The present invention relates to a grid structure, to a method of making a grid structure and to apparatus for use in the method. The invention is primarily concerned with a grid structure suitable for use as flooring.

Flooring which has the form of a grid and is formed of metal has been made and used for many years. It is common for the flooring to comprise a plurality of load bearing bars which are spaced from one another and a plurality of transverse bars also spaced from one another and connected with the load bearing bars. The transverse bars retain the required spacing between the load bearing bars and prevent the load bearing bars falling over or twisting. To achieve the required strength with the minimum amount of material, the load bearing bars generally have a rectangular cross-section with the longer dimension vertical and a smaller dimension horizontal.

Flooring of the kind described is most commonly manufactured by supporting a number of the load bearing bars in the required relative positions, then placing transverse bars on upper edges of the load bearing bars, passing an electric current from electrodes in contact with the transverse bars, through those bars to the load bearing bars, whereby heat is generated in the transverse bars and in the load bearing bars, where these cross, and then pressing the transverse bars into the load bearing bars so that depressions are forged in the load bearing bars to receive the transverse bars and the bars are welded together. This process produces satisfactory flooring. However, large and expensive machinery is required and the consumption of energy is high. It is generally practicable to use this process only at a site where an unusually high powered electrical supply is available. Heat imparted to the grid structure during manufacture cannot readily be recovered in a useful way and the process is therefore wasteful of energy.

Alternative ways of manufacturing flooring of the kind described have been proposed but, although these alternative procedures may be less wasteful of energy, they are unsatisfactory in other ways. In G.B. 1 ,536,573, there is disclosed flooring in which the load bearing bars are formed with holes and transverse bars are inserted through aligned holes in successive load bearing bars. Those parts of the transverse bars lying between adjacent load bearing bars are then deformed to make the transverse bars captive in the load bearing bars. One cross-sectional dimension of those parts of the

transverse bars lying between the load bearing bars is increased to a value significantly greater than the corresponding dimension of the openings in the

*- , j load bearing bars. This is achieved by squeezing the transverse., bars at positions between the load bearing bars.

Squeezing of the transverse bars between horizontally spaced tools is difficult, because access is restricted by adjacent transverse bars. Flooring produced by this process rattles, when subjected to vibration, since movement of each transverse bar relative to each load bearing bar is not reliably prevented.

In G.B. 1,339,593, there is disclosed flooring in which the load bearing bars are formed with non-rectilinear openings. Transverse bars are inserted through these openings whilst having a cross-sectional shape corresponding to that of the openings. Subsequently, those parts of the transverse bars lying outside the load bearing bars are deformed to render the transverse bars captive in the load bearing bars. With this arrangement also, movement of each transverse bar relative to each load bearing bar is not entirely prevented. Furthermore, a substantial number of operations are required to produce the flooring, which is therefore expensive.

In G.B. 652,793, there is disclosed a further process for the manufacture of flooring of the kind described, in which transverse bars are deformed, after being passed through apertures formed in load bearing bars, to render the transverse bars captive in the load bearing bars. In this case, the openings are large, as compared with the cross-sectional area of the transverse bars. Flaps on the load bearing bars adjacent to the openings may be riveted or otherwise secured to the transverse bars but this operation is expensive. Furthermore, the large openings in the load bearing bars reduce the strength of these bars to an unacceptable degree.

In G.B. 2, 106,948A, there is disclosed flooring in which transverse bars are welded to the load bearing bars, after having been inserted into pre¬ formed openings. Whilst the energy consumed in the welding operation may be -less than that required for the forging and welding operation hereinbefore described, a greater number of operations is required to produce the flooring and the pre-formed openings extend downwardly from upper edges of the load bearing bars, thereby weakening these bars significantly.

According to a first aspect of the present invention, there is provided a method of manufacturing a grid which includes the steps of forming in each of a plurality of first bars a plurality of openings spaced along the bar,

introducing second bars into the pre-formed, aligned openings of the first bars and deforming the first bars into-vgripping relation with the/second bars at the boundaries of said openings.

The step of deforming the first bars is preferably carried out with the bars substantially at ambient temperature. Heating of the bars is not necessary and therefore the power consumed in the manufacture of a grid of given area can be substantially less than that required to produce a grid of the same area by the forge welding method hereinbefore described. 1 have found that the first bars can readily be deformed sufficiently to prevent entirely movement of the second bars relative to the first bars.

