Heat-setting means in a thermoplastic yarn rebound texturizing apparatus
United States Patent [191 Guenther 51 Apr. 29, 1975 1 HEAT-SETTING MEANS IN A THERMOPLASTIC YARN REBOUND TEXTURIZING APPARATUS Lloyd M. Guenther, Severna Park, Md.  
 [75] Inventor:  
 [73] Assignee: Chevron Research Company, San  
 Francisco, Calif.  
  22 Filed: Dec. 28, 1973 211 Appl. No.: 429,057  
 Primary Examiner-Louis K. Rimrodt Attorney. Agent, or FirmBurns, Doane, Swecker &amp; Mathis [57] ABSTRACT In a bounce crimping appartus for texturizing multifilament thermoplastic yarn including a yarn texturizing chamber, a means for introducing heated fluid into the yarn texturizing chamber for drawing yarn into the chamber, a foraminous surface transversely positioned across a longitudinal fluid outlet of the yarn texturizing chamber, a J-tube for receiving and heat treating the crimped yarn while maintaining the yarn substantially free from longitudinal tension. the improvement comprising a member positioned between the lateral yarn outlet of the texturizing chamber and the J-tube for directing the yarn into the .l-tube substantially along a central longitudinal axis thereof and a generally upright inlet portion of the J-tube crosssectionally being dimensioned large enough to accommodate a substantial body of yarn to be heat treated and to thereby insure movement of the yarn in a loose substantially untensioned mass downwardly through the interior of the J-tube under the influence of gravity and the inlet portion of said J-tube being concomitantly small enough in cross section to dynamically constrain, against lateral tumbling, a conical pile of incoming yarn at the top of the descending mass of yarn being heat treated with the J-tube.  
 5 Claims, 13 Drawing Figures HEAT-SETTING MEANS IN A THERMOPLASTIC YARN REBOUND TEXTURIZING APPARATUS BACKGROUND OF THE INVENTION This invention relates to an apparatus for texturizing synthetic thermoplastic yarn. More specifically, the in vention relates to an improved apparatus for bounce crimping thermoplastic yarn.  
  Synthetic thermoplastic yarn materials, as produced, are composed of continuous, straight, smooth filaments. Such yarns have little bulk, and their utility in textile applications is rather limited.  
  In order to enhance the bulk and texture of synthetic yarns as required for many end uses, a variety of crimping processes have been used in the past. For thermoplastic yarns, a basic technique is to bend the yarn filaments and heat the yarn while the filaments are in bent or crimped configurations.  
  Recently, a basic advance has been achieved in texturizing thermoplastic yarn. This texturizing technique, known as a rebound or bounce crimping process, yields strikingly improved results as far as crimp quality is concerned.  
  Bounce crimping entails hurling yarn, by a heated fluid, through a jet in a continuous stream-like flow against a foraminous surface upon which the yarn impinges and from which the yarn instantaneously rebounds or bounces. The impact of the yarn upon the foraminous surface axially buckles and crimps individual filaments of the yarn while the heated fluid passes through the foraminous surface. The texturized yarn progresses without tension and substantially by rebound inertia away from the crimping zone and is guided to a collection station where the yarn is heated and then cooled to heat set the crimp prior to winding upon a storage spool.  
  Thermoplastic yarn texturized by the foregoing bounce crimping process possesses, inter alia, exceptional covering capability and a high degree of resiliency as disclosed in United States Clarkson et al US. Pat. No. 3,686,848 issued Aug. 29, 1972.  
  The basic process and apparatus for practicing the process is featured in US. Clarkson Pat. No. 3,665,567 issued May 30, 1972. In brief summary, the Clarkson structure entails feeding a yarn through an elongate slender tube by a jet of steam and hurling the yarn longitudinally against a foraminous screen. The yarn is thereby crimped or texturized and freely rebounds laterally through a passage from which the yarn descends into a J-tube receiver for heat setting.  
  Notwithstanding singular advantages provided the synthetic textile industry by the abovenoted Clarkson bounce crimping process and apparatus, room for significant improvement remains. In this connection, one area of particular concern is the uncontrolled delivery of yarn from the texturizing chamber into the J-tube. More particularly, yarn falling into the J-tube to be heat treated tends to build up in piles which themselves topple irregularly in different directions. Not only does this toppling or tumbling action introduce irregularities in the density of the material moving through the treating zones, it also is responsible for undesirable knotting and tangling effects.  
