Classifications

• • E—FIXED CONSTRUCTIONS
  • E06—DOORS, WINDOWS, SHUTTERS, OR ROLLER BLINDS IN GENERAL; LADDERS
  • E06C—LADDERS
  • E06C1/00—Ladders in general
• • E—FIXED CONSTRUCTIONS
  • E06—DOORS, WINDOWS, SHUTTERS, OR ROLLER BLINDS IN GENERAL; LADDERS
  • E06C—LADDERS
  • E06C7/00—Component parts, supporting parts, or accessories
  • E06C7/08—Special construction of longitudinal members, or rungs or other treads
• • E—FIXED CONSTRUCTIONS
  • E06—DOORS, WINDOWS, SHUTTERS, OR ROLLER BLINDS IN GENERAL; LADDERS
  • E06C—LADDERS
  • E06C7/00—Component parts, supporting parts, or accessories
  • E06C7/08—Special construction of longitudinal members, or rungs or other treads
  • E06C7/081—Rungs or other treads comprising anti-slip features
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16B—DEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
  • F16B11/00—Connecting constructional elements or machine parts by sticking or pressing them together, e.g. cold pressure welding
  • F16B11/006—Connecting constructional elements or machine parts by sticking or pressing them together, e.g. cold pressure welding by gluing

Definitions

• the present invention relates to a structural support assembly, more particularly to a structural support assembly incorporating a joint and to processes for making same.
• Typical structural support assemblies are ladders, scaffolds and trusses.
• wooden refers to the property of having wood or wood fibres. Accordingly, timber, chipboard, high density chipboard and wood fibres encased in a polymeric matrix are all encompassed by this definition.
• a "clearance fit” refers to the property of having space between two connectable portions of two members for a major portion of the surface area of the portions, preferably between 70% and 100% of the surface area of the two portions, more preferably 90% to 100% of the surface area of the two portions, most preferably in excess of 95% of the surface area of the two portions.
• Wooden structural supports are useful, for example, in the construction and maintenance trades for performing work that, inter alia, requires that persons be electrically insulated whilst on the structures.
• An example of this type of work is high voltage conductor repair and installation.
• Examples of the wooden structural supports contemplated are ladders, scaffolds, trusses and any other supports containing wooden members that involve wooden/wooden, wooden/metal, and wooden/plastics joints.
• wooden structural supports suffer from the disadvantage that they can break. Such breakages are often caused by fractures or weak points in the wooden member at or near the joints. In the case of ladders with wooden stiles, these fractures are at or near the joint between the stiles and the rungs.
• wooden structural supports can also suffer from the disadvantage that the wooden member adjacent a joint is sufficiently deformable to cause the joint to become flexible, eventually leading to fracturing, play in the joint or separation of the members. If the companion member to a wooden member is hollow at the joint, such as a hollow rung on a ladder, this can also deform to allow flexibility of the joint. It will be appreciated that even having play in a joint can mean that the support becomes dangerous to use.
• structural supports have the further requirement that they must resist both translational and rotational forces applied to the joints.
• ladders must resist racking, twisting and sideways forces as applied to the ladder as a whole.
• Ladders must also resist rotational forces applied to rungs, particularly where the rungs are of the 'D' section type where the orientation of the stepping surface of the rung with respect to the stile is important.
• joints of the type described by Goto suffer from the disadvantage that, although the glued joint itself may be relatively strong, the weak portion in such joints is often close to the glued surfaces in the wood itself. Such joints tend to weaken and fracture in the wood immediately proximal the joint.
• US 4,925,331 also provides a solution for connecting wooden members. This is achieved by the insertion of a power transmitting bar into a blind bore in a wooden member, inserting retaining dowels perpendicularly to the power transmitting bar and a rigid casting compound which fills the space between the sides of the blind bore and the power transmitting bar to form a composite block.
