TECHNICAL FIELD

The present invention relates to a method of manufacturing load-bearing members in reinforced plastic and relates particularly, although not exclusively, to a method of manufacturing scaffold planks of fibreglass reinforced plastic and a plank manufactured in accordance with this method.

BACKGROUND ART

The present invention will be described with reference in particular to scaffold planks, however the method of manufacturing disclosed will have wider application to the manufacture of other kinds of load-bearing members such as, for example high tensile beams and roof trusses for building structures. The method of manufacture can also be applied to railway sleepers to provide an alternative reinforced plastic sleeper to the currently used wooden or steel sleepers. Similar comments apply with respect to prior art railway sleepers as are given below with respect of the problems associated with prior art scaffold planks.

In most uses of scaffolding, safety standards are laid down by appropriate regulating authorities, both in regard to the nature and manner of erection of the scaffolding, and in regard to the strength and condition of the various components, including scaffold planks. In view of the adverse environmental and use conditions in which scaffolding and scaffold planks are commonly used, they are frequently subject to accidental misuse and mishandling that may cause damage thereto and that reduces the physical strength of the scaffold components, such as scaffold planks. Accordingly, the useful life of such components

may be relatively short, and hence the level of wastage and the cost of replacement is relatively high.

In regard to scaffold planks in particular, they are normally used in the manner of a beam supported at spaced locations and accordingly any damage to a scaffold plank which impairs its mechanical strength is considered unsafe, and thus such damaged scaffold planks must be discarded. A large proportion of scaffold planks are made of timber, usually of Oregon or similar lightweight high strength timber. Although timber planks can withstand considerable misuse without a significant impairment of their strength, they are prone to splitting in the longitudinal direction, particularly after they have been exposed to outdoor weather conditions for a considerable period. Longitudinal splitting of wooden planks is not conveniently repairable to a standard that retains the required strength, and accordingly, safety regulations normally require the discarding of scaffold planks once significant longitudinal splitting has occurred.

Metal planks have also been used, which do not suffer from the problem of longitudinal splitting, but because of the non solid nature thereof, comparatively minor bending or deformation of sections of the plank can severely impair the mechanical strength thereof. In regard to steel planks, it is necessary, because of the high density of steel, for the plank to be manufactured from a relatively thin gauge metal strip or plate, which is formed with appropriate flanges or ribs to create the required strength. However, any bending or deformation of the flanges or ribs severely reduces the mechanical strength of the plank and it is difficult to effect repairs which will return the plank to its original design strength. Metal planks have also been made from extruded aluminium sections, or plain fabricated aluminium strip, which although much lighter than steel, is of significantly less mechanical strength and higher cost per unit weight. The use of aluminium does reduce the weight ^" of the plank,

which is a major disadvantage of steel planks, however aluminium is generally more easily bent and distorted than steel and would therefore suffer more damage from mishandling. Generally, it is a requirement of safety regulations that once a metal plank has been significantly bent or distorted in use, it cannot be merely straightened and reused, but must be considered unserviceable.

Further, it has been proposed to improve the weather and split resistance of timber planks by encasing them in a fibreglass reinforced resin sheath. Although this does substantially increase the normal life of the plank, the addition of the fibreglass resin sheath substantially increases the total weight of the plank and thus makes them more difficult to handle, particularly in view of the substantial amount of manual handling required in the normal erection and dismantling of scaffolding. There have been proposed in previous patents and patent applications, including my own Australian patent application No. 75601/87, to fabricate scaffold planks of a fibreglass construction including the provision of internal longitudinally extending stiffening walls, which are basically essential in such planks to provide the required strength without excessive weight. Although these prior proposals are believed to normally produce an effective scaffold plank, the method of manufacture is such that they are relatively costly and present some manufacturing problems, particularly in regard to ensuring the achievement of an effective bond between the respective components, particularly where some components are preproduced in a final cured form and then bonded to other components.

OBJECT AND SUMMARY OF THE INVENTION

It is therefore a principal object of the present invention to provide a method of manufacturing load-bearing members of reinforced plastics material that is relatively simple to perform and wherein all components are assembled and integrated prior to any curing to achieve maximum bonding.

