Special Features of the Turning Process

Two turning processes are being distinguished: Horizontal turning and vertical turning. Horizontal turning means that the chuck jaw turns out of the machine in horizontal direction. In this type, an appropriate hood design and the installation of metal sheets in the direct trajectories of the chips may avoid excessive bombarding of the safety pane with chips. The results are a long service life and resistance to facture of the safety pane. With vertical turning machines, this cannot be accomplished. This machine type will always eject chips directly against the pane. For this reason, these machines are more critical in respect to safety, since the operator will always watch the chuck jaw unit moving towards him.

A frequently asked question is:

"Why is the chuck jaw a problem when the parts are much heavier in many cases?"

In the case of fracture of the t-fixture, which holds the chuck jaw in its place, the jaw will be ejected from the chuck on this trajectory and moves with all its energy on a lateral course that leaves the orbit tangentially. The clamped work piece will also move in horizontal direction, but in a stable position on its axis of rotation. If it breaks in itself, the part will move inside the machine on an undefined course. This may be called "bouncing effect". A direct effect of the total mass of the turned part on the window is not to be expected. For this reason, the European standard was adapted to the danger caused by the chuck jaw. (link to standards).

Aging

Effects of chemicals and low UV resistance have shown that polycarbonate is subject to aging, especially when being used in turning machines. The material will become brittle. Normally, a polycarbonate pane is flexible and will retain even part with high mass. When the molecular chains have become brittle, they will break. This is a disadvantage in the use with turning machines due to the high masses.
SEGE recommends a replacement period of 8 years.
Although aging tests have shown that the retaining capacity of a SEGE safety window may remain unchanged for a period of 13 years, but no predictions can be made on the changes of machining processes to be expected in the future. A SEGE safety pane may be expected to remain safe even after ten years, i.e. that specific aging effects may not occur. Resistance to aging is accomplished by an overall protection of the polycarbonate pane against the chemical medium. An inside protection by glass and an outside protection by coating or by an additional pane as well as the stainless steel frame which provides mechanical resistance of the complete assembly.