GB2133328A - Straightening machine - Google Patents

Abstract

In a machine for cold-straightening tubes or rods having a circular cross- section the straightening tools include at least one ring (2, 3, 4) with a convex inner surface. There are preferably three of the said tools, substantially coaxial with the tube or rod (1), but in such a way that their axis are skew with respect to the axis of the tube at an angle ( alpha ) which is the same for all of them and, at least for the two outer rings (2, 4), which are driven by a motor and caused to rotate at the same speed, is oriented in the same direction and gives rise to a helicoidal movement of the tube (1). The middle ring (3), on the other hand, is idle in the sense that it is free to rotate around the tube or rod (1) to be straightened, but is constrained in the axial direction and with regard to height, so that it imparts to the tube or rod (1) a downward force which approaches the yield limit. <IMAGE>

Description

SPECIFICATION Straightening machine for tubes or rods, wherein the straightening tools include at least one ring with a convex inside surface The present invention concerns machines for straightening tubes or rods having a circular crosssection, and, in particular, machines wherein the straightening tools include at least one ring with a convex inner surface, there being preferably three of such rings.

In order to straighten tubes or rods, for a long time the so-called "pad" method has traditionally been adopted, according to which a pad is lowered onto the tube to be straightened, which is positioned with its convexity facing upwards on two bearings at an appropriate distance apart, until the yield limit of the tube has been exceeded at that point. This method which is substantially static, is however imprecise and rather slow, requires the intervention of trained personnel for the visual checks and, at present, is adopted only in very special cases.

Procedures for straightening by means of traction are also known, wherein the tube is clamped very tightly at each end between two pairs of jaws which are then moved away from each other in the axial direction, giving rise to a yielding effect as a result of stretching rather than bending. This method also has several drawbacks such as discontinuity and hence slowness, causes large amounts of shavings at the ends, which ends must be eliminated after being crushed by the jaws, and requires a considerable power amount.

Methods of straightening by means of vibration are also known, wherein the section is pushed through stands of shaped rollers which are located alongside each other and arranged on two planes, the said planes being mutually perpendicular and both containing the ideal axis of the section, so that the vibrations obtained in the two planes by means of a set of cams can cause the yield limit to be reached in all the fibres of the cross-section.

Although these methods have the advantage of being continuous, i.e. operating with a single pass of the work, they are however used practically only in cases of non-circular cross-sections. In fact, these systems would be antieconomical for circular cross-sections since they do not entail the helicoidal movement of the section, which could be more easily exploited.

Finally, there are the straightening methods which are known and widespread today in the majority of cases relating to tubes and rods, wherein the tube is caused to pass through a set of shaped rollers which are oriented so that their axes are skew with respect to the axis of the tube itself, the latter thus being subjected to a helicoidal movement which contributes in a decisive manner to its straightening with respect to all the various planes containing its ideal axis.

These rollers, besides having different diameters and shapes, depending on the various applications, may all be powered or some may be idle, and they may be arranged singly, in pairs or in threes, in the sense that there may be more than one simultaneously making contact on the circumference of a same section of the tube.

It is known, on the other hand, that the rigid rotation of a segment around a line which is skew with respect to it generates a surface of revolution known as a "hyperboloid of one sheet", this being a quadratic surface systems of straight lines, despite the freedom of shaping mentioned above, generally this curved surface has been adopted so that a generatrix of the tube can be made to coincide always with one of the generatrices of the hyperboloid. This is so as to obtain, between roller and tube, not just linear, but even rectilinear contact, thereby reducing wear, power consumption and, in particular, deterioration resulting from impressions and marks made on the external surface of the tube as a result of relative slipping of the same.The use of rollers arranged in pairs or in threes also prevents any ovalization of the tube, which could not be avoided with a single peripheral contact.

