Title of Invention	"IMPROVED METHOD AND APPARATUS FOR SHAPING THERMOPLASTIC TUBES"
Abstract	\A method and apparatus for forming a bend in a tube 1 of thermoplastic material by heating a pre-formed bend to a pre-determined temperature and maintaining the temperature substantially constant by the pulsed emission of infra-red radiation from one or more infra-red sources 2 in response to the surface temperature of the tube 1 detected by a remote temperature sensor 5,

Full Text

METHOD FOR HEAT SHAPING A BEND IN THERMOPLASTIC TUBES This invention concerns an improved method for heat shaping a bend in thermoplastic tubes'. As used herein, the term "tube" includes hoses, pipes and similar conduits, whether of single or multi-layer construction. A method and apparatus for shaping a thermoplastic tube by contactless heating a pre-formed bend region of the tube with a pulsed emission of infra-red radiation to conform the tube to a required bend configuration followed by cooling to retain the required bend configuration whilst the tube is supported on a former is known. In this prior art method and apparatus, the pulsed emission is effected by switching one or more remote infra-red sources on and off to provide a series of separate pulses of which the duration of each pulse and the interval between successive pulses is timed. For a given pulse duration and pulse interval, the overall number of pulses to achieve the required heating can be calculated. For example, a heating cycle may consist of 20 pulses of which the duration of each pulse is 1.2 seconds and the interval between successive pulses is 2.0 seconds. Although the prior art method and apparatus above-described generally performs satisfactorily, it has been found that such time based control of the heating cycle can cause problems if substantial differences in ambient temperature occur requiring "running changes" to be made to the number of pulses. It is an object the present invention to provide an improved method and apparatus for shaping thermoplastic tubes to remedy this drawback. It solves the problem of time based control of the pulsed emission of infra-red radiation by employing a temperature based control of the pulsed emissions which compensates for changes in the ambient temperature. More particularly, the invention provides a method of forming a ben.d in a tube of thermoplastic material by contactless heating of a pre-formed bend region of the tube with a pulsed emission of in.fra-red radiation to conform the tube to a required bend configuration followed by cooling to retain the required bend configuration whilst the tube is supported on a former characterised by sensing the temperature of the tube and controlling the pulsed emission of infra-red radiation in response to the sensed temperature of the tube for initially heating the tube to a pre-determined temperature and then maintaining the pre-determined temperature substantially constant for conforming the tube to the required bend configuration. Preferably, the tube is heated to the pr.e-determined temperature by a single pu!se of infra-red radiation with one or more subsequent pulses, typically of shorter duration, being used to maintain the pre-determined . temperature substantially constant. Advantageously, the pulsed emission of infra-red radiation is responsive to the surface temperature of the tube. The pulsed emission of infra-red radiation may be'responsive to the surface temperature of the tube at one position. Alternatively, the pulsed emission of infra-red radiation.may be responsive to the average surface temperature of the tube at a plurality of positions, preferably spaced apart circumferentially. Apparatus for carrying out the invented method preferably includes a former for supporting the tube to pre-form a bend region having a required configuration, means for contactless heating of the pre-formed bend region .of the tube with a pulsed emission of infra-red radiation to conform the tube to the required bend configuration, and means for cooling the tube to retain the required bend configuration whilst the tube is supported on the former characterised by means for sensing the temperature of the tube, and means for controlling the pulsed emission of infra-red radiation in response to the sensed temperature of the tube for initially heating the tube to a predetermined temperature and then maintaining the pre-determined temperature substantially constant for conforming the tube to the required bend configuration. Preferably, the sensor means is a remote sensor for producing an output representative of the temperature of the tube and the control means is a controller responsive to the output for controlling at least one infra-red emitter. Accordingly there is provided a method of forming a bend in a tube of thermoplastic material by contactless heating of a pre-formed bend region of the tube with a pulsed emission of infra-red radiation to conform the tube to a required bend configuration followed by cooling to retain the required bend