  A swingable flapper is provided at the outlet of a yarn texturizing chamber according to heretofore known apparatus. This flapper serves to generally direct the texturized yarn into the J-tube. In ordinary operation, the  
 flapper swings back and forth unpredictably in response to pressure gusts. The foregoing noted toppling effect tends to be accentuated by erratic operation of such a pivotal structure.  
  Accordingly, it would be highly desirable to provide an improved bounce crimping apparatus wherein yarn toppling within a heat treating J-tube may be minimized.  
  Further, in prior designs the heat treating J-tube is composed of a straight heating section having a circular cross section and a curved cooling section having a larger rectangular cross section. In at least some instances irregularities and tangling have been occasioned as the yarn body in the .I-tube transitions from one section to another.  
  Further, in prior known devices the J-tube heat setting portion is surrounded by a longitudinally extending insulated steam chamber which is used to conduct heat through the walls of the J-tube to heat the yarn within the tube by conduction. Additionally air bleed lines are introduced within the interior of the J-tube for introducing heated air into the crimped yarn. The J-tube cooling portion is located downstream of the heating portion and entails a plurality of ambient air bleed lines introduced into the interior thereof to issue cooling air into the heated texturized yarn to set the yarn. The yarn is withdrawn from the cooling chamber by the provision of a set of godet rolls. The rate of rotation of the rolls is controlled by a lever and switch assembly extending into the uppermost portion of the J-tube. When the yarn falling into the chamber builds up past the lever, the switch is actuated to increase the takeup of the godet rolls. By the provision of such a lever arrangement the buildup of yarn within the J-tube may be controlled.  
  These previously known J-tube structures have been found to be inefficient. Moreover, tubes and levers positioned within the interior of the J-tube tend to obstruct the free and unencumbered flow of yarn through the heat treating process.  
  Accordingly, it would be highly desirable to provide an improved heat treating means for a bounce crimping apparatus wherein heating efficiency may be increased and the flow of yarn through the .I-tube heat treating member will be substantially unobstructed.  
 OBJECTS AND BRIEF SUMMARY OF THE INVENTION Objects In light of the foregoing, it is a general object of the invention to provide an improved yarn rebound texturizing apparatus which will obviate or minimize deficiencies and provide enhanced properties of the type previously described.  
  It is a particular object of the invention to provide an improved bounce crimping apparatus wherein texturized yarn issuing from a bounce crimping chamber is placed into a J-tube for heat setting in a laminar manner and without tangles caused by build up and toppling of yarn.  
  It is a further object of the invention to provide an improved bounce crimping apparatus wherein rearrangement of yarn within a .I-tube heat setting chamber after it has been laid down is minimized and obstructions and/or irregularities within a heat setting J-tube structure are eliminated.  
  It is still a further object of the invention to provide an improved bounce crimping apparatus wherein heated gas may be directly and efficiently introduced into the interior of a texturized yarn receiving J-tube to uniformly heat the yarn without obstructing the free flow of the yarn through the J-tube.  
  It is yet a further object of the invention to provide an improved bounce crimping apparatus wherein a high volume of cooling air may be directly introduced into a cooling portion of a J-tube without providing an obstruction to the passage of yarn through the cooling portion of the .I-tube.  
  It is another object of the invention to provide an improved bounce crimping apparatus wherein a full measure of texturized yarn may be dynamically maintained within a heat setting J-tube structure without introducing obstructing members into the yarn passage chamber.  
