GB1562186A

GB1562186A - Heat-recoverable article

Info

Publication number: GB1562186A
Application number: GB3458475A
Authority: GB
Original assignee: Raychem Corp
Current assignee: Raychem Corp
Priority date: 1975-08-20
Filing date: 1975-08-20
Publication date: 1980-03-05
Also published as: FR2321754A1; CA1092766A; FR2321754B1

Description

(54) HEAT-RECOVERABLE ARTICLE (71) We, RAYCHEM CORPOR ATION, a Body Coporate, organised according to the laws of the State of California, United States of America, of 300, Constitution Drive, Menlo Park, California 94025, United States of America, 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 relates to heat-recoverable articles, more especially to such articles for use in protecting the ends of a length of cable, and to processes for their use.

When electric cables, for example power or telecommunications cables, having a number of conductors surrounded by a jacket of insulating material are manufactured, they are frequently cut into lengths suitable for transport and storage on a former, for example a spool. The cut ends are protected against attack by water or other damaging media, and against mechanical injury by a covering which may be a wrapping of a tape or by a heat-shrinkable "end-cap." The end cap is a generally tubular article, having one closed and one open end, which is capable of shrinking radially when heated above a certain temperature or temperature range. The article is made, for example, by moulding a thermoplastic composition containing a chemical crosslinking agent, in an appropriate shape having a diameter slightly smaller than the smallest diameter of cable in the range of sizes for which it is to be used. The crosslinked moulded article is then heated, expanded by air or mechanical pressure, cooled while maintaining the pressure, and then the pressure is released. In use, the article is placed over the end of the cable to be protected, and heated to cause it to shrink.

The inner surface of the article may, if desired, be provided with a coating that assists in bonding the cap to substrate cable, and in preventing moisture ingress, for example a hot melt adhesive, or a non-crystalline layer of, for example, mastic.

Although the use of a heat-shrinkable "end-cap" has been accepted, there remains a problem, which is also present when other means of protecting cable ends, for example with tape-wrapping, are used.

The problem generally arises from the nature of the winding of the conductors during cable manufacture. The conductors are each present in the form of a helix, and have a tendency to unwind during transport, storage, or other processes which allow relaxation, with a resulting increase in length, relative to the more stable length of the jacket insulation. As the end covering is firmly attached to the outside of the jacket, rather than to the inner conductors, the conductors will force their way through the closed end of the protective covering, allowing moisture ingress, etc.

The present invention provides a heat-shrinkable hollow article an open end, the wall defining its internal cavity being shaped to provide stop means projecting into the internal cavity at a position or positions between the open end of the cavity remote from the open end the stop means being dimensionally heat-unstable and retracting from the cavity on heating. The stop means, otherwise known as locating or positioning means, is or are so positioned and of such dimensions that when a substrate, for example, the end of a cable, is inserted into the open end it does not occupy the whole length of the cavity but instead abuts the stop means. After heating the hollow article to cause it to shrink about the substrate, a space will remain between the end of the article and the end of the cavity remote from the open end, which remote end will normally be a closed end wall of the cavity.

Advantageously, the top means is or are dimensionally heat-unstable with a dimensionally stable form which does not project into the internal cavity of the article.

It will be appreicated that the form and location of the stop means may vary, depending inter alia on the exposed extent of growth of the conductor relative to the insulation and the wall thickness of the jacket as a proportion of the diameter of the cable.

The stop means is or are advantageously formed in the inner wall of the article during the stage of manufacture that includes expansion. For example, while the article is being heated and subjected to forces to expand it, the wall may be deformed inward at the location(s) where stop means is or are required, and the deformation retained until the article has been cooled. The stop means may take the form of finger-like projections in the circumferential wall, an annular ridge in the end or circumferential wall (formed, for example, by making a corresponding groove in the outer surface), one or more embossments or dimples in the inner surface of the closed end wall, steps or ridges, recoverable or otherwise as required, in the internal diameter of the article, etc. Since the stop means are dimensionally unstable, at least in part, they will retract on heating, thus allowing the growth in conductors to take place with reduced possibilities of damage to the protecting end cap.

