Field of the invention

This invention relates generally to the bending of metal bar or rod, and has particular though by no means exclusive application to the bending of steel bar or rod being fed from an offcoil straightening machine.

Throughout this specification, where the terms "bar" or "steel bar" are employed, they are respectively intended to embrace "rod" and "steel rod".

Background of the invention

Steel bar is conventionally formed into segments of varied profile in an offcoil machine, which straightens the bar as it is delivered from a coil and delivers it to a bending head.

The bar is formed into a predetermined bent profile by a pusher pin which engages the bar and guides it about the bending head as the straightened bar emerges from a channel feed into the centre of the head: the bar can be bent either way by adjusting the position of the pin, and more complex shapes are formed by presetting a sequence of pusher pin movements.

Typically, steel reinforcing bar has deformations and longitudinally spiralling ribs that together cause the bar to twist outward from the bed of the machine during bending. To prevent this outward twisting, it is common practice worldwide for the operator of the offcoil machine to use his or her hand to lightly press against the side surface of the bar in the bending region. The bar is in its plastic state during the bending at the bend location, that is the machine has done the harder work to move the bar up the steep elastic portion of the stress-strain curve and is in the relatively flat plastic portion of the curve. Hence, only a relatively small force is required to prevent the bar twisting out of its feed plane, and the practice of "palming", as it is generally known, therefore requires only a relatively light force application.! For this reason, the practice is not viewed as dangerous, although it clearly breaches optimum safety practice and certainly breaches the operating instructions of offcoil machine suppliers and owners. Notwithstanding

these concerns, no one to date has proposed an effective and practical solution that eliminates operators' preference for maintaining the palming practice.

It is accordingly an object of the invention to provide an improvement that minimises twisting of the bar as it is bent and eliminates the perceived need for palming.

Summary of the invention

The inventor has realised that a solution to the aforementioned problem lies with the pusher pin component of the bending machine, and in particular proposes the provision of a peripheral shoulder for bearing on a side of the bar to minimise twisting of the bar out of its feed plane.

More particularly, the invention provides a metal bar bending machine, including:

bar feed means; and

a rotatable formation positionable for engaging the bar fed from the bar feed means and forming it into a predetermined bent profile;

wherein said formation includes a peripheral shoulder for bearing on the bar to minimise twisting of the bar out of its feed plane.

Typically, the bar is in a plastic state as said shoulder bears on the bar to prevent said twisting of the bar out of its feed plane.

Said rotatable formation may typically be a cylindrical pin. The peripheral shoulder is preferably provided by an undersurface of a head of the pin. The peripheral shoulder is preferably chamfered and, where the formation is a pin, may be chamfered relative to an axis of the pin.

The rotatable formation is preferably positionable at a variety of selectable positions whereby the bar may be bent to either left or right and said curved profile is variable in

radius. For this purpose, the rotatable formation may be outstanding from a rotatable disc.

Brief description of the drawings

The invention will now be further described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of the bending head of an offcoil machine for bending steel reinforcing bar;

Figure 2 is a diagrammatic front elevation illustrating the manner in which the bar is formed into a bent profile as it is fed through the bending head; and

Figure 3 is a cross-sectional view of the pusher pin of the apparatus illustrated in Figures 1 and 2.

Detailed description of preferred embodiment

The partly illustrated offcoil machine 10, for use in bending rollformed steel reinforcing bar, includes a bending head 11 having bar feed means in the form of a channel 12 along which the bar is fed from a delivery port 14. Typically, the bar will have been treated by a straightening machine where bar from a coil is straightened and fed to port 14. Channel 12 terminates in a bending head 16 that defines a symmetrically arranged pair of semi-cylindrical surfaces 17 about which the bar is formed by a pusher pin 20. Pusher pin 20 projects from a rotatable disc 22 having a flat surface 23 that forms a flush component of a bed or table 18 of the machine.

Pusher pin 20 is positionable by rotation of disc 22 for engaging the bar 5 fed from channel 12 and forming it into a bent profile. This process is depicted in Figure 2 and it will be seen that the position of the pin 20 will determine to which hand, left or right, the bar is bent, that is, about which of surfaces 17 it is wound, and also the radius of the initial curved profile. Typically, the bar stops feeding during bending but feeding at bending may be simultaneous.

Typically, disc 22 is also translatable in and out from its position flush with bed 18, and the motion of disc 22 is automated and managed by a programmable controller for producing a variety of different reinforcing bar segments for varied end-uses.

The form of pusher pin 20 is best depicted in Figure 3. It comprises a cylindrical sleeve body 24 of lesser diameter that acts on bar 5 to bend it, and an enlarged head 26 for body 24 which is of larger diameter and defines a peripheral chamfered undersurface 30. Surface 30 defines a shoulder for bearing on the bar 5, as it is fed and bent. Sleeve body 24 is rotatably supported by a roller bearing 29 on a fixed spigot 28 . Spigot 28 is secured in a flat plate 35 in turn fixed by rivet 36 to disc 22.

It will be appreciated from Figures 2 and 3 in particular that, as bar 5 is fed from channel 12, engaged by pin 20 and formed into a bent profile, shoulder 30 bears on the bar to minimise, and indeed substantially prevent, twisting of the bar out of its axial feed plane in the bending region. Alternatively, it may be said that the shoulder 30 effectively pushes the bar flat onto the bed or table 18 while it is in the plastic state, hence preventing out-of-plane twisting.

The inventive improvement can be readily adapted to bars of different diameter by providing various sizes of removable sleeve body 24 for spigot 28, so as to define variable spacings between undersurface 30 and surface 23 of disc 22.

Once a segment is bent to its predetermined profile, ie bent by a preset sequence of pusher pin movements, the segment is severed from the bar by a rotatable cutter device 13 adjacent to delivery port 14.