According to a second aspect of the invention, there is provided a grid comprising a plurality of first bars arranged side-by-side and a plurality of second bars arranged transverse to the first bars, wherein the second bars extend through respective openings in the first bars and wherein the first bars are in gripping engagement with the second bars at boundaries of said openings.

The gripping engagement is characterised by mutual engagement of surfaces of the first bars and second bars respectively but these surfaces remain distinct. The bars are not united by fusion and a portion of a first bar bordering one of the openings would fall away from the second bar, if surrounding parts of the first bar were removed.

The cross-sectional shape of the first bars is preferably elongated and the openings are preferably spaced from both edges of these bars. By the edges, is meant the surfaces which face upwardly and downwardly when the grid is in use as flooring. Generally, these faces will be narrower faces of the bar, wider faces being vertical, as required to achieve maximum load-bearing ability with minimum use of materials. However, the cross-sectional shape of the first bars may be other than rectangular. For example, an edge which is an upper edge in use may be presented by a flange of the bar.

I have found that spacing of each opening from an edge of the first bar in which the opening is formed by a distance of 6mm, in the case of 5mm thick steel bars, and by 6.5mm, in the case of 3mm thick steel bars, gives particularly advantageous results. If the spacing is reduced considerably, the strength of the bar is impaired. If the spacing is increased considerably, the deformation which is necessary to prevent entirely movement of a transverse bar within the opening is less easily achieved. Preferably, the spacing between each opening and an adjacent edge of the bar in which the opening is

formed lies within the range 5mm to 8mm. However, the spacing may be

*-' within the range 3mm to 10mm.

According to a further aspect of the invention, there is provided apparatus for carrying out a method in accordance with the invention, said apparatus comprising a rotatable member formed with a surface of revolution centred on an axis of rotation of the member and formed with at least one eccentric element protruding radially outwardly beyond the surface of revolution, whereby rolling of a bar by the member produces an indentation in the bar where said element contacts the bar. BRIEF DESCRIPTION OF THE DRAWINGS

Examples of grids in accordance with the invention made by a method in accordance with the invention and examples of apparatus for use in the method will now be described, with reference to the accompanying drawings, wherein:-

F1GURE I is a perspective view of a first example of a grid;

FIGURE 2 is a similar illustration of a second example of grid;

FIGURE 3a is a fragmentary elevation of one load bar and one transverse bar of the grid shown in Figure 1;

FIGURE 3b is a plan view corresponding to Figure 3a;

FIGURE 4a is a fragmentary elevation of one load bar and one transverse bar of a further grid;

FIGURE 4b_ is a plan view corresponding to Figure 4a;

FIGURE 5a is a fragmentary elevation of one load bar and one transverse bar of a further example of grid;

FIGURE 5b_ is a plan view corresponding to Figure 5σ;

FIGURE 6a is a fragmentary elevation of one load bar and one transverse bar of a further example of grid;

FIGURE 6b is a plan view corresponding to Figure 6a;

FIGURE 7 illustrates apparatus for use in making grids of the present invention;

FIGURE 8 is a sectional view of the apparatus shown in Figure 7;

FIGURE ?£ is a fragmentary view of a load bearing member and solitary transverse member and another embodiment of deforming apparatus; and

FIGURE 9b illustrates the load bearing member and transverse member shown in Figure 9a after having been deformed by the deforming member.

DETA1LED DESCRIPTION

In Figure V, there is shown α..< pαrt of α grid structure, ^% this part comprising four load bearing bars I I to 14 and two transverse bars 17, 18. Each of the bars is elongate and rectilinear. The cross-sectional shape of each of the load bearing bars is rectangular. These bars are arranged with their larger faces vertical and with those smaller faces which extend along the length of the bar, called herein edges, horizontal. The load bearing bars are parallel to one another and the transverse bars are parallel to one another and perpendicular to the load bearing bars.

There is formed in each of the load bearing bars I I to 14 a row of apertures, two of which are indicated at 15 and 16 in the load bar I I . These apertures are spaced downwardly from the upper edge of the load bearing bar by a distance within the range 5mm to 8mm. Thus, the surface of the load bearing bar which defines the boundary of each aperture extends completely around that aperture. Each of the transverse bars 17 and 18 extends through respective aligned apertures- in the load bearing bars and is gripped by surfaces of the load bearing bars bounding the apertures. Thus, the shape of each aperture complements, to at least some degree, the cross-sectional shape of those parts of the transverse bars which lie in the apertures. However, the apertures are not necessarily completely filled by the transverse bars.

