The thin film component of the pillow dome is the covering for the dome which seperates the interior from the exterior environment. The gas filled pillows also provide additional structural integrity. Jay recommends using DuPont's Tefzel thin film.
Two layers of Tefzel are heat sealed together and a valve is inserted to allow gas to be injected between the Tefzel layers. This produces an "air" pillow. ("Air" is not used because in cold weather the moisture will condence and you will end up with water in the pillows.) A third film between the two outer films may be added for insulation purposes. (For example, Southwall Technologies' "Heat Mirror" might be added as the third film between the two Tefzel films. This would decrease infra-red heat lose.)
Here is a list of performance considerations which I will be using in evaluating the applicability of the film for pillow domes. Once the performance list is created, a rating system can be developed to determine which film is the "best" film to use. This is not an absolute rating system since some of the performance requirements need to be strictly adheard to while others need not.
Research needs to be done to determine what is the best film currently available for these Pillow Domes. Some films that I am currently considering are listed below. If you know of other films which should be investigated, please send me an e-mail note.
There are some web pages containning information on films which need to be further researched for applicability to the pillow dome project.
We will be conducting a puncture test for each of the thin films to be considered for use in the Pillow dome. The "standard" for comparison will be DuPont's Tefzel film, 5 mil thick (0.005 inches). This is the material which Jay Baldwin has used in previous Pillow domes.
Two types of tests will be performed. The first is a static load test in which a round ball fixed at the end of a stiff rod is placed in contact with the film. A force is increamently applied in descrete steps until the ball breaks through the materail. Data for balls of various diameters will be recorded and tabulated below. The second test is a dynamic puncture test. The ball is raised a fixed distance above the material and allowed to fall upon the film. Varying the weight attached to the ball will allow us to vary the force of impact.
Entries in the table give the applied force (lbs.) applied to the ball which resulted in the ball breaking through the film.
| Material | Ball #1 | Ball #2 | Ball #3 |
|---|---|---|---|
| Tefzel 500 | 0 | 0 | 0 |
| Tefzel T2 250 | 0 | 0 | 0 |
| Tefzel T2 150 | 0 | 0 | 0 |
The entries in the table below give the speed (ft/sec) for
which the ball punctured through the material.
| Material | Ball #1 | Ball #2 | Ball #3 |
|---|---|---|---|
| Tefzel 500 | 0 | 0 | 0 |
| Tefzel T2 250 | 0 | 0 | 0 |
| Tefzel T2 150 | 0 | 0 | 0 |
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