Method for turning a flexible tube inside out

Abstract

A method for turning a flexible tube inside out which comprises the steps of turning a flexible tube inside out at its one terminal end, fixing the terminal end having been turned inside out, inflating the flexible tube to almost a circular shape in cross section at the turning point where the tube is turned inside out and at that portion extending from said turning point to said fixed terminal end having already been turned inside out, while squeezing the unturned successive portion of the flexible tube extending from said turning point to the other terminal end. The portion which has been turned inside out and the unturned portion of the flexible tube is permitted to move along an axis extending outward from the fixed terminal end, thereby continuously shifting the turning point from the fixed terminal end to the other terminal end over the full length of the tube. The present method is effectuated either by applying fluid pressure internally to a confined chamber containing the flexible tube, said chamber being provided with a means for withdrawing one terminal end of the tube from the chamber or by using a self-rotatable endless doubletubing while drawing the flexible tube which is fixed at one terminal end thereof.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a method of turning a flexible tube inside out. More particularly, the present invention relates to a method for turning a flexible tube inside out (evaginating), said tube having been manufactured to purposely have reversed inner and outer surfaces for convenience of manufacturing conditions.

In the manufacture of hoses such as a fire hose, it is known to coat the external surface of a textile jacket made of woven or knitted fibers in a tubular form with a film of a rubber or a synthetic resin and then to turn the externally coated jacket inside out to produce a hose with a lining of said rubber or synthetic resin. For example, British Patent 957,929 discloses a process for manufacturing a fire hose by inserting a hollow mandrel into an externally coated flexible tubular jacket, turning one end thereof into the mandrel and drawing the turned in end of the jacket through the mandrel by means of a wire whereby the externally coated jacket is evaginated over the full length thereof. However, in this process wherein the flexible tubular jacket is brought into contact with the hollow mandrel over its entire length, a considerable force is required to smoothly draw the jacket which is in contact with the mandrel. In this case, the jacket is desirably thin and flexible as it is turned in over a nose provided at the terminal end of the hollow mandrel and drawn therethrough. If the jacket contains a certain amount of stiffness, friction will be created between the turned portion and the unturned portion at said nose which will disturb the smooth turning of the jacket. Once the running jacket is obstructed, forced drawing of the jacket will cause cracks, punctures or similar problems. Accordingly, the process of said British patent is only operable when using an extremely thin flexible tubular jacket and a strong drawing force. Also, there are additional problems in the process of the British patent in that the hollow mandrel should have approximately the same length as the flexible tubular jacket to be turned inside out and should be sufficiently strong to withstand the strong drawing force while being supported at only its one terminal end. Additionally, a number of different size mandrels must be available since the diameter of the mandrel used will vary as that of the flexible tubular jacket. It is therefore difficult to prepare many different types of long, heavy, strong mandrels and to be required to change them frequently depending on the size of the flexible tube to be turned inside out. Accordingly, there is a large demand for the development of an improved method for smoothly turning a flexible tube inside out which eliminates the above prior art problems.

BRIEF SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide an improved method for smoothly turning a flexible tube inside out utilizing a weak drawing force.

Another object of the present invention is to provide an economical method for turning a flexible tube inside out without encountering the problems found in the prior art.

Still another object of the present invention is to provide a flexible tube with a lining of a rubber or a synthetic resin having an even thickness and being substantially free of imperfections.

These and other objects and advantages of the present invention will become apparent to those skilled in the art from a consideration of the following specification and claims, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred embodiments of the present invention are shown in the accompanying drawings which are not to be considered as being limitative and wherein;

FIG. 1 is a sectional view of a pressure apparatus for carrying out evagination of a flexible tube externally coated with a film of rubber or a synthetic resin of even thickness;

FIG. 2 is a sectional view of another embodiment of the apparatus of FIG. 1;

FIG. 3 is a sectional view of an evagination means using a self-rotatable endless double-tubing;

FIG. 4 is a sectional view of a self-rotatable endless double-tubing;

FIG. 5 is a cross-sectional view of the self-rotatable endless double-tubing of FIG. 4 taken along line A--A'; and

FIG. 6 is a sectional view of another type of evagination means using a self-rotatable endless double-tubing.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention, there is provided a method for turning a flexible tube inside out which comprises the steps of turning a flexible tube inside out at its one terminal end, fixing the terminal end having been turned inside out, inflating the flexible tube to almost a circular shape in its cross section at the turning point where the tube is turned inside out and at that portion extending from said turning point to said fixed terminal end having already been turned inside out while squeezing the unturned successive portion of the flexible tube extending from said turning point to the other terminal end. The portion which has been turned inside out and the unturned portion of the flexible tube is permitted to move along an axis extending outward from the fixed terminal end, thereby continuously shifting the turning point from the fixed terminal end to the other terminal end over the full length of the tube.

