US3434860A

US3434860A - Method and apparatus for coating tubular fabric

Info

Publication number: US3434860A
Application number: US499589A
Authority: US
Inventors: Leslie A Ferguson; George M Williams
Original assignee: Uniroyal Inc
Current assignee: UNIROYAL HOLDING Inc WORLD HEADQUARTERS MIDDLEBURY CONNECTICUT 06749 A CORP OF NEW JERSEY
Priority date: 1965-10-21
Filing date: 1965-10-21
Publication date: 1969-03-25
Anticipated expiration: 1986-03-25
Also published as: BE688580A; SE322337B; GB1166649A; DE1635671A1; FR1500470A; USB499589I5; NL6614839A

Description

March 25, 1969 L. A. FERGUSON ETAL 3,434,360

METHOD AND APPARATUS FOR COATING TUBULAR FABRIC Filed Oct. 21, 1965 Sheet of 2 lNVENTORS FIg. l Leslle A. Fer uson A 8 George M. Wi lioms Y ATTORNEY M rcl 1 5 1969 A. FERGUSON ETAL 3,434,360

METHOD AND APPARATUS FOR COATING TUBULAR FABRIC Filed Oct. 21, 1965 Sheet 2 of 2 Fig. 2. Fig. 5.

JNVENTORS Leslie A. Fer uson George M. Wi lioms ATTORNEY United States Patent US. Cl. 117-7 11 Claims ABSTRACT OF THE DISCLOSURE A method of and apparatus for coating stretchable tubular fabrics having a predetermined wall thickness and diameter, wherein the fabric wall is radially compressed in a coating zone, between a non-magnetic, outer, cylindrical member and a magnetically supported, inner, mandrel, to squeeze entrapped air therefrom and to facilitate entry of coating material thereinto; or wherein the tubular fabric is radially expanded to a greater diameter in the coating zone, by the mandrel, to enlarge the interstices of the fabric and to facilitate entry of coating material thereinto; or wherein both of the foregoing are performed concurrently to improve penetration of the coating material into the tubular fabric, the coated tubular fabric returning to substantially its predetermined wall thickness and/ or diameter prior to being cured.

This invention relates to methods and apparatus for coating or impregnating a tubular fabric with a liquid coating material.

In the conventional process of coating or impregnating a tubular fabric with a coating material in liquid form, the fabric tube is passed through a coating zone wherein the fabric tube is coated or impregnated by the coating material, and often two or more passes through coating zones are made to eliminate pinholes and permit greater build-up of the coating thickness. The coated tube is then passed through a curing zone where, depending on the nature of the coating material, it is either air-cured or oven-cured, or the like. It then passes on to a take-up system, preparatory to subsequent handling, packing and shipping. Such a process is often employed in the manufacture of garden hose, electrical insulation and other types of impervious flexible tubular conduits. It may also be used in the manufacture of impervious rigid conduits.

In such a conventional coating or impregnating process, the tubular fabric, having a generally flat cross-sectional shape, is taken from a let-off roll and passed through a bath or reservoir of the coating composition while in such flat form. It is then passed over a spherical or cylindrical mandrel which is located internally of the fabric tube and is held in a fixed position in space by a powerful permanent or electromagnet positioned about the fabric tube. The spherical or cylindrical mandrel usually. serves to reshape the flat tube into the conventional round tube configuration. Thereafter, the rounded tube passes through the heating and drying zone at which the coating material is cured on the round tube and the material is taken up on a take-up roller, when flexible, or cut to predetermined lengths, when rigid.

