Abstract:
The present invention is directed to a down-sizable fitting for transferring a high-temperature, high-pressurized special chemical fluid which should be under strict control used in a high technology field or industry. A fitting according to the invention comprises a fastener ( 9 ) engaging a two-plied section including a folded-back portion ( 1   c ) which is formed such that one end section of a tube ( 1 ) is folded or turned back outwardly, and a fitting body ( 4 ) for fitting into the fastener ( 9, 11 ); 
     the fastener ( 9, 11 ) having an engaging portion ( 9   c ) for receiving said two-plied section of the tube ( 1 ), a contact portion ( 9   b ) for contact with the outer surface of the folded-back portion ( 1   c ) of the tube ( 1 ), and a threaded portion ( 9   d ) formed on the inner surface thereof; 
     the engaging portion ( 9   c ), the contact portion ( 9   b ) and the threaded portion ( 9   d ) are axially aligned; 
     the fitting body ( 4 ) including a cylindrical section ( 4   a ) which has an end for abutting against the U-shaped end ( 1   c ) of the two-plied section of the tube ( 1 ), the cylindrical section ( 4   a ) provided at the outer surface thereof with a threaded portion ( 4   b ).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a fitting or a fitting structure of a synthetic resinous material mainly used in a tubing system in a high technology field or industry such as fabrication of semiconductors, for example, for transferring a high-temperature, high-pressurized special chemical fluid which should be under strict control because of its environmental impact, for example. 
     2. Prior Art 
     There are known fitting structures for plastic pipes or tubes, which use fluid-tight screws, ferrules, or a variety of other fluid-tight structures. Because of inherent natures of fluoroplastics, fitting structures made of a fluoroplastic material, for example, TFE (tetrafluoroethylene), PFA (copolymer of polytetrafluoroethylene and perfluoroalkylvinylether), or FEP (copolymer of polytetrafluoropropylene), are often used for transferring high-temperature, high-pressurized chemical fluids, particularly chemical liquids which need careful handling. However, conventional fluoroplastic fitting structures involve the problem of leakage of fluids. Namely, these fitting structures repeatedly experience expansion and contraction during the heat cycle, and creeps are produced in the fitting structures. These creeps result in making microscopic gaps between connected elements, and this is a major reason of the leakage problem. It is extremely difficult to prevent these gaps from being made. 
     To solve the problem a tube fitting as shown in FIG. 7 has been proposed. The prior art fitting shown in FIG. 7 is used for connecting a tube to an associated device, for example. In FIG. 7, the reference numeral  1  represents a tube made of a fluoroplastic material. One end or a forward end section of the tube  1  is folded back to outwardly overlap the remainder main portion of the tube  1  to form a folded-back portion of a predetermined length. As a result, the tube  1 , in the folded shape, defines a folded-back end which is U-shaped in its cross section. 
     A fitting for connecting the tube  1  is made up of an insert  10 , a fitting body  6  and a ring member  8  which are all made of a fluoroplastic material. 
     The insert  10  has a tubular shape and it is mounted on the tube  1  such that one end section (lower end section in FIG. 7) of the insert  10  sits between the main body of the tube  1  and the foldedback portion thereof. 
     The fitting body  6  includes an annular groove  6   a  whose bottom is U-shaped in its cross section to fit the U-shaped forward end of the tube  1 ; a cylindrical portion  6   c  encircling the annular groove  6   a  to define an inner wall surface  6   b  for contact with the outer wall of the folded-back portion of the tube  1  and an outer wall surface threaded to form a threaded portion  6   f ; and a connecting portion  6   e  threaded on its outer circumferential surface to form a threaded portion  6   d  for connecting the fitting body  6  to an associated device or apparatus. 
     The ring member  8  includes an inner ring portion  8   a  for engagement with the other end (upper end in FIG. 7) of the insert  10 , and an outer cylindrical portion  8   b  whose inner wall surface is threaded to form a threaded portion  8   c  for threading engagement with the threaded portion  6   f  of the fitting body  6 . 
     For fabricating the fitting structure, one end section of the tube  1  is first folded back outwardly by a predetermined length, and the insert  10  is inserted between the main portion and the folded-back portion of the tube  1 . Then, the semi-assembly of the tube  1  and the insert  10  is joined to the fitting body  6 . After that, the portion  6   f  of the fitting body  6  is threadedly engaged with the portion  8   c  of the ring member  8  until the insert  10  tightly compresses the U-shaped forward end of the tube  1  onto the annular groove  6   a  of the fitting body  6 . 
     As a result, the tube  1  is firmly connected to the fitting, and the above-mentioned leakage problem is removed. 
