Fire doors are generally made for the purpose of stopping or delaying the transfer of thermal energy (i.e., heat), from one side of the door to the other side. Current fire-resistant doors generally contain a fire-resistant core usually encased in a door-shaped shell, wherein the shell is made from various materials generally known to those of ordinary skill in the art. The core is customarily bonded or glued to both inside surfaces of the shell.
Fire doors, as used in residential, commercial, and industrial applications, typically are employed in conjunction with fire walls to provide fire protection between different zones of a structure, and particularly to isolate high fire risk areas of a building from the remainder of the structure, such as the garage of a dwelling from its living quarters. Fire doors usually are not capable of indefinitely withstanding the high temperature conditions of a fire but, rather, are designed to maintain the integrity of the firewall for a limited time to permit the occupants of a building to escape and to delay the spread of fire until fire control equipment can be brought to the scene.
Various tests have been designed for fire doors and are based on factors, such as the time that a given door would withstand a certain temperature while maintaining its integrity, and hose stream tests which involve the door's ability to withstand the forces of a high pressure water stream. The American Society for Testing Materials (ASTM) has devised tests to establish fire door standards and these standards are incorporated into building codes and architectural specifications. One such standard, ASTM Method E 152, requires a door to maintain its integrity for period ranging up to 1.5 hours while withstanding progressively higher temperatures and erosive effects of a high pressure stream of water from a fire hose at the conclusion of the heat (fire) exposure.
Considerations in fire door design, in addition to retarding the advance of fire, include the cost of raw materials and the cost of fabrication. Furthermore, the weight of the door is important, both from the standpoint of ease of handling and cost of transportation. The strength of the door is also a significant factor, since fire doors must pass the above-described water stream test as well as have the requisite strength to withstand normal use and abuse.
Fire-resistant doors have been made using a variety of constructions and utilizing a number of different materials, including wood, metal, and mineral materials. Early forms of fire doors simply comprised wooden cores faced with metal sheeting. Although wood of ample thickness is an effective fire and heat retardant, doors of such construction tend to be heavy and are expensive to fabricate and transport.
Mineral fibers have also been employed in the manufacture of fire doors. The core of a commercial metal fire door principally comprises a composition including mineral fibers and a binder. Such doors suffer, however, from a lack of strength, and handling the friable cores results in the production of irritating dust particles during the manufacturing process.
Current fire-resistant cores are generally constructed using such materials as perlite (which functions as an inorganic filler), gypsum (which functions as the fire resistant material), cement (which functions as a further fire resistant material and counteracts shrinkage of the core), a solution of polyvinyl alcohol and water (which also acts as a binder and increases the viscosity of the mixture of ingredients while also hydrating the gypsum) and fiberglass (which functions as a reinforcing material). See for example U.S. Pat. No. 4,159,302, the disclosure of which is incorporated herein by reference.
It has also been proposed to make fire doors wherein the core comprises particles of expanded perlite, which are bound together by the use of various hydraulic binders including gypsum, cement, and inorganic adhesive material. In order to provide sufficient strength, particularly to withstand handling of the core during manufacture, the core typically is compressed to compact the mixture to a relatively high density, resulting in a heavy door.
Other fire doors have included conventional gypsum wallboard panels as a core material. However, in order to produce sufficient fire resistance, the thickness required of the wallboard is such as to result in an excessively heavy door. Furthermore, internal structural members such as rails or mullions have been found necessary to support and strengthen wallboard panels. The need for such reinforcing elements increases the cost of materials and assembly of such doors. In addition to the above-mentioned considerations, fire doors must, in order to be commercially acceptable, also have other properties that are related to the manufacture, installation and service of the fire door.
Fire door cores that contain a significant proportion of gypsum may lose their fire resistant capabilities in the course of a fire. As is well known, gypsum calcines when contacted with sustained heat. During a fire, calcination of the gypsum in a door core may cause the core to lose strength and integrity, especially when thereafter exposed to water, such as a high pressure stream of water from a hose. Thus, the fire resistance and structural integrity of such a door core is degraded. Furthermore, current fire-resistant door cores containing gypsum exhibit high water absorption rates thereby increasing both their size and density.
U.S. Pat. No. 6,340,389 describes a fire door cores made from expanded perlite, a fireproof binder such as an alkali metal silicate, fire clay or vermiculite, and optionally one or more viscosity-enhancing components, fiberglass, or both. The fire door core is made using a semi-continuous batch press method wherein water, the expanded perlite, the fireproof binder, fire clay or vermiculite are mixed; and the wet mixture is compressed in a mold, and the compressed mixture dried.
There exists a commercial need for building materials suitable for use as a door core that not only is fire-resistant, but also closer to being fire-proof. In order to meet this commercial need, the door core must maintain its strength and integrity after being exposed to heat. Additionally, in order to be commercially viable the door core must be easily manufactured using techniques well-known in the art, and have improved hose stream resistance after heat exposure. The present invention fulfills these commercial needs by using a fast setting cementitious composition as the major structural component.