The present invention relates to a window sash structure and in particular to a window sash structure made of extruded plastic frame members held together by a tensioned band about the periphery of the sash.
A variety of materials have been used in window sash construction, most notably wood and metal. The use of each of these materials in a window sash presents certain problems. Wood sashes require constant maintenance in the form of painting to prevent rotting of the wood. Metal frames provide a high degree of thermal conductivity that results in excessive condensation on the inside of the sash during winter months. A metal frame sash does have the advantage of being able to be extruded with an irregular shape in a single manufacturing process. As such, a metal frame has an advantage over a wood frame which may require several manufacturing steps to form the frame into the necessary shape.
To overcome the problems associated with both wood and metal frames, extruded plastic frame members have been developed which provide the manufacturing ease associated with an extruded metal frame but without the disadvantage of condensation associated with a metal frame. However, joining the individual frame members together at the corners of the window sash has remained a difficulty with the plastic frame sash. One method of joining the frame members is the use of an adhesive. However, this is a time consuming process and it is difficult to form a strong joint with the small surface area available. In addition, disassembly of the sash for repair of broken glass is difficult or impossible with an adhesively joined frame. The use of screw fasteners is also difficult with a thin wall hollow extruded frame because there is little material available for the screw threads to bite into to form a secure connection. To provide the necessary material for a quality screw joint requires a significant increase in the amount of plastic material used throughout the entire length of the extrusion when only a small portion of that material would actually be needed for the screws at a joint. The excessive material usage significantly increases the cost of the frame.
Accordingly, it is an object of the present invention to provide an improved method of joining plastic frame members in a window sash.
It is a feature of the present invention to extrude the frame members with a recess along the outer periphery which extends inwardly into the hollow section of the frame member. The frame is held together by a tensioned band disposed in the recess, firmly engaging the frame members and extending around the periphery of the sash. The recess about the periphery is formed by a pair of spaced intermediate walls extending from the outer wall of the frame members into the hollow interior of the frame members. A base wall at the bottom of the recess connects the two intermediate walls to one another. The spaced intermediate walls of the recess act to strengthen the frame member by increasing its bending resistance and enabling the frame member to withstand the load applied to the frame members by the tensioned band used to hold the frame together.
In a preferred form of the invention, the tensioned band is made of plastic for corrosion resistance and for ease of assembly. The two ends of the band are joined to one another by a welding process in which the ends are heated to melt the two ends together. For repair of broken glass, the band is simply cut allowing the frame to come apart. A replacement band is then applied to secure the frame members around the replacement glass.
Further objects, features and advantages of the invention will become apparent from a consideration of the following description and the appended claims when taken in connection with the accompanying drawings.