Appendix B 
EFFECT OF GASKETS ON THE SHORT-TERM STRENGTH 
OF FLAT DISC ACRYLIC WINDOWS 
DISCUSSION 
Flat disc acrylic plastic windows require for satisfactory perform- 
ance gaskets either for sealing, or cushioning in the flange. Although 
sealing may be accomplished by other means besides a gasket, like for 
example a radially compressed o-ring!, gaskets are still generally 
required on the high and low pressure faces of the window for cushioning 
the window against contact with the metallic flange and the metallic 
retaining ring. When gaskets are used, the dimensional tolerances on 
flatness of the flange seat and retaining ring can be relaxed lowering 
the cost of the flange assembly appreciably. Also, the use of gaskets 
almost completely eliminates the danger of unforeseen point loads by 
the flange and retaining ring on the window surface that may serve as 
crack initiators. 
Before the gaskets are chosen for a given window, some consideration 
has to be given to their effect on the structural performance of the 
window. Since gaskets may vary in thickness, hardness, and viscoelasti- 
city, some knowledge of their effect on the catastrophic failure of windows 
is required so that proper gaskets can be specified for each application. 
A brief review of existing meager literature on flat disc acrylic plastic 
windows revealed the absence of any experimental or analytical work 
dealing with the subject of gaskets for such windows. In view of this, 
a few exploratory tests with different gasket materials were performed 
at NCEL on flat disc acrylic plastic windows. 
TEST PROGRAM 
The objective of the test program was to explore the effect of 
(1) gasket thickness, (2) gasket material, and (3) retaining ring on 
the short-term strength of flat disc acrylic plastic windows. The 
scope was limited to only (1) one window thickness, (2) one window 
diameter, (3) acrylic plastic, (4) three kinds of gasket materials, and 
(5) three gasket thicknesses (Table B-1 and Figure B-1). 
Test specimens were fabricated from shrunk and unshrunk Plexiglas 
"G" and Swedlow 350 flat disc acrylic plastic windows of 4.450-inch 
diameter and nominal l-inch thickness (Table B-2). Because of manufac-— 
turer's casting tolerance on thickness, the actual measured thickness 
varied from 0.944 to 1.092 inches. Thus, the actual thickness of test 
specimens was sometimes less than thickness of the windows supplied to 
EDU. Still for the purposes of this exploratory investigation on gaskets, 
the findings of this exploratory study are applicable directly to the 
EDU windows. 
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