 Brief Summary A bounce crimping apparatus according to a preferred embodiment of the invention intended to achieve at least some of the foregoing objects includes a yarn texturizing chamber, a means for introducing heated fluid into the yarn texturizing chamber for drawing yarn into the chamber, a foraminous surface transversely positioned across a longitudinal fluid outlet of the yarn texturizing chamber and a J-tube for receiving and heat treating the crimped yarn while maintaining the yarn substantially free from longitudinal tension. A guiding member is positioned between the lateral yarn outlet of the texturizing chamber and the J-tube for directing the yarn into the J-tube substantially along a central longitudinal axis thereof. The J- tube is cross-sectionally dimensioned large enough to accommodate a substantial body of yarn to be heat treated and to thereby insure movement of the yarn in a loose substantially untensioned mass downwardly through the interior of the J-tube under the influence of gravity while concomitantly being small enough in cross section to dynamically constrain, against lateral tumbling, a conical pile of incoming yarn at the top of the descending mass of yarn being heat treated with the .I-tube.  
  The J-tube is formed with a cylindrical heating portion and a toroidal cooling portion both of which are circular in cross section. Moreover, the cylinders are fashioned with approximately equal cross-sectional areas so that the yarn body within the J-tube will readily and smoothly pass from the heating portion into the cooling portion of the .I-tube with a minimum amount of yarn body reorientation, so as to further reduce the occurrence of tangles and knots in the treated yarn.  
  A housing is coaxially positioned about at least a portion of the J-tube for forming a heating fluid plenum chamber between the .I-tube and the housing. Apertures are fashioned through a wall portion of the J-tube for directly introducing the heated fluid from the plenum chamber into the .I-tube for heating the crimped yarn within the J-tube without obstructing movement of the crimped yarn therethrough.  
  In a similar vein a second housing is positioned adjacent the J-tube to form a cooling fluid plenum chamber. A plurality of arcuate apertures are fashioned through the wall of the .I-tube and enable cooling air to be blown directly into the texturized yarn without obstructing movement of the yarn through the J-tube.  
  A photoelectric switching assembly is mounted at an upper end of the .I-tube to dynamically regulate the height of yarn within the .I-tube during a heat treating operation. This new system eliminates entirely all contact between the yarn being treated and the detector devices serving to sense the height of the yarn body in the .I-tube and obviate irregularities associated therewith.  
 THE DRAWINGS Further objects and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, wherein:  
  FIG. 1 is a front elevational view, partially broken away, of a bounce crimping apparatus for texturizing synthetic thermoplastic continuous filament yarn;  
  FIG. 1A is a cross-sectional view taken along section lA-lA in FIG. 1 and discloses a yarn texturizing chamber including a foraminous yarn rebound screen.  
  FIGS. 2a-c represent the prior art and sequentially show the random introduction of texturized yarn into a heat setting chamber wherein back and forth toppling of the yarn is encountered;  
  FIGS. 3a-c schematically disclose controlled and uniform introduction of texturized yarn into a heat setting J-tube of a defined cross-sectional area according to to the subject invention;  
  FIG. 4 is a side elevational view of a means for receiving texturized yarn and for controllably introducing the yarn coaxially into a yarn heat setting .I-tube;  
  FIG. 5 is a cross-sectional view taken along section line 55 in FIG. 1 and discloses a smooth circular transition zone between a yarn heating and cooling portion of a tubular heat setting J-tube;  
  FIG. 6 is a cross-sectional view taken along section line 6-6 in FIG. 1 and discloses a plenum chamber for introducing heating fluid directly into texturized yarn to be heated;  
  FIG. 7 is a cross-sectional view taken along section line 77 in FIG. 1 and discloses a cooling plenum for introducing cooling air into a zone downstream of the heating plenum for cooling and heat setting texturized yarn within the bounce crimping apparatus; and  
  FIG. 8 is a cross-sectional view taken along section line 88 in FIG. 1 and discloses a photoelectric switching mechanism utilized to regulate the volume of texturized yarn within the heat setting .I-tube without introducing a physical structure into the .I-tube.  
 DETAILED DESCRIPTION The improvements of the subject invention are in specific combination with a bounce crimping apparatus according to the abovereferenced Clarkson US. Pat. No. 3,665,567. The entire disclosure of this Clarkson patent is hereby incorporated by reference as though set forth at length.  
  Briefly, however, the basic bounce crimping structure of the subject combination invention may be appreciated by reference to FIG. I which discloses an elevational view, partially broken away, of a bounce crimping apparatus 10.  
