There are also important differences between rotary wedge welding and rotary hot air welding. Typically, hot air is a much faster welding process that hot wedge. A wedge welder uses a small metal wedge to deliver heat to the fabric immediately before it passes between the drive wheels where pressure is applied to seal the fabric together. The advantages of the wedge welder are that it uses less power and is relatively quiet compared to the noise of the airflow from hot air welders. Hot air welders use a hot air nozzle instead of a metal wedge to deliver heat. This simple difference gives the hot air welder several distinct advantages. Heat Build-up Hot air welders are not subject to the heat build-up experienced when stopping and starting a wedge welder. Whenever the seaming process is interrupted or stopped, the heat in the wedge builds up. When the wedge is reintroduced to the fabric for seaming, it can often burn the fabric at the start point. Uniform Heat Transfer Contamination on the surface of the wedge can block the transfer of heat from the wedge to the fabric, affecting the uniformity of the weld. This contamination can come from two sources: dirt on the fabric, picked up during the material handling process, or bits of melted coating that adhere to the wedge while welding. Since hot air welders use air rather than metal to deliver heat, they are not subject to this problem. Surface Irregularities Irregularities on the surface of the fabric being welded, particularly a cross seam, raise the wedge as it goes over the irregularity. On the back side of the irregularity, this momentarily leaves the rigid metal wedge too far above the bottom piece of fabric to ensure a good weld. Since hot air is not rigid, it can flow over surface irregularities, ensuring a better weld. These advantages make the hot air welder more versatile than the wedge welder. While the wedge welder is suitable for welding relatively simple products made from less technically advanced fabric that have few or no cross seams, the hot air welder is used in a much broader field of applications with more advanced design and fabrics.
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