Apparatus and Process for Forming a Tapered Tip End on a Plastic Tube

It is quite often desirable to provide a feathered tip or feathered distal end zone on a relatively thin walled tube, such as a flexible catheter for injecting fluids intravenously into a patient. Such a tip should be smooth and gradually tapered. In the past this has been a difficult structure to produce. In the prior art it is known to grind the ends of plastic tube lengths to provide a taper or cut a taper on the end of such tubes. Because the same are thin walled this is a difficult, time-consuming and relatively expensive process. This invention is of an apparatus and process for forming a feathered tip on a plastic tube rendering it suitable for use as a medical catheter. It is also important that a plastic tube length, not only have a feathered tip but that the feathered tip closely conforms to a needle extending through and from the feathered end of the catheter so that when the needle jacketed by the catheter is inserted, flesh particles do not become trapped in the gap between the needle and the feathered catheter tip restricting movement of the catheter along with the needle to a point of positionment within a vein so that the needle can be withdrawn and the flow take place through the flexible relatively soft catheter. Also in the prior art, although it is known by various means other than that disclosed herein to taper the tips of such catheters for the purpose mentioned above, there is an additional problem. If the taper proceeds axially to a very thin feathered end, the end zone is relatively weak and hence susceptible to damage during insertion. Hence, it is preferred to provide a taper of the catheter tip zone in two stages, a proximal stage of tapering and a rather abrupt distal end zone taper so that the axial length of the thinnest portion is relatively short at the distal end. Finally, there is an additional problem and that is that after a tip has been processed according to prior art techniques it is important that the diameter of the tip zone be sized so as to snugly fit the needle so that a smooth insertion can take place of a needle jacketed by a catheter. It is believed that in the prior art it has been known to insert the end of a previously tapered tube into a heated die in an effort to form it by reducing the diameter to a proper configuration to mate with a needle to be used with it.

Further, it is believed that some in the prior art heat a die while engagedly the tip is being formed and retain it in engagement until the tube, tube tip and the forming die has been cooled by some type of cooling means.

The present invention is of an apparatus to rapidly and inexpensively make catheters with feathered tips as is described more fully hereinafter.

It has been found that when a tube to be feathered at a tip is formed by a die, such as a Teflon tube, which is the material preferred in this invention, heat must be applied to the tip to taper it with the die having a generally conical recess. When the heat is applied that portion of the tube adjacent the die tends to deform and wrinkle on the exterior and the interior surface rendering it unsuitable for insertion into the skin and a vein of a patient. This invention is of a die in two portions to be moved over a mandrel jacketed by a tube to be tipped wherein the portion of the die which moves axially furtherest over the tip is cooled or cooler relative to another portion of the die at the tip zone being formed so that wrinkling does not occur with the cooled die portion circumferentially supporting the tube while it is being formed by the heated or hotter portion of the die, which is quite difficult to do because the die being metal has high heat exchange or heat conductive qualities. Hence, one object of this invention is to provide a die in two portions, one portion comprising a generally cylindrical portion which includes a heat sink or cooling means and another portion which is tapered generally conically which is heated to feather the tip at the distal end of the tube.

It is another object of this invention to provide a die which is preferably in two pieces which are maintained in spaced axial relation from one another when not in use forming a tip and which are in abutting engagement with one another while the tip forming process is taking place and wherein a cooling means, such as a water cooling jacket is provided for the portion of the die about the cylindrical zone adjacent the feathered end of the tube and the heated portion does not transfer all of the heat required to form the tip but, rather, a temperature gradient is maintained between the two pieces so that the cooled portion is at all times at a lower temperature than the heated portion.

It is another object of this invention to provide a cyclical pulsing of the die during the forming process so that there is a reciprocal axial movement so that heat exchange between the heated portion and the tubing formed, preferably of Teflon, at the feathered tip permits an intermediate application of heat and the heat transfer time required is altered or adjusted as the heat is applied and air may be released between the mandrel on which the tube is positioned and the die and it can escape from between the mandrel, die and tube tip being formed.

It is another object of this invention to provide a means for yieldingly supporting the tube for relative axial movement of adjustment as axial forces are applied by the die to the tube tip.

It is a further object of this invention to provide a second biasing means for the mandrel about which a tube is positioned so that during the tip forming process the mandrel is able to move axially in movements of adjustment relative to the tube being formed so that movements of adjustment in response to axial forces applied by the die can yieldingly in a cushioned fashion take place.