In the case where a flexible tube is evaginated, the turning position, where a portion of the tube having been evaginated and a portion of the tube not yet evaginated are in contact with each other, should be set in the neighborhood of one terminal end thereof. Since the evaginated portion and the unevaginated portion of the tube are each equal in their diameters, either one of the portions can be forcedly inserted into the other. Thus, the portion inserted inside will inevitably form wrinkles and possess a wavy peripheral wall. At the turning point, the portion having a smooth wall is connected at a very short distance to the portion having a wavy wall, thus creating an unnatural distortional state. If the turning point in said state is shifted, some friction will be produced between said two portions to cause obstruction to evagination.

According to the method of the present invention, shifting of the turning point can be smoothly achieved without damaging the external rubber or synthetic resin coating by inflating the tube at the turning point and in its portion previously turned inside out (i.e., an outer portion) while squeezing a subsequent portion not yet turned inside out (i.e., an inner portion). In this case, the space between the evaginated outer tube and the unevaginated inner tube is enlarged and the externally coated inner tube having a wrinkled and wavy wall can be turned inside out very smoothly at a certain extended distance to form a roundly inflated outer tube with the desired lining.

In accordance with one embodiment of the present invention, fluid pressure is utilized for inflating the tube at the turning point and in the previously evaginated portion while squeezing the tube in a subsequent unevaginated portion. In this case, a flexible tube usually arranged in a coiled condition is placed in a confined pressure container and one terminal end of the tube is fixed to the container, while the other terminal end is allowed to extend outside of the container through a nozzle provided therein. A portion of the tube extending outside of the container is evaginated and the terminal end is fixed onto the external surface of the nozzle. A fluid such as air or a liquid such as water is introduced into the container under pressure whereby the tube is inflated at the turning point and in the previous evaginated portion while the tube in the subsequent unevaginated portion is squeezed or compressed. By maintaining an adequate inner pressure, the tube squeezed in the container is gradually unwound and is directed toward the nozzle whereby the turning point is shifted from the terminal end evaginated outside the nozzle to the other terminal end over the full length of the tube. Accordingly, the fluid pressure functions not only for inflating and simultaneous squeezing the tube but also as a propellant for extruding the squeezed tube from the nozzle whereby evagination is automatically attained.

Since, in the above-mentioned embodiment, evagination of the tube cannot be effected smoothly if it is made of a relatively stiff material or has a relatively small diameter, according to a further embodiment of the present invention, the squeezed tube is reeled off in a twisted condition whereby the tube becomes smaller in its size and easily passes through the inside of the evaginated tube with a negligible frictional resistance. In this embodiment the tube is reeled off from the terminal end near the core of the coiled tube.

In accordance with another embodiment of the present invention, a self-rotatable endless double-tubing is utilized as a means for inflating the tube at the turning point and in the previously evaginated portion for a certain distance. In this case, the tube supported on a mandrel or wire can smoothly be turned inside out by a relatively weak force without using a confined pressure container and fluid pressure. The self-rotatable endless double-tubing is quite unique in the art and can generally be manufactured by turning a tubing made of a natural or synthetic rubber such as butyl rubber inside out from its one end to half of its full length and bonding the evaginated end to the other end of the tubing not yet turned inside out. Thus, the external surface of one end of the tubing is bonded, after evagination, to the internal surface of the other end of the tubing to form a double-tubing which, in longitudinal section, looks like a caterpillar or endless belt. This double tubing may thus be considered a three dimensional tubular endless belt and is easily self-rotatable by friction when an external force is added onto the external surface of the double-tubing in its longitudinal direction. In actual use, the endless double-tubing is fully charged with a gaseous and/or liquid substance so that the double-tubing may be inflated to almost a circular cross sectional shape. Simultaneously a small amount of friction is created between the internal surface of the flexible tube and the external surface of the double-tubing inserted thereinto which produces its self-rotation. To avoid mechanical damage such as the frictional abrasion of the double-tubing, the surface of the double-tubing may be appropriately treated. A preferable surface treatment includes coating the surface with cloth or other anti-abrasion layers. The manufacture of the endless double-tubing is relatively simple and the size thereof, i.e., the diameter and length, can adequately be determined according to the size of the flexible tube to be evaginated.

