EP0169564A2 - Method and apparatus for bending elongate work pieces, in particular tubes - Google Patents

Abstract

The invention relates to a method and a device for bending elongated workpieces, in particular pipes, by applying a bending moment to the workpiece while inductively heating a cross-sectional zone of the workpiece with uneven temperature distribution along the circumference of this cross-sectional zone by means of an induction loop surrounding the workpiece and while cooling the Workpiece in at least one neighboring zone. According to the method of the invention, it is provided that within a portion of the circumference of the workpiece to be attached that is to be set to relatively low temperatures, the electrical current of the induction loop is compressed into several partial currents, at least one of which is primarily the cross-sectional interest to be heated and at least one other is primarily one Neighboring zone of the workpiece is inductively affected, and that the inductive heating of the respective neighboring zone is partially or completely canceled by cooling. The device can be branched by a bypass line (15) which branches the induction loop (11).

Description

The invention relates to a method for bending elongated workpieces, in particular pipes, according to the preamble of claim 1, and to a device for carrying out the method according to the preamble of claim 11. As the inductively heatable and thus electrically conductive elongated workpieces come in addition to the Tubes in particular also include rods and, more generally, all such elongated workpieces which can be bent along the circumference of a heated, usually narrow, circumferential zone due to uneven temperature distribution.

Uneven heating of the cross-section, for example of pipes to be bent and more generally elongated workpieces, is of great importance in some special cases and moreover has particular advantages in general. Namely, there are materials which, when strong plastic deformation, particularly elongation, are susceptible to cracking when the deformation ^g at temperatures above the Umwandlun spunktes AC3 (about 800 ° C austenite) takes place. If you keep the temperature on the stretching or stretching side, the so-called extrados, low, e.g. to 750 ° C, and on the upsetting side, the so-called Intrados, high, e.g. 950 ° C, while bending a sheet, the temperature changes neutral bending line towards the Extrados; this results in more compression on the intrados and less stretching or stretching on the extrados. Less stretch on

Extrados is not only beneficial; because the risk of cracking is reduced there, but less stretching means less thinning of a pipe wall. By using the correct temperature difference between Extrados and Intrados, it is possible to produce elbows based on pipes with normal wall thickness that meet the conditions of the maximum permissible wall thinning (on the Extrados) or wall thickening (on the Intrados), e.g. prescribed in DIN 2413.

Heating elongated workpieces, e.g. Pipes by means of an inductor for their progressive bending are widely known, e.g. generally seen from NL-PS 142 607 and DE-PS 2 112 019.

The uneven heating by means of an inductor for the progressive bending of pipes and other elongated workpieces with the aim of influencing or correcting the degree of deformation or wall thickness change is known according to a first embodiment from DE-PS 2 738 394, which provides an asymmetrical arrangement of the inductor. Similar aims one of several alternative embodiments of DE-OS 22 20 910, according to which the part of the inductor enclosing the extrados should have a greater distance from the pipe surface than the part enclosing the intrados.

For the same purpose from DE-OS 22 20 910, second alternative, the possibility is known of achieving an uneven or asymmetrical heating by means of laminated cores which are attached locally in the vicinity of the inductor and which serve as yoke plates and by means of which the intensity of the inductive heating is influenced can. A third complex and spatially difficult to control alternative of DE-OS 22 20 910

finally provides, in combination with such yoke sheets, to provide a first inductor for preheating with a second inductor for main heating at the heating cross section.

For the same purpose, an inductor is known from US Pat. No. 4,177,661, in which part of the induced energy is collected by a shield which is placed between the inductor and a pipe to be bent. A device is also described there according to which an extra heating source is applied to the Intrados in front of the ring-shaped and inductively operating heating source.

All these known methods and devices for the. however, uneven heating of the bending cross-section of pipes or other elongate workpieces to be bent progressively has certain disadvantages and does not lead to good success, or does so only with great difficulty.

The asymmetrical heating by means of eccentric installation or radial adjustment of the inductor has the disadvantage that when the inductor is adjusted transversely to lower the temperature of the extrado, the temperature of the intrado is increased at the same time, although in order to avoid undesired thinning of the wall, for example a pipe on the extrado, The temperature would only need to be changed on the extrados and excessive compression on the intrados would also not be desirable. Furthermore, the inductors used usually have spray holes which spray water at a certain angle in the forward direction onto the pipe which has already been bent, in order to limit the heated zone. By transverse adjustment of the inductor also changes the place where the water jets hit the tube, with the result that the width of the heated zone becomes uneven and this has an adverse effect on the bend.