• the Bertsche joint is complex in manufacture, requiring a number of components and steps in its construction. Owing to its complexity, it is also difficult to implement as a consequence of the number of components involved in joint members where space is at a premium. The Bertsche joint may therefore be problematic in joints for ladders, stiles and trusses. Finally, Bertsche is silent as to how to prevent breakage that often occurs in the wood around a joint rather than in the joint itself.
• a potential solution to the airlock problem is to drill a hole into the hollow member to equalise the pressure between the inside and the outside of the member, thereby preventing an airlock.
• An example of such a Standard is AS NZS 1892 1996. This Standard requires in part 1 clause 2.5.2.b, part 3 clause 2.6.2.b and in the draft of part 4 clause 2.5.2.b that "Where stiles are manufactured from hollow section material, means shall be provided to prevent the retention of water within the stile.” Additionally, holes not within the joint may act as starting points for future failure of the structural member.
• a hole could be drilled in a non structural part of a ladder stile to permit the free flow of air, which hole could be plugged after curing of the binding material.
• this has the disadvantage that it introduces an extra step into the process of joint construction.
• the finish of the completed article may also be negatively impacted by the presence of such drilled and filled holes.
• the present invention provides a structural support assembly comprising at least a male member in engagement with a settable binding material in engagement with a wooden female member, wherein: the male member has an open-ended hollow projection, the projection defining an inner wall and an outer wall;
• the female member has a socket defined therein by a groove in the form of a closed loop having opposing walls, the groove being shaped to receive said projection of the male member such that the projection of the male member forms a clearance fit with the socket of the female member;
• the binding material contacts opposing walls of the socket of the female member and the inner and outer walls of the projection of the male member;
• said binding material has permeated and strengthened the wooden female member adjacent the socket.
• a further aspect of the invention provides a support structure comprising at least a first and a second structural support assembly as defined in accordance with the first aspect, wherein one of the members of the first assembly is a member of the second support assembly.
• a yet further aspect of the present invention provides a process for manufacturing a structural support assembly comprising the steps of :
• male member having an open-ended hollow projection which defines an inner wall and an outer wall such that it forms a clearance fit with the socket of the female member;
• the invention extends to ladders, scaffolds and trusses containing at least one joint of the invention.
• the settable binding material in its unset state, to have a fraction with a viscosity of between 200 and 1000 centipoise. It is also preferred for the fraction to comprise at least 5% by weight of the total binding material.
• the binding material prefferably contact a major proportion of the opposing walls of the socket of the female member, more preferably 80%. It is also preferred for the binding material to contact a major portion of the portion of the inner and outer walls of the projection of the male member within the confines of the socket, more preferably 80%.
• At least one of the members is elongate, more preferably, that both members are elongate.
• the projection may be an end of the male member.
• the projection may alternatively protrude from a portion along the length of the male member.
• the socket may be defined by an end of the female member.
• the socket may alternatively be defined in a portion along the length of the female member.
• the structural support assembly be incorporated into a construction selected from a ladder, stepladder, scaffold and truss.
• Either member may be a stile. Where one of the members is a stile, the other member may be a rung. Multiple structural support assemblies may be employed in a single construction. It will be appreciated that the construction may have multiple rungs and multiple stiles. Each stile may have multiple attachments for rungs. Conventionally, rungs also have two ends for attachment to two stiles.
• the male member is a rung and the female member is a stile.
• the male member such as in ladders, may be provided with other portions, such as clamps and hooks. In such cases, the projection that is received into the socket may not necessarily be the end of the male member. However, any projection that is capable of being received into the socket will suffice for the purposes of the invention.
• a support structure preferably comprises a plurality of structural support assemblies. It is particularly preferred that a support structure comprises two female members and a plurality of male members. Alternatively, a support structure may comprise two male members and a plurality of female members.
• Both male and female members may be wooden. Where both members are wooden, one member is preferably of a stronger wooden material than the other member.
• the male and female members may be made of any practicable material having strength, stiffness, ductility and durability. Suitable materials for the male member include metals, preferably aluminium, wood, FRP (fibre reinforced plastics) and plastics. FRP may also include plastics reinforced with wood fibres. It is preferred that the members be weatherproof.
