Receptacles – Separate reinforcing element – Molded container with embedded reinforcing element
Reexamination Certificate
1999-03-29
2001-02-27
Castellano, Stephen (Department: 1722)
Receptacles
Separate reinforcing element
Molded container with embedded reinforcing element
C220S644000, C220S675000
Reexamination Certificate
active
06193099
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention concerns a method for forming raised or reinforced regions on a rotationally molded part, such as a tank or vessel. More particularly, it is concerned with a process whereby a platform is provided within the mold and incorporated in the molded part to present a rib which structurally reinforces the part.
2. Description of the Prior Art
Rotational molding, as recognized by those in the art, is a process which is useful in forming parts from synthetic resin materials. The process of rotational molding is characterized by the provision of a mold separable into at least two mold sections, into which synthetic resin, such as polyethylene, is placed. Although heated liquid synthetic resin can be employed, the synthetic resin is typically provided in powdered or other solid form. By heating the mold within an oven-like chamber while the mold is rotated, preferably around more than one axis, the synthetic resin particles are distributed throughout the mold, thereafter melting to a gooey consistency when engaging the heated mold. The rotation of the mold results in the resin particles being substantially evenly distributed, with the resin filling in cavities in the mold and conforming to the interior configuration of the mold. Once the melting and distribution is complete, the mold is removed from the oven and cooled while rotation continues. Such cooling may be in ambient air temperature well below the melting point of the synthetic resin, or accelerated by the use of cooling water in hot environments.
Heretofore, molded articles have been provided with ridges or gussets through the use of kiss-offs or kiss-throughs. A kiss-off is that area of the molded part where two mold surfaces are separated by a sufficiently small distance that the resin collecting on the mold surfaces bridges the gap therebetween. A kiss-through is that area of the molded part where mold surfaces of two mold sections meet, thereby forming an opening in that area of the molded part where the mold surfaces met.
However, as increasing demands have been made on rotationally molded parts in regard to capacity, lifting strength, ability to resist compression, and resistance to impact, there has grown a need to provide for reinforcement in the form of ribs which may be formed in the parts to meet those demands. Such ribs would preferably be formed to provide additional material and strength, and could be molded into the part in areas where kiss-offs would be impractical.
SUMMARY OF THE INVENTION
The demands for an improved rotational molding process for forming a reinforcement which meets these demands has largely been met by the present invention. That is to say, the present invention provides for an improved reinforcement which is not only capable of location in a variety of positions, incorporates the platform into the finished part, and coats and effectively integrates the platform from being a component of the mold into the part in a rotational molding process. The reinforcement may use a metallic material as a platform even in corrosive environments because of the ability of the resin to coat the platform portion exposed within the interior of the mold and thus the interior of a containment vessel molded thereby. The nature of the process of rotational molding involving substantial dynamic balancing of the mold and the difficulty of positioning removable mold components within the mold is circumvented by the use of lightweight platforms which remain with the part. Furthermore, because of the size and type of parts typically produced by rotational molding, the capabilities now offered by the present invention represent substantial improvements over the prior art.
The present invention broadly employs a platform onto which synthetic resin may be deposited. The platform is connected to the mold used in a rotational molding process which is conventional except for that it is configured to hold the platform during the molding process and then release the platform therefrom during removal of the part. The mold is thermally connected to and directly proximate the platform so that heat from the mold is transferred by conduction and, to a lesser extent, radiation to the platform.
After the resin is deposited within the mold and the latter is securely closed and coupled to a conventional rotational molding machine, the mold is rotated and inserted into a heated room or chamber. The mold is rotated on two or more axis to thoroughly distribute the resin throughout the mold. The platform is effectively a part of the mold, but is coated with resin on the portions exposed within the mold, a part of the platform being masked by the mold against the deposit of resin thereon. Once the resin becomes molten and viscous so as to thoroughly and evenly coat the interior of the mold and the exposed portion of the platform, the mold is cooled. After cooling of the mold and the part formed therein to a sufficient temperature, the mold, typically in two or more mold sections, is removed from the rotational molding machine and separated. The part can be removed, with the platform remaining with the part.
As a result, a variety of improvements in the nature of rotationally molded parts, and in particular bulk containers, can be provided. For example, the present invention allows the use of lifting or hoisting tubes to be directly incorporated at a variety of locations which strengthen the part both with regard to internal and externally applied forces. Baffles can be placed at a number of locations around the interior of the mold and thus the part or parts to be molded. Gussets and other reinforcements may be formed which incorporate the properties of both the material used as the platform and the synthetic resin. By using perforate platforms or filament mats as platforms, the platform is both effectively adhered and mechanically more securely incorporated into the part. Particular advantages and applications in the parts made in accordance with the present invention will be readily apparent with respect to drawings and detailed description which follows.
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Bolzer Todd
Garton Darwin
Castellano Stephen
Hovey Williams Timmons & Collins
Snyder Industries, Inc.
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