Coated or impregnated fabric tubes made in the foregoing manner are generally satisfactory for the purposes intended where the coating material employed is a relatively slow-setting liquid coating material, as, for example, insulating varnish, natural rubber or synthetic rubber. However, where quick-setting liquid coating materials are employed, such as polyurethanes for example, the bond between the coating material and the fabric tube is often inadequate due to the facts that: (l) the quick-setting material often does not sufiiciently penetrate into the fibers of the fabric tube wall; and, (2) air is often trapped at the interface of the coating material and the fibrous wall. Moreover, in the case of tubular stretchable fabrics, past practices have not achieved sufficient penetration of the coating material into the interstices of the fabric to produce a good, impervious coating on the tubular fabric. Further, the prior art use of a relatively stagnant bath in connection with coating the fabric tube is not practical in the case of quick-setting materials due to the fact that the materials in the bath begin to set up, causing interference with the coating operation.

Accordingly, it is the primary object of this inventio to provide an improved method of coating tubular fabrics.

It is a further object of this invenion to provide a method of coating tubular fabrics in which an improved bond between the coating material and the fabric is achieved.

Yet another object of this invention is to provide an improved method of coating tubular fabrics in which greater penetration of the coating material into the wall of the fabric is achieved.

It is yet a further object of this invention to provide an improved method of coating tubular fabrics in which improved penetration of the coating material into both the interstices of and the fibers of the fabric wall is achieved, and in which trapping of air at the interface of the.coating material with the tubular fabric wall is minimized.

Another object of this invention is to provide, in a method of coating tubular fabrics with a quick-setting liquid coating material, for the elimination of dead spaces wherein the quick-setting material can accumulate and set up prior to its being coated onto the tubular fabric.

It is yet another object of this invention to provide improved apparatus for coating elongated tubular fabric with a liquid composition.

Another object of this invention is apparatus for coating elongated tubular fabric with a liquid coating material which provides an improved bond between the coating material and the fabric wall. I

Still another object of this invention. is apparatus for coating tubular fabric with a liquid coating material which provides improved penetration of the coating material into the fibers and interstices of the wall of the tubular fabric.

Further objects and advantages of this invention will become apparent as the following description proceeds.

Briefly stated, and in accordance with one embodiment of this invention the method of this invention is practiced by pulling a length of tubular fabric with a given tensile force through a coating zone adapted to receive liquid coating material and apply the material to the fabric, the tubular fabric having a predetermined wall thickness under the given tensile force; applying a radial compressive force to the wall of the tubular fabric in the coating zone to compress the thickness of the wall in the zone to at least 10% less than the predetermined thickness and expel air from the fibers therein; removing the compressive force so that the fabric wall expands to substantially the predetermined thickness and draws the coating material into the fibers thereof to replace the expelled air; and, curing the coating material on the tubular fabric.

An apparatus for coating elongated tubular fabric with a liquid coating material in accordance with one embodiment of this invention, the fabric being under tension and having a predetermined wall thickness when so tensioned, comprises a means for creating a magnetic field; .a nonmagnetic tubular member having a predetermined inter nal diameter mounted within the magnetic field; a magnetic element located in the tubular member and having a circular cross-section of predetermined maximum diameter in at least one plane normal to the axis of the tubular member, one-half of the difference between the internal diameter and the maximum diameter being at least 10% less than the predetermined wall thickness; means to deliver the liquid coating material to the interior of the tubular member, and means to feed the tubular fabric through the tubular member with the magnetic element fitting within the tubular fabric and being magnetically held in place against withdrawal from the apparatus, whereby the wall of the tubular fabric is compressed as it passes between the tubular member and the magnetic element to squeeze entrapped air therefrom to facilitate entry of the liquid coating material thereinto.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter regarded as this invention, it is believed that the invention will be better understood from the followng description, taken in connection with the accompanying drawings, in which;

FIG. 1 is .a diagrammatic view of one form of apparatus embodying the invention;

FIG. 2 is an enlarged plan view taken along the line 22 of FIG. 1;

FIG. 3 is an enlarged sectional view taken along the line 3-3 of FIG. 2;

FIG. 4 is an enlarged sectional elevational view similar to FIG. 3 showing an alternate coating head or doctor ring assembly that may be used with this invention; and

FIG. 5 is a sectional elevational view taken along the line 5-5 of FIG. 1.

