GB1585382A

GB1585382A - Method and apparatus for continuous vulcanising of articles of elastomeric material

Info

Publication number: GB1585382A
Application number: GB24007/77A
Authority: GB
Original assignee: General Engineering Co Ltd
Current assignee: General Engineering Co Ltd
Priority date: 1977-06-08
Filing date: 1977-06-08
Publication date: 1981-03-04
Also published as: IT7849750A0; FR2393669A1; IT1156808B; JPS543890A; DE2824784A1

Description

(54) METHOD AND APPARATUS FOR CONTINUOUS VULCANISING OF ARTICLES OF ELASTOMERIC MATERIAL (71) We, THE GENERAL ENGINEERING COMPANY (RADCLIFFE) LIMffED, a British Company of Bury Road, Radcliffe, Manchester, M26 9UR, 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: This invention concerns a method and apparatus for the continuous vulcanising and cooling of electric cable insulation material and is particularly concerned with the insulation applied to cables which are to be used under conditions of high electrical stress.

It is known to vulcanise insulation material continuously by a process including the steps of advancing the material through a vulcanising chamber containing a heat exchange liquid consisting, for example, of eutectic mixture of inorganic salts such as sodium and potassium nitrates and nitrites, which mixture is stable in the liquid phase over a temperature range of 1500 to 4000 C.

It is also known to use as insulation material natural rubber, SDR, polychloroprene, nitrile rubbers, estereo-elastomers (such as polyisoprene and polybutadiene 1.4 cis) crosslinkable polyethylene or polypropylene and cross-linkable copolymers of ethylene and propylene and the like.

In the case of cable coatings it is essential, particularly where the coating is subjected to high electrical stress to ensure that it has the minimum number and minimum size of voids within which ionisation of gases can take place with consequent failure of the insulation and destruction of the cable. Vulcanisation of the currently used cross-linkable materials to minimise the creation of voids is thus carried out in conditions of high pressure using steam (or more recently nitrogen). The use of gases and in particular steam, as the pressure creating medium has the disadvantage that the medium tends to diffuse into the insulation with the consequent risk, on cooling of the insulation, of the production of voids.

Vulcanisation (cross-linking) has been carried out using a stable liquid medium as the heat exchange liquid in a vulcanising chamber which is straight and generally inclined relative to the horizontal plane although in some instances a catenary form of vulcanising chamber is used. It is, however, also possible to use vertically disposed vulcanisation chambers.

In addition to the vulcanising chamber there ig also provided a cooling chamber for the vulcanised insulation. Such apparatus requires the application of pressure during vulcanisation.

Normally water is used as the cooling medium.

Other forms of continuous vulcanising apparatus are known, for instance there may be provided a vulcanising chamber in which the vulcanising temperature is achieved using radiant heat sources, however the present invention is not concerned with this type of apparatus.

An object ofthe present invention is to provide an apparatus for the continuous vulcanisation and cooling of insulation materials in which the process of continuous vulcanisation and cooling can be carried out in an advantageous manner to result in the production of a cable insulation substantially mitigating the disadvanatages mentioned above.

Thus an apparatus for the continuous vulcanisation of elastomeric insulation material includes a vulcanisation chamber having an inlet and an outlet for the elastomeric material, and adapted to contain a stable vulcanising liquid medium which is an eutectic mixture of inorganic salts there being means for circulating the liquid through the chamber at the requisite vulcanising temperature and pressure, a cooling chamber connected to the outlet from the vulcanising chamber, said cooling chamber being equipped with means for circulating under pressure, a gaseous cooling medium of a kind which does not interfere with the crosslinking action and which does not react with the insulation material, said means including a gas cooling unit and gas circulating pump. The stable vulcanising liquid salt is a eutectic mixture of inorganic salts.

Preferably means is also provided for partially cooling, under pressure, the vulcanised insulation prior to its entry into the gas cooling chamber, said means including a cooling apparatus and circulating means for liquid coolant.

Advantageously the liquid coolant is also a eutectic mixture of inorganic salts, preferably of identical composition to the vulcanising liquid. In one form the cooling liquid is drawn from the circulating liquid vulcanising medium and is cooled prior to entry into a partial cooling chamber located between the vulcanising chamber and the gaseous cooling medium chamber.

Additionally there may be provided (in addition to the gaseous medium cooling chamber) a liquid coolant chamber equipped with means for circulating a cooling liquid therethrough, the liquid coolant chamber being connected to the outlet of the gaseous medium cooling chamber and separated therefrom.

It is still further modification there may be provided a partial cooling chamber between the gaseous medium cooling chamber and the vulcanising chamber, there being a final liquid cooling chamber connected to the outlet of the gaseous medium cooling chamber.