configuration whilst the tube is supported on a former characterized by sensing the temperature of the tube and controlling the pulsed emission of the infra-red radiation in response to the sensed temperature of the tube for initially heating the tube to a pre-determined temperature and then maintaining the predetermined temperature substantially constant for conforming the tube to the required bend configuration. The invention will now be described in more detail by way of example only with reference to the accompanying drawings wherein:- FIGURE 1 shows prior art apparatus for heat forming a thermoplastic tube to a required configuration; FIGURE 2 shows control means for temperature based control operation of the apparatus of Figure 1 in accordance with the method of the present invention; and FIGURE 3 is a graph comparing the prior art time based control of the apparatus of Figure 1 with the temperature based control of the present invention. Referring to the accompanying drawings, a brief description will first be given of a prior art method and apparatus for heat forming a thermoplastic tube 1 with reference to Figure 1 followed by a description of the improvements thereto according to the present invention with reference to-Figures 2 and 3. The apparatus shown in Figure 1 comprises a plurality of infra-red emitters 2 such as tungsten halogen lamps having a peak energy emission at short wavelengths for heating the tube 1 to conform the tube 1to a required configuration and a plurality of outlets 3 for a fluid such as blown air for cooling the tube 1 to retain the required configuration. The emitters 2 and outlets 3 are arranged for localised contactless heating and cooling of pre-formed bend regions of the tube 1 whilst supported on a former jig 4. The number and'position of emitters 2 and outlets 3 can be altered to suit the required configuration of the tube 1. The tube 1 is heated by a pulsed or intermittent emission of infra-red radiation from the emitters 2 which provides a dwell time between successive pulses or bursts of infra-red radiation allowing thermal conduction through the mass of the tube 1. In this way, the thermoplastics material is uniformly heated around the circumference of the tube 1 for conforming to the required configuration without causing the tube wall to collapse. The pulsed or intermittent emission of infra-red radiation is controlled for time based operation of the emitters 2 to set the number and duration, of each pulse or burst of infra-red radiation and the interval between successive pulses or bursts to obtain the desired heating for the wall thickness and thermoplastic material of the tube 1. Referring now to Figure 2, control means is shown for temperature based operation of the emitters 2 to provide a pulsed or intermittent emission of infra-red radiation to heat the tube 1 according to the method of the present invention. The control means includes a temperature sensor 5 for monitoring the surface temperature of the tube 1 and generating an output signal representative of the surface temperature which is fed to a controller 6 for controlling operation of the emitters 2 via an external solid state relay 7. Where the relay 7 controls two or more emitters 2, a heat sink (not shown) may be provided. In this exemplary embodiment, the temperature sensor 5 is an OS37-10-K non-contact adjustable range infra-red thermocouple having a minimum spot size = 13mm and a field of view = 10:1 available, from Omega, and the controller 6 is a CN76000 series microprocessor based temperature controller also available from Omega. The sensor 5 is positioned a distance 10d from the outer surface of the tube 1 where d is the measurement spot diameter and the controller 6 is arranged for operation of the emitters 2 to heat the tube 1 to obtain and maintain a pre-determined surface temperature for a period of time sufficient to conform the tube 1 to the required configuration. For such temperature based control, the tube 1 is initially heated by a single main pulse or burst of infra-red radiation until the pre-determined surface temperature is detected with subsequent supplementary pulses or bursts of infra-red radiation being used to maintain the pre-determined surface temperature substantially constant. The controller 6 switches the emitters 2 on and off according to the surface temperature of the tube 1 detected by the sensor 5 so that changes in the ambient temperature are automatically compensated by adjusting the, duration of the main pulse or burst to achieve the pre-determined surface temperature. The emitters 2 may have 4-axes of movement for adjusting the position of the emitters 2 to heat different tube configurations. For example, the apparatus may be adapted to read an identification code such as a bar code corresponding to each tube configuration and to adjust automatically the position of the emitters 2 using electric motors or pneumatics or hydraulics to the correct position for heating the tube 1. The emitters 2 may be arranged to form more