Claims
- 1. Method for expanding and conferring a cup shape to a terminal junction segment of biaxially oriented pipes made of thermoplastic by means of a calibration expander able to expand the terminal junction segment, which is preventively heated to a plastic state, by shaping the terminal junction segment to include therein a circumferential annular seat for housing a corresponding sealing gasket within the terminal junction segment, comprising the following phases:heating within a first furnace the terminal junction segment to a differentiated temperature which increases towards the end of the terminal junction segment and which is controlled so that the inner diameter (DN) of the terminal junction segment itself is progressively reduced as temperature increases, which temperature becomes a maximum temperature (Tmax) at the end of the terminal junction segment; further preventively heating, circumferentially dilating and thickening by friction the terminal junction segment simultaneously in a second furnace, the terminal junction segment being heated to a plastic deformation temperature in the second furnace and being circumferentially dilated and thickened by friction by means of an inner rigid element located within the second furnace; heating the calibration expander; progressively and forcedly introducing the heated expander inside the preventively heated terminal junction segment to shape and expand the terminal junction segment; and cooling at least the outer surface of the terminal junction segment shaped by the heated expander prior to extraction of the expander.
- 2. Method according to claim 1, wherein the terminal junction segment of the pipe inside the first furnace, during its differentiated heating, undergoes a phase whereby its length is reduced by a measure, correspondingly increasing the thickness of thermoplastic material in the terminal junction segment.
- 3. Method according to claim 1 wherein, during the forced introduction of the expander in the terminal junction segment, a phase automatically sets in whereby there is a thickening of the terminal junction segment such that the terminal junction segment reaches a final thickness (S2) greater than an initial thickness (S1).
- 4. Method according to claim 1, wherein the maximum temperature (Tmax), located at the inner end of the terminal junction segment inside the first furnace, is such that a minimum inner diameter (Dmin) of the terminal junction segment is greater than a minimum diameter (dmn) of a front end of the expander.
- 5. Method according to claim 1, wherein the expander is heated to a temperature (TM) that is greater than or equal to the maximum temperature (Tmax) located at the end of the terminal junction segment.
- 6. Method according to claim 1, wherein, after the forced introduction of the expander in the terminal junction segment and prior to cooling, an intermediate phase is provided whereby additional direct heat is developed on the terminal junction segment, thereby inducing the terminal junction segment to contract and conform closely to the expander in order to match its shape perfectly.
- 7. Method according to claim 1, wherein the inner rigid element inhibits, at least during the further preventively heating, circumferentially dilating and thickening phase, any possibility of retraction by the terminal junction segment thereby contributing to dimensional stabilization of the terminal junction segment in such a manner as to favor its subsequent introduction on the calibration expander.
- 8. Method according to claim 7, wherein the thickness of the terminal junction segment of the pipe progressively increases during differentiated heating inside the first furnace, undergoing a phase whereby its length (L1) is reduced by a measure (ΔL), during the forced introduction of the expander in the terminal junction segment, and, lastly, during the further preventively heating, circumferentially dilating and thickening phase,wherein during the further preventively heating, circumferentially dilating and thickening phase, a considerable thickening of the terminal junction segment sets in, since the rigid element, with a greater diameter than the inner diameter (DN) of the end of the terminal junction segment, is forcedly and progressively introduced inside the terminal junction segment of the pipe, which is locked in place, in a first direction as the end of the terminal junction segment is blocked by a stop which is fixed with respect to the rigid element and then is retracted, in a second opposite direction while the terminal junction segment prevented from lengthening.
- 9. Method according to claim 7, wherein the maximum temperature (Tmax), located at the end of the terminal junction segment inside the first furnace, is such that a minimum inner diameter (Dmin) of the terminal junction segment is greater than a minimum diameter (dmn) of a front end of the rigid element.
- 10. Method according to claim 7 wherein the rigid element is heated.
