The process in brief:
In weaving cloth, the warp is the set of lengthwise yarns that are held in tension on a frame or loom. The yarn that is inserted over-and-under the warp threads is called the weft, woof, or filler. Each individual warp thread in a fabric is called a warp end or end. Warp means “that which is thrown across” (OldEnglish wearp, from weorpan, to throw, cf.German werfen, Dutch werpen).
Very simple looms use a spiral warp, in which a single, very long yarn is wound around a pair of sticks or beams in a spiral pattern to make up the warp.
Because the warp is held under high tension during the entire process of weaving and warp yarn must be strong, yarn for warp ends is usually spun and plied fiber. Traditional fibers for warping are wool, linen, alpaca, and silk. With the improvements in spinning technology during the Industrial Revolution, it became possible to make cotton yarn of sufficient strength to be used as the warp in mechanized weaving. Later, artificial or man-made fibers such as nylon rayon or glass fibers were employed.
In Glass Fiber weaving, the most common weave patterns are
- Basket Weave
- Plain Weave
- Satin Weave
- Twill & Broken Twill Weave
In Basket weave or Panama weave, groups of warp and weft threads are interlaced so that they form a simple criss-cross pattern. Each group of weft threads crosses an equal number of warp threads by going over one group, then under the next, and so on. The next group of weft threads goes under the warp threads that its neighbor went over, and vice versa.
Basketweave can be identified by its checkerboard-like appearance made of two or more threads in each group.
Schematic of a plain weave, which would be woven by a shuttle loom (left).
The right schematic represents the modern Plain weave, as the fiber is not anymore continuous throughout multiple sheddings, but it is cut after each shedding takes place.
Allthough shuttle looms are still in use mostly for narrow fabrics, they have been widely replaced by other, more efficient weaving technology:
Airjet Weaving * Projectile Weaving * Rapier Loom Weaving * Waterjet weaving.
The satin weave is characterized by four or more fill or weft yarns floating over a warp yarn or vice versa, four warp yarns floating over a single weft yarn. Floats are missed interfacings, where the warp yarn lies on top of the weft in a warp-faced satin and where the weft yarn lies on top of the warp yarns in weft-faced satins. These floats explain the even sheen, as unlike in other weaves, the light reflecting is not scattered as much by the fibres, which have fewer tucks.
In glass fiber weaving, satin fabrics are popular when high drape ability is required. If the fabric has to be layed around corner or edges.
This Schematic also shows a traditional shuttle loom woven Satin Pattern.
Twill fabrics technically have a front and a back side, unlike plain weave, whose two sides are the same. The front side of the twill is the technical face; the back is called the technical back. The technical face side of a twill weave fabric is the side with the most pronounced wale; it is usually more durable, more attractive, most often used as the fashion side of the fabric, and the side visible during weaving. If there are warp floats on the technical face (i.e., if the warp crosses over two or more wefts), there will be filling floats (the weft will cross over two or more warps) on the technical back. If the twill wale goes up to the right on one side, it will go up to the left on the other side. Twill fabrics have no up and down as they are woven.
The fewer interlacings in twills allow the yarns to move more freely, and thus they are softer, more pliable, and drape better than plain-weave textiles. Twills also recover from wrinkles better than plain-weave fabrics do. When there are fewer interlacings, yarns can be packed closer together to produce high-count fabrics. In twills and higher counts, the fabric is more durable.
Schematic of Twill Woven Fabric:
Weaving Glass Fibers:
Due to the low elongation coefficient (% of stretch before it breaks) of approx. 2.0 – 3.5 %, weaving Glass Fibers require very precise machine adjustments. It becomes a little simpler when the yarns have been texturized, as the extra bulk in essence increases the elongation coefficient by the grade of texture.
Due to the “brittle” nature of glass fibers, the finer yarns require preparation to withstand the harsh friction caused by the reed. This preparation is called Slashing.
While Roving or texturized yarns typically do not need any special additional treatment of seizing, the finer yarns typically do.
Slashing is a process in which the strand will be applied an additional seizing, aiding the weaving process. Without this additional seizing, the yarn in the warp will be starting to create “fuzz” from broken filaments. This is due to the reed rupturing the warp strands. The fuzz in return will influence the shedding behavior of the neighboring fibers. This may cause those fibers not to clearly separate from each other, when the shedding takes place. This will result in either a simple miss pick or in a complete yarn breakage in the warp.
The slashing typically handles two production steps in one;
a) application of the required additional seizing
b) warping the strands to a loom beam. (Note:Slashing can also be offered on a “bobbin-to-bobbin”-process, as well.)
In case of slashed bobbins, a second process will have to take place, which is called warping.
Warping is the process in which single strands of fibers (yarns) will be wound to a beam which is called a loombeam. This loombeam can then be either attached or connected to the weaving loom or put on a separate A-Phrame construction.
Depending on the desired weave construction, at times, two loombeams can be implemented. In that case, a top beam stand is mounted to the machine, holding the second beam.
There are three basic Warping Techniques:
a) Sample Warping
Sample Warping is typically for around 30 yards or under 100 yards, as needed, just for weaving samples. Other lengths apply, but in essence it is meant for short runs.
b) Sectional Warping
A Sectional Warper draws e.g. 200 single ends at a time and winds it to a loombeam. This is then called a section. After the desired quantity has been wound, e.g. 5,000 yards, the second section will be applied with the same yard count. In order to do so, the warper will be moved a small distance on a rail system, to be centered again in front of the next section. This process will be repeated, until the desired total end count has been reached.
C) Direct Warping
A Direct Warper draws all the required strands at one time and applies the desired quantity of yards in this one process. Therefore, while Sectional Warping and Direct Warping both result in the same end count with the desired max quantity per strand, the sectional warping process calls for multiple production steps, while the Direct Warper produces it in one production step.
The choice of the correct warping system depends on the mill’s setup.
Caution with warping, as glass fiber has a very low elongation coefficient, precise machine adjustments and tension systems are required.
More dense or heavier yarns, around 270 tex and up, are preferably woven on creels.
Two basic creel designs:
a) Pin Creel
Here, the bobbin is stuck on a pin.
B) Shelf Creel
Here the bobbin stands on a shelf.
While there are many different designs of pin creels or shelf creels, it appears that the shelf creel provides more flexibility, as some glass fiber manufacturers provide rovings for inside and some for outside unwinding. Rovings with inside unwinding cannot be used for pin creels.