than one bend simultaneously in one stage. Alternatively, the emitters 2 may be arranged to form multiple bends in separate stages with the former jig 4 being indexed or moved by any suitable means such as a conveyor from one stage to the next. Referring now to Figure 3, a graph is shown comparing the temperature based control of the emitters 2 according to the present invention with the time based control of the emitters 2 according to the prior art method to achieve a target surface temperature of approximately 135°C for conforming the tube 1 to the required configuration. As can be seen, with the temperature based control of the present invention, the target surface temperature is achieved in approximately 13 seconds by a single main pulse with supplementary pulses of much shorter duration being used to maintain the target surface temperature substantially constant. In comparison, with the time based control of the prior art, the target surface temperature is achieved in approximately 40 seconds by a plurality of separate pulses each of relatively short duration. As a result, as shown by the shaded area of the graph, much more energy is added to the thermoplastic material of the tube without increasing the overall heating cycle time with temperature based control of each pulse of infra-red radiation according to the method of the present invention compared to the time based control of each pulse employed in the prior art method. Alternatively, for certain applications, the overall heating cycle time may be decreased improving efficiency without reducing quality. Furthermore, by using temperature based control of the pulses, the duration of each pulse and the interval between successive pulses is automatically adapted to the ambient temperature. As a result, problems caused by substantial differences in the ambient temperature are avoided. In addition, by using shorter pulses after the initial long pulse, the predetermined target temperature can be more accurately controlled and the soak time for absorbing the energy to uniformly heat the tube is optimised. As a result, quality control of the heating cycle is greatly improved. The present invention is not limited to the exemplary embodiment above-described and includes modifications to the method and/or apparatus without departing from the general principle of temperature based control of infra-red radiation for conforming a tube of thermoplastic material to a required configuration. We Claim: 1. A method of forming a bend in a tube of thermoplastic material by contactless heating of a pre-formed bend region of the tube with a pulsed emission of infra-red radiation to conform the tube to a required bend configuration followed by cooling to retain the required bend configuration whilst the tube is supported on a former characterized by sensing the temperature of the tube and controlling the pulsed emission of the infra-red radiation in response to the sensed temperature of the tube for initially heating the tube to a pre-determined temperature and then maintaining the pre determined temperature constant for conforming the tube to the required bend configuration. 2. A method as claimed in claim 1, wherein the tube is heated to the pre determined temperature by a single main pulse or burst of infra-red radiation. i • 3. A method as claimed in claim 2, wherein the pre-determined temperature is maintained constant by one or more supplementary pulses or bursts of infra-red radiation. 4. A method as claimed in claim 3, wherein the or each supplementary pulse or burst of infra-red radiation is of shorter duration than the main pulse or burst of infra-red radiation. 5. A method as claimed in any one of the preceding claims, wherein the pulsed emission of infra-red radiation is responsive to the surface temperature of the tube. 6. A method as claimed in claim 5, wherein the pulsed emission of infra red radiation is responsive to the average surface temperature of the tube at a plurality of positions. 7. A method as claimed in claim 6, wherein the plurality of positions are spaced apart circumferentially. 8. A method as claimed in any one of the preceding claims, wherein more than one bend is formed simultaneously. 9. A method as claimed in any one of claims 1 to 7, wherein multiple bends are formed in separate stages. 10. A method of forming a bend in a tube of thermoplastic material substantially as hereinbefore described with reference to the accompanying drawings.

Documents:

2742-del-1996-abstract.pdf

2742-del-1996-claims.pdf

2742-del-1996-correspondence-others.pdf

2742-del-1996-correspondence-po.pdf

2742-del-1996-description (complete).pdf

2742-del-1996-drawings.pdf

2742-del-1996-form-1.pdf

2742-del-1996-form-13.pdf

2742-del-1996-form-19.pdf

2742-del-1996-form-2.pdf

2742-del-1996-form-3.pdf

2742-del-1996-form-4.pdf

2742-del-1996-form-6.pdf

2742-del-1996-gpa.pdf

2742-del-1996-pct-409.pdf

2742-del-1996-petition-137.pdf

2742-del-1996-petition-138.pdf

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