Plastic article or earthenware shaping or treating: apparatus – Control means responsive to or actuated by means sensing or... – Control means responsive to product weight or dimension
Reexamination Certificate
2003-03-12
2004-11-09
Eashoo, Mark (Department: 1732)
Plastic article or earthenware shaping or treating: apparatus
Control means responsive to or actuated by means sensing or...
Control means responsive to product weight or dimension
C425S171000, C425S173000, C425S378100
Reexamination Certificate
active
06814557
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention pertains to an apparatus and a method of producing ultra-thin walled extruded polymer products using a polymer extruder. Polymer extruders are used to produce polymer tubes and ducts and to coat with polymers circular, rectangular, stranded and coiled conductors, such as electrical wires, ribbons, cables and coils.
A common type of extruder employed in manufacturing such extruded polymer products is a “⅜-inch single screw cross-head” extruder
300
. In such an extruder, polymers in the form of pellets are placed in a feed hopper
310
and thus fed into an extruder barrel
320
. See FIG.
10
. Extruder barrel
320
houses a helical extruder screw
330
. It should be noted that commercially available pellets must be repelletized, i.e., resized, to a smaller size for use in ⅜ inch extruders to avoid damage to the extruder screw. The polymer fills the spaces between the surface of extruder screw
330
and the interior walls of extruder barrel
320
. The screw is rotated about its longitudinal axis by an electric motor
340
while extruder barrel
320
remains stationary. The
340
while extruder barrel
320
remains stationary. The rotation of extruder screw
330
transports the polymer through extruder barrel
320
creating pressure and friction between the polymer and the interior walls of the extruder barrel
320
. The combination of pressure, friction and additional heat provided by heaters melt the polymer. In polymer extrusion, the additional heat is most commonly supplied by electric resistance heaters, which are placed along the exterior of extruder barrel
320
.
By the time the polymer has traveled the length of the extruder barrel, it is completely melted. The molten polymer, i.e., polymer melt, is then forced through a breaker plate
345
, which is housed in the body of the adapter
346
. Breaker plate
345
causes the polymer melt to flow in a linear direction as opposed to a helical direction.
Breaker plate
345
is a metal cylinder which provides five channels, for polymer melt flow, running along the length of the cylinder. For example, the breaker plate that is provided in a typical ⅜-inch extruder is approximately 0.377 inches in length and has an overall diameter of approximately 0.748 inches and provides five channels each having a diameter of approximately 0.110 inches. Accordingly, the overall cross-sectional area of the standard breaker plate is 0.439 square inches and the cross-sectional area provided for polymer flow is approximately 0.047 square inches (the sum of the cross-sectional area of all five channels). Accordingly, the ratio of the total cross-sectional area provided for polymer flow to the overall cross-sectional area of the breaker plate is 0.107.
Breaker plate
345
may also support a filter which is used to remove contaminants from the polymer melt. Typical filters used in polymer extrusion range from 100 to 400 mesh (100-400 lines per square inch).
The polymer melt, after flowing through the breaker plate and filter exits the adapter and enters a crosshead assembly
350
where it is forced through an extruder die
360
. The polymer melt emerging from the extruder die
360
is referred to as an extrudate. The shape of the extrudate immediately leaving the extruder die is not the final shape. For example, in wire coating, a wire
318
travels along a wire path through the crosshead assembly where it comes into contact with the polymer melt which coats the wire. Upon emerging from extruder die
360
, the walls of the polymer coating rather than being uniformly concentric and parallel forms a cone around the wire. This phenomena is partially attributed to extrudate swell. As the wire is further drawn away from the extruder die, the coating walls become uniformly parallel.
Currently available extruders are unable to effectively produce ultra-thin wall, less than 50.8 microns (0.002 inch) in wall thickness, pin-hole free, polymer products. This inability is in part due to the presence of polymer melt contaminants, such as gels and thermally degraded polymers, and the rheological properties of the polymer. Ultra-thin coating is necessary in biomedical implants, where wires with diameters as small as 25.4 microns (0.001 inch) are used and must substantially retain their inherent flexibility and small diameters. Complete coverage of the wire with polymer is necessary to prevent unintended contact between the bare conductor and body fluids and tissue. When attempts to place ultra-thin coatings on such wires have been made, the resulting coating is incomplete or covered with pinholes.
In addition, currently available extruders do not provide an effective method for instantaneous visual inspection of the ultra-thin extrudate. Such inspection would be advantageous as it would allow an extruder operator to determine whether the extrudate is being uniformly formed, i.e., that the polymer coating extruded on a wire is uniform in thickness and concentric. Consequently, an extruder may be operated for a long period before any defect is noticed. This results in wasted material and loss of production time.
Non-uniformity of the extrudate walls may be corrected by adjusting the position of the extruder die
360
along different lateral axes. However, such extruder die adjustments are made cumbersome by the current adjustments mechanisms incorporated in currently available extruders (see FIG.
11
). Present extruders commonly employ four adjustment screws
370
that act directly on die
360
to adjust the die's position. Consequently, adjusting the die position is time consuming because each screw must be manipulated to adjust the die. On many small extruders, such as a ⅜-inch extruder, at least one of the four adjustment screws
370
is placed in a difficult to accessed location. Unlike thicker walled wire coating, attempts to produce thin walled polymer coatings over wire do not provide the capability to adjust the concentricity of the coating without stopping the coating process. Consequently, the extruder must be stopped to make time consuming die adjustments. This results in numerous trial and error runs to achieve a uniform product.
BRIEF SUMMARY OF THE INVENTION
The present invention is an extruder, and a method of using the same, that provides instantaneous inspection of the extrudate. The invention incorporates the use of video equipment, to provide magnified observation of the extrudate, and may use associated mirrors to observe the extrudate as it exits the die along multiple views.
The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 3635621 (1972-01-01), Miyauchi et al.
patent: 4605525 (1986-08-01), Baxter
patent: 4642686 (1987-02-01), Nagano et al.
patent: 4684487 (1987-08-01), Gawrisch
patent: 4710114 (1987-12-01), Garner
patent: 4871493 (1989-10-01), Goto
patent: 4909630 (1990-03-01), Gawrisch et al.
patent: 5272649 (1993-12-01), Campbell et al.
patent: 5431867 (1995-07-01), Matsushita et al.
patent: 5458830 (1995-10-01), Shin et al.
patent: 5498145 (1996-03-01), Sikora et al.
patent: 5608637 (1997-03-01), Wang et al.
patent: 5723517 (1998-03-01), Campo et al.
patent: 5795531 (1998-08-01), Salzmann et al.
patent: 6250904 (2001-06-01), Reddy et al.
Rauwendaal, Chris, Polymer Extrusion, 1994, pp. 68-79, 102-107,310-315.
Frados, Joel, Plastics Engineering Handbook of the Society of the Plastics Industry, Inc., fourth edition, pp. 188-191.
Rucker Lucien M.
Swanson John W.
Advanced Neuromodulation Systems, Inc.
Eashoo Mark
Law Office of Timothy E. Siegel
Siegel Timothy E.
LandOfFree
Apparatus and method of producing ultra thin wall extrusions... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus and method of producing ultra thin wall extrusions..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus and method of producing ultra thin wall extrusions... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3320307