Expanded metal can be a difficult product to fully understand, thanks, in part, to a nomenclature that does not always describe the opening and/or gauge, and to a large variance in the number of specifications and terminologies used. The purpose of this post is to try and clear up some of the confusion and remove some of the mysteries surrounding expanded metal.
How is expanded metal manufactured?
In the beginning of the manufacturing process, a sheet or coil stock is fed into a press, where tooling comes down on the material, slitting and expanding it. When the tooling raises, it moves to either side by one half of the pattern, and the process repeats. After the sheet or coil has been expanded, the material is often fed through leveling rollers to flatten it. At this point, the material is raised (or standard) expanded metal. The material can then be fed through flattening rollers, flattening the raised ridges of the expanded metal. This expanded metal is referred to as flattened expanded metal and is normally denoted by an F in its orientation. Heavy expanded metal (used for catwalks and walkways) is referred to as grating, and very light expanded metal (material used underneath tile work) is called metal lath.
Terminology and specification (see Expanded Metal Specifications below):
- SWO – The short way clear opening of the diamond
- LWO – The long way clear opening of the diamond
- SWD – The short way dimension, centre to centre of bond, short way
- LWD – The long way dimension, centre to centre of bond, long way
- Strand thickness – The thickness of the original material (for raised material) and the thickness of the overall material (for flattened material)
- Strand width – The width of the strand
- Orientation – 48” SWD x 96” LWD – This is the most common form, meaning that the SWD is parallel to the 48” width of the material, and the LWD is parallel to the 96” length of the material. It is safest to specifically note the SWD and LWD orientation, as not all expanded metal is oriented this way
- Nomenclature - a fraction (usually from 1/4" to 2”) followed by a number (ranging from 20 to 9) followed by an F (only if flattened, no letter implies raised or standard)
- For example: 1/4 – 18F
- The fraction very roughly describes the SWD of the material and the number its thickness. The number is also not necessarily the gauge of the material, though in some cases it can be. The higher the number, the thinner the material (same as gauges). If there is no letter in the spec – in this case, 1/4 – 18 – it is implied that the material is raised (or standard). It is always best to refer to manufacturers’ charts when specifying expanded metal.
- For example: 1/4 – 18F
Expanded metal can be a very useful material, but it does have a few drawbacks. Firstly, it can have very sharp edges; there are also limited customization and sizing options for orders. In addition, the raised expanded metal can present fabrication challenges, due to its ridges. Finally, it is a fairly imprecise material due to the manufacturing process; manufacturers state dimensional tolerances of up to +/-10%.
Despite this, expanded metal is a very useful material that sees notable use in design and architectural industries. To learn more, or to begin the process or ordering, feel free to contact us anytime.