Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting – Positioning of a mold part to form a cavity or controlling...
Reexamination Certificate
2002-01-30
2004-01-06
Heitbrink, Jill L. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
Positioning of a mold part to form a cavity or controlling...
C264S328100, C425S140000, C425S150000, C425S169000, C425S173000, C425S577000
Reexamination Certificate
active
06673283
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to molding processes using core pins, and in particular, to a process of molding barrel-shaped vials for use with levels.
BACKGROUND OF THE INVENTION
The molding process for making barrel-shaped vials or other tube-like items with elongate cavities typically utilizes injection molding around a core pin. Injection molding of plastic materials is well known in the art and is well suited for forming a large number of discrete items such as vials.
During the injection molding process, a core pin is inserted into a molding cavity such that the space between the pin and cavity defines the shape of the intended product mold. When the pin is positioned in the cavity, a plastic material, such as acrylic, polycarbonate, polystyrene, butyrates or the like, is injected into the space between the pin and the cavity.
After the material has been allowed to cool, the pin is withdrawn from the cavity and an ejection ring or stripper located on the proximal end of the pin ejects or forces the molded plastic off of the core pin. The process is then repeated to form another vial.
Barrel-shaped leveling vials typically have circular cross-sections at any plane normal to the body axis (though there are vials with spherical radii having other cross-sections such as squares, rectangles, etc.). In order to function properly, the largest cross section must be formed at a known point between the proximal and distal ends of the vial. This requires that the core pin on which the vial is formed also has its largest cross section at a known point between the distal end and the ejection ring or stripper where the plastic mold ends.
Computer numerically controlled (CNC) grinder tools are typically utilized to fabricate core pins for use in level vial molding. While such grinders typically allow for great precision, in practice it is extremely difficult to fabricate core pins having the proper positioning and alignment of the largest cross section. Compounding that difficulty is the fact that the measurement of the position of the largest circular cross section on the core pin is extremely difficult to obtain. For instance, a core pin having a spherical radius of 9 inches, as an example, will have a radial decrease of only 0.000005556 inches from the largest cross section to a cross section located 0.01 inch away in either direction. Therefore, verification of the position of the largest cross section on the core pin is practically impossible.
Because the position of the core pin's largest cross section is so difficult to determine, core pins used for molding barrel-shaped level vials are inherently imprecise. Only upon the molding of numerous vials from one core pin and the optical inspection of these vials can the position of the largest cross section on that core pin be calculated. If the position is determined to be too close to the distal end, the core pin is defective and cannot be used. If the position is determined to be too far from the distal end of the core pin, the core pin can be ground further to center the position; however, this process is expensive and does not always result in a more precise core pin.
Therefore, an improved core pin and method of use thereof which addresses these problems of known core pins would be an important advance in the art.
OBJECTS OF THE INVENTION
It is an object of the invention to provide an improved core pin which can be adjusted after fabrication to allow the centering of its largest cross section.
Another object of the invention is to provide an adjustable core pin which can be secured to have a permanent determined length.
Another object of the invention is to provide an adjustable core pin which can be secured so that its largest cross section is permanently established at the desired position.
Another object of the invention is to provide an improved core pin which alleviates the need for adjustment of the molding plates or bases.
Another object of the invention is to provide an adjustable core pin with sufficient strength to withstand the stresses involved in injection molding.
Another object of the invention is to provide a method of use of the improved adjustable core pin which allows users to efficiently locate the largest cross section and center it in the cavity of the formed vial.
Still another object of the invention is to provide a method of use of the improved adjustable core pin which allows for readjustment of its crest at the desired position.
Yet another object of the invention is to provide a method of producing precise vials for use with levels and other leveling devices.
How these and other objects are accomplished will become apparent from the following descriptions and the drawings.
SUMMARY OF THE INVENTION
This invention is an improved core pin for molding vials for use in levels and method of use thereof The invention represents a significant advance over the state of the art by providing novel elements, including an multi-piece core pin which is adjustable to accurately position the vial's maximum inner diameter.
The adjustable core pin includes an elongate rod which has a proximal end, proximal and intermediate portions with preferably circular cross sections, and a distal end including a barrel-shaped section having a crest at the cross section with the greatest diameter. The intermediate portion has a smaller outer diameter than the proximal portion so that the rod has a shoulder at the junction of the proximal and intermediate portions.
The adjustable core pin also includes a rod retainer which has an elongate rod retainer cavity extended from a distal opening to a proximal opening. The elongate rod-retainer cavity receives the rod such that the distal end projects from the distal opening for a determinable length. The determinable length is adjustable so that the crest is placed at a preferred position for vial molding.
The preferred elongate rod-retainer cavity has first and second segments. The first segment has a first inner diameter substantially equal to the outer diameter of the proximal portion of the rod. The second segment has a second inner diameter substantially equal to the outer diameter of the intermediate portion of the rod. Therefore, the rod-retainer cavity has an inner shoulder at the junction of the first and second segments. In a preferred embodiment of the invention, the determinable length that the rod extends out of the rod retainer can be adjusted by the insertion or removal of shims between the shoulder and the inner shoulder so that the crest is properly positioned for vial molding.
The adjustable core pin preferably includes a stripper bushing which has a stripper-bushing cavity extending from a first end to a second end. A stripper surface is positioned at the second end so that when the stripper-bushing cavity receives the rod retainer and the stripper bushing and rod retainer are engaged, the stripper surface is adjacent to the distal end of the elongate rod. The stripper bushing is movable from this engaged position toward the distal portion of the rod so that the stripper surface is able to contact any vial molded on the distal portion and eject the vial from the rod at the conclusion of the molding cycle.
The preferred rod retainer comprises two integral sections, including a proximal section having a outer cylindrical shape and a distal section having an outer conical shape. In an alternate embodiment, the distal section may have a cylindrical shape. The rod retainer's distal section has a smaller outer diameter than the proximal section at the junction between the distal and proximal sections thereby forming a stripper shoulder. The preferred stripper-bushing cavity has a conical shape which corresponds to the outer conical shape of the distal section of the rod retainer (though it is foreseen that the stripper-bushing cavity may have a cylindrical shape to correspond with a rod retainer having a cylindrical distal section). The corresponding shape of the stripper-bushing cavity allows the stripper bushing to rest on the surfac
Coel Joseph B.
Stanford Roger D.
Empire Level Mfg. Corp.
Fontaine Monica A
Heitbrink Jill L.
Jansson & Shupe & Munger Ltd.
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