Abstract:
The invention concerns a new seal system for resolving the problem of the contamination of special fluids carried in pumps and moreover providing improved sealing by virtue of its special geometry and design. According to the invention, one of the elements to be connected can replace the seal owing to the fact that the seal system includes a combination of two elements to be connected with a fine film ring, one of the elements to be connected having a geometry able to effect a double indentation on the film ring. The invention may be used in pumps and circuits for fluids of the semiconductor industry. The three elements of the seal system, including the pump body, tube, and film ring, may be made of PFA.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention concerns the technical sector of seals included in fluid transfer systems and more particularly seals for tubes and generally circuits carrying special fluids. 
     2. Background Information 
     In this application, special fluids are understood to be fluids requiring the use of special materials. One non-restrictive example is given by corrosive fluids. Also to be denoted under this category are fluids which must not be contaminated by the components of fluid transfer systems. One non-restrictive example is provided by certain fluids used in the semiconductor industry. 
     The present invention also concerns the technical sector of tubes, pumps and other components of fluid transfer systems for special fluids using these seals and in particular the technical sector of pumps comprising these inlet or outlet pumps. One non-restrictive example is provided by pumps and tubes carrying fluorinated material. 
     In the semiconductor industry, fluids, defined here as “special”, are currently used. In particular they can be bases, acids, solvents, water or watery fluids containing abrasive materials and similar substances well known to those concerned with this field. 
     A particularly serious technical problem concerns the circulation of fluids, such as acids, which are then used to etch silicon wafers used in the production of semiconductors. Any pollution, and particular any particulate pollution of the fluid carried, maybe detrimental to the quality of the semiconductor. 
     However, the systems used to carry these fluids and in particular pumps and tubes typically need to make use of seals like any system of this type. 
     In this field, metal seals with a studied section have been examined to improve sealing. 
     This particular field also includes toroidal seals universally known as “O-rings”. These O-rigs are usually placed in grooves or housings and then compressed by a collar to ensure sealing. In the case of a seal between two tubes or a seal in a tube/pump body connector or another component of a fluid transfer system, tightening is effected by hand by a tightening collar. 
     In the technical sector in question, these seals are mainly made of elastomer materials. However, they are likely to result in a particulate contamination of the fluids carried. In fact, their purity is notoriously inadequate and can free metal or other types of particles which can be extremely damaging in “ultrapure” industries, as in the semiconductor industry. 
     The problem is more particularly evident in pumps carrying a fluorinated material as described earlier, the pumps comprising tubes needing to be seal connected with the aid of seals. 
     SUMMARY 
     The invention concerns a new seal forming system and is able to resolve the problems mentioned above, especially the problem of the contamination of carried fluids and in addition, and generally provides improved sealing by virtue of its particular geometry and design. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other characteristics and advantages of the invention shall appear more readily from a reading of the following description with reference to the accompanying drawing on which: 
     FIG. 1 is a cutaway view of a pump element for special fluids, especially an “ultrapure chemical” pump used in the semiconductor industry, and having a seal forming system according to the invention; 
     FIG. 2 is a sectional view on larger scale of a portion of FIG.  1  and showing an embodiment of the seal forming system of the invention and the elements surrounding it; 
     FIG. 3 is a diagrammatic section of an embodiment of the seal forming system of the invention as used on FIGS. 1 and 2; and 
     FIGS. 4 a  and  4   b  are diagrammatic sections of two sealing methods according to the prior art. 
    
    
     On the accompanying figures, the same references have the same significances which are the following: 
       1  tube 
       2  pump body 
       3  pump bellows 
       4  pump body seal housing 
       5  pump body seal according to the patent application filed on the same day as the present application in the name of the Applicant 
       100  tightening collar 
       110  housing of the tube seal of the invention 
       150  tube seal of the invention comprising a lower portion  170  and co-operating with 
       200  film ring or fine sealing film according to the invention at the level of the indentation zone  190   
       400  and  700  fixed elements of valves of the prior art 
       410  and  710  valve body of the prior art 
       500  and  800  sealing film rings for valves of the prior art 
       600 ,  650 ,  850  conventional elastomer O-type seals or similar type 
       820  groove 
     F and arrow: fluid pressure direction on the seal system 
     F 1  and arrow: first channel or path for passage of the fluid outside 
     F 2  and arrow: second channel or path for passage of the fluid outside 
     B and arrow: direction of application of the force of the tightening collar. 