• the binding material should be chosen to be sufficiently strong so as not to break when loaded or stressed by the usual loads placed upon the joint in use.
• the binding material may be a polymer, preferably a resin.
• the resin may be any durable, hard, strong, settable resin including, but not limited to, one selected from the group comprising epoxy, polyester, polyurethane, and acrylic.
• the cured binding material It is generally important for the cured binding material to have a high solids content in the form of high molecular weight components to ensure rigidity.
• the extensive use of solvents in binding material should therefore be minimised to prevent cracking of the binding material due to shrinkage caused during the setting process. It is therefore preferred that the binding material be substantially non-shrinking during curing. This also prevents the binding material from pulling away from the members during curing.
• epoxy-based resins and reactive hot-melt resins are most preferred.
• Hot-melt resins include isocyanate-based and polyurethane-based resins, either alone or in combination.
• the binding material In order to permeate the wood adjacent the socket, it is preferable for the binding material be chemically curable.
• the uncured binding material should have a fraction component of at least 5% of the binding material by weight which has a viscosity of between 200 and 1000 centipoise in order to permit the resin to permeate the wood adjacent the socket prior to curing .
• the fraction component should be at least 10%, more preferably at least 20%.
• the overall viscosity of the binding material to be between 200 and 10,000 centipoise, more preferably between 2000 and 7000 centipoise, most preferably between 4000 and 6000 centipoise in order to achieve a high solids content and a low viscosity component fraction.
• the binding material adheres to the wooden member. It is particularly preferred that the binding material adheres to both male and female members.
• the binding material is an acrylic resin which is two part settable and which binds to wooden articles and to aluminium.
• the resin may also be reinforced by addition of glass fibres or other reinforcing materials.
• the male member is a 'D' section rung, alternatively an 'O' section rung.
• the male member is hollow proximal at least one end. It is particularly preferred for the male member to be tubular.
• the rung may have grooves extending longitudinally across its surface to improve the grip of the rung in use. Where the rung is a 'D' section rung, it is preferable for grooves to extend on the flattened surface of the 'D' alone. Also in the case of the 'D' sectioned rung, it is preferred for the flattened surface to be at an angle of between 90 degrees and 65 degrees to the longitudinal axis of the stile, more preferably 75 degrees.
• the socket be an annular groove.
• the male member projection must necessarily be hollow in order to seat in the socket.
• the groove can be of any practicable shape. In this specification, in a closed loop groove, the walls nearer the enclosed portion of the loop are called inner walls, whereas the opposing walls are called outer walls. It is particularly preferred that the socket be a trepanned annular groove, in which case the opposing walls of the groove define an inner and an outer wall of the socket.
• the projection of the male member be of a different shape from the socket in cross section such that it contacts both the inner and outer walls of the socket at different portions in cross section, more preferably, that the projection be a smoothed polygon. It is most preferred that the smoothed polygon has three sides and therefore be generally triangular in shape, thereby matching the shape of the rest of the preferred and so-called D-sectioned rung.
• the male member has protrusions which contact at least one of the walls of the socket, preferably the inner wall(s).
• the projection on the male member is deformed so as to have a different profile in cross section along its length proximal an end. The purpose of this is to enable the male projection to be anchored in the binding material when set.
• the projection of the male member has at least one hole which is filled with binding material.
• the settable binding material in its unset state, to have a fraction with a viscosity of between 200 and 1000 centipoise. It is also preferred for the fraction to comprise at least 5% by weight of the total binding material.
• the binding material prefferably contact a major proportion of the opposing walls of the socket of the female member, more preferably 80%. It is also preferred for the binding material to contact a major portion of the portion of the inner and outer walls of the projection of the male member within the confines of the socket, more preferably 80%.
• the process may additionally comprise forming a projection on the male member.
• the precursor monomer and a curing agent may be pre-mixed.
• the binding material may be applied to the projection, the socket or both.
