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Why Weldable Webbing™?
By Jim Logan
Note: For more information about the methods of welding fabrics, please be sure to read “Welded Onto Fabrics” appearing in the July 2008 issue of Sign Builder Illustrated.
There are many ways to finish banners and vinyl sign edges. PVC-coated Weldable Webbing™ is one method.
PVC-coated Weldable Webbing is recommended, instead of hemming, when banners:
* will be hung outdoors in conditions that may involve significant wind or rain;
* are expected to last for several months outdoors;
* will be taken down and re-hung several times;
* are so large that their own weight demands extra reinforcement;
* and/or when the span between anchor points is long.
PVC-coated Weldable Webbing adds the flexible strength of webbing to various vinyl-coated fabrics as needed in different applications. It has become a standard structural component in the fabrication of curtain-side truck walls and in building tents and tensile structures. Manufacturers are able to place increased tensile strength where they need it, based on the design and load characteristics of their products. (Note: This same strength is available to vinyl sign and banner printers to be sure that their creations can be hung with confidence.)
PVC-coated Weldable Webbing is a tightly woven polyester narrow fabric with finished edges, engineered for longitudinal “tensile” strength (end-to-end pull strength). The polyester yarn inside is the same fiber that is used to weave rugged “sling webs” or flexible “round slings” used by riggers to lift heavy loads. It is strong stuff. The webbing is woven with tightly finished edges, just like the seatbelt in your car. (It is not a strip of narrow material slit off a wider roll.)
The woven inner “scrim” of PVC-coated Weldable Webbingis finished with a special vinyl coating, formulated to be compatible with the surfaces on coated or laminated vinyl fabrics commonly used in the tent, curtain-side truck, and sign industries. In the finishing process, heated PVC paste is applied to the scrim using a special process that actually impregnates vinyl completely through the woven fibers, not just on the surface, to be sure of maximum adhesion.
When positioned against another vinyl-coated fabric (or another piece of PVC-coated Weldable Webbing), the vinyl material on facing surfaces can be welded. A chemist would say that vinyl is a polymer, and thus its molecules can be easily disassembled and rejoined with other vinyl molecules—combining the two separate surfaces into one single construction. On the practical, industrial level, the essential point is that heat, radio waves, or chemical solvents can soften vinyl. If two surfaces are similarly softened and pressed together while still soft, they will join and re-harden together.
(Note: Despite all the discussion here about fabric welding, PVC-coated Weldable Webbing itself is still a woven textile product. It can also be stitched, as would any other webbing.)
There are several uses and many different methods of applying PVC-coated Weldable Webbing in the sign and banner business. The primary benefit is, of course, added strength.
There are as many examples of how to use the webbing as there are sign makers, but some of the key points to remember are:
1. When applied to the back edges of a banner (called “trim to edge”), the webbing takes up the entire corner-to-corner load so there is no worry about your banner fabric ripping or stretching. Since material stretch is the primary cause of grommet failure, grommets installed in the webbing are much more structurally secure. The “trim to edge” technique also allows designers to use the full dimensions of their printed fabric.
2. With welded-on webbing edges, there is no need to hem. Hemming (folding material over and attaching it to itself) creates a finished look that has become traditional for cloth banners. In fact, hemming has been necessary since the dawn of scissors; it has been necessary to fold material over to prevent an unfinished, cut edge from fraying. Hemming also creates a double or triple layer of material that becomes a thicker edge in which to cut holes for mounting grommets. Some hems are stitched, while others are accomplished by using an adhesive tape. But neither type of hem significantly strengthens the span from corner to corner.
For indoor and short-use banners, a simple hem may be sufficient. For outdoor banners exposed to the elements, for any banner or sign that will hang for a long time, or for banners that may be taken down and re-hung several times, the extra strength provided by PVC-coated Weldable Webbing is recommended.
3. To keep both costs and weight under control, banner and sign makers are always on the lookout to find ways to use lighter materials. PVC-coated Weldable Webbing can provide several advantages in considering structural options. The first question to consider is the weight and type of fabric to be used. In many cases, building a banner with strong webbing reinforcement can allow moving down in fabric weight or moving from solid fabric to mesh.
Using lighter fabric definitely does require a good plan for proper reinforcement. This almost always includes applying webbing around the perimeter of the sheet.
In addition, webbing is sometimes sandwiched inside overlap seams or placed behind butt seams. For large, multi-panel banners and for building wraps, designers may also add “runners” or “ribs” of webbing horizontally or vertically across large sheets to stabilize the fabric against edge curl or to resist pulling on the bias.
Even with mesh or lighter fabric, the physical weight of a large wrap covering a construction scaffold or a giant sign spanning the entire side of a building necessitates the use of proper webbing reinforcement. Those calculations are made based on the weight of the sign or banner fabric itself, plus calculations of additional loads due to environmental forces.
4. Applying PVC-Coated Weldable Webbing is faster and easier than sewing—especially for small banners. Some shops estimate that they can cut down their finishing time by 75 percent versus sewing hems. With the proper equipment, any shop can do it in-house. And there is no need for the added expense or the lost time waiting for jobs sent out to be finished elsewhere.
Jim Logan is director of marketing at Louis A. Green Corp., in Braintree, Massachusetts.More information on Weldable Webbing including product specifications and pricing plus links to a number of welding equipment manufacturers can be found at www.louisagreen.com.
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