WO2012131579A1

WO2012131579A1 - Steel bar

Info

Publication number: WO2012131579A1
Application number: PCT/IB2012/051455
Authority: WO
Inventors: Justin Graeme CORBETT
Original assignee: Rand York Castings (Proprietary) Limited
Priority date: 2011-03-30
Filing date: 2012-03-27
Publication date: 2012-10-04

Abstract

This invention relates to a hot-rolled steel bar 10, suitable for use as a tensile bar in civil and engineering construction. As can be seen in Figure 1, the steel bar 10 comprises alternating plain lengths 12 and deformed lengths 14. Two of the plain lengths 12 define opposite end lengths of the steel bar 10. Each deformed length 14 has a length L1 and each plain length 12 has a length L2 and a round cross-section. L1 and L2 are variable in different embodiments of the steel bar 10 provided that 25mm ≤ L2 ≤ 350mm and 400mm ≤ L1 + L2 ≤ 2000mm. Each deformed length 14 includes two opposite series of essentially conventional diagonal ribs 16 and two opposite conventional longitudinal ribs 18.

Description

STEEL BAR

THIS INVENTION relates to a hot-rolled steel bar.

The invention relates, more particularly, to a hot-rolled steel bar suitable for use as a tensile bar in civil and engineering construction and to a pair of steel mill rolls for use in the manufacture of such a steel bar. Possible applications of such a steel bar include a concrete reinforcing bar, a rock bolt bar, a geotechnical anchor bar, and other similar applications.

Many engineering applications require one steel bar to be coupled to another, end to end, by means of a coupler or to be coupled to an anchor or nut. It is known to cut or roll a screw thread on an end of such a steel bar for coupling it to another via a coupler, or for coupling it to anchors and nuts. A male threaded end of such a steel bar will engage with an internal female screw threaded part of such a coupler, anchor or nut. Such screw threading causes a decrease in the effective diameter of the steel bar, with a consequent reduction in tensile strength. To facilitate threading of a deformed bar end, the longitudinal and cross ribs must be peeled off. This adds to the manufacturing cost.

In order to prevent the effective diameter of the peeled and screw threaded length from being less than that of the remainder of the steel bar, or to minimize the amount by which it is less, it is known to up-forge such an end prior to screw threading. Such up- forging adds cost.

The current invention aims to ameliorate at least some of the above problems associated with coupling or anchoring of steel bars and to maximise the available tensile strength for a given bar size.

Reference is herein made to an effective diameter of a length of steel bar under consideration. Effective diameter means the diameter of a circle having the same cross- sectional area as the minimum cross-sectional area of the length of steel bar at any position along its length. According to a first aspect of the invention there is provided a steel bar including alternating plain lengths, of round cross-section, and deformed lengths, each plain length having a length in the range 25mm to 350mm and the plain lengths being at centre-to-centre spacings in the range 400mm to 2000mm.

The steel bar may be cut to any suitable length for use in any application. Typically, it may be cut to leave at at least one of its ends an end length which is at least a part of a plain length, providing for the end length to be screw threaded for coupling to a matching coupling or anchor. For coupling purposes, a plain length may be screw threaded and there is no need for peeling before screw threading as is the case with a conventional deformed steel bar which is deformed along its entire length.

The deformed lengths may, conventionally, define any of longitudinal ribs, transverse ribs, and diagonal ribs.

The plain lengths may, particularly, all be of the same length. Their centre-to-centre spacings may, particularly, be constant along the length of the steel bar. The plain lengths may all have the same diameter and the deformed lengths may all have the same effective diameter.

Each plain length may have a diameter larger than the effective diameter of each deformed length. The minimum effective diameter of the screw threaded length will then exceed that of an end of an equivalent conventional deformed steel bar after peeling and screw threading.

An effective diameter of a screw threaded length of the steel bar may be not less than an effective diameter of a deformed length of the steel bar.