• the precursor monomer and curing agent may be separately applied to the socket and projection and mixed by the joining of the two members. However, premixing the monomer and curing agent is more preferred.
• the process may additionally comprise retaining the members in a jig until the binding material has hardened.
• the process may additionally comprise forming at least one hole in the male member projection. It is preferred that the at least one hole be drilled. It is also preferred that the at least one hole be filled with binding material when inserted into the socket. Without wishing to be bound by theory, it is believed that such holes are advantageous as they are ultimately covered in binding material, which may permeate through the hole and assist in binding the male member to the female member. The hole is also not a water trap or a weakening point in the male member as it is ultimately filled with binding material.
• a preferred process of manufacture is as follows: the female member is manufactured and finished with a finish, if required.
• the finish chosen may be a varnish or a paint.
• the female member should preferably not be oiled as this may inhibit the permeability of the wood by the binding material and/or prevent the bonding of the binding material to the female member.
• a socket is formed in the female member.
• the socket is formed by trepanning an annular groove into the female member.
• the socket walls comprise unfinished material.
• Further socket may be formed in the same female member, as required. Unfinished socket walls tend to be more permeable to binding material than finished socket walls.
• the male member may then be prepared if not pre-prepared beforehand. Where the male member is wooden, the ends should be bare wood which will soak up resin. Where the male member is a metal, the ends should preferably be deformed and/or drilled to provide mechanical attachment to the binding material. Where the male member is FRP (fibre reinforced plastics), the ends should be abraded to remove any surface resins, waxes or paints and may optionally be drilled to form holes therein.
• the female member may be placed on a substantially horizontal level surface with the socket facing upwardly.
• the projection of the male member is placed in the socket.
• the male member may be oriented with respect to the female member, if required.
• the flat surface of the rung is preferably rotated to an angle of 75° from the longitudinal axis of the stile.
• the flat surface should preferably be a non-slip surface.
• the male and female members may be placed in a retaining device, preferably a jig, in order to retain the male member at the desired rotation angle and orientation with respect to the female member. Alternatively, a jig retaining just the male members may be employed.
• multiple male members may be inserted into multiple sockets in a female member. This is preferably done sequentially as per the above whereby each step is repeated for each joint to be completed and only advancing to the next step once all of the members have been subjected to said step.
• the retaining device may be utilised to retain all of said members.
• Such a multiple male member retaining jig may, in addition to the previously mentioned functions, be utilised to separate the male members from one another at set distances apart.
• the measured parts may now be mixed.
• the volume of unset binding material introduced into the socket may be pre-measured.
• a volume of unset binding material is preferably loaded into an open top end of each male member.
• the unset binding material is actually poured to run down the inside faces of the male member and not to immediately form a plug which would form an undesirable airlock within the male member when the base of the plug is above the level of the socket.
• the unset binding material running down the inside faces of the male member fills the socket.
• Soakage into the wood adjacent the socket is made up for by the rest of the resin running down off the side walls so that, after a short time, typically less than 10 minutes, the top of the resultant plug of resin reaches and remains flush with the upper surface of the female member.
• Another method for ensuring that the resin fills the socket to the required extent is to refill the socket with unset binding material at least once more to the desired level after time has been allowed for soakage into the wood to occur.
• the unset binding material may be loaded directly into socket and allowed to soak into the wood.
• the male member may be pre-treated with unset binding material at the end to be placed into socket to ensure a good resin coverage.
• the temperature may be controlled. Typically, this is by way of placing the structural assembly into a temperature controlled environment. Higher temperatures tend to make unset binding material less viscous until set, but decrease the setting time. Lower temperatures generally increase the viscosity of the unset binding material but increase the setting time. Thus, by altering the temperature, the degree of invasion into the wood by the unset binding material can be altered.
• An hermetically sealed chamber for housing the structural support assembly may therefore be provided with a pressure altering device, preferably a pump for increasing pressure and reducing pressure within the chamber.
• a pressure measuring device may also be provided for determining the pressure within the chamber.
