1. Cold Curving
a. PALSUN sheets can be cold bent or curved, within their minimal permitted bending radius, without damaging their mechanical performance. Moreover, based on our experience and observations, the internal stresses induced by curving give them extra strength and rigidity in both directions, as in pre-stressed concrete elements.
b. Rigidity and support spans increase progressively as the curve radius is reduced (down to the minimal permitted radius). A shallow curve should be considered virtually the same as a flat panel, while a deep curve may add significantly to the bridging ability.

2. Brake Forming
A. General Notes
1) PALSUN sheets can be cold-bent in a straight line (line bending). Standard metalworking tools, like a brake press, may be used for bending. The bending process results in a permanent plastic deformation. the degree and quality of this change depend on the thickness of the PALSUN sheet, the final bending angle required, and the actual tools used.
2) When brake forming of PALSUN is applied, the internal elastic stresses induced along the bent line reduce the mechanical properties, UV resistance, and chemical resistance of the sheet along the bending line. We recommend using the process for less demanding applications, and protecting the cold bent areas of the sheet from contact with aggressive chemicals or excessive forces.
3) Annealing (page 34) can reduce the residual stress level induced by the cold bending process, improving the sheet’s mechanical properties.
4) The maximum angles that can be obtained using this process depend on PALSUN sheet thickness, and the extent of the internal elastic strain. We recommend a 24-48 hours delay for sheet’s stress relaxation after bending.
In order to achieve the desired angle, the sheet has to be bent 20-40 degrees in excess of that angle, depending on the angle and sheet thickness. During stress relaxation period immediately after bending, the bent sheet will expand and regain the required shape.
5) Certain types of sheets are not suited for either cold or thermal forming, like PALGARD (mar protected sheet).
This type is supplied with a tough, scratchproof finish, which can not be bent and must be installed as is.

B. Practical Recommendations & Work Instructions
1) Preparations of the PALSUN Sheets and Tooling for Bending:
a. Cut the sheet to its required pre-bent size, after careful design.
We recommend leaving the protective film on both sides during the cutting, edge preparation and cold bending operations.
b. Sand and polish the sheet’s edges to a very smooth finish. Rough edges or the tiniest fissure may initiate cracks and fractures at the vicinity of the bending lines, due to internal stresses induced by the bending process.
c. We recommend doing preliminary bending tests on small samples of the same (or varied) thickness of the intended sheet, and try a few different values of excess bending. After arriving at a satisfactory result you can start production.
d. It is advised to use special tooling, like blades and anvils, designed for plastic sheet bending. Standard metalworking blades and anvils are not necessarily suitable for bending plastic sheets.
For plastics, we recommend using a special bending blade with a straight, rounded business edge. The edge radius should be about 4-6 mm (0.16 to 0.24 in.). The thicker the sheet, the larger edge radius required.
The anvil channel outer “banks” (corners) should be rounded. Both blade and anvil are to be smooth and polished, with no projections, irregularities or rough edges.
The anvil channel for plastics bending is different than the metalworking one. It has wider, flat bottom and much steeper “banks”.

2) Cold Bending Fabrication:
a. Bending a sheet with an UV protected side (the printed protective film side) on the exterior of the bend gets best results. Therefore, unless otherwise requested, lay the sheet to be bent with the printed side face down.
b. For optimal results perform the brake forming quickly, with additional 20-40 degrees, as explained above, then leave for stress relaxation for 1-2 days.
3) Installation:
a. Cold bent polycarbonate is more sensitive to mechanical or chemical abuse in the vicinity of the bend.
Therefore we recommend a design that offers better protection for bent areas from any detrimental influence.
b. Avoid putting additional strain on bent parts, like forcing a bent angle in or out to fit into an existing framework position.