AU645404B2 - Ladder and method of construction - Google Patents

Description

P/00/0011 Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT ORIGINAL4 I. Name of Applicant: Actual Inventor(s): MICHAEL WALSH MICHAEL WALSH C C

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Address for service in Australia: CARTER SMITH BEADLE, Qantas House, 2 Railway Parade, G~amberwell, Victoria, 3124, Australia, Attorney Code SA.

Invention Title: LADDER METHOD OF CONSTRUCTION The following statement Is a full description of this invention, including the best method of performing it known to me/us: -1I- 2 TITLE: LBDDER METHOD OF CONSTRUCTION INRODUCTION TO INVENTION: This invention relates to constructs in fibreglass and in particular to constructs involving fibreglass members adapted to withstand shear forces and bending about a plurality of axes, for example ladders. The invention provides an improved method of joining such fibreglass members and an improved joint per se.

BACKGROUND OF INVENTION: Fibreglass as a constructional material enjoys a broad range of characteristics which render it a useful and versatile medium. In particular, fibreglass is readily mouldable into a tough, durable material having highly predictable strength characteristics. Fibreglass has a high strength to weight ratio and good thermal and electrical insulating properties. Fibreglass also has excellent resistance to corrosion and other beneficial properties which render it a particularly attractive material for the construction of ladders and the like.

However, among the restrictions that fibreglass suffers is a limitation applied to its workability by virtue of its lack of ductility. Ductility allows a 25 material to be pressed and pushed into shape. Hence, in the construction of multiple molding constructs of fibreglass, any joints must be either welded, glued or fastened together to effect a reliable joint. Such requirements place a considerable limitation on the type of joining economically available to fibreglass constructs and in particular to small surface area, medium to high stress joints exposed to shear forces mwspe#6442 92 3 11 -3and bending about a plurality of axes, for example the rungs of a ladder as they are joined to the stiles. Such joints are difficult to execute in fiberglass as the usual method of pressing ferrules formed in the rungs abutting the stiles cannot be formed on a non-ductile material like fiberglass. The use of glues or welding is limited by the difficulty of injecting sufficient glue into the joint so as to effect maximum bonding of the small surface areas involved.

OBJECT STATEMENT OF INVENTION: One object of the instant invention is to provide an improved method of joining wherein at least one component of the joint is in fiberglass and an improved resultant joint.

A further objection of the invention is to provide an improved ladder or other device incorporating the said joint.

Accordingly, the invention provides a method of jointing a fiberglass component where a first member formed of a hollow section channel and having one or a plurality of sockets in the form of holes therein is provided with internal annuli aligned with said holes and a second member having a sealed end and being adapted to snugly fit into said socket is engaged with said first member wherein a setting medium is injected into said socket-second member interface and pressure is applied to engage the first and second members such that said setting medium is distributed 20 to said interface and surrounds.

The first member may be formed of hollow section channel with the sockets formed by boring holes into the side of the channel such that the inside of the channel is exposed, wherein annuli can be inserted into the internal cavity of the channel and aligned with the holes to effect sealed sockets.

25 The internal annuli may be formed of high density polyethylene tubing or most preferably injection moulded tubing, flanged at either end such that the combination of the annuli and the holes form the receiving sockets in the first member.

Once the sockets are formed, either as detailed above, or by other methods MAWNB:6442Jipc 30 Stembr 1993 -4detailed later in the description, the setting medium may be injected into the socket such that once the second member is engaged with the socket and locked into place the setting medium is forced to squeeze into place and then to conform to the pressure of the engagement by exuding into the interface between the annuli and the second member.

In a particularly preferred form of the invention further aimuli may be placed on the outside of the channel member to receive any excess fixing medium and this excess may provide a further aspect of adhesion to the joint.

The above jointing may be used to join fiberglass to fiberglass or fiberglass to another material, for example aluminium.

The preferred setting medium is an epoxy resin or a thermosetting resin.

In a further aspect, the invention provides an article incorporating a jointed fiberglass component where a first member formed of hollow section channel and having one or a plurality of sockets in the form of holes formed therein and suitably aligned internal annuli is engaged with a second member having a sealed end and being adapted to snugly fit into said socket wherein said jointed component is characterized by a setting medium injected into said socket-second member interface wherein application of pressure to said setting medium effects distribution thereof to said interface and surrounds.