The flexible tube may be made of any of the fibrous materials which are woven or knitted in a tubular form and externally coated with a film of natural or synthetic rubber of a synthetic resin. The flexible tube may also be a water permeable or impermeable plastic resinous material shaped into a tubular form and coated with a different type of water impermeable resin. Preferred fibrous materials are natural and synthetic organic fibers and inorganic fibers such as cotton, linene, glass, regenerated cellulose, polyamides, polyesters, and the like.

This invention will now be described in more detail with reference to the accompanying drawings.

FIG. 1 shows a pressure apparatus for turning flexible tubes inside out, including a flexible tube 1 having an evaginated portion 1-a, an unevaginated portion 1-b and a portion 1-c at the turning point. A pressure container 2 supported by legs 7 has a nozzle 3 fixed to the container 2 and may be closed tightly with a cover (not shown). The nozzle 3 is provided at its pointed end with a metal fastner 4 which functions to fix the evaginated terminal end of the flexible tube 1. The container 2 is provided, for example, at its bottom portion, with an inlet 5 through which a fluid can be introduced under pressure by means of a pump (not shown). A shaft 6 is mounted to the inner wall of the container 2.

A flexible tube 1 wound into a coil is disposed on the shaft 6 in the pressure container 2 and an outer terminal end of the tube 1 is drawn and passed through the nozzle 3 from the interior of the container 2. The terminal end of the tube 1 is then turned inside out and secured to the metal fastener 4. The pressure container 2 is then closed tightly and a fluid is introduced into said container through the inlet 5. Water is most suited as the pressure fluid. As the fluid is pumped into the container, the portion 1-c and the already evaginated portion 1-a are inflated to a round shape by the inner pressure of the fluid while the unevaginated portion 1-b is maintained in a floating condition. The portion 1-c at the turning point is inflated internally by the fluid pressure and then turned inside out to form the evaginated portion 1-a with the simultaneous and continuous forward movement of the portion 1-b toward the turning point. Accordingly, the portion 1-b changes at the turning point to portion 1-c which is then evaginated to form portion 1-a. The tube in the pressure container 2 is continuously removed from the reel and allowed to move through the nozzle 3 toward the turning point where the tube is turned inside out. Since the portion 1-c and the evaginated portion 1-a are inflated to a round shape by the internal fluid pressure and since the unevaginated portion 1-b is maintained in a squeezed state by the fluid pressure, the flexible tube 1 can be turned inside out smoothly without any difficulty. Where the unevaginated portion 1-b is passed through the inside of the evaginated portion 1-a, some friction is produced between the inner surface of the portion 1-a and the outer surface of the portion 1-b. However, the pressurizing fluid functions as a lubricant which substantially reduces the friction. It should be noted that the use of the apparatus of this type is not suitable when the material of the tube is relatively stiff or the diameter of the tube is relatively small, for example, as small as about 1 inch. In such a case, the friction between the portions 1-a and 1-b is substantial and thus evagination cannot be achieved unless an extremely high pressure is applied to the apparatus. This is due to the fact that portion 1-b passing through the portion 1-a internally inflated to a cylindrical form is maintained in a flattened condition and the folded edge portions thereof lose their flexibility and resist evagination at the turning point.

FIG. 2 shows an improved variant of the apparatus of FIG. 1. The flexible tube 1, which is wound into a coil, is placed on a table 8 in the pressure container 2. The table 8 is preferably curved circularly as shown in the drawing to stabilize the tube against rolling. The tube is drawn from the core of the coil, passed through nozzle 3 and then treated as explained with reference to FIG. 1. According to this improved embodiment, the tube is drawn from the central portion of the tube coil without permitting any rotation of the coil, thereby maintaining the tube in a twisted state as shown in the drawing. When a tube in the flattened state is twisted, the flattened tube will curl in its cross section so as to depict a "C"-shape and, in an extreme case, the folded edge portions of the flattened tube will become adjacent to each other and form almost a circular shape in cross section. Thus, the size of the portion 1-b is smaller and thus readily passes through the evaginated portion 1-a without any substantial amount of frictional resistance. In actual operation, using the apparatus of FIG. 2, a hose having a three-fourths inch diameter is easily turned inside out by an application of pressure of about 5 kg./cm.sup.2 or less, whereas the same hose could not be turned inside out in a similar operation using the apparatus of FIG. 1, even by using a pressure of 8 kg./cm.sup.2 or more. When using a tube having a diameter of at least 2 inches, either of the apparatus of FIGS. 1 and 2 may be employed. However, when the apparatus of FIG. 1 is employed, it is preferred to use a guid assembly for curving the flattened tube to a U-shape or C-shape in its cross section prior to passing the tube through the evaginated portion 1-a, thereby effectively minimizing the frictional resistance.

