Nylon fiber comes to the mill in one of two yarn forms: BCF or Staple.
- BCF is an acronym for Bulked Continuous Filament and refers to synthetic fibers in a continuous form - miles long, formed into yarn bundles of a given number of filaments and texturized to increase bulk and cover. Texturizing changes the straight filaments into kinked or curled configurations.
- Staple fibers are chopped up fibers in the natural, unprocessed undyed state that must be spun or twisted into yarn, as opposed to continuous filament. Most staple fibers are 4 – 7 inches long.
When staple fibers arrive at the carpet mill in bales (very large cubical bundles looking very much like cotton bales), the bales are opened up; they are blended with other bales of staple to assure uniformity, and then are “carded” to make the fibers lie parallel to each other. Then a continuous yarn called a sliver (rhymes with “diver”), a large, soft, untwisted strand or rope of fibers, is formed. The slivers go to a pin-drafting machine that combs and stretches the fibers to the desired sliver weight. The yarn then goes to the spinning machine that stretches the sliver to the proper size and adds twist to improve the appearance of the finished product (the higher the twist the better). The single strands of yarn are usually twisted with other strands of yarn to make the final yarn.
Since BCF already arrives as a single yarn, it is normally twisted with another yarn (two-ply) and bulked before being heat set. Bulking is processing yarn to fluff it up and give more coverage with the same weight. Bulking also adds to fiber resiliency. Crimping creates “bulk” in individual filaments by creating a saw-tooth, zigzag, or random curl relative to the fiber.
The yarns must be heat-set if used in cut pile carpet (except plushes) but are often not heat-set if used in loop pile constructions. The process used to set the twist in the yarn uses heat and sometimes moisture. There are three heat-setting methods: Autoclave (steam and pressure in a batch process), Superba (continuous steam and pressure) and Suessen (dry heat). This allows the yarn to retain its shape and twist.
The yarn then usually goes to a tufting machine.
The primary backing into which the tufts are inserted may be made of jute, kraftcord, cotton, woven or non-woven synthetics, but normally polypropylene.
There are several ways to make carpet from yarn: Tufting, weaving, knitting, needle punching, fusion bonding and flocking.
The yarn then usually goes to a tufting machine. Over 95% of the carpet manufactured in the United States is tufted. A tufting machine is essentially a huge sewing machine with hundreds of needles that insert loops of yarn into the primary backing. Yarn is fed from a creel, one tube of yarn for each needle, and threaded through the needles. The tufting machine is set up to produce level loop, multi-level loop, cut pile, and cut and loop pile structures. A tufting machine is like a big sewing machine, usually twelve feet wide. The tufting machine’s needles punch the yarn through the primary backing, which is fed into the machine from the rear. The looper forms the pile and determines the pile height. Loopers with a cutting knife attached are used to produce cut-pile or plush carpet. The carpet is manufactured “fuzzy side down”. A loop-pile machine does not have those knives, leaving the loops uncut.
Flocking is where short, chopped fiber or flock is adhered, usually by electrostatic processes, to a base fabric resulting in a very short pile material with a velvety texture. Flocked carpet resembles velour. Flocked carpets are resilient and crush-resistant. A secondary backing material usually is applied to this structure, adding body and dimensional stability. A few flocked carpets are made for bedrooms and bathrooms, but the majority is used in vehicles: cars, planes, and buses.
Knit carpet is made by a process similar to hand knitting. A coat of latex and secondary backing material is applied to the fabric back to provide dimensional stability and strength. Some variation in color, pattern and texture is possible in knit carpet.
Needle-punched carpeting is made by barbed felting needles punching bating into a center fabric. This forms a flat fabric like carpet mainly used for indoor-outdoor carpeting, artificial grass surfaces, and some carpet tiles. Needle-punched carpet can be printed, flocked or embossed. Different textural effects, such as corduroy, can be attained by mixing fiber deniers and angling the needle in various ways. A coating of weather-resistant latex or similar material is applied to the back.
Weaving is making a carpet (or rug) on a loom with face yarns held in place by intertwining them with warp and weft yarns. Warp, in woven carpet, refers to yarns running lengthwise. The easiest way to remember that warp is associated with length is to think of “warp speed” as in Star Trek®. Weft, in woven carpet, refers to yarns running width-wise between warp yarns. The easiest way to remember that weft is associated with width is to think “weft” and “right”.
There are two major rug-weaving techniques: pile (or knotted) weave and flat weave.
Pile weave or knotted weave is the method of weaving used in most rugs. In this technique the rug is woven by creation of knots. A short piece of yarn is tied by hand around two neighboring warp strands creating a knot on the surface of the rug. After each row of knots is created, one or more strands of weft are passed through a complete set of warp strands. Then the knots and the weft strands are beaten with a comb securing the knots in place. A rug can consist of 25 to over 1,000 knots per square inch.
