CA1167225A

CA1167225A - Making shrink-fit hoses

Info

Publication number: CA1167225A
Application number: CA000364244A
Authority: CA
Inventors: Hermann U. Voigt; Gerhard Klein; Hans M. Schmidtchen
Original assignee: Kabelmetal Electro GmbH
Current assignee: Kabelmetal Electro GmbH
Priority date: 1979-11-08
Filing date: 1980-11-07
Publication date: 1984-05-15
Also published as: DE2945048A1

Abstract

ABSTRACT OF THE DISCLOSURE An extruded and cross-linked polymer hose is heated and expanded in steps, the expansion steps being interspersed with sizing steps of minimal contact with the hose. The expansion is carried out by pressure differential between the interior and exterior of the hose, inside a low-pressure water tank.

Description

r ~ACKGROUND OF THE INVENTION
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The present invention relates to the making of shrink-hoses from ex-trudable material, and by means of extrusion; more particularly, the invention relates to the subsequent expanding of such hoses.
Austrian Patent 188,510 proposes a method of extruding or injection-molding a thermoplastic hose of a relatively small diameter, ~eating and expand-ing that hose under pressure while it is forced against the inside wall of a heating duct, following which the hose is cooled so that the expanded state l'freezes" the dimensions of the hose while subsequent heating will cause it to shrink again.
This known method has a number of disadvantages; among them, a limita-tion on the material employed. The material should not have the tendency of adhering to other surfaces, such as the heating duct, unless the Lriction is, additionally, reduced through appropriate separation and lubrication coatings.
Since the expanded material is coated, such adhesion can readily develop even in material that has no adhesive tendencies at room temperatures. Even without such adhering tendency, the approach of permitting the soft, expanded hose to slide along the coating tube is detrimental to the surface texture of the hose;
it may even develop weak spots which may later develop into a source of corro-sion of the object under (or, better, inside) the hose.
In a companion application by one of us and others, Serial ~o.
361,652 , it has been suggested to use a polymer as base material, to graft upon the macromolecules of the polymer a low molecular compound such as organo silane, and to obtain cross-linking in the presence of moisture - to be complet-ed prior to expanding the material from the shape given to it during the cross-linking, or earlier. This method was found to be highly suitable, and the present invention relates also to an improvement of the expansion of a See also U.S. Patent 4,366,107 ~ ~ .

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hose made in accordance with the application.
DESCRIPTION O~ THE INVENTION
The present invention seeks to provicle a new and improved method and equipment for making shrink-fit-type hoses.
In accordance with the preferred embodiment of the present invention, it is suggested to expand a hose as made in a plurality of sequential expansion steps~ under utilization of a pressure differential between the interior and the exterior of the hose and without external contact of the hose with a surface, each step followed by a sizing step, whereby sequential sizing steps provide for larger outer dimensions. Thereafter, the expanded hose is cooled in order to, thereby, retain its expanded shape. The expansion is preferably carried out by means of a low-pressure liquid bath, primarily for concurrently and continuously lubricating ; the expanded hose as it passes slidingly through a plurality of sizing disks; the liquid film that remains on the hose separates the hose's material from the disks.
Thus in a first aspect this invention provides in a method of making shrink hoses, wherein a hose is extruded, the improvement ~; 20 comprising:
providing a pressure differential between the inside and outside of the hose, a lower pressure being on ~he ou~side, in order to obtain a stepwise expansion of the hose, each expansion step increasing the inner diameter of the hose; and providing a plurality of sizing steps respectively in ; between sequentially occurring expansion steps, so that each portion of the hose is subjecked to alternating expansion and sizing :
for stepwise increasing the diameter of the hose.