Attaching yoke sheets to the inductor at the point of the inductor where a higher temperature is desired is a very cumbersome and time consuming job. However, once the desired effect has been achieved for a certain tube wall and the bending radius, this inductor is only suitable for this case.

In practice, attaching a shield between the inductor and the workpiece to be heated is very difficult since the available gap between the inductor and the workpiece is small. The shield also needs to be water-cooled to prevent overheating, so there is practically no space left. Here, too, the effect is difficult to predict, and the position and dimensions must be determined empirically, with success only valid for one particular case.

Locating an extra heat source locally with the purpose of achieving a higher temperature on the inside of the arch, i.e. on the intrados, has the disadvantage that the heated zone is made extra wide at this point, which is disadvantageous for maintaining a good round Tube (missing bulges or upsetting points) during bending.

The invention proceeds generically from the possibility either to set up the inductor eccentrically in accordance with the notorious prior art for asymmetrical inductive heating of the workpiece (for example DE-PS 2 738 394) or to partially shield the induction in the case of concentric installation (US Pat. No. 4,177) 661). The former Fall does not allow a concentric inductor arrangement a priori; the second case is complex and difficult to implement. The genus can also be read on the arrangement with yoke plates according to DE-OS 22 20 910, which, however, can only be matched precisely to a specific workpiece in a very inefficient manner.

The invention is therefore based on the object of providing a method and a device for bending elongated workpieces, in particular pipes, with uneven temperature distribution along the circumference of an inductively heated cross-sectional zone of the workpiece, which allow a concentric or almost concentric inductor installation and make it possible in a simple manner to set different bending radii with the same inductor.

This object is achieved according to the invention in a method according to the preamble of claim 1 by the characterizing features of claim 1 and in a device according to the preamble of claim 11 by the characterizing features of claim 11.

The invention enables the inductor to be strictly or approximately concentrically around the workpiece, i.e. with approximately the same radial distance with respect to the object to be bent, e.g. a pipe, and in the peripheral region of the workpiece, where a lower temperature is desired, to branch the inductor into two or more parallel currents and to completely or partially dissipate the heating energy induced by the branched partial currents in the object to be bent , e.g. by means of the usual spraying directed and adjustable water jets.

The implementation of the invention is relatively simple, without having to rely on an asymmetrical arrangement of the inductor with respect to the tube. After radial adjustment in relation to the workpiece to be bent, a radial transverse adjustment with changing bending radii, which can be implemented with the same inductor, is usually not at all and at least less frequently and to a lesser extent than in known methods and devices. The necessary adjustments can be made based on the location and extent of the cooling. Virtually any desired temperature profile can be set along the circumference of the heated cross-sectional zone of the workpiece, so that undesired upsets on the intrados can also be avoided. More generally speaking, in relation to pipes, the wall thickness can be particularly well controlled _. reliably adjust the circumference of the bent pipe, even for pipes with different thick walls. The same applies with regard to a uniform cross-sectional stress of workpieces with a full cross-section, for example bars, in particular also profile bars, for example with a T or H profile. It is also worth mentioning the possibility of introducing the induction energy into the workpiece with little dissipation and distributing it over the bending cross section. Spray elements combined with the inductor can also be distributed uniformly over the circumference of the workpiece to be bent, in particular, but not exclusively, when the inductor is arranged concentrically or almost concentrically with respect to the workpiece.

If the generic term of claims 1 and 11 already refers to cooling of the workpiece in at least one neighboring zone, the quenching of the already bent workpiece behind the cross-sectional zone heated to bending temperatures is hereby addressed, in order to be as possible there soon to make the workpiece a rigid lever element again within the entire bending device. In the prior art, this cooling is usually already effected by a water jet, often directly through a plurality of small side holes from the cooling liquid of the inductor itself or through a separate cooling ring. However, there are also bending devices in which the cooling takes place behind the heating zone instead of by means of cooling liquid by means of cooling air (for example forced-forced forced compressed air). All of these possibilities are included in the scope of the invention. This also applies to a transmission of the possibility known per se only when bending plastic pipes to provide cooling both in front of and behind a heating zone (US Pat. No. 2,480,774).

