GB1573574A

GB1573574A - Manufacture of tubular sheaths

Info

Publication number: GB1573574A
Application number: GB51612/77A
Authority: GB
Original assignee: ATO Chimie SA
Current assignee: ATO Chimie SA
Priority date: 1976-12-16
Filing date: 1977-12-12
Publication date: 1980-08-28
Also published as: FR2374149B1; FR2374149A1; DE2756039A1; IT1088777B

Description

(54) IMPROVEMENTS IN AND RELATING TO THE MANUFACTURE OF TUBULAR SHEATHS (71) We, ATO CHIMIE, a French Company, of Tour Aquitaine, 92080 Courbevoie, France, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention is related to apparatus for shaping and calibrating a sheath in a tube-inflating installation for manufacturing substantially tubular extruded sheaths of thermoplastics material which apparatus comprises an internal cooling mandrel.

It is well known that one important problem encountered in the field of manufacturing such sheaths resides in the fact that it is difficult to obtain a sufficient capacity of deformation of the extruded sheath in the molten state, for allowing a satisfactory elevated inflating rate to be applied with a view to conferring the desired mechanical properties to the final product.

In the field of inflating tubular sheaths it is conventional practice to use a tubeextruding die through which a thermoplastic resin which is to be shaped into such sheath is extruded, while the tube thus produced is inflated by an internal pressure and passes along an internal cooling mandrel having a diameter greater than that of said die, which mandrel has an ogive-shaped upstream portion adjoining a cylindrical cooling downstream portion. While passing along the mandrel the extruded sheath is cooled to the final cooling temperature and thus shaped in accordance with its desired definitive diameter. It is very difficult to maintain a precise convenient inflating without causing an excessive deformation.

It is an object of the invention to provide a calibrating and shaping apparatus of the kind defined herein-above, which operates in a particularly reliable manner.

According to the invention there is provided apparatus for shaping and calibrating a sheath in a tube inflating installation for manufacturing substantially tubular extruded sheaths of thermoplastics material, comprising a tube extruding die located in an extruding head and a mandrel substantially coaxial with the said die and adjacent thereto, along which mandrel the extruded sheath can slide, the mandrel having a tapered upstream portion adjoining a cylindrical cooling downstream portion, the apparatus further comprising a sleeve adapted to surround the sheath being extruded, coaxial with the die and the mandrel, and extending axially from a location in the vicinity of the extrusion outlet opening of the die, the sleeve comprising at least one transverse wall member having a central aperture the edge of which surrounds the mandrel and the sheath surrounding the mandrel, and is spaced from them, the arrangement being such that said sleeve defines at least one annular chamber surrounding said sheath upstream of the transverse wall member, the apparatus further comprising at least one opening in the annular chamber, through which air may be withdrawn to reduce the pressure in the chamber and means for adjustably increasing the reduced pressure to a predetermined value.

In a preferred embodiment the abovementioned sleeve is fixed directly to the downstream face of the extrusion head, which face constitutes one of the walls of the chamber.

The sleeve may comprise at least over a portion of its length between two transverse wall members spaced axially along the sleeve, a double wall portion of which the outer wall is provided with openings for connection to pressure-reducing means, while the inner wall is a porous or perforated wall and delimits, together with the sheath, said chamber.

The sleeve may include air inlet means provided with air inlet flow adjusting means and located in the vicinity of the die.

The invention will be described herein after in a more detailed manner with reference to the appended drawing which shows by way of illustration but not of limitation various embodiments of the invention.

Fig. 1 is a schematical sectional view of a portion of a tube blowing or inflating machine for manufacturing extruded tubular sheaths, which installation comprises shaping and calibrating apparatus according to the invention.

Fig. 2 is a view similar to Fig. 1 and shows another embodiment of the shaping and calibrating apparatus of the invention.

The portion of the shaping and calibrating apparatus shown in Fig. 1 comprises an annular die extrusion outlet passage 10 provided in an extrusion head 11; thermoplastic material fed from an extruder (not shown) is extruded through said annular die passage 10 so as to be shaped into a sheath 12.