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In a second aspect this invention provides an apparatus for making a shrink hose, the hose having been extruded, comprising;
means for heating and maintaining the hose at an elevated operating temperature;
container means, disposed downstream from the means for heating, and through which the hose passes;
a plurality of sizing disks in the container means disposed therein spaced-apart relation, the disks having apertures and being placed so that the hose passes through the apertures, the apertures respectively having diameters which increase in downstream direction.
In the preferred form, it is practical to provide the expansion in steps that follow each other in immediate sequence so that the plurality of individual expansionary steps results, in effect, in a steady expansion; sizing steps are consequently being interposed. Alternatively, one may carry out the expansion in spatial and, timewise, separated steps whereby the radial dimensions, following each sizing, are kept constant for a certain length of the hose's travel path until the next expansion is provided, and so forth. This approach will depend upon the material and the dimensions; it may not be advisable to proceed too rapidly, particularly not with relatively thin~walled hoses.
Prior to expansion, the hose should be reheated, e.g. by means of a liquid bath (consisting of water and glycerin); infra-red heating, or high fre-`~ ~
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quency. In the case o~ a very considerable overall diameter increase, it may be advisable to increase heating of the hose in downstream direction. As far as the pressure differential is concerned, mere low, external pressure may suf-fice; but slightly active pressurization of the interior of the hose (support pressure) may be advisable; particularly so if, along the travel path of the integral hose, the tendency of collapse develops when the hose is too soft, has rather thin walls, and so forth.
The main aspect of the invention is the fact that the expansion per se is carried Ollt without any external sliding support against ~hich the hose is forced. Rather, the hose expands freely and is sized by a plurality of nar-row sizing disks. Thus, sizing is preferably carried out by means of spaced-apart aperture disks whose apertures increase in downstream direction; the ex-pansion steps are carried out respectively behind and ahead of the disks. The disks should also be spaced farther in downstream direction in order to avoid binding or even tearing of the hose because the hose's material is by and large quite soft. The procedure proposed here ensures high-quality hoses of pleasing appearance withou-t surface defects.
In the preferred form of practicing the invention, the hose should have cross-linked prior to expansion. While applicable to any kind of hose ; 20 material, the present expansion method and equipment is, as to the best mode of càrrying out the invention, to be practiced in conjunction with the method set forth in Canadian Application 361,652 mentioned above.
DESCRIPTION OF THE DRAWINGS
While the specification concludes with claims, particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed that the invention, the objects and features of the invention,

-3-' ~, , and further objects, features and advantages thereof, will be better understood from the following description taken in connection with the accompanying draw-ings, in which:
Figure l is a schematic view of an expanding device in accordance with the preferred embodiment of the invention;
Figure 2 is an enlarged, schematic section view of a detail in Figure ~igure 3 is a schematic view of a modified device; and Figure 4 is a schematic view of a still further modification.
Proceeding now to the detailed description of the drawings, it is assumed that a hose l has been made of any kind of material which is suitable for obtaining a shrink-fit or heating. In the preEerred form the hose may have been made as described in Canadian Patent Application 361,652. However, for purposes of the present invention, the hose may be of any kind of polyethylene, or even polyvinylchloride. The PE may be cross-lin~ed or not. Also, as the hose leaves, e.g., an extruder, it is passed through a vacuum chamber with sizing rings in order to provide the hose with the desired dimensions which it is to memorize. The pressure inside the hose may be, or may be made, rather high.
The hose 1, as arriving, has thus the desired dimensions it is to have prior to expansion. Shape stability at these dimensions, as a memory, is obtained best through cross-linking, such as by grafted silane (supra). In the case of moisture cross-linking as per application 361,652 supra, that cross-linking has been completed. High-density polyolefin, for example, can also be cross-linked by means of electronic beams in order to obtain a three-dimensional, cross-linking network of its molecules. The, preferably complete cross-linked, hose 1 is first fed into and through a heating device . - ' ' .

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2, such as a tank of hot water, a water-and-glycerin mixture, or an infrared heater. This heating step is required, unless the hose arrives still sufficient-ly hot from extrusion and/or cross-linking. The temperature depends on the material; silane-grafted polyethylene should be heated to about 140 C to 180 C.
The next step is carried out in a sizing station 33. This station is a tank which is filled with warm water. ~ small entrance tank 4 is primarily provided in order to wet the surface of the hose quite thoroughly right from the beginning. One could use spray nozzles instead, or other suitable means for wetting hose 1 for purposes of lubrication before the hose passes through aperture disks 6. These disks are arranged in coaxial relation to each other, and their apertures increase in diameter, in downstream direction. The disks each are very thin, particularly when compared with the spacing between them so that there is very little contact with the hose, hardly any friction (water lubrication 1), and just enough to obtain, indeed, sizing. The disks are completely submerged; water may reach up to a surface level 7 in tank 3. The space 8 above that level is at a low water pressure of 8 meter water column.
A pump 17 provides the low pressure so that the hose expands under the resulting pressure differential.
Considering the process in greater detail, the arrangement provides for a stepwise but rather gradual increase in the hose's diameter. In between two disks 6, the hose portion there-between expands a little as the respective downstream disk has a rather wide diameter. This expansion is not carried o~lt as against any surface, and the contact between the hose and the sizing disks is minimal. ~liS alternating, stepwise expansion and sizing proceeds until the diameter of the hose has been reached, this constituting the diameter from which it will shrink later.
The disks 6 are also spaced at increasing spacing in downstream direc-.