• Such pressure differentials may be created locally within the joint where one of the members is tubular.
• a male tubular member may be sealed on one end, effectively sealing in a volume of gas within the member when a volume of unset binding material seals the other open end.
• Unset binding material in the male member can be made to act as a separation barrier between gas trapped inside the member and ambient gas surrounding the support assembly.
• the pressure of the gas inside the member increases.
• a decrease in the pressure surrounding the member, or an increase in pressure within the member causes a net force to be exerted on the unset binding material thus driving it out of the member.
• the pressure inside the member may be decreased or the ambient gas pressure surrounding the support assembly may be increased, thereby exerting a net force on the unset binding material driving it into the member.
• Pressure within the member may be increased and decreased by increasing and decreasing the temperature, respectively. Accordingly, means to adjust the temperature locally within the member may be provided by, for example, applying a heating element to the member. External ambient pressure may be adjusted by altering the pressure within the hermetically sealed chamber.
• the amount of force exerted on the unset binding material is alterable.
• the amount of pressure force chosen to be exerted on the unset binding material depends upon a number of factors, including the viscosity of the unset binding material, the setting time of the binding material, and the permeability of the wooden material in the female member.
• a further effect that can be produced from the pressure differential is contemplated where an increase in pressure can be used to drive the binding material into the wooden female member.
• an increase in pressure can be used to drive the binding material into the wooden female member.
• the amount of pressure to exert on the binding material depends upon the nature of the binding material and the nature of the wood, including permeability. If the wood has a considerable number of large resin tracks, a large increase of pressure may be undesirable as this drives the resin a considerable distance through the tracks while limiting localised wood permeation of the binding material.
• a useful pressure increase on the inside of the tubular member is of the order of about 0.25 psi (about 1700 Pa) for medium density woods.
• the joint assembly may be held until the unset binding material has set sufficiently to be safely moved without disturbing the joint.
• Basic cure times for setting the binding material vary widely depending on the nature of the binding material used. For most epoxy-based adhesives, this time is generally of the order of between 60 minutes and 500 minutes. Basic curing times may be utilised, provided the binding material is sufficiently set, to enable handling of the structural support after basic curing. Full cure may take up to one week.
• the free end of the male member may be treated with a volume of liquid resin.
• a volume of resin may be loaded into the open end of the member.
• a socket of a second female member may be placed over the open end of the male member.
• the entire assembly may then be turned such that the second female assembly is now face up. Where no or insufficient resin has been loaded into the member, more resin may be loaded into the second female socket.
• the assembly may now be retained in a jig. The whole assembly should be so retained until the resin has set sufficiently for removal without disturbing the second joint.
• the joint assembly or joint assemblies should be kept in storage, ensuring it/they remain straight, square and free of twist, until resin has cured sufficiently for use. This is typically more than 24 hours.
• the procedure most preferred is similar to that above.
• the resin may be poured into the socket in the upwards-facing female member and the male member lowered into the resin pool so formed while the male member is held in said jig.
• the jig may be set up to lower the male member into the socket at a predetermined rate to ensure that the rate of volume of male member inserted into the socket is of a similar order to the rate of volume of resin permeating the wood. It is preferred that the male member be lowered into the socket such that the male member's bottom surface abuts the lower surface of the socket.
• the inventor believes the strength of the joint disclosed herein is imparted because it provides an increased surface area of contact of binding material with the surrounding wooden female member and provides a gradient of binding material, binding material and wood and wood, instead of the usual binding material and wood junction of conventional joints.
• Figure 1A is a plan view of a grooved socket in a female member of the invention, for example, a stile of a ladder.
• Figure IB is a transverse sectional side view through a socket of a female member through B-B, as shown in Figure 1 A;
• Figure 2 is a plan view of a joint according to the invention with a D section rung with projections in a socket of a female member.
• Figure 3 is a side view of a male member with holes according to the invention in a cut-away section of a socket and surrounding wood.
• Figure 4A is a plan view of a joint of a ladder according to the invention.
