Pressure/vacuum reinforcement

Hose specifications need to be based upon a number of requirements. Some hose criteria include size, delivery temperature, maximum pressure, chemical properties of the fluid, hose material, and end fittings. The major components of a chemical hose are the end fittings, an inner core, pressure/vacuum reinforcement, and the protective outer cover. The exact selection of hoses is beyond the scope of this text. [11]... 

Variations on this basic process are (i) vacuum bag moulding and (ii) pressure bag moulding. In the former process a flexible bag (frequently rubber) is clamped over the lay-up in the mould and a vacuum is applied between the moulding and the bag. This sucks the bag on to the moulding to consolidate the layers of reinforcement and resin. It also squeezes out trapped air and excess resin. The latter process is similar in principle except that pressure is applied above the bag instead of a vacuum below it. The techniques are illustrated in Fig. 4.67(b) and (c). 

In this process, resin is injected into a closed mold containing the reinforcement preform. The resin can be injected either under pressure [22] or under vacuum [23]. The potential advantages of this process are (I) low mold cost, (2) inserts can be incorporated, (3) low pressure requirements, (4) accurate fiber orientation, (5) automation possibilities, and (6) versatility. The resin formulation and process variables are selected so that no significant polymerization occurs until the mold cavity has been completely filled. This is achieved by the ad-... 

Resin transfer molding With vacuum assisted RTM, this process can be called infusion molding. RTM usually uses liquid TS plastics that is transferred or injected into an enclosed mold usually at low pressures of about 60 psi (410 kPa) in which reinforcement... 

General Motors has also been experimenting with H2/02 fuel cells to power an Opel Zafira minivan in which the H2 is supplied directly, stored either in ultrahigh-pressure tanks or at a very low temperature as a liquid. For liquid H2 storage GM has developed a double-walled, vacuum-insulated steel tank that holds about 10 lb of H2(l) at —435°F, good for about a 250-mile range. Alternatively, the H2 can be stored as a gas in two carbon-fiber-reinforced, 10,000-psi tanks that hold a total... 

Vacuum degassing of the mix tanks is required when fiberglass reinforcement is used as its incorporation tends to carry large volumes of gas into the mix. Following degassing, the dissolved nitrogen in the tank is adjusted by control of nitrogen pressure. 

The liquid resin is then injected into the mould, typically from the bottom mould, assisted by pressure and vacuum to aid in providing an even resin distribution and achieving the removal of voids. A key processing consideration here is that the resin flow should match the wetting out and impregnation of the reinforcement. 

Spray and Baked Dispersion Electrostatic spray FEP (10 mils), PFA (10 0 mils and up to 80 mils when reinforced or filled) PVDF (20-40 mils and up to 90 mils when reinforced with carbon cloth) ETFE (up to 50 mils), FEP (10 mils), PFA (25 0 mils) ECTFE (35-90 mils), PVDF (35 0 mils) Primer and multicoated conventional spray equip Each coat baked Shop only Primer and multicoated Each coat baked Shop only Pressure OK Vacuum OK Pressure OK Vacuum OK 12xl2x 37 12 Visual Spark Visual Spark By hot patching Testing recommended By hot patching Testing recommended... 

Stirring bar are filled into part/I of the vessel, and the whole apparatus is carefully evacuated on a suitable vacuum line with a crude manometer ranging from 0 to 1000 torr. Anhydrous sulfur dioxide is dried by storing it over phosphorus pentoxide in a metal or reinforced glass cylinder with Teflon valve. The approximate amount of SOj is condensed into the flask at -78° (Dry Ice/acetone) by closing the vacuum line to the pump and opening the storage tank. The total pressure should not exceed 300 torr. 

Bag Molding Bag molding is essentially an extension of the lay-up process. The lay-up structure is covered by a flexible airtight bag and either an external pressure is applied or vacuum is created inside the bag-mold enclosure. This improves the properties of the resultant composite by driving out volatile substances and increasing the volume fraction of reinforcement. 

In vacuum-bag molding the reinforcement and the resin mixed with catalyst are placed in a mold, as in the hand layup method, and an airtight flexible bag (frequently rubber) is place over it. As air is exhausted from the bag, atmospheric air forces the bag against the mold (Figure 2.46). The resin and reinforcement mix now takes the contours of the mold. If the bag is placed in an autoclave or pressure chamber, higher pressure can be obtained on the surface. After the resin hardens, the vacuum is destroyed, the bag opened and removed, and the molded part obtained. The technique has been used to make automobile body, aircraft component, and prototype