The present invention also provides a process for covering a substrate, for example the end of a cable, which comprises so positioning the article of the invention and the substrate that the stop means and a portion of the substrate are in abutment, and heating the article to cause recovery about the substrate and retraction of the stop means so that the stop means is no longer in abutment with the portion of the substrate. Advantageously, the open end region of the article is heated to cause it to recover first, so that the end grips the substrate to prevent or inhibit relative movement of article and substrate when the stop means changes dimension, as the remainder of the article is heated.

The invention also provides a substrate covered by the article or the process of the invention, especially a cable covered by an end-cap.

The heat-recoverable article may be made for example of any of the materials known to be capable of being rendered heat-recoverable, for example those described in United States Patents Nos.

2,027,%2, 3,086,242 or 3,597,372 the disclosures of which are incorporated by reference herein. The materials may be crosslinked, by radiation or by chemical means, and may contain any of the usual additives, for example, fillers, pigments, flame-retardants, fungicides and antioxidants. The inner surface may be coated with suitable lining material, and the outer surface may have means, for example thermochrome paint, to indicate when the article has reached a desired temperature.

Several forms of article constructed in accordance with the invention will now be described in greater detail, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a cross-section of a first form of article constructed in accordance with the invention, in position for recovery over a cable end; Figure 2 is a cross-section of the article of Figure 1 after recovery; and Figures 3, 4 and 5 illustrate other shapes of articles constructed in accordance with the invention.

Referring now more especially to Figures 1 and 2, a heat-shrinkable end-cap, indicated generally by the reference numeral 1, comprises a circumferential wall 2 and an end wall 3, the latter having in its dimensionally heat-unstable form a boss or dimple 4 extending axially inwards to form a stop or positioning or locating means for the end of a cable, indicated generally by refence numeral 5, comprising a jacket 6 and a plurality of individually insulated conductors 7, wound helically.

As illustrated by Figures 1 and 2, the end cap is originally positioned over the cable 5 so that the dimple 4 is in abutment with the ends of the central conductors 7. The end cap is then heated to cause it to shrink, the open end preferably being shrunk first, and the dimple 4 recovers so that the end wall 3 becomes generally planar, leaving a gap 8 into which the conductors 7 may safely "grow" during handling.

Figures 3, 4 and 5 illustrate other forms of the cap 1. In Figure 3, an annular groove and ridge 31 are provided in the end wall 3.

In Figure 4, a dimple 41 is provided, deeper than in Figure 1, to allow for greater growth, while in Figure 5, a plurality of conical projections 51 into the interior provides a stop that locates the end of a cable in the cap.

It will be appreciated that the provision of heat retractable locating or stop means in heat-recoverable articles has applications other than those described herein for use with end caps for electrical cables, and the scope of the invention includes the use of any substrate.

WHAT WE CLAIM IS: 1. A heat-shrinkable hollow article having an open end affording access to an internal cavity, the wall defining the internal cavity being shaped to provide stop means projecting into the cavity at a position or positions between the open end and the end of the cavity remote from the open end, the stop means being dimensionally heatunstable and retracting from the cavity on heating.

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

Claims

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

depending inter alia on the exposed extent of growth of the conductor relative to the insulation and the wall thickness of the jacket as a proportion of the diameter of the cable.

The stop means is or are advantageously formed in the inner wall of the article during the stage of manufacture that includes expansion. For example, while the article is being heated and subjected to forces to expand it, the wall may be deformed inward at the location(s) where stop means is or are required, and the deformation retained until the article has been cooled. The stop means may take the form of finger-like projections in the circumferential wall, an annular ridge in the end or circumferential wall (formed, for example, by making a corresponding groove in the outer surface), one or more embossments or dimples in the inner surface of the closed end wall, steps or ridges, recoverable or otherwise as required, in the internal diameter of the article, etc. Since the stop means are dimensionally unstable, at least in part, they will retract on heating, thus allowing the growth in conductors to take place with reduced possibilities of damage to the protecting end cap.

The present invention also provides a process for covering a substrate, for example the end of a cable, which comprises so positioning the article of the invention and the substrate that the stop means and a portion of the substrate are in abutment, and heating the article to cause recovery about the substrate and retraction of the stop means so that the stop means is no longer in abutment with the portion of the substrate. Advantageously, the open end region of the article is heated to cause it to recover first, so that the end grips the substrate to prevent or inhibit relative movement of article and substrate when the stop means changes dimension, as the remainder of the article is heated.

