Static structures (e.g. – buildings) – Specified terranean relationship – Subterranean enclosure with portal opening; e.g. – storm or...
Reexamination Certificate
2000-06-07
2002-08-20
Stephan, Beth A. (Department: 3635)
Static structures (e.g., buildings)
Specified terranean relationship
Subterranean enclosure with portal opening; e.g., storm or...
C052S080200
Reexamination Certificate
active
06434896
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to prefabricated housing and, more particularly, relates to underground tornado shelters.
BACKGROUND OF THE INVENTION
Tornadoes are among the most devastating of natural phenomena. A single tornado can destroy houses and neighborhoods. Because tornadoes are difficult to predict, tornadoes can strike with little notice to the people threatened by them.
Scientists know that some geographic areas are prone to have tornadoes. Accordingly, people who live in those areas should take precautions to protect their lives in the event of a tornado. Specifically, someone who lives in an area prone to tornadoes can install an underground tornado shelter that enables the person to survive a tornado that destroys the person's home.
Underground tornado shelters are known in the art. Typically, tornado shelters are constructed from concrete, steel, or fiberglass. Fiberglass tornado shelters have been popular in recent years because they offer many advantages over concrete or steel tornado shelters.
To make a conventional fiberglass tornado shelter, a manufacturer typically constructs a dome-shaped mold for the upper half of the tornado shelter and a hemispherical mold for the lower half of the tornado shelter. A worker then sprays layers of fiberglass material onto the molds. When the fiberglass hardens, the worker removes the upper half and the lower half from the molds. The upper half and the lower half of the tornado shelter each have a single wall of fiberglass forming the structure. The worker then attaches the upper half of the tornado shelter to the lower half of the tornado shelter using bolts. The manufacturer may then transport the tornado shelter to the customer.
To install the tornado shelter, workers excavate the earth to form a hole. They then place the tornado shelter into the hole. There are many different ways to anchor the tornado shelter in the hole. In one example, the workers insert pipes into cylindrical receptacles in the bottom of the lower half of the shelter. The pipes extend beyond the bottom of the lower half of the shelter. Once the workers have placed the shelter in the ground, they put concrete slabs over the portions of pipe extending beyond the bottom of the lower half of the shelter. These concrete slabs anchor the tornado shelter inside the ground. Other systems known in the art are also useful for anchoring the tornado shelter in the ground. The workers then bury the tornado shelter with dirt, leaving only an entrance to the tornado shelter exposed to the surface.
Although fiberglass tornado shelters are currently the industry standard, construction of tornado shelters from fiberglass has several disadvantages. For example, the molding process is slow, so production capacity is limited. Furthermore, molding a tornado shelter from fiberglass in the described manner requires a skilled operator. Because skilled operators command relatively high wages, the molding process using fiberglass is relatively expensive. Also, the thickness of the fiberglass walls greatly affects the cost and structural integrity of the shelter. Because the thickness of the fiberglass walls is difficult to control, the quality of the finished product varies according to the skillfulness of the operator. Furthermore, fiberglass is brittle, so tornado shelters constructed of fiberglass are sometimes damaged during transport to the installation location.
Due to the nature of the molding process using fiberglass, only the surface of the fiberglass wall that was in contact with the mold is smooth. The side of the wall opposite the side contacting the mold is rough, resulting in an unappealing finish.
Additionally, the nature of the molding process using fiberglass does not easily allow the creation of bolt holes on the upper half of the shelter that match corresponding bolt holes on the lower half. Thus, attaching the upper half of a tornado shelter made from fiberglass to the lower half is difficult. Furthermore, the completed tornado shelter is often not leak-proof because bolts are an imperfect method for joining the upper and lower halves together. Although a gasket material may be used to improve the seal between the upper half and the lower half, the gasket material may fail and is difficult to repair. As a result of the disadvantages inherent in a fiberglass tornado shelter built as described, there is a need in the art for an improved tornado shelter and an improved method for manufacturing a tornado shelter.
SUMMARY OF THE INVENTION
The present invention meets the needs described above in an improved tornado shelter constructed through a rotational molding process from any moldable material, such as high-density polypropylene or linear medium-density polyethylene. These materials are more durable and impact resistant than fiberglass. Accordingly, a tornado shelter constructed of such material is less likely to be damaged during transport to the installation location than a tornado shelter constructed of fiberglass.
By using rotational molding to construct the tornado shelter, numerous other advantages are realized. For example, the quality of the finished product is less dependent on the skill of the worker manufacturing the components of the shelter. Accordingly, the manufacturer of the shelter saves expenses because the manufacturer can more easily train workers to produce high quality tornado shelters. Furthermore, the manufacturer's production capacity is increased because producing a tornado shelter through rotational molding is quicker than producing a tornado shelter using fiberglass.
According to one aspect of the invention, the rotational molding process is used to create an improved tornado shelter having a double-hull design. In other words, both the upper half and the lower half of the tornado shelter have an inner wall of linear medium-density polyethylene, an outer wall of polyethylene, and an optional layer of insulation between the inner and outer walls. Although linear medium-density polyethylene is used in a preferred embodiment, those skilled in the art will appreciate that other moldable materials such as polypropylene could also be used. This double-hull design offers numerous advantages over a conventional fiberglass tornado shelter having only a single layer of fiberglass. For example, the visible interior and exterior surfaces of the tornado shelter are smooth. This creates a more appealing and finished appearance than can be achieved with conventional single-hull fiberglass tornado shelters. Additionally, the layer of insulation provides structural support for the improved tornado shelter. Also, the insulation layer helps to prevent condensation from forming on the interior walls of the improved tornado shelter, which is a frequent problem with conventional single-hull fiberglass tornado shelters.
Through the rotational molding process, more exact design specifications can be met, allowing the manufacturer to realize additional advantages. For instance, the two halves of the improved tornado shelter can be manufactured with flanges around the periphery of their external surfaces. The flange on the upper half of the shelter is constructed to mate with the flange on the lower half of the shelter. This allows the person building the improved shelter to more easily align the halves and fasten them together. Also, due to the nature of the rotational molding process, the manufacturer can accurately control the amount of polyethylene or other material used to construct the shelter. Thus, the present invention enables the manufacturer of the improved tornado shelter to ensure that the thickness of the inner and outer walls of the tornado shelter match design specifications.
According to another aspect of the invention, the upper half of the tornado shelter is attached to the lower half by placing a bonding material (e.g., linear medium-density polyethylene or high-density polypropylene) embedded with wire between the flanges located on each of the halves of the shelter. An example of such a bonding ma
Applied Solar Technology, Inc.
King & Spalding
Slack Naoko
Stephan Beth A.
LandOfFree
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