Patent Application
20160298387
Screen doors are available in a variety of materials, including metal, typically aluminum, and which tends to corrode, and wood, often from rain forest trees and which requires painting from time to time. Newer screen doors are made of foamed polymer and do not need to be painted but have their own drawbacks.
Screen doors made of foamed polymer are otherwise similar in appearance to conventional screen doors. They have two stiles (vertical members) and at least two and often three rails (horizontal members) formed into a simple frame. To join the stiles and rails at corners, either wooden dowels or screws with wooden pegs, or a combination, are used to form the joint. Holes are drilled in the ends of the rails and in the sides of the stiles near their ends. Dowels are inserted in the holes. The ends of a stile and a rail are pushed together with the dowels running from one to the other to form a joint. Alternatively, they are fastened together casing deep-set screws and then the holes above the screws are filled with plastic pegs to form the joint.
In time, the wood of the dowels can start to rot. Screen doors are invariably exposed to the elements so moisture will inevitably enter the joint. Eventually the joints will fail.
The screens of polymer screen doors are installed by forcing them into grooves routed into one side of the stiles and rails of the screen door frame. The screen is held in place in its groove by a rubber spline. The rubber spline, being resilient, is compressed when pressed into the groove and thus holds the screen in place by friction. However, the spline and the screen can be pulled out if sufficient force is applied in a direction normal to the screen. Typically, the repeated pressure of someone's hand on the screen to open the screen door will gradually cause the screen to deform, or bag, until eventually it loosens.
Thus, there is a need for a better foamed polymer screen door, one in which the door's joints and screen securement are as durable as the foamed polymer of the frame.
The present invention is a screen door in which the joints are not only more durable than those made with dowels but are much stronger, and the manner in which the screen is held to the frame is much more secure.
The joint may made by first removing the thin “skin” on the surface of foamed polymer near the ends of a stile to expose its foamed interior. Then that exposed portion is heatwelded to the cut end of a rail. This joint is more than ten times stronger than a joint made with dowels and will not fail before the door fails.
To make a better securement for the screen, the cylindrical spline is replaced with a flat spline and the rectangular groove, with a spline groove, shaped to make use of the flat spline shape. The flat spline groove is not formed by routing the polymer, but is extruded in the process of forming the stiles and rails. The shape of a spline groove is wider in the interior than at its entrance and resists the pull from normal forces on the screen much more effectively than a round spline in a rectangular groove.
These and other features and advantages will be apparent to those skilled in the art of screen doors from a careful reading of the Detailed Description of Embodiments accompanied by the drawings.
In the drawings,
Referring now to the figures,
Left and right stiles 12, 14, are connected to upper, lower, and middle rails 18, 20, 22, to form a rectangular frame 30. Frame 30 with middle rail 22 has an upper opening 32 and a lower opening 34. Without middle rail 22, there would be just one opening.
The terms left and right, upper and lower refer to the screen door when installed and with its major dimension oriented vertically with respect to the floor. In that orientation and with a handle 38 on the right, left stile 12 is on the left-hand side of screen door 10 and right stile is on the right-hand side of screen door 10. Upper rail 18 is at the top of screen door 10 and lower rail 20 is at the bottom of screen door 10. Middle rail 22 is somewhere between upper and lower rails 18, 20.
Different structural components, such as pickets, may be used for the interior of frame 30 in addition to middle rail 22 or in lieu of it. These different components may serve utilitarian purposes or decorative or both without departing from the present invention.
Screen door 10 will also be equipped with hinges (not shown), and perhaps with return springs or air cylinders to facilitate controlled closing of screen door 10.
Screen door 10 has a spline groove 44 formed in left and right stiles 12, 14 and in upper and lower rails 18, 20. Spline groove 44 runs generally parallel to the major dimensions of both left and right stiles 12, 14 and upper and lower rails 18, 20, and there may be no spline grooves 44 or two spline grooves 44 in middle rail 22, depending on whether a single screen is desired over both openings 32, 34 or over each opening 32, 34. Spline groove 44 is an important feature of the present invention, and will be described more fully below.
A screen mesh 50 is used to cover openings 32, 34. Screen mesh 50 may be any conventional screen mesh, which is typically a woven grid of wires with a mesh spacing dimensioned to be small enough to prevent flies and other small flying insects from passing through screen mesh 50 but to allow air and light to pass and to have only a limited effect on visibility though openings 32,34. Wires for screen mesh 50 are commonly made of polyester, fiberglass, aluminum, brass but other materials may be used.
Since the ends of the extruded stiles 12, 14 are cut to the appropriate length, their interiors are already exposed at those ends. Accordingly, the joint will place both rail interiors at their cut ends and stile interiors at their notched sides near their ends against each other, such as when notch 42 of stile 12 is placed against the end of rail 18. As taught by
Attaching stiles and rails by heat welding is well-suited for a manufacturing process and results in a very strong bond. Testing of a heat-welded joint according to the present invention shows it to be over three times stronger than the joint made with dowels, and allows consideration of using less material in the stiles and rails while still providing sufficient strength. Thus, not only is the issue of wood rot eliminated and the new joint highly resistant to water damage but, the joint has surprising strength in comparison to the prior art joints.
It is also possible to join rails 12 and stiles 14 using a 45 degree cut as shown in
As best seen in
As best seen in
Stile 84 and rail 88 are made with spline grooves 96, 100, respectively, for receipt of screen 104 and splines 108, 112, as described above.
The combination of the heat-welded joint of rails 12, 14 and stiles 18, 20, 22, and use of a flat spline 52 in a flat spline groove 44 results in a screen door 10 that is surprisingly strong. In a test of the strength of the flat spline 52 in groove 44, approximately 1000 pounds was applied normal to the surface of the screen without pulling it free. Tests of the present stile-rail joints show it is four times stronger than a dowel joint.
The additional strength of screen door 10 can result in a material savings by making rails 12, 14, and stiles 18, 20, 22, thinner. The extrusion of rails 12, 14, stiles 18, 20, 22, with flat spline grooves 44 formed in them also avoids the milling step previously used to form the prior art groove. Also the labor and materials of joining rails and stiles with dowels, screws, plugs and glue is completely avoided.
Those skilled in the art of screen door manufacturing will appreciate that many modifications and substitutions may be made to the foregoing preferred embodiments without departing from the spirit and scope of the appended claims.
