Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Layered – stratified traversely of length – or multiphase...
Reexamination Certificate
2002-05-17
2003-11-11
Mackey, James P. (Department: 1722)
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Layered, stratified traversely of length, or multiphase...
C264S171260, C264S209400, C425S071000, C425S113000, C425S114000, C425S326100, C425S377000
Reexamination Certificate
active
06645410
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the area of tubular members of definite or indefinite length, including the wall structure of the tubular members. In particular, the present invention relates to manufacturing multi-layer tubing or pipe made from a thermoplastic material, which tubing or pipe comprises at least one inner tube or pipe that is internally positioned or situated within and separate from an outer tube or pipe.
BACKGROUND OF THE INVENTION
In industries such as the semiconductor or chip processing industry where several kinds of dangerous chemicals are being used at several processing and manufacturing stages, it is important to have tubing and/or pipes to transport these chemicals and that is non-reactive with the chemicals, flexible enough to bend between connections, and provide containment in the event that the immediate tube transporting the chemical ruptures or otherwise breaks. Various materials to make these tubes and pipes are known to those skilled in the art, such as thermoplastic tubing. In this Application, unless the context indicates otherwise, the terms “tubing” and “tube” likewise refer to “piping” and “pipe”.
Common practice to produce thermoplastic tubing uses a plasticating extruder with an annular die to form a hollow tube that is pulled into a sizing device for sizing and shaping and where the thermoplastic solidifies into finished tubing. Nested tubing can be made or manufactured by various mechanical methods. Tubing having a smaller outer diameter than the inner diameter of other tubing can be manually pushed or pulled inside the other tubing. The process may be assisted by a machine. This process is generally limited to finished product lengths, however, because frictional forces cause the tubes to bind as one tube traverses the other. Lubricants can be used in some circumstances to reduce the effects of these frictional forces, but frictional forces eventually come into play again and, in many circumstance, it is undesirable to introduce the lubricant into the tubing.
Alternatively some tubing extrusion processes can produce nested tubing by producing one tube over the top of another tube. These extrusion processes rely on parts designs and/or bonding one tube to another to make multi-walled hollow tubes having rigidly interconnected walls or to hold one tube concentrically in the other tube. Examples of multi-walled hollow tubes having rigidly interconnected walls are disclosed in Hosono et al., U.S. Pat. No. 4,906,496, Double-Walled Tube Assembly and Hegler et al., U.S. Pat. No. 5,976,298, Method of Producing Multilayer Thermoplastic Pipe, both of which are incorporated herein by reference. Hosono discloses “feeding the inner tube and the extruded outer tube into a sizing die device, contracting the outer tube in a softened state toward the outer peripheral surface of the inner tube in the sizing die device until the distal ends of the ribs of the outer tube are fused to the outer peripheral surface of the inner tube, and cooling and solidifying the outer tube. Hegler discloses “heating to welding temperature at least the outer surfaces of the externally profiled shape . . . and extruding a tube of plastic material on to the outer surfaces of the pipe of externally profiled shape . . . and welding together the tube and outer surfaces. and cooling the multilayer pipe”. Rigid tubing suffers from an inability to easily bend the tubing without creating stress cracks in the tubing.
A bonding process is exemplified by Takahashi, U.S. Pat. No. 4,157,194, Thermoplastic Multi-Walled Pipes and Takahashi, U.S. Pat. No. 4,236,953, Process for Producing Thermoplastic Multi-Walled Pipes, both of which are also incorporated herein by reference. To avoid the disadvantages of rigidly fixed multi-walled pipe or tubing, Takahashi uses “ribs for spacing the inner and outer tubular members”. The “rib . . . is so formed that the bond per unit area between the rib . . . and inner tubular member is weaker than the bond per unit area between the rib . . . and outer tubular member” so that “[i]f the weak-bond temperature is properly selected at a temperature between the forming temperature and the melting temperature of resin depending upon the kinds of resin used, the inner and outer tubular members may be easily separated from each other, and the structural strength of the multi-walled pipe will not be impaired”. Although these tubings are more flexible, especially when “breakaway” bonds are used, there is still some stress caused by the bonding and the ribs or spaces can interfere with the bending and twisting and the operation of the tube.
Another alternative is disclosed in Wolf et al., U.S. Pat. No. 5,433,252, Fluid Containing Coaxial Tube for Control Systems, also incorporated herein by reference. Wolf discloses a coaxial tube comprising a “fluid-tight outer tube and a fluid-tight inner tube with spacers between the tubes . . . [to] maintain the inner tube at least substantially coaxial with the outer tube” wherein “the spacer is integral only with the outer tube or the inner tube [so] that the inner tube and the outer tube are able in a limited way to freely axially shift relative to each other”. To manufacture the coaxial tube, “first the inner tube is manufactured separately, preferably by extrusion, and then it is cooled”. The outer tube is “shaped in a second extrusion station in the direction of extrusion around the inner tube, and in particular this will be done using the technique of coaxial sheath extrusion”. The inner tube “will be already sufficiently cold and solid. so that, during the ensuing molding of the outer tube around the inner tube, neither the wall thickness of the inside tube will be lessened or changed, nor is the outer tube able to bond to the inner tube”. The tubing in Wolf can be very flexible; however, the problem that the ribs and spacers can interfere with the bending and twisting and the operation of the tubing still exists.
It would be advantageous if an apparatus and method for manufacturing multiply contained tubing could be developed that produced both tubing that was very flexible and was ribless, i.e., the inner surface of the outer tube and the outer surface of the inner tube could be produced without ribs, spacers, or like structural features.
SUMMARY OF THE INVENTION
The present invention provides a manufacturing apparatus and method for multiple containment tubing. The apparatus produces continuous or virtually endless, nested tubing, or one tube within another tube, without having to fix the space between the tubes or position them concentrically. Consequently the tubing is very flexible and with uniform wall thickness. Moreover, because the inner surface of the outer tube and the outer surface of the inner tube are ribless, these kinds of features cannot interfere with the bending and twisting and the operation of the tubes comprising the tubing. The space between the tubes, or free space, has sufficient volume to contain a range of contents of the inner tube, as a safety containment device, if the inner tube ruptures, cracks, or otherwise breaks. In particular, resins of PFA, FEP, Olefin such as HDPE or PP materials, or other fluorinated hydrocarbons or similar materials that have chemical resistance suitable for the electronics industry or combinations of these resins are applicable to this invention.
In preferred embodiments, the apparatus comprises an outer tube extruder, an outer tube sizing device, and a hollow annular guide. The outer tube extruder includes an extruder body, a mandrel, and a die body. The mandrel and the die body have a longitudinal direction and are approximately longitudinally aligned, and the die body circumscribes the mandrel. The mandrel and the die body are connected to the extruder body so that a melt pool can be forced through the extruder body, into a cavity between the die body and the mandrel, and out from between the die body and the mandrel in the form of and to create an outer tube. A bore passes through the mandrel
Entegris, Inc.
Leyson Joseph
Mackey James P.
LandOfFree
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