The induction loop also mentioned in the generic term is usually a single loop. In practice, however, the individual loop can be assembled into a wider inductor loop, for example by bridging two parallel induction loops with a connecting plate. A repeated loop through the screw shape of the inductor is less common without it also being excluded from the outset (e.g. mentioned in the generic DE-OS 22 20 910).

As a rule and according to the underlying general theory, the temperature reduction by branching the inductor will only be provided on the stretch side of the arc, the so-called extrados. However, within the scope of the invention, the reverse possibility should at least theoretically be included if the teaching of DE-PS 28 22 613 should still make a technical sense, according to which a reverse temperature application is provided.

In the normal case, the branching will extend over about half the circumference of the pipe or the circumference of the other workpiece. It is entirely possible to overlap the stretching zone on both sides, which is covered qualitatively with the upper limit of 60% of the circumference of the workpiece, which is not to be taken exactly numerically. It is possible with much simpler and more variable means than in the generic DE-OS 22 20 910, as aimed there to bring only about a quarter of the circumference to a low temperature and the rest to a higher temperature, in particular the forging temperature.

The heating cross section does not necessarily have to be arranged perpendicular to the workpiece axis, but can also run obliquely or kinked, for example, according to FIGS. 4 and 5 of DE-OS 22 10 715.

The invention is also invariant with regard to the way in which the bending moment is applied. It is thus possible both to move the workpiece axially relative to the stationary inductor and, conversely, to shift the inductor relative to the stationary workpiece or even to make both elements displaceable and to focus only on a relative movement.

It is widespread to advance the workpiece continuously or incrementally and to arrange the inductor in a fixed position, apart from control movements, cf. DE-PS 21 12 019.

The bending moment can be either by axially pressing on the unbent tube (DE-PS 27 38 394) or by introducing it a torque on the bending arm (see. DE-OS 19 35 100) or else, for example after a flash bow tension (see. US-PS 783 716), are applied.

In this regard, the invention is in no way limited.

Within the scope of the invention, not only inductors with a round cross section, but also e.g. those with angular, in particular approximately rectangular, triangular or trapezoidal, cross-section are used, the profile being able to be both transverse and longitudinal to the connections.

The inductor can be branched, for example, by a right-angled fork-like bend. Streamlined oblique bends are preferred, which not only have flow-related advantages, but at the same time can also represent an adaptation to the different heating along the circumference of the workpiece.

In practice, induction frequencies between 500 and 1000 Hz can be used. 1000 Hz has a penetration depth of approx. 16 mm for steel pipes, 500 Hz a penetration depth of approx. 22 mm. The relatively high frequencies for thin-walled pipes and the relatively low frequencies for thick-walled pipes are used. In borderline cases, lower or higher frequencies can also be used.

• 1. Zwei oder mehr Teilströme wirken unmittelbar auf den zu erhitzenden Querschnitt.
• 2. Außerhalb der vornehmlich zu erhitzenden Zone wird mehr als ein Teilstrom vorgesehen.

The following solutions are possible within the scope of the invention:

• 1. Two or more partial flows act directly on the cross section to be heated.
• 2. Outside the zone to be heated primarily, more than one partial flow is provided.

These two or more partial flows can all be arranged on the same side of the inductor, in particular if they are to be used to control or regulate the desired conditions and for this purpose require a larger area, for example in order to distribute the cooling liquid over a wider area.

According to claims 2 and 16, at least one neighboring zone of the heating cross section, which is covered by the partial flows, and in which a complete or partial cancellation of the inductive heating takes place, is arranged in the bent part of the workpiece. This makes it possible to render certain current components ineffective for inductive heating and also to make the coolant used to cancel the inductive heating usable at the same time to deter the pipe behind the heated cross-sectional zone or at least to avoid undesirable interactions between the two coolants. For example, if water is flushed out of the inductor to quench the bent tube behind the heated cross-sectional zone, it may mix with cooling water to partially remove the inductive heating applied in the sense of the invention, e.g. in the sense of the formation of a united spray jet. The same applies to air cooling.

One can even think of not actively cooling the bent part of the workpiece behind the respective bending point, but instead of using an already performed cooling of the pipe in order to prevent the already bent pipe from softening. In this sense, the cooling of the pipe that had already occurred would be the cooling in the sense of the main claim, which is then not introduced from the outside, but introduced by the pipe becomes. In the same sense, one could also preheat the pipe again by means of a branched partial stream by installing a relatively long distance between the preheating and the actual heating zone and thus achieving a cooling effect in the sense of the main claim.

