SS perforated sheet, corrugated sheet and shim sheet: how to specify each

A perforated sheet is described by four numbers: thickness, hole diameter, pitch (centre-to-centre distance between holes) and pattern. Round holes on a 60° staggered pattern are the most common, because they pack the most holes into a given area while leaving even bridges of metal between them. A straight (90°) pattern lines holes up in rows and columns.

Open area, the percentage of the sheet that is hole, controls flow, drainage, light and airflow. For round holes it is calculated as follows. With 60° staggered holes, open area % = 90.69 × (hole ÷ pitch)². With straight-line holes, it is 78.54 × (hole ÷ pitch)². A 3 mm hole on a 5 mm staggered pitch gives about 32.6% open area. More open area means more flow, but less strength and stiffness.

Punching sets a practical limit on hole size. Tool makers generally want the hole at least as large as the sheet thickness, and stainless, being tougher than mild steel, often needs more margin. Also say whether you need plain unperforated margins around the edges for fixing or welding. Punching leaves a slight burr on the exit side of each hole, so for sieves, trays and conveyor panels state which face must be smooth, or ask for deburring.

Corrugating rolls a wave or trapezoidal profile into thin sheet, which adds a great deal of stiffness without adding thickness. Stainless corrugated sheet is used for roofing, wall cladding and partitions in places where galvanised sheet does not last: chemical and fertiliser plants, effluent areas, coastal buildings and pickling or plating shops. For coastal and chemical exposure, 316 holds its appearance much better than 304.

Specify the profile (pitch and depth of the corrugation), the effective cover width after overlap, thickness and sheet length. Fix it with stainless screws and washers. Galvanised or carbon steel fasteners rust quickly and stain the sheet around every fixing. Our electroplating and surface finishing page covers one of the harshest environments for building sheet.

Shim sheet, also called shim stock, is thin stainless sheet rolled to an accurate thickness. Maintenance fitters cut it to pack under motor and pump feet during alignment, to set clearances in dies, fixtures and bearing housings, and to take up wear. Stainless is preferred over brass or carbon steel shim where moisture or chemicals are present, because it does not corrode and squeeze out of the joint.

Shim is usually supplied in short flat sheets so it stays flat in the toolbox; rolls are handy for cutting long strips but need flattening. Thickness accuracy is the whole point, so check it with a micrometer on receipt. Use as few shims as you can in a stack. Several thin shims compress and settle more than one shim of the same total thickness, which lets an aligned machine drift. Thicker packing is better made from stainless steel sheet or plate.

• Perforated: grade, thickness, sheet size, hole shape and diameter, pitch, pattern (60° staggered or straight), margins, and finish.
• Corrugated: grade, thickness, profile, cover width, length, and number of sheets.
• Shim: grade, exact thickness and tolerance, sheet or roll size, and quantity per thickness.
• For all three, mention the standard or test certificate your client requires.

• Asking for a percentage open area without a hole size, which can be met by many different patterns with very different strength.
• Specifying holes smaller than the sheet thickness, which most punching tools cannot produce cleanly in stainless.
• Fixing stainless roofing with galvanised screws.
• Building up a 1 mm alignment pack from ten thin shims instead of one or two.
• Choosing 304 perforated screens for brine, salted food or chlorinated washwater, where 316 is the safer grade.