Spring devices – Rubber
Patent
1992-12-10
1995-04-25
Oberleitner, Robert J.
Spring devices
Rubber
267292, 267293, 114220, F16F 136, B06G 1122
Patent
active
054091993
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a shock absorbing fender formed of polyurethane material, and also describes herein, a method and apparatus used to manufacture such a polyurethane shock absorbing device. In particular it relates to a shock absorbing device of substantially cylindrical or tubular construction.
BACKGROUND OF THE INVENTION
Shock absorbing devices of cylindrical construction which are used for protection, find applications in a wide variety of situations. At one extreme of size are marine fenders which are employed to minimize the possibility of damage to wharves and ships during docking procedures, or in heavy seas. At the other extreme of size are shock absorbing components utilised in machines and instrumentation. The aim of this invention is to produce a fender having stable operative characteristics and large energy absorbing ability, relative to its mass and size, coupled with a maximum reaction force when compressed over its designed deflection characteristics which do not exceed the strength of the surfaces or members being protected.
The use of marine fenders to protect ships, wharves, drilling rigs and similar marine structures is well known. Typically these are of substantially cylindrical or tubular construction and may be of circular, D, trapezoid or rectangular cross-section. Various other designs have been employed including inflatable fenders and floating fenders.
Typically tubular fenders are comprised of rubber material or in particular styrene butadiene rubber (SBR). In addition some fenders are formed with metal or hard plastic sections or inserts to provide additional durability, toughness and means of mounting.
Tubular fenders are usually designed to absorb energy by axial or radial elastic compression. The majority of fenders loaded axially are contained within or attached to complex rigid structures or have sophisticated mounting requirements and shapes to handle large deflections which are desirable to minimise the reaction force, which becomes critical when cushioning larger vessels especially those above 150,000 tons, as their steel plate thickness does not increase in direct proportion to their mass. Thus their cost effectiveness becomes less with increasing size. In addition any of these mounting structures which have a considerable inertial mass which is added to the inertial mass of the rubber fender further increases the reaction force to a degree where the vessel's hull is damaged especially where the closing velocity is high.
Similarly prior art tubular fenders which are compressed radially and having other than a substantially circular cross section also contain complexities which reduce their cost effectiveness. Furthermore as these more complex shapes need to be molded as monolithic rubber members for maximum effectiveness and durability there is a practical limitation to their unit size and mass dictated by technological and tooling cost considerations.
Conversely currently used rubber tubular fenders which are compressed radially and having substantially circular cross-sections may be manufactured by a process whereby a strip of uncured rubber is wound around a mandrel until the desired diameter is reached. This lamination is then contained, and cured with heat and pressure. This allows for the manufacture of very large fenders weighing up to 15 tons and costing tens of thousands of dollars. And although their energy absorption per unit mass may not be as efficient as smaller more complex shapes their relatively lower manufacturing maintenance and mounting costs sees their increasing use, even in smaller sizes, typically of 0.4 m O.D. and 0.2 m I.D. where they are installed in lengths secured to docksides or vessels by wires or chains threaded through their hollow cores. Even so it will be appreciated that the larger items are expensive and both labour and material intensive to produce and difficult to handle.
In addition the above fenders commonly of substantially cylindrical construction with a hollow core may be supported by a member or members passed thr
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Oberleitner Robert J.
Schwarz Chris
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