GB2054695A - Concrete-reinforcing rods - Google Patents

Abstract

The invention relates to concrete- reinforcing rods of the kind having helically extending ribs which form partial pieces of a screw-thread upon which a body having a corresponding counter-screw-thread can be screwed, wherein the partial pieces (5) of the screw-thread of successive screw- thread courses are arranged in a continually-staggered manner with relation to one another, and each gap (6) between the screw-thread partial pieces is at least partially overlapped in the axial direction by a screw- thread partial piece of the following screw-thread course. A rod blank is first formed with ribs which are arranged in spaced pairs on either side of the rod surface, with gaps between the ribs of each pair, said ribs running obliquely to the longitudinal axis of the rod and being oriented in one direction and preferably enclosing an angle of 40 to 60 degrees to the longitudinal axis of the rod, the rod blank is then subjected to twisting or torsion while being held straight, in order to form a self-arresting screw-thread consisting of screw-thread partial pieces with gaps therebetween. <IMAGE>

Description

SPECIFICATION Concrete-reinforcing rod, particularly an anchor rod, and method of manufacturing it The invention relates to concrete-reinforcing rods, such as an anchor rod, of the kind having helically-extending ribs which form partial pieces of a screw-thread, upon which a body, such as an anchoring body, having a corresponding counterscrew-thread can be screwed. The invention also relates to a method of manufacturing such rods.

In one known example of such a reinforcing rod, according to United States Patent No. 1,151,947, the ribs are at a steep angle to the longitudinal axis of the rod, and are disposed in groups; the ribs of successive groups being directed toward one another and partially overlapping. Apart from the too-great a pitch of the ribs, a screw-thread effect cannot be attained from such a rod, even approximately, due to the opposing orientation of the groups of ribs.

In another known example of reinforcing rod, according to German Patent No. 1,077,854, profilings are provided in the form of ribs, for improving adhesion in the concrete, and are so disposed that they lie on a helix and form part of a screw-thread. In this way, no chip-removing work such as incising, or non-cutting forming work such as cold rolling a screw-thread onto the ends of the rods is necessary for installing screwed connecting and/or anchoring bodies. Reinforcing rods according to this example have been manufactured in such a manner that the ribs which form the partial screw-thread lay only on one side of the rod, the opposite side of the rod being left smooth. The unilateral introduction of force thus brought about can have an unfavourable influence on the fatigue strength of the rod.A further drawback of such a reinforcing rod lies in the fact that, because of the opposite smooth side of the rod, it cannot be inserted as rib steel in normal steel-concrete construction.

A reinforcing rod according to German Patent No. 1,199,470 avoids some of these drawbacks.

On the side of the rod opposite the ribs, it has cavities (or recesses, or indentations) likewise formed in the path of a warm rolling process, between which ribs remain standing, the ribs being so disposed that their external boundary lies on the continuation of the circular cylindrical surface of the other side of the rod, which forms the core of the rod. In their position with relation to those ribs on the opposite side of the rod, which form the partial screw-thread, these. ribs between the recesses are so disposed that when a connecting or anchoring body is screwed onto the rod, it lies with its internal surface on the external boundary of these ribs. However, this does not result in a flawless connection. This reinforcing rod, is very suitable for use as a simple concretereinforcing rod, because it has profilings on both sides.However, it is disadvantageous when used with anchoring or connecting bodies, because there is a unilateral introduction of force. Because of its asymmetrical form in cross-section, it is also difficult to align (or straighten) it in so-called aligning (or straightening) machines. Also such a reinforcing rod is difficult to manufacture, because the surface on the opposite sides of the rod, which surfaces are formed by rolling, are at different distances from the axis of the rod and necessitate different surface velocities of the rollers during manufacture. A further general problem encountered in the manufacture of concretereinforcing rods with hot-rolled ribs forming a partial screw-thread is that there is a tendency for variation in the texture of the steel to occur during rolling of the ribs, resulting in variations in tensile strength.These variations in tensile strength appear primarily in the vicinity of the points where the individual rib projects outwardly from the surface of the rod. Notch tensions occur at these points, which lead to a diminution of the width of oscillation of the rod, These notching tensions act most strongly when the ribs run perpendicularly to the axis of the rod, when their adhesion-improving effect is naturally at its greatest. In this case, the material of the ribs must be considered as a dead weight, because a cross-section perpendicular to the axis of the rod does not necessarily intersect a rib. No notching tensions occur when the ribs run in the longitudinal direction of the rod, and the material of the ribs can be added fully to the crosssection of the rod; however an adhesionimproving effect is then not possible because there is no direct support on the concrete.For this reason, the ribs are normally disposed inclined to the longitudinal axis of the rod in the case of concrete-reinforcing steels. In general, this inclination amounts to between 40 and 60 degrees. Then the cross-section projection of the ribs can be relied upon for the adhesion-improving effect, while the notching tensions are kept within bounds. ~ If the ribs lie on a helix and are designed to form a screw-thread, then the inclination of the ribs to the longitudinal axis of the rod may not be greater than that an anchoring body reliably obstructs with its internal screw-thread adapted to the partial screw-thread. However, the pitch of the screw-thread ribs which is possible under this condition is then so small that notching tensions cannot be avoided, and the material of the ribs cannot be added to the carrying cross-section surface.The result is a smaller width of oscillation of the rod and a poorer utilization of the material.