Both cooling for deterrence and cooling in the sense of the invention for the partial abolition of inductive heating can also be carried out from the inside of a pipe if necessary.

In the case of, for example, a three-way branch, it is also possible to provide a controlled system before the main heating and a constant cooling system after the heating. In the still unbent area, if necessary, more or less heat can be added beforehand by more or less strong extinguishing of inductively input heat, and a completely desired temperature profile can be obtained at the cross-sectional point to be heated to bending temperatures.

However, it has been shown that it is sufficient to carry out an induction heat input only behind the cross-sectional zone of the workpiece used for the bending in the sense of claims 2 and 16, and at the same time the favorable interaction explained with that required to quench the tube after bending To get cooling.

The sub-claims not mentioned describe advantageous developments of the invention. This is explained in more detail below, for example using schematic drawings.

• Fig. 1 eine Draufsicht einer Basiskonstruktion einer Biegevorrichtung;
• Fig. 2a und 2b Drauf- und Seitenansicht eines konventionellen Induktors;
• Fig. 3a, 3b und 3c Draufsicht (nach Pfeil B in Fig. 3b), Seitenansicht und Rückenansicht (nach Pfeil A in Fig. 3b) eines erfindungsgemäßen Induktors.
• Fig. 4 einen Querschnitt durch einen erfindungsgemäßen Induktor mit Sprühlöchern für Kühlwasser unter Darstellung des verzweigten Induktorbereichs und eines gebogenen Rohrabschnittes, bezogen auf eine rechtwinklig zum ungebogenen Rohr verlaufende erhitzte Querschnittszone (Biegezone); und
• Fig. 5 eine Modifikation von Fig. 4, bezogen auf eine schräg bzw. S-förmig zum ungebogenen Rohr verlaufende Querschnittszone.

Show it:

• 1 is a plan view of a basic construction of a bending device;
• 2a and 2b top and side view of a conventional inductor;
• 3a, 3b and 3c top view (according to arrow B in Fig. 3b), side view and back view (according to arrow A in Fig. 3b) of an inductor according to the invention.
• 4 shows a cross section through an inductor according to the invention with spray holes for cooling water, showing the branched inductor region and a bent tube section, based on a heated cross-sectional zone (bending zone) running at right angles to the unbent tube; and
• Fig. 5 shows a modification of Fig. 4, based on a cross-sectional zone running obliquely or S-shaped to the unbent pipe.

Fig. 1 shows the basic principle which is applied to a bending device and is intended to serve as a starting point for an explanation of the invention. A pipe 1 (only as an example) to be bent is passed through a fixed guide 2 in the direction of arrow P (exerting a compressive force P for the pipe feed) through an inductor 3, which heats the pipe up to a temperature in the narrow zone 4 , in which the tube 1 can experience the desired deformation at this point. At the location of the heating over, the tube is cooled by a circle of water jets 5 directed obliquely forward (in the direction of advance of the tube) and exiting from the inductor 3, for example, and conducted in an arc 6 around the point 7, at which the bent part is at one around the point 7 freely rotatable arm 8 be rigid is consolidated. Together with this arm 8, the already bent pipe part 6 practically forms a rigid unit and thus a lever, which is always perpendicular or almost perpendicular to the longitudinal direction of the unbent pipe section, a line perpendicular to the pipe leading through the heated zone 4 and the pivot point 7 . A compression effect occurs on the inside 9 of the sheet, the so-called intrados, and a stretching action occurs on the outside 10 of the sheet, the so-called extrados. The degree of upsetting and stretching depends on the bending radius R and on the temperature or the deformation resistance of the material to be bent at the different points. Without prejudice to the simplified illustration given here, within the scope of the invention the adjustability of the specified reference values, for example item 7, can also be given within the meaning of DE-PS 2 112 019.

• M_b = (Da-S)² × S × σ_t.

The bending moment is determined by the pipe cross-section and the strength (yield strength) of the material. As a rule of thumb you can start with:

• M _b = (Da-S) ² × S × σ _t .