The weight per unit length of each plain length may be the same as that of each deformed length. This means that, in a rolling pass in a hot-rolling process for making such a steel bar, constant speed rotation of a pair of mill rolls will not cause localized lateral expression of excess steel . According to a second aspect of the invention there is provided a pair of mill rolls shaped and configured for rolling a steel bar, in accordance with the first aspect of the invention.

Each roll may be configured to define, angularly spaced about its rotational axis, any practical number of recesses for forming plain lengths of the steel bar.

The pair of rolls will naturally be used in a final rolling pass of the steel bar.

Further features of the invention will become apparent from the description below of an example embodiment of a steel bar, in accordance with the first aspect of the invention, of which the manufacture involves a final rolling pass through a pair of rolls, in accordance with the second aspect of the invention, with reference to the accompanying diagrammatic figures. In the figures:

Figure 1 shows a broken side view of an embodiment of a steel bar, in accordance with the first aspect of the invention;

Figure 2 shows a broken, enlarged partial side view of the steel bar of Figure 1 ;

Figure 3 shows an approximate cross-section of the steel bar of Figures 1 and 2, along line Ill-Ill in Figure 2; and

Figure 4 shows a partial side view of the steel bar of Figure 1 , after screw threading of an end portion thereof, aligned with a conventional deformed steel bar (partially shown), after peeling and screw threading of an end portion thereof (threaded end portions of the respective bars being shown in long section).

In the drawings, an example embodiment of a steel bar, in accordance with the first aspect of the invention, is designated generally by the reference numeral 10.

With reference initially to Figure 1 , the steel bar 10 comprises alternating plain lengths 12, of which there are five, and deformed lengths 14, of which there are four. Two of the plain lengths 12 define opposite end lengths of the steel bar 10.

With reference particularly to Figure 2, each deformed length 14 has a length L1 . Each plain length 12 has a length L2 and has a round cross-section. L1 and L2 are variable in different embodiments of the steel bar of the first aspect of the invention, provided that 25mm <= L2 <= 350mm and 400mm <= L1 +L2 <= 2000mm.

In typical embodiments of the steel bar of the invention, L1 > L2.

L1 + L2 represents the centre-to-centre spacing or pitch of the plain lengths 12. This spacing is constant along the length of the steel bar 10.

With reference particularly to Figures 2 and 3, each deformed length 14 includes two opposite series of essentially conventional diagonal ribs 16 and two opposite conventional longitudinal ribs 18.

Each deformed length 14 has a core diameter or effective diameter D1 (neglecting the negligible effect of the longitudinal ribs 18 on the cross-sectional area of the deformed length 14. Each plain length 12 has a diameter D2. D2 > D1 , i.e. D2 - D1 > 0mm.

In Figure 4, a screw thread 20 has been cold rolled into a former plain length 12 (see Figure 1 ) at an end of the steel bar 10 to define a screw threaded length 22. The screw thread 20 has a minor diameter D3, which is the minimum effective diameter of the screw threaded length 22. Alternatively, a screw thread may be cut into the plain length 12. In the steel bar 10, D3 < D1 . However, in other embodiments of the steel bar of the invention it may be that D3 > D1 .

The steel bar 10 is shown aligned with and opposing a conventional deformed steel bar 21 having a core diameter D1 , identical to that of the steel bar 10. An end length 22 of the steel bar 21 has been peeled to a diameter D4 < D1 . A screw thread 24 has been cold rolled into the peeled length 22 to define a screw threaded length 26. The screw thread 24 has a minor diameter D5, which is the minimum effective diameter of the screw threaded length 26.

The screw thread 24 was cold rolled into the peeled length 22, having a diameter D4, in the same fashion as the screw thread 20 was rolled into the plain length 12 (see Figure 2), having a diameter D2. The screw threads 24 and 20 therefore have identical profiles, including identical penetration P (not shown in the figures) into the respective surfaces into which they were rolled. It follows that D3 = D2 - 2P and D5 = D4 - 2P. Since D4 < D1 and D2 > D1 , it follows that D3 > D5.