Experiments to diminish the unfavourable effects of the notching tensions on the width of oscillation by rounding-off the profile of the ribs have not led to a desirable result. Moreover, specially-shaped tools are necessary, and the service life of the rollers must be kept very short in order to maintain the required profile with certainty, which means an increased need for tools.

According to German Patent No. 1,659,067, the helically-disposed ribs can be arranged in the form of a double-thread on two opposite sides of the circumference of the rod. The double-thread screw-thread makes possible the manufacture of a steeper pitch of screw-thread and, therewith, a rod which can be manufactured more readily by rolling. A disadvantage is the small and insufficient extent of height of the full screw-thread in relation to the circumference of the rod. As may be seen from a comparison of Figures 2 and 3 of the German Patent Specification, the height of the rib depends decisively on the angle to the longitudinal axis. The flatter the angle of the rolled rib, the flatter, lower and less distinctly can the latter be rolled.Added to this is the further drawback that the transmission of force to the counter-screwthread in the nut (or female screw), conditioned by the short screw-thread segments which lie one behind another in the longitudinal direction, and are only slightly raised (or in relief), takes place only to an insufficient extent. As a result of the unavoidable roller tolerances, which also must be taken into consideration in the counter-screwthread, the small, utilizable surface of the screwthread segments is diminished still further.

A reinforcing rod as described in United States Patent Specification No. 4,137,686 also exhibits the same disadvantage of a relatively short height of screw-thread with reference to the circumference of the rod and the segments of screw-thread lying spaced one behind another in the longitudinal direction of the rod.

An object of the invention is to provide a rod which avoids these drawbacks.

According to one aspect of the invention, in a concrete-reinforcing rod of the kind referred to hereinbefore, the partial pieces of the screwthread of successive courses, which preferably extend over more than half of the circumference of the rod, are arranged in a continually-staggered manner with relation to one another, and each gap between the screw-thread partial pieces is at least partially overlapped in the axial direction by a screw-thread partial piece of the following screwthread course, so that the screw-thread partial pieces, which form a self-arresting screw-thread, or the gaps, run helically around the rod.

According to another aspect of the invention, the manufacture of such a rod is characterised in that a rod blank is formed with ribs which are arranged in spaced pairs on either side of the rod surface, with gaps between the ribs of each pair, said ribs running obliquely to the longitudinal axis of the rod and being oriented in one direction and preferably enclosing an angle of 40 to 60 degrees to the longitudinal axis of the rod, the rod blank then being subjected to twisting or torsion and being held straight in order to form a self-arresting (or self-blocking, or self-obstructing) screw-thread consisting of the screw-thread partial pieces with gaps therebetween.

Thus, in the first stage of manufacture, a rod blank with ribs is produced, preferably by hotrolling. However, the pairs of ribs situated on the two opposite sides of the rod surface are not arranged at an opposing angle, in known manner; rather, they are in the form of separate, spaced, angled coil turns around the rod. Because of the oblique angle to the longitudinal axis, the ribs, while avoiding any notching tensions in the rod, can be rolled to be not only very long, but also relatively high and distinct. In the second and essential stage of manufacture, the rib steel is twisted ortorsioned in the direction in which the ribs are inclined.In that way, the angle of the ribs becomes ever flatter with increasing twisting, so that a functional, self-arresting screw-thread now originates from the original coil-turn arrangement of the ribs; it is advantageous that the ribs, already originally long, become still longer due to the stretching of the steel as a result of the torsion applied to it, so that the ribs reach over more than half of the circumference of the rod. This nowformed screw-thread winds helically around the rod. In that way, every individual screw-thread partial piece is displaced (or staggered) in a clockwise direction with relation to the next one, so that every individual screw-thread-rib gap is overlapped in the axial direction by the next screw-thread partial piece. The pitch of the screwthread can be continuously (or stagelessly) varied by control of the degree of torsion applied to the rods.Right-hand or left-hand screw-threads are possible, according to the position of the ribs and the corresponding direction of torsion applied.

