Industrial Perforated Plate Screens Irregularities Caused by Perforating Process
Industrial perforated plate screens irregularities caused by perforating process includes breakaway on holes , burrs on holes, shearing burrs, wavy edge, edge bow, and missing holes.
Breakaway on holes
When the punch has penetrated deeply into the metal plate from the punch side, material will begin to tear, or break away, mainly from the reverse side of the plate.
It is not possible to predict the precise shape and dimensions of the breakaway zone, but its height t3 does not usually exceed two-thirds of the plate thickness t. The width of the breakaway wb is roughly related to the plate thickness t and does not usually exceed the nominal hole size w by an amount of 0.15 t.
IPSI-1: Breakaway on holes, burrs on holes and shearing burrs.
Burrs on holes and shearing burrs
Burrs will occur during both the perforating and the cutting (shearing) operations.
While burrs on holes occur on the reverse side of the plate only, shearing burrs may occur on either the punch side or the reverse side, depending on the manufacturing procedure adopted.
Not more than 10% of the number of holes or 10% of the length of a cut edge of a perforated metal plate shall have burr heights in excess of the values stated in table 1.
Measure the burrs on holes with a depth micrometer and the shearing burrs with a vernier calliper.
| Nominal Plate Thickness, t | Maximum Height of Burr, t4 |
|---|---|
| t≤0.6 | 0.15 |
| 0.6<t≤1.5 | 0.17 |
| 1.5<t≤3 | 0.2 |
| 3<t≤6 | 0.28 |
| 6<t≤10 | 0.5 |
| 10<t≤12.5 | 0.75 |
Wavy edge
Stresses during perforation can distort the plate and cause variations in flatness in the margin areas, producing a so-called "wavy edge", particularly if the margins on opposite sides are greater than the plate thickness f + 0.5p.
The maximum permissible deviation from the flatness of edges g shall be agreed before ordering.
IPSI-2: Measurement of wavy edge.
Edge bow (camber)
Stresses during perforation and subsequent roller levelling processes can distort the plate, producing curving of the edges (edge bow/camber), particularly if the longitudinal margins e1 and e2 are unequal and parallel to the direction of perforation.
Edge bow is defined as the greatest deviation h of the edge from a straight line extending over the length of the concave side and shall be measured with the aid of a straightedge of sufficient length having a scale graduated in millimetres.
The maximum permissible edge bow shall be agreed before ordering.
IPSI-3: Edge bow measurement of industrial perforated plate screens.
Missing holes
Punches may break during the perforation process and fail to perforate in certain positions. The number of holes missed for this reason should not exceed 5% of the total number of holes in a perforated plate.
When a multitool punch is used, it may not be possible to complete the pattern of perforations. For example, to minimize tool damage, punches of diameter less than 5 mm are usually spaced wider apart than the pitches of the holes. This arrangement, however, unavoidably results in missing holes in one or more rows at both ends of the plate (incomplete rows).
IPSI-4: Missing holes of perforated plate screen (the positions of the punches in the tool are shown in black).