     However, the prior art fitting structure is bulky in diameter because of the radially overlapped arrangement of the insert  10 , the cylindrical portion  6   c  of the fitting body  6  and the outer cylindrical portion  8   b  of the ring member  8  around the tube  1  with threads being formed on the portions  6   c  and  8   b  for firm engagement between the fitting body  6  and the ring member  8 . With the prior art fitting, the diametrical bulkiness of the fitting will make it impossible to arrange a plurality of tubes closely side by side for connection with the associated device. 
     SUMMARY OF THE INVENTION 
     The invention overcomes the above-mentioned problems by providing a fitting for connecting one tube to another tube or an associated device, said fitting comprising a fastener for engagement a two-plied section including a folded-back portion which is formed by folding or turning back one end section of said tube outwardly, and a fitting body for fitting into said fastener; 
     said fastener having an engaging portion for receiving said two-plied section of said tube, a contact portion for contact with the outer surface of said folded-back portion of said tube, and a threaded portion formed on the inner surface thereof; 
     said engaging portion, said contact portion and said threaded portion being axially aligned; 
     said fitting body including a cylindrical section which has an end for abutting against the U-shaped end of said two-plied section of said tube, said cylindrical section being provided with a threaded portion on the outer surface thereof. 
     The fitting according to the invention may include a insert having one end section to be inserted between the main body of the tube and the folded-back portion in the two-plied section. In this case, the fastener preferably has an engaging portion which is engageable with the other end of the insert. 
     According to the fitting of the invention, since the threaded portion is arranged axially offset from the engaging portion and the contact portion, it is possible for the fastener to have a decreased outer diameter in comparison with the prior art fitting. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The below detailed description makes reference to the accompanying drawings, in which: 
     FIG. 1 is a cross-sectional view of a fitting structure according to the first embodiment of the invention; 
     FIG. 2 is an exploded, cross-sectional view of a fitting shown in FIG. 1; 
     FIG. 3 is a cross-sectional view of a fitting structure according to the second embodiment of the invention; 
     FIG. 4 is a cross-sectional view of a fitting structure according to the third embodiment of the invention; 
     FIG. 5 is a perspective view of the fitting structure shown in FIG. 4, partly cut out to show the interior structure; 
     FIG. 6 is a cross-sectional view of a fitting structure according to the fourth embodiment of the invention; 
     FIG. 7 is a cross-sectional view of a conventional fitting structure. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings attached, preferred embodiments of the invention will be described below. 
     FIGS. 1 and 2 illustrate a first embodiment of the invention. In FIG. 1, the reference numeral  1  represents a tube of a fluoroplastic material, one end section of which is folded or turned back outwardly to form a predetermined length of U-shaped two-plied section. 
     A fitting for connecting the tube  1  includes a fitting body  4  and a fastener  9 , which are made of a fluoroplastic material. The fastener  9  has a cylindrical shape including an upper opening, as shown in FIG. 2, through which the tube  1  is set. In FIGS. 1 and 2, the reference numeral  9   c  represents an engaging portion of the fastener  9 . The engaging portion  9   c  includes an interior surface, the inner diameter of which is substantially equal to the outer diameter of the tube  1 . 
     The reference numeral  9   b  indicates a contact portion positioned just below the engaging portion  9   c . The contact portion  9   b  has an inner diameter which is substantially equal to the outer diameter of the folded-back portion  1   c  of the tube  1  and has a length which is substantially equal to that of the folded-back portion  1   c.    
     As seen from the above, the engaging portion  9   c  is formed so as to protrude inwardly by a distance substantially equal to the thickness of the tube  1  to define a circumferential step  9   c   1  between the engaging portion  9   c  and the contact portion  9   b.    
     As shown in FIG. 1, the fastener  9  is set and positioned at the folded-back portion  1   c  of tube  1  by using the engaging portion  9   c  and the contact portion  9   b  thereof. That is, since the contact portion  9   b  has the inner diameter and the length which are substantially equal to those of the folded-back portion  1   c  of the tube  1 , the fastener  9  is closely fitted onto the outer surface of the folded-back portion  1   c  of the tube  1 . And also, the engaging portion  9   c , which has the inner diameter substantially equal to the outer diameter of the tube  1 , can prevent the tube  1  from moving in a direction indicated by the arrow B in FIG. 1 because the end  1   d  of the folded-back portion  1   c  abuts against the step  9   c   1 . 
     The reference numeral  9   d  represents a threaded portion positioned just below the contact portion  9   b . The threaded portion  9   d  is threadedly engageable with a threaded portion formed on the fitting body  4 , which threaded portion of the fitting body  4  will be described below. 