20 The article may take the form of a ladder having fiberglass stiles as the first 9 member and aluminium rungs as the second members wherein said members are joined according to any of the aforesaid methods.

Another form of the invention is a grate.

The injection of the setting medium can be accomplished in a number of ways 25 either from an external source or an internal source activated by S* o

S

9*S* ii *0 MAWNB:#6442pc 30 Sclmb 9 5 penetration of the stile sockets by the rungs.

In the case of an external source of setting medium, the rung ends may be provided with a number of radial holes adapted to communicate directly with the annular sleeve and provide a means of injecting the setting medium into the joint. Alternatively the rung end could be provided with a cap adapted to deflect an injection of setting medium around the end of the rung and into the sleeve-rung interface.

In the case of an internal source of setting medium, a telescopic cap, or reservoir, may be provided in the end of the rung which is filled with setting medium and adapted to expel said setting medium into the sleeve-rung interface upon penetration of the stile by the rung.

The stiles may incorporate either a blind through socket and in either case may incorporate an annular sleeve adapted to fit within the hollow member S" so as to form an integral part of the said socket and effect efficient adhesive distribution and an increased surface area for bonding.

DETAILED DESCRIPTION OF THE INVENTION: The invention shall now be described in greater detail by reference to the following particularly preferred embodiment as detailed herein: Figure 1 shows a cross-section of a completed •joint; Figure 2 details the formation of the annuli; Figure 3 shows detail of section B-B of figure 1 Figure 4 shows the loading factors associated with the joint of the invention; Figure 5 shows the force comparison between mwspe#6442 92 3 11 6 double place joints and single plane joints; Figures 6 7 detail glue flow considerations as they apply to the instant invention with figure 6 showing optimal press rate, figure 7(a) showing the results of a slow press rate and figure 7(b) showing the results of a fast press rate.

Figures 9 and 10 detail end and cross-sectional representations of the ladder joint of an alternative embodiment of the invention.

Figures 9a,b represent an internal source of setting medium using telescopic reservoirs.

Figure 10 represents an end cap method of external delivery.

Figures 11-13 represent alternative setting methods.

Figure 14 represents a method of installing the annular sleeves.

Referrir; firstly to figure 1, the particularly preferred form of the joint is detailed herein 9 utilizing a hollow channel fibreglass section as the first member 1 having an internal side 3 and an external side 2. The socket is formed in this first member by boring a hole 4 through the inside face of the first member thereby exposing the inside of the channel. In order to form the socket, annulus of polyethylene 5 is inserted into the internal cavity of the channel so as to align with the bored hole 4.

Once aligned, the annulus forms a sealed socket in the first member into which a setting medium or epoxy resin 6 may be injected.

Once a suitable amount of epoxy is injected into the socket the second member 8 having a sealed end 9 mwspe#6442 92 3 11 7 may be pressed into the socket. The action of pressing will compress the epoxy until the whole of the bottom of the socket is covered with glue wherein continued engagement will cause the glue to migrate up the annulus second member interface 10 and, if a suitable quantity of glue is used shall migrate through the hole 4. In order to utilize the excess glue and optimize the joint strength a further external annulus 11 may be used to capture the glue and form a third bead of glue.

Figure 2 gives a detailed demonstration of the formation of the annuli where high density polyethylene tube 12(A) is provided with internal splines (13) and then cut into suitable lengths. The aniuli are then provided with a collar 14 which is :660.. subsequently flared Figure 3 details a section B-B of; figure 1 showing the spline allowance 13 of the annuli and the' snug relationship of the second member 8 and the socket or annulus.

Figures 6 and 7 detail the method of the invention where the rate of assembly of the component members has an influence of the quality of the joint.

FiQgre 6 shows an optimal rate of engagement of the 9 25 second member 8 into the socket or hole 4 such that the end result of the jointing action is a small air bubble at the bottom cavity which is ejected through the annulus with the final pressing of the joint.

Figure 7a shows the possible result of engaging the members too slowly where the end of the second member becomes wetted too early.

Figure 7b shows the possible result of engaging mwspe#6442 92 3 11 8 the members too quickly where a surge of flue can compromise the formation of an optimal S-shaped meniscus at the air bubble.