Also according to the present invention there is provided a method of continuously vulcanising an elastomeric insulation material comprising the steps of passing the material through vulcanising chamber containing a stable vulcanising liquid medium which is an eutectic mixture of inorganic salts, which medium is maintained at the requisite vulcanising temperature and at a predetermined pressure and advancing the vulcanised material through a cooling chamber through which is circulated, under pressure, a gaseous cooling medium of a kind which does not interfere with the cross-linking action and which does not react with the insulation material.

Conveniently the method also includes the additonal step of subjecting the vulcanised material to partial cooling in a chamber through which cooled heat exchange liquid is circulated the partially cooled material then being passed through the gaseous cooling medium.

The method according to the invention may alternatively include the step of passing the material, subsequent to subjecting it to the cooling action of the gaseous cooling medium, through a liquid coolant chamber in which liquid coolant is circulated.

The method according to the invention may comprise the steps of passing the material through a vulcanising chamber containing a stable vulcanising liquid salt under pressure, passing the vulcanised material through a partial cooling chamber containing liquid, salt under pressure passing the partially cooled material through a gaseous coolant and subsequently passing the material through a liquid cooling medium.

The invention will now be described further, by way of example only and with reference to the accompanying schematic illustrations in which: Figure 1 shows one form of apparatus for continuously vulcanising an insulating material in the form of an extruded covering of an electric cable; and Figure 2 shows a modification of the apparatus of Figure 1.

In the drawings like parts are indicated by identical reference numerals.

As shown in the drawing there is provided an apparatus including an extruder 10 through which extends a cable 11 to be coated. As the cable 11 passes through a die head 12 of the extruder 10 it is coated with an insulation material and passes througth a vulcanisation chamber 13, a partial cooling chamber 14, a gas cooling chamber 15 and a final liquid cooling chamber 16 from which the insulated cable 17 emerges to be wound onto a cable drum (not shown).

The vulcanising chamber 13 is connected to the die head 12 by means of a connecting tube 18 which is slidably mounted in the inlet end of the vulcanising chamber 13. The tube 18 is slidably connected to the chamber 13 in a gas tight manner and is arranged to be secured to a seal collar 19 of the die head 12, also in a gas tight manner. Vulcanising fluid (referred to below) does not contact the die head 12 since it flows down a conduit 22 (referred to below).

A pressure gas conduit 20 is attached to the tube 18 and serves to create and maintain the requisite pressure in the chamber 13. A similar gas conduit 20a is provided at the downstream end of the chamber 13 (relative to the direction of movement of the cable).

As shown the vulcanising chamber 13 is downwardly inclined from its inlet end to its outlet end. While this chamber 13 is illustrated as being straight it may have a catenary form if desired.

Between the vulcanising chamber 13 and the partial cooling chamber 14 there is provided a connector unti 21 having an axially disposed through bore along which the coated cable passes. Surrounding this through bore are a series of vulcanising fluid supply bores parallel to the connector axis over part of their length and thereafter inclined to the axis to enter the chamber 13 at its cable end. Alternatively the connector unit 21 may be provided with a fluid inlet, surrounding the axial bore, which is of annular form over part of its length, there being a frusto-conical end region which opens into the chamber 13. The chamber 13 is provided, in the region of its cable inlet end, with an outlet conduit 22 for vulcanising fluid and this is connected to a fluid heating and supply tank 23. Downstream (in the cable movement sense) of the connector until 21 is a fluid return line 30 which is also connected to the fluid tank 23. Also connected to the fluid supply tank 23 is a fluid pump 24 by means of which fluid can be pumped to the connector unit 21 through a conduit 25 and thus into the chamber 13. The vulcanising chamber 13 conduits 22 and 25 and tank 23 are preferably jacketed and provided with heating means whereby vulcanising fluid may be heated and maintained at the requisite temperature for vulcanising the insulation during its passage through the chamber 13.

A pump 26a serves to pump a cooling fluid identical to the vulcanising fluid from a heater cooler unit 26 via a conduit 28 and connector unit 29 into chamber 14 and via conduit 27 back to the heater/cooler 26' The cooling fluid return conduit 27 is connected to the partial cooling chamber 14 between the connector unit 29 and the conduit 30.

Downstream (in the cable movement sense) of the connector unit 29 is a fluid return line 30a which is also connected to the heater/cooler unit 26. The cooling chamber 14, conduits 27, 30a and 28 are jacketed and provided with heating means. The heater/cooler 26 is provided with heating and cooling means whereby the cooling fluid may be heated or cooled and maintained at the requisite temperature for partially cooling the insulation during its passage through the chamber 14.

