GB2100159A

GB2100159A - Apparatus for manufacturing cable having a metal sheath

Info

Publication number: GB2100159A
Application number: GB8210318A
Authority: GB
Original assignee: Cables de Lyon SA
Current assignee: Cables de Lyon SA
Priority date: 1981-04-07
Filing date: 1982-04-07
Publication date: 1982-12-22
Also published as: IT1155508B; FR2503442B1; IT8267462A0; GB2100159B; FR2503442A1; IT8221496V0

Abstract

An apparatus for manufacturing mineral insulated electric cable having a metal sheath includes successive pairs of grooved rolls arranged at 90 DEG to each other. The rolls (5) have grooves whose width and depth decrease progressively from one to the next and the inlet angle of the grooves is 60 DEG , except for the last pair. The cable is annealed between passes, and suffers less deformation per pass than in the past. <IMAGE>

Description

SPECIFICATION An apparatus for manufacturing mineral insulated electric cable having a metal sheath The present invention relates to apparatus for manufacturing electric cable having compressed mineral insulation and a surrounding metal sheath. This is done by preparing a preform whose diameter is much greater than that of the cable, then lengthening the preform in successive passes, between which the preform is anneaied. Such electric cables are su.itable in particular for installations in which high resistance to heat, fire or corrosion is required. The compressed mineral insulation is generally made of magnesia or alumina and the sheath is generally made of stainless steel or nickel-chromium-iron alloy with a high nickel content.

French patent No 1,137,437 already describes apparatus for manufacturing such cable which apparatus has pairs of successive roller cylinders provided with grooves whose width and depth gradually decrease going from one pair to the next. The pairs of cylinders are arranged with their axes alternately in planes at 90 to each other, e.g. alternately in a vertical plane and in a horizontal plane. The groove profiles are shaped like quarter circles.

After each pass, the cross-section of the preform becomes elliptical with a major axis that is alternately horizontal and vertical.

Such apparatus pushes preform material alternately in one direction then in a direction perpendicular thereto, so that a very large amount of work is done on the preform before the final cable is obtained.

Preferred embodiments of the present invention reduce the deformation work necessary to obtain the final cable by reducing the amount of material deformation at each pass.

The present invention provides apparatus for manufacturing a mineral insulated electric cable having a metal sheath from a preform of much greater diameter than that of the final cable, the apparatus including successive pairs of rolling cylinders provided with grooves whose width and depth decrease gradually going from one pair to the next, the axes of the pairs of cylinders are alternatively in planes which lie at 90 from each other, wherein the grooves of the cylinders, except for those of the last pair, have an inlet angle as defined by the angle between the cones which are tangential to their edges, of about 60".

A method and apparatus for manufacturing an electric cable which has a compressed mineral insulation are described hereinafter with reference to the accompanying drawing, in which: Figure 1 illustrates a series of successive rolling mill cylinders.

Figure 1A is an illustration on a larger scale of the groove in one of the cylinders (detail A of Fig. 1).

In the following description, the mineral insulation is magnesia and the sheath is made of stainless steel. The Applicant commercialises cable made from these materials under the trade mark PYROTENAX.

The preform is prepared by a conventional method such as pelletizing at a high pressure or by the method which consists of extruding a cylindrical structure constituted by the mineral insulant and an organic binding agent; cutting said structure into determined lengths; burning off the organic binder; inserting the hot insulant into metal tube designed to serve as a sheath; and inserting the conductor(s).

This method is described in the Applicant's French patent application number 80, 20, 393 filed 23rd September, 1 980.

The preform is stretched so as to jam together the components of the preform; the tube, the mineral insulant and the conductors.

The resulting blank 1 is then made to pass through successive grooves of decreasing width and depth in the rolls of a rolling mill.

The cylinders performing odd numbered operation, such as cylinders 2A, 2B, 4A, 4B, 6A, 6B will, for example, have a horizontal axis and be provided with grooves which tend to reduce the vertical dimension of the blank 1, while the cylinders performing even numbered operations such as cylinders 3 and 5, have vertical axes and serve to reduce the horizontal dimension of the blank 1.

The depths of the grooves preferably decrease in a geometrical progression, and their inlet angle, as defined by the angle of the tangents to their edges, are about 60 , except for the last grooves, which are semi-circular.

While the cylinder 5 has a relatively deep groove 8, the preceding vertical axis cylinders have grooves 8A, 8B, etc. which are successively less deep.

At the end of the last pass through the rolling mill, a substantially cylindrical blank is obtained with a diameter a little larger than the final required diameter for the cable.

The blank is then brought to the required final diameter by a final drawing operation through an orifice so as to obtain a perfectly circular cable.