- 11. Method according to claim 10 wherein the thickness of the terminal junction segment of the pipe progressively increases during differentiated heating inside the first furnace, undergoing a phase whereby its length (L1) is reduced by a measure (ΔL), during the forced introduction of the expander in the terminal junction segment, and, lastly, during the further preventively heating, circumferentially dilating and thickening phase,wherein during the further preventively heating, circumferentially dilating and thickening phase, a considerable thickening of the terminal junction segment sets in, since the rigid element, with a greater diameter than the inner diameter (DN) of the end of the terminal junction segment, is forcedly and progressively introduced inside the terminal junction segment of the pipe, which is locked in place, in a first direction as the end of the terminal junction segment is blocked by a stop which is fixed with respect to the rigid element and then is retracted, in a second opposite direction, therefrom while the terminal junction segment is prevented from lengthening.
- 12. Method according to claim 7, wherein the further preventively heating, circumferentially dilating and thickening phase occurs at a differentiated temperature, increasing toward the end of the terminal junction segment and with an average value greater than that measurable in the first furnace, in order to facilitate the subsequent introduction of the expander into the terminal junction segment by making progressively more rigid the pipe downstream of the end of the terminal junction segment.
- 13. Method according to claim 12 wherein the rigid element is heated.
- 14. Method according to claim 12, wherein the thickness of the terminal junction segment of the pipe progressively increases during differentiated heating inside the first furnace, undergoing a phase whereby its length (L1) is reduced by a measure (ΔL), during the forced introduction of the expander in the terminal junction segment, and, lastly, during the further preventively heating, circumferentially dilating and thickening phase,wherein during the further preventively heating, circumferentially dilating and thickening phase, a considerable thickening of the terminal junction segment sets in, since the rigid element, with a greater diameter than the inner diameter (DN) of the end of the terminal junction segment, is forcedly and progressively introduced inside the terminal junction segment of the pipe, which is locked in place, in a first direction as the end of the terminal junction segment is blocked by a stop which is fixed with respect to the rigid element and then is retracted, in a second opposite direction, therefrom while the terminal junction segment is prevented from lengthening.
- 15. Method for expanding and conferring a cup shape to the terminal junction segment of biaxially oriented pipes made of thermoplastic material by means of a calibration expander having a front end comprising a long tapered segment able to expand a terminal junction segment, preventively heated to a plastic state, by shaping the terminal junction segment with a circumferential annular seat for housing a corresponding sealing gasket within the terminal junction segment, comprising the steps of:applying a temperature distribution inside a furnace that uniformly increases with the distance from an inlet to the furnace, inserting the terminal junction inside the furnace and heating the terminal junction segment inside the furnace to a corresponding differentiated temperature that increases approaching the end of the terminal junction segment, controlling the differentiated temperature so that the inner diameter (Dmin) of the terminal junction segment itself is progressively reduced as the temperature increases, which temperature becomes the maximum temperature (Tmax) at the end of the terminal junction segment, the maximum temperature (Tmax) being such that the resulting minimum inner diameter (Dmin) of the terminal junction segment must be greater than the minimum diameter (dmin) of the front end of the calibration expander, the terminal junction segment of the pipe spontaneously undergoing a reduction in its length (L1) by a measure (ΔL) with a corresponding increase in its thickness while being heated within the furnace such that the terminal junction segment is tapered and converges toward its end, applying heating means able to heat the calibration expander to a temperature (TM) that is greater than or equal to the maximum temperature (Tmax) located at the end of the terminal junction segment to prevent the expander from removing heat from the terminal junction segment during a subsequent phase of forcibly introducing the calibration expander; forcibly introducing the front end of the calibration expander inside the terminal junction segment which is tapered and converges toward its end to shape and deform the terminal junction segment; and applying means for cooling at least the outer surface of the shaped terminal junction segment prior to the extraction of the calibration expander.
Priority Claims (2)
Number |
Date |
Country |
Kind |
RN98A0002 |
Jan 1998 |
IT |
|
RN98A0006 |
Feb 1998 |
IT |
|
Parent Case Info
This is a divisional of application(s) U.S. Ser. No.(s) 09/259,470 filed on Feb. 26, 1999, now U.S. Pat. No. 6,220,846.
US Referenced Citations (11)
Foreign Referenced Citations (1)
Number |
Date |
Country |
98 83 07633 |
Dec 1998 |
EP |