The connector unit 29 is conveniently of the same construction as the connector unit 21 and thus the vulcanised insulation of the cable passes, in use, through the axial bore of the connector 21 into the partial cooling chamber 14 to be partially cooled before passing into chamber 15 through the axial bore of the connector 29. Seals are not required between the chambers 13 and 14 since the cable is, during its passage through these chambers, immersed in the same fluid which, in the vulcanising chamber 13 is normally maintained at a temperature of between 20-300 C. By virtue of the provision of the cooler 26 the cooling fluid is maintained in the chamber 14 ata temperature in the region of 170" C. Since no seals are required to isolate the two chambers one from the other, the insulation is not subjected to contact with a seal and thus cannot be adversely affected.

The vulcanising and partial cooling fluid used is a eutectic mixture of inorganic salts which are stable in the liquid phase over the range of temperatures required for both vulcanisation and pre-cooling of the elastomer.

For example a mixture of potassium nitrite 53%, sodium nitrite 40% and sodium nitrate 7% may be used.

From the connector unit 29 the coated, partially cooled cable passes into the main cooling chamber 15 through which is circulated a gas which does not interfere with the crosslinking action and which does not react with the insulation material. Nitrogen is found to be suitable for the purpose of cooling the insulation material. For the circulation of the gas there is provided a pump 31 connected to a gas cooler 32. From the pump 31 a conduit 33 extends to the end of the chamber 15 adjacent the connector 29 and a similar conduit 34 extends from the cooler 32 to the end of the chamber 15 remote from the connector 29. The cooler 32 is provided with a condensate drain 35.

Between the chamber 15 and the chamber 16 is provided a connector 36 in which may be provided a seal through which the now substantially cooled cable passes. The presence of this seal, due to the amount by which the vulcanised insulation has been cooled, will not adversely affect the cable covering. The final cooling of the cable is achieved in the chamber 16 through which the cooling liquid, preferably water, is circulated by means of a pump 37. In addition to the pump 37 there are provided inlet and outlet conduits 38 and 39 respectively and a cooler 40, the inlet conduit 38 is connected to the chamber 16 at its end remote from the connector 36 and the conduit 39 is connected to the chamber adjacent the connector 36.

To limit loss of cooling liquid there is provided a seal 41 at the end of the chamber 16 from which the cable leaves the apparatus.

In the apparatus described above the flow of vulcanising and cooling liquids is opposite to the direction of travel of the cable but this is not essential.

For example the vulcanising liquid and the liquid coolants may be sprayed onto the cable from nozzles located at spaced intervals along the chambers 13, 14 and 16 if desired. Alternatively the flow of fluids can be in the same direction as the travel of the cable. Figure 2 shows diagramatically an apparatus in which the flow of cooling gas in the main cooling chamber 15 and the flow of cooling liquid in the final chamber 16 are in the same direction as the travel of the cable 17.

As shown partially cooled and coated cable passes from the connector unit 29 through a short tube 46 and connector 45 (similar to connectors 21 and 29) into the main cooling chamber 15 through which a suitable cooling gas is circulated. For the circulation of the gas there is provided a pump 31 connected to a gas cooler 32. From the pump 31 a conduit 33 extends to the connector 45 and a similar conduit 34 extends from the cooler 32 to the end of the chamber 15 remote from connector 45. A further conduit 42 connects the cooler 32 with the tube 46. The cooler 32 is provided with a condensate drain 35.

Between the chamber 15 and the chamber 16 is provided a connector 43 (similar to the connectors 21, 29 and 45) through which the now substantially cooled cable passes. The final cooling of the cable is achieved in the chamber 16 through which cooling liquid, preferably water, is circulated by means of a pump 37.

The pump 37 is connected to cooler 40 and from the pump a conduit 44 extends to the connector 43. The cooling liquid returns to the cooler via the conduit 38 and any liquid coolant which has passed through connector 43 into chamber 15 returns to cooler 40 via conduit 39.

To limit the loss of cooling liquid there is provided a seal 41 at the end of the chamber 16 from which the cable 17 leaves the apparatus. Losses which do occur are made up by forcing cooling liquid into the cooler 40 via conduit 46.

It should also be borne in mind that, while we have described an apparatus in which a partial cooling chamber and a final cooling chamber are disposed one at each end of the gas cooling chamber that either one or both of these chambers may be omitted if desired.

Thus the essential chambers are the liquid salt vulcanising chamber 13 and the gas cooling chamber 15.