1. Apparatus for manufacturing a mineral insulated electric cable having a metal sheath from a preform of much greater diameter than that of the final cable, the apparatus including successive pairs of rolling cylinders provided with grooves whose width and depth decrease gradually going from one pair to the next, the axes of the pairs of cylinders are alternatively in planes which lie at 90 from each other, wherein the grooves of the cylinders, except for the those of the last pair, have an inlet angle as defined by the angle between the

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION An apparatus for manufacturing mineral insulated electric cable having a metal sheath The present invention relates to apparatus for manufacturing electric cable having compressed mineral insulation and a surrounding metal sheath. This is done by preparing a preform whose diameter is much greater than that of the cable, then lengthening the preform in successive passes, between which the preform is anneaied. Such electric cables are su.itable in particular for installations in which high resistance to heat, fire or corrosion is required. The compressed mineral insulation is generally made of magnesia or alumina and the sheath is generally made of stainless steel or nickel-chromium-iron alloy with a high nickel content. French patent No 1,137,437 already describes apparatus for manufacturing such cable which apparatus has pairs of successive roller cylinders provided with grooves whose width and depth gradually decrease going from one pair to the next. The pairs of cylinders are arranged with their axes alternately in planes at 90 to each other, e.g. alternately in a vertical plane and in a horizontal plane. The groove profiles are shaped like quarter circles. After each pass, the cross-section of the preform becomes elliptical with a major axis that is alternately horizontal and vertical. Such apparatus pushes preform material alternately in one direction then in a direction perpendicular thereto, so that a very large amount of work is done on the preform before the final cable is obtained. Preferred embodiments of the present invention reduce the deformation work necessary to obtain the final cable by reducing the amount of material deformation at each pass. The present invention provides apparatus for manufacturing a mineral insulated electric cable having a metal sheath from a preform of much greater diameter than that of the final cable, the apparatus including successive pairs of rolling cylinders provided with grooves whose width and depth decrease gradually going from one pair to the next, the axes of the pairs of cylinders are alternatively in planes which lie at 90 from each other, wherein the grooves of the cylinders, except for those of the last pair, have an inlet angle as defined by the angle between the cones which are tangential to their edges, of about 60". A method and apparatus for manufacturing an electric cable which has a compressed mineral insulation are described hereinafter with reference to the accompanying drawing, in which: Figure 1 illustrates a series of successive rolling mill cylinders. Figure 1A is an illustration on a larger scale of the groove in one of the cylinders (detail A of Fig. 1). In the following description, the mineral insulation is magnesia and the sheath is made of stainless steel. The Applicant commercialises cable made from these materials under the trade mark PYROTENAX. The preform is prepared by a conventional method such as pelletizing at a high pressure or by the method which consists of extruding a cylindrical structure constituted by the mineral insulant and an organic binding agent; cutting said structure into determined lengths; burning off the organic binder; inserting the hot insulant into metal tube designed to serve as a sheath; and inserting the conductor(s). This method is described in the Applicant's French patent application number 80, 20, 393 filed 23rd September, 1 980. The preform is stretched so as to jam together the components of the preform; the tube, the mineral insulant and the conductors. The resulting blank 1 is then made to pass through successive grooves of decreasing width and depth in the rolls of a rolling mill. The cylinders performing odd numbered operation, such as cylinders 2A, 2B, 4A, 4B, 6A, 6B will, for example, have a horizontal axis and be provided with grooves which tend to reduce the vertical dimension of the blank 1, while the cylinders performing even numbered operations such as cylinders 3 and 5, have vertical axes and serve to reduce the horizontal dimension of the blank 1. The depths of the grooves preferably decrease in a geometrical progression, and their inlet angle, as defined by the angle of the tangents to their edges, are about 60 , except for the last grooves, which are semi-circular. While the cylinder 5 has a relatively deep groove 8, the preceding vertical axis cylinders have grooves 8A, 8B, etc. which are successively less deep. At the end of the last pass through the rolling mill, a substantially cylindrical blank is obtained with a diameter a little larger than the final required diameter for the cable. The blank is then brought to the required final diameter by a final drawing operation through an orifice so as to obtain a perfectly circular cable. CLAIMS

1. Apparatus for manufacturing a mineral insulated electric cable having a metal sheath from a preform of much greater diameter than that of the final cable, the apparatus including successive pairs of rolling cylinders provided with grooves whose width and depth decrease gradually going from one pair to the next, the axes of the pairs of cylinders are alternatively in planes which lie at 90 from each other, wherein the grooves of the cylinders, except for the those of the last pair, have an inlet angle as defined by the angle between the cones which are tangential to their edges, of about 60 .

2. Apparatus for manufacturing a mineral insulated cable, substantially as herein described with reference to and as illustrated in the accompanying drawing.