Using PVC-Coated Weldable Polyester Webbing
in the Transportation Industry

Various grades of PVC-coated webbing, and the techniques of welding them into place, are now established materials and methods for building curtainside enclosures and making tarps.

By far the largest quantity of PVC-coated webbing used worldwide is in the manufacture of curtainside trailers. Coated webbing is an important building component in many types of vinyl tarps, load covers, and temporary storage structures. It is used in curtainsides for moving ribs, suspended from a rolling bracket above and tightened to the bed of the truck with a tensioning buckle. But it is also used as an edge reinforcement to strengthen or eliminate the need for hems on many other types of fabric covers. Several generalizations should be understood to best understand the products and their applications.

1. Webbing is Webbing. Beneath the outer vinyl coating is simply a woven polyester webbing exactly similar to like-rated webbings without coatings. Because they are woven to be inside a coating, these weaves are termed "scrim". They are usually raw yarns, not dyed or treated with any special finish, because they are meant to be coated. In fact, it is best that they are clean and not contaminated with any foreign substances to obtain the strongest adherence with the vinyl coating. Nevertheless, the weave structure of these scrim webbings is designed and calculated just as if the web were to be used uncoated. That is, the yarn counts, the edge finishes, the density, the flexibility, and the general performance factors such as stretch and tensile strength are all skillfully considered and managed as they would be in any industrial weaving application.

2. Advantages of Coating. Depending on how it is formulated, vinyl (PVC) can provide a strong but flexible, waterproof coating over various types of scrim fabric. Clearly, coated tarp and curtainside fabrics have proven to be superior structural and weatherproof materials for many types of covers compared to canvas. Similarly, coated webbing also has a waterproof outer surface that both repels moisture and is easier to clean. Coated webbing, thus, offers many performance advantages over traditional materials just due to its non-wicking composition. Most importantly, the pvc coating on the webbing can also be welded to the pvc coatings on many types of industrial vinyl fabrics. Thus coated webbing can be an ideal structural component.

3. Welding Considerations. Achieving a satisfactory fabric-to-webbing weld can be a complicated matter. Different welding methods and equipment offer a variety of material handling advantages. But the method used to actually perform the weld, and the range of possible materials to be welded, creates a sometimes challenging experimentation and testing process for production workers. In some cases, welding equipment can be left alone and used just as if it were set up to weld two exactly similar edges of tarp fabric. In other cases, however, the density of the webbing can vary from that of the lighter cover materials. This can require using lighter power and/or longer dwell times on high frequency equipment. With hot air welders, heat is directed between (not through) the materials and thus it should be in the right place. But it is necessary to control the heat so that the lighter tent fabric is not damaged while attaining sufficient temperature to soften the coating on the heavier webbing. Heat can also cause vinyl coatings and the underlying polyester scrim fibers to stretch, shrink, or otherwise distort. Thus it is always desirable to consult with your equipment manufacturer and to run several test welds before applying webbing to finished work. Ideally, the appropriate webbings can be easily joined with ample adhesion using a swift welder head speed for fast production runs.

4. Product Advantages and Concerns. Coated webbing offers a clean, shiny appearance and does not pick up dirt as easily as porous, non-coated products. Because it is sometimes sewn to add reinforcement to foldbacks at hardware locations, it is helpful to note that the unavoidable needle holes caused by stitching can usually be resealed by lightly passing a heat gun over them after the sewing is done. It is important to remember that the surface of the vinyl coating, while flexible, can be worn or cracked by folding it too tightly over fastening hardware or repeatedly running it through ratchet devices. Coated webbing provides an ideal edge for installing as an edge reinforcement to strengthen or eliminate the need for hems grommets.