Referring to FIG. 1 of the drawings, there is illustrated an apparatus and method for coating or impregnating a continuous strip of tubular fabric with a liquid coating material. As shown, a continuous strip of tubular fabric is supplied from a reel 11 carried by a support 12. The continuous tubular strip 10 is led from reel 1.1 over a pulley 13 through a first coating head assembly, shown generally at 14, and through a second coating head assembly, shown generally at 15. First and second coats of liquid coating material are applied to the tubular fabric strip 10 at

assemblies

14 and 15, respectively. Depending on the nature of the liquid coating material and whether or not there is a need to accelerate the curing thereof, optional heaters, shown in broken lines at 16 and 17, respectively, may be employed to cure the coating material on the fabric tube. After passing through the second heater 17, the coated fabric tube passes about pulley 18 and is wound up on a take-up reel 19 carried on a support 20. Reel .19 is driven by suitable drive means (not shown) which cause a predetermined tension to be exerted on the taubular fabric strip 10 in order to move the fabric from let-off reel 11 through the various coating heads to take-up reel 19.

The liquid coating materials which are applied to fabric strip 10 at coating head assemblies 14 and may be prepared in identical reaction devices, shown generally at 21 and 22, respectively, and delivered to the coating head assemblies via

conduits

23 and 24, respectively. In the case of quick-setting coating materials, the

reaction devices

21 and 22 should be positioned as closely adjacent to the

coating head assemblies

14 and 15 as possible. This is done in order to facilitate rapid transfer of the quick-setting materials from the reaction devices to the coating head assemblies during operation and thus prevent gelling or setting up of the coating materials within the

conduits

23 and 24.

Referring to FIG. 5, wherein the reaction or mixing device 22 is shown in greater detail, the components to be reacted to form a coating material are admitted through

nozzles

25, 26 and 27 and are further mixed by means of a stirrer 28 driven by a drive means, such as an electric motor 29. The mixture, comprising the liquid coating material thus obtained, leaves device 22 through outlet conduit 24 and leaves device 21 (FIG. 1) through outlet conduit 23. The reaction devic 2 and 22 4 are supported in their respective positions adjacent

coating head assemblies

14 and 15 by

suitable brackets

30 and 31, respectively.

A preferred coating head assembly 14 is shown more clearly in FIGS. 2 and 3. The assembly comprises a high strength magnet, such as the permanent magnet shown at 35, or a suitable DC electromagnet of similar strength. The magnet 35 is fixed to a support wall by means of a bracket 36 and is provided with

end poles

37 and 38. A magnetic ball or mandrel 39 is centrally supported within the tubular fabric strip 10 by means of the magnetic lines of force passing between the

end poles

37 and 38 of magnet 35. A non-magnetic (e.g., brass) doctor ring 40 surrounds the fabric tube 10 and the magnetic ball 39. The doctor ring 40 is positioned between the

end poles

37 and 38 and, as will appear in greater detail hereinafter, it is supported in such a manner as to be adjustable relative to the end poles.

In order to support doctor ring 40, upper and

lower support plates

41 and 42 are fixed to the outer surface of the doctor ring.

Plates

41 and 42 are horizontally adjustably bolted to respective upper and lower

intermediate brackets

43 and 44 by means of bolts 43a and 44a.

Brackets

43 and 44, in turn, are vertically adjustably fastened to respective wall brackets 45 and 46 (FIG. 1) by means of bolts 45a and 46a. Accordingly, doctor ring 40 is capable of being horizontally and vertically adjusted relative to the

magnetic poles

37 and 38 in order to allow for control over the magnetic pull which the poles exert on the magnetic ball 39. This allows the apparatus to be adjusted in such a manner as to apply coating material to the fabric tube equally about the circumference of the tube and avoid over-abundance and starved conditions therein.

