Process for manufacturing a flexible cylindrical body

A process for manufacturing a flexible cylindrical body includes the steps of providing a flexible preform of non-resilient synthetic material which is inflatable to cylindrical form, inserting the preform into an elongated coil of an electrically conductive material having a diameter relative to that of the preform in its inflated cylindrical form such that the preform is expanded in an unstressed condition into engagement with the inner diameter of the coil, the inner face of the coil being coated with an adhesive material, and applying a predetermined voltage to the coil to thereby fuse the adhesive material and connect the coil and preform.

The present invention relates to a process for manufacturing flexible 
cylindrical articles and more particularly to the manufacture of such 
articles made of a non-resilient textile sheet material supported in its 
cylindrical form by adhesion to an outer elongated coil of an electrically 
conductive material. 
Articles of the type to which the present invention relates have been found 
useful as conduits for conducting air and other gases and as oil fences in 
seas, rivers and other bodies of water. 
In the past the manufacture of such flexible cylindrical bodies has posed 
various difficulties owing primarily to the fact that the material is 
relatively soft and is not self-supporting without being impregnated with 
a resin or the like which adds stiffness to the material. A particular 
difficulty encountered heretofore has been in connection with the securing 
of the material to the surrounding coil. Heretofore resort has been had to 
the use of a resilient material which can be expanded into engagement with 
the coil. In the practice of such techniques the material from which the 
cylindrical article is to be made is expanded beyond its normal unstressed 
diameter and is adhesively secured to the coil in such stressed condition. 
Following setting of the adhesive and the consequent bonding of the 
flexible material to the coil the cylindrical tube is permitted to shrink 
to its normal diameter. However, at the points of connection with the coil 
the joints so formed are subjected to continued stress since the material 
of the cylindrical article at such locations cannot return to its original 
unstressed condition. The resultant article, therefore, includes adhesive 
joints which, without additional reinforcement of the article, limits its 
utility to environments where it is subject to relatively small stresses. 
SUMMARY OF THE INVENTION 
It is one object of the invention to provide a process for manufacturing 
flexible cylindrical articles supported within an outer elongated coil by 
which the completed article is substantially free of stress. 
It is another object of the invention to provide a process for 
manufacturing flexible cylindrical articles supported within an outer 
elongated coil of electrically conductive material which does not require 
the use of mandrels or complex apparatus. 
It is still another object of the invention to provide a process for 
manufacturing flexible cylindrical articles supported within an outer 
elongated coil of electrically conductive material which is simple to 
perform and results in secure attachment of the cylindrically formed 
material to the coil by means of relatively unstressed joints. 
Other objects and advantages of the invention will become readily apparent 
from the following description of the invention. 
According to the present invention there is provided a process for 
manufacturing a flexible cylindrical body supported within an elongated 
coil of an electrically conductive material comprising: preparing an 
elongated flexible substantially closed preform envelope of non-resilient 
material having an inlet therein for the admission of an inflation gas, 
said preform being adapted to be expanded into cylindrical form; inserting 
the substantially uninflated preform into an elongated coil of an 
electrically conductive material which is coated on at least the inner 
faces of the turns thereof with an adhesive material; the diameter of said 
preform in its unexpanded condition being sufficiently large relative to 
the inner diameter of said coil such that it can be expanded into 
cylindrical form and into engagement with the said coil in an unstressed 
state; inflating said preform into cylindrical form within said coil and 
into engagement therewith in an unstressed state; applying a predetermined 
voltage to said coil for fusing the adhesive material thereon and to 
secure said coil to said cylindrical preform; and thereafter releasing the 
inflation gas from the cylindrical preform and obtaining a flexible 
substantially unstressed cylindrical article.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to the drawings, and particularly to FIGS. 1 and 2 thereof, there 
is shown an elongated preform 10 consisting essentially of an envelope 
which is completely closed except for opening 11 by which a gas, such as 
air, can be introduced to inflate the preform into a cylindrical shape 14. 
The preform is made of a non-resilient sheet material such as canvas or a 
synthetic material and is desirably rendered water and gas tight in any 
conventional manner. Thus, the preform may comprise a tarpaulin containing 
film, leather, sheet fiber or the like. Basically the preform is flexible 
so as not to be self-supporting when shaped into a cylindrical 
configuration. 
The preform shown in FIG. 1 is placed within an elongated coil 12 of an 
electrically conductive material. The coil is coated on the inner face of 
the turns thereof with an adhesive material 16 capable of securing the 
preform to the coil at their points of engagement. One adhesive found 
suitable is a paste of vinyl chloride. The preform should be of such 
diametral dimension, relative to the coil, that upon inflation to its 
cylindrical form it is not stressed into engagement with the turns of the 
coil. In a preferred embodiment of the invention the width of the preform 
is greater than the inner diameter of the coil. Accordingly, since the 
material of the preform is non-resilient, even when its inflated diameter 
approximates that of the inner coil diameter, the material of the preform 
will not be subjected to stress when inflated into engagement with the 
turns of the coil. 
Once the preform has been inflated into engagement with the turns of the 
coil a predetermined voltage is applied to the coil in order to heat the 
coil for the purpose of fusing the adhesive layer to the preform at the 
points of engagement with the coil. Desirably the temperature of the coil 
is regulated so as to produce some softening of the preform under the 
elevated temperature to obtain a good bond between the preform and the 
coil. The specific temperature to which the coil is raised, the voltage to 
be applied to the coil, and the time duration for application of the 
voltage to the coil are determined primarily by the particular adhesive 
material selected. Once the adhesive material has set so as to bond the 
preform to the coil at their points of engagement the gas is released from 
within the cylindrical body. 
As clearly shown in FIG. 2, the preform in its cylindrical form and secured 
to the coil does not exhibit any sags or corrugations as is characteristic 
of prior art articles of this type which have been formed from a resilient 
material and have been expanded byond their normal diameter and 
subsequently been permitted to shrink back to normal diametral size. It is 
apparent that the final article produced in accordance with this invention 
is relatively free from stress created during the manufacturing process. 
Referring to FIG. 3 of the drawings there is shown the use of an elongated 
inflatable member or sack 18 having an opening 20 at one end thereof for 
the introduction of an inflation gas thereinto. The preform 10 in this 
instance may be closed at one end or open at both ends so as to 
accommodate insertion of the sack thereinto. Upon insertion of the sack 18 
into the preform, and either with or without the preliminary introduction 
of any inflation gas into the sack, the sack and preform are positioned 
within elongated coil 12. The inflatable sack 18 is thereupon inflated to 
the extent necessary to expand the preform from its collapsed condition 
into cylindrical form in engagement with the turns of the coil. As in the 
process described with reference to FIG. 1 of the drawings a predetermined 
voltage is applied to the coil so as to effect a fusing of the adhesive 
material which is coated on at least the inner faces of the coil turns and 
thereby bond the preform to the coil at such points of engagement. Once 
fusion has been effected the sack is deflated and withdrawn from within 
the cylindrical body. As with the embodiment described in conjunction with 
FIG. 1, the diameter of the preform in its unexpanded state is 
sufficiently large relative to the inner diameter of the coil as to permit 
expansion of the preform into its cylindrical form and into engagement 
with the turns of the coil in a substantially unstressed state. 
By the process of this invention a flexible cylindrical article supported 
within an elongated coil can thus be easily produced with secure points of 
connection between the cylindrical body and coil and with the avoidance of 
stressed joints. It will be apparent that variations and modifications of 
the process may be made within the scope of the claims herein without 
departing from the spirit of the invention.