• M_b = Biegemoment in kgcm (oder Ncm)
• Da = Außendurchmesser des Rohrs in cm,
• S = Wandstärke in cm und
• õ_t = Streckgrenze des Materials bei Tempera-
• tur t in kg/cm² (oder _Ncm )

Mean:

• M _b = bending moment in kgcm (or Ncm)
• Da = outer diameter of the pipe in cm,
• S = wall thickness in cm and
• õ _t = yield strength of the material at temperature
• tur t in kg / cm ² (or _N cm)

The required bending moment M _b is introduced into the tube by a shear force P and the lever (bending radius R) according to the formula M _b = P x R.

From this it can be seen that as the bending radius becomes smaller, the required thrust force increases and thus also the compression force which is exerted on the heated zone. If the temperature of the intrados and extrados remains the same, the wall thinning increases as the bending radius becomes smaller. If you increase the temperature on the intrados compared to the extrados, the inner wall will compress more and the outer wall will stretch less, i.e. dilute less. A good temperature setting, if necessary regulated, is therefore very important.

A conventional inductor 3, as can usually be used in the bending device according to FIG. 1, is shown in FIGS. 2a and 2b. It has a tube 12, bent into a simple circular induction loop 11 in one plane, made of a material which is conductive for medium-frequency current (500 to 1000 Hz), for example copper or a copper alloy. The free internal cross section of the induction loop 11 is dimensioned such that the tube 1 can be passed through it approximately coaxially to the induction loop at a radial distance therefrom according to FIG. 1. At a circumferential point of the induction loop 11, two connecting tubes 13 protrude radially from the induction loop 11. They are bent somewhat apart at their free ends and each carry a connecting flange 14 at their free ends. The connecting flanges 14 serve for connection to an inductor power supply unit (not shown) working with the medium frequency mentioned, and also expediently for connection to a cooling water source. This applies in particular if spray nozzles for the cooling water jets 5 according to FIG. 1 are formed in the induction loop 11 axially forwards and radially inwards. In this case, the inductor tube 12 also serves as a cooling water line for cooling water which is passed from one connecting flange 14 to the other. If the Inductor 3 should not also serve as a cooling water spray element, the same cooling water flow (or flow of a different cooling fluid) can serve to cool the inductor.

3a, 3b and 3c show an inductor modified according to the embodiment of FIGS. 2a and 2b according to the invention. As in the case of FIGS. 2a and 2b, the inductor tube 12 forms a circular induction loop 11, which is connected to the connecting tubes 13 at a circumferential point. The relationships are essentially the same as in the embodiment of Figs. 2a and 2b, so that the description, e.g. with regard to the connecting flanges 14, which are no longer shown separately.

The special feature according to the invention consists of the following:

A bypass line 15, which is also formed from the inductor tube 12, extends from the connecting tubes 13, each adjoining a connecting tube 13, over approximately 60% of the entire circle described by the induction loop 11, that is to say also over approximately 60% of the circumference of a tube 1 to be inserted. which extends in a parallel plane to the induction loop 11 and is aligned with it in plan view.

Without restricting generality, the bypass line 15 merges directly into the connecting pipes 13 here. The free ends of the induction loop 11 are each connected to the associated connecting pipe 13 by an oblique connecting tube 16 and the free ends of the bypass line 15 are each connected to the adjacent section of the induction loop 11 by an oblique connecting tube 17. The level of the bypass line 15 coincides with the level of the connecting pipes 13, while the induction loop 11 is axially offset. The direction of inclination of the connecting pipes 16 and 17 corresponds to the direction of flow indicated by arrows of the coolant flowing through the inductor 3.

In the embodiment according to FIGS. 3a to 3c, it is assumed that the coolant should only serve to cool the inductor 3, but not to cool the tube 1. In this case, special coolants not shown in the tube 1 from the bypass line 15 from the inductive heating are provided for partial or complete cancellation.

4 and 5 now show two modifications of the inductor of FIGS. 3a to 3c in an application in which the inductor itself serves as a coolant source acting on the tube 1. The basic structure of the inductor 3 is the same as in FIGS. 3a to 3c. Particularly noteworthy / is, however, a certain sequence in FIGS. 4 and 5 of the circular induction loop 11 on the one hand and the bypass line 15 on the other hand with respect to the direction of displacement of the tube 1, which here corresponds to the direction of the arrow P exerting pressure. In connection with the fact that the inductor 3 is itself a spraying device for cooling water jets 5 acting on the pipe 1, the two alternative arrangements of FIGS. 4 and 5 also result in a different arrangement of the spraying nozzles.

Because of the elements of the inductor 3, reference can again be made to the preceding FIGS. 3a to 3c in connection with 2a and 2b.

