Abstract:
A wafer for use in selectively connecting and disconnecting plastic tubes is in the form of a heatable plate having side walls and having a leading end and a trailing end. An outwardly extending scoop is formed on each of the side walls between and spaced from the leading end and the trailing end. A pair of slits is formed in the trailing end in line with the scoops for reducing the amount of plastic material remaining on the wafer.

Description:
BACKGROUND OF THE INVENTION 
     The present invention is directed to the total containment welding of plastic tubes. Various prior art exists disclosing different approaches to welding plastic tubes together and to the cutting of a plastic tube for separation into two tube segments. A general approach when welding two plastic tubes together is to clamp each tube in a tube holder with a portion of the tube extending outwardly of its holder. Each tube may be, for example, bent so that the bent ends of the two tubes are disposed toward each other. A heated wafer then passes through the bent ends of the two tubes to melt the bent ends and remove the bent portions. After the wafer is moved downstream away from the tubes, the tubes are pressed into contact with each other so that the melted tubes are welded together. This results in two main portions of the tubes being in communication with each other to form a unitary welded tube. In addition, the free ends or stubs of the bent tubes are also welded together and may be discarded or used for purposes of collecting samples, etc. 
     One known form of wafer is a metal plate which is folded upon itself to create a pair of sides. When the wafer is heated the lead end of the wafer begins to melt the plastic tubes as the wafer begins to pass through the spacing where the tubes extend from their holders. The melted plastic material is then deposited on the sides of the wafer. An advantageous form of this wafer is to include a scoop on each of the side walls so that the scoop collects the melted material at the bent ends when the wafer passes through the spacing between the holders. 
     SUMMARY OF THE INVENTION 
     An object of this invention is to provide a heatable wafer which includes structure for assuring an effective weld of the melted tube sections. 
     A further object of this invention is to provide such a wafer which increases the resulting weld strength of the welded tubes. 
     In accordance with this invention the wafer is in the form of a heatable plate having opposed side walls and a leading end and a trailing end. An outwardly extending scoop is formed on each of the side walls between and spaced from the leading end and the trailing end. Each scoop is open toward the leading end to remove a portion of the material of the plastic tubes as the heated wafer is moved between and in contact with the exposed portions of the tubes. In accordance with this invention a plurality of, and preferably two, slits are formed in the trailing end of the wafer in line with the scoops for minimizing the amount of plastic material that would remain on the wafer when the wafer is removed from the weld area. 
     The slits are of sufficient length to permit the melted plastic to be easily removed from the moving wafer and remain available as a weld pool when the melted ends of the tubes are pressed into contact with each other. A preferred length of the slits is 2 mm. 
     The invention may be practiced where the scoops have a leading surface that is tapered inwardly to facilitate the plastic material being collected into the scoops. 
    
    
     THE DRAWINGS 
     FIG. 1 is a side elevational view of a prior art wafer; 
     FIG. 2 is a cross-sectional view taken through FIG. 1 along the line  2 — 2 ; 
     FIG. 3 is a side elevational view of a wafer formed in accordance with this invention; 
     FIG. 4 is a top plan view of the wafer shown in FIG. 3; 
     FIG. 5 is a front elevational view of the wafer shown in FIGS. 3-4; 
     FIG. 6 is a rear elevational view of the wafer shown in FIGS. 3-5; 
     FIG. 7 is a side elevational view similar to FIG. 1, but of the wafer shown in FIGS. 3-6; 
     FIG. 8 is a cross-sectional view showing the wafer of FIGS. 3-7 when the scoops contact the plastic tubes; 
     FIG. 9 is a cross-sectional view taken through FIG. 7 along the line  9 — 9 ; and 
     FIG. 10 is a cross-sectional view taken through FIG. 3 along the line  10 — 10 . 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates one form of generally known wafer  10 . As shown therein wafer  10  is made from a flat plate of heat conductive material, such as copper bent upon itself (see FIG. 4) so as to result in a pair of side walls  12 . Wafer  10  also includes a leading end  14  and a trailing end  16 . Wafer  10  could be used in a total containment device such as disclosed in U.S. Pat. No. 5,279,685, all of the details of which are incorporated herein by reference thereto. The device would include a pair of tube holders  18 , 18  (see FIGS.  2  and  8 ). Each tube holder would have a tube receiving area in which a plastic tube which could be bent upon itself (see FIG. 8) would be inserted and clamped. The tube holders  18 , 18  are capable of moving toward and away from each other. As shown in FIG. 8 the bent ends  20 , 20  of the tubes  22 , 22  would be disposed very close to each other. Tubes  22  are made of conventional medical plastic material, such as PVC. Wafer  10  would be heated in the total containment device and then would be moved into the spacing between the tube holders  18 , 18  to contact the tube ends  20 , 20 . Contact by the heated wafer would cause the tube ends  20 , 20  to melt. 