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tion. It was found that this feature avoids that the stationary disks areforced into the soEt hose material as the latter expands. Of course, the hose should not tear or rupture. Downstream increase in expansion length per step and corresponding spacing in between sequential sizing steps ascertains, indeed, a gentle step-by-step process, with negligible wear on the material.
Reference n~m~eral 9 refers to the expanded hose as it leaves tank 3 and is now cooled in a water tank lO in order to freeze the dimensions of the expanded hose. The expanded and stabilized hose is wound on a drum, other suitable cooling and storage devices, for storage until further use. Alter-natively, the cool hose 9 may be cut into short-length sleeves if used as shrink-fit fittings, or the like, around splices. The hoses or sleeves have an excellent, elastic memory, particularly when made as per the companion ap-plication, repeatedly mentioned above.
Figure 2 illustrates the expansion device in still greater detail.
The lubricating tank (~) has been omitted, but hose l does receive a lubricating water film before entering sizing and expanding device 3. The entrance's boundary is established by a plate 11, being a wall of tank 3 and having a bevelled aperture 12. The disks 6 are closely spaced at first, but their spac-ing is increased as their aperture diameters increase. The disks are held on ~' 20 plate 11 by means of bolts 13.
The hose is externally completely surrounded by warm water, heating of the hose enhances the expanding process. Also, continued water lubrication of the hose ascertains that the expansion process does not bind the hose against the disks.
~' The equipment shown in Figure 3 is a modification in the sense that the preheating tank and the sizing tank are combined. The common tank has a relatively long front chamber ~illed with a water-and-glycerin mixture, and the J~

s;zing chamber 15 occupies the rear part of that tank, there being a partition, equivalent to plate 1l, interposed. The stepwise expanded hose is cooled as before.
Figure 4 illustrates an expansion procedure being divided into major steps, whereby in between each major step the diameter is kept constant for a certain travel distance. Moreover, the different sizing tanks 18a, 18b, and 18c differ in temperature; the tank water temperature will increase in down-stream direction.
The invention is not limited to the embodiments described above; but all changes and modifications thereof, not constituting departures from the spirit and scope of the invention, are intended to be included.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a method of making shrink hoses, wherein a hose is extruded, the improvement comprising:
providing a pressure differential between the inside and outside of the hose, a lower pressure being on the outside, in order to obtain a stepwise expansion of the hose, each expansion step increasing the inner diameter of the hose; and providing a plurality of sizing steps respectively in between sequentially occurring expansion steps, so that each portion of the hose is subjected to alternating expansion and sizing for stepwise increasing the diameter of the hose.

2. In a method as in Claim 1, the expansion being carried in a low pressure liquid bath.

3. In a method as in Claim 1, the expansion including expanding in separated steps, whereby no expansion occurs in between these separated steps.

4. In a method as in Claim 1 or 3, including the step of increasing the temperature of the hose with increasing expansion.

5. An apparatus for making a shrink hose, the hose having been extruded, comprising:
means for heating and maintaining the hose at an elevated operating temperature;
container means, disposed downstream from the means for heating, and through which the hose passes;
a plurality of sizing disks in the container means disposed therein spaced-apart relation, the disks having apertures and being placed so that the hose passes through the apertures, the apertures respectively having diameters which increase in downstream direction.

6. Apparatus as in Claim 5, said disks being spaced at a distance which increases with increasing aperture.

7. Apparatus as in Claim 5, the aperture's size increasing gradually.

8. Apparatus as in Claim 5, the aperture's size increasing groupwise in steps.

9. In a method of making shrink hoses, the hoses having been extruded, comprising the steps of:
heating the hose;
stepwise expanding the hose under a pressure differential, the interior pressure being higher each expansion step operating without support of the hose from the outside;
sizing the hose respectively in between sequential expanding steps and at a correspondingly increasing sizing diameter for sequential sizing steps; and cooling the expanded hose.

10. In a method of expanding a hose to a larger size from which, later, the hose is to shrink under higher pressure, comprising the steps of:
expanding a portion of the hose by internal pressure without causing the outer surface of the hose to engage any boundary;
sizing the portion by means of a sizing disk by passing the portion through an aperture of the disk; and repeating the last two steps several times for increasing expansion and increasing sizing diameters.

11. In a method as in Claim 9 or 10, the expansion being carried in a low pressure liquid bath.

12. In a method as in Claim 9 or 10, including the step of increasing the temperature of the hose with increasing expansion.