• Figure 4B is a sectional side view through B-B as depicted in Figure 4A.
• Figure 4C is a sectional view through C-C as depicted in Figure 4B.
• Figure 4D is a sectional view through D-D as depicted in Figure 4B.
• Figure 4E is a sectional side view through E-E as depicted in Figure 4A.
• Figure 4F is a sectional side view through F-F as depicted in Figure 4A.
• Figure 5 A is a perspective view of a rung useful in the invention.
• Figure 5B is a further perspective view of the rung shown in Figure 5 A.
• Figure 6 is a set of standard layout composite views of the rung depicted in figures 5A and 5B.
• Figure 7A is a partial plan view of a stile useful in the invention.
• Figure 7B is a sectional side view through B-B as depicted in figure 7A.
• Figure 8 is a schematic representation of a curing box useful in the invention.
• Figure 9 is a partial sectional side view through a stile, rung and jig stile assembly.
• Figure 10 is a partial plan view of a jig stile useful in the processes of the invention.
• Figure 11 is a partial side view of a stile, rung and jig stile assembly.
• a female member in the form of a ladder stile is depicted and generally indicated as (10).
• the stile comprises an elongate wooden body (12) with a trepanned annular socket (14) therein.
• the socket (14) has inner (16) and outer (18) walls defined therein.
• a male member in the form of a rung (20) for a ladder is depicted.
• the rung comprises inner (22) and outer (24) surfaces.
• a non-slip top surface (26) to the rung is provided on the outer surface (24) and inwardly directed protrusions (28) extend from the inner surface (22) of the rung.
• the rung (20) is generally triangular with rounded corners (30, 32 and 34) in cross section.
• the outer surface (24) of at least one of the corners (30, 32 or 34) engages against the outer walls (18, Figure 1) of the socket.
• the inwardly directed protrusions (28) alone engage against the inner wall (16, Figure 1), typically in an interference fit engagement.
• the non-slip surface of the rung (26) may also engage against the outer wall (18, Figure 1).
• the rung can be provided without inwardly directed protrusions as shown in Figures 5A, 5B and 6, discussed more fully below.
• Figure 3 depicts an end of a hollow rung (36) wherein holes (38 and 40) have been formed in the rung below the depth of insertion into a socket. In use, the rung is inserted into a socket and binding material at least partially fills the holes.
• an aluminium rung (42) is shown inserted into a trepanned annular groove socket (44) in a wooden stile (46).
• Binding material in the form of resin (48) fills the socket and permeates into the wood surrounding the socket (50).
• the resin used by the inventor is obtainable from Protective Paints Limited, PO Box 58152, Greenmount, Auckland, New Zealand.
• the epoxy resin and hardener from this source are mixed together in a ratio of 4: 1.
• a pumping machine which mixes the correct proportions of resin and hardener and delivers the mixture may be used.
• the rung is deformed as depicted in figures 4B to 4F from a rounded triangular cross section proximal the top of the socket (50) ( Figure 4C) to a substantially round cross section (Figure 4D) at the base of the socket (50).
• the deforming of the rung (42) prevents withdrawal from the socket (44) by means of being trapped in the resin (48) around the deformed portions thereof.
• an extruded 'D' section hollow aluminium ladder rung (52) with longitudinal gripping grooves (54) is depicted.
• the rung is pressed to deform it at one end from the 'D' shape into a substantially circular shape in cross section (56).
• the deforming process is performed by any one of a number of standard die processes.
• a more detailed view of the deformation of the rung is shown in the cut away sections depicted in Figure 6.
• the deforming process is repeated for the other end of the rung (not shown).
• the deformed rung provides a non- uniform cross section about which epoxy adhesive can set and retain the rung.
• a female stile (58) in the form of an elongate length of smooth timber is formed by cutting to the length required for a ladder (not shown).
• Preferred timbers include Pinus radiata, Eucalyptus delegatensis and Eucalyptus regnans. Cut-outs (60) are optionally removed at regular intervals along the length in order to lighten the member without significantly weakening it.