According to one aspect of the present invention there is provided a method of manufacturing a load-bearing member comprising: a) forming a first cover layer of uncured fibre- reinforced plastic material in a mould having a length and cross- section substantially that of the finished member, the cover layer being dimensioned to cover substantially the whole area of a face of the member; b) locating in the mould on the cover layer a plurality of side by side elongate formers extending the length of the mould; c) interlacing with each of two adjacent formers an elongate locking strip of uncured fibre-reinforced plastic material, with a marginal portion of said locking strip overlaying one of said two adjacent formers and another opposite marginal portion underlying the other of said two adjacent formers; d) forming a second cover layer of uncured fibre- reinforced plastic material overlying said plurality of formers and interlaced locking strips; and e) curing the resulting assembly whereby said cover layers and interlacing locking strips form an integral unitary structure.

Preferably, said first and second cover layers are formed by a single cover web of uncured fibre-reinforced plastic material, the first layer preferably being formed by laying up the web in the mould and having a marginal portion projecting over at least one longitudinal edge of the mould, and said second layer being formed by folding the projecting marginal portion or portions of the cover web about the assembled formers and locking strips to substantially completely wrap thereabout.

According to another aspect of the present invention there is provided an elongate load-bearing member comprising:

a cover layer of fibre-reinforced plastic material forming an outer wall encasing a plurality of longitudinal extending elongate formers; an elongate locking strip of fibre-reinforced plastic material interlaced with each of two adjacent formers, with a marginal portion of said locking strip overlaying one of said two adjacent formers and another opposite marginal portion underlying the other of said two adjacent formers, said over and underlying marginal potions being bonded to the outer wall to form an integral unitary structure.

Preferably, said elongate formers are strips of expanded plastic foam material such as expanded polyurethane or polystyrene, which are sufficiently rigid to support the assembly prior to curing. Conveniently the strips of rigid foam material are continuous throughout the length of the member, as also are the locking strips, however, as the foam strips are primarily a former to hold the locking strips in place during curing, it is not essential for each strip to be a single continuous piece. Further as the thermosetting plastics impregnated fibre reinforced material can be conveniently joined, the locking strips may be of two or more pieces with overlapping portions at the junction thereof. Such a lap joint in the locking strips will form an effective integral one piece locking strip during the curing of the plastics material.

It will be appreciated that when the locking strips are assembled in the overlying and underlying relationship with adjacent strips of foam, each of the intermediate strips of foam will have a marginal portion of a locking strip on both the top and bottom of the foam strip, however, the terminal foam strips in the assembly will only have a marginal portion of a locking strip on one of the top and bottom faces, and thus, in order to provide a relatively level flat face on the top and bottom of the finished member, it is preferable for a further strip of plastics

impregnated fibre-reinforced material to be provided on the relevant upper and lower face of the terminal strips of foam material. If desired, these additional strips of plastics impregnated fibre-reinforced material may be of an L-shape so that one arm of the L underlies or overlies the foam strip as the case may be, and the other arm of the L extends along the terminal side face of the respective strip of foam. This will result in each longitudinal edge of the member having a double layer of resin impregnated fibre as does the top and bottom of the member.

The invention will be more readily understood from the following description of one practical arrangement of the construction and method of manufacture of a load-bearing member in the form of a scaffold plank, given by way of example only, as depicted in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, Figure 1 is a perspective view of a completed plank showing one end in a cross-section. Figure 2 is an exploded view of the components of the plank shown in Figure 1. Figure 3 is a perspective view of the component used in the plank construction to cover the respective ends of the plank.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to Figure 2 of the accompanying drawings, a mould 10 is of an elongated form of uniform rectangular cross- section, that cross-section corresponding, to the desired cross- section of the finished plank. The three elongate rectangular formers 11, 12 and 13 of polyurethane or like foam material together have a cross-section complementary to the mould 10 but of reduced cross-sectional dimensions to permit the assembly therewith of the fibreglass components as hereinafter described.

