CARPET CONSTRUCTION


It is important to understand carpet construction in order to apply the variables that affect performance of a specific installation. Tufted carpet consists of the following components: the face yarn, which can be cut pile, loop pile, or a combination of cut and loop pile; primary backing fabric; a bonding compound, usually SB latex, but may be polyurethane, PVC, or fabric; and (often) a secondary backing fabric.

The development of the broadloom tufting machine and the introduction of synthetic carpet yarns in the early 1950s transformed the American carpet industry from low-volume production of woven luxury products to mass production of high quality and comfortable, yet popularly priced, goods. The explosive growth of carpet sales in the United States in the ensuing years paralleled the continual development of tufting technology, the proliferation of high-speed tufting machines, and the development of synthetic carpet fibers and alternative backing systems. As a result, today’s carpet is both better and less expensive.

Figures 1.1 and 1.2 illustrate how these elements are combined to form carpet.

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The primary carpet fabric construction methods include tufting, weaving, knitting, needle punching, and bonding.

TUFTING

Over 90% of carpet produced is tufted, the most prevalent carpet construction method. Tufting machines are similar to giant sewing machines, using hundreds of threaded needles in a row across the width of the machine. Today’s machines are increasingly complex and sophisticated, providing a wide variety of styles and constructions.

The creel, located in front of the tufter, may be racks of many yarn cones or multiple large spools, referred to as beams, and containing many individual strands of yarn. From the creel, the yarns are passed
overhead through guide tubes to puller rolls. The speed of the puller rolls controls the amount of yarn supplied to the tufter and, along with other factors, determines the carpet’s pile height.

The eyed needles, which number up to 2,000 for very fine gauge machines, insert the yarn into a primary backing fabric supplied from a roll of  material located in front of the machine. Spiked rolls on the front and back of the tufting machines feed the backing through the machine.

Below the needle plate are loopers, devices shaped like inverted hockey sticks, timed with the needles to catch the yarn and hold it to form loops. If a cut pile is called for, a looper and knife combination is used to cut the loops. For cut-loop combinations, a special looper and conventional cutting knife are used.

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Tufting has reached a high degree of specialization, utilizing a variety of patterning devices, many of which are computer-controlled. Stepping, or zigzag moving, needle bars, and individually controlled needles greatly expand patterning possibilities. Such patterned carpet is frequently referred to as a graphics pattern. Other advanced tufting techniques are loop over loop and loop over cut (LOC) machines

After completion of tufting, the unbacked tufted carpet is dyed (if precolored yarns were not used) then followed by a finishing step to add an adhesive compound backing and, usually, a secondary backing material.

Tufted carpet styles range from loop, cut pile, and combinations of both in solids, tweeds, stripes, and patterns from the most simple to the exotic and complex. The designer has an endless variety of carpet choices due to advances in tufting–technology, coloration options, and finishing techniques.

WEAVING

While there are several methods of weaving and several types of looms, there are basic similarities to all. In general, woven carpet is formed by the interweaving of warp and weft yarns. The warp yarns are wound from parallel or heavy beams that unwind slowly as weaving progresses. Two main types of warp yarns form the carpet back: chain and stuffer. Chain yarns provide structure and stability while stuffer warp yarns increase bulk and stiffness of the fabric. The face yarns of woven carpet are also pre-dyed warp yarns that are normally fed into the loom from a yarn creel.

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The warp yarns run through a heddle, a series of vertical wires, each having an eye in the center through which the yarn is threaded. The heddle controls the action of the warp yarns. The wires are  mounted on two frames that rise alternately to form a space or shed.

The face of the carpet is formed with warp yarns moving into the loom from yarn creels. These pile yarns are looped over wires that lie at right angles to the warp yarns that are then bound with a yarn known as the weft, which is shot through the shed with a shuttle or other means. When a cut pile carpet is desired, wires with a knife blade at one end are used.

KNITTING

A carpet knitting machine, known as a double needle bar knitter, has a row arrangement of hundreds of latch needles that move in an up-and-down motion in conjunction with yarn guide bars. Yarn guide tubes are attached to a guide bar that passes the yarns between and about the needles, thus laying down the pile face yarns and weft backing yarns. Separate sets of guide bars control each of the yarns–knitting, backing and face yarns. Additional bars may be used for color and design variety.

Knitted carpet is used mainly for commercial loop construction and is sometimes referred to as woven interlock. It often is used in school applications.

NEEDLEPUNCHING

In the needle punching process, several webs of staple fibers are superimposed to create a thick, loose batting. The batting is then tacked, or lightly needled, to reduce its thickness before it is fed into the  machine. As the batting is fed into the machine, it passes between two plates. The stationary lower plate contains many holes, while the upper plate, or headboard, contains several rows of barbed needles. The batting passes between the plates and the headboard moves up and down, passing the barbed needles through the fibers. As the needles pass through the fibers, they carry fiber ends from the top of the batting to the bottom, and when they are withdrawn, vice versa. The needles are passed repeatedly through the batting as it moves through the machine to form the carpet.

Needlepunch carpet is used mainly for outdoor applications and may include uses like entrance mats, marine uses, wall coverings and automotive applications. Surface patterning creates a large number of design possibilities.

BONDING

Fusion bonded carpet is produced by implanting the pile yarn directly into a liquid polymer, usually PVC, which fastens it directly to the backing. This results in very little buried yarn compared to other processes. The yarns can be closely packed, producing very high densities suitable for high-use areas. This process is used most frequently to produce carpet to be cut into carpet tiles or modules. Fusion bonded carpet may be loop construction, but most often is a cut pile product, made by a two-back process, slicing apart two simultaneously made carpets that are mirror images.

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