Most yarns are spun from staple fibers made using one of three of systems- the Cotton Process, the Woolen Process, and the Worsted Process. These processes vary only sightly from each other and they all included the basic steps of Loosening and Cleaning, Carding, Drawing and Spinning.
The Cotton Process is used to spin cotton fibers between 3/4" and 2" in length. Sythetic fibers can also be blended in with the cotton to form blended yarns. Likewise the Worsted and Woolen Processes are used to spin wool fibers and wool blends.
All three processes are similar and vary only in a few steps. Additionally because Levi Strauss uses mainly cotton yarns only the Cotton Process is discussed in detail. Also because the woolen and worsted processes are so similar they are discussed together and only their differences from the cotton process are discussed.
Cotton Process
Ring Spinning is the most widely used method for spinning yarn for denim. This method employs seven steps in the spinning process:
- Opening & Loosening
- Carding
- Combing
- Drawing
- Roving
- Spinning
- Winding
Opening & Loosening
Upon arrival at the mill the cotton bails are opened and loosened. This helps separate and clean the cotton before it is fed into carding machines.
Carding
Carding machines further loosen and separate the cotton fibers by passing the fibers between two rotating metal drums covered with wire needles. This aligns the cotton in a thin web of parallel fibers which is formed into a ropelike strand called a sliver. The sliver is collected in a sliver can in preparation for roving.
Combing
For high quality yarns the sliver is combed after carding to make the fibers more parallel and remove smaller fibers.
Drawing
Slivers are then drawn out, blending the fibers and making them more parallel. No twist is added to the sliver during drawing. Several slivers can be blened together during drawing. Slivers can go through multiple drawings for further parallelization and blending.
Roving
Drawn out slivers are then fed to the roving frame where they are drawn further while a slight twist is added. The roving strands are collected in cans and fed to the spinning machine.
Spinning
The spinning machine draws out the roving strand adds twist, and winds the yarn onto bobbins.
Winding
Multiple bobbins of yarn are then wound onto larger spools called cheeses. Now the yarn is ready for texturing and dying and finally weaving into fabric.
