since fibrils adjacent the surface ould be cut. Further. we have also rejected a square section rod t isted into a helix as the rod would become in effect a coil spring which would increase elongation under load in the mass as compared to the elongation of parallel fibrils per se. The present invention therefore provides an elongate article of fibrilar oriented polymer within which the fibrils are substantially parallel to one another throughout the length, substantially without helical twist and at least substantiall continuous along the whole length of the article, said elongate article having a cross-section differing in orientation at various points along at least part of the length of said elongate article but of substantially the same cross-sectional area at those various points to provide at least one abutment surface extending transversely of the length of said elongate article capable of having force applied thereto or therethrough into or through said elongate article. The present invention also provides a method of forming an elongate article of fibrilar oriented polymer within which the fibrils are substantially parallel to one another throughout the length, substantially without helical twist and at least substantially continuous along the whole length of the article, said method comprising deforming a body of such oriented polymer at a temperature below the melting point thereof to produce said at least one abutment surface extending transversely of the length of said elongate article capable of having force applied thereto or therethrough into or through said elongate article. The elongate article may be formed as rod or tube, although the former will normally be preferred. In a particularly preferred instance said article was produced b passing said rod through a die ha ing a cylindrical bore therethrough and helical groo es in the bore whereby said article was produced with an abutment surface of helical form. In this instance the die was rotated as the rod was passed therethrough. The pitch of the said abutment of helical form may be such as to achieve
a surface area of said abutment surface of helical form as is desired. Although the description above is of deforming a rod which has been preformed to have oriented fibrils, it is also possible to deform the rod in the process of orienting and/or immediately thereafter. Thus, in one preferred instance a billet of polymer was passed through a die to orient the polymer and immediately thereafter was passed into a die to form said abutment surface. The elongate article embodying the invention may be put to use in lieu of rockbolts and as a substitute for steel reinforcing rods in concrete. It also has application in stabilizing a matrix including soil. Other applications include those in which longitudinal stress is applied. If desired, the article may be formed with longitudinally extending grooves or flattened areas to assist the article in resisting twisting in use under applied tensile loads. The polymer of which said elongate article is made is not of itself critical but it is believed that polyolefins, particular po 1 yethy 1 enes will be of most value. Other suitable linear ma c r omo 1 e cu 1 es include poly vinyl , polyethylene terephthalate and polyamide polymers. Brief Description of the Drawings : Several embodiments this invention and a preferred method of production will now be described with reference to the accompanying drawings in which: Fig. 1 is a fragmentary elevation of a rod according to one embodiment of the invention; Fig. 2 is a sectional end elevation of the rod of Fig. 1; Fig. 3 is a somewhat schematic sectional elevation of a machine for forming the article of Figs. 1 and 2, and Fig. 4 is a fragmentary longitudinal cross-section of the rod of Fig. 1 in the form of a drawn representation of a scanning electron microscope picture; Figs. 5 and 6, 7 and 8, 9 and 10 are fragmentary elevations and sectional end elevations respectively of
three further embodiments of the invention. Description of Preferred Embodiments : The rod 1 sho n in Figs. 1, 2 and 4 is formed of fibrilar oriented polyethylene in a generally circular cross-section having a multiplicity of upstanding helical ribs 2 providing abutment surfaces 3 defined by the rounded sides of the ribs 2. It will be observed that the rod 1 is of constant cross-sectional area throughout its length but that the orientation of the cross-section is different at different points along the length due to the formation of the helical ribs 2. However, as will be evident from Fig. 4, the oriented fibrils forming the rod remain essentially parallel along the length of the rod, notwithstanding the formation of the helical ribs 2. Thus, the formation of the helical ribs 2 in the surface of the rod 1 provides generally helically extending abutment surfaces 3 by means of which the resistance of the rod to ithdrawal from a concrete matrix or from an adhesive or grouting material ill be substantially increased without any significant reduction in the tensile strength of the rod provided by the parallel oriented fibrils contained therein. Referring to Fig. 3 of the dra ings, the rod 1 is made by initially drawing a cylindrical billet la of isotropic polyethylene through a die 10 having a central opening 11 of gradually reducing diameter to produce a rod lb of already entered fibrilar form. Billet la is heated to a temperature of about 100°C for the drawing process, and a drawing speed of about 5 to 10 cm/min may be used. The Youngs Modulus of the oriented rod lb is about 25 GPa. The oriented rod lb is then (or subsequently) passed through a further die 21 surrounded by an outer sleeve 24, and having a conical lead-in bore 26, a cylindrical bore portion 27 and a series of shaped helical grooves 28. The die 21 is free to rotate as the rod lb is drawn therethrough, and to this end, the die is mounted on a bearing 29. If desired, the die may be rotatably driven. The drawing of the rod lb through the die 21 is
achieved by applying the required longitudinal force in the direction of the arrow 23 to a gripping clamp 22 attached to the free end of the resulting formed rod lc. Prior to entering the die 21, the rod lb is heated to a temperature of about 120° to 125°C to allow the formation of the shaped helically ribs 3 on the rod lb. This drawing temperature should be as high as possible, but must be less than the melting temperature of the rod material, which is about 138° to 140°C. If a temperature higher than about 130°C is used, the Youngs Modulus of the resulting rod lc will deteriorate significantly. The ribs 2 may be of any desired profile, although the gently rounded convex form shown in Fig. 2 of the drawings is presently preferred. The ribs 2 may be oriented at any suitable helix angle, and angles of 60° and 70° have been found to be satisfactory. However, other angles may produce acceptable results. Referring now to Figs. 5 to 10 of the drawings, two modifications of the above described embodiment, and a further embodiment of the invention are shown. In the first modification shown in Figs. 5 and 6 of the drawings, the formed rod 1 is formed with three equal ly spaced longitudinally extending grooves 6. The grooves 6 may be formed by drawing the formed rod while still heated through a further die (not shown) having three longitudinally extending abutments, or by machining the grooves 6 in the surface of the rod. This modification offers the additional advantage of providing a rod which will resist twisting within the matrix, adhesive or grouting under applied load. It will be appreciated that the concrete, adhesive or grouting will enter the groove 6 to thereby further key the rod into the surrounding material in a manner which resists twisting of the rod. A somewhat similar effect may be achieved by forming diametrically opposed flattened areas 7 on the formed rod 1 in the manner shown in Figs. 7 and 8 of the drawings. This flattening of the formed rod 1 may be achieved by the use of heated rollers through which the required compressive force
is applied to the rod 1. In an experimental flattening operation performed in a hot press, a temperature of 10G°C was used at a flattening force of 1 tonne/10 cm of length. It will be appreciated that the formation of the flattened areas 7 on the formed rod will cause the rod to resist twisting within the surrounding matrix. In a still further embodiment of the invention, an oriented rod is drawn through a generally hexagonal die in hich each surface of the hexagon extends helically ith respect to the longitudinal axis of the die. The resulting rod has six flat portions 9 which extend helically around the rod in the manner shown in Fig. 9 of the drawings. As an alternative to the embodiment of Figs. 5 and 6, 7 and 8 and 9 and 10, the embodiment of Figs. 1 and 2 may have its surface treated chemically to improve the bonding between the surface and the surrounding matrix.
Next Patent: MOULDING METHOD