The apparatus herein described employs the permanent magnet 35 to support magnetic ball 39. However, as indicated earlier, electromagnets of the DC type can be used. As an optional feature, it may be desirable in some applications to provide a means for heating the mandrel 39. In such an event an AC electromagnet can be used in conjunction with either the permanent magnet 35 or a DC electromagnet, and the fluctuating field of the AC electromagnet may be utilized to cause a heat build-up in the mandrel 39, thereby providing means for heating the mandrel to a controlled degree.

As indicated earlier, a drive means (not shown) associated with take-up reel 19 causes reel 19 to pull the fabric strip 10 from let-off reel 11 through

coating head assemblies

14 and 15 and onto reel 19. During continuous operation of the apparatus of FIG. 1, a predetermined tensile force is applied to the strip 10 at reel 19 and, although friction at the

various rollers

13 and 18,

coating head assemblies

14 and 15, and at let-off reel 11 causes the actual tensions at various points in strip 10 to differ from the tension in the strip at the input to reel 19, the value of the tensile stress in strip 10 at such points bears a definite relationship to the tensile stress in strip 10 at the input of reel 19.

Under a given predetermined tensile stress in the fabric strip 10 at each of the

coating head assemblies

14 and 15, the walls of the tubular fabric strip at these points will have predetermined thicknesses. Accordingly, considering assembly 14, the diameter of magnetic ball 39 and the internal diameter of doctor ring 40 are selected to be of such dimensions as to cause the wall portions of strip 10 passing between the point 48 (FIG. 3) of closest approach of ball 39 to the inner surface of ring 40 to be compressed at least 10% by a radial compressive force. This compression causes air to be squeezed out of the wall of strip 10 within coating head assembly 14 and, upon release of the compressive force as the wall portions move past point 48, the wall portions expand and, like sponges, absorb coating mat rial thereinto.

In order to facilitate the application of coating material to the expanding wall portions of strip 10, the inner wall of doctor ring 40 is provided with an annular recess or groove 50 to which the conduit 23 (FIG. 1) is connected at a plurality of circumferentially spaced points via branch conduits 23a and 23b. Preferably, the conduits 23a and 23b enter the doctor ring 40 at an angle, rather than radially, so as to introduce a tangential rotary component of flow to the coating material in the annular grove 50. This enhances movement of the material through the groove 50 and helps avoid the formation of dead spaces or stagnant areas therein at which quick-setting coating material might gel before being applied to the fabric strip 10.

The arrangement of components is such that the magnetic forces acting on the ball 39 between

magnetic poles

37 and 38 keep the ball 39 centered at a point just above the annular groove 50. Accordingly, as the wall portions of fabric tube begin to expand after passing the point 48 of closest approach of the ball 39 to ring 40, the wall portions come into contact with the coating material exiting from the annular groove 50. Thus, coating material is applied to the fabric tube 10 at the groove 50 and, at the same time, the expanding wall portions draw in the coating material and improve the penetration of the material into the fibers of the fabric wall.

For purposes of definition, the area encompassed between the point of inlet of the tubular fabric strip 10 into the doctor ring 40 and the point of exit of the fabric strip from the doctor ring is considered to be a coating zone in which coating material is applied to the strip of tubular fabric moving therethrough. Thus, the radially directed compressive force which is exerted on the wall of the strip of tubular fabric at point 48 occurs within the defined coating zone.

As will be apparent from an inspection of FIGS. 1 and 3, the coating material prepared in reaction device 21 is delivered to the doctor ring 40 of coating head assembly 14 in a single direct pass of the coating material from the reaction device to the tubular fabric, there being no dead spaces in the interconnecting system for the accumulation of coating material during movement of the material from the reaction device to the tubular fabric. The same is true in the case of reaction device 22 and coating head assembly 15, as will appear hereinafter. This is particularly desirable when quick-setting coating materials are employed in order to prevent gelling of the materials prior to their being applied to the fabric tube.

