What Is Slub Yarn?

Slub yarn is a type of yarn with uneven thickness along its length. Some sections are fine, while others are thicker and raised. These thicker parts are call “slubs” because they look similar to the joints of bamboo.

In the early stage of textile production, slubs were usually consider yarn defects. During spinning, problems such as unstable drafting or uneven fiber feeding could cause local variations in yarn fineness. As a result, raised thick spots appeared on the yarn, which affect fabric quality.

However, when these bamboo-like thick spots are distribut in a planned and balance way on the fabric surface, It can create a special texture and a distinctive visual style. Therefore, slub yarn is now intentionally produce by changing yarn density regularly or irregularly during spinning. Yarn is then used to make slub yarn fabrics with unique surface effects.

1. Features of Slub Yarn

The yarn has an uneven appearance, with thick and thin sections along the yarn body. It is one of the most widely used types of fancy yarn.

Common types include:

Thick-and-thin slub yarn

Knot-like slub yarn

Staple fiber slub yarn

Filament slub yarn

This Yarn can be used in lightweight summer fabrics as well as heavy winter fabrics. It is suitable for apparel fabrics and decorative fabrics. The fabric surface usually has a clear pattern, a special style, and a strong three-dimensional effect.

2. Formation Principle and Production Methods of Slub Yarn

Formation Principle

The yarn can be produce on a conventional ring spinning frame by adding a special device. This device changes the speed of the front roller or makes it stop for a short time. As a result, the normal drafting ratio changes, and a thick section suddenly appears on the base yarn. Because this thick section looks like a bamboo joint, the yarn is call slub yarn.

Production Method

One common method is to use an electromagnetic clutch to control the stopping and starting of the front roller.

Spinning the base yarn, the clutch remains engage, and the front roller runs normally.

The moving plate and fixed plate separate, causing the front roller to stop. Meanwhile, the middle and back rollers continue running, so the delivere fibers accumulate between the middle roller and the front roller.

When the clutch is power again, the front roller starts running and takes away the accumulate fibers. A slub is then form on the base yarn.

The longer the front roller stops, the more fibers accumulate. Therefore, the slub becomes thicker. This method is more suitable for producing relatively coarse slubs.

Another method is to suddenly overfeed the middle and back rollers. This also changes the drafting ratio and forms slubs.

Other production methods include front roller speed variation driven by a stepping motor and middle/back roller overfeeding driven by a servo motor.

When the yarn is produce by changing the front roller speed, the system has high sensitivity. It is suitable for producing dense slubs and offers good control over slub length and thickness.

However, front roller speed variation may affect production output. Since the front roller speed changes while spindle speed remains constant, yarn twist can also be affect.

When hte yarn is produce by overfeeding the middle and back rollers, the sensitivity is not as high as front roller speed variation for short and dense slubs. In addition, the manufacturing cost is usually higher.

Important Production Notes

When producing the yarn, the centrifugal force at the slub section is relatively large. And yarn balloon may become larger and smaller during spinning. Therefore, a slightly heavier traveler should be selecte.

At the same time, because the slub section is thicker, it may have difficulty passing through the traveler. For this reason, a larger traveler is usually recommend.

If yarn is produce by stopping or changing the speed of the front roller, the twist should be controll at a slightly lower level.

When producing dense slub yarn, the front roller speed changes constantly. Therefore, the machine speed should be reduce properly. Otherwise, the end breakage rate may increase.

When stopping the machine manually for doffing, it is better to stop at the base yarn section and avoid stopping at the thick slub section. Since the slub section has lower twist, stopping there may increase end breakage when the machine starts again.

3. Applications of Slub Yarn

Common slub yarn counts are usually 12-84 tex, roughly Nm 83-12. The raw materials include pure cotton and chemical fiber blend yarns. Staple fiber yarn is the most common, but medium-long fibers and wool-type fibers can also be used.

In general, the slub length should not be shorter than the fiber length. Therefore, cotton slub yarn usually has shorter slubs, while wool-type fiber slub yarn usually has longer slubs.

The thickness of the slub depends on the product design and fabric style.

Because the difference between the thick slub section and the base yarn is large, the twist in the thick section is very low. This makes the slub section easier to become hairy and lower in strength.

Knitted or woven fabrics made with this yarn usually have a rough surface and a distinctive style. In some cases, slub yarn can also be processe on a fancy twisting machine to make wave yarn. Because the wave at the thick section is very large and looks similar to corn, it is also called popcorn yarn.

4. Relationship Between Slub Yarn Parameters and Fabric Style

The main parameters of slub yarn include base yarn count, slub thickness, slub length, and slub spacing. Due to the special structure of slub yarn, the final fabric style is closely relate to these four parameters.

Different combinations of these parameters can create different fabric appearances. The main effects are as follows:

First, the slub section is thicker, and the twist add to this part during spinning is lower. Therefore, the fibers in the slub section are looser. During dyeing, the thick and thin sections absorb dye differently. Depending on the slub length, the fabric may show a raindrop or rain-streak effect.

Second, different raw materials create different styles. For example, slub fabrics made from ordinary cotton or polyester single yarn usually have more obvious slubs.

However, when special-shaped fibers such as cationic polyester, bright polyester, or viscose are used to form finer slubs and then twist with ordinary yarn, the fabric can be made into a higher-end textile product.

Third, slub yarn of 48.6-58.3 tex, roughly Ne 12-10, can be produced on rotor spinning machines. The slub thickness can be 1.3-1.8 times higher than the normal yarn. By adjusting slub spacing and length, high-grade fabrics with a linen-like style can be develop.

Fourth, by changing slub length, slub thickness, spacing, and raw materials, manufacturers can develop a wide range of fabric varieties with different styles. This helps meet the needs of different consumer groups.

5. Base Yarn Count and Overall Yarn Count of Slub Yarn

The nominal count of slub yarn is usually name after the base yarn count. For example, C14.5 tex slub yarn refers to the count of the normal yarn section between slubs, while the count at the slub section is higher.

In actual production, when slub yarn is produced by front roller speed variation, the high-speed value and twist value of the base yarn are usually set first. After the normal base yarn count is produced, the low-speed value and other slub parameters are set to produce slub yarn.

Yarn count of slub yarn refers to the combined count of the base yarn and the slub sections. In general, the design overall count and the actual spun overall count may be different. Different types of slub yarn devices can also create different levels of variation in the final overall count.

Overall yarn count is an important basis for daily control of yarn weight deviation in production. It is also a key indicator for calculating cotton cost in slub yarn production.

Some mills use the base yarn count to control the weight deviation of slub yarn. May make the actual base yarn slightly lighter and allow more fabric length to be woven. This approach may work for yarns with fine and sparse slubs. However, for slub yarns with thick and dense slubs, it base yarn may become too fine, which can cause more end breaks during later processing.

The design overall count refers to the plan comprehensive count of slub yarn. It is calculate as a weight average of the base yarn count and the slub yarn count. The weights are based on the percentage of slub spacing and slub length within a certain cycle.

It should be noted that the total yarn length within a cycle should be calculate according to the slub arrangement pattern.

For regular slub yarn, the cycle length is base on one full repeat. If five slubs form one small repeat, the total length of these five slubs and their spacing can be use as one cycle.

For irregular slub yarn, the overall count can be estimate according to the design average slub length, spacing, and thickness ratio.

The actual overall count is the real count of the spun slub yarn. It usually differs from the design overall count. Therefore, in daily production, testing should be carry out according to national yarn standards. The actual overall count should reach or stay close to the design overall count. The batch weight deviation should generally be controll within ±2.5%, and the monthly deviation should be controll within ±0.5%.