METHOD FOR BENDING A PLASTIC TUBE AND DEVICE FOR CARRYING OUT THE METHOD

Abstract

Method for bending a plastic pipe including arranging a bending portion of a plastic pipe in a heating zone of a heater and performing contactless local heating of the bending portion, wherein the heater is adapted to provide a first predetermined temperature difference between a neutral zone of the bending portion and a compression zone of the bending portion and a second predetermined temperature difference between the neutral zone and the compression zone, of the bending area and an expansion zone of the bending area, introducing bending forces on holding regions arranged on the plastic pipe at a distance from the bending area and/or introducing bending forces on the bending area for deforming the plastic pipe into a deformation position and cooling the plastic pipe in the deformation position.

Claims

1. A method for bending a plastic pipe comprising the steps: arranging a bending area of a plastic pipe in a heating zone of a heater and carrying out contactless local heating of the bending area, wherein the heater provides a first predetermined temperature difference between a neutral zone of the bending area and a compression zone of the bending area and further provides a second predetermined temperature difference between the neutral zone of the bending area and an expansion zone of the bending area; introducing bending forces onto holding regions arranged on the plastic pipe at a distance from the bending area and/or introducing bending forces on the bending area for deforming the plastic pipe into a deformation position; cooling the plastic pipe in the deformation position; wherein the first predetermined temperature difference and the second predetermined temperature difference are chosen in such a way that the compression zone of the bending area and the expansion zone of the bending area are heated to a material-specific glass transition temperature for the plastic tube and that the neutral zone of the bending area has a temperature below the material-specific glass transition temperature.

2. The method according to claim 1, wherein the heater for performing the deformation of the plastic pipe effects a heating of the compression zone and of the expansion zone above a material-specific melting temperature, so that the compression zone and the expansion zone are in a thermoplastic state and wherein the first temperature difference and the second temperature difference are selected such that neutral zones adjacent to the compression zone and the expansion zone are in a thermoelastic state.

3. The method according to claim 2, wherein the first temperature difference between the neutral zone and the compression zone and/or the second temperature difference between the neutral zone and the expansion zone is in an interval of 100 degrees Celsius to 160 degrees Celsius for polyamide materials and is in an interval of 140 degrees Celsius to 180 degrees Celsius for polyphenylsulfide materials.

4. The method according to claim 1, wherein the heater comprises two heating sources spaced apart from each other for heating strip-shaped surface portions of the bending area from opposite spatial directions, respectively.

5. The method according to claim 4, wherein a first heating source performs a contactless radiation heating of the compression zone with a hot gas stream or with electromagnetic waves and wherein a second heating source performs a contactless radiation heating of the expansion zone with a hot gas stream or with electromagnetic waves.

6. The method according to claim 4, wherein the heating sources provide electromagnetic waves as a parallel beam or as a diverging beam to the bending area.

7. The method according to claim 1, wherein a rotational relative movement is performed between the plastic pipe and the heater about a longitudinal axis of the plastic pipe and the first and second temperature differences between the neutral zone and the compression zone as well as the expansion zone are caused by variation of a rotational speed of the plastic pipe and/or a radiation intensity of the heater.

8. The method according to claim 1, wherein the introduction of the bending forces onto the holding areas arranged at a distance from the bending area on the plastic pipe is carried out when the expansion zone has reached a thermoplastic state by heating above the material-specific glass transition temperature.

9. An apparatus for carrying out the method according to claim 1, wherein a fixture for fixing the plastic pipe and a heater for heating the plastic pipe are arranged on a machine frame, and wherein the fixture is designed for a rotational relative movement of the plastic pipe with respect to the heater or wherein the heater is designed for a rotational relative movement with respect to the fixture and with a drive for providing the relative movement and with a controller for a variation of a rotational speed of the drive and/or for a variation of an energy flow from the heater onto the plastic pipe.

10. The apparatus according to claim 9, wherein a second fixture is associated with the fixture and that the fixtures are arranged at a distance from one another on the machine frame, an wherein the heater is arranged in a region between the two fixtures and wherein at least one of the fixtures is assigned an actuator which is designed to initiate a relative movement between the two fixtures, the controller being connected to the heater and to the moving device and being designed to control the heater and to control the actuator.

Description

[0026] An advantageous embodiment of the invention is shown in the drawing. Here shows:

[0027] FIG. 1 a purely schematic sectional view of a plastic pipe before a bending process is performed,

[0028] FIG. 2 a purely schematic sectional view of the plastic pipe after a bending operation has been performed,

[0029] FIG. 3 a schematic front view of a bending apparatus for performing the bending process for the plastic pipe according to FIGS. 1 and 2,

[0030] FIG. 4 a schematic top view of the bending apparatus as shown in FIG. 3,

[0031] FIG. 5 a schematic top view of the plastic pipe and a heating source associated with the plastic pipe,

[0032] FIG. 6 a schematic front view of the plastic pipe received in the bending apparatus with two associated heating sources, and

[0033] FIG. 7 a schematic front view of a second type of bending apparatus, in which the plastic pipe is heated by a single heating source while the plastic pipe performs a rotational relative movement with respect to the heating source.

