Fiber Preparation for Spinning

Fiber Opening

After the appropriate fiber properties have been decided, the bales with matching specifications are prepared and arranged for their placement into a laydown. This allows for the proper dispersion of variables across the bales.

Then, a bale plucker moves back and forth along the laydown, removing a small amount of fiber from each bale on every pass. This minimizes the amount of fiber removed from each bale while allowing them to blend efficiently.

From the plucker, the opened tufts are moved to the next machine using fans, airflow, and a series of ducts, much like those used in heating and air conditioning systems. To further ensure good blending, a multi-cell blender may be used along the way. This machine randomly fills and then empties its chambers back into the process flow.

Fiber Cleaning

From the opening and blending processes, the open fiber tufts are transported to the first of what may be multiple cleaning machines. The first steps in fiber cleaning are designed to be coarse cleaners, removing the larger and heavier trash particles. Fine cleaners are found last in the carding line, just before carding.

Cleaning machines use gravity, centrifugal force, and airflow combined with mechanical beating action to remove trash or unwanted contents in the opened tufts of fiber, which are normally denser and heavier than the good fiber.

Grid bars are found under the beaters in most cleaning machines. Unwanted trash falls out between the bars and is sucked away to a central collection point. The grid bars can be adjusted to set the amount of trash that should be removed depending on the fiber being used, the spinning process, and the end product requirements.

Fine Cleaning and Contamination Detection

State of the art cleaning technology removes unwanted plastic contamination and large organic material from the fiber mass. A series of cameras detects properties such as shininess, color, transparency, fluorescence, and shape that differ from natural cotton properties. A jet of air ejects contamination from the moving tufts of cotton, effectively removing contaminants that challenge other cleaning methods.

Batt Formation

After opening and cleaning, the fiber must be prepared for carding through batt formation. The batt former (sometimes called chute feed) further opens the fiber tufts and forms a continuous matt-like, or batt, structure. This step ensures the carding process will receive a consistent weight of material so the output of the card will be as consistent and level as possible.

Fiber Carding

Carding is the foundation process of yarn manufacturing: the previously loose, unoriented cotton fiber first takes on a textile form known as a sliver. The card is made up of a series of cylinders, which are wire-wound. This wire has tiny teeth that transport a small number of fibers through the machine. There are also wire-covered surfaces called flats, where most of the carding action takes place. The wire-wound cylinders acting against one another, in conjunction with the flats, straighten, align, and parallel the fiber. The card further cleans the fibers, removing a significant amount of trash and dust particles.

Drawing

Drawing’s main purpose is to further align, parallel, and blend the semi-oriented fiber after carding. Anywhere from six to eight card slivers are combined for the initial drawing process, sometimes called breaker drawing.

A series of rollers are used to reduce the multiple slivers back down to the approximate weight of one sliver. To do this, the rollers turn at different speeds as they pull the slivers through, which is called drafting. The back pair turns the slowest, and the rollers gradually build in speed through the front set. The trailing ends of the gripped fibers, which may not be completely straight, are straightened out by the slipping and pulling action of the rollers.

As the drafted fiber web exits from the front set of drafting rolls, it is condensed back into sliver form using a trumpet-like device. The resulting sliver is coiled into a can for transport to the next process. Depending on what spinning system will be employed and the desired final product, this output sliver may go through the drawing process again (called finisher drawing).

Combing

Combing removes short fibers from the yarn-making process. Depending on the cotton fiber being combed and the settings of the comber itself, what qualifies as “short” can vary. Usually, it means fibers that are half an inch or less in length.

Generally, combing is done to increase the yarn count range of the material being processed. A finer yarn can be made from combed cotton which tends to result in an end product with extra sheen, drape, and improved hand. Combed yarns and the resulting yarns or fabrics tend to be softer and more durable. From an engineering standpoint, combing may be required for some yarn counts and product performance standards. For other products, combing may be a price point decision.

The combing process starts by preparing what is known as a lap, or drawn slivers  wound in a ribbon-like fashion onto a spool. This wound lap becomes the input for the combing process.

For each combing cycle, a measured amount of the lap is fed out and held fast for the pass of the half-lap. The half-lap is a wire or needle-covered section mounted on a rotating shaft that passes its teeth or needles through the held beard — the measured lap that has been fed out and held fast.

The fibers that are not held fast are removed by the half-lap and are often recycled into less critical yarn counts or have potential to become a valuable input for some nonwoven products due to it being exceptionally clean. The combed webs are drafted and condensed back into a sliver and coiled into a can for transport to the yarn spinning process.

Roving

The roving process is a preparatory process used only for ring spinning. Finisher-drawn carded or combed slivers are fed into a simple roller drafting system where the linear weight is reduced to a size optimum for the yarn count to be spun.

Since the linear mass is now drafted to a very light weight, some twist insertion is also necessary to give the roving enough integrity to be pulled from the bobbin on the ring-spinning frame. The roving is wound in a precise manner onto a bobbin ready for the ring spinning process.