Method and apparatus of forming extruded article

An article such as a length of plastic tubing is integrally formed by melt extrusion and having opposite ends which in turn are provided with different flexibilities. The apparatus and extrusion method by which such articles are forming in a running length includes a gear assembly rotatable between at least two alternate positions whereby two different but mixable resins are alternatively extruded as product.

BACKGROUND AND OBJECTS OF THE INVENTION 
This invention relates to an article of extruded plastic wherein one end 
thereof has a varying physical characteristic from the other end thereof, 
e.g., varying flexibility, including the method and apparatus for 
producing such an article. 
An example of an area where such an article might be used is the medical 
field such as a substitute for presently available catheter tubes. It is 
desirable in such catheter tubes that one end be relatively stiff while 
the other end by relatively flexible such that the more flexible lead end 
aids in insertion and is less traumatic once inserted into the body vessel 
by the doctor or medical technician. For this purpose, it is now known to 
join two hollow extruded plastic tubes of dissimilar flexibilities by a 
melt bonding technique, i.e., the butt ends of the tubes are heated to the 
softening point, and the adjacent areas fused to join their ends to form a 
continuous tube of dissimilar flexible ends. It is also known to 
adhesively connect the base ends of such tubes as by radio frequency 
bonding to form the desired result. However, such connections can and 
sometimes do fail under use such as upon being pressurized for injection 
(e.g., injection of contrast media); and, accordingly, a less labor 
intensive and more fail-safe article including such above-mentioned 
physical characteristics is needed. 
Accordingly, the primary object of this invention is to supply such an 
article that is highly reliable yet can be produced at a reasonable cost. 
Another and further object of the present invention is the provision of a 
method and apparatus for reasonably and assuredly forming such articles as 
indicated above. 
These and other objects of the present invention are accomplished by the 
provision of a continually melt extruded length of article comprising 
first and second terminal end portions formed of compatible first and 
second melt mixable plastics and an intermediate connecting portion 
connecting joining said end portions wherein said first and second end 
portions have varying physical characteristics such as flexibility and 
said intermediate portion being a melt extrusion blending of said first 
and second plastics. The above article is formed in an unique melt 
extrusion process wherein two extruders are connected at a common head, 
and a gear assembly receives the output of such extruders such that the 
gear system may be driven between first and second positions in which 
similar, i.e., compatible, plastic resins from the extruders are 
alternately directed into an extrusion die such that a bridging section of 
mixed resins is formed as a connecting portion. The dwell period in which 
the dissimilar resins are mixed is of very short duration such that a 
fairly pronounced demarcation line is formed between the two end portions 
of the article length. 
Other objects, features and advantages of the invention shall become 
apparent as the description thereof proceeds when considered in connection 
with the accompanying illustrative drawings.

DETAILED DESCRIPTION OF THE INVENTION 
Turning now to the drawings and particularly FIGS. 1 and 2 thereof, the 
novel construction of the article of the present invention is best shown. 
Therein a running length of article 10 is depicted. Such article, as best 
shown in FIG. 2, is of hollow tubular construction and may be adapted for 
medicinal purposes such as the flexible shaft portion of a catheter. 
Although the subject invention will be described with respect to such 
specialized medicinal use, it should be pointed out that other uses may 
indeed by placed upon such article, and it may be of a profiled 
configuration or even in the form of a coating upon an interior core 
instead of hollow. Generally for such specialized catheter uses, it is 
desirable to have the end to be inserted into a body vessel (artery, vein 
or other body passage) flexible and the other end stiff to aid in 
insertion. 
