Binder Preform

Fibres may be in the form of continuous strand mat or chopped strand mat with insoluble binder. Preforms may be used which are produced... 

The mixed Hquid is pumped into the area, where it cures and forms a slab. It may be poured in two layers to eliminate imperfections in the base. The first layer may be a preformed mbber slab which is glued to the base, or a mixture of reground mbber and binders or mbber and polyurethane. A textured surface maybe imparted to the second coat with sand or chips. 

AH forms and compositions of reinforcements, ie, mats, woven roving, glass, carbon, and aramid, are commonly used with these processes. Special continuous glass strand mats with a thermoplastic binder aHow preforms to be made using thermoforming techniques. These processes are used for tmck and autobody components, medical equipment cabinets, transportation seating, and other parts needed in the intermediate volume range (1,000—10,000 parts/yr). 

Small quantities of higher molecular weight resin in powder form are also manufactured. They are used in solution or emulsion form as binders for glass-fibre preforms and also for the manufacture of preimpregnated cloths. 

Preforms. Preformed shapes may be made by depositing glass fibres on to a preform mould. The fibres are then held together by spraying them with a binder. 

Chemical engineers could also work to devise processes to improve the flow characteristics of powders after they are formed. Such research would help control agglomeration of particles in subsequent processing steps as well as facilitate the production of compacted ceramic preforms. For example, gas-solid chemical reactions might be used to tailor the chemical composition of powders. As another example, better methods of componnding powders with binders might be achieved by processes that mix powders with suitable binders in a liquid and then spray dry the resulting suspension. 

The majority of work done on VGCF reinforced composites has been carbon/carbon (CC) composites [20-26], These composites were made by densifying VGCF preforms using chemical vapor infiltration techniques and/or pitch infiltration techniques. Preforms were typically prepared using furfuryl alcohol as the binder. Composites thus made have either uni-directional (ID) fiber reinforcement or two-directional, orthogonal (0/90) fiber reinforcement (2D). Composite specimens were heated at a temperature near 3000 °C before characterization. Effects of fiber volume fraction, composite density, and densification method on composite thermal conductivity were addressed. The results of these investigations are summarized below. 

Whiskers can be incorporated into the metallic matrix using a number of compositeprocessing techniques. Melt infiltration is a common technique used for the production of SiC whisker-aluminum matrix MMCs. In one version of the infiltration technique, the whiskers are blended with binders to form a thick slurry, which is poured into a cavity and vacuum-molded to form a pre-impregnation body, or pre-preg, of the desired shape. The cured slurry is then fired at elevated temperature to remove moisture and binders. After firing, the preform consists of a partially bonded collection of interlocked whiskers that have a very open structure that is ideal for molten metal penetration. The whisker preform is heated to promote easy metal flow, or infiltration, which is usually performed at low pressures. The infiltration process can be done in air, but is usually performed in vacuum. 

The reinforcements amenable to RTM are similar to those used for pultrusion, except that they need not be continuous in nature. Thus, E-glass, S-glass, aramid, and carbon fibers are commonly used, as are discontinuous filaments such as wood fiber and polyesters. Even metal and ceramic fibers can be used in this technique. In one method, the preform is fabricated by spraying 12- to 75-mm-long chopped fiber rovings onto a preshaped screen. A binder sprayed with the fibers keeps them in place and holds the preform shape, which is then placed in the mold. 

Figure 12.4 Compaction behavior of a woven carbon fiber fabric. The solid curve shows the behavior at room temperature the other two lines show the behavior at 100 C and 110°C. The fabric was factory treated with an epoxy preform binder...

Maucovrt, J., and Combette, C. (1988) Preformed inhibition based on rubber gum for a composite propellant with a PU binder. Eur. Pat. Appl. EP, 254618 Chem. Abstr., (1988) 108, 134462j. 

Preform. A metal screen is made in the shape of the final product. Glass fiber is chopped 2 in. long and sprayed uniformly all over the shaped screen, using vacuum on the back side of the screen to assist the process. A small amount of binder, typically 5 percent of polymer in latex form, is sprayed onto the fiber to hold its shape. It is then removed from the screen, placed in the mold, saturated with an equal weight of liquid resin, and the mold is pressed at 1380 kPa (200 psi) and heated until cured, typically 3-15 min. This early process has been largely replaced by SMC. 

The rovings in a plenum chamber are fed into a cutter and after being cut to the desired lengths, fall either into a plenum chamber or perforated screen where the air is exhausted from under the screen. A plastic binder of usually up to 5wt% is applied and is later cured. As the glass falls into the plenum chamber, the air flow pattern and baffles inside the screen control its distribution. Preform screen rotates and sometimes is tilted to ensure maximizing uniform deposits of the roving. 

There is a possible reduction in the mechanical properties of the structures due to binders or tackifiers in preforming fabrics. 

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