Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Corrugating
Reexamination Certificate
2000-04-27
2002-11-26
McDowell, Suzanne E. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Corrugating
C264S519000, C264S520000, C264S521000, C264S319000, C264S327000, C264S328140, C264S328150
Reexamination Certificate
active
06485666
ABSTRACT:
TECHNICAL FIELD
The invention relates to the post-extrusion processing of extruded profiles, such processing including blow molding the profile to a larger internal diameter while correspondingly imparting at least one bend into the expanded profile as well as optionally compression molding ends onto the profile, blow molding a second region of the profile into another shape, e.g., bellows or in-line check valve, and injection overmolding. In one embodiment, the process will include the bending of at least two angles into the profile, the angles being non-planar with respect to each other. The process involves heating at least a portion of the essentially linear extruded profile in a profile heating means to a first temperature at which the profile becomes formable or pliable or bendable, yet which still has at least some degree of structural integrity at this point which permits it to be physically manipulated without compressing the profile by the application of external pressure or by the weight of gravity itself. This preheating step is followed by additional heating to a second higher temperature at which the profile becomes melt processable and permitting radial expansion under pressure or melt fusion under pressure.
BACKGROUND OF THE INVENTION
There are various primary polymer processing technologies which are applicable in the manufacture of parts of various designs and shapes. Each technology as discussed below, has design constraints which limit its implementation in the fabrication of variously configured components.
Blow molding is a process typically used for the production of hollow thermoplastic components. The most widely known blow molded objects are bottles, jars, cans, and containers of all kinds for the food, beverage, cosmetic, medical, pharmaceutical and home products industries. Larger blown containers are often used for the packaging of chemicals, lubricants, and bulk materials. Among other blow molded items are balls, bellows, and toys. For the automotive industry, fuel tanks, car bumpers, seat banks, center consoles, and armrest and headrest skins are blow molded.
The most prevalent blow molding grade plastic raw material is high-density polyethylene. Most of the milk jugs are made from this polymer. Other polyolefins, e.g., low density polyethylene, polypropylene, are also widely processed by blow molding. Depending on the application, styrenes, vinyls, polyesters, polyamides, polyurethanes, polycarbonates, and other thermoplastics are blow molded.
More than half of all blow molded parts are made by extrusion blow molding. The extrusion process is defined as making a product (extrudate) by forcing material through an orifice or die. The extrusion blow molding process consists of five steps: (1) extrusion of a plastic parison (hollow plastic tube); (2) closing of two mold halves on the parison, clamping the mold and cutting the parison; (3) blowing the parison against the cooled walls of the mold cavity, calibrating the opening, and holding it under air pressure during the cooling time; (4) opening the mold and removing the blown part; and (5) finishing the part by trimming off the flash.
A basic blow molding machine comprises an extruder, an extrusion head, a press section containing the mold, a calibration, a parison separation device, and an electrical control station. This fundamental unit is called a “blow-and-drop” machine. Plastic pellets are fed into the hopper mounted to the extruder. A motor-driven rotatable screw moves the material toward the blow molding or extrusion head and through the die.
Most extruders used in the blow molding are single-screw, either smooth-barrel or grooved barrel. Extruder output is determined by the geometry of the water-cooled feed zone and the feed capacity of the screw per revolution. With continued extrusion, a symmetrical or asymmetrical tube (parison) is formed by the die and pin in the extrusion head. An asymmetrical parison is developed by shaping or ovalizing the tooling in the head. Die and pin often move relative to each other during the extrusion process. This is caused by parison programming. Continuous extrusion is used with shuttle-type and wheel-type machines. Since the parison is extruded continuously, an open mold is positioned periodically around the parison. With the parison at its proper length, the mold is closed and clamped, and the parison is cut. Thereafter, the mold moves back under the calibration station, where the parison is blown into the shape dictated by the mold cavity. The neck of the bottle or container is calibrated simultaneously, in most cases by top blowing. Objects without openings are often needle-blown. Single-station shuttle machines have the mold positioned at the left or the right of the extrusion head while double-station machines have molds to the right and left of the head.
A blow molding machine's productivity is governed by its cycle time, 80% of which is cooling time. This long period of time is required for cooling the hot plastic material prior to demolding, to prevent post-warpage and dimensional distortion of the finished part. Modern molding machines are built-in stations for post-mold cooling. Articles are transferred out of the mold into post-cooling devices that basically consist of a cooling mold, i.e., mold without pinch-offs. Cooling is accomplished via liquid cooling in the shell of the mold, and CO
2
, refrigerated air, or nitrogen cooling inside the container. Advantages are seen in shorter cycle times and control of the part distortion inherent in parts with asymmetric configuration and thick walls.
After leaving the cooling stations, containers are accepted by trim or punching devices for flash removal. Wall thickness control and minimal generation of flash avoid the problems associated with flash removal, e.g., the need to regrind and reprocess the flash and the possibility that its removal may expose seams, which in turn can contribute to container cracking and splitting on impact. Continuous blow molding machines can cost between $250,000 to $1.5 million and are typically run at parison extrusion rates of ten feet per minute using pressures of from between 80-125 psi. This process has significant inherent rate limitations.
The other type of blow molding is injection blow molding which is a two stage process for producing completely finished plastic containers. In the first stage, the plastic is injection molded into a preform cavity where the parison is formed. The neck finish of the container is molded, as well as the shape of the parison, as the plastic is injected around the core pin and into the preform. Temperature and conditioning of the parison takes place at this stage. The parison then is transferred via the core pin to the blow mold, and air is introduced through the core pin to blow the parison to the shape of the blow mold. The completed container is then transferred to the ejection station.
Injection blow molding offers a number of advantages: (1) it produces scrap-free, close tolerance, completely finished bottles that do not require any secondary operations; (2) it offers positive weight control in the finished container; (3) neck shapes and finishes, internally and externally can be molded with accuracy; (4) repeatable weight and bottle dimensions are possible with the process; (5) improved clarity and strength due to the effect of some amount of biaxial orientation; (6) bottles are controlled and oriented at the ejection station; and (7) there is a minimum of operator supervision required. There are however, limitations to this process, relating primarily to the sizes and shapes of bottles that can be produced profitably on existing injection-blow molding machines.
Compression molding has been used for such thermosetting compounds are urea, phenolic, epoxy, melamines and rubber. The most apparent advantage of compression molding of thermosets is the simple system involved. The material is placed in a heated cavity and is pressurized for the required cure time. Tooling costs are inexpensive because of the simplicity. Materi
Buckingham Doolittle & Burroughs LLP
McDowell Suzanne E.
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