Longitudinal curvature can occur even in a solid sheet. Additional curvature may appear during the perforating process. There are no general values which can be applied to the curvature apex. This effect will be amplified by the material, open sieve areas, differing margins at the long edges, dimensions of the perforated sheet (thickness, width, length). The curvature apex may in some cases be corrected by trimming the long edge of the perforation plate although the deviation in the perforation pattern will remain. Tolerances as per DIN.
Elongation of the perforated plate
The material in the perforation zone will be stretched during the punching process; the width and length of the panel will change. The extent of such elongation will depend on the material, its thickness, the perforation and the pitch; it cannot be predicted precisely in advance. The perforated plate and the perforation zone will be stretched in addition by subsequent mechanical straightening. If there are dimensional tolerances which may not be exceeded, then they must be specified.
Residual waviness, which cannot be entirely avoided even after several mechanical leveling operations, often occurs where perforated plate exhibits a ratio of hole diameter to strand size to sheet thickness which is greater than 1; further influences are exerted by the nature of the material, in perforated panels with a large open area, and where panels have widely differing unperforated margins, strips, or zones.
After perforation the plates are leveled or flattened mechanically as per DIN standards. The plates are, however, not entirely flat and free of stresses following this procedure. The perforation process will induce strain in the plate, the extent depending on the hole design. Wide, non-perforated margins or non-perforated zones in certain materials will cause especially great strains. As a consequence it is hardly possible to deliver perforated plates which are absolutely perfect. Please inform us if you have particular expectations in regard to the flatness of perforated plates.
There is always the danger that rams will break during the perforation process. The risk rises dramatically if the sheeting is thicker than the hole diameter and/or strand size. In these cases the defects which thus arise will not be repunched or drilled. "Risky perforations” shall be indicated on our offers and acknowledgements.We mention the risks in our inquires and orders.