Returning to the description, the article 10 includes first and second end 
portions 12 and 14 respectively. Although the entire article is preferably 
formed from similar or the same material having different physical 
characteristics, e.g. of differing flexibility, at its opposite ends 12 
and 14, it is only necessary that the compositions forming the respective 
first and second ends 12 and 14 be compatible such that an intermediate 
connecting portion 16 be made up of differing quantities of each of the 
plastics forming the respective first and second ends 12 and 14. It is 
important, however, that the transition zone 16 be of relatively short 
length. For instance, with a 0.092 mil OD tubing with a 0.012 wall 
thickness formed of radiopaque plasticized nylon, it has been found 
desirable for the above-discussed medical application to have a transition 
zone 16 completed in a length of five inches. Other applications, however, 
may require shorter or longer lengths and such can be accomplished through 
programmed forming apparatus as will hereinafter be discussed. 
Turning now to FIG. 3 of the drawings, the overall extrusion apparatus for 
carrying out the process of the present invention is depicted. Therein an 
extrusion head 18 is regulated by a control device 20 such that plastic 
material entering such extrusion from extruders 1 and 2 is progressively 
fed through an extrusion assembly 17 into a cooling trough or station 22 
and then to a wind-up reel or station 24. 
The extrusion assembly 17 is further shown in the remaining drawings 
including FIG. 4 wherein the relationship of a piston assembly 26 with the 
extrusion assembly 17 is best depicted. Therein the extrusion head 18, 
which in turn includes a gear or valve assembly 28 and a die assembly 30, 
is operatively associated with the piston assembly 26. The piston assembly 
26 includes a hydraulically-operated piston 32 that is actuated back and 
forth between first and second positions by fluid power carried by the 
hydraulic hoses 34 and 36 and in turn controlled by the control programmer 
20 as is conventional. The piston assembly 26 is further comprised of an 
elongated housing 38 including plate or plates 39 connected to the forward 
face of the extrusion head 18 with bolts 40. The cylinder 42 is held 
between upper and lower caps 44 in turn connected to the plate 39 such 
that the piston 32 reciprocated between opposed upper and lower positions 
and maintains one or the other of such positions for a length of time 
determined by the program such that a rack 46 connected thereto moves the 
gear assembly 28 between at least two operable positions as will 
hereinafter by more fully brought out. 
Extruder 1 and extruder 2 shown best in Figs. 4 and 5 are connected to the 
base section or plate 48 of the head 18 which may in turn by heated by 
electric rods 49. The generally circular-shaped head 18 includes the base 
or rear section 48 and a forward section or plate 51 joined together with 
bolts 40. The base plate 48 in turn is provided with a central recess 52 
of a partial circular configuration, that is, provided with a projecting 
inset 54, in turn forming shoulders or stop surfaces 56 and 58. Centrally 
of the recess 52 is an upstanding circular boss 60 preferably formed from 
a softer material such as brass than the tool or stainless steel normally 
used in forming the remaining portions of the extrusion assembly 17. 
Openings 61 and 62 connected respectively to passageways 1A and 2A 
respectively exit at the face of the recess 52 in a centrally offset but 
within a radial arc and positioned generally adjacent to each other. The 
recess 52 includes a cut-out section 53 which extends to the base plate 48 
periphery for a purpose which will hereinafter be made clear. 
A first element or gear 64 of the gear assembly 28 is positioned in the 
recess 52 and in turn includes a circular recess (not shown) for co-action 
with the brass boss 60 such that the gear 64 may be easily rotated within 
the limits provided by the stops 56 and 58. In that regard, it should be 
pointed out that the gear 64 is also of partial circular configuration but 
has an arcuate circumferential cut-out 65 of a slightly greater arcuate 
extent than that of the inset 54 and in this manner provides the ability 
of the gear to partially rotate between the two positions determined by 
contact with stops 56 and 58 by the gear. The gear 64 periphery includes 
teeth 66 adapted to partially extend into a vertical channel 68 formed in 
the base section 48 and in which the rack 46 is positioned. Such rack 
includes teeth 70 adapted to engage the teeth 66 such that the 
reciprocating piston movement 32 will move the gear 64 between a first 
position such as shown in FIGS. 6 and 7 and a second alternative position 
such as shown in FIG. 8. 