In order that the invention will be readily understood, one embodiment of anchoring rod in accordance with the invention, will now be described, with reference to the accompanying drawing in which: Figure 1 is a portion or a length of the anchoring rod before torsion is applied to it, i.e. a rod blank.

Figure 2 is a view of the same portion after torsion has been applied, and Figure 3 shows in cross-section, a series of possible forms of ribs.

Referring to Figure 1 , the rod 1 has ribs 2, which are arranged obliquely in pairs on opposite sides of the surface of the rod. The ribs 2 enclose an angle of about 45 degrees with the longitudinal axis of the rod, and are manufactured by a hotrolling process. As a result of being arranged obliquely, the ribs 2 are relatively long, but because of gaps 3 left between each pair of ribs 2 at their upper and lower ends, each rib embraces less than half of the circumference of the rod. The gaps 3 between the pairs of ribs lie diametrally on the circumference of the rod along a generatrix of the cylinder which forms the rod 1. The rod 1 constructed as shown in Figure 1 may have one of a number of preferred forms of ribs and these ribs may be made of any required height without any manufacturing problems.

Referring now to Figure 2, the rod blank 1, constructed as in Figure 1, is then twisted (or torsioned) about its longitudinal axis so that displacement of the surface ribs 2 occurs, and, simultaneously with said twisting, the rod is held straight (or aligned). This twisting movement tends to work harden the steel of the rod, which is thereby strengthened. Said twisting movement causes a rod 4 in accordance with Figure 2 to be developed, in which all the pairs of ribs 2 generally form a screw-thread comprising partial pieces 5 lying closely adjacent one another. The gaps 6 no longer lie along a generatrix, as in the case of Figure 1; instead they are displaced so that they lie along a helix on the rod.Because of stretching due to the twisting movement, the screw-thread partial pieces 5 resulting from the ribs 2 (Figure 1) now embrace more than half of the circumference of the rod. Also, adjacent screw-thread partial pieces 5 of the next screw-thread course are displaced (or staggered) in such a manner that the screw-thread partial pieces overlap in the axial direction. Therefore, a screw-on nut, with its counter-screw-thread is in engagement to a large extent with the screw thread courses of the rod 4.

It will be appreciated that only because of the twisting operation does a screw thread which is self-arresting, and which is of sufficient stability, originate from the originally formed diagonal ribs of the rod blank, which latter serve no sort of screw-thread function.

Figure 3 shows in cross-section various forms of screw-thread courses which are especially suited for the manufacture of a reinforcing rod as described above.

Claims (6)

1. A concrete-reinforcing rod of the kind having helically extending ribs which form partial pieces of a screw-thread upon which a body having corresponding counter-screw-thread can be screwed, characterized in that the partial pieces of the screw-thread of successive screw-thread courses are arranged in a continually-staggered manner with relation to one another, and each gap between the screw-thread partial pieces is at least partially overlapped in the axial direction by a screw-thread partial piece of the following screwthread course, the arrangement being such that the screw-thread partial pieces, which form a selfarresting screw-thread, or the gaps, run helically around the rod.

2. A method of manufacturing a concretereinforcing rod, according to Claim 1, characterized in that a rod blank is formed with ribs which are arranged in spaced pairs on either side of the rod surface, with gaps between the ribs of each pair, said ribs running obliquely to the longitudinal axis of the rod and being oriented in one direction and preferably enclosing an angle of 40 to 60 degrees to the longitudinal axis of the rod, the rod blank then being subjected to twisting or torsion and being held straight, in order to form a self-arresting screw-thread consisting of screwthread partial pieces with gaps therebetween.

3. A method according to Claim 2, wherein the lengths of the ribs on the rod blank are less than half the circumference of the rod, and are chosen such that, after torsioning the rod blank, said ribs are stretched to extend over more than half said circumference.

4. A method according to Claim 2 or 3, characterized in that the rod is torsioned to an extent necessary to achieve a desired angle of pitch for the screw thread.

5. A concrete-reinforcing rod constructed, arranged and adapted for use substantially as hereinbefore described with reference to the accompanying drawings.

6. A method of manufacturing a concretereinforcing rod as claimed in Claim 5, substantially as herein before described.