A cooling mandrel 14 along which said sheath is adapted to pass is arranged coaxially with respect to die 10; mandrel 14 comprises a tapered upstream portion 15 and a cylindrical downstream portion 16 the diameter of which corresponds to the desired final diameter of the sheath to be produced. Mandrel 14 is integrally connected to the extrusion head by a rod 17 one end of which is attached to the upstream portion of the mandrel, while the other end of said rod 17 is located in a central bore of the extrusion head.

Rod 17 contains conduits connecting cooling circuits provided in mandrel 14 to one or more sources of cooling fluid located outside of said mandrel.

In the embodiment shown in Fig. 1 the apparatus further comprises a cylindrical sleeve 20 coaxial with mandrel 14, one end 21 of said sleeve being fixed directly to the downstream face 22 of extrusion head 11, while the other end 23 of said sleeve is provided with a transverse wall member 24.

Wall member 24 has a central aperture 25 which is shaped in such a manner that it surrounds at a certain distance the periphery of the cylindrical portion 16 of the mandrel 14 and the periphery of the sheath surrounding said mandrel.

Thus, the downstream face 22, wall member 24 and the inner wall of sleeve 20 define with the outer peripheral surface of sleeve 12 an annular chamber 27 which is connected to pressure-reducing means (not shown in the drawings) by a conduit 28 extending through the wall of sleeve 20. Due to this arrangement it is possible to establish in chamber 27, and particularly in the zone of the extruded sheath issuing from the extrusion die, a region of reduced pressure around said sheath, which enhances the deformation of the latter, the inside of said sheath being in communication with the atmosphere or possibly submitted to a certain elevated pressure.

Fig. 1 further shows an adjusting means 30 adapted to adjust the valve of the reduced pressure established within the annular chamber 27 defined by the sleeve.

This adjusting means comprises a closed container 31 partially filled with a liquid 33, such as water, and communicating by its upper portion with chamber 27 through a conduit 32. A vertical tube 34 opening into the outer atmosphere extends through the upper wall of container 31 and dips into mass of liquid 33; the immersed portion of tube 34 has a length indicated by d in the drawing. This length d corresponds to the reduction in pressure which is to be created within the sleeve. When this pressure decreases the level of the liquid within tube 34 tends to lower and air will enter the tube, which re-establishes the inital value of the pressure. Thus, it is impossible to establish too low a pressure around the sheath which might lead to an excessive deformation of the sheath.

The reduced pressure thus established within chamber 27 causes the sheath to expand and facilitates its sliding onto mandrel 14.

Aperture 25 may be preferably defined by an iris-diaphragm 36 having an adjustable diameter, whereby a comparatively efficent seal is obtained between the sheath and the edge of aperture 25 or whereby-at least-air is prevented from leaking or entering in this zone, this arrangement further allowing adjustment within certain limits of the pressure within the extruded sheath.

Fig. 2 shows another embodiment of the apparatus according to the invention. In this Figure similar elements are indicated by reference numerals which are identical to those used in Fig. 1.

In this embodiment the shaping and calibrating apparatus according to the invention comprises a sleeve 40 coaxial to extrusion die 10 and a mandrel 14, in a manner similar to the previously described embodiment, said sleeve surrounding a mandrel 14 and sheath 12 sliding along said mandrel.

Sleeve 40 has an upper portion 42 adjacent to the outlet of die 10, which upper portion 42 is connected directly to extrusion head 11 and which is delimited at its lower end by a transverse wall member 43 having a central aperture 44; aperture 44 preferably is provided with an iris diaphragm 45 adapted to surround sheath 12 at a certain annular distance.

Openings 46 are provided in the wall of sleeve 42 and communicate with a collector 47 surrounding said sleeve, the inner spaces of said collector being connected to the other atmosphere through a conduit 48 comprising an adjustable valve 49.

Sleeve 40 further comprises a lower portion 50 constituted by an outer envelope 52 extending from wall member 43 down to a similar wall member 53 adjacent to the cylindrical portion of mandrel 14, said transverse wall member 53 comprising a diaphragm 55; said lower portion of sleeve 40 also comprises an inner envelope 54 coaxial with the previously mentioned envelope, said inner envelope extending between the transverse wall members 43 and 53. It will be seen that this inner envelope 54 defines an annular chamber 57 surrounding extruded sheath 12 and communicating with annular chamber 58 defined by the upper portion 42 around said sheath, the communication between said two annular chambers being established by the annular passage provided by diaphragm 45 surrounding the extruded sheath.