In the arrangement according to FIG. 4, the circular induction loop 11 is arranged in the direction of displacement of the tube 1 in front of the bypass line 15. The induction loop 11 causes a narrow heating zone 4 in the tube 1 at right angles to the axis of the tube in the sense of claim 1 Direction front, ie the edge of the heating zone 4 facing the already bent tube, is generated by a first row of water jet nozzles 18 formed on the induction loop 11, which emit the water jets 5 in the sense of FIG. 1 obliquely forward and radially inward onto the tube 1 and form said quenching edge of the heating zone 4 thereon.

For the partial or complete cancellation of the inductive heating of the tube 1 from the bypass line 15, two further water jets 5a and 5b directed obliquely forward and radially inwards onto the tube 1 are used from two further rows of water jet nozzles 19 and 20 which face the bent tube 1 on the one hand are still distributed on the front flank of the induction loop 11 and on the other hand on the front flank of the bypass line 15 over the circumference of the inductor which is occupied by the bypass line 15. It can be seen that the water jets 20 also extend along the connecting tube 17.

5, in which the induction loop 11 is arranged in the direction of displacement of the tube 1 at the front, ie facing the curved tube 1, the heated cross-sectional zone 4 of the tube 1 is instead formed S-shaped by moving it from the Bypass line 15, the associated connecting pipes 17 and the peripheral portion of the induction loop 11 to which the bypass line 15 together with the connecting pipes 17 is not parallel. Accordingly, the first row of water jet nozzles 18 also extends in an S-shaped manner over all three elements of the inductor 3 mentioned. The axial sequence of the further rows of water jet nozzles 19 and 20 is then as in the case of FIG. 4, but on other elements of the inductor arranged. The water jet nozzles 19 are here on the bypass line 15 and the water jet nozzles 20 on the area the induction loop 15, which runs parallel to the bypass line 15.

In both arrangement cases of FIGS. 4 and 5, the water jet nozzles 19 and 20 render part or all of the inductive heating of the tube 1 ineffective, specifically on the peripheral area which is described by the bypass line 15. This means that in the section in which the induction loop 11 runs parallel to the bypass line 15, less heat is exerted on the pipe 1 from the inductor 3 than in the area in which the induction loop 11 runs unbranched - and the full induction heat takes effect in tube 1. The transition between the different heating zones on the circumference of the tube can be set as desired by appropriate inclination of the connecting tubes 17 and corresponding arrangement of the water jet nozzles 19 and 20. It can be seen that in the embodiments of FIGS. 4 and 5 the heating on the intrados 9 is large and that on the extrados 10 is small, since the full induction heat acts on the extrados in the heating zone, while it is weakened in the area of the extrados.

In a conventional manner, not shown, if the material of the inductor tube 12 is expediently the same, the individual line sections formed by it in the inductor 3 can be adapted by selecting different cross sections of the inductor tube 12 and, if appropriate, its wall thickness so that the current branching in the individual line sections strictly according to Kirchhoff's law Law, or alternatively in a desired different manner. Depending on the choice, the metal cross section of the bypass line 15 and the branched line section of the induction loop 11 can be chosen to be the same or different.

An auxiliary element is further explained on the arrangement according to FIG. 4, which can also be provided in the arrangement according to FIG. 5. It is a blower tube 21 connected upstream of the inductor 3 in the feed direction of the tube 1, with air jet nozzles which, in accordance with the flow arrow 22 directed obliquely inwards and forwards, generate an air flow in the direction of the tube 1 pushed through the inductor 3. This ensures that the cooling water emerging from the water jet nozzles 18, 19 and 20 cannot strike back into the narrow cross-sectional zone 4 to be heated on the pipe. The strength and direction of the blower radiation must be coordinated with the strength and direction of the cooling water radiation from the cooling water nozzles 18 to 20 mentioned.

As has already been made clear on the basis of the embodiments of FIGS. 3a and 3b, instead of the cooling water jets 5, 5a and 5b emerging from the inductor 3 itself, special cooling elements can be provided, which are ring-shaped separately from the inductor 3, for example in the manner of the annular blower tube 21 can be arranged around the tube 1 at a suitable location and in a suitable design. Although this is more complex than the combined design of the inductor explained with reference to FIGS. 4 and 5 at the same time as a cooling element, it offers the advantage of greater variability in the application of the coolant. It is particularly easy to design individual nozzles or groups of nozzles to be adjustable in terms of the amount of coolant and preferably also in the direction of the coolant, and sometimes to use desired flat jet nozzles.