     INT.: Inside of the pump (fluid under pressure) (or of the valve on FIG. 4) 
     EXT.: Outside of the pump (or of the valve on FIG.  4 ). 
     Throughout the present invention, the abbreviations have the following significances: 
     PTFE polytetrafluoroethylene 
     DETAILED DESCRIPTION 
     By way of convenience and so as to orient the figures and their numeric references, the descriptions shall be given with respect to “the inside” of the pump and respectively to the “outside”. 
     As can be seen on FIG. 1, a housing  110  is normally placed within a pump body  2 . 
     Sealing is effected at the level of the seal  150  so as to avoid fluid F leaking outside the pump via the paths F 1  or F 2  (FIG.  3 ). The seal  150  may also be referred to herein as a sealing member. It should be noted that the terms seal and sealing member are not used in a manner consistent with the dictionary definition of the term “gasket”, i.e., a deformable material used to make a joint gas or liquid tight. In contrast, the seal or sealing member of the present invention is constructed of a relatively hard material that is typically not easily compressed relative to a component joined thereto. 
     The invention generally concerns a method for sealing between an element made of a relatively hard material, such as a housing  110  having a seal disposed thereon, and an element  1  intended to be applied against the seal by a tightening device  100  according to which a complex system is used as a seal and formed by the combination of i) a seal  150  integral with the element  1  or rested on the element  1  and made of a relatively hard material, ii) a film ring or fine film  200  made of a relatively hard material, said seal  150  comprising a support protuberance  180  on its face  170  intended to co-operate in the indentation zone  190  with the film ring or fine film  200 , and iii) a seat  112  of the housing  110 , also made of a relatively hard material. 
     According to a preferred embodiment, the seal  150  appears in a cross section like a closed asymmetrical shape comprising at the lower part a “V” shape which forms a protuberance  180  (FIG. 3) with respect to the lower portion  170 , the “V” shape preferably having a rounded contour as shown on the accompanying drawing and asymmetrically only occupying one portion of the lower face  170 , also as shown, whereas one of the branches of the “V” continues asymmetrically, thus forming one of the lateral walls of the seal  150 . 
     An expert in this field could easily envisage other similar shapes having the same function, especially the co-operation function with the film ring  200  in the indentation zone  190 . 
     The three materials are preferably identical for the element  2  (that is the seat  112  of the housing  110 ), the seal  150  and the film ring or fine film  200 . 
     As can be seen in FIG. 3, the protuberance  180  is intended to form a double indentation in the zone  190  of the film ring or fine film  200  providing two sealing lines against the paths F 1  and F 2 . The term ‘double indentation’ refers to a deflection of each surface  202  and  204  of film  200 , as shown. These deflections thus provide a fluid-tight surface-to-surface engagement between the protuberance  180  and surface  202  of the film  200 , and between surface  204  of the film  200  and the seat  112 , respectively. As also shown, the engagement of protuberance  180  and surface  202  of the film effectively prevents fluid F from passing therebetween, i.e., blocking path F 1 . Similarly, the surface-to-surface engagement of surface  204  with seat  112  in the zone  190  effectively prevents fluid F from flowing past the periphery of the film  200  (as indicated by F 2 ) and between the seat  112  and film  200 . 
     According to a preferred embodiment of the invention, the material constituting the element  2 , the seal  150  and the film ring of fine film  200  is a PFA. 
     It is also possible to consider using polymers whose hardness characteristics and resistance to compression are situated in a range combining the characteristics of the PFA with those of PVDF. 
     According to a particular embodiment, the PFA is one sold by Du Pont de Nemours under the name of Teflon PFA (™). 
     The resistance to compression values at the yield point according to the standard ASTM D 695 are respectively: 
     24 Mpa for Teflon PFA™—relatively hard material—and 12 Mpa for Teflon PTFE™—relatively soft or flexible material. 
     The Shore D hardness values according to the standard ASTM D 2240 would respectively be: 
     60 for Teflon PFA™—relatively hard material—and 55 for Teflon PTFE (™) which is a relatively flexible or soft material. 
     By way of comparison, an FEP (ethylene-propylene fluorine resin) would have a resistance to compression of 15.2 Mpa and a Shore hardness of 56-57 according to the same standards. 
     A PVDF (polyvinylidene fluoride) has a resistance to compression of 75 Mpa and a Shore hardness of 77 according to the same standards. 
