Needle felts

A needled felt, on the other hand, is a fabric composed of natural, synthetic, or a combination of natural and synthetic fibers physically interlocked by the action of a needle loom with or without combination of other textile fabrics and with or without suitable combination of mechanical work, chemical action, moisture, and heat, but without weaving, knitting, stitching, thermal bonding, or adhesives (16). 

Two principal types of fabric are adaptable to filter use woven fabrics, which are used in shaker and reverse-flow filters and felts, which are used in reverse-pulse filters. The felts made from synthetic fibers are needle felts (i.e., felted on a needle loom) and are normally rein-... 

Polypropylene fibers are used for face pile of needle felt, tufted carpets, upholstery fabrics, etc. 

South roof 0.15 mm single layer transparent polyethylene (south roof was covered with 10 mm needled felt heat blanket at winter nights) 510... 

Two principal types of fabric are adaptable to filter use woven fabrics, which are used in shaker and reverse-flow filters and felts, which are used in reverse-pulse filters. The felts made from synthetic fibers are needle felts (i.e., felted on a needle loom) and are normally reinforced with a woven insert. The physical properties and air permeabilities of some typical woven and felt filter fabrics are presented in Tables 17-6 and 17-7. The air permeability of a filter fabric is defined as the flow rate of air in cubic feet per minute (at 70°F, 1 atm) that will pass through 1 ft2 of clean fabric under an applied differential pressure of Vt in water. The resistance coefficient KF of the clean fabric is defined by the equation in Table 17-6, which may be used to calculate the value of KF from the air permeability. If Ap, is taken as 0.5 in water, t as 0.0181 cP (the viscosity of air at 70°F and 1 atm), and Vj as the air permeability, then //, = 27.8/air permeability. 

Antistatic agents for carpet backing gives a complete antistatic carpet in combination with conductive pile material can be used in adhesives for secondary backing also, compatible with binders for needle felts. 

Lenzing P84. [Lenzing AG] Aromatic polyimide high performance thermoplastic used fin prod, of needle felts for high temp, filtration, as reinforcement for FIFE, as competing, ingred. for inj. moldable polymers. ... 

Needled felt media (Fig. 10.48b) consists of intertwined short fibers, pressed together, and mechanically fixed with a needle punch machine. The efficiency of such filter media varies with its density, composition, and relative thickness. Needled felt media is strong and durable, but, for maximum filtering efficiency requires the build-up of a dust layer (see below). 

Bayer SBR Latex. [Bayer] Styrene-butadiene latex to blended latex goods, p r imptegnatitm, carpet backing, needle felt rdnforcement binder. 

The many uses of SB copolymer dispersions in the textile sector include tufting, textile, and carpet coatings needle felt and card web reinforcement textile finishes and impregnation. 

Two types of commercial C/C composites were used in this study a two directional randomly chopped pitch fiber reinforced composite with charred resin/CVI matrix (CC-A21) and a three directional composite with needled felt ex-PAN fibers and CVl matrix (CC-D21). The C/C composites were kindly provided by Honeywell Aircraft Landing Systems. The as-received densified C/C composite samples were heat-treated at 2100°C in a graphitization furnace (Model TP-4X10-G-G-D64A-A-27, Centorr Associates Inc) with protective argon atmosphere. 

Reinforcement chopped liber needled felt balanced 8HS fabric 3 1, 5HS fabric Anie interlock needled fabric... 

Some of the dust collection techniques employed do not employ textile filter media e.g. settling chambers, electrostatic precipitators, cyclones and wet scrubbing devices, and whilst these are mentioned here for completeness, for the remainder of this section it is intended to concentrate solely on dust collectors that engage textile filter media comprising woven or (mainly) needle felt constructions. 

Where the filter medium is in the form of a needle felt (as found in pulse-jet collectors), some manufacturers have offset the deficiencies found in some of the above fibres by producing composite structures, e.g. polyar-amid, polyimide or PPS fibres on the surface of the felt with a PTFE scrim or base-cloth providing a framework of support. Although under certain physicochemical conditions the surface fibres become degraded, it has been found that the skeleton of support provided by the PTFE base-cloth is often sufficient to enable satisfactory performance to continue. 

The linear densities of the fibres that are used in needle felt constructions are usually in the range 1.66-3.33 decitex. In many cases, such fibres will be blended, typically in ratios of 50/50 or 66/34 the greater the proportion of finer fibres, the greater the fibre surface area and thus the more efficient the final structure. For example, it can be shown that the specific surface area of 1 kg of 3.33 decitex polyester fibre is 166 m, whereas for the same weight of 1.66 decitex fibre, the surface area is 234 m. For this reason, in recent times the use of micro-denier fibres (typically < 1 decitex or < 10 pm) has found favour where fine dusts are collected, ensuring a much greater surface filtration area and therefore less dust penetration into the body of the felt. However, as productivity rates are much slower with these fibres (they... 

Whilst needle felts are produced to countless specifications in order to address the nature, volume and velocity of the dust being collected, the type of filter employed, to meet a standard test requirement or an equipment manufacturer s specification, their area densities will generally fall between 340 and 640 gm the greater the dust load and intensity of cleaning, the greater is the area density. 

The calendering process also increases the density of the fabric (especially needle felts) the pore size is reduced and dust penetration into the body of the needle felt thus restricted. In practice, the polymer type largely dictates the surface temperature of the heated bowl whilst the pressure, which may be up to 300 da N m and speed are adjusted to achieve the desired density and air permeability. 

In depth filtration (see Fig. 7.8c), as the suspension passes through the filter, assisted either by gravity or pressure, particles are again captured within the body of the medium, even though the majority may be small enough to pass through. On this occasion, particle capture is largely attributed to attraction by electrical or attractive van der Waal s forces, or by (mutual) attraction to particles already deposited. Whilst this mechanism can be applied to fabrics such as needle felts, it is more normally assodated with deep-bed sand filters. 

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