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Flex-Ride Night Raider Plastic Boat: The art of Widmer’s internally molded truss.
Staples, MN – A Minnesota company is exploring an innovative and patent pending truss design for large rotationally molded parts such as the 23 foot Flex-Ride Night Raider. Rotationally molded Items to 100 feet long are now possible.
By: Andy Stone
In general, as the dimensions of a rotationally molded product increase, the amount of shrinkage increases, and also the amount of deflection (sag) in the finished product increases. The compressible truss addresses both of these problems by adding to the strength and rigidity of the finished product. The thermoplastic materials used in rotational molding are known to cause the molded articles to shrink upon removal from the mold by approximately 5% or less, typically approximately 3% in the case of polyethylene, the most common material. However, once shrinkage is complete, no further shrinkage or expansion is expected under normal circumstances. It is important to remember that due to the rotational molding process, all exposed surfaces of the molded-in truss will be covered with molten plastic material that will cool to direct contact with the truss. Thus, once the molded article has cooled and the compressible truss has contracted, the resulting article is extremely strong not only because of the inherent strength of the truss itself, but also because of the significant amount of surface area represented by the polymer/truss interface. Once the compressible truss is assembled to the article, the combination has significantly greater strength (from the truss) and may be relatively large (such as the 7 meter Navy test boat we produced http://www.widmerboat.com ) yet when it is exposed to substantial external forces, the compressibility of the truss keeps the assembly from being too stiff to absorb the applied forces.
Preferred applications are boats which are required to withstand blast, impact, and/or structural loads when they are used to blow up mines, when moving through rough seas at high speed and/or when they are hoisted aboard another structure (e.g. another vessel or a platform). Standard hull designs currently used by naval forces and others requiring such performance are made of aluminum or fiberglass. Aluminum hulls do not withstand successive blasts well, and fiberglass hulls break when moving through rough seas at speeds as low as 30 knots. The watercraft described here are more flexible (less breakable) and thus more resistant to impacts from blasts and waves, unsinkable, resilient to small arms fire, low maintenance and cost effective to manufacture. Although the principles above are described and illustrated primarily with respect to boats and other watercraft, docks, and the like, such articles are only examples. Components of structures could also be such articles. For example, walls or roofs of buildings and similar structures are possible, as are portions of containers, transportation vehicles, and the like. The strength and reduced weight provided by the sliding truss system permit the manufacture and use of structures previously believed to be "too big" for manufacture and use. Examples include military or civilian bridge structures. Similar examples include load bearing floors, walls, and roofs for low cost housing, and deck planks. Further examples include the connectable sections of floating platforms which could be as large as 12 feet by 50 feet. These platforms take advantage of the inherent buoyancy of hollow molded plastic articles yet because of the sliding truss(es) within them, they are strong enough to support substantial weight. Such platforms could easily be stacked or otherwise arranged to be joined together as required. They could be used as modular floating deck platforms in shipyards, ports, and other similar installations involving large marine vehicles or equipment. In any embodiment, it is possible to include molded-through or molded-in holes or channels or other features for drainage, or for attachment of other structures, accessories, etc.
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About Stanley Widmer Associates, Inc. We Design, Engineer & Manufacture with Advanced Methods and Materials. Stanley Widmer Associates, Inc., founded in 1971, has offices in Staples, MN and is a leader in the Rotational Molding and Marine markets. More information about Stanley Widmer Associates, Inc. can be found at http://www.widmerboat.com/
Page Updated Last on: Feb 20, 2012