• the member is varnished (not shown) to improve weatherproofness of the wood and to improve the finish.
• a preferred varnish is a single-pack polyurethane varnish.
• the stile may be painted.
• a preferred paint is a high-gloss enamel.
• a curing box (64) is provided to hold all the parts, rungs and stiles, in their correct relationship to each other while a binding material is allowed to set the joints of the ladder.
• the box has a sufficient length to accommodate the different lengths of stiles used to make ladders of different lengths. In width, it preferably accommodates multiple stiles, and hence ladders, stacked side by side.
• the box (64) has a substantially level setting table (68), perpendicular surrounding walls (70) and a removable lid (72).
• the walls (70), setting table (68), and lid (72) are thermally insulated. When the lid is fitted, the box becomes an enclosed vessel within which the ambient pressure and temperature may be controlled.
• a set of fans (74 and 76) is provided to circulate air inside the box (64) in a swirling motion so as to thoroughly mix the air and ensure that the temperature remains even throughout the box (64).
• the box (64) is additionally fitted with a heater (78) and a sensitive programmable thermostat (80).
• Ladders (complete ladder not shown) are built one stile at a time.
• the stile (96) described above with reference to Figures 7A and 7B, with annular groove sockets (62 of Figure 7), one of which is shown as (98), are placed uppermost and are each filled with a measured volume of binding material (100) in the form of premixed liquid resin and hardener.
• a tubular 'D' section rung (102) with a deformed end (103), as described above with reference to Figures 5 and 6, is now inserted completely in to the bottom (104) of the annular groove (98) such that the deformed portion thereof (103) and part of the undeformed portion thereof (106) are below the level of the binding material (100).
• the binding material (100) is displaced such that it now completely fills the groove (98) to the top (108), but no more.
• the process with respect to the rung insertion is repeated for each rung to be inserted into the stile (96).
• a jig stile (110) is now fitted over the uppermost ends (1 12) of all of the rungs (102) and the jig stile (110) is also pushed into the same corner as the lower stile (96) described above with reference to Figure 8.
• the jig stile (114) has shouldered holes (116) which are not round holds but 'D' shaped in plan view and arranged so that they hold the top grip surface of the rungs (not shown) at an angle of 75 degrees to the longitudinal axis of the stiles.
• the 'D' profile portion of the hole goes most of the way through the jig stile and the smaller portion of the hole (118) above the shoulder is round and extends all the way through the jig stile.
• Additional ladders may now be assembled in the same manner and likewise pushed up to the end of the box (described above with reference to Figure 8) and held against the edge of the previous ladder. Thus all ladders assembled into the box are held straight and square and free of twist.
• the binding material (100) will have soaked somewhat into the wood (101 and 103) surrounding the groove (98) and the top surface of the binding material will thus be not be at the top of the groove (98). Although the binding material (100) will have begun to polymerise it will still be liquid at this stage in the process. At a chosen stage in the process a further small quantity of binding material (not shown) is pumped through all of the holes (105) in the top surface of the jig stile(s) (described above with reference to Figure 10). This binding material falls to the bottom of the grooves (104) and flows around the embedded ends of the rungs.
• the binding material is still liquid and the rung ends (107) have apertures designed to facilitate the binding material flow.
• the further binding material refills the grooves (98) back to level with the top face of the bottom stile. At this stage in the process the binding material no longer soaks into the wood as it has set sufficiently to prevent this.
• the binding material level remains at the top of the groove (108).
• the lid (72) is now placed on the box (64) and the box (64) is gently heated using the heater (78) in order to speed the setting of the binding material.
• the heating cycle is controlled by the thermostat (80).
• the cycle comprises heating gently because heating the binding material too fast causes bubbles to form in the binding material leading to a weaker assembly.
• the heating is increased more rapidly after the binding material has gelled in order to rapidly harden the binding material to the point that the ladder can be removed from the box (64) for the next process without deforming the stile (82) and rungs (84) and binding material (figure 4, 48) which now form an assembly (86).