It should be pointed out that the speed of the tubular fabric passing through the doctor ring 40 should be adjusted to be so related to the delivery rate of the liquid coating material thereto as to insure that all of the liquid coating material delivered to the doctor ring is applied to the tubular fabrc and that sufficient liquid coating material is delivered thereto as to completely cover all of the tubular fabric passing through the doctor ring. This insures that the application of the coating material to the tubular fabric is continuously maintained without blockage thereof due to the setting up or gelling of the coating material prior to its application to the tubular fabric.

When a tubular stretchable fabric is to be coated and it is desired to not only fill the fibers in the walls of the fabric tube 10 by means of compression of the walls during passage of the tubular fabric through the doctor ring 40, but also to impregnate the interstices of the fabric between the adjacent woven or knitted loops or strands therein, the diameter of the magnetic ball 39 is chosen to be at least 10% greater than the diameter of the fabric tube 10 under the tension applied to the fabric tube to move it through the coating head assembly. Thus, as can be seen in FIG. 3 the diameter of the fabric tube is expanded as it moves over the magnetic ball 39, thereby stretching the fabric in the walls of the tube to increase the size of the interstices of or the spacing between adjacent loops or strands in the fabric. Accordingly, as portions of the fabric walls pass by the groove 50 and the coating material is applied thereto, the coating material enters the enlarged interstices of the fabric to achieve greater penetration thereinto.

In the foregoing variation of the invention a tubular stretchable fabric is coated with liquid coating material by pulling the tubular fabric with a given tensile force through the coating zone, the tubular fabric having a predetermined diameter under the tensile force before entering the coating zone. While in the coating zone, a radially expanding force is applied to the tubular fabric to stretch the fabric diameter at least 10% greater than the predetermined diameter in order to enlarge the interstices of the fabric and facilitate peneration of the coating material into the fabric wall in the coating zone, and then the expanding force is removed prior to the curing of the coating material so that the tubular coated fabric returns to substantially its predetermined diameter. Thereafter the coating material on the tubular fabric is cured, either by air curing or by the addition of heat in the

heaters

16 and 17.

A modified coating head assembly 15 has been shown and illustrated in FIG. 4. In this case the doctor ring 40 of FIG. 3 has been replaced by a funnel-like doctor ring 55 which is provided with a conical upper end portion 56 and a cylindrical lower portion 57. Instead of the annular groove 50 utilized in the doctor ring 40 of the FIG. 3 embodiment, doctor ring 55 employs the conical end 56 as a reservoir in coating the fabric tube 10. In this case liquid coating material is delivered from reaction device 22 (FIG. 1) to the conical end 56 of doctor ring 55 by the delivery conduit 24 (FIG. 4), the rate of flow of the coating material to the doctor ring 55 being such, relative to the speed of the movement of fabric tube 10 through the doctor ring, that a slight, continuously changing, bank or reservoir 58 is formed at the conical end 56 of the doctor ring. In this embodiment, as in the embodiment of FIG. 3, the inner diameter of the doctor ring 55 and the outer diameter of the ball 39 are so chosen as to provide for at least 10% compression of the walls of the fabric during passage of the fabric tube between the ball and the doctor ring. In addition, in the case of stretchable fabrics the diameter of the ball 39 may be selected to be at least 10% greater than the inner diameter of the fabric tube 10 under the tensile force needed to pull the tube 10 through the doctor ring. As before, this is done in order to enlarge the interstices of the fabric in the walls of tube 10 when deep impregnation of the coating material into the wall of the tube is desired.

In the case of tubular fabrics wherein the weave or knit of the fabric is so tight as to preclude passage of coating material completely through the wall to the internal surface of the fabric tube, it will be apparent that a cylindrical magnetic mandrel may be employed in place of magnetic ball 39. However, where penetration of the coating material into and through the walls of the fabric tube is desired, or is possible, a spherical mandrel or ball 39 is preferable to a cylindrical mandrel. The reason for thi is that a ball will continually rotate in a random manner, causing its outer surface to be continually wiped clean and precluding the build-up of hardened coating material on the ball surface. On the other hand, the material build-up on a cylindrical mandrel would cause improper operation of the apparatus.

