GB2238499A

GB2238499A - Forming threaded bars

Info

Publication number: GB2238499A
Application number: GB8925372A
Authority: GB
Inventors: Raymond John Barratt Bentley; Dennis George Scott
Original assignee: D G SCOTT Ltd; HY TEN REINFORCEMENT Co L
Current assignee: D G SCOTT Ltd; HY TEN REINFORCEMENT Co L
Priority date: 1989-11-09
Filing date: 1989-11-09
Publication date: 1991-06-05
Also published as: GB8925372D0

Abstract

A screw thread is formed on the end of a reinforcing bar 30 by means of pressing. A press 10 for carrying out the pressing operation comprises a lower die portion 14 fixedly mounted to a frame 18, 20, 22 and an upper die portion 12 slidably disposed on the frame and displaceable by means of a hydraulic ram 24. The die portions are each provided with one half of a screw thread formation, whereby if the end of a bar 30 is placed into the press and the upper die portion 12 displaced downwardly, a screw thread is formed on the end of the bar. Two screw-threaded bars may be screwed into a threaded sleeve (32, Fig. 4) to join them together. <IMAGE>

Description

DESCRIPTION METHOD AND APPARATUS FOR FORMING THREADED BARS The present invention relates to a method and apparatus of threading bars, and to the bars formed thereby and the joints comprising such bars.

It is often necessary to secure one end of a reinforcing bar to another element, for example to the end of a second reinforcing bar. This is particularly so in the case of reinforced concrete, where the reinforcing bars of adjacent sections of reinforced concrete sometimes have to be secured together. The securing is achieved by forming screw threads on the ends of the two bars to be joined, and to screw them into an internally screw-threaded connecting sleeve. At present, there are three ways of providing the screw thread on the ends of the reinforcing bars, namely screw cutting, hot forming and roll forming, but each of these has its own disadvantages.

With reference to screw cutting, it is firstly necessary to machine the bar down to a circular crosssection and then to screw cut a thread onto the round end of the bar thus formed. The effective diameter of the end of the bar is clearly reduced, and this thus reduces the strength of any joint subsequently formed.

Moreover, it is difficult, if not impossible, to use the apparatus for forming such screw threads when on site, and in any case the formation of the screw threads must be carried out by a skilled or semiskilled operator.

With reference to hot forming, this method produces irregularities in the thread form due to the heat which is applied, and the effect of these can only be reduced by means of additional lock nuts and by the bending of the thread by torque loading. Again, this method and the apparatus required for it prevent this method from being carried out on site.

Roll forming can only be carried out using complex and physically large apparatus, and this makes the formation of screw threads on site by this method unattractive.

It will thus be appreciated that none of the methods presently in use can be easily carried out on site, which means that unless the screw threads are formed during the manufacture of the reinforcing bars, the subsequent provision of screw threads on the ends of the bars is both inconvenient and costly. Also, the known methods require a skilled or semiskilled operator.

It is an object of the present invention to provide a method and apparatus for forming a screw thread on a bar which allows the formation of screw threads on site, and which allows such formation by an unskilled operator.

It is a further object of the present invention to provide a screw-threaded bar and a joint comprising such a bar wherein the screw thread can be formed on site by an unskilled operator.

In accordance with a first aspect of the present invention, a method of forming a screw thread on a reinforcing bar comprises pressing a screw thread onto the bar.

Pressing the screw threads can be carried out by an unskilled operator, and since the pressing apparatus is relatively simple, the screw thread can be easily formed on site.

If the bar on which the screw thread is to be formed has raised portions, then the screw thread may be formed only on the raised portions. Alternatively, the screw thread may be formed in areas other than the raised portions.

In one embodiment, the pressing operation is a coining operation.

In accordance with a second aspect of the present invention, an apparatus for forming a screw thread on a reinforcing bar comprises a first die portion and a second die portion movable relative to the first die portion, each portion being provided with a surface for forming a portion of a screw thread on a bar inserted into the die, and means for relatively displacing the two die portions towards and away from one another.

Preferably, the displacing means comprises a fluidactuated ram, for example a hydraulically-actuated ram.

The method and apparatus described above can be used on site by an unskilled operator. Moreover, sheared ends of a reinforcing bar can be used in the aforementioned method and apparatus, thus dispensing with the requirement for sawn bar ends, as is the case with the prior art methods and apparatus.

The present invention also includes a reinforcing bar provided with a screw thread by virtue of the aforementioned method and/or apparatus.

The present invention further includes a joint comprising two screw-threaded bars and an internally-screw threaded sleeve, the ends of each of the bars being received in a screw-threaded portion of the sleeve, wherein the screw-threaded portion of one or both of the bars is formed in accordance with the present invention.