Figure 8 gives clear representation of another type of the joint where the hollow first member 1 has two holes 4 forming a through socket. The second member 8 is of hollow, circular cross-section having a diameter less than that of the said socket and forming an interface 10 therein, between itself and the first member. The second member has radial bores 14 forming the channels for communication and insertion of the setting medium 6. The holes particularly facilitate very thorough delivery of the setting medium into the interface. In order to further facilitate efficient use of setting medium, a sleeve or annulus 5 can be inserted into the first member to form a shield to disperse the setting medium as well as a further anchorage point to increase the surface area for t bonding. The annulus should preferably have a diameter about the same or greater than the diameter of the holes 4.

PARTICULAR DETAILS OF JOINT CONFIGURATION: The closed hollow rectangular section is inherently better in torsion about its central axis, 25 parallel to the stile, than the C or I sections used in many ladders presently produced. This structural section reduces twisting and swaying tendencies which are disconcerting and can be dangerous to the ladder user. Accordingly, this section is the preferred form for the invention.

The closed section also offers two webs forming parallel planes to which the rung may be attached.

mwspe#6442 92 3 11 9 Forces transferred through the joint are shared by each web and reduce as the distance between the webs increase. The moment capacity of the joint is greatly increased compared with a single web joint (see figure Connection between the rung and each web or side wall of the stile is made by a suitable adhesive appropriately moulded within the joint to mechanically fix the two members together. Epoxy type adhesives are preferred for this application as their viscous flowing properties and strong adhesion to materials used in the construction of ladders fibreglass and aluminium) facilitate optimal assembly and strength.

STRENGTH CONSIDERATIONS To assess the strength of the joint, a standard test was adopted to simulate stresses that a ladder would experience under conditions of sway, twist and racking. Forces applied to the ladder to set up such **seeo conditions are quantified in the American standard, ANSI 14.5 for F/G ladders and served as a minimum '*criteria for strength. The standard test described in figure 4 however presents more severe conditions on the test joint than the forces applied to a complete e 25 ladder. It gives a useful scale on which to compare different joints and if satisfying this test they should pass tests for whole ladders. Other tests such as rung pull out and twisting of the rung about its own axis were carried out after the joint was optimized for the bending test which we deemed to be the most important.

The critical part of the joint under stress from mwspe#6442 92 3 11 10 this test proved to be the region where the end of the rung connected the outside stile web plane. Drilling all the way through the outside web to gain a mechanical lock decreased joint strength due to weakening of the web and limitations of physically attaching the two members with glue.

The strongest configuration for both F/G and aluminium rungs proved to be an end plug, being of similar material to the rung, pressed, and glued in the case of F/G into the end of the hollow rung to form a square flat end. This creates maximum surface area for bonding between rung and stile and allows even distribution of the shear force between the relatively stiff stile web and plugged rung end.

Reducing the glue thickness between these surfaces allows the connection to reply on the adhesive properties of the glue rather than its structural properties for transferring load. As shown in figure 4 there is tensi- Aid compression on this plane also. These forces ,iol the mode of failure when fracture occurs on is iplane. The top of the rung (from the diagram) reaches critical stress first due to the addition of maximum tension and sheer force. Initial fracture at the top of the interface 25 results in reduced bearing area causing the fracture to propagate from top to bottom and joint failure occurs. This is heard as a loud sudden crack.

9 In this type of failure either the bond between rung end and glue, or glue and stile results depending on which interface was strongest. F/G rungs when properly prepared for the glue typically fail by leaving the plug attached and breaking the rung and mwspe#6442 92 3 1 11 the fillet of glue around the end of the rung. This indicates that we are surpassing the limitations of the rung's circumferential strength and the fillet of glue before that of the glue plug. It was found that square profile concentric circles about the axis of the rung proved to efficient for this connection and lifted the joint strength to a level where rung strength became the limiting factor. Failure usually occurred by yielding of the rung circumferentially and breaking of the outer fillet of glue. By the time this was achieved the joint displayed a strength of nearly -three to four times that required for full ladder tests according to standards.

The rounded fillets of glue at each end of the annulus and the stile side of the wear strip act to distribute forces evenly from rung to stile and hold 4 the inside web of the stile securely. This was 0. evident as no failure occurred at this point during 0. any of the tests.

