Yarn Spinning

Yarn Spinning

There are three different methods for spinning, or twisting, the prepared cotton fiber into yarn. These processes differ in the manner in which they insert twist, resulting in distinctly different yarn structures. The result of these different structures can be seen and felt in the final product.

Ring Spinning

Ring spinning is the oldest and most established spinning system. It is based on the very first yarn spinning methods ever employed and continues to be quite popular to this day. While it has changed little in principle, new ring spinning machines are a far cry from the earliest versions. Production rates are still low when compared to rotor, or open-end, and air-jet systems but the yarn quality is still the benchmark for even these newest, high-production systems. The ring spinning system still enjoys the widest possible yarn count range and excels at producing very fine counts. The hand (softness) of ring-spun yarn-produced fabrics is judged to be second to none.

The ring spinning process is quite simple. The roving is the input for the process and passes through a basic, and usually 3 roll, drafting system. After drafting, the fiber is twisted into a yarn structure by a whirling spindle, which has a removable bobbin on it. The winding of the yarn onto the bobbin takes place due to the traveler and ring combination. Thus the term ring spinning.

Ring spinning requires a subsequent winding step. That is, the full bobbins must be wound onto a cone or cheese to create a much larger package that is then usable for weaving or knitting. These additional steps of roving and winding, combined with the slow production rate (when compared to rotor and air-jet), are the primary reasons for the higher cost differences for ring-spun yarn.

Rotor Spinning

Rotor or open-end spinning came into widespread use in the late ’70s and early ’80s. It is still in use today and comprises a large percentage of the 100% cotton yarn spun in the United States. It is very fast when compared to ring spinning, up to 10 times the production per spindle. From a cost standpoint, it doesn’t require the roving process step and it does not require an extra winding step. Yarn is ready for use directly from the machine. The process today is highly automated and includes automatic piecing (restarting of broken ends) and doffing (removal of full packages). For these important economic reasons, rotor spinning became the yarn-making system of choice through the early ’90s in the U.S.

Yarn count range is somewhat limited when compared to ring spinning. Rotor spinning doesn’t perform well at much above Ne 40/1 and is really most productive in the yarn counts below Ne 20/1. More than 95% of denim yarn produced in the U.S. is made using rotor spinning.

The rotor spinning process is difficult to conceptualize. A sliver is used as the input and is fed into a small carding device called a combing roll (or opening roll). This individualizes the fibers and performs the drafting. The loose fibers are sucked into a rotating rotor cup where they are attached to the rolling, open-end of yarn found there, thus the name, open-end spinning. The yarn is withdrawn and the process becomes continuous.

Air-Jet Spinning

Air-jet spinning first appeared for production use in the early ’80s. It has continued to grow in its popularity, especially for cotton and polyester blend yarns.

The largest end-use market up to this point has been for sheeting and print cloth. Recent advancements in the latest generation of machines have made this high-production system more forgiving to shorter fiber length, and thus to cotton use. This has broadened the technology’s versatility and appeal to more end-use possibilities.

This spinning system uses sliver as its input, thereby taking advantage of the cost savings afforded by deleting the roving step required by ring spinning. Much like rotor spinning, it also produces a wound package that is ready for subsequent use in weaving or knitting. This negates the need for a separate winding step.

The air jet machine uses roller drafting as the means for reducing linear mass in the fed sliver. The drafting system is not unlike the drafting configuration found on the ring spinning system. After exiting the front pair of drafting rolls, the fiber is pulled into an orifice by a suction airflow created by the vortex that will perform the twist insertion. As the fiber enters the vortex zone, it is literally spun into a yarn structure by the whirling air currents. Like rotor spinning, there is some degree of random fiber entanglement that is also involved. This is the main reason for the somewhat lower yarn strengths of air jet yarns when compared to their ring spun counterparts.

Just as in rotor spinning, this process is highly automated with the automatic piecing of broken ends and automatic doffing (removal) of full yarn packages.

Yarn Twist

No matter the spinning system employed, all yarns contain twist to hold the fibers together. The frictional forces created by the twist are the means by which all yarns are held together.

Most single yarns will be produced with a “Z” twist. That means the helix angel is the “Z” direction. Sometimes “S” yarns will be produced for special technical reasons. An “S” twist yarn’s helix angle is in the “S” direction.

Because of its mechanical design, yarns produced on the OE system will always be “Z” twist yarns.

Both ring and air-jet spinning systems can be set up to produce an “S” twist when it is required.

Twist Multiple (TM) is a common way of designating how much twist a yarn contains. TM is a relationship between yarn number (or count) and the turns per inch in the yarn. Using number English or cotton count, that relationship is represented as follows:

TM = TPI√ Ne.