An outer envelope 52 is impervious and provided with pipes 60 distributed over its periphery and connected to a pressurereducing means (not shown), while inner envelope 54 is porous or perforated, said inner envelope being made for example of a porous material such as a sintered metal or alloy. Outer envelope 52 and inner envelope 54 define between them and with wall members 43 and 53 an external annular chamber 61 which communicates directly with one or more pressure-reducing means through pipes 60.

The lower portion of sleeve 40 may comprise only two chambers, such as 57 and 61, respectively, delimited by wall members 43 and 53: however, these two chambers may also each be divided into chambers 57a and 57b, 61a and 61b, respectively, by an intermediate wall member 63 provided by an iris diaphragm 65 as shown in Fig. 2. The pipes 60 connecting chambers 61a and 61b to the pressure-reducing means are indicated by numerals 60a and 60b, respectively.

It will be understood that any convienient number of intermediate wall members such as the one indicated at 63 may be provided.

The device according to Fig. 2 operates in the same manner as previously described with reference to the embodiment shown in Fig. 1. Chambers 61 or 61a and 61b are connected to the pressure-reducing means.

Thus a reduced pressure is progressively established within chambers 57 or 57a and 57b due to the porosity of wall 54.

Furthermore due to the communication established by the iris diaphragm, a reduced pressure is established with respect to the pressure prevailing within the extruded sheath (which latter pressure may be, e.g.

equal to the atmospheric pressure). By conveniently adjusting valve 49 the various iris diaphragms 45, 55 and 65 as well as the amount of pressure reduction provided by the pressure-reducing means (such as vacuum pump, venturi pump) the value of the pressure established, respectively, in the various annular chambers surrounding the extruded sheath, and consequently the forces of deformation acting on said sheath, can be adjusted at will.

It may be convenient, for example, to apply a comparatively low pressure in the upper chamber 58 where the extruded sheath is still in the molten state, while a higher pressure is applied to the zone wherein the sheath is solidifying. In this manner it is possible to monitor easily the operating conditions in such a way that the extruded sheath undergoes a deformation with a convenient predetermined inflating rate, while said sheath is prevented from engaging the inner wall of the sleeve.

It will be understood that one or several devices 30 for adjusting the reduced pressure may be provided in the installation shown in Fig. 2.

WHAT WE CLAIM IS: 1. Apparatus for shaping and calibrating a sheath in a tube inflating installation for manufacturing substantially tubular extruded sheaths of thermoplastic material, comprising a tube extruding die located in an extruding head and a mandrel substantially coaxial with said die and adjacent thereto, along which mandrel the extruded sheath can slide, the mandrel having a tapered upstream portion adjoining a cylindrical cooling downstream portion, the apparatus further comprising a sleeve adapted to surround the sheath being extruded, coaxial with the die and the mandrel, and extending axially from a location in the vicinity of the extrusion outlet opening of the die, the sleeve comprising at least one transverse wall member having a central aperture the edge of which surrounds the mandrel and the sheath surrounding the mandrel, and is spaced from them, the arrangement being such that said sleeve defines at least one annular chamber surrounding said sheath upstream of the transverse wall member, the apparatus further comprising at least one opening in the annular chamber, through which air may be withdrawn to reduce the pressure in the chamber and means for adjustably increasing the reduced pressure to a predetermined value.

2. Apparatus according to Claim 1, wherein the sleeve is fixed directly to the downstream face of the extrusion head, so that said face constitutes one of the walls of the chamber.

