With the whole environment gone highly technical and specialized, industrial fabrics
are used widely today for making many products such as inflatable boats
, sewn technical clothing, tents
, truck tarpaulins
, filter bags
, airships, bag
& luggage, inflatable toys, advertising banners etc. Sewing, seam taping, gluing etc. have gone obsolete for sealing such fabrics that have to be ultra safe and efficient. Thus, for producing these specialized textile products
, heat and pressure are applied to the seams of pattern pieces to fuse them together, thus making an airtight and watertight seal. This work of fabric welding
is done with the help of a variety of heat sealing machines.
Fabric Welding- What and Why
Fabric welding is the process of joining pieces of fabrics
using heat and pressure. Thermoplastic coatings, such as polyvinylchloride (PVC), polyurethane (PU), polyethylene fabric (PE) and polypropylene (PP) are used for heat sealing.
Fabric welding is not required for the usual daily clothings or products. Only when the product needs to be made specialized with highly functional effects, then only fabric welding is done. Such requirements arise when the product has to get-
- Water resistant
- Abrasion resistant at the seam
- Resistant to thread decay
- Fine appearance
Once done, fabric welding reduces maintenance cost as there is no need of threads
, sewing machines
, seam tapes or any other such material.
Categories of Fabric Welding
There are basically two types of fabric welding- Dielectric Welding and Rotary Welding. They are further categorized into many types of welding of which four are mostly used by the professionals.
- Water resistant
- Hot Air Welding
- Hot Wedge Welding
- Radio Frequency Welding
- Ultra Sonic Welding
Hot Air, Hot Wedge, and Ultrasonic welding are generally categorized as rotary welding. In this type, the fabric moves continuously through the machine while it is being welded. Radio Frequency welders are a stamping type machine. The fabric pieces don't move but are held in place while they are being welded.
Dielectric Welding and Rotary Welding
Dielectric Welding is the older of the two types of welding. In this method, a die is lowered onto the two fabric pieces that are supported by an underlying base plate. A timed pulse of radio frequency energy is sent between the die and the base plate. The fabric between the die and base plate gets heated enough so as to melt the thermoplastic coating on a temporary basis. With the melting of this coating, both pieces of fabric are fused together. The die is then lifted and new pieces of fabric move into position, and the whole process is repeated again.
Rotary welding is a continuous process where the fabric pieces move continuously through the welding area, usually pulled along by a pair of drive wheels. Heat is sent through any of the sources like heated metal wedge or hot air, just before the fabric passes between the drive wheels. On the drive wheels, the welding pressure is applied which seals the fabric permanently.
Rotary welding is faster than dielectric welding. The speed increases with the length of the products and seams. Welding speeds of up to 20 feet (6 meters) per minute and even higher can be achieved through it. However, rotary heat sealing requires a skilled and well trained operator to achieve full speed and flexibility. It is also capable of producing three dimensional finished products (products that do not lie flat) like garments, inflatable boats, bags, and luggage. As dielectric welding uses flat base plate, it restricts its application to the products whose seams must lie flat during the sealing process. However, nowadays, certain specialized dielectric welders have three dimensional dies, base plates and vacuum systems for holding the fabric pieces in position while the dies are applied but they are very costly.
Hot Air Welding and Wedge Welding
Although rotary wedge welding and rotary hot air welding are both the types of rotary welding, there are certain differences between them. The hot air welding is a faster welding process than the hot wedge welding. In wedge welding, a small metal wedge is used to deliver heat to the fabric immediately before it passes between the drive wheels where pressure is applied to seal the fabric together. In hot air welding, a hot air nozzle instead of a metal wedge is used to deliver heat.
When the seaming process is interrupted for a short while, the heat in the wedge builds up and when the fabric is again put in for seaming, it can sometimes burn the fabric at the initiating point itself. When using hot air welding, there is no such problem of heat build-up. As the wedge welding uses metal to deliver heat, some or the other type of contamination like dirt or melted coating bits, sometimes block the heat transfer, thus resulting in its non uniformity. Hot air welders use air to deliver heat and so results in uniform heat transfer. Surface irregularities of fabric, such as a cross seam, raise the wedge as it goes over the irregularity hampering the quality of welding which is not in the case of hot air welding as air is not rigid and flows over the surface irregularities. However, wedge welding consumes less power and relatively produces less noise when compared to the airflow sounds coming out from hot air welders.
When analyzing these differences, it appears that wedge welding is more suitable for welding relatively simple products that are made from less technically advanced fabrics having regular and smooth surfaces. Hot air welding, on the other hand, can be used for more advanced designs and fabrics.