The pressure apparatus of FIG. 1 or FIG. 2 may have a plurality of nozzles to enable the evagination treatment to be conducted on several tubes at one time. In any case, the terminal end of the tube 1 placed in the pressure container 2 has to be closed very tightly. If several tubes are treated at one time, they will not be evaginated at the same time and the one most susceptible to evagination will first be evaginated. If the terminal end of the tube in the pressure apparatus has not been suffficiently closed, the pressurizing fluid in the pressure container will be violently projected through the hollow evaginated tube, thus making it impossible to continue the evagination treatment for the remaining tubes. Closing of the terminal end of the tube placed in the pressure container is particularly recommended when the above embodiment of the present invention is adopted for manufacturing a hose by evaginating an externally coated tubular textile jacket. The pressure test and pinhold detecting test of such hose can be made at one time in the same pressure container after manufacture of the hose.

FIG. 3 shows another embodiment of the present invention, wherein a flexible tube 1 is first placed closely on a shaft 9 with its one end fixed. A self-rotatable endless double-tubing 10 is then placed on the flexible tube 1 and positioned near the fixed end of the shaft 9. The terminal end of the tube 1 near the fixed end is evaginated and placed on the external surface of the double-tubing 10 whereby an evaginated portion 1-a and a portion 1-c at the turning point of the tube are inflated by the fluid pressure of the double-tubing 10 whereas the unevaginated portion 1-a is drawn parallel to the shaft 9 along an axis extending in the opposite direction from the fixed end of the shaft. The endless double-tubing 10 moves on the shaft 9 in the same outward direction (toward the left side of the drawing) from its original position by its self-rotation and the portion 1-b is smoothly turned inside out in compliance with the movement of the double-tubing 10. In this case, no strong drawing force is required and thus the turning point is shifted from one terminal end to the other terminal end over the full length of the tube 1 by a relatively weak drawing force. The resulting evaginated tube is free of wrinkles and other imperfections unlike the case of said British patent 957,929, where a tube is turned into a hollow mandrel having an inner diameter less than that of the tube.

FIGS. 4 and 5 show a self-rotatable endless double-tubing 10 comprising an internal tube 11 and an external tube 12, each made of the same flexible material such as rubber or a synthetic resin. The external and internal tubes unite at their left and right ends to form an endless double-tubing. Since the internal tube 11 and the external tube 12 each have an equal diameter, the internal tube exists in the state of being forcedly inserted into the external tube. When a pressurizing fluid is charged into the endless double-tubing 10, the external tube 12 is inflated into a circular cross sectional shape while the internal tube 11 is squeezed out of shape. Since the internal and external tubes 11 and 12 have an equal diameter and are made of a flexible material, self-rotation of the double-tubing caused by friction between the external tube and a tube placed thereon alternates the external tube with the internal tube. In FIG. 4, the internal tube 11 moving on account of the frictional force is turned inside out at the right end to form the external tube 12 while the external tube 12 moving with the drawn tube by friction is reversed in its running direction at the left end and pulled inside to form the internal tube 11. Such self-rotation of the double-tubing 10 is continuous and looks, in its sectional (longitudinal) view, as if it were the motion of an endless belt or caterpiller. The double-tubing 10 is provided on its internal surface with a fluid charging means B, e.g., a rubber tip as seen in a tennis ball or an air valve as seen on inner tubes of tires, through which a pressurizing fluid substance, e.g., air is injected into the internal space of the double-tubing 10.

