Transitioning to welded seams
In recent years, fabric welding has replaced many traditional sewing methods. Not only do welded seams have a better aesthetic appearance than sewn seams, but they also have a longer service life in the field. Currently, it is still more cost effective to sew many applications, but many manufacturers are making the transition to welded seams due to the quality improvements that they can achieve, and because innovations in welding equipment are happening every day to make it more cost effective.
The decision to weld starts with the application. Standard welded products include party tents, tension structures, military shelters, and digitally printed tents, sidewalls and banners. The most commonly used material for welded applications is a PVC coated or laminated polyester.
The manufacturing process begins in the cutting department. Celina uses an Eastman automated conveyor cutting system. All projects are first laid out in an AutoCAD® file and then transferred to the Eastman. This machine enables the engineering staff to make precision cuts and label any construction marks needed during the manufacturing process.
This is a fairly advanced piece of equipment and not all manufacturers have access to it. Many manufacturers typically have a layout table where they use patterns, scissors, and other cutting tools to achieve the same end goal.
After the job has been cut, it moves into the assembly/welding area. The four main welding options in this industry are hot air,RF (radio frequency), acrylic, and hot wedge. Each process has distinct advantages.
RF welding. RF stands for “radio frequency,” which is energy that is created by the equipment to weld specific types of thermoplastics. RF excites the molecular structure of the material, causing it to heat very rapidly. Once heated, a die that is forced into the material by a press determines the final shape and characteristics of the finished product. This process is typically used to weld small reinforcement areas, although it is sometimes used to weld long straight seams.
Hot air welding. Hot air rotary heat sealing is a welding process used to join thermoplastic industrial fabrics and films using very precise heat, speed and pressure settings. The correct combination of these three parameters allows one to achieve a complete weld. In the case of hot air, heat is provided by compressed air blowing across electrical heat elements and is injected at the welding point. The tightly controlled temperature can range from 400 to 1350 degrees Farenheit. This process is typically used for very long straight seams, and it is generally the most efficient process of the four.
Hot wedge welding. As in hot air welding, hot wedge rotary heat sealing is a process used to join thermoplastic industrial fabrics and films using a very precise heat speed and pressure. However, in the case of hot wedge welding, a heated wedge is precisely positioned at the weld point providing the required heat. The fabric or film is then pulled across the heated wedge. The tightly controlled temperature of the wedge can range from 400 to 1350 degrees Farenheit, producing a perfect weld. This process is sometimes preferred over hot air because it does not produce the noise or fumes that hot air machines produce.
Acrylic welding. Hot air rotary heat sealing is a welding process that can also be used to seam acrylic fabrics for the fabrication of awnings, boat covers and other applications. Miller Weldmaster offers a special laminated tape that has a very strong adhesive on both sides. The adhesive is heat activated followed by pressure from the weld rollers, producing a very strong bond. This process is used when the materials being welded are not a thermoplastic material and need to have an additional adhesive tape to complete the weld.
Making the decision
When choosing between a welding process and a sewing process there are many variables to consider.
- What is the product’s application?
- Will seams that potentially leak water affect the product’s function?
- Is the material being used in the product capable of being welded?
- Can the product be manufactured faster by welding it or sewing it?
Testing is essential
An in-house quality assurance laboratory to perform tensile tests on all of your heat seals will assure that the heat seals being manufactured meet your specifications. All tests need to be performed in accordance with ASTM (American Society for Testing and Materials) standards. Some products have very high strength requirements and therefore the heat seals must be tested to ensure a good quality weld. There are many independent laboratories that can perform the tests for manufacturers that do not have this equipment.
Finishing and sewing
The last process in the manufacturing process is finishing and sewing, when hardware or reinforcements are sewn to the products. It is usually preferable to do minimal sewing due to the tendency of threads to dry rot, mildew, and leak water when exposed to weather for long periods of time. However, in high stress areas, a sewn mechanical connection is preferred for reinforcements, such as webbing tiebacks, and hardware assemblies. This is mostly because the webbings being used are not made from a thermoplastic material and therefore must be sewn.
Wide format options
Recently, it has been possible to use wide format more and more to construct very large party tents, while minimizing the amount of heat seals needed to manufacture these structures. The standard width of material for the tent industry is 61 inches. Using wider material gives the manufacturer the ability to put logos on tents without concerns about matching up parts of the image or text that runs through a heat seal. Large companies, such as Microsoft® and Coors, have taken advantage of this capability to have tents manufactured to their specifications.
Everyone stands to benefit as advances in welding have provided more viable options for manufacturers to better serve their customers.
Gabe Lehman is director of engineering with Celina Industries Inc., a PVC fabricator located in Celina, Ohio. Celina specializes in fabric cutting, hot air welding, RF welding, and sewing.