Nevertheless, even the hyperboloidal contour, the manufacture of which is often difficult, requiring special templates and having to take into account the quality of steel used, does not eliminate slipping completely, since at the points of the roller which are at different distances from its axis there are different rim speeds. On the other hand, rectilinear contact between the generatrices can only occur when the angle of skewness of the roller axis with respect to that of the tube corresponds to the characteristic angle of the hyperbola, i.e. the angle formed by the asymptotes with its transverse axis. Therefore, one finds in practice contour surfaces other then the theoretical hyperboloid, either more sophisticated or more empirical, up to the circular contour, these often being obtained by the users who re-machine the rollers themselves.

In any case, if there are only two hyperboloidal rollers, the said characteristic angle should be fairly small in order to limit slipping; this means, therefore, that the rollers will have a fairly large axial length in order to create sufficient adhesion to move the tube forward, the speed of which movement is proportional to the sine of the said angle. If, on the other hand, there are several rollers arranged consecutively in the axial direction, the bulk on the axis can often have negative consequences in view of the need for extensions and pinion stands, with the further resultant disadvantage of having considerable shavings at the ends, bending of which cannot be prevented.

It is the object of the present invention to provide a machine for straightening bars having a circular cross-section (tubes or rods), including at least one rotating ring which has any outer surface, a convex inner surface and, in particular, a diametral cross-section consisting of a hyperbola.

in accordance with a preferred embodiment of the present invention, the said machine has three of the said rings, arranged in succession along the axis of the tube, each with its own axis skew with respect to the tube axis by the same angle. The two outer rings are caused to rotate at the same speed and are powered, whereas the middle ring is idle and is forced to rotate on account of the friction with the tube itself. The angle of skewness is oriented. for the two end rings, in the same direction, i.e. in the direction in which the tube moves forward, whereas the middle ring may even be inclined in the opposite direction.

Other objects, advantages and characteristics of the machine in accordance with the present invention will become apparent to those skilled in the art from the following detailed description of some of its embodiments, given by way of nonlimiting examples, with reference to the attached drawings, in which: FIGURE 1 is a schematic side view, limited to the three straightening rings, of a machine according to the present invention; FIGURE 2 is a plan view, from above, of the three rings shown in Fig. 1; FIGURE3 is a side view of an embodiment of the entire machine, according to the present invention, the machine being provided with three rings as shown in Fig. 1; FIGURE4 is a schematic view, as in Fig. 1, of a different embodiment according to the present invention; and FIGURE 5 is a schematic view of a further alternative embodiment.

With reference to the drawings, Figs. 1 and 2 diagrammatically show the arrangement, around a steel tube 1 to be straightened, of three rings being part of a machine according to the present invention.

The two end rings 2 and 4 are driven by any known motor means (not shown) and caused to rotate at the same speed in the direction of arrow F, as a result of which the tube 1 not only rotates in the direction of the arrow F, but is also subjected to a component of translation motion in the direction of the arrow G, thus moving forward with a helicoidal motion. One of the rings, namely ring 2, is shown as though it were transparent, in order to reveal its inner contour which is in fact identical to that of the other two rings, i.e. it has ideally a diametral cross-section consisting of a hyperbola, or in other words it defines on the inside a hollow hyperboloid of one sheet.The angle of skewness a with respect to the axis of the tube 1 is the same for all the three rings, but the middle ring 3 could also be oriented in the opposite direction as will be better seen in Fig. 3.

Furthermore, the said middle ring 3 is displaced downwards with respect to the two end rings, making contact with the tube 1 along the upper generatrix rather than along the lower one as is the case with the other two rings, so that the tube behaves like a beam on two unilateral bearings with a load in the middle.

It can be noted that even a small angle of skewness a can give rise to a winding or gripping angle which is three or four times greater than that obtainable using the end rollers according to the prior art. This fact, which also gives rise to a slower rate of movement forwards and hence to more closely arranged strips of area on the tube which are subjected to the yield limit, therefore has the effect that substantially the entire surface of the tube, rather than just a helicoidal strip, is immediately covered in a single pass, tnereby avoiding the need for further subsequent passes.