By way of example only, specific embodiments of the present invention will now be described, with reference to the accompanying drawings, in which: Fig. 1 is a perspective view of an embodiment of screw thread forming apparatus in accordance with the present invention; Fig. 2 is a view of a first embodiment of screwthreaded bar in accordance with the present invention; and Fig. 3 is a view of a second embodiment of screwthreaded bar in accordance with the present invention; and Fig. 4 is a cross-sectional side elevation of an embodiment of joint in accordance with the present invention.

Referring firstly to Fig. 1, a screw thread forming press 10 comprises a die having an upper die portion 12 and a lower die portion 14, the interior of each of which is provided with half of a screw-threaded formation. The lower die portion 14 is fixedly mounted at the base of a rectangular framework in the form of a square, flat base plate 18, an identical upper plate 20 and four vertical cylindrical support posts 22 interconnecting the upper and lower frame members.

The upper die portion 12 is mounted on an intermediate plate 21 which is slidably disposed on each of the vertical posts 22 and is displaceable towards and away from the lower die portion 14 in the longitudinal direction of the posts 22 by means of a double-acting hydraulic ram 24, one end of which is connected to the upper plate 20 and the other end of which is connected to the intermediate plate 21. The pressurised hydraulic fluid for the ram 24 is provided by means of supply hoses 28.

In use, the pressurised hydraulic fluid is supplied to the ram 24 to withdraw the upper die portion 12 from the lower die portion 14, thereby allowing the end of a reinforcing bar 30 to be located on the lower die portion 14. The pressurised hydraulic fluid is then supplied to the ram 24 to displace the upper die portion 12 downwardly towards the lower die portion 14, thereby impressing the screw-threaded formations of the internal surfaces of the upper and lower die portions 12, 14 onto the end of the reinforcing bar 30 in a coining operation.

It will be noted from Figs. 2 and 3 that a typical reinforcing bar comprises a cylindrical or elliptical bar having a plurality of recesses/protrusions formed in a "herringbone" pattern. This assists in securing the bar into the concrete which it is to reinforce.

In one embodiment, illustrated in Fig. 2, it will be noted that the thread is impressed onto all portions of the bar, but the screw thread is obviously deeper in the raised portions than it is in the recessed portions. An alternative embodiment is illustrated in Fig. 3, in which the screw-threaded portions are impressed only onto the raised portion of the bar.

The cross-section of a joint comprising two screwthreaded bars of Fig. 3 together with an internallythreaded connecting sleeve 32 is illustrated in Fig. 4.

The ends of the respective reinforcing bars are located on the respective ends of the threaded sleeve, and the sleeve is rotated to secure the ends of the two bars together.

The present invention is easy and quick to use by an unskilled operator, and the apparatus itself is compact enough for it to be used on site. Moreover, the only power requirement is a source of hydraulic fluid.

Furthermore, shearded reinforcing bars can be used directly with the present invention, thus dispensing with the necessity to provide sawn ends, in contrast to the prior art devices.

The invention is not restricted to the details of the foregoing embodiments.

Claims

1. A method of forming a screw thread on a reinforcing bar, comprising pressing a screw thread onto the bar.

2. A method as claimed in claim 1, comprising coining the screw thread onto the bar.

3. A method as claimed in claim 1 or claim 2, wherein the screw thread is formed on an end portion of the bar.

4. A method as claimed in any of claims 1 to 3, wherein the screw thread is substantially continous in the region of application of the screw thread.

5. A method as claimed in any of claims 1 to 3, wherein the screw thread is discontinuous in the region of application of the screw thread.

6. A method of forming a screw thread on a reinforcing bar, substantially as herein described, with reference to and as illustrated in, the accompanying drawings.

7. An apparatus for forming a screw thread on a reinforcing bar, comprising a first die portion, a second die portion movable relative to the first die portion, each die portion being provided with a surface for forming a portion of a screw thread on a bar inserted into the die, and means for relatively displacing the two die portions towards and away from one another.

8. An apparatus as claimed in claim 7, wherein the means for relatively displacing the die portions comprises a hydraulically-actuated ram.

9. An apparatus as claimed in claim 8, wherein the hydraulic ram comprises a double-acting ram.

10. An apparatus as claimed in any of claims 7 to 9, comprising a frame upon which the die portions and the means for relatively displacing the die portions are mounted.

11. An apparatus as claimed in claim 10, wherein one die portion is displaceably mounted on the frame.

12. An apparatus as claimed in claim 11, wherein the displaceable die portion is slidably disposed on the frame.

13. An apparatus as claimed in any of claims 10 to 12, wherein the first die portion and the displacement means for relatively displacing the two die portions are fixedly mounted to the frame and the second die portion is movably disposed on the frame between the first die portion and the displacement means.

14. An apparatus for forming a screw thread on a reinforcing bar, substantially as herein described, with reference to, and as illustrated in, the accompanying drawings.

15. A reinforcing bar comprising a screw threaded portion formed by the method of any of claims 1 to 6.

16. A joint comprising two screw threaded bars as claimed in claim 1 and an internally, complementarily screw-threaded sleeve, the screwthreaded portions of the bars being adapted to be received in the sleeve.