     The threaded portion  9   d  is located at such a place that when the fastener  9  is set on the tube  1 , the threaded portion  9   d  is positioned in front of the two-plied section of the tube  1  (below the folded section of the tube  1  in FIG.  1 ). Namely, as shown in FIG. 1, the tubular fastener  9  is designed so that the engaging portion  9   c , the contact portion  9   b  and the threaded portion  9   d  are axially aligned and located adjacently, respectively. In other words, the inner surface of the tubular fastener  9  is provided at the upper area thereof with the engaging portion  9   c , at the central area with the contact portion  9   b , and at the lower area with the threaded portion  9   d , and the portions  9   c ,  9   b  and  9   d  are located adjacently, respectively. 
     As seen from the above, the threaded portion  9   d  is arranged axially offset from the engaging portion  9   c  and the contact portion  9   b , and it is therefore possible for the fastener  9  to have a decreased outer diameter in comparison with that of the ring member  8  shown in FIG.  7 . Namely, it is necessary in the prior art fitting to consider the sum of the outer diameter of the tube  1 , thicknesses of the tubular insert  10 , the folded-back portion  1   c  of the tube  1 , the ring portion  6   c  of the fitting body  6  and the outside ring portion  8   b  of the ring member  8  in order to determine an outer diameter of the ring member  8 . In contrast, an outer diameter of the fastener  9  according to the invention is determined in consideration for the sum of the outer diameter of the tube  1  and thicknesses of the fastener  9  and the folded-back portion  1   c  thereof. As a result, the fastener  9  according to the present invention can be designed to have an outer diameter smaller than that of the prior art ring member  8 . 
     Referring again to FIG. 1, the fitting body  4  is of an cylindrical shape and defines an axially straight passage  4   c  passing therethrough for a flow of chemical liquid which should be under strict control. An inner diameter of the passage  4   c  is designed to be substantially the same as the inner diameter of the tube  1 . And also, the fitting body  4  has an upper end for contact with the tube  1 . The upper end of the fitting body  4  has formed an annular groove  4   e  which is U-shaped in its cross section. The annular groove  4   e  is adapted to receive the U-shaped end  1   a  of the tube  1  to make a seal therebetween for preventing leakage of a liquid. 
     The width of the upper end of the fitting body  4  is substantially the same as the thickness of the two-plied section of the tube  1 . This causes the upper end of the fitting body  4  to be closely fitted on the U-shaped end  1   a  of the tube  1 . The fitting body  4  has a cylindrical section  4   a  whose outer surface forms a threaded portion  4   b . The threaded portion  4   b  is adapted to threadedly engage with a threaded portion  9   d  of the fastener  9 . 
     As shown in FIGS. 1 and 2, the fitting body  4  has a connecting section  4   d  which is formed integrally with the cylindrical section  4   a . The connecting section  4   d  is provided on the outer surface thereof with a threaded portion by which the fitting body  4  can be connected to an associated device A such as a pump. 
     A process to make up the fitting structure according to the first embodiment of the invention will be described below. 
     First, as shown in FIG. 1, one end section of the tube  1  is folded or turned back by a predetermined length thereof to make the folded-back portion  1   c . The length of the folded-back portion  1   c  is substantially the same as that of the contact portion  9   b  of the fastener  9 . Next, the fastener  9  is set on the tube  1 . The operation to set the fastener  9  on the tube  1  is performed as follows. First, the other end of the tube  1  is faced to an opening of the threaded portion  9   d  of the fastener  9 . Next, the tube  1  is inserted into the fastener  9  from the threaded portion  9   d . After that, the tube  1  is abutted with its end  1   d  of the folded-back portion  1   c  against the step  9   c    1  of the fastener  9 . 
     After the operation, the threaded portion  4   b  of the fitting body  4  is threadedly engaged with the threaded portion  9   d  of the fastener  9  to compress the end  1   a  of the U-shaped two-plied section of the tube  1  onto the U-shaped groove  4   e  of the fitting body  4 . As a result of the above operation, the fitting structure including the tube  1  is completed. 
     As described above, the flow passage  4   c  of the fitting body  4  has the inner diameter which is substantially the same as that of the tube  1 . Therefore, once the fitting body  4  is firmly fixed to the tube  1 , a smooth path is formed between the fitting body  4  and the tube  1 . Namely, no gap is made along junction between the fitting body  4  and the tube  1 , causing a liquid to smoothly pass throughout the actual length of the fitting body  4  and the tube  1 . 