Claims (19)

1. Process for bending elongated workpieces, in particular. their pipes, by applying a bending moment to the workpiece while inductively heating a cross-sectional zone of the workpiece with an uneven temperature distribution along the circumference of this cross-sectional zone by means of an induction loop surrounding the workpiece and cooling the workpiece in at least one neighboring zone,
characterized,
that, based on a portion of the circumference of the workpiece to be bent, which is to be set at relatively low temperatures, the electrical current of the induction loop is branched over a portion of its circumference into a plurality of sub-currents, of which at least one primarily relates to the cross-sectional zone to be heated and at least one other primarily a zone outside the zone of the workpiece to be heated is brought into action inductively, and that the inductive heating of the respective neighboring zone is partially or completely eliminated by cooling. 2. The method according to claim 1, characterized in that at least one such neighboring zone with all or part wise cancellation of inductive heating is arranged in the bent part of the workpiece. 3. The method according to claim 1 or 2, characterized in that 30 to 50% of the total current of the induction loop are branched off as partial flow or partial flows for the primary effect on at least one neighboring zone of the cross-sectional zone to be heated. 4. The method according to any one of claims 1 to 3, characterized in that the degree of cancellation of the inductive heating of the workpiece in the respective neighboring zone is selected by adjusting (controlling and / or regulating) the cooling of this neighboring zone. 5. The method according to claim 4, characterized in that 30 to 100% of the inductively introduced amount of heat of the neighboring zone (s) are canceled. 6. The method according to any one of claims 1 to 5, characterized in that the cooling of the inductively heated neighboring zone is carried out using cooling water and / or cooling air. 7. The method according to any one of claims 1 to 6, characterized in that the predominantly inductively acting on the cross-sectional zone to be heated current components of the induction loop are arranged concentrically or almost concentrically with respect to the workpiece. 8. The method according to any one of claims 1 to 7, characterized in that the partial current inductively acting on a neighboring zone of the induction loop describes a path with a varying distance from the workpiece. 9. The method according to any one of claims 1 to 8, characterized in that the inductive heating of the respective neighboring zone is canceled to different degrees by different cooling along the circumference of the workpiece. 10. The method according to any one of claims 1 to 9, characterized in that the branching of the electrical current of the induction loop along 20 to 60%, preferably 25 to 40%, most preferably about a third, of the circumference of the workpiece is carried out. 11. Device for bending elongated workpieces, in particular pipes, for carrying out the method according to one of claims 1 to 10, with a bending moment on the workpiece (1) applying device (2,7,8), with a surrounding the workpiece to be bent Inductor (3) and with a cooling device (18), the coolant of which is directed to at least one adjacent zone of the cross-sectional zone (4) of the workpiece to be bent, which can be heated by means of the inductor to different bending temperatures along the circumference of the workpiece,
characterized,
that along a portion of the circumference of the workpiece (1) to be bent, at least one bypass line (15) of the inductor (3) opposite at least one in relation to the cross-sectional zone (4) of the workpiece, which is to be heated inductively to the bending temperature, in the longitudinal direction of the workpiece offset adjacent zone of the workpiece, and that coolant (5a, 5b) is directed to this adjacent zone. 12. The apparatus of claim 11 with inductor cooling, characterized by a cooling device separate from the inductor cooling, the coolant of which is directed to the adjacent zone. 13. The apparatus of claim 11 or 12, characterized in that the cooling device has an adjusting device for the amount of coolant, preferably separately, for individual nozzles or groups of nozzles. 14. Device according to one of claims 11 to 13, characterized in that the direction of the coolant discharge on the workpiece is adjustable, preferably separately for individual nozzles or groups of nozzles. 15. The device according to one of claims 11 to 14, characterized in that the cooling device has flat jet nozzles. 16. The device according to one of claims 11 to 15, characterized 'in that the coolant (5a, 5b) is directed to the bent part of the workpiece (1). 17. The device according to one of claims 11 to 16, characterized in that the inductor (3) is branched into only two lines (on 11, 15). 18. The apparatus according to claim 17, characterized in that the bypass line (15) is formed the same as the other branched line section (on 11). 19. The apparatus according to claim 17, characterized in that the bypass line (15) differs from the other branched line section (at 11) in the metal cross section.

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