Should it be desired to coat only the .inside surface of a fabric tube, it will be apparent that the .input portions of the apparatus, comprising let-off reel 11, support 12 and roller 13, can be replaced by an overhead. circular knitting or weaving machine which fabricates the fabric tube 10 directly at the input to a coating head assembly of the type shown at 15. In this case the delivery conduit 24 would be redirected to pass through such machine so as to discharge coating material into the interior of fabric tube 10. Accordingly, a bank or reservoir of coating material would be formed inside the fabric tube at ball 39, rather than outside the fabric tube at conical end 56, and the interior of the fabric tube would thus become coated.

The amount of coating material applied to the internal surface and the depth of penetration of the coating material into the fabric tube wall depend, to a great degree, on the tightness of the weave or knit of fabric tube It), the diameter of the ball 39, the internal diameter of the doctor ring 55, the tension in fabric tube 10 and the rate of delivery of coating material to the coating head assembly 15. The same factors apply in the case of coating the external surfaces of fabric tubes in accordance with the embodiments previously described. Accordingly, it will be appreciated that by judiciously selecting appropriate values for the foregoing factors, the thickness of the coating on, and the depth of penetration of the coating material into, the fabric tube wall can be controlled to a relatively high degree.

As herein used, the term stretchable fabric is intended to encompass knitted fabrics comprised of essentially nonstretchable yarns, such as, for example, cotton, linen, flax, silk, rayon, wool, nylon, glass, polyester, and the like, or mixtures thereof, and it is also intended to encompass woven or braided fabrics made of stretchable yarns such as, for example, spandex or yarns having elastic cores covered with fibrous material, or mixture thereof.

As herein used, the term quick-setting liquid coating material is intended to encompass liquid coating materials which gel or harden within a few minutes after being prepared or reacted. It includes polyurethanes and epoxy resins, such as, for example, the air-curable coating materials prepared in accordance with the following three examples:

Example I A polyester is prepared from 0.98 mole of ethylene glycol, 0.42 mole of 1,2-propylene glycol and 1.0 mole of adipic acid. The polyester is reacted with toluene diisocyanate (80% 2,4-isomer and 20% 2,6-isomer) to form a polyester prepolymer. Thereafter, 100 parts by weight of this prepolymer is mixed and reacted with 11 parts by Weight of methylene-bis-ortho-chloroaniline which is heated to 290 before mixing. Suitable plasticizers, antioxidants and pigments are added as desired, depending upon the requirements of the final product. After or before mixing, the viscosity of the urethane composition is reduced to a suitable level for coating by heating the composition to 120 to 130 F. just prior to coating the tubular fabric. The gel time of the foregoing composition is minutes, after which it becomes a semi-solid, well on its way toward a cure and unuseable thereafter as a coating resin.

Example II In this case, a polyester prepolymer similar to that prepared in Example I above is again prepared. Thereafter, 100 parts by weight of the polyester prepolymer is mixed and reacted with 13 parts by weight of methylene diamine. This formulation has a pot life (time to gel) of from to 45 seconds depending upon whether the polyester prepolymer resin is heated, or is used at room temperature.

Example III A prepolymer comprising a condensation product of epichlorohydrin and his phenol-A is prepared. Thereafter, 100 parts of this prepolymer is mixed with 10 parts of triethylenetetramine. In the formulation the prepolymer is heated to 250 F. (a liquid state) so that it can be mixed with the cold triethylenetetramine. This formulation has a gel time of approximately 30 minutes. However, it solidifies almost immediately, allowing handling during its curing period.