In accordance with these and other objects which will become apparent hereinafter, the instant invention will now be described with reference to the accompanying drawings in which:

FIG. 1 is a front plan view, partially in cross section, of a device for forming a tapered end on a plastic tube;

FIG. 2 is an enlarged view, similar to the lower portion of FIG. 1, illustrating a first step in the process of forming a tapered tip end on a plastic tube;

FIG. 3 is a view similar to the upper forming die means of FIG. 1, illustrating a second step in the process;

FIGS. 4 and 5 are views similar to FIG. 2, illustrating subsequent steps in the process;

FIG. 6 is a view similar to FIG. 3, illustrating a final step in the tip end forming process;

FIGS. 7, 8 and 9 are substantially enlarged cross sectional views of the tip forming die members as disclosed generally in FIGS. 4, 5 and 6;

FIG. 10 is a bottom plan view of the upper tip forming die of FIGS. 7, 8 and 9; and

FIG. 11 is a fragmentary plan view of the tapered tip end of a plastic tube in accordance with the present invention.

In the preferred embodiment, the diameter of the mandrel is between 0.020 and 0.060 inches with the catheter lengths usually being between 3/4 inches and up to 18 inches if desired. The diameter of the tube is such as to closely jacket or snugly jacket the mandrel and provide a relatively easy slide fit for positioning of the tube. The wall thickness of the Teflon tubes in the preferred use of the invention is between 0.005 and 0.010 inches.

The taper at the tip is about 0.002 inches in thickness to the knife edge at the very distal most end, where in the preferred embodiment it converges at an angle of about 30 degrees to the mandrel whereas the main tapered length is about 2 degrees of taper. Generally speaking Teflon softens at about 500.degree. F.; and the heat of the heated portion of the die is such as to cause a softening of the Teflon, that is, preferably at a temperature between 500.degree. F. and 600.degree. F. Excessive heats, that is, heats substantially above 700.degree. F. are not utilized. This is to avoid a rapid heat exchange to the mandrel itself at the seat. If allowed such excessive temperatures would, by conduction, cause the length of the mandrel to become heated rapidly, thereby causing wrinkling or buckling beyond the cooled support portion of the die which surrounds the tube. In a preferred operation, it will be appreciated that the application of the heat may take place in stages, such as at a three stage location where the heat is applied in three successive phases of operation of heat application depending upon the amount of forming to be done at the tip. For example, a turn table operation with three separate applications of the die may be utilized to complete the forming of a tube configuration at the tip.

Referring to the drawings wherein like reference characters designate like or corresponding parts throughout the several views, FIG. 1 is a general view, partially in cross section, illustrating a catheter C mounted on a mandrel 10 of a mandrel operating assembly 12, fixed relative to a work table assembly 14. A die assembly 16 is disposed above the mounted catheter C in a carriage assembly 18, the die assembly 16 being operably connected at 20 to an operator cam 22.

With particular reference to the work table assembly 14, FIGS. 1, 2, 4 and 5, three generally horizontal plates are illustrated, a top plate 24, intermediate plate 26 and a bottom plate 28. A housing 30 is bolted at 32 beneath the bottom plate 28 and a vertically operating piston 34 includes a lower end portion 36 disposed within an interior chamber 38 of housing 30. A stop ring 40 is fixed relative to piston 34 within lower chamber 38 to provide axial engagement with a compression spring 42 disposed in chamber 38 between said ring 40 and a screw plug 44 engaged through the bottom of housing 30, and limit upward movement thereof in response to the compession spring 42.

An upper chamber 46 is defined in an upper portion of housing 30 and a lower piston sleeve 48 disposed about piston 34 includes an enlarged headed lower end 50, slidably engaged in upper chamber 46. Piston sleeve 48 is slidably engaged in a sleeve bearing 52, fixed through the intermediate and bottom plates 26 and 28, and an upper piston sleeve 56 disposed about an upper reduced diameter piston portion 54 of piston 34 is slidably engaged through the top plate 24.

The mandrel 10 is fixed relative to upper piston portion 54 and extends axially outwardly therefrom through a hole 58 in a top end of the upper piston sleeve 56. Said piston sleeve 56 includes a top end nipple 60 and defines a seat for the conventional cupped outer end 62 of a catheter C.

Respective fittings 64, 66 connect a pair of tubes 68, 70, from a suitable compressed air source (not shown), to lower chamber 38 and upper chamber 46 for a purpose to be subsequently described.

With particular reference to the die assembly 16, it includes an upper tip end forming die member 80 fixed within a cavity 82 in a lower end of a block 84 formed of a suitable heat conductive material, and electric heater means 86 fixed about block 84 and connecting to a suitable electric source by leads 88, 90. Block 84 is fixed to a lower end of a slide rod 92 journaled through a pair of lower and upper blocks 94, 96, fixed to an upright member 98, fragmentarily illustrated. A cam follower roller 100, rotatably supported in a yoke member 99, fixed to an upper end of rod 92, is engaged against the operator cam 22 by conventional tension means such as a spring (not shown). Cam 22 is fixed to a shaft 101 which is power operated in any conventional manner such as by an electric motor (not shown).

