Specifying patterned stainless steel finishes and their applications

Introduction

On stainless steel flat products (sheets), 'patterned' finishes are usually taken as relief or three-dimensional effects formed by either texture rolling or pressing (embossing). The relief effect can be either on one side only, with a plain, flat surface on the reverse side or as deeper three-dimensional patterns formed through the sheet, by rolling through pairs of mating, matched male-female patterned rolls. Patterned finishes are produced at the manufacturing mill or at specialist processors, using patterned or textured rolls to form the surface features by cold rolling.

Specifying patterned stainless steel flat products

Table 6 of BS EN 10088-2 only covers the patterned sheets and plates with the reverse side flat as special finish M. These can be either 1M, if based on a hot rolled sheet or plate, or 2M, if based on a cold rolled sheet or plate. The 1M finish is typified by chequer (durbar) plate patterns, which are used for floor plate applications. The 2M finishes are defined in BS EN 10088-2 as having a finer texture for 'architectural applications'. The specific design of the patterns is not defined in the standard. This has to be agreed. Similarly the 'through thickness' textured patterns produced on mating rolls are available in a range of pattern styles, which have to be agreed with suppliers.

Designs include low reflective surfaces, produced using lightly roughened rolls ('matt rolled' finishes) and deeper 'random' (within the limits of roll repeat) and regular patterns such as diamonds, dimples, stripes etc. which can be abstract, or simulate other materials such as leather grain or woven fabrics. Examples of these can be found in the Architects' Guide to Stainless Steel (SCI-P-179). The patterns are usually applied to cold rolled material with 2D, 2B and 2R mill finishes and can be used in conjunction with a range of pre-coloured finishes to produce a wide range of finishes and textures.

Matt rolled surfaces are designated as finish 2F in Table 6 of BS EN 10088-2.These are produced by 'skin pass' rolling the flat cold rolled stainless steel coil on roughened rolls, rather than on the polished rolls that are used to produce the smooth 2B finish. The 2F finish is described as a uniform non-reflective matt surface.

Sheets patterned by these processes can be produced in thicknesses from 0.1 mm. A range of sheet lengths can be produced, although fabrication and handling of lengths over 4000 mm is difficult.

The BSSA Buyers Guide can be used to find member companies who can help with the specification and supply of patterned finishes. At the 'Member Products and Services' page type 'patterned' in the 'Find What' box with the 'Product Supplier' button selected. Click on the 'Search' button with 'Sheet-patterned-Flat Products' highlighted to view a contacts list.

Matching the finish on large cladding areas

Patterned rolled sheets usually have some visual directionality that can be picked out on large areas of cladding composed of many sheets. If these sheets are not all installed with the same sheet direction in relation to the rolling direction, then under certain lighting conditions, some panels may have an undesirably different appearance. To avoid this, the steel manufacturer should be asked to mark their rolling direction on the reverse side of all sheets.

Applications for patterned stainless steel sheets

The cold rolling of patterns on austenitic stainless steel sheets commercially available grades, which include 1.4301,304 and 1.4401,316, results in increased strength and sheet (panel) rigidity over that normally expected from the out-of-plane shape change. These steel types work harden significantly, adding to their strength and hence the stiffness of patterned stainless steel panels.

This increased strength can also be used to save weight offering a distinct advantage for patterned stainless steel, compared to both non-patterned stainless steel sheet finishes or other lower work-hardening patterned sheet metals.

The patterned surface can also help suppress the visual impact of out-of-plane effects ('oil canning') sometimes seen on un-patterned sheets. This makes patterned stainless steel sheets particularly useful for large internal and external clad features. In addition the discontinuous, work-hardened surface of these rolled or pressed finishes also helps mask the effects of scratches and finger-marks. This makes these finishes particularly suitable for high traffic contact areas such as lift doors, lining panels and fascias as well as other building contact areas such as wall panels, column cladding, vending kiosks etc.

The finer texture patterns can also be used to reduce sliding friction in applications such as food and drink machinery and dispensing equipment, supermarket check-out desks, photographic machinery etc. Compared to flat stainless steel sheet, patterned finishes also improve the dissipation of heat and so can be used to reduce the casing temperatures of domestic appliances that generate heat.

See http://www.euro-inox.org/fla_240_EN.html for examples of finishes.

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