Expanded metal has been around for years. It’s an extraordinarily versatile material and used for enclosure, protection, manufacturing, construction, support and decoration.
It is commonly produced in carbon steel, aluminum and stainless steel. In sheet form, the strong, rigid, non-raveling open mesh permits free passage of light, sound, heat, air and liquids while preventing unwanted objects (or persons) from entering. Expanded metal grating contains no joints or welds, as each sheet is a single piece of sturdy steel.
Expanded metal comes in two basic forms: Standard Expanded Metal
(SXM) and Flattened Expanded Metal (FXM).
SXM is a finished product as it comes from the press after having been die cut and expanded. The strands and bonds are at a sharp angle to the original plane of the solid sheet. Many times, SXM is referred to as “raised.”
FXM has been cold rolled, leaving a flat, smooth surface. It’s about 5 percent lighter than it’s SXM counterpart.
In selecting an appropriate type of grating, the designer must decide first on the general characteristics required, such as safety, open area and ease of maintenance. After the basic product is selected, the proper style of grating to satisfy the load-and-span conditions must be determined. The following will help you select the proper style for the job:
- Determine the clear span
- Determine the load condition and the amount of load
- Select the appropriate grating style
There are important things to remember when ordering your expanded metal. First, the sheet size SWD (Short Way of Diamond) is always specified first and the sheet size LWD (Long Way of Diamond) is second; e.g., SWD x LWD.
If your expanded metal grating is for a catwalk application, the LWD will typically run the short way of the sheet. This is because a shorter LWD provides greater support over the span of the walkway. For example, 30 pieces, 3.0# carbon steel expanded metal grating catwalk, 10-foot SWD by 3-foot LWD.
Should special sheet sizes be required, state exact sheet size and type of shearing wanted, or dimensional tolerance allowed. Expanded metal grating is normally furnished bond sheared on the first bond over the specified dimension (both SWD and LWD). However, in some cases it can be furnished random sheared to a closer tolerance, if required.
You should always specify the type of metal wanted when ordering. For example: carbon steel, stainless steel, aluminum, etc.
And most importantly, the following information should always be included when placing an expanded metal order:
- Specify the number of pieces wanted
- Specify the nominal dimension of the diamond SWD (e.g., 3/4-inch)
- Specify the style of the sheet (e.g., #18; or if aluminum, 0.081)
- Specify whether standard or flattened
- Specify the type of material wanted (e.g., carbon steel, stainless steel, etc.)
- Specify the sheet size wanted (e.g., 4-foot SWD by 8-foot LWD)
Some notable terminology is also worth brushing up on when talking about expanded metal.
Side Shearing is the process of cutting a piece of expanded metal parallel to the long dimension of the diamond.
Random Side Shearing is a cut made parallel to the LWD dimension of the sheet, which usually leaves open diamonds. Standard tolerances of the SWD dimension is +/- 1/16-inch when both sides are sheared.
Bond Side Shearing is a cut made along the length of the sheet on the center line of the bond over a specified width. In most cases, it is not practical to attempt to bond side shear either, regular or flattened metal, due to camber.
End Random Shearing is the process of shearing a piece of expanded metal to a specified length (LWD). This cut normally leaves open diamonds at both ends, but accomplishes close tolerance (+/- 1/16-inch) when both are sheared.
End Shearing is the process of cutting a piece of expanded metal parallel to the short way of the diamond.
End Bond Shearing involves shearing a piece of expanded metal to a specified length (LWD). A +/- 1/16-inch tolerance applies when both ends are sheared. One end is cut on the bond parallel to the SWD, the other end usually has open diamonds.
(NOTE: When end bond shearing is requested for both ends, the sheet is sheared at the center line of the bond over the specified length with the tolerance of +/- 1/2 diamond.)
Squareness is when all four sides of a sheet are sheared. The maximum tolerance will be +/- 1/16-inch per foot of width.
One last thing to know is that bond shearing provides closed diamonds that facilitate handling and safety, but frequently result in higher cost and always require greater dimensional tolerance. Random shearing is normally less costly, except where the scrap (“drop-off”) is excessive, is more difficult to handle and presents a greater safety risk due to the sharp edges left on the open diamond.
So as you can see, the world of expanded metal is far from flat. It’s multi-dimensional with many factors that must be considered when choosing the right type and cut for your project. It’s a good rule of thumb to always consult a licensed architect and/or contractor for your specific job.
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Larry Robertson is the director of marketing and advertising at Dallas-based King Architectural Metals. To learn more, visit www.kingmetals.com.