[0034] A plastic pipe 1 shown schematically in FIGS. 1 and 2 symbolically represents a large number of differently shaped and differently profiled plastic pipes, which may possibly be provided with a connection piece at least at one end region. For example the plastic pipe 1 has a circular-cylindrical cross section before a bending process is performed and the plastic pipe 1 extends with this circular-cylindrical cross section along a straight extension line 2 as shown in FIG. 1.

[0035] The plastic pipe 1 has an inner diameter 3, which is bounded by a circularly shaped pipe wall 4, whereby a wall thickness 5 of the pipe wall 4 is exemplary constant over the entire circularly shaped cross-section. The plastic pipe 1 is preferably made of a thermoplastic material such as polyethylene (PE), polypropylene (PP) or polyvinyl chloride (PVC). In particular the plastic pipe 1 is produced seamlessly in a plastic extrusion process.

[0036] As an example, it is intended that the plastic pipe 1 should be plastically deformed in a bending area 6 in order to be able to use the plastic pipe, just for example, in a cooling system not shown, in particular in a motor vehicle. Therefore the plastic pipe 1 has be transferred from the straight-line configuration of FIG. 1 to a curved configuration according to FIG. 2, whereby a pipe cross-section of the plastic pipe 1 shall be at least substantially constant along the extension line 2 after the bending method has been carried out. Furthermore, an at least substantially constant wall thickness 5 for the pipe wall 4 shall be ensured over the entire extension of the plastic pipe 1 even after the bending method has been carried out. Here it is provided that the plastic pipe 1 is to be bent with a bending radius 7 around a center of curvature 8, whereby the bending radius 7 is larger than the inner diameter 3 of the plastic pipe 1 and is therefore arranged outside the plastic pipe 1.

[0037] To perform the bending process, it is intended to accommodate the plastic pipe 1 as shown in FIG. 1 in a bending apparatus 10 shown in FIGS. 3 and 4. The bending apparatus 10 comprises a base plate 15, on which a first clamp 16 and a second clamp 17 are arranged. The first clamp 16 is fixed to the base plate 15 and is adjustable to reliably fix an end area 11 of the plastic pipe1. The second clamp 17 is also adjustable to reliably fix an end area 12 of the plastic pipe 1. In addition, the second clamp 17 is movably mounted on the base plate 15 and is coupled to an actuator (not shown), which is designed to perform a pivoting movement of the second clamp 17 relative to the first clamp 16.

[0038] Furthermore, the bending apparatus 10 comprises a heater 20, which is designed for a heating of the bending area 6 of the plastic pipe 1 and which comprises a first heating source 21 and a second heating source 22, which are described in detail below in connection with the FIGS. 5 and 6. As an example, the two heating sources 21 and 22 are each mounted on linear guides 23, 24, which allow a linear movement of the respective heating source 21, 22 with respect to the base plate 15 and can thus be moved from a functional position as shown in FIG. 3 to a rest position close to the base plate 15. Each of the heating sources 21 and 22 comprises a multitude of light sources, in particular laser diodes, which are designed to provide electromagnetic radiation for the local heating of the plastic pipe 1, as shown in FIG. 6.

[0039] Due to the dimensioning of the two heating sources 21 and 22 and the light sources arranged thereon, it results from the illustration in FIG. 6 that each of the heating sources 21 and 22 is designed to provide a beam of radiation 25 which is only schematically shown and which has a longitudinal extension 26 along the extension line 2 shown in FIG. 5 and a transverse extension 27 transverse to the extension line 2 shown in FIG. 6. As can be seen from the illustrations in FIGS. 5 and 6, the beam of rays 25 determines a surface section on the plastic pipe 1, also referred to as the interaction area 28, which is defined by the fact that electromagnetic rays of the beam of rays 25 impinge directly on an outer surface 29 of the plastic pipe 1. In this interaction area 28, the beam of rays 25 causes local heating of the plastic pipe 1, depending on the material of the plastic pipe 1 on the surface and/or in the depth of the pipe wall 4. It is intended that in a central section of the interaction area 28, which extends along the extension line 2, a stronger heating occurs due to the almost perpendicular orientation of the electromagnetic rays compared with edge areas of the interaction area 28, since the rays of the beam of rays 25 impinge on the edge areas at an angle to the outer surface 29 and the rays are at least partially reflected, so that only a reduced heating occurs here.

[0040] Since the material of the plastic pipe 1 has at least a certain thermal conductivity, zones of the plastic pipe 1 that border on the interaction area 28 are also heated, whereby a rapid temperature drop occurs outside the interaction area 28 due to the rather limited thermal conductivity of the plastic pipe 1.