As illustrated in FIGS. 2 through 9, the tip forming die member 80 includes an axially extending through cavity 102 including a minor cylindrical lower portion 104 of a diameter to receive the normally straight tip end 106 of a catheter tube T. The major upper portion 108 of cavity 102 is gently tapered to an upper terminal end portion which is provided with a substantially increased degree of taper at 110.

A lower portion 112 of the die assembly 16 is fixed through a heat sink or coolant receptacle 114 and includes an axially extending through aperture 115, cylindrically sized to receive the tube T therethrough and including a rounded bottom lead in entrance opening 116. The top side of die portion 112 includes an annular flange 118 and an upwardly, inwardly tapered central extension 120 for nested engagement within a mating, tapered recess 122 in the bottom face of die member 80, as best seen in FIGS. 7, 8, 9 and 10. As best illustrated in FIG. 10, preferably the bottom face of die portion 112 includes a plurality of radially disposed slots 124, 126 for reducing heat exchange contact between portions 80 and 112.

The coolant receptacle 114 defines an inner chamber 128 for reception of a suitable coolant, such as water, and is provided with respective inlet and outlet conduits 130, 132. A pair of slide rods 134, 136, vertically fixed relative to respective sides of receptacle 114 are slidably engaged through lower block 94 and fixed at upper ends to a tie bar 144. A pair of compression springs 140, 142 are disposed about respective rods 134, 136 between fixed block 94 and the tie bar 144.

Cam 22 is illustrated in a neutral position with a dwell portion 150 thereof in engagement with the follower roller 100. The major operating portion 152 of cam 22, preferably includes a plurality of lobes 154 for a purpose to be described relative to the operation of the device.

In practice, the above described apparatus may be duplicated at a plurality of stations about an indexing table, however, the drawings and above description relates to a single device and the process of taper forming the tip end of a catheter tube on a mandrel. However, it is to be understood that pluralities of loading, forming and unloading stations may be provided for production purposes.

In the illustration of FIGS. 1 and 2, a catheter C is inserted over the mandrel 10 and seated over the nipple 60 on the piston sleeve 56 and the table assembly 14, as illustrated, is indexed to axially align the catheter tube T with the aperture 115 and cavity 102 of the die members 112 and 80. The die member 80 is heated by the heater 86 and block 84, and a coolant is circulated through the receptacle 114 to maintain the die member 112 in a relatively cool condition.

As the cam begins its rotation, indicated by arrow 160, the heater 86 and die block 84 are driven downwardly, FIG. 3, to seat the tapered extension 120 of die member 112 in the bottom recess 122 of die member 80.

Further movement of cam 22 drives the coolant receptacle 114 with die member 112 downwardly, FIGS. 4 and 7, against the forces of springs 140, 142 until the normally straight cylindrical tip end 106 of Tube T passes through aperture 115 of die member 112 and engages the wall bend 164, FIG. 7, at the bottom end of the taper portion 108 of cavity 102. It is to be noted that a tip end portion 165 of mandrel 10 normally projects beyond the tip end of catheter C to seat against the increased taper portion 110, closely adjacent to the inner periphery thereof.

Further movement of cam 22 drives the piston 34, 54 downwardly against the forces of spring 42 and compressed air in chamber 38 from conduit 68, and forces the end portion 165 of mandrel 10 securely against the taper portion 110 to provide an effective seal for the top end of the taper portion 108 of cavity 102. Simultaneously, the catheter C depresses the piston sleeves 48, 56 by means of the contact of the tip end 106 of tube T with wall bend 164.

At this point the heated die member 80 is softening the tip end 106 and compressed air in chamber 46 from conduit 70 forces the piston sleeves 48, 56 and catheter C upwardly and the tip end 106 of tube T begins to taper within the cavity portion 108, as at 166, FIG. 8. FIGS. 6 and 9 illustrate the final phase of the forming operation in which the tapered end 168 of tube T is completed with an increased taper 170 at the very tip end as defined by the cavity terminal end 110.

The plurality of lobes 154 on cam 22 serve to jog the dies 80, 112 during the forming operation to relieve the air pressure build-up which would normally occur within the cavity portion 108.

While the instant invention has been shown and described herein in what is conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope of the invention, which is therefore not to be limited to the details disclosed herein but is to accorded the full scope of the claims so as to embrace any and all equivalent apparatus and processes.