The gear 64 is further provided with three centrally offset but arcuately 
aligned openings 72, 74, and 76. The alignment of the openings 72, 74, and 
76 and the openings 61 and 62 is such that in the first position, as shown 
in FIGS. 6 and 7, two of the three gear 64 openings are aligned with both 
of the openings 61 and 62 but in the alternate positions, as shown in FIG. 
8, two different openings of the three openings provided in the first gear 
64 are aligned with the extrusion openings 61 and 62. The first gear is 
also provided with a pair of alignment pins 78 and four threaded openings 
80 for receipt of bolts 82 such that a second gear similarly shaped to the 
first gear 64 may be aligned and bolted together to form the unitary gear 
assembly 28. This two-piece gear construction forms a practical manner of 
forming the appropriate plastic flow paths, but the gear assembly could be 
formed in other ways such as by casting. 
The second element or gear 84 is provided with a rear face 86 such as shown 
in FIG. 9 which includes a flow channel 88 connecting a central opening 90 
with the middle of the three openings in the first gear 64, that is, 
opening 74. In addition, a pair of dump channels 92 and 94 respectively 
connect the openings 72 and 76 to the peripheral edge of the gear assembly 
28 via dump openings 93 and 95 respectively. The cross-sectional extent of 
such dump openings roughly approximates that of the extrusion orifice 
through which the desired article is forced such that the extrusion 
pressures between the product path and the material being dumped is 
roughly equal. Such is desirable so that when the gear assembly 28 is 
switched back and forth between the first and second positions, the 
product flow pressure is not unduly changed which could cause undesirable 
changes in the density, shape and other article characteristics upon 
extrusion. The openings 93 and 95 face cut-out 53 such that resin from the 
extruder being dumped simply passes out the appropriate opening into the 
cut-out 53 and thence out of the head 18 to waste. 
As best shown by reference to FIGS. 9 through 13, it should be clear that 
plastic resin from either one of the two extruders 1 or 2 will move from 
the base section 48 through the gear assembly 28 and thence to the forward 
section 51 of the head 18 through a central opening 100 provided therein 
and in which the die assembly 102 is mounted. Which resin is extruded into 
product through the die assembly and which resin is dumped from the gear 
assembly will, of course, depend on the position of the gear assembly at 
any given time. 
Such die assembly 102 includes conventional portions but with modifications 
which will be referred to as the following description proceeds. The face 
of the forward section 51 of the extrusion head 18 is provided with a 
large central recess 104 and a contiguous countersunk recess 106. The 
forward outer section 108 of a die assembly is mounted in the larger 
recess 104 with an apertured plate 110 secured to the face 112 of the 
front section 51 via bolts 114. Adjustment is provided by conventional 
adjusting screws 116 radially positioned about the face 112 which provides 
for the proper positioning of the outer die portion 108 vis-a-vis a 
centrally disposed die mandrel 118. The mandrel 118 is further mounted in 
a holder 120 which in turn includes a plurality of openings 122 circularly 
disposed about the mandrel opening periphery 124 such that extrusion or 
resin coming from the opening 90 of the gear assembly 28 is diverted 
through the openings 122 and thence through the extrusion passage 126 
formed between the mandrel 118 and the similarly shaped opening 128 in the 
outer die portion 108. The generally conical face 130 of the mandrel 118 
is provided with a series of grooves 132 to, in effect, increase the 
laminar flow properties imparted to the molten resin as it passes through 
the passage 126 and thence to the die opening 132 where the resin is 
subsequently cooled and taken up in the intended manner. 