FIG. 6 shows another embodiment of the present invention using an endless double-tubing 10, wherein a flexible tube 1 is wound at one terminal end into a coil 13 through which a tape 14 is inserted over the entire length of the tube 1. The endless double-tubing is placed on the flexible tube 1 at its one terminal end and the tube 1 is turned inside out at this end so as to cover the endless double-tubing 10, the evaginated portion 1-a and the portion 1-c at the turning point are inflated while the unevaginated portion 1-b is pressed against the tape 14. The evaginated terminal end of the tube 1 is secured in this state to a suitable support and the tape 14 is then drawn along an axis extending outward from the secured end (in the right-hand direction in the drawing), whereby the turning point is shifted from one terminal end to the other terminal end over the full length of the flexible tube 1 with the continuous self-rotation of the double-tubing 10, to produce the smooth evagination of the flexible tube 1. Any type of cordage such as wire, rope, a belt or the like can be used in place of the tape 14. It is desirable that the endless double-tubing 10 have an almost equal diameter to the internal diameter of the flexible tube 1. If the diameter is too large, it will become difficult to place the evaginated terminal end of the tube 1 on the endless double tubing 10. On the other hand, if the diameter is too small, the portions 1-a and 1-c will be insufficiently inflated, thus making smooth evagination difficult. However, the external diameter of the endless double-tubing 10 will not have to be strictly the same as the internal diameter of the flexible tube 1 and may be such that the already evaginated portion 1-a can be maintained in an almost circular cross sectional shape.

In the embodiments of the present invention using the self-rotatable endless double-tubing, evagination of a flexible tube may be carried out by two alternative methods. One method comprises inserting a core shaft into a flexible tube, fixing one end of the shaft to a support and drawing one terminal end of the tube in contact with the external tube of the double-tubing along an axis extending outward from the fixed end as shown in FIG. 3 and the other method comprises inserting a core shaft or cord into a flexible tube, fixing one terminal end of the evaginated tube to a support and drawing the core shaft or cord along an axis extending outward from the fixed end as shown in FIG. 6. It is also possible to draw both of the core shaft and the flexible tube in the opposite direction to each other.

The method of the present invention is featured by inflating the flexible tube at its turning point and where it has been evaginated while squeezing the unevaginated portion of the tube through the application of internal fluid pressure or the use of a specific endless double-tubing. Thus, passing of the unevaginated portion through the evaginated portion becomes easier and evagination of the tube proceeds smoothly at the turning point, requiring only a relatively weak drawing or extruding force.

In the embodiment using the pressure container of FIGS. 1 or 2, the pressure container must be able to tolerate a high internal pressure and can be used for treating, at one time, one or more flexible tubes of various diameters from about one-half inch to about 5 inches. A tube of any different size can be treated in the same pressure container by merely exchanging the nozzle according to the size of the tube to be treated. This present process brings about a great economical advantage in the hose manufacturing industry.

The embodiment using a self-rotatable endless double-tubing is also advantageous in that it eliminates the need for large-scale, complicated equipment, since a flexible tube can easily be turned inside out with the use of only two simple elements, i.e., a core member and a specific endless double-tubing. This embodiment enables the treatment of flexible tubes having a variety of inner diameters by simply exchanging the endless double-tubing according to the size and internal diameter of the tubes to be turned inside out. In the embodiment shown in FIG. 3, the use of a long shaft equal in length to the flexible tube to be turned inside out is required but the force needed for evagination is so small that drawing of the tube can be attained manually with the power of only one operator.

The method of the present invention is particularly useful as a step for evaginating an externally coated tubular textile jacket in a method for manufacturing a hose for high pressure liquids, for example a fire hose. This is achieved by forming a coating of rubber or a synthetic resin on the external surface of a tubular textile jacket and turning it inside out. Thus, the method of the present invention is generally applicable for manufacturing a tubular material with a lining having an even thickness and being free from any imperfections by the evagination technique applied to an externally coated tubular material.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, but all such modifications are intended to be included within the scope of the following claims.

Claims

What is claimed is:

1. A method for turning a flexible tube inside out which comprises the steps of inserting a core material into the flexible tube, passing the tube through the internal surface of a flexible self-rotatable endless double-tubing, evaginating one terminal end of the tube around the evaginated end on the external surface of the double-tubing and causing the evaginated portion of the tube and the core material to move in opposite directions with respect to each other thereby turning the flexible tube inside out.

2. A method according to claim 1 wherein a stiff shaft with its one end fixed to a support is used as the core material and the evaginated portion of the flexible tube is drawn along the axis extending away from the fixed end.

3. A method according to claim 1, wherein a flexible cordage is used as the core material, a terminal end of the evaginated portion of the flexible tube is fixed to a support and the cordage is drawn along an axis extending outward from the fixed end.