WHAT WE CLAIM IS: 1. An apparatus for the continuous vulcanisation of an elastomeric insulation material including a vulcanisation chamber having an inlet and an outlet for the elastomeric material, and adapted to contain a stable vulcanising liquid medium which is an eutectic mixture of inorganic salts, there being means for circulating the liquid through the chamber at the requisite vulcanising temperature and pressure, a cooling chamber connected to the outlet from the vulcanising chamber, said cooling chamber being equipped with means for circulating under pressure, a gaseous cooling medium of a kind which does not interfere with the cross-linking action and which does not react with the insulation material, said means including a gas cooling unit and gas circulating pump.

2. An apparatus as claimed in Claim 1, in which means is provided for partially cooling, under pressure the vulcanised insulation prior to its entry into the gas cooling chamber, said means including a cooling apparatus and circulating means for liquid coolant.

3. An apparatus as claimed in Claim 1 in which there is provided (in addition to the gaseous medium cooling chamber) a liquid coolant chamber equipped with means for circulating a cooling liquid there-through, the liquid coolant chamber being connected to the outlet of the gaseous medium cooling chamber and separated therefrom.

4. An apparatus as claimed in any one of Claim 1 in which there is provided a partial cooling chamber between the gaseous medium cooling chamber and the vulcanising chamber, there being a final liquid cooling chamber connected to the outlet of the gaseous medium cooling chamber.

5. An apparatus as claimed in Claim 1 in which the vulcanising chamber is connected to a die head for extruding the elastomeric material by means of a tubular connecting member slidably mounted on the vulcanising chamber.

6. A apparatus as claimed in Claim 5 in which a pressure gas inlet means is provided on the tubular connecting member.

7. An apparatus as claimed in any one of the preceding claims in which the vulcanising chamber at least is of catenary form.

8. An apparatus as claimed in any one of the preceding claims in which, in use, the flow of fluids in the chambers is counter to the direction of movement of the elastomeric material being vulcanised.

9. The method of continuously vulcanising an elastomeric insulation material through vulcanising chamber containing a stable vulcanising liquid medium which is an eutectic mixture of inorganic salts, which medium is maintained at the requisite vulcanising temperature and at a predetermined pressure and advancing the vulcanised material through a cooling chamber which is circulated, under pressure, a gaseous cooling medium of a kind which does not interfere with the cross-linking action and which does not react with the insulation material.

10. The method as claimed in Claim 9 including the step of passing the elastomeric material through a partial cooling chamber, circulating, under pressure, a liquid coolant prior to gaseous cooling, said liquid coolant consisting of a eutectic mixture of inorganic salts.

11. The method as claimed in Claim 9 including the step of draining liquid from the vulcanising liquid supply, cooling same and circulating it, when cooled, through a partial cooling chamber located between the vulcanising chamber and the gaseous cooling medium chamber.

12. The method as claimed in Claim 9 including the step of passing the material, subsequent to subjecting it to the cooling action of the gaseous cooling medium, through a liquid coolant chamber in which coolant is circulated.

13. The method as claimed in Claim 9 including the steps of passing the material through a vulcanising chamber containing a stable vulcanising liquid salt under pressure, passing the vulcanised material through a partial cooling chamber containing cooled liquid salt under pressure passing the partially cooled material through a gaseous coolant and subsequently passing the material through a liquid cooling medium.

14. Apparatus for the continuous vulcanisation of an elastomeric material substantially as hereinbefore described with reference to and as illustrated in Figure 1 or the apparatus of Figure 1 as modified in Figure 2 of the accompanying drawings.

15. The method of continuously vulcanising an elastomeric material substantially as hereinbefore described with reference to and as illustrated in Figure 1 or the apparatus of Figure 1 as modified in Figure 2 of the accompanying drawings.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. forcing cooling liquid into the cooler 40 via conduit 46. It should also be borne in mind that, while we have described an apparatus in which a partial cooling chamber and a final cooling chamber are disposed one at each end of the gas cooling chamber that either one or both of these chambers may be omitted if desired. Thus the essential chambers are the liquid salt vulcanising chamber 13 and the gas cooling chamber 15. WHAT WE CLAIM IS:

1. An apparatus for the continuous vulcanisation of an elastomeric insulation material including a vulcanisation chamber having an inlet and an outlet for the elastomeric material, and adapted to contain a stable vulcanising liquid medium which is an eutectic mixture of inorganic salts, there being means for circulating the liquid through the chamber at the requisite vulcanising temperature and pressure, a cooling chamber connected to the outlet from the vulcanising chamber, said cooling chamber being equipped with means for circulating under pressure, a gaseous cooling medium of a kind which does not interfere with the cross-linking action and which does not react with the insulation material, said means including a gas cooling unit and gas circulating pump.