The greater winding angle, with respect to rollers of the prior art, also reduces the possibility of knocks and jamming at the entrance to the rollers and of side skidding at the front and rear ends, thus also limiting the accidents.

With reference to Fig. 3, the machine can be seen in its entirety, in a preferred embodiment, in which each of the three rings is enclosed in a stand for holding the ring, respectively 12, 13 and 14, which stand has the possibility of rotating around its own vertical diametral axis until the required angle of skewness is reached.

Mechanical, hydraulic or oleodynamic connections are of course provided between the axles 6 and 8 of the two end stands 12 and 14 in order to ensure that the latter have the same angle of skewness. In Fig. 3 these connections are represented diagrammatically by a lever 9 at the ends of which are pivoted respectively the axles 6 and 8 of the stands 12 and 14 and which also has a central pivot 10 on which the arm 7 is mounted, the said arm being used to support and adjust the height of the central stand 13. All of the rings are able to rotate around their own axes within their own stands; bearings (not shown) are provided for this purpose as well as, for the end rings, toothed rims and motors, preferably hydraulic, for actuation of the rings themselves.Each stand is mounted on a base 11 which is divided into distinct portions corresponding to the various stands, the central portion 11' being mobile in height with respect to the other portions and being actuated by the said adjusting arm 7 provided, for example, with a screw jack, so as to obtain adjustment in the vertical direction with respect to the diameter of the tube to be straightened and in accordance with the residual camber deflection.

Since on each hyperboloidal surface two systems of parallel straight lines can be identified, both having the same characteristic angle but with an inclination which has an opposite sign with respect to the axis of the tube, the middle stand 13, and hence the ring 3, can in some cases be rotated in the opposite direction to the two outer stands of the powered rings, as shown in Fig. 3. In this case the ring 3 is moved at a slow angular speed and carries out a slight braking action, which is more or less desirable, whereas on the other hand, the axial bulk is increased and therefore the residual camber deflection is somewhat greater. This bulk, however, can be sufficiently limited if the arrangement shown in Fig. 1 is adopted with rings all of which are mutually parallel, this resulting in a reduction of the overall axial bulk of the machine and of the span formed by the tube 1 inside of it, with the enormous advantage of an even greater reduction in the residual camber deflection which is proportional, for a given diameter, to the square of the length, i.e. the distance between the two end rings 3 and 4. A further advantage which cannot be overlooked is that of reducing drastically, for the same reason, the residual bending at the ends and the shavings resulting therefrom, which instead are unavoidable in known multi-roller straightening machines.

The embodiment of Fig. 3, with stands which completely enclose the associate ring, is also particularly suited for actuation of the powered end rings by means of hydraulic motors (turbines) instead of electric motors, providing the rings themselves with a radial peripheral blading and introducing working fluid inside the stands via electro-valves 22, 22', 24 and 24', as shown schematically in Fig. 3. In this way the drawbacks due to the drives can be avoided and synchronization between the two powered rings can easily be obtained by means of a hydraulic circuitry arrangement such as according to the diagram shown in the figure.

From the foregoing, however it results that the main advantage of the present invention is the extreme structural simplicity which not only greatly facilitates adjustment of the straightening elements, but also allows very low installation and running costs.

Of course more complex embodiments are also possible where there are series of more than three rings, all of which operate as described above, or combinations of rings with rollers, such as that shown schematically in Fig. 4, where the central idle ring is replaced by a pressure roller which is also idle. In particular, if bilateral bearings are necessary, it is possible to arrange a hyperboloidal roller inside a ring according to the present invention, the said ring having a surface similar and complementary to that of the roller, in order to obtain a calibrating effect and to prevent any ovalization of the tube. This solution is also shown schematically in Fig. 5.

On the other hand, the unilateral bearings prevent the tube from being flattened, particularly in the case of small thicknesses, and allow a considerable power amount to be saved. Finally, using the machine described here, it is possible to straighten tubes with ready-machined ends (threaded, upset, bell-and-spigot ends, etc.) simply by displacing at the appropriate time and vertically the middle stand, associated with the idle ring, as a result of which the end lengths of the tube are able to pass through loosely, which end lengths would otherwise hinder the movement forwards and must be handled carefully.