     FIG. 3 is a sectional view illustrating a fitting structure according to the second embodiment of the invention. In FIG. 3, identical elements to the first embodiment are indicated by the same reference numerals. As seen from FIG. 3, the fitting according to the second embodiment has such a configuration as to be lengthwise symmetrical with respect to a central portion  7  and is adapted to be used for connection of two tubes  1  and  1 . 
     FIGS. 4 and 5 illustrate a fitting structure according to the third embodiment of the invention. In the drawings, the reference numeral  1  indicates a tube, which has the folded-back portion  1   c  as hereinbefore described in the first embodiment. 
     A fitting to be connected to the tubes  1  includes a fitting body  4  and a fastener  11 . The fastener  11  comprises an inserts  2  which is partially inserted between the main body of the tube  1  and the folded-back portion  1   c  thereof, and a fastener body  3  which has an engaging portion  3   a  abutting against the other end of the insert  2 . 
     The insert  2  is made of a fluoroplastic material and has a tubular shape, the inner diameter of which is designed to be substantially the same as the outer diameter of the tube  1  as best shown in FIG.  4 . As shown in FIG. 4, the insert  2  is set on the two-plied section of the tube  1  such that one end section (lower end in FIG. 4) of the insert  2  sits between the main body of the tube  1  and the folded-back portion  1   c . Consequently, the width of the two-plied section of the tube  1  is enlarged by the width of the insert  2 . 
     The insert  2  has, at the other end thereof, a flange  2   a  extending circumferentially and outwardly. The flange  2   a  is adapted to come into contact with the under surface of the engaging portion  3   a  and with the inner surface of the fastener body  3 , causing the fastening force by the fastener body  3  and the fitting body  4  to be adequately transmitted to the two-plied section of the tube  1 . 
     In addition to the flange  2   a , the insert  2  is provided on the outer surface thereof with a ridge  5  which extends circumferentially and outwardly. The circumferential ridge  5  forces the folded-back portion  1   c  of the tube  1  outwardly and presses it against the fastener body  3  into intimate contact therewith. 
     The fastener body  3  is substantially the same in structure as the fastener body  9  of FIGS. 1 and 2 except the width thereof, namely the outer diameter of the fastener body  3  is designed to be slightly larger than that of the fastener body  9  in consideration for the enlarged width of the two-plied section of the tube  1  by insertion of the insert  4  into the two-plied section. 
     The engaging portion  3   a  has such a shape as to extend in the radially inward direction to abut against the flange  2   a  of the insert  2 . 
     The fitting body  4  is substantially the same in structure as the fitting body  4  shown in FIGS. 1 and 2, but the width of the end having the annular groove  4   e  or the thickness of the fitting body  4  is larger than that of the fitting body  4  according to the first embodiment. Namely, since the width of the U-shaped two-plied section of the tube  1  is enlarged by the thickness of the insert  2  which is set on the U-shaped two-plied section, taking it into consideration, the thickness of the fitting body  4  according to the third embodiment is designed to be larger than that of the fitting body  4  according to the first embodiment. 
     A process to make up the fitting structure according to the third embodiment of the invention will be described below: 
     First, one end section of the tube  1  is folded or turned back by a predetermined length thereof. The length to be folded back is determined so that the end  1   d  of the folded-back portion  1   c  can be positioned apart from the flange  2   a  of the insert  2  to define a small gap between the end  1   d  and the flange  2   a . Next, the insert  2  is inserted between the main body of the tube  1  and the folded-back portion  1   c  to sit on the two-plied section of the tube  1 . Then, the other end of tube  1  is faced to the threaded portion  3   c  of the fastener body  3  to insert the tube  1  into the fastener body  3 . After that, the flange  2   a  of the insert  2  is abutted against the engaging portion  3   a  of the fastener body  3 . As a result of the above operation, it is completed to assemble the tube  1  and the fastener body  3 . Thereafter, the threaded portion  4   b  of the fitting body  4  is threadedly engaged with the threaded portion  3   c  of the fastener body  3  and the end  1   a  of the tube  1  comes into contact with the groove  4   e  of the fitting body  4 . The fastener body  3  is further threaded into the fitting body  4  to compress the end  1   a  of the tube  1  against the groove  4   e  of the fitting body  4 . 
     The fitting structure according to the third embodiment defines a larger contact area between the tube  1  and the annular groove  4   e  of the fitting body  4  than those of the fitting structures according to the first and second embodiments, and ensures more reliable sealing between the tube  1  and the fitting. 
     FIG. 6 is a fitting structure according to the forth embodiment of the invention, which is adapted to connect two tubes  1  and  1 . 
     The fitting structure shown here is symmetric in its lengthwise direction about its own center  7 , and the insert  2 , the fastener  3  and the fitting body  4  are identical to those of the third embodiment.