Protecting national treasures is an open-and-shut case
The Rotunda of the National Archives Building in Washington, D.C., contains display cases housing the Declaration of Independence, the Constitution, and the Bill of Rights. Flanking these are two sets of seven cases lining the Rotunda's curved walls that display the "American Originals" document collection. Both banks of cases have seven individual glass lids, each framed in ornate bronze castings.
Custom hinges from Weber Knapp counterbalance the massive 140 to 180 lb lids, cutting opening and closing forces to just 10 lb. The hinges are part of a renovation by a National Archives and Records Administration (NARA) team. NARA specs say case lids must stay put (indefinitely) without additional support at any point in their travel. Moreover, no hinge materials can produce emissions that could potentially harm the documents. The hinge assembly must also remain invisible from the case front so as not to detract from the viewing experience. Another challenge: the hinges must follow the curve of the rotunda wall.
The resulting design uses a combined counterbalance/mechanical linkage that fits between the wall and document stands. A special gooseneck arm attaches the hinges to the lid frames. Closed, the lids slope down at 25° and rotate up 60° to their full-open position. The design prompted no major changes to the cases themselves only a fiber-optic light bar needed a slight redesign to accommodate pivoting motion of the arm. NARA says hinges must last a minimum of 10,000 cycles. Weber Knapp has successfully tested the hinge to 36,500 open/close cycles.
Weber Knapp Co., Jamestown, N.Y., www.weberknapp.com