Where TM is twist multiple, TPI is turns per inch, and Ne is number English (or cotton count).

Twist level may also be expressed in other ways, such as turns per meter. When communications between parties involve twist, it’s important to know the terms and units being used.

Yarn Plying

All yarns are originally spun as single yarns, but for certain end uses, single yarns may be twisted together to produce a ply yarn. Most common are two-ply yarns, formed by twisting two single yarns together. The plying twist is in the opposite direction of the singles twist. That means most ply yarns will contain an “S” twist.

Ply yarns are used where extra strength and evenness are required.

When a yarn is plied, the ply can be indicated in the yarn number.

A single yarn and a plied yarn may have the same effective yarn count, but the plied yarn would be made up of two singles yarns which are half the size of the final, total yarn count.

For the English Cotton Count yarn numbering system, a singles yarn would be written with the count/1 while a doubles or plied yarn would be written with the size/2.

For two yarns both equaling an N_e 24 yarn number, in which one yarn was a singles or un-plied and the second yarn was a doubles or 2-ply, the singles yarn would be written N_e 24/1 and the doubles yarn would be written N_e 48/2. These would be read out loud as “24 singles” or “48 doubles.”

Remember that English Cotton Count is an indirect yarn numbering system, and so an N_e 48/1 yarn would be half the size of an N_e 24/1 yarn. Two N_e 48/1 yarns plied together would have an equivalent count to a N_e 24/1 yarn.

Yarn Numbering

Yarn numbering is a term used to describe a yarn’s physical size or, more specifically, its linear density.

Since short-staple spun yarns, like those containing cotton, can vary greatly in their bulk, measuring a yarn’s diameter, in a consistent way, can be almost impossible. For this reason, it is necessary to employ a more precise way of describing a yarn’s physical size.

Direct Yarn Numbering System

There are two main methods for assigning a yarn number. One method is called the direct yarn numbering system. In this method, the yarn’s linear density is denoted as a weight-to-length ratio. This method is commonly used for synthetic or man-made fiber.

For example, a 70 denier yarn means that there are 70 grams per 9000 meters. Denier is just one of the direct yarn numbering units but it is one of the more common direct units used for synthetics. Here are some others:

Direct Yarn Numbering Units:

• Decitex = weight in grams/ 10,000m
• Tex = weight in grams/1,000m
• Denier = weight in grams/9,000m

Indirect Method

The other method for describing a yarn’s linear density is called the indirect method. In this method, the yarn’s size is described in length to weight units. For cotton yarn, it is typical to see the denotations Ncc or sometimes Ne. These denotations are otherwise known as cotton count or number English. For example, a Ne 30/1 100% cotton or blend. Yarn means 30 times 840 yards per pound. 840 yards is known as a hank. There are also some other indirect units.

• Worsted Count = number of 560 yard lengths / Pound
• Woolen Run = number of 1600 yard lengths / Pound
• Woolen Cut = number of 300 yard lengths / Pound
• Number Metric (Nm) = number of 1000 meter lengths / Kilogram

With all this said it is important to realize that there are other yarn numbering units that may be encountered. It is impossible to cover all of them. This is especially true in China and some other foreign countries where many variations of yarn numbering may have evolved. Be aware that not everyone speaks or even knows all of these terms and their relationships.

Common Conversions

It is possible and often necessary to convert between the different yarn numbering systems in order to better communicate with your yarn supplier. Some common conversions include:

• Nm ÷ 1.69 = Ne
• 5315 ÷  Denier = Ne
• 590.6 ÷  Tex = Ne
• Denier ÷ 9 = Tex
• Decitex ÷ 10 = Tex
• Nw ÷ 1.5 = Ne

The above counts all represent ways to describe short-staple spun yarns. Short staple spun yarns can be made up of natural fibers which naturally grow to a staple length (such as cotton), synthetic filament fibers which have been cut to a staple length, or a blend of the two.

When describing yarns made up of filaments that have not been cut to a staple length, a yarn numbering system like this may be used:

2/150/34/1.25S/SB

• The first number represents the number of filament yarns plied together (in this case 2 filament yarns are plied together).
• The second number represents the linear density of each filament yarn in the ply (in this case each individual yarn has a size of 150 deniers).
• The third number represents the number of filaments in each filament yarn (in this case each yarn has 34 filaments).
• The fourth number represents the twist of the ply (in this case the ply twist is 1.25 turns per inch) and the direction of the ply (in this case the yarn is plied in the “S” direction).
• The fifth group of letters may represent the fiber luster (in this case the luster is Semi-Bright).