It will be appreciated that the strips of foam material are substantially for the purpose of providing a form about which

the fibreglass may be shaped, and are not a substantial factor in the final strength of the plank. The strips of foam material conveniently individually extend the full length of the proposed plank, however, as they are not a major structural component of the plank, each strip may be made of two or more pieces arranged in an end to end relation. The formers are preferably of foam material since this is lightweight and sufficiently rigid to support the impregnated fibreglass prior to curing. However, any suitably rigid material would suffice such as strips of wood, or plastic or metal sections.

The locking strips 14 and 15 are preferably of fibreglass mat and are interlaced between respective pairs of adjacent foam strips. The fibreglass locking strip 14 overlies the foam strip 11 passes between the opposed vertical faces of adjacent foam strips 11 and 12 and underlies foam strip 12. Similarly fibreglass locking strip 15 overlies foam strip 12 passes between the opposed vertical faces of foam strip 12 and 13 and underlies foam strip 13. It will be appreciated that the number of fibreglass locking strips is equal to the number of strips of foam material minus one, and if required, the plank may include any number of foam strips and a complementary number of fibreglass locking strips.

Two corner strips of fibreglass mat 16 and 17 are provided, the strip 16 embracing the outer face and lower face of the terminal foam strip 11 and the fibreglass strip 17 embracing the outer side and upper face of the terminal foam strip 13.

The cover or wrapper web 18 of fibreglass mat is of a length corresponding to the length of the proposed plank and of a width corresponding to the perimetal dimension of the cross section of the finished plank with provision for a degree of overlap of the longitudinal edges of the cover web when assembled.

The above components of the plank are assembled together in the following manner:

1) The cover web 18 of fibreglass is impregnated with suitable resin so that the web is saturated with the resin. 2) The cover web is then placed over the mould 10 and the web worked into the mould so as to extend across the bottom face 9 of the mould and up the respective opposite sides 20 and 21 of the mould, leaving respective marginal portions 22 and 23 of the cover web overhanging the edge of the mould 10. Preferably the overhanging marginal portions 22 and 23 are each of a dimension so that when subsequently folded over the foam strips, the edge potions 22 and 23 will overlap on the upper face of the plank.

The corner strip 16 is impregnated with the resin so as to be saturated therewith and is then placed in the mould to form a double layer of fibreglass along the vertical side 20 of the mould 10 but does not extend upwardly beyond the portion of the cover web 18 on the side 20 of the mould. The remainder of the width of the corner strip 16 extends across the base of the mould for an extent substantially equal to the width of the foam strip 11.

With the fibreglass corner strip so placed in the mould,it is rolled in a conventional manner to achieve a integration between resin on the corner strip 16 and the resin in the abutting portion of the cover web 18 in the mould 10. The strip of foam 11 is then placed in the mould in intimate contact with the vertical and horizontal portions of the corner strip 16 and pressed firmly there against so that intimate contact is achieved between the resin in the corner strip 16 and the abutting faces of the foam strip 11.

The locking strip 14 of fibreglass is then coated with resin and rolled to obtain saturation thereof with resin. The saturated strip 14 is then placed in the mould so that one end portion overlies the foam strip 11, the adjoining portion

extends down the exposed vertical face of the foam strip 11 and the remainder of the strip 4 extends across the cover web 18 located on the base 9 of the mould 10. After so positioning the locking strip 14 it is further rolled to obtain intimate contact between the relevant faces of the foam block 11 and the cover web 18 with the locking strip 14.

The second foam strip 12 is then placed in position to abut the vertical portion and the horizontal base portion of the locking strip 14 and is pressed into firm intimate contact therewith. The locking strip 15 is then placed in position over the top face of the foam strip 12 and down the exposed vertical face thereof and then across the remainder of the base of the cover web 18 located in the mould 10. This locking strip 15 is then again rolled on the three sections thereof to obtain intimate contact between the resin therein and the faces of the foam block 12 and the base portion of the cover web 18.

