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Perforated metal sheets - Production process


Sectional presses

Sectional presses can perforate single metal sheets which are fixed on a progress table. Metal sheets are larger than the tool. After the first longitudinal perforating pass, there is a lateral displacement which has the same length of the tool. At this point a second perforating pass is performed; the second pass is followed by another lateral displacement, and so on to reach the full perforation of the metal sheet.
 
 

Pros of this system:
- great versatility of the presses;
- perforated and/or unperforated areas (even very patchy ones, e.g. disc-shaped) can be made;
- Reasonable tooling cost;
- Very thick metal sheets can be perforated, by reducing the number of punches and by increasing the passes;
- quick preparation of the machineries;

Cons:
- long perforation times, and thus high incidency of labor costs;
- coils cannot be perforated;
- high investment cost.
Sectional presses are basically used for small series, high thickness, very irregular perforated areas.

Perforating lines

Pitch-to-pitch feed presses, or "perforating lines" consist of:

- an unwinding reel with straightener;

- an all across perforating press

- a shearing machine for lengthways cuttings or a winding reel.

The tools on these presses cover the entire width of the strip (or coil) that is dragged thanks to feeding rollers in couples.

Every down stroke of the tool is followed by a movement of the rollers, which corresponds to the perforating pitch.

When the plate reaches the desired length, the equipment stops working and the shearing machine cuts the plate.

If on the contrary an uninterrupted perforated stripe is required, the shearing machine is disconnected and the metal strip is re-winded thanks to a suitable winding reel.
   

This system has the merits of...

- having a great perforating speed (and thus reduced costs of labour);

- making possible the perforation from coils (resulting in lower raw material costs);

- making possible the supplying of metal sheets with or without edges on the short sides;

... and some drawbacks:

- high tooling cost;

- limited possibilities of irregular perforated areas;

- limited possibilities regarding the thickness of the sheet to be perforated;

- relatively high costs of the line setting.

Perforating lines are mainly used for large series, to obtain continuous perforated strips, and on thin and medium thicknesses.


Flattening of perforated metal sheets

Perforation causes tensions to the metal sheet, deforming it. It is therefore necessary a subsequent flattening performed by suitable multi-cylindrical flattening machines. For large metal sheets, wide unperforated areas, broad or irregular edges, or materials that are very hard or with “difficult” perforated areas, the tension can be so strong to compromise the flattening process. Perforated metal strips winded in coils are not flattened, therefore when the coils are unrolled the flatness is not guaranteed.
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