The screw threaded length 22 of the steel bar 10 therefore has a greater effective diameter and tensile strength than the threaded length 26 of the steel bar 21 . This is a consequence of the diameter D2 of plain lengths 12 which had been formed into the steel bar 10 being greater than the diameter D1 .

The above example illustrates how the steel bar of the invention, due to the provision of plain and deformed lengths therein during manufacture, provides two advantages over a steel bar which is deformed along its entire length. First, peeling of an end length of the steel bar prior to screw threading is avoided in the steel bar of the invention. Second, a threaded length with a greater tensile strength may be formed in the steel bar of the invention.

The steel bar 10 or a part thereof may be used for different purposes, for example as a concrete reinforcement bar, a rock bolt bar, or a geotechnical anchor bar.

With reference to Figure 1 , the steel bar 10 may be cut to any of various lengths, as required, for example at any of positions 30.1 , 30.2, and 30.3. A rock bolt bar having a length of L1 + L2 may be obtained by cutting through the steel bar 10 at positions 30.1 and 30.2. A rock bolt bar having a length of 2(L1 + L2) may be obtained by cutting at positions 30.1 and 30.3. Similarly, a concrete reinforcement bar of any of various lengths, as required, may be cut from the steel bar 10.

In each case, the steel bar 10 may be cut so that at least one of the ends of the resulting bar is a plain length 12 or a part thereof, providing for a screw thread to be cut into it for cooperation with an internally screw threaded part of a coupler or anchor. The steel bar 10 may be manufactured by means of an essentially conventional hot-roll process, in which at least in a final rolling stage, a pair of rolls shaped to form the steel bar 10 is used. Those skilled in the art will be able to design such rolls. The rolls will define recesses for forming the plain lengths. It may be that a single such recess is provided along the circumference of each roll. Alternatively, more than one such recesses may be provided, angularly equally spaced about the rotational axis of each roll.

It is conceivable that, in alternative embodiments of the steel bar of the invention, the centre-to-centre spacing of the plain lengths may be variable along the length of the bar. The rolls would then be shaped to form such a bar, each such roll clearly defining at least two recesses as referred to above.

Any roll shaped to form any steel bar, in accordance with the first aspect of the invention, is a roll, in accordance with the second aspect of the invention.

Claims

1 . A steel bar including alternating plain lengths, of round cross-section, and deformed lengths, each plain length having a length in the range 25mm to 350mm and the plain lengths being at centre-to-centre spacings in the range 400mm to 2000mm.

2. A steel bar as claimed in claim 1 , wherein the bar is cut to leave at at least one of its ends an end length which is at least a part of a plain length, providing for the end length to be screw threaded for coupling to a matching coupling or anchor.

3. A steel bar as claimed in claim 1 or claim 2, which includes a plain length which is at least partially screw threaded.

4. A steel bar as claimed in claim 3, wherein an effective diameter of a screw threaded length of the bar is not less than an effective diameter of a deformed length of the bar.

5. A steel bar as claimed in any of the preceding claims, wherein the deformed lengths define any of longitudinal ribs, transverse ribs, and diagonal ribs.

6. A steel bar as claimed in any of the preceding claims, wherein the plain lengths are all of the same length.

7. A steel bar as claimed in any of the preceding claims, wherein the centre-to-centre spacings of the plain lengths are constant along the length of the steel bar.

8. A steel bar as claimed in any of the preceding claims, wherein the plain lengths all have the same diameter and the deformed lengths all have the same effective diameter.

9. A steel bar as claimed in any of the preceding claims, wherein each plain length has a diameter larger than an effective diameter of each deformed length.

10. A steel bar as claimed in any of the preceding claims, wherein the weight per unit length of each plain length is the same as that of each deformed length.