The transverse bars illustrated in Figures I and 3 have a non-circular transverse cross-section so that gripping by the load bearing bars prevents rotation of the transverse bars relative to the load bearing bars. Furthermore, the transverse bars are twisted so that longitudinal sliding of a transverse bar through an aperture in a load bearing bar would necessarily be accompanied by rotation of the transverse bar. The transverse bars may have alternative forms which facilitate prevention of movement of the transverse bars within the apertures. For example, the transverse bars may be knurled.

To produce the structure illustrated in Figure I, the apertures are punched in the load bearing bars I I to 14 and bars having a square cross- section are twisted to form the transverse bars. The load bearing bars are then assembled in a jig which holds the load bearing bars in the required relative positions with apertures of adjacent bars in alignment. The transverse bars are then passed through the aligned apertures. It will be appreciated that the transverse bars are initially a free sliding fit in the apertures of the load bearing bars. Subsequently, the load bearing bars are

deformed to contract the apertures and establish a gripping relation between the boundary surfaces of the aperture^- and the transverse bars-^To achieve this deformation, opposed forces are exerted on upper and lower edges of the load bearing bars to squeeze these bars. The force exerted on lower edges of the load bearing bars is preferably distributed along a substantial length, or the entire length, of each load bearing bar. In contrast with this, force is exerted on the upper edges of the load bearing bars only in localised regions adjacent to the apertures 15 and 16. Such local application of force produces indentations 1 and 20 in upper edges of the load bearing bars by causing flow of metal.

As shown in Figure I, there may be a single indentation in each load bearing bar above each transverse bar. Alternatively, two indentations may be produced in the immediate vicinity of each transverse bar, these indentations lying on opposite sides of a plane which contains the longitudinal centreline of the adjacent transverse bar and is perpendicular to the upper edge of the load bearing bar.

Deformation of each load bearing bar into gripping engagement with a transverse bar produces slight thickening of the load bearing bar in the immediate vicinity of the aperture and adjacent indentation. Thus, the resulting structure preferably has load bearing bars which have a substantially uniform thickness, except in the vicinity of the apertures containing the transverse bars, where the thickness is slightly greater. The deformation of the load bearing bars into gripping engagement with the transverse bars also causes some deformation of the transverse bars by transmission of force to the transverse bars via the load bearing bars. The thickness of each transverse bar is reduced slightly where the transverse bar passes through the aperture in a load bearing bar so that there is formed in the transverse bar a slight neck which is disposed in the aperture. At opposite ends of this neck, there are slight shoulders on the transverse bar, at least at upwardly and downwardly directed apices of the transverse bar. These shoulders abut the load bearing bar and restrain relative movement of the bars in a direction along the transverse bar. Deformation of the bars is carried out at ambient temperature.

The grid structure shown in Figure 2 comprises load bearing bars 25, 26 and 27 arranged in the same manner as are the load bearing bars of the structure shown in Figure I. Transverse bars 30 and 31 extend through apertures in the load bearing bars, two of these apertures being indicated by

the reference numerals 28 and 29. The -transverse bars are arranged in the same manner as those of the structure shown in Figure 1 but, in this example,

**' may have a circular cross-section. The ^' transverse bars may be knurled.

The load bearing bars 25, 26 and 27 are provided at their upper edges with notches and therefore have a castellated form which reduces the risk of footwear slipping on the upper surface of the structure. The notches are produced by shearing of the load bearing bars when the apertures are punched therein. Subsequent steps in assembly of the structure illustrated in Figure 2 correspond to those hereinbefore described with reference to Figure I .

Referring now to Figures 3 to 6 (a and b), various alternatives in the cross-section of the apertures formed in the load bars and the transverse bars are shown.

Figures 3a and 3b show a load bar 35 having an aperture 36 of substantially round cross-section, the transverse bar 37 being of twisted square cross-section.

Deformation 38 of the load bar 35 will tend to squash the aperture 36 causing mechanical interaction between the transverse bar 37 and the load bar 35.

Referring now to Figures 4a and 4b, a load bar 40 is shown having a circular aperture 41 and a transverse bar 42 having a circular cross-section.

Figures 5a and 5b_ illustrate a load bar 45 having an aperture46 of triangular cross-section, the transverse bar 47 being also of triangular cross- section.