Typical ultimate moment carrying capacity for the final joint under this test were 170 Nm to 190 Nm for F/G rungs 2.5mm thick and 1.6mm aluminium rungs.

S. Rung twist tests about rung axis were 90Nm to The joint strength could conceivably be raised if e 25 necessary by introducing reinforcement into the fillet of glue around the end of the rung to support it and prevent failure of the rung from either fracture (F/G rungs) or yielding (aluminium rungs). This has been demonstrated by using thicker aluminium rungs which improved joint strength presumably from the higher forces required to yield the end of the rung. The reinforcement could take the form an aluminium ring mwspe#6442 92 3 11 12 slipped in during annulus loading or even glass fibres placed around the fillet cavity.

PERFORMING THE JOINT The key aspect to performing this type of joint lies in forming cavities inside and outside the style to contain and direct the glue to the right places while minimising air entrapment. This needs to be relatively easy to affect for production reasons and the cost of components within the joint kept to minimum.

The annulus which forms the inside cavity is made from extruded High Density Polyethylene type about thick. A number of channels run longitudinally along the inside for the F/G rung joint but is left plain for aluminium rungs. (The ribs that form the grip on the outside of the rung form communication channels for glue ilow through the joint). The tube .is cut to size, inside ends shaved to about thickness and then flared to 45 degrees (see figure S 20 The outside cavity follows a similar procedure except that only one end is formed. This we call a "wear strip" because it also acts as a protective strip around the rung preventing fibreglass wear on the other ladder and latch wear.

The annulus is made to be a tight fit within the stile to form a press seal on each lip of the flare and effect a closed cavity. Both the annulus and wear strip are a friction fit over the rung so that wear strip forms a seal on the outside of the &sile during the pressing of the rung into the joint. When this pressing is completed, the friction fit of the rung in the annulus prevents the rung from springing back out mwspe#6442 92 3 11 13 and therefore maintains this outer seal. Due to the right arrangement of these seals, the joint is quite rigid before the glue sets and the ladder can be handled without the aid of clamps immediately after pressing.

The F/G r ngs are prepared by either sandblasting or other suitable means for abrasion to expose the non-glass surface tissue so the glue can properly wet the surface and affect a good bond. It also prepares the rung for a non-slip coating of epoxy and finely graded sand. A bead of glue is placed at the end of the rung around the inside edge to receive the F/G plug designed to press fit into the end of the rung.

We have designed the drill that sizes the holes in the stile so that the waste core may be used to form the 0 end plug. It is then press fit 0.3mm to 0.4mm past 0 the end of the rung to break edges of the core and 00 obtain a neat fit. Both ends are pressed in a rig at S' the same time and left to set before the ends are 20 shaved to leave a fresh square flush end. It was deemed necessary to glue the F/G plugs into the ends !as the pres-fit could not be relied on to stay fixed during joint pressing. It also adds strength to the joint by rigidly adhering the plug to the rung helping 25 prevent pull out.

Aluminium rungs, having corrugations on the outside for grip and as a means of communicating the glue through the joint, do not require all over sandblasting or abrasion of the surface, as with F/G rungs. However, the ends of the rungs with their flush aluminium ends need to be prepared by either abrasive or chemical cleaning after machining the end mwspe#6442 92 3 11 14 pattern. A chemical substrate air drying paint is then applied to thb aluminium rung ends to which the epoxy can bond strongly. With the rungs and stiles suitably prepared for gluing we may introduce the glue and press the ladder together.

As can be seen from the foregoing, the instant invention provides a unique and highly reliable jointing method applicable to non-ductile materials and in particular to fibreglass.

Numerous items, for example, ladders are particularly well suited to fibreglass construction being light, strong and not electrically conductive.

The joint disclosed herein is particularly adaptable as the rung and stile joint allowing the construction S. 15 of a particularly sturdy and safe ladder.

Similarly, grates can be produced from fibreglass having high corrosion resistance and high rigidity.

The method of manufacture using the instant invention may involve alignment of a plurality of .i 20 joining members and a plurality of sleeves inside the Sfirst members. Such alignments may be assisted by annuli adapted to sit tightly on the second members to facilitate insertion and alignment into the first members, but wherein said annuli have a plasticity 25 which allows them to deform and expand under pressure of the setting material as it is injected such that the annuli expand out into the first member.

