Opening, cleaning, and blending
Staple fibers arrive at the yarn processing plant in large bales. To make yarns, fibers must be of similar length and relatively uniform so that the spun yarn can be of uniform quality. To accomplish this, fibers from a variety of production lots, fields, or animals must be blended together.
Several bales or cartons of fibers are placed in the opening, cleaning, and blending area. Some fibers from each bale or carton are fed into the opener and blender. It is important to separate or “open” the fiber mass to a single fiber state, or as close to that as possible. The opening and blending machines separate the fibers and blend fibers from the different bales or cartons. The technique used differs according to the type of opening or blending machine used.
In the intermittent system the fibers are separated from the bales and fed onto a spiked apron or lattice that carries the fibers from the feed area to the cleaning and opening area. The opening operation separates the fibers into a loose, fluffy mass. These loose fibers are fed into a hopper, where a measured amount is laid on a conveyor belt and delivered to the picking unit, where additional blending occurs. The picker further opens, cleans, and blends fibers through a system of rollers and forced air. The blend of fibers is blown onto a collecting cylinder to form a fiber layer. As the cylinder rotates, the layer of fibers is rolled off to form the picker lap. This is then taken to the card unit.
During this operation most of the dirt and impurities that might be present are removed by either gravity or centrifugal force. Cotton fibers receive more opening and blending than man-made fibers, since they have more impurities and greater variation than do man-made fibers.
The continuous system for making ring-spun yarns takes fibers directly from the bale and processes them automatically through to at least the card sliver state. Further steps may be connected to the card so that the card sliver moves on through additional processes automatically. The various steps in making ring-spun yarns are descried in the following paragraphs.
Bales are placed into some type of automatic fiber feed unit. Metal fingers pull tufts of fiber from the bale. These fibers are fed to the opening, cleaning, and blending area; they are then conveyed to a hopper for direct feed to the carding frame. Slivers from the card go directly to the drawing frames and may actually be fed continuously through to the roving process.
Yarns made on automatic equipment tend to be more uniform and may be stronger than discontinuous process yarn. Production speed is considerably faster for continuous processes, labor costs are reduced, and plants stay cleaner.
No matter which system is used, the quality of the final yarn is dependent largely on the selection of fibers and on the thoroughness of the opening, cleaning, blending, and picking operations.
In the intermittent or discontinuous systems the picker lap is placed at the rear of the card frame to supply fibers. In the automatic system the fibers are held in a hopper and fed in a loose form directly to the card. Carding continues the cleaning of the fibers; it removes fibers too short for use in yarns. The process partially aligns the fibers so that their longitudinal axes are some what parallel. Carding is accomplished by wire cards or granular cards. Wire cards contain two layers of card clothing consisting of wire flats (rectangular shapes) in which free wire fine wire pins are anchored. The flats are attached to a steel cylinder and to an endless belt that rotates over the top portion of the cylinder. The two sets of pins move in the same direction, but at different speeds, to tease the fibers into a filmy layer, so that a thin web of fibers is formed on the cylinder. This thin web is gathered into a soft mass and pulled into a rope like strand of fibers, called a sliver. The sliver is pulled through a cone-shaped outlet and doffed or delivered to cans or to a conveyer belt. Granular cards are similar to wire cards except that the card clothing is made of a rough granular surface somewhat similar to rough sandpaper.
The card sliver is not completely uniform in diameter, and the fibers are somewhat random in arrangement. Some fabrics are made of yarns that have received only this carding operation prior to drawing and roving formation. However, some fabrics require yarns of finer quality, particularly fine-quality cotton fabrics, and these require combed yarns rather than carded. When cotton and man-made fibers are combined. It is common for the cotton fibers to receive the combing step before the two types of fibers are combined. For yarns that require the additional step, the card sliver goes through the breaker-drawing step and then to the combing operation.
For high quality cotton yarns of superior evenness, smoothness, fineness, and strength, fibers are combed as well as carded. Card slivers are fed to the breaker-drawing frame, where several card slivers are combined. The break-drawing unit pulls out the fibers into a thin layer, and reforms a new sliver. The drawing is accomplished by controlling the speed of a series of rollers. Each set of which operates faster than the one behind it. The layer of slivers is pulled through the rollers at increasing speeds; as the layer leaves the unit, the fibers are pulled into a new sliver and delivered to cans ready for the combing frame. Forty-eight slivers from the breaker-drawing unit are combined to form the lap for the comber. The slivers are fed through a lapper that makes them to a thin layer of fibers that is wound onto a roll. These rolls, each weighing about 13.6 kg, are taken to the combing frame. The layer of fibers is fed into the combing area, where fine metal wires clean out remaining short fibers and impurities and further parallel the fiber in the comber lap.
During the combing operation as much as 20 percent of the fibers may be removed. This waste is sold to manufacturers of non woven products and to others who have use for short fibers. The fibers remaining form a thin web or layer; this web of fibers is pulled together, fed through a cone and under a geared wheel that helps to hold the fibers together, and delivered as a comb sliver.
Slivers from either the carding unit or the combing unit, depending on the ultimate yarn desired, are processed through the finisher-drawing or drafting frame. This is the process by which fibers of different types can be blended together to form blended yarns. Eight slivers are draw get her to produce the drawn sliver. If a 50/50 polyester/cotton blend is to be made, there will be four slivers of polyester fiber and four of cotton; if a 65/35 blend is ordered, there will be five polyester slivers and three cotton. As with breaker drawing, rollers moving at different speed smooth and combine the slivers and pull them into a thin layer and then into the drawn sliver.
The finisher-drawing operation is usually repeated. The second time, however, eight slivers from the first fisher -drawing step are subjected to the same operation. The drawn sliver is about the same size as, or perhaps slightly smaller than, the card or comb slivers. As yet no twist has been ‘imparted into the fiber assemblage, although the delivery of the sliver to the cans tends to twist the sliver slightly.
Slivers from the finisher drawing are taken to the roving frame, where each sliver will be attenuated until it measures approximately one-eighth of its original diameter. The drawn sliver is fed between sets of rollers. Each set of rollers rotates faster than the set behind it, the front rollers rotate about ten times faster than the back set of rollers. This pulls the fibers out, reduces the diameter of the strand, and further parallels the fibers. A slight amount of twist is imparted to give strength. The new strand, called roving, is laid onto a bobbin. Roving is wound onto the bobbin package at approximately 27 meters per minute. The full bobbins are doffed from the frame and delivered to the spinning frame.
The final process in ring spinning of single yarn is the spinning operation. During spinning the roving is attenuated to the desired diameter, called the final draft, and the desired amount of twist is inserted. The roving is fed down into the spinning area, where it feeds between sets of rollers. Just as in the roving step, the front set of set rotates faster than the back set. In spinning, the front set rotates about 30 times faster than the back set. This difference in speed attenuates the yarn and makes it even, smooth, and uniform. The attenuated yam is fed down, guided through a U-shaped guide, called a traveler, which moves around the take-up package or bobbin on a ring, hence the name “ring spinning”. The movement of the traveler and the turning of the spindle on which the bobbin is held combine to introduce twist into the yam. The spindle turns at about 13000 revolutions per minute; the traveler is slightly slower. Approximately 11 meters of yarn is wound onto the bobbin per minute. The size of yarn and the amount of twist, cited as turns per meter, can be controlled. The yam manufacturing steps discussed to this point produce a single yarn.