The invention also provides a substrate covered by the article or the process of the invention, especially a cable covered by an end-cap.

The heat-recoverable article may be made for example of any of the materials known to be capable of being rendered heat-recoverable, for example those described in United States Patents Nos.

2,027,%2, 3,086,242 or 3,597,372 the disclosures of which are incorporated by reference herein. The materials may be crosslinked, by radiation or by chemical means, and may contain any of the usual additives, for example, fillers, pigments, flame-retardants, fungicides and antioxidants. The inner surface may be coated with suitable lining material, and the outer surface may have means, for example thermochrome paint, to indicate when the article has reached a desired temperature.

Several forms of article constructed in accordance with the invention will now be described in greater detail, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a cross-section of a first form of article constructed in accordance with the invention, in position for recovery over a cable end; Figure 2 is a cross-section of the article of Figure 1 after recovery; and Figures 3, 4 and 5 illustrate other shapes of articles constructed in accordance with the invention.

Referring now more especially to Figures 1 and 2, a heat-shrinkable end-cap, indicated generally by the reference numeral 1, comprises a circumferential wall 2 and an end wall 3, the latter having in its dimensionally heat-unstable form a boss or dimple 4 extending axially inwards to form a stop or positioning or locating means for the end of a cable, indicated generally by refence numeral 5, comprising a jacket 6 and a plurality of individually insulated conductors 7, wound helically.

As illustrated by Figures 1 and 2, the end cap is originally positioned over the cable 5 so that the dimple 4 is in abutment with the ends of the central conductors 7. The end cap is then heated to cause it to shrink, the open end preferably being shrunk first, and the dimple 4 recovers so that the end wall 3 becomes generally planar, leaving a gap 8 into which the conductors 7 may safely "grow" during handling.

Figures 3, 4 and 5 illustrate other forms of the cap 1. In Figure 3, an annular groove and ridge 31 are provided in the end wall 3.

In Figure 4, a dimple 41 is provided, deeper than in Figure 1, to allow for greater growth, while in Figure 5, a plurality of conical projections 51 into the interior provides a stop that locates the end of a cable in the cap.

It will be appreciated that the provision of heat retractable locating or stop means in heat-recoverable articles has applications other than those described herein for use with end caps for electrical cables, and the scope of the invention includes the use of any substrate.

WHAT WE CLAIM IS:

1. A heat-shrinkable hollow article having an open end affording access to an internal cavity, the wall defining the internal cavity being shaped to provide stop means projecting into the cavity at a position or positions between the open end and the end of the cavity remote from the open end, the stop means being dimensionally heatunstable and retracting from the cavity on heating.

2. An article as claimed in claim 1,

wherein the remote end is a closed end.

3. An article as claimed in claim 1 or claim 2, wherein the stop means has or have a dimensionally heat-stable form that does not project into the internal cavity.

4. An article as claimed in any one of claims 1 to 3, wherein the stop means comprise projecting fingers, an annular ridge, an embossment or a step in the cavity wall.

5. An article as claimed in claim 1, substantially as described with reference to and as illustrated by any one of Figures 1, 3 4 or 5 of the accompanying drawings.

7. A process for preparing a covered substrate, which comprises positioning an article as claimed in any one of claims 1 to 6 about the substrate with a portion of the substrate in abutment with the stop means and heating the article to cause shrinkage about the substrate.

8. A progress as claimed in claim 7, wherein the open end region of the article is heated first.

9. A substrate, whenever covered by a process as claimed in claim 7 or claim 8.

10. A process for covering the end of a cable which comprises positioning over the end a heat-shrinkable cap having heat-retractable stop means projecting into its internal cavity at a position between the open and closed ends of the cap so that the end of the cable abuts the stop means, and heating the cap to cause it to shrink about the cable end and the stop means to retract so that at least a part of the end of the cable no longer abuts the stop means.

11. A process as claimed in claim 10, wherein the stop means are as specified in any one of claims 3 to 5.

12. A cable end covered by a process as claimed in claim 10 or claim 11.