In daily life, various masks such as disposable medical masks, disposable protective masks and non-woven fabric masks are used on many occasions. Ear loops form an integral part of a mask. When the ear loops are stretched and hooked over both ears, the mask fits snugly against the face. This creates a filter between the human respiratory tract and ambient air, which serves to block dust, droplets and germs.

Ear loops are categorized by shape into round and flat types, and by manufacturing process into knitted and woven styles. The ear loops used for ordinary masks are mostly round knitted ones. Standard specifications of round ear loops include 3.0mm, 4.0mm and 5.0mm. Each knitting head can crochet 1.5 to 2 meters of ear loops per minute, delivering relatively high production efficiency.

Performance requirements for ear loops are as follows: high elasticity, excellent recovery, smooth and soft texture, comfortable to wear, safe, eco-friendly. Machines used to produce ear loops are called ear loop machines, a category of ribbon looms. Cylinders of knitted ear loop machines are available in specifications of 4-needle, 6-needle, 8-needle, 12-needle, 16-needle, 18-needle and 20-needle models, suitable for manufacturing ear loops with different performance standards.

Now let's take a look at the production floor of an ear loop manufacturing factory. Finished ear loops are stored inside plastic bags underneath the machines.

The raw materials for manufacturing ear loops are spandex and nylon DTY. Each knitting head is equipped with one cone of 140D spandex filament and two cones of 70D/24F nylon DTY, which are combined into a 140D/48F double-ply yarn during production.

The spandex filament adopts side let-off feeding; no additional drafting is applied besides the unwinding tension. After direction change, it feeds vertically into the cylinder and exits directly from the cylinder bottom. Serving as the core yarn, it does not participate in knitting and only provides elasticity under tension.

Nylon filament forms the outer layer of the ear loop to deliver tensile strength. It is knitted by crochet hooks and fully wraps around the spandex core inside the cylinder.

In terms of application requirements, as the core yarn, spandex only needs adequate elasticity and breaking strength, while other regular physical properties become negligible - such as yarn evenness, elongation at break, tensile modulus, cohesion and oil pick-up rate. Its quality threshold is relatively low.

For this reason, spandex manufacturers can combine three strands of 40D/3F yarn into a thicker single strand to produce 140D/9F spandex within a short timeframe, without any machine component replacement required. Nevertheless, products made by this process will inevitably trigger various practical issues during downstream customer processing.

1.The spandex yarn is prone to slipping and sagging during side let-off, which will come into contact with the nylon yarn underneath and disrupt unwinding.

Root Cause Analysis

140D spandex has heavy linear weight and excellent unwinding performance, yet the adhesion between filaments is weak. This results in insufficient tension during side let-off. After reaching the highest point of the yarn path, the filament suddenly drops to the lowest position and sags along the yarn guide track. This issue becomes more severe when the cheese has a larger diameter and narrower winding width.

Improvement Solutions

Reduce oil pick-up rate and increase unwinding tension;

Raise winding contact pressure to enhance cohesion between filaments;

Consider increasing the pre-draft ratio;

Alternatively, cut down the cheese weight and diameter, or adjust winding forming parameters to widen the cheese width.

Root Cause Analysis

This problem can be analyzed in conjunction with poor initial winding occurring during production. 140D single-tube spandex suffers from a high incidence of poor initial winding; a large number of spandex cheeses have yarn wound outside the paper core and have to be downgraded. Poor initial winding indicates defective winding right when spandex filaments are first wound onto the paper tube, which explains the disordered yarn layers.

In addition, 140D spandex is relatively thick. After the spandex filament is cut, the yarn end cannot be buried at the bottom of the cheese in a timely manner and springs out instead, which is a major cause of bottom-end yarn breaks.

Improvement Measures

Causes of poor initial winding include unlevel bobbin holders, loosely expanded paper tubes, and oversized inner diameters of paper tubes, which need to be verified case by case. Furthermore, slotting the middle section of the paper tube can optimize spandex splicing performance and prevent exposed yarn ends.

3.After the ear loops are produced and laid flat in a relaxed state, they fail to stay straight.

Improvement Measures

There are numerous factors leading to spiral yarn formation, including excessive air flow and overly high pressure during false twisting, uneven denier among individual filaments of the multi-filament yarn, poor quality of spinning dope causing uneven filament tension, and inappropriate spinning processes. Each factor needs to be inspected and verified one by one. For severe spiral defects, reducing the spinning speed is also a feasible solution.