The particular mode of application of the setting material may be facilitated by the use of a tool adapted to inject the material through the communication channels at an appropriate pressure.

mwspe#6442 92 3 11

Claims (15)

1. A method of jointing a fiberglass component where a first member formed of a hollow section channel and having one or a plurality of sockets in the form of holes therein is provided with internal annuli aligned with said holes and a second member having a sealed end and being adapted to snugly fit into said socket is engaged with said first member wherein a setting medium is injected into said socket-second member interface and pressure is applied to engage the first and second members such that said setting medium is distributed to said interface and surrounds wherein either one or both of said first and second members is made of fiberglass.

2. A method according to claim 1 wherein said holes are formed in one side of said channel only such that said internal annuli form a sealed socket.

3. A method according to claim 1 wherein said annuli are flanged at one S :o or both ends. 15 4. A method according to claim 1 wherein a second annuli is fitted external to and abutting said first member for receiving excess setting medium.

5. A method according to claim 1 wherein said annuli are constructed of S extruded high density polyethylene tube.

6. A method according to claim 1 wherein said setting medium is injected 20 into said socket prior to insertion of said second member whereupon engagement thereof applies said pressure to the setting medium causing same to migrate along the socket-second member interface and effecting the joining thereof.

7. A method according to claim 1 wherein both first and second members are constructed of fiberglass.

8. A method according to claim 1 wherein either one of first or second members is constructed of aluminum.

9. A method according to claim 1 wherein said setting medium is an epoxy resin. A method according to claim 1 which is a ladder having a fiberglass first member as the stiles thereof and aluminum second members thereof as the Ar

16- rungs. 11. A method according to claim 1 wherein the second members have a sealed end in the form of terminal plugs provided with square profile concentric circles about the axis of the member, 12. A method according to claim 1 which is a grate. 13. An article incorporating a jointed fiberglass component where a first member formed of hollow section channel and having one or a plurality of sockets in the form of holes formed therein and suitably aligned internal annuli is engaged with a second member having a sealed end and being adapted to snugly fit into said socket wherein said jointed component is characterized by a setting medium injected into said socket-second member interface whereina application of pressure to said setting medium effects distribution thereof to said interface and surrounds wherein either one or both of said first and second members is made of fiberglass. S14. An article according to claim 13 wherein said holes are formed in one side of said channel only such that said internal annuli form a sealed socket. 15. An article according to claim 13 wherein said annuli are flanged at one "or both ends. 16. An article according to claim 13 wherein a second annuli is fitted external to said first member for receiving excess setting medium. 20 17. An article according to claim 13 wherein said annuli are constructed of extruded high density polyethylene tube.

18. An article according to claim 13 wherein said setting medium is injected into said socket prior to insertion of said second member whereupon engagement thereof applies said pressure to the setting medium causing same to migrate along the socket-second member interface and effecting the joining thereof.

19. An article according to claim 13 wherein both first and second members are constructed of fiberglass. An article according to claim 13 wherein either one of first or second members is constructed of aluminium. A 30 21. An article according to claim 13 wherein said setting medium is an MAWSM-6442.cL 5 Novtmlbt 1993 17 epoxy resin.

22. An article according to claim 13 which is a ladder having a fiberglass first member as the stiles thereof and aluminium second members thereof as the rungs.

23. An article according to claim 13 wherein the second members have a sealed end in the form of terminal plugs provided with square profile concentric circles about the axis of the member.

24. An article according to claim 13 which is a grate. A method according to any one of claims 1 to 12 substantially as hereinbefore described.

26. An article according to any one of claims 13 to 24 substantially as hereinbefore described. DATED: 5 November 1993 0 CARTER SMITH BEADLE a 9 Patent Attorneys for the Applicant: MICHAEL WALSH *5. MAWSM-6442.CL S November 1993 X- ABSTRACT A method of joining fibreglass components where a first member with a sealed socket therein is engaged with a second member having a sealed end and being adapted to snugly fit into said socket wherein said method is characterized by injection of a setting medium into said socket second member interface wherein application of pressure to said setting medium effects distribution thereof to said interface and surrounds. 9* S *o O *0 00* 0 *44 0 00 mwspe#6442 92 3 11