felt

felt, a class of fabrics or fibrous structures obtained through the interlocking of wool, fur, or some hair fibres under conditions of heat, moisture, and friction. Other fibres will not felt alone but can be mixed with wool, which acts as a carrier. Several industries manufacture goods through the use of these properties. The goods produced include wool felt in rolls and sheets; hats, both fur and wool; and woven felts, ranging from thin billiard tablecloths to heavy industrial fabrics used for dewatering in the manufacture of paper.

Nonwoven felts are considered to be the first textile goods produced and many references may be found to it and its uses in the histories of ancient civilizations. The nomadic tribes of north central Asia still produce felts for clothing and shelter, utilizing the methods handed down from antiquity.

Wool felts of the “true” or nonthread structure class are produced as both rolls and sheets. Roll felts are made in thicknesses from 1/16 to 1 1/2 inches (1.6 to 38 mm) and up to 80 inches (2 metres) wide and 60 yards (55 metres) long. Sheet felts are produced up to 4 inches (10 cm) thick and usually as 36 inch (91 cm) squares but other rectangular sizes as well as ovals and circles are made. Wool felts of better grades are made of all wool but the felting power of wool is such that as little as 10 percent wool in a blend with nonfelting fibres is sufficient to produce a felt.

The wool fibres selected for felting are usually less than 1 1/2 inches (38 mm) in length and must be of good felting quality and strength. The fibres are scoured, treated to remove tar, paint, and vegetable matter such as burrs, and then opened and blended to form a batch. The prepared blend is fed to a carding machine, which further opens, blends and combs the fibres into a web of single fibre thickness that is laid down on an endless apron to form a batt. In most roll felt manufacture two or more cards are set at right angles to each other so that the web from at least one is laid down at right angles to the others to produce “cross” in the batt and dimensional stability in the finished felt.

The carded batts are produced to predetermined weights, after which one or more batts, but usually several to a felt, are laid on a hardening machine and sprayed with water. Hardening consists of drawing the moistened laid-up batts between aprons across a steam chamber. Steam is forced into the batts to activate the fibres, after which the steamed section is drawn beneath a heavy heated platen. The platen is lowered onto the moist, hot batt and is agitated in a horizontal plane. The heat, moisture, and friction is sufficient to felt and interlock the fibres from the individual batts into a unified mass. After a requisite time the platen is raised, the hardened section drawn forward, and the next area, which has been steamed meanwhile, is subjected to the action of the platen. This operation is plate hardening; a similar operation done on a continuous basis between rollers is called roller hardening.

After the hardening operation, the lightly felted piece is rolled and allowed to cool and drain. Only the thickness of the batts is affected by hardening, whereas area shrinkage or felting up to as much as 50 percent is accomplished in the next operation known as fulling. The hardened batt is passed through a fulling aid, usually a solution of soap or acid, although occasionally warm water will suffice, and is rolled up and placed in the fulling mill. One type of fulling mill consists of a binlike receptacle with a concave front, straight sides, and a back that consists of one or more movable hammers that pound, turn, and shrink the goods to the desired dimensions. The scouring, dyeing, treating, and finishing operations that follow are done much as for the production of woolen cloths. Sheet felts follow much the same process except that after carding the batts are cut up and plied to specified sizes and weights and then hardened, fulled, and washed as individual sheets. Maximum dimensional stability, density, and strength are obtained in the sheet felt process.

The uses of felt are myriad. Some of the more important include wicking, absorption, vibration isolation, insulation, padding and packaging, polishing, sealing and gasketing, as well as apparel and decorative fields. Most felts are made to close specification requirements, particularly for mechanical and industrial applications where high standards of quality, reproduction, and tolerances are constantly met. Hair felts, widely used in polishing operations, are made much as described above for sheet felts and are an important specialty item to the wool felt industry.

Hat felts are made of both wool and fur. Wool hats are made much as already described for wool felts except that a narrow web is taken from the card and is collected on an egg-shaped mandrel. Two cone-shaped pieces are obtained from this starting shape by further felting operations from which the finished hat bodies are shaped and formed. Beaver, hare, and rabbit furs are among the fibres used in fur felt hats and all of these must first be treated with strong chemicals such as mercury. This operation, known as carroting, provides the fibres with optimum felting power. The release of mercury fumes during the felting process led to an especially high rate of mercury poisoning within people working in the industry.

In the manufacture of fur felt hats a blend of furs is laid on a rotating perforated cone surface with a wet cloth and with a vacuum pulling from within. The fur collects and is removed as a fragile cone shape. After many wet finishing operations, including dyeing, the felted cone is molded to a rough hat shape. Many more dry finishing operations are required to reduce the rough hat to the finished article.

The manufacture of woven felts follows to a large degree the conventional woolen cloth practice. Wools of selected fineness, length, and felting property are scoured, blended, combed, and spun into yarns. The yarns are woven into the rough cloth structure required depending upon the type of end goods planned. The rough cloth is soaped and fulled or milled in the fulling mill where felting or shrinkage is carefully controlled to preset dimensions after which scouring, dyeing (in the case of some of the lighter cloths), and other textile finishing operations follow.

Some special felts for the papermaking trade are made as endless belts 200 inches (5 metres) or more in width. Highly skilled operators hand weave or join the ends to produce the endless belt so that no joint or seam is discernible. Special machines are used to make this class of woven felts since the goods must be run as belts and therefore have to be loaded and unloaded from the side of the machines rather than from the front or back as is conventional.