Figures 6a and 6b illustrate a load bar 50 having an aperture 51 of rectangular elongate form, the transverse bar 52 being of similar cross- section.

It will be appreciated that many different configurations of transverse bar and aperture may be provided, the nature and dimension of the aperture and its respective transverse bar depending on the use to which the metallic structure is to be put and the strength required.

In each of the examples illustrated, the apertures formed in the load bearing bars are spaced from both upper and lower edges of those bars, being nearer to the upper edges. Alternatively, the apertures may extend to upper edges of the load bearing bars or to depressions formed in those edges by deformation of the load bearing bars.

The load bearing bars are preferably deformed in a press equipped with a tool capable of deforming all of the load bearing bars concurrently at

respective positions lying adjacent to one transverse bar. The grid would be advanced through, the press in steps corresponding to the spacing- between adjacent transverse bars to effect gripping of all of the transverse bars.

Referring now to Figures 7 and 8, apparatus for use in the manufacture of metallic structures is shown, the apparatus comprising an indenting roller 60 and support rollers 61, 62 and 63.

The indenting roller 60 is provided with radial projections, for example those shown at 64 and 65, and guide rollers 66.

In use of the apparatus, the assembled metallic structure is passed beneath the rotating roller 60 so that the radial projections such as those shown at 64 and 65 contact the load bar 67 at positions immediately, above the aperture 68 through which the transverse bars have already been positioned. The projections indent the upper surface of the load bar 67 and cause deformation of the aperture 68 and interaction between the metal of the load bar 67 and the transverse bar 63.

The centres of the supporting rollers 61 to 63 and the centre of the indenting roller 60 may be relatively adjustable in order to deform load bars of different height.

The indenting roller 60 is provided with guide rollers 66 each side thereof, which guide, rollers 66 extend either side of the load bar being indented in order to guide the passage of the metallic structure into a correct position. The guide rollers 66 are provided with indentations adjacent the radial projections 64, 65 to prevent the guide rollers 66 from deforming the transverse bar 68.

The indenting roller 60 may be of a size so that it may simultaneously indent either one, or any desired number of load bars depending on the power input available, the size of the metallic structure and the force necessary to produce the required deformation of the through bores and mechanical interaction between the load bars and the transverse bars.

Referring now to Figures 9a and 9b, an alternative embodiment of apparatus for use in the manufacture of metallic structures is shown.

A deforming punch 70 has a part 71 having spaced protrusions 72 and 73. The punch 70 may be carried by an automatically operated press or alternatively the apparatus shown in Figures 7 and 8 may have the radial projections, such as those shown at 64 and 65, each replaced by a pair of projections, such as those shown at 72 and 73 spaced by a small distance.

The load bearing member 75 is situated below the punch 70 and positioned such that the plane 76 in which lies the longitudinal a;x_is of the transverse member 77 and which also extends substantially at right -angles to the longitudinal axis of the load bearing member 75, is aligned with the direction of movement of the punch 70, the projections 72 and 73 being spaced equidistant therefrom.

The punch 70 is moved downwardly with considerable force into contact with the load bearing member 75 which is deformed as shown in Figure 9b. The projections 72 and 73 concentrate the deformation in an area surrounding the transverse memebr 77, i.e. either side thereof, so as to move the material from which the load bearing member 75 is made into the gaps between the transverse member 77 and load bearing member 75 to ensure satisfactory mechanical interaction between the load bearing member 75 and transverse member 77.

The structures illustrated in the accompanying drawings are preferably formed entirely of metal, various steels being suitable materials. The depth of the load bearing bars, that Is the separation between upper and lower edges, is typically within the range 10mm to 100mm and the thickness of these bars is typically within the range 2mm to 12mm. Grids comprising load bearing bars and transverse bars only, called in the art "mats", may be produced in one size only or in a limited range of sizes. From these mats, there may be produced panels for incorporation in a floor. The panels may include additional members, for example members connecting together corresponding ends of bars of the mat. Furthermore, the panels may be smaller than a mat and have a shape different from that of a mat, a mat being cut up to produce one or more panels. The panels may include a frame or supporting bars welded or otherwise secured to the bars present in the mat. The spacing between adjacent load bearing bars is dependent on the use to which the mat is to be put and is typically within the range 12mm to 50mm.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result may, separately or any combination of such features, be utilised for realising the invention in diverse forms thereof.