Flexible Duct Connector Roll Forming Production Line Manufactured by Dongguang Hengfu Roll Forming Machine Co., Ltd. Flexible duct connectors are consumables in ventilation and air-conditioning installation — needed on almost every duct run, yet difficult to make efficiently by hand. This production line turns that manual job into one continuous automatic process: galvanized edge strips are formed, punched and pressed onto fire-retardant fabric, then cut to length and