3. Apparatus according to Claim I or Claim 2, wherein the sleeve comprises, at least over a portion of its length between two transverse wall members spaced axially along the sleeve, a double wall portion of

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. portion 50 constituted by an outer envelope 52 extending from wall member 43 down to a similar wall member 53 adjacent to the cylindrical portion of mandrel 14, said transverse wall member 53 comprising a diaphragm 55; said lower portion of sleeve 40 also comprises an inner envelope 54 coaxial with the previously mentioned envelope, said inner envelope extending between the transverse wall members 43 and 53. It will be seen that this inner envelope 54 defines an annular chamber 57 surrounding extruded sheath 12 and communicating with annular chamber 58 defined by the upper portion 42 around said sheath, the communication between said two annular chambers being established by the annular passage provided by diaphragm 45 surrounding the extruded sheath. An outer envelope 52 is impervious and provided with pipes 60 distributed over its periphery and connected to a pressurereducing means (not shown), while inner envelope 54 is porous or perforated, said inner envelope being made for example of a porous material such as a sintered metal or alloy. Outer envelope 52 and inner envelope 54 define between them and with wall members 43 and 53 an external annular chamber 61 which communicates directly with one or more pressure-reducing means through pipes 60. The lower portion of sleeve 40 may comprise only two chambers, such as 57 and 61, respectively, delimited by wall members 43 and 53: however, these two chambers may also each be divided into chambers 57a and 57b, 61a and 61b, respectively, by an intermediate wall member 63 provided by an iris diaphragm 65 as shown in Fig. 2. The pipes 60 connecting chambers 61a and 61b to the pressure-reducing means are indicated by numerals 60a and 60b, respectively. It will be understood that any convienient number of intermediate wall members such as the one indicated at 63 may be provided. The device according to Fig. 2 operates in the same manner as previously described with reference to the embodiment shown in Fig. 1. Chambers 61 or 61a and 61b are connected to the pressure-reducing means. Thus a reduced pressure is progressively established within chambers 57 or 57a and 57b due to the porosity of wall 54. Furthermore due to the communication established by the iris diaphragm, a reduced pressure is established with respect to the pressure prevailing within the extruded sheath (which latter pressure may be, e.g. equal to the atmospheric pressure). By conveniently adjusting valve 49 the various iris diaphragms 45, 55 and 65 as well as the amount of pressure reduction provided by the pressure-reducing means (such as vacuum pump, venturi pump) the value of the pressure established, respectively, in the various annular chambers surrounding the extruded sheath, and consequently the forces of deformation acting on said sheath, can be adjusted at will. It may be convenient, for example, to apply a comparatively low pressure in the upper chamber 58 where the extruded sheath is still in the molten state, while a higher pressure is applied to the zone wherein the sheath is solidifying. In this manner it is possible to monitor easily the operating conditions in such a way that the extruded sheath undergoes a deformation with a convenient predetermined inflating rate, while said sheath is prevented from engaging the inner wall of the sleeve. It will be understood that one or several devices 30 for adjusting the reduced pressure may be provided in the installation shown in Fig. 2. WHAT WE CLAIM IS:

1. Apparatus for shaping and calibrating a sheath in a tube inflating installation for manufacturing substantially tubular extruded sheaths of thermoplastic material, comprising a tube extruding die located in an extruding head and a mandrel substantially coaxial with said die and adjacent thereto, along which mandrel the extruded sheath can slide, the mandrel having a tapered upstream portion adjoining a cylindrical cooling downstream portion, the apparatus further comprising a sleeve adapted to surround the sheath being extruded, coaxial with the die and the mandrel, and extending axially from a location in the vicinity of the extrusion outlet opening of the die, the sleeve comprising at least one transverse wall member having a central aperture the edge of which surrounds the mandrel and the sheath surrounding the mandrel, and is spaced from them, the arrangement being such that said sleeve defines at least one annular chamber surrounding said sheath upstream of the transverse wall member, the apparatus further comprising at least one opening in the annular chamber, through which air may be withdrawn to reduce the pressure in the chamber and means for adjustably increasing the reduced pressure to a predetermined value.

which the outer wall is provided with openings for connection to pressurereducing means, while the inner wall is a porous or perforated wall and delimits together with the sheath said chamber.

4. Apparatus according to any of Claims 1 to 3, wherein the central aperture of said at least one transverse wall member is constituted by the aperture of an adjustable iris diaphragm.

5. Apparatus according to any of Claims 1 to 4, wherein the sleeve includes air inlet means provided with air inlet flow adjusting means and located in the vicinity of the die.

6. A shaping and calibrating apparatus substantially as herein described, with reference to Fig. 1 of the accompanying drawing.

7. A shaping and calibrating apparatus substantially as herein described, with reference to Fig. 2 of the accompanying drawing.