Fiber Presses

The first industrial hardboard was developed by W. Mason in the mid-1920s he found that a mat of wet fiber pressed in a hot press would produce a self-bonded flat panel with good strength, durabiUty, and stabiUty. The product was patented in 1928, trademarked as Masonite, and commercial production began. Over time several other processes for producing hardboards have been developed from modifications of the original process. Brief descriptions of these processes foUow and a flow chart of the process is shown in Figure 5. 

The mats are moved along the line to the press loader. When the loader is filled and the press opens to remove the load of freshly pressed boards, the loader pushes the new boards into the unloader and deposits the load of mats on the press platens. The press closes as quickly as possible to the desired panel thickness. More pressure, as much as 4.8—6.9 MPa (700—1000 psi) is required to press high density dry-process hardboard, because the dry fiber exhibits much more resistance to compression and densification than wet fiber. Press temperatures are also higher, in the range of 220—246°C. No screens are used in the dry-process, but the moisture in the mats requires a breathe cycle during pressing to avoid blowing the boards apart at the end of the cycle. Because no screens are used, the products are called smooth-two-sides (S-2-S), in contrast to the wet-process boards, which have a screen pattern embossed into the back side and are known as smooth-one-side (S-l-S). 

Applications. Boron fibers are used as unidirectional reinforcement for epoxy composites in the form of preimpregnated tape. The material is used extensively, mostly in fixed and rotary wing military aircrafts for horizontal and vertical stabilizers, mdders, longerons, wing doublers, and rotors. They are also used in sporting goods. Another application is as reinforcement for metal matrix composites, in the form of an array of fibers pressed between metal foils, the metal being aluminum in most applications. 

Polymers themselves, cast into membranes, spinned into hollow fibers, pressed into sheets, or extruded into selected shapes and configurations, have been widely used as compartments for the generation and stabilization of... 

The coarse texture of the fibrous gas diffusion media can further amplify the contact stress exerted on the MEA. Figure 3 shows the relative size of a carbon fiber with respect to the typical thickness of the electrode and the electrolyte membrane. It can be seen that the diameter of the carbon fiber in the gas diffusion media is comparable to the thickness of the electrode. The rigid carbon fiber pressed onto the porous electrode layer can produce in-prints which can later become a stress-concentration and defect-initiation sites at the electrode-electrolyte interface. A microporous layer, if used, tends to smooth out the surface of the GDM and reduces fiber inprint. Thicker electrode layer also offers protection against fiber in-prints. 

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). 

Pumice is a natural porous ceramic. It is produced by volcano eruptions and the gas is trapped inside the solid as it rapidly cools. The matrix is mainly glass, but it can contain small crystals. Synthetic ceramic foam is illustrated in Eigure 15.15. Uses for ceramic foam are summarized in Table 15.3. One of the best-known applications for a porous ceramic is the space shuttle tile. An SEM image of such a tile is shown in Eigure 15.16. Notice that in this case, the ceramic consists mainly of fiber (pressed not woven), so the principle is the same as for ceramic (glass) fiber for house insulation. 

Figure 8. Ulustrutes wash water outlets on a fiber press.

Figure 15 summarizes a method to mount arrays of metallic nanostructures on the facets of optical fibers. Pressing down on a floating slab with the tip of an optical fiber submerges the slab, which wraps itself around the tip of the fiber upon withdrawal from the water-filled trough of the ultramicrotome. After allowing the water on the tip of the fiber to evaporate, exposure to an air plasma using a... 

---