[0041] A schematic temperature distribution over the cross section of the plastic pipe 1 is shown in FIG. 6, whereby a distance 31 of a temperature line 30 to the pipe wall 4 at least qualitatively represents the respective temperature of the respective pipe wall section. As an example, heating of the plastic pipe 1 is provided in such a way that, due to the interaction of the beam of rays 25 with the plastic pipe 1, a process temperature of the pipe wall in a compression zone 32 as well as in an expansion zone 33 is above a material-specific glass transition temperature for the material of the plastic pipe 1, whereas a process temperature of the pipe wall in neutral zones 34, 35 is below the material-specific glass transition temperature. As an example, a first temperature difference between the neutral zone 34 and the compression zone 32 of the bending range 6, which is determined between a measuring point 40 and a measuring point 41, is approx. 50 degrees Celsius. Furthermore, a second temperature difference between the neutral zone 35 and an expansion zone 33, which is determined between a measuring point 42 and a measuring point 43, is exemplarily approx. 60 degrees Celsius. A temperature difference between measuring points 41 and 42 is thus approx. 10 degrees Celsius.

[0042] By specifically heating the bending area 6 of the plastic pipe 1, the compression zone 32 and the expansion zone 33 are thermoplastically deformable, while the neutral zones 34 and 35 are thermoelastically deformable. As a result this has the effect that neither cracking in the expansion zone 33 nor undulation in the compression zone 32 occurs on plastic pipe 1 during the bending movement when the deformation process is carried out. The bending movement is indicated by the dashed lines in FIGS. 3 and 4 and is carried out in a swivel plane 36 by swiveling the clamp 17 relative to the clamp 16. Rather, the temperature distribution in the plastic pipe 1, as caused by the heating sources 21 and 22, ensures that the neutral zones 34, 35 are at least almost exclusively elastically deformed and thereby exert a stabilizing effect on the compression zone 32 and the expansion zone 33, which are at least predominantly plastically deformed.

[0043] To carry out a bending process, the following procedure may be provided: in a first step a plastic pipe 1 with a straight extension line 2 is inserted into the bending apparatus 10 and fixed there with the aid of the two clamps 16, 17. Then, the two heating sources 21 and 22 are activated so that the plastic pipe 1 is heated locally both with respect to its extension along the extension line 2 and with respect to its outer surface 29. The heating is carried out until the plastic pipe 1 has reached its material-specific glass transition temperature in the compression zone 32 and in the expansion zone 33, while in the neutral zones 34 and 35 there is a temperature at which it is guaranteed that the material-specific glass transition temperature is not reached there. Subsequently, the two heating sources 21 and 22 are moved with the aid of the linear guides 23 and 24 from the functional position opposite to the plastic pipe 1 into a rest position (not shown) close to the base plate 15, so that subsequently the relative movement of the clamp 16 with respect to the clamp 17 can be performed, at which the bending of the plastic pipe 1 takes place. Subsequently, the plastic pipe 1 is cooled down at least below the glass transition temperature, so that there is no re-deformation of the plastic pipe 1 apart from a possible elastic recovery when the plastic pipe 1 is removed from the holding clamps 16, 17.

[0044] According to another embodiment of a bending apparatus (not shown), it is intended that only that heating source is displaced by means of the associated linear guide which is located in the pivoting range of the plastic pipe to be deformed. The other heating source which heats the expansion zone of the plastic tube remains activated during the bending process and, if necessary, performs a relative movement with respect to the base plate in order to ensure the most uniform heating of the expansion zone of the plastic pipe during the bending process while maintaining a distance from the plastic pipe.

[0045] In an alternative design of a bending apparatus 50, as shown in FIG. 7, the plastic pipe 1 is attached to two rotary bearings 51, 52. Each of the rotary bearings 51, 52 comprises a mandrel, whereby only the mandrel 53 of the rotary bearing 52 is shown in FIG. 7. The mandrels engage with the ends of the plastic pipe1.

[0046] The mandrel 53 is rotatably mounted on the rotary bearings 52 and can perform a rotational movement about a central axis 54 of the plastic pipe 1 by means of a drive not shown in detail. As a result, the initially straight plastic pipe 1 is also set into a rotational movement.

[0047] Furthermore, the bending apparatus 50 comprises a heater 70, which has, for example, a single heating source 71 designed as a hot gas source, which is designed for a lateral supply of a hot gas stream 55 onto the outer surface 29 of the plastic pipe 1.

[0048] As an example, it is provided that an angular velocity for the rotation of the plastic pipe 1 around the central axis 54 is varied in such a way that, assuming at a constant hot gas flow 55 onto the plastic pipe 1, the same temperature distribution is achieved as shown in FIG. 6.

[0049] Subsequently, the rotary bearing 52 can be brought from a position not visible in FIG. 7, in which the mandrel 53 is coaxially aligned with a mandrel (not shown) of the rotary bearing 51, into the bending position for the plastic pipe 1 by a pivoting movement about a pivot axis 57. FIG. 7 shows the rotary bearing 52 in the final position for the bending process as a dashed line.

[0050] For the bending process, care must be taken to ensure correct rotational alignment for the plastic pipe 1 before the swivel movement is performed, so that the compression zone (not shown in FIG. 7) and the expansion zone (not shown in FIG. 7) are each cut in half by a bending plane 56 which is horizontally aligned as shown in FIG. 7 and comprises the central axis 54, while the neutral zones not shown in FIG. 7 are cut in half by a bending plane 56 which is horizontally aligned as shown in FIG. 7 and comprises the central axis 54 above the bending plane 56 are arranged mirror-symmetrically to the bending plane 56.