  A multi-filament synthetic thermoplastic yarn 12 is fed from a supply package (not shown) to a first roll pair consisting of a driven godet roll 16 with separator roll 14 and then into a second roll pair consisting of a driven godet roll with separator roll 18. Godet rolls 16 and 20 may be heated and rolls l8 and 20 advance the yarn at a much greater speed than do rolls l4 and 16 so that the yarn I2 is drawn between the two sets of rolls.  
  From roll 18 yarn l2 advances to a yarn texturizing chamber indicated generally by reference character 22. Live steam is introduced into the yarn texturizing chamber 22 through a regulating valve 24, and a plumbing tee 26. Live process steam within the yarn texturizing chamber 22 heats the yarn and hurls the yarn against a foraminous screen 21 to axially crimp or texturize the yarn fibers. The texturized or crimped yarn then rebounds laterally out of the texturizing chamber 22 and is guided in a manner to be discussed more fully hereinafter into a tubular heat setting J-tube 28.  
  The heat setting .l-tube 28 comprises a first heating portion 30 and a downstream cooling portion 32. Texturized yarn which is introduced into the heating portion 30 is first heated and then axially progresses into a cooling zone chamber 32 so that the crimp in the yarn may be heat set.  
  The texturizing heat set yarn 12 is then drawn from the cooling chamber 32 in the form of a strand over idler rollers 34, 36 and 38 by a pair of godet rolls 40 and 42. From godet rolls 40 and 42 the yarn 12 advances over idler roll 44 to a standard take-up mechanism where the yarn is wound in a package 46 for storage and shipment.  
 Not until the yarn has been fully heat set and cooled is the texturizing yarn subjected to substantial longitudinal tension. More particularly, as the yarn is drawn over idler rolls 34, 36 and 38 the yarn passes over a baffle 48 and through an eyelet 50 which tends to remove gross tangles in the yarn. To further remove any persistent tangles a series of tension vanes 52, 54, 56 and 58 are provided. These vanes are simply thin pieces of sheet metal shaped to close the chamber 32 and are pivoted at hinges 60, 62, 64 and 66, respectively, so as to fall by gravity counterclockwise against an opposing wall 68 of the chamber. The yarn as it advances upwardly from eyelet 50 is pinched gently by the vanes 52-58 in succession which tends to pull out any persistent tangles in the yarn as it is led from a yarn mass in cooling chamber 32.  
  The yarn now once again in substantially linear form is pulled over idler rolls 34, 36 and 38 by pull out godet rolls and 42 and is fed forward to be wound-up in a package 46 in a conventional manner as previously noted.  
 J-Tube Yarn Processing Referring now specifically to the schematic illustrations of FIGS. 2a, 2b and 2c, there will be seen a representation of the random manner in which texturized yarn has been, in the past, received within a yarn receiving J-tube 28. In this connection the yarn l2 spews from the texturizing chamber 22 in a bouncing random manner generally along a central axis 74 of the receiving end of the J-tube 28 and forms a small mound or pile 70. As the pile builds, an asymmetric peak 72 will typically be formed with respect to the central longitudinal axis 74 of the .l-tube (FIG. 2b). The vertical walls of the J-tube are spaced substantially from the tip of the peak 72 and, upon further delivery of yarn into the J- tube, the unsupported peak 72 will topple or tumble down in a location such as 76 wherein an upper surface portion 78 may fall upon a lower surface portion 80 of the yarn within the tubular member 28. Accordingly yarn will accumulate within the J-tube in a back and forth random toppling pattern.  
  In sum, with prior devices, yarn tumbling 0r toppling was occasioned within a yarn heat treating J-tube due primarily to incomplete support and asymmetric deposit of yarn being fed into the J-tube. As the J-tube 28 fills with such back and forth random tumbling, undesirable density variations and knotting or tangling of the yarn result.  
  Referring now to FIGS. 3a-c there will be seen a schematic representation of the buildup of yarn within a J-tube according to a preferred embodiment of the invention. More specifically, it has been discovered that one way to minimize toppling or tumbling of yarn within the entrance zone of the J-tube 28 is to crosssectionally size the J-tube small enough to provide lateral support for a base portion 82 of the incoming yarn cone within the J-tube. At the same time it is necessary to size the J-tube large enough so that a sufficient quantity of yarn will build up within the .I-tube to insure movement of the yarn body through the tube by gravity action upon the yarn mass and to provide adequate heat setting time within a unit of reasonable length.  