• the lid (72) is removed from the box (64) and the jig stiles (88) are removed from the tops of all of the rungs (84).
• the box (64) and contents are now allowed, or assisted by forced air circulation by the fans (74), to cool.
• a measured volume of premixed resin and hardener binding material is now poured into the open, upper, ends of all the rungs (90). This volume of resin poured into the upper end of each rung (90) is the same quantity or a slightly larger quantity of total binding material introduced into the each groove described above with reference to Figure 9.
• the completed ladders are now turned over so that the outside face of the second stile is placed on the setting table (68) of the box and the ladders are pushed up to one side and one end of the box, as described above.
• the ladders are thus held straight and square and free of twist and the rungs are held at the correct angle and parallel to each other.
• the unset binding material now runs down to what is now the bottom of the rung (84) and partially fills the associated annular groove in the second stile.
• the binding material flow around the end of the rung to completely fill the groove is inhibited because of an air-lock which forms inside the rung.
• the first method which can be used to flow the binding material to the correct level so as to fill the groove to level with the top face of the stile is to gently heat the whole assembly using the heater (78). This heats air trapped inside each rung (84) and thus increases the pressure inside the rung. This increased pressure drives the binding material down the rung and through the apertures or holes in the rung to fill the groove outside the rung as well as inside the rung.
• the lid (72) is placed on the box (64) and the fans (74 and 76) are set in motion to drive the air around inside the box to create the mixing effect.
• the thermostat (80) is set at the required temperature and the heater (78) switched on. The process is controlled so as to very gently heat the inside of the box (64) evenly.
• the temperature is increased very slightly and very gradually so that the excess binding material within the rung is displaced to fill the groove completely on the outside of the rung as well as still leaving it filled on the inside of the rung to at least the level of the top of the socket. This displacement also compensates for the soakage into the wood surrounding the annular groove, which will occur during the first part of the process of this first method.
• the temperature is carefully monitored until the binding material has gelled and thereafter the temperature is increased to a higher temperature and more quickly so as to set the binding material hard without undue delay so that the ladders can be completed and the box used for another batch.
• the second method which can be used to drive the binding material through the apertures or holes in the rungs to the correct level is to reduce the air pressure in the box (64) surrounding the rungs.
• the pressure differential thus drives the binding material to the correct level.
• the lid (72) is placed on the box (64) and sealed so the box (64) is airtight.
• the pressure inside the box (64) is now reduced by a pump (92) and carefully controlled and monitored by a pressure gauge (94) so that the binding material fills the groove level with the top face of the lower stile.
• the pressure will be lowered very gradually during the first part of the process cycle so as to account for the soakage of the binding material into the wood.
• PLC programmable logic controller
• a combination of the two methods outlined above can be used to provide a faster cycle time. If the box (64) is appropriately designed and made the temperature inside the box can be increased rather more that would be the case for the first method above and the excess pressure inside the rung (which would drive the binding material too far and overflow the groove) is compensated for by increasing the pressure of the air inside the box.
• a temperature cycle can be designed to take advantage of the best setting time for the binding material without bubbling it and the level of the binding material is controlled by the pressure regime while the whole process is run by the PLC in conjunction with the level sensor.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Ladders (AREA)
• Joining Of Building Structures In Genera (AREA)

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• 1999
  • 1999-03-16 NZ NZ33469699A patent/NZ334696A/en not_active IP Right Cessation
• 2000
  • 2000-03-16 EP EP00911508A patent/EP1169523A4/de not_active Withdrawn
  • 2000-03-16 WO PCT/NZ2000/000028 patent/WO2000055442A1/en not_active Application Discontinuation
  • 2000-03-16 AU AU33374/00A patent/AU773026B2/en not_active Ceased
  • 2000-03-16 CA CA002366008A patent/CA2366008A1/en not_active Abandoned
  • 2000-03-16 ZA ZA200108396A patent/ZA200108396B/xx unknown

Patent Citations (4)

Non-Patent Citations (1)

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