The edge of the corner strip 17 of fibreglass is impregnated with resin and located so that a potion thereof overlies the portion of the cover web 18 abutting the vertical wall 21 of the mould and the overlapping portions rolled into intimate contact. The final foam strip 13 is then placed in position in the mould so as to contact on one side and the underface, the relevant portions of the locking strip 15 and to also contact the portion of the corner strip 17 extending up the wall of the mould. After the foam strip 13 has been placed in position, the remaining portion of the corner strip 17 is folded over the top of the foam strip 13 and rolled into intimate contact therewith.

After the three foam strips and the two corner strips and two locking strips of fibreglass have been placed in position in the mould as above described, it is preferable that the longitudinal edges of the respective strips which overlie the foam strips abut one another so as to form a continuous top layer of resin impregnated fibreglass. However, the presence of a small

gap therebetween is not detrimental to the quality of the finished plank.

The plank is now finished by folding the marginal portions 22 and 23 of the cover web 18 across the finished assembly in the mould 10, preferably with the longitudinal edges of the portions 22 and 23 slightly overlapping, to form a top cover layer for the assembly. The whole top face of the assembly is now rolled in the conventional manner to obtain intimate penetration of the resin between the various overlying sections of the fibreglass to form an integrated assembly. The complete assembly is then permitted to cure in the mould until it is in a condition for removal without damage to the assembly.

The completed assembly after curing is illustrated in Figure 1 of the drawings, from which it can be seen that the plank comprises top and bottom walls 30 and 31, sidewalls 32 and 33 and vertical internal stiffening walls 34 and 35. Each of the top and bottom, and side walls are comprised of a double thickness of fibreglass with internal stiffening walls being of a single thickness. The above described constructions provides an extremely strong plank of a comparatively light weight and of high durability.

In order to provide a suitable tread surface on at least the upper face of the plank, the following treatment is carried out after the final curing. The plank is sanded preferably on all four sides but at le≤st on those sides to which the tread treatment is to be applied. After sanding a fine layer of resin is sprayed onto the surface or surfaces of the plank to be treated and before the resin has cured, a fine layer of sand or similar grit is applied and then a final layer of resin is sprayed over the sand or grit. After further curing an effective non-slip surface is available for the workmen to walk upon in safety, even in wet conditions.

In the above described method of manufacture, no reference has been made to covering the ends of the plank, and

this may be achieved by locating an end strip of resin impregnated fibreglass into each end of the mould prior to the commencement of the assembly of the components as previously described. An example of the end strip and how it is located in the mould is depicted in Figure 3 of the drawings. The end strip 25 is placed in the mould so that a portion 26 thereof lies on the bottom of the mould with an adjoining portion 27 extending up the end wall of the mould, and a further portion 28 extends over and beyond the end wall of the mould. An end strip 26 is located in this arrangement at either end of the mould and the cover web is then inserted into the mould so as to overlie the portions 26 at either end of the base of the mould. The foam strips and locking strips are then assembled into the mould as previously described, and the cover web folded thereover. After the closure of the cover web, the portions 28 of the respective end strips 25 are folded over the top of the cover web and rolled thereinto to establish intimate bonding with the cover web. This folding of the end strip is performed prior to the curing process as previously referred to, during which the end strips 25 are also subsequently cured.

Any suitable thermosetting plastic material may be used together with an appropriate reinforcing fibre material. Good results .are achieved using a random fibreglass mat together with a polyurethane resin and these are the materials employed in the above described preferred embodiment.

It will be apparent to those skilled in the appropriate arts that many variations and modifications may be made to the described embodiment without departing from the basic inventive concepts. For example, the mould employed is shaped to produce the appropriate shape of a rectangular scaffold plank. However, any shaped mould can be devised to create a load-bearing member of the required dimensions and shape. Substantially the same method of manufacturing the member can be followed to produce a railway sleeper on any other type of beam structure using a

different mould and appropriately sized formers and locking strips. All such variations and modifications are to be considered within the scope of the present invention the nature of which is to be determined from the foregoing description and the appended claims.