     These values shall enable an expert in this field to evaluate what the invention means concerning a “relatively hard” material in relation to the resistance to compression and Shore D hardness value difference which, although seeming numerically low, is considerable. A specialist in this field would therefore select the appropriate materials and determine the acceptable “hardness” ranges. 
     In the prior art, there are two valve technology systems that are shown on FIGS. 4 a  and  4   b.    
     On FIG. 4 a , sealing is ensured by two conventional lateral toroidal seals  600 ,  650 , i.e., O-rings, made of elastomer and by a film ring  500 , which rests on the seat of the valve. As can be seen, the fluid pressure is exerted on the face of the film ring. 
     On FIG. 4 b , sealing is ensured by a conventional lateral toroidal seal  850  and by a film ring  800  on which the fixed element of the valve  700  is tightened by means of a ridge  820  which marks the film ring with its imprint. The fluid pressure is exerted on the bottom of the film ring shown also on FIG. 4 b.    
     In these two cases, the valve body  410  or  710  and the film ring  500  or  800  are made of PFA. On the other hand, the fixed elements of the valves  400  and  700  are made of a material harder than PFA, namely PVDF. 
     Thus, it was not obvious that the technology of FIG. 4 b  can be transposed to a technology for tubes, especially tubes of fluorinated materials, such as according to the present invention, in which the pressure of the fluid is exerted on the top and not the bottom of the film ring or fine film. In addition, the support element of FIG. 4 b  is harder than the PFA of the film ring. Thus, the unpredictability of sealing behavior was increased. The fact that the valve configuration of FIGS. 4 a  and  4   b  have been in use for 10 or 20 years whereas the problem posed by the sealing of tube connectors for special fluids has-still not been resolved confirms that the technology of the present invention was not used in this field when the need existed. 
     According to the invention, the seal  150  made of a relatively hard material shall preferably be an extension of the element  1  that needs to be seal-connected to the element  2 . In the prior art using flexible elastomer seals, it was clearly impossible to embody a tube made of the same elastomer material. According to the invention, this is now possible since the three components combined to form the joint are made of a relatively hard material. 
     According to a less preferred variant of the invention, the three components shall be made of a relatively hard material with the elements  110  and/or  150  being able to be harder than the element  200 . 
     The film ring must be sufficiently hard to prevent the system from leaking. 
     One of the important advantages of the invention is thus of providing forming a seal as a simple extension of one of the elements to be connected. A preferred embodiment of the present invention uses one of the elements to be connected to serve as the seal. 
     An expert in this field shall understand that this preferred variant of the invention is quite contrary to the instructions of the prior art, whether it concerns valves, pumps or tubes made of fluorinated materials. 
     According to the preferred embodiment of FIG. 1 or  2 , the element  2  is a pump body, especially a pump made of a relatively hard fluorinated material, such as PFA, and the element  1 , integral with the seal  150  which is a simple extension of it, is an inlet or outlet tube made of PFA, whereas the film ring or fine film  200  is also made of PFA. 
     Comparative tests have shown that, without any film ring or fine film  200 , the system of the invention leaks. The two elements to be connected (in particular in the preferred example the pump body  2  and the tube  1  extended by the element  150 ) thus co-operate fully with the film ring of fine film  200 . These tests also surprisingly show that the imperviousness of the system of the invention, depends on a film ring which would not have logically bound to play this decisive role and which, if reference is made in particular to the prior art of FIG. 4, should previously co-operate with one or several elastomer seals. 
     The advantage of the fine film ring  200  also derives from the fact that it is the only warped element and thus the only element to be replaced during maintenance. 
     The invention further concerns seal forming systems described above, including their variants. 
     The invention further concerns the applications of the method of the invention and seal forming systems of the invention in all industries having strict or even drastic sealing criteria, such as the semiconductor industry, and generally the electronics, aeronautics and space, pharmaceutical, chemical industries and new technological and similar industries. 
     In particular, the invention concerns pumps and tubes for carrying special fluids, especially corrosive fluids, and/or in particular corrosive, and/or in particular fluids not having to be contaminated by the seal, characterised in that they comprise at least one sealing system or seal forming system as described above and in that the two elements to be connected are directly used to take part in the seal forming system. 
     The invention further concerns implementation, embodiment and materials selection variants, and applications and uses directly accessible to specialists in this field from a reading of the present description.