comprising glass fibre, carbon fibre or aramid fibre in the form of chopped strand, mat, knitted braids, unidirectional rovings and woven rovings, or in the form of biaxial, triaxial or quadraxial woven fabrics or RovicoreTM. 0

5. A method as in Claim 1 wherein the composite assembly is a ladder. Dated this 21st day of December, 2004 HILLS INDUSTRIES LIMITED By its Patent Attorneys N MADDERNS S (N