     As shown in FIG. 1 a scoop  24  is provided on the side wall  12  of wafer  10 . A mirror image scoop would be provided on the opposite side wall of wafer  10 . If desired, the wafer could also be provided with wings such as illustrated in U.S. Pat. No. 5,525,186, all of the details of which are incorporated herein by reference thereto. The melted plastic material resulting from the bent ends  20 , 20  of tubes  22 , 22  being heated and placed in a molten condition by wafer  10  would result in the scoops  24  collecting the melted material. As the wafer continues to move through the spacing between tube holders  18 , 18  the tube holders would be moved toward each other to maintain contact of the melted ends of tubes  22 , 22  with wafer  10 . In the conventional type wafer where trailing end  16  has a straight uninterrupted edge some of the molten material  26  collects on the walls  12 . As a result, when the wafer  10  is moved completely out of contact with the molten ends of tubes  22 , 22  the collected material  26  is no longer available for use in welding the remaining tube sections of tubes  22 , 22  together. Thus, when the wafer scoops the bent tube ends  20 , 20  the amount of tube material left on the exposed portions of the melted tubes  22 , 22  is used for making the weld by use of the melt pool principal. The exposed portion each tube occupies is the distance between the wafer sides  12  and the ends  28  of the tube holder clamps. See FIG.  2 . The clamps of the holders  18 , 18  function to control the spacing of the tubes from each other. The clamps initially move forward to press the scooped tubes against the hot wafer  10  in preparation to make a weld with the molten plastic tube material. As the wafer again moves forward or downstream some of the molten plastic  26  adheres to the wafer while it is still effecting a melt pool of hot plastic as a pathogen barrier. FIG. 1 shows in phantom the extent of the material  26  being dragged by wafer  10 . This material tends to leave the wafer exit area deprived of tubing material thereby making one side of the tube stronger than the other, due to the lack of depleted material  26  remaining on the wafer sides  12 . 
     The present invention provides structure to make a uniformly strong weld from the molten material after securing its function as a pathogen barrier. FIGS. 3-10 illustrate a modified wafer  30  in accordance with this invention. Like reference numerals are used in FIGS. 3-10 for like parts with regard to the known wafer  10  shown in FIGS. 1-2. Thus, the wafer  30  also includes a pair of mirror image scoops  24 , 24  which may further include slits or slots  32  extending inwardly from the lead edge  34  of each scoop. 
     In accordance with this invention a slit  36  and preferably a pair of generally horizontal slits  36 , 36  is provided in each side  12  in the trailing end  16  of wafer  30 . The slits in each of the sides are aligned with the slits in the other to form two sets of vertically spaced slits. U.S. Pat. No. 5,525,186 discloses a wafer which includes a single slit preferably having a length of 7 mm and a width of 0.5 mm. As stated in that patent the slit is intended to permit the molten material from the tubes to begin contacting each other at an earlier time while the tubes are still in the area of the wafer. No disclosure is made in the patent of use with bent tubes. Instead the tubes are straight which are in the flattened condition when contacted by the wafer. In practice the 7 mm length would correspond to at least the thickness of the flattened straight tube. In contrast the present invention is preferably used with bent tubes. The length of slits  36  would cover only about 30% of the thickness of the clamped bent tubes. The front or upstream portion of the weld would have a sufficiently strong weld. The slits  36  are intended to deposit just enough material at the end of the cut to strengthen that part of the weld. Thus, shorter length slits  36  can be used than the length of the single slit in U.S. Pat. No. 5,525,186. 
     In accordance with this invention the pair of slits  36 , 36  is intended to provide during the melt cycle sufficient plastic material to be able to not only maintain a pathogen seal, but also to permit a portion of the plastic material to flow into the slits  36 , 36  and make bonding contact with the tubes. When the wafer  30  is advanced, the plastic material in the slits  36 , 36  stay with the molten tubes thus making a stronger weld at 80-90% of the raw tubing strength. The invention thus could result in a wet-to-wet weld strength that can be increased by approximately 15-20% simply by making the noted changes. 
     While U.S. Pat. No. 5,525,186 discloses a single slit having a length which is preferably 7 mm, the slits  36 , 36  need only be long enough to permit the molten material  26  to make bonding contact with the remaining portions of the heated tubes  22 , 22 . A preferred length of slits  36 , 36  is 5 mm or less and most preferably 2 mm. Each slit  36 , 36  may be about 0.5 mm. The distance from the outer edge of one slit  36  to the outer edge of the other edge  36  is preferably about 1.75 mm. 
     Thus, in accordance with the practice of this invention instead of having molten material  26  remaining on the sides  12 , 12  of the wafer, the sides  12 , 12  are virtually free of such molten material in the practice of this invention as shown in FIGS. 7-8. 
     FIG. 10 illustrates a further aspect of this invention wherein the lead edges  38 , 38  of the scoops  24 , 24  are tapered to form a knife edge. The taper is in a direction toward the interior of each scoop to facilitate the molten plastic material entering the scoop interior. Generally, the thickness of the scoop wall would be 0.001 inches wide. With scoops formed in accordance with U.S. Pat. No. 5,525,186 where there is no taper on the lead edge, a blunt face is presented against the plastic tubes. Since the plastic tubes are initially cold the blunt lead edge does not necessarily direct the plastic material to completely flow into the scoops. By making a tapered knife edge  38  the material would be pushed into the scoops to improve the function of the scoops. Such tapered edge may be provided completely along the lead edge of the scoops including being into the slots  32 . 
     Although the invention is preferably practiced with a set of two slits  36 , 36 , in its broad application the invention could include more than two slits as the plurality of slits exposed from the trailing edge of the wafer. Although not as preferred the invention could also be practiced with a single slit. In such practice of the invention the single slit need only be long enough to permit the plastic material on the side walls of the wafer to flow into the slit and make bonding contact with the tubes and thereby remain contacting the tubes after the wafer has been removed from the location of the clamps in the tube holder. 
     The tube welding operation would proceed as in a conventional manner by the clamps in the holders  18 , 18  moving the molten tube ends into contact with each other. Where a bent tube  22  is used, the resulting welding operation would create two sets of welded tubes which are formed from the aligned portions of the bent tubes shown, for example, in FIG.  9 . One set of welded tube sections would generally comprise a main tube which could be used, for example, in dialysis to connect a new bag having its tube to a tube leading to the patient. The bent ends or stubs from the used bag tube and from the patient would also be connected together and could be discarded or used as a sample tubing.