Proper Sheet Metal Fold Orientation for Bullet Resistant Steel Door and Window Frames

Proper Sheet Metal Fold Orientation for Bullet Resistant Steel Door and Window Frames
The following information is provided by Close Focus Research (CFR) to aid designers on how to orient their sheet metal folds in order to prevent ballistic failure of their Bullet Resistant Steel Door and Window Frames.

If your Bullet Resistant Metal Door and Window Frames incorporate sheet metal folds, then depending on your design, it may be better to orient the sheet metal folds towards the impact (threat) side of the frames in order to prevent projectile fragments from passing through the sheet metal fold areas. Most Bullet Resistant Steel Door and Window Frames contain a small air gap between the frame and the door / window. If a bullet happens to strike within this gap area, then some of the bullet fragments can pass completely through the frame if the sheet metal folds are facing towards the rear side of the frame.

For example, the table below contains photographs of a Bullet Resistant Steel Door and Window Frame showing both a front facing sheet metal fold and a rear facing sheet metal fold. In photos 1 and 2, you can see that the sheet metal folds are facing the rear side of the frame. If you look closely at photo 2, you can see some bullet fragments from the projectile exited the frame within the sheet metal fold area. If the ballistic standard calls out for the use of a witness plate placed behind the test sample, then this frame could fail because bullet fragments may penetrate the witness plate.

In photos 3 and 4, you can see that the sheet metal folds are oriented towards the impact (threat) side of the frame. In this case the bullet fragments did not completely penetrate the frame and therefore would pass the required ballistic test.

Bullet Resistant Steel Door and Window Frame Sheet Metal Fold Orientation
Photo 1: Impact Side
Shot #2 within Frame / Door / Window Gap
Photo 2: Rear Side
Shot #2 within Frame / Door / Window Gap
Photo 3: Impact Side
Shots #3 and #5 within Frame / Door / Window Gap
Photo 4: Rear Side
Shots #3 and #5 within Frame / Door / Window Gap

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