  It has further been determined that the design of the J-tube to meet the foregoing requirements is a function of yarn size or denier. The most desirable results have been produced when the J-tube is designed with 0.5 to 0.9 square inches in cross sectional area for each 100 denier of yarn being processed. For example, 1800 denier multifilament polypropylene upholstery yarns have been handled quite satisfactorily in a J-tube having a 3.83 inch internal diameter (i.e., having an internal cross sectional area of about I 1.5 square inches), and similar, but smaller, 900 denier yarns have been handled satisfactorily in a J-tube having a 2.83 inch internal diameter (i.e., having an internal cross-sectional area of about 6.3 square inches).  
  In order to achieve controlled axial placement of the yarn 12 within the J-tube a guide (FIG. I) is provided between the yarn texturizing chamber 22 and the J-tube 28. The guide 90 receives the yarn l2 spewing from the texturizing chamber, collects the yarn and axially and uniformly deposits the yarn into the J-tube a: at 92.  
  An alternate preferred embodiment of a yarn receiving and guiding mechanism according to the inventior comprises a tubular member 96 (note FIG. 4) directly fitted onto the texturizing chamber 22 and bent downwardly approximately 90 so that its outlet end 98 is coaxial with respect to the end of the yarn receiving J tube 28.  
  When the .l-tube is sized in accordance with the di mensional criteria and the yarn is received within tht J-tube substantially along the central longitudinal axi: 74 thereof, the yarn will build up within and fill the J tube in a uniform nontoppling manner such as sequen tially depicted in FIGS. 3a, 3b and 3c. Such uniforn placement of yarn within the texturized yarn receiving tube 28 enhances uniformity and minimized knottin; or tangling of filaments from one yarn section witl other yarn sections further down the length of the yarn As previously noted, the J-tube 28 is comprised of first straight tubular heating portion 30 and a seconi arcuate tubular cooling portion 32. As may be noted in FIG. each of the tubular portions 30 and 32 is circular in cross section and of approximately the same diameter. Accordingly the sections may be intimately joined as at 100 (FIG. 1). Accordingly, the yarn body within the J-tube may smoothly pass from the heating section 30 into the cooling section 32 downstream thereof without meeting interior obstacles of any kind and without undergoing any substantial change in cross section, -so that there is nothing to disturb the substantially uniform density of the body of texturized yarn within the J-tube during the treating operations.  
  Turning now specifically to FIGS. 1 and 6 of the drawings, it will be seen that the J-tube 28 is fitted approximately midway of the heating portion 30 thereof with a concentric housing 102 having a longitudinal extent approximately equal to its diameter. The housing 102 in combination with the exterior surface of the tubular wall 104 of the heating portion 30 provides an annular heating fluid plenum chamber 106. A threaded fitting 108 connects into the plenum chamber 106 through the housing wall 102 and serves to fluidically communicate heated air from a source, not shown, into the annular heating plenum chamber 106.  
  As specifically illustrated in FIG. 1 an upper set 110 and a lower set 112 of apertures are fashioned through the tubular wall 104 in a regular circular pattern. The apertures 110 and 112 provide a means for introducing the heated air from the fluid plenum chamber 106 directly into the interior of the tubular heating section 30 of the J-tube 28.  
  The introduction of heated air directly into the texturized yarn by the foregoing structure rapidly and efficiently heats the yarn to an approximately uniform extent without objectionably blocking movement of the yarn through the heating section 30.  
  Referring now to FIGS. 1 and 7, the cooling section 32 is provided with an exterior housing 120 at a lowermost portion thereof. The housing is fitted with an inlet conduit 122 for receiving ambient cooling air. Ambient cooling air is collected within a plenum chamber 124 provided by the interior surface of the housing 120 and the exterior surface 126 of the cooling section 32. A plurality of arcuate apertures 128 are fashioned through the wall 126 of the cooling section 32 and serve to introduce a high volume of cooling air uniformly into the texturized yarn to cool the yarn without presenting a physical obstruction to the uniform and ready passage of crimped yarn through the cooling section. Air entering the arcuate apertures 128 may exit from the cooling section 32 by an aperture 130 cut within a top portion of the tubular wall 126.  