Possible additions, variations and modifications can be made by the skilled in the art to the abovedescribed and illustrated embodiments of the machine according to the invention, without going beyond the scope of the invention itself, in the description of which all the already known considerations and the already adopted measures for multi-roller tube-straightening machines have been omitted.

Claims (11)

1. A machine for cold-straightening tubes or rods having a circular cross-section, including three operating tools of which at least one is a rotating ring having any outer surface and a curved and convex inner surface, with a minimum internal diameter greater than the outer diameter of the tube to be straightened, and mounted around the latter with its axis of rotating skew with respect to the axis of the tube, so as to eliminate the clearance existing between them.

2. A machine as claimed in claim 1, including at least two of the said rings (2, 3 and 4), which are mounted for rotating around the tube (1) to be straightened, at least one of the said rings being driven to rotate around its own axis and impart to the tube itself a motion of rotation and simultaneous translation in the direction of the axial forward movement component, the angle (a) of skewness between ring and tube being the same for all the powered rings, which rotate at the same rim speed at the points of contact with the tube.

3. A machine as claimed in claim 2, wherein said rings (2, 3 and 4) are in number of three and are mounted in succession and close to one another with the minimum bulk along the tube (1), the two external rings (2 and 4) being motorized and hence pulling the tube itself, and parallel to each other with the same angle of skewness (cog) with respect to the axis of the tube, with the middle ring (3) being mounted idle but also constrained in the axial direction, having its axis of rotation at a predetermined and adjustable height, so as to rotate by friction with the tube (1) while imparting to the latter a downward force which approaches the yield limit of the material.

4. A machine as claimed in claim 3, wherein the said rings (2, 3 and 4) are enclosed respectively in stands (12, 13 and 14) being mounted on platform sections 1 and 11') which in turn are connected, on support bearings, to axles (6 and 8) for adjusting the angle (a) of skewness of the external stands (12 and 14) as well as for adjusting the angle of skewness (a) and the vertical rod (7) of the middle stand (13), the said vertical axles (6, 7 and 8) being connected to each other via transmission means (9).

5. A machine as claimed in claim 4, wherein the said external stands (12 and 14) are containers sealed around the corresponding rings (2 and 4) and the latter have a bladed external surface, thereby functioning as a turbine under the action of a working fluid introduced under pressure into the said stands by a hydraulic motor through electro-valves (22, 22', 24 and 24') actuated in a synchronized manner.

6. A machine as claimed in claim 1, wherein the profile of the internal surface of each of the said rings (2, 3 and 4) is a hyperbola and the free volume inside each of the said rings has the shape of a hyperboloid of one sheet coaxial with the said ring.

7. A machine as claimed in claims 3 to 5, wherein all three rings (2, 3 and 4) are parallel to each other and have the same angle of skewness (a) oriented in the same axial direction.

8. A machine as claimed in claims 3 to 5, wherein the middle ring (3) has the same angle of skewness (cog) with respect to the axis of the tube (1) but is oriented in the opposite direction with respect to the two external rings (2 and 4), thus exerting a braking action on the tube to be straightened.

9. A machine as claimed in claim 2, including two external motorized rings and a central roller which has a concave outer surface, being mounted idle with its axis at a predetermined height, so as to exert a downward pressure on the tube (1) and be caused to rotate by it as a result of friction action.

10. A machine as claimed in claim 3, wherein a known roller with a concave outer surface which is similar and complementary to the inner surface of the said ring is inserted between each of the two motorized external rings (2 and 4) and the tube to be straightened, thereby transmitting by friction the inverted rotary motion of the corresponding ring.

11. A machine for straightening rods with a circular cross-section wherein the straightening tools are rings, substantially as described above and illustrated in the accompanying drawings.