The present invention relates to a mullion assembly and, more particularly, to a mullion assembly for a double door mounted in a double doorway.
It is usual to mount a mullion assembly in a double doorway for engaging with two latches of two doors (or known as a double door) pivotably mounted on opposite sides of a door frame. Easy removal of the mullion assembly is required when a full door opening is desired for unobstructed pass purposes. Furthermore, to prevent the doors from being opened when exposed to a fire, it is desirable for the mullion assembly to have enhanced structural strength and fire resistant functions. In a proposed design, the mullion assembly includes a top fitting mounted to the top of a door frame, a bottom fitting assembly mounted to the bottom of the door frame, a mullion head detachably engaged with the top fitting, and a mullion tube mounted between the mullion head and the bottom fitting assembly. A fusible spacer is disposed between the top fitting and the mullion head for accommodating thermal expansion of the mullion assembly in case of fire to resist warping of the mullion assembly. The top fitting includes a vertical slot into which a locking bolt extends. The locking bolt moves upwardly in the vertical slot due to thermal expansion of the mullion assembly to maintain the locked condition without buckling the mullion assembly when the fusible spacer melts due to the heat of the fire. However, a high pressure gas could be generated due to high temperature of combustion or explosion in the fire to destroy the mullion assembly. This is because the engaging force between the mullion tube and the top fitting depends only on the locking bolt and is, thus, insufficient to withstand the high pressure gas, resulting in undesired opening of the doors and flowing of smoke and fire from the outside into the inside.
Thus, a need exists for a mullion assembly with a removable post that allows easy assembly while having improved structural strength to withstand fire.