Flat weave refers to a technique of weaving where no knots are used in the weave. The warp strands are used as the foundation and the weft stands are used as both part of the foundation and in creating the patterns. The weft strands are simply passed through the warp strands. Some examples of this weaving method can be seen in kilims, soumaks and brocades. These weavings are called flat weaves since no knots are used in the weaving process and their surface looks flat. Kilims are the best-known group of flat-woven rugs. Because they take less time to weave, they are generally less expensive than (knotted) rugs. The main difference between kilims and pile rugs is that in kilims the weft strands create the colorful patterns. No rows of knots are added. The weft strands, unlike a pile rug, are discontinuous. They do not pass through the warp strands from selvage to selvage (edge to edge). The weft strands are passed through a few warp strands; then, they loop back around when they reach a section where a new color weft is needed.
The Soumak weaving technique refers to a method of flat weaving where the wefts are passed over two or four warps and back under one or two warps.
Brocade is also a form of flat weaving. Brocades already have a foundation (a warp and a weft). The foundation is patterned by additional colored weft strands, which can be continuous or discontinuous, and are passed through the already existing warp and weft strands.
The three most important weaving methods for carpet are Axminster, Velvet and Wilton.
In Axminster, the loom has control over each tuft of yarn making up the carpet. Axminster carpets are usually complicated designs and are always cut-pile. Spools of yarn that feed the loom can hold different colors and even different kinds of yarn.
In the Velvet loom, the pile yarn loops are formed over “wires”, one wire for each row of tufts. The wires are then pulled out, leaving a row of tufts. A knife blade, similar to a razor blade, may be attached to the end of the wire. As the wire is extracted, the tuft is cut to form a cut pile carpet. If no blade is attached, the carpet remains a loop pile.
The Wilton loom uses a mechanism to regulate the feeding of pile yarns into the loom to form a pattern. Joseph Marie Jacquard invented this in 1801. Sculptured carpets are made by controlling pile height and cutting, or not cutting loops.
The three primary dimensions to carpet are: Gauge (Width), Stitch rate (Length), and Pile height (Height).
Gauge is the distance between the needles. For example 1/8 gauge simply means there is 1/8 inch between each needle, or there are 8 needles per inch.
Stitch rate (or stitches per inch) defines the number of times per inch a stitch occurs, just as gauge expresses the frequency of tufts across the width. Stitch rate is the number of times an individual needle inserts a tuft into the primary backing as the primary backing moves one inch through the tufting machine. This is sometimes abbreviated SPI. Therefore 8 stitches per inch means that as the primary backing moved through the tufting machine, a single needle form 8 tufts or stitches.
Pile height is the length (expressed in decimal parts of one inch) of the tuft from the primary backing to the tip. All other factors being equal, a carpet with a higher pile height will possess more yarn on the wearing surface and will essentially be more durable.
Other common measurements are:
Denier or yarn denier: Unit of weight for the size of a single filament or yarn bundle. The higher the denier, the heavier (coarser) the yarn and the more resilience it will offer. Denier is expressed as the weight in grams of 9,000 meters of yarn. 9,000 meters of an 18 DPF (denier per filament) would weigh 18 grams and 9,000 meters of a 1230/2-ply yarn would weigh 2,460 grams. The higher the DPF, the greater the fiber’s resilience and its resistance to bending, but also the harsher it feels to the hand. DuPont Tactesse® has a denier of 12, which gives it a softer feel than the 15-18 denier more commonly used in carpet fibers.
Density or Pile density: The weight of a pile yarn (including buried portions of the pile yarn) in a unit volume of carpet, which is expressed in ounces per cubic yard. Also called “Average pile yarn weight”. The closer the tufts are to each other, the denser the pile and the less weight each individual tuft has to support. Pile density is not only evaluated by the closeness of the tufts but also by the height and weight of the pile yarn. All other things being equal, the greater the pile density, the greater the wearability of the carpet and the longer it will last.
Face (or pile) weight: The total weight of the face (above and below the backing) yarns in the carpet. The more ounces per square yard, the denser the pile and, potentially, the greater the wearability of the carpet.
Twist: Twist is the process whereby two or more spun yarns are twisted together. Twist is counted by the number of turns per inch (TPI) of the yarn. The performance of cut pile carpet is highly dependent on the rate of twist and twist retention. Heat setting helps stabilize yarn twist by subjecting the yarn to high temperature steam under pressure. Most carpet yarns have 2.5 to 6.0 twists per inch. A higher twist level usually results in better texture retention and better resilience. A high twist will result in a frieze, a medium twist will produce a Saxony, and low twist will result in a velour or Saxony plush style.
Tuft bind: Loop pile styles have closed loops, so twist is not a major factor. Rather, tuft bind is a consideration. Tuft bind is the relative strength of the attachment of the yarn loops to the backing of the carpet.
Staple yarn size: The size of staple yarns is most often expressed in what is known as the cotton count system. In this system, a yarn count is an inverse system; i.e., the larger the numerator, the smaller the yarn, and is based on the number of 840 yard hanks required to weight 1 pound. For example, a 1 cotton count (cc) yarn has 1 hank per 840 yards, while a 2.5 cc yarn would require 2.5 hanks (2100 yards) to weigh 1 pound. The denominator represents the ply count of the yarn.
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