As described herein, the greatest advantages of this invention are achieved when the invention is employed to coat tubular stretchable fabrics with quick-setting liquid coating materials. However, it will be obvious to those skilled in the art that the invention can also be utilized to advantage in coating other tubular fabrics in addition to stretchable fabrics. Moreover, the invention can be beneficially employed in coating tubular fabrics with coating materials that are not necessarily quick-setting as defined herein.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A method of coating tubular fabrics with a liquid coating material, comprising:

(a) providing a length of said tubular fabric;

(b) pulling said length of fabric with a given tensile force through a coating zone adapted to receive said liquid coating material and to apply said material to said fabric, said tubular fabric having a predetermined wall thickness under said tensile force;

(c) applying a radial compressive force to the wall of said tubular fabric in said zone to compress the thickness of said wall in said zone to at least 10% less than said predetermined thickness and expel air from the fibers therein;

(d) removing said compressive force so that the fabric wall expands to substantially said predetermined thickness and draws said coating material into the fibers thereof to replace the expelled air; and

(e) curing the coating material carried by said tubular fabric.

2. A method as described in claim 1 wherein said tubular fabric is a stretchable fabric having a predetermined diameter under said tensile force, and further including:

(f) applying, concurrently with the application of said compressive force, a radially expanding force to said tubular fabric to stretch said fabric to a diameter at least 10% greater than said predetermined diameter and facilitate penetration of said coating material into the interstices of said fabric; and,

(g) removing said expanding force before said coating material sets so that said tube of coated fabric returns to substantially said predetermined diameter prior to curing of the coating material thereon.

3. A method of coating tubular, stretchable fabrics with a liquid coating material, comprising:

(a) providing a length of said tubular, stretchable fabric;

(b) pulling said length of fabric with a given tensile force through a coating zone adapted to receive said liquid coating material and to apply said material to said fabric, said tubular fabric, having a predeter- 50 mined diameter under said tensile force;

(c) applying a radially expanding force to said tubular fabric to stretch said fabric to a diameter at least 10% greater than said predetermined diameter while it is in said coating zone and facilitate penetration of said coating material into said fabric in said zone;

(d) removing said expanding force before said coating material sets so that said tube of coated fabric returns to subtantially said predetermined diameter; and

60 (e) curing said coating material carried by said tubular fabric.

4. A method as described in claim 3 wherein said stretchable fabric is a knitted fabric having a predetermined wall thickness under said tensile force, and further including:

(f) concurrently with the application of said expand ing force to said fabric, applying a radially compressive force to the wall of said tubular fabric at a point therein where said expanding force is being applied to decrease the thickness of the wall of said fabric in said zone to at least 10% less than said predetermined thickness and expel air from the fibers therein; and, thereafter,

(g) releasing said radially compressive force before said coating material sets,

whereby upon release of said radially compressive force the thickness of the fabric Wall increases to substantially said predetermined thickness and said liquid coating material is drawn into the fibers thereof to replace the expelled air.

5. A method of coating elongated, tubular, knitted fabric with a quick-setting liquid coating material, comprising the steps of:

(a) providing a zone in which said liquid coating material may be applied to said tubular fabric;

(b) pulling said tubular fabric with a given tensile force through said zone, said tubular fabric having a first diameter and a first wall thickness under said tensile force;

(c) applying a distending force to the wall of said tubular fabric to expand the diameter of the tubular fabric to a second diameter at least greater than said first diameter as it passes through at least a portion of said zone to enlarge the interstices of the fabric therein;

(d) applying a radially compressive force to the wall of said tubular fabric at a point therein where said distending force is being applied to decrease the wall thickness of said fabric to a second wall thickness at least 10% less than said first wall thickness while it is distended in said zone, thereby to squeeze at least some of the air out of the strands of fabric in said wall;

(e) applying said liquid coating material to said tubular fabric in said zone to at least partially fill the enlarged interstices of the fabric tube; and

(f) discontinuing the distending and compressive forces to allow the fabric tube to retract to substantially said first diameter and the wall thickness to expand to substantially said first wall thickness,

whereby at least some of the coating material in said interstices is squeezed therefrom and absorbed into the strands of fabric in said wall to improve the bond between the coating material and said fabric tube.

