Two terms are used to describe the distance between the holes:

Pitch of holes t: The pitch is defined as the distance from centre of hole to centre of hole in two adjacent rows.

Width of bridge c: This signifies the smallest unperforated space between 2 holes in adjacent rows.

Note: t = w + c

In the case of the long hole, a distinction is made between bridge and side bridge.

Guideline: Approximately the same proportion of the bridge c to the thickness of the material s is applicable as for the hole diameter w (relation bridge c to thickness s approx. 1:1). Depending on the material, the hole diameter w and the pitch t, relations of less than 1 are also possible.

Minimal burr formation on the outlet side of the punch is unavoidable. The degree of burr depends on the material, the tolerances of the punching tools, the wear of the tool and various other factors.

Our tools, manufactured by state-of-the-art machinery, guarantee punching with the smallest possible burr. Nevertheless, an absolutely smooth surface can be obtained only by suitable treatment (such as brushing, grinding).

The direction of feed is very important with screening plates. It indicates the direction in which the goods are carried across the plate. The best screening result is achieved if the holes are staggered across the feeding direction.

The direction of feed is defined clearly in the DIN standards 24041 and 4185. It is always parallel to dimension a1.

Le sens de passage est particulièrement important pour les tôles de criblage. Le sens de passage (ou sens de transport) indique la direction dans laquelle le matériau à cribler est transporté. Le meilleur résultat est obtenu lorsque les trous sont disposés en quinconce perpendiculairement au sens de transport.

Le sens de transport est défini clairement dans les normes DIN 24041 et 4185. Il est toujours parallèle à la dimension a1.

The blank margin is the distance from the plate’s edge to the first line of punched holes. The blank margin is dependent on the spacing of the tool and the dimensions of the plate.

If no indications are given concerning the blank margins, the term "smallest possible blank margin" is often used. In this case, the smallest possible blank margins are chosen under consideration of the tools used.

Plates without blank margins are usually cut out of larger plates or punched in the all-across press by lengthwise cutting from a coil.

Unperforated stripes or areas may be manufactured by using the respective tool variation, blank advancing, by automatic tool control, or by double action. However, in this case, particular attention must be given to the tensions in the plate (see levelness).

Levelness:
Generally, perforated plates are levelled once mechanically in order to keep their levelness within the DIN standards. Particularly in the case of

• dissimilar side margins
• unperforated areas or stripes
• large open surface
• certain materials

residual tensions in the plate are sometimes unavoidable. In such cases, it is essential to clarify beforehand the levelness required and the resulting additional treatment.

Sabre Shape:
Perforated plates with dissimilar side margins e1, e2 may become sabre shaped. The extent of the sabre shape is affected by the material, the material thickness, the length and width of the plate and the relative open surface A0.

While the sabre shape of the plate can be eliminated by cutting, the sabre shape of the perforated area cannot be eliminated. In this case too, it is advisable to clarify the admissible tolerances.