Seamless Underwear Making Machine Factory Floor Demonstration

I've worked in knitting mills in three countries and one thing always grabs my attention: the machines that run without anyone cutting fabric or stacking pattern pieces. An underwear seamless making machine is different from a traditional sewing machine. It does not bond individual panels. Rather than doing all that in separate steps it does the whole garment (body, leg openings, waistband) all in one go. This article describes what really happens when these machines are used in actual production environments and run eight-hour shifts.

The Knitting Process: A Single Tube
At the heart of the system is a circular knitting machine of the cylinder and dial type. This machine knits in the round rather than flat knitting, which makes rectangular panels of fabric. The yarn is fed from cones on the top of the machine, through tensioners and into the knitting zone. The needles go up and down and make stitches which join up together to make a tube. The cylinder turns.
Especially for underwear it is advantageous that the stitch density can be varied within one round. It can knit tighter elastic for the waist band, a looser structure for the hip area and a denser zone for the front panel, all without stopping. This is possible through electronically controlled feeders that can change yarn types or stitch lengths as necessary.

Helping the Counting Machines
The main knitting machine is not a stand alone machine. Further down the production line, equipment completes what the circular machine began. Ultrasonic edge trimmers cut the leg openings and also melt the cut edge, preventing fraying. This is important because seamless garments often use synthetic yarns that won't unravel if heat-sealed properly.
Then, for some special premium items, hot air taping machines. They put a thin strip of sticky tape along the top of the waistband and around the bottom of the leg openings. The tape reinforces those high-stress areas so the edge doesn't curl up after washing. A common use is for sports bras where the underband gets stretched repeatedly. If you don't tape it, the garment loses its shape after twenty or thirty wears.

What products actually use this technology?
The scope of application has expanded from mere briefs. Sports bras are one of the biggest categories because seamless construction means there are no side seams that can cause chafing while running. Yoga leggings have their advantages too – the lack of an inner thigh seam reduces friction when you're in poses.
Swimwear makers have turned to seamless machines for their resistance to stretch. The garment moves with the body. No seam restrictions. Even some light outerwear like seamless T-shirts is now coming off these machines. What they all have in common is a demand for four-way stretch and a low profile at contact points.

What Production Managers Look For
There are a few variables to consider when running these machines. Yarn tension is important for fabric weight and recovery. A little difference – a few grams – in tension can leave the waistband too tight on one side. Needle condition is important too. Damaged needles cause dropped stitches which look like holes. Most factories change their needles every 800-1000 hours of operation as a precaution.
The diameter you choose determines the size of the garment. Adult mediums are printed on a 15-inch cylinder; children's wear on a 12-inch cylinder. Changing diameters requires a different machine, not just a change of setting. That's why you'll usually find several machines running at different diameters in a mill.

A Quick Reality Check
The price of buying something is less than the price of owning it. The machine uses a lot of electricity to power the motors, the electronic controls and the compressed air for the feeders. A Santoni machine uses about 3.5 kilowatts per hour. That's a lot in a 24-hour shift. But that's offset by material savings – waste runs under 5% vs cut-and-sew where fabric waste can be 20%+

Final Thoughts
The underwear seamless making machine is not a magic box. It is a production ecosystem that combines the main knitting with edge finishing and reinforcement machines. The real value in application is to match the machine gauge, diameter and auxiliary tools to the specific garment category you intend to run. To get an idea of these machines nothing could be better than seeing them in action, in person.