I’m trialing ultrasonic seams on a 78/22 recycled nylon-elastane warp knit and seeing cleaner edges than 4-needle flatlock, but peel strength drops after 10 wash cycles at 40C. Has anyone dialed in horn frequency or anvil pattern to keep recovery without scorching, or should I move to PU film bonding with a 0.04 mm layer?
, when stretch recovery tanks after ‘10 wash cycles at 40C’ it’s usually too much energy density — try a 35 kHz horn with a fine diamond anvil (about 0.3 mm pitch) and keep bond area around 25%, then back off amplitude/dwell to curb scorching. If you jump to the 0.04 mm PU route, a soft low-melt TPU (Shore about 70–80A) can help, but you may need 0.05 mm to claw back peel without trashing hand. What frequency and anvil pattern are you running now?
I kept peel up past “10 wash cycles at 40C” on a 78/22 warp knit by adding a 0.4 s post-hold under pressure with a cooled backup so the bond sets without cooking the elastane… Can your rig add a post-hold/cool stage, or are you locked to dwell only? If not, the 0.04 mm PU film will pass peel but the seam gets noticeably stiffer.
Switch to collapse mode and stop at about 0.07 mm; that kept peel and recovery on my 78/22 warp knit without singeing, whereas energy mode kept over-driving — are you set up for collapse control, @weftworks?