  Turning now to FIGS. 1 and 8 there will be seen a mechanism for dynamically maintaining a substantially uniform volume of texturized yarn within the heat setting .I-tube 28 without presenting an obstruction within the interior ofthe .l-tube which may tend to disturb uniform placement and advance of yarn through the heating section 30.  
  In this connection a light projecting source 132 is connected to an upper end of the heating section 30 at an elevational location selected to be the optimum buildup point of yarn within the J-tube 28. Opposed from the light source 132 is a light sensitive receiving member 134 of a conventional commercial design operable to receive a light beam 136 from the light projecting member 132. The light sensitive receiving means is operably connected to an electric circuit which serves to control the rate of takeup provided by the pair of godet rolls 40 and 42. Thus when yarn piles up within the J-tube 28 above the level of the light beam 136, the beam will be broken and the set of godet rolls 40 and 42 will speed up to increase the rate of yarn withdrawal from the discharge end of the J-tube and lower the level of yarn at the input end. Conversely, when the yarn drops below the light beam, the godet rolls will slow down thus allowing the yarn to build up within the .I-tube to a higher level.  
  The foregoing described photoelectric switching mechanism provides a means for dynamically controlling the level of texturized yarn within the yarn receiving chamber 28 without obstructing the free collection and passage of yarn through the chamber.  
 SUMMARY OF MAJOR ADVANTAGES In describing in detail improvements in a bounce crimping apparatus according to a preferred embodiment of the invention, several significant advantages have been delineated.  
  The dimensional sizing of the J-tube of 0.5 to 0.9 square inches per denier of yarn minimizes the tendency of yarn received within the .l-tube to topple and form an irregular dispensing within the J-tube while simultaneously providing continuous movement of the yarn through the .l-tube by gravity. Moreover. the provision of a guide to receive yarn spewing from the texturizing chamber and axially delivering the yarn into the J tube further minimizes the tendency of yarn to topple within the J-tube.  
  Another aspect of the subject invention entails the smooth transition between a straight tubular heating portion of the .I-tube into an arcuate tubular cooling portion of the J-tube, both of which are circular in cross section.  
  Further, it will be appreciated that the heating collar or housing along with apertures through the heating tube permits the introduction of heated air directly into the interior of the yarn receiving chamber 28 to efficiently and uniformly heat the yarn without presenting a material obstruction or disruption to the uniform flow or passage of yarn through the heating section. In this same vein, a cooling plenum chamber is provided exteriorly of the .l-tube which permits the introduction of a high volume of cooling air into the cooling section by the provision of arcuate slots. The cooling air is admitted without the introduction of tubular conduits or the like which may tend to retard or detract from a uniform flow of texturized yarn through the heating and cooling tube.  
  Additionally, yarn is maintained at an optimum elevation within the tubular receiving member 28 by the provision of a photoelectric switching mechanism operative to control the speed of takeup of the set of godet rolls and thereby to control the rate of withdrawal of yarn from the .l-tube.  
  While the invention has been described with reference to preferred embodiments, it will be appreciated by those skilled in the art that additions, deletions, modifications and substitutions or other changes not specifically described may be made which will fall within the purview of the appended claims.  