In addition to the above specialized configurations to impart laminar flow 
to the extrusion mass, the channel 88 in the second gear 86 is also 
provided with a series of grooves 96 shown best in FIG. 10. It is 
particularly important that laminar flow rather than a more normal 
viscosity profile occur in the extrusion passages. In other words, a 
channeled melt flow is desired to reduce the time in which mixing of the 
two resins takes place upon switching extrusion positions. As the resins 
move from either of the extruders through the extrusion assembly 17, the 
flow of a first resin through the orifice 132 is quickly changed to the 
flow of the second resin without a gradual mixing of the resins from 
decidedly slower flowing resin adjacent the extrusion passage walls as 
would exist with a normal viscosity profile of melt flow in a round 
channel. The quick change from one resin to the other with channeled melt 
flow is the desired process operation of the above-described apparatus to 
form the article 10 in the intended manner. Thus if normal turbulent flow 
was permitted, the time or length distribution in the final article 10 
would be increased, that is, the material being extruded as product would 
tend to mix with peripheral portions or the previously extruded material 
and thus take a longer time period to emerge as a pure material from the 
orifice 132. Other features which facilitate this overall result includes 
a streamlined die and mandrel to eliminate any dead spots where the 
material would tend to mix and therefore not transfer quickly, and by 
keeping the overall mixing sections of the two materials to a minimum, 
i.e., under two inches, keeps the chance of the two materials mixing to a 
minimum. Also, a quick smooth movement of the gear has been accomplished 
by using the brass bushings at all contact points. 
It should thus be apparent that the overall concept of the invention is to 
provide constant extrusion from two extruders 1 and 2 to the common 
extrusion head 18. The extruder size is a variable and varies according to 
the tubing geometry or the material type being extruded. Each extruder is 
connected by a threaded adapter to the main head 18. 
The gear assembly 28 has two positions. Thus in the first position as shown 
in FIGS. 6 and 7, product is being formed, that is, extruded from the 
orifice 132, by material coming from extruder 1 via path 1A and opening 62 
while the material being fed from extruder 2 via path 2A and opening 61 is 
being dumped, that is, simply allowed to pass through opening 76 and 
channel 94 and ooze between the plates 64 and 86 and thence outwardly from 
the recess 53 to waste beneath the extruder head 18. Thus in the alternate 
position, as shown in FIG. 8, the gear assembly 28 has been rotated 
counter-clockwise such that it abuts stop 58 such that the product 
extrusion path is from opening 61 via opening 74 and channel 88 into 
opening 90 and thence through the die assembly, and the flow from extruder 
1 via path 1A and openings 62 is dumped via channel 92 through opening 76. 
It can be important to control the dump or back pressure of the extrusion 
path not producing product such that the extrusion pressures of both paths 
are equal such as when the program calls for movement of the gear assembly 
to the alternate or second position such as shown in FIG. 8. Such pressure 
difference could undesirably cause momentary changes in the configuration, 
density, or appearance of the product being extruded. 
Turning now to FIG. 14, the manner in which back pressure may be controlled 
by regulating, in effect, the size of the dump orifices 93 and 95 will be 
hereinafter described. 
It will be thus apparent that a boss 150 is positioned in a bore 152 in the 
second gear 4. The bore 152 passes through the gear 4 and includes an 
allen or slotted head 154 opening in the upstream side of the gear face 
156. In order to make the slotted head 154 accessible from the outside of 
the head 18 while the extrusion process is being carried out, a pair of 
bores 158 are provided through the front section 51 and terminate in 
openings 160 at the front face thereof. The bores 158 terminate and are 
respectively aligned with the bores 152 such that the bosses 150 may be 
adjusted inwardly or outwardly of the dump channels 92 and 94 so as to 
regulate the effective cross sectional thereof and thus the extrusion 
pressure therein. This can be done while the operation is running as with 
a wrench or screw driver so that the pressure of each of the dump paths 
can be adjusted to substantially equal that of the article extrusion path. 
While there is shown and described herein certain specific structure 
embodying this invention, it will be manifest to those skilled in the art 
that various modifications and rearrangements of the parts may be made 
without departing from the spirit and scope of the underlying inventive 
concept and that the same is not limited to the particular forms herein 
shown and described except insofar as indicated by the scope of the 
appended claims.