6. A method of continuously coating a tubular fabric with a quick-setting, liquid coating material, comprising the steps of:

(a) pulling with a given tensile force a length of said tubular fabric in tubular form through a coating zone, said tubular fabric having a predtermined wall thickness under said tensile force;

(b) applying a radial compressive force to the wall of said tubular fabric in said zone to compress the thickness of said wall in said zone to at least 10% less than said predetermined thickness and expel air from the fibers therein;

(c) preparing said quick-setting, liquid coating material in a reaction device;

(d) delivering said liquid coating material to said coating zone and applying said liquid coating material to the compressed wall of said tubular fabric therein in a single, direct pass of said liquid coating material from said reaction device to said tubular fabric,

(1) there being no dead spaces for accumulation of stagnant liquid coating material in communication with said liquid coating material during its movement from said reaction device to said tubular fabric,

(2) the speed of the tubular fabric passing through said coating zone being related to the delivery rate of said liquid coating material thereto in such a manner as to insure that all of the liquid coating material delivered to the coating zone is applied to the tubular fabric and that suflicient liquid coating material is delivered thereto to completely cover all of the tubular fabric passing through,

(e) removing said compressive force so that the fabric Wall expands to substantially said predetermined thickness and draws said coating material into the fibers thereof to replace the expelled air,

whereby the application of the liquid coating material to the tubular fabric is continuously maintained without blockage due to the setting up of the liquid coating material prior to its application to the tubular fabric.

7. Apparatus for coating elongated tubular fabric with a liquid coating material, the fabric being under tension and having a predetermined wall thickness when so tensioned, comprising:

(a) means for creating a magnetic field;

(b) a non-magnetic, tubular member having a predetermined internal diameter mounted within said magnetic field;

(c) a magnetic element located in said tubular member and having a circular crosssection of predetermined maximum diameter in at least one plane normal to the axis of said tubular member, one-half of the difference between said internal diameter and said maximum diameter being at least 10% less than said predetermined wall thickness;

(d) means to deliver said liquid coating material to the interior of said tubular member; and,

(e) means to feed said tubular fabric through said tubular member with said magnetic element fitting Within said tubular fabric and being magnetically held in place against withdrawal from said apparatus,

whereby the wall of said tubular fabric is compressed as it passes between said tubular member and said magnetic element to squeeze entrapped air therefrom and facilitate entry of said liquid coating material thereinto.

8. Apparatus as described in claim 7 wherein said magnetic element is spherical in shape and wherein said tubular member is provided with a circularrecess about its internal periphery, said liquid coating material being delivered to said circular recess for application to the tubular fabric, the construction and arrangement being such that said spherical magnetic element is magnetically supported immediately upstream of the circular recess within said tubular member.

9. Apparatus as described in claim 7 wherein said magnetic element is spherical in shape and wherein said tubular member is provided with a conical, funnel-shaped upstream portion, said liquid delivery means delivering said liquid coating material to the funnel-shaped upstream portion of said tubular member to form a liquid coating material bank through which said tubular fabric passes, said spherical magnetic element being magnetically supported within said tubular member at a point downstream from said conical, funnel-shaped upstream portion.

10. Apparatus as described in claim 8 and further including means for adjustably positioning said tubular member relative to said magnetic field means.

11. Apparatus as described in claim 9 and further including means for a djustably positioning said tubular member relative to said magnetic field means.

References Cited UNITED STATES PATENTS 2,324,645 7/1943 Prehler.

2,602,959 7/1952 Fenlin 118-405 X 2,874,411 2/1959 'Berquist 118-405 X 3,207,616 9/1965 Cohn et a1. l177 ALFRED L. LEAVITT, Primary Examiner.

A. GRIMALDI, Assistant Examiner.

US. Cl. X.R.