 What is claimed is:  
  1. In bounce crimping apparatus for texturizing multi-filament thermoplastic yarn including;  
 a yarn texturizing chamber having an inlet, a fluid outlet longitudinally aligned with said inlet, and a lateral yarn outlet,  
 means for introducing a heated fluid into said yarn texturizing chamber for drawing yarn into said chamber,  
 a foraminous surface transversely positioned across said fluid outlet of said chamber, said heated fluid introduced into said chamber for drawing yarn into said chamber further serving to hurl the yarn against said foraminous surface to axially compress and crimp the yarn filaments and rebound the yarn through said lateral outlet of said yarn texturizing chamber, and  
 means for heat treating the crimped yarn to heat set the yarn while maintaining the yarn substantially free from longitudinal tension, said means for heat treating including a J-tube into one end of which yarn is fed substantially continuously and from the other end of which yarn is withdrawn substantially continuously and within which a body of yarn moves slowly from one end to the other to permit heat treatment thereof on a continuous basis,  
 the improvement comprising:  
 means positioned between said lateral yarn outlet of said texturizing chamber and said J-tube for directing the yarn from said texturizing chamber into an inlet end of said J-tube substantially along a central longitudinal axis thereof; and  
 a generally upright inlet portion of said .l-tube having a defined internal cross-sectional area selected in accordance with the size of the yarn being processed such that approximately 0.5 to 0.9 square inches of tubular cross-sectional area are provided for each 100 denier of yarn being texturized, wherein said inlet portion of said J-tube is large enough in cross section for accommodating a substantial body of yarn to be heat treated and thereby insure movement of the yarn in a loose substan- 40 tially untensioned mass downwardly through the interior of the .l-tube under the influence of gravity and wherein said inlet portion of said J -tube is concomitantly small enough in cross section so as to dynamically constrain against lateral tumbling a conical pile of incoming yarn at the top of the descending mass of yarn being heat treated with the tube.  
 2. A bounce crimping apparatus for texturizing multifilament thermoplastic yarn as defined in claim 1 wherein the improvement further comprises:  
 a first generally upright straight section of said J-tube for heating yarn passing therethrough and a second generally arcuate section of said J-tube positioned downstream of said straight section for cooling yarn passing therethrough, said first and second sections being fashioned from tubular members each having a circular cross section and wherein an outlet end of said first section is fitted into and an inlet end of said second section and the internal cross-sectional areas at the junction of said first and second sections are approximately equal.  
 3. In bounce crimping apparatus for texturizing multi-filament thermoplastic yarn including;  
 a yarn texturizing chamber having an inlet, a fluid outlet longitudinally aligned with said inlet and a lateral yarn outlet,  
 means for introducing a heated fluid into said yarn texturizing chamber for drawing yarn into said chamber,  
 a foraminous surface transversely positioned across 5 said fluid outlet of said chamber, said heating fluid introduced into said yarn chamber for drawing yarn into said chamber further serving to hurl the yarn against said foraminous surface to axially compress and crimp the yarn filaments and rebound the yarn through said lateral outlet of said yarn texturizing chamber,  
 J-tube means having an inlet end positioned beneath said yarn texturizing chamber to receive said crimped yarn for heat treating said yarn within said J-tube means while maintaining the yarn substantially free from longitudinal tension, and  
 take-up means for withdrawing the crimped yarn from a discharge end of said J-tube means, the improvement comprising:  
 housing means coaxially positioned about at least a portion of said J -tube means for forming a heating fluid plenum chamber between said J-tube means and said housing means, means connected to said housing means for introducing heated fluid into said plenum chamber, and  
 aperture means fashioned through a wall portion of said J-tube means for directly introducing the heated fluid from said plenum chamber into said J-tube means to raise the temperature of crimped yarn therein without obstructing movement of the crimped yarn through said J-tube means.  
  4. A bounce crimping apparatus for texturizing mutlifilament thermoplastic yarn as defined in claim 3 wherein the improvement further comprises:  
 second housing means connected to said J-tube means downstream from said heating fluid plenum chamber for forming a cooling fluid plenum chamber between said J-tube means and said housing means;  
 means connected to said second housing means for introducing cooling fluid into said second housing means; and  
 aperture means fashioned through a wall portion of said J-tube means for introducing cooling fluid from said second plenum chamber into said J-tube means for lowering the temperature of the crimped yarn therein without obstructing movement of the crimped yarn through said J-tube means.  
  5. A bounce crimping apparatus for texturizing multifilament thermoplastic yarn as defined in claim 3 and including switching means for so controlling the speed of said take-up means as to dynamically maintain a predetermined desirable quantity of yarn within the 1- tube, said switching means comprising:  
 light projecting means connected to said J-tube means at the inlet end thereof for projecting a beam of light through said J-tube means, light sensitive receiving means connected to the upper end of said J-tube means in a posture opposed to said light projecting means for sensing the presence of light projected from said light projecting means through said J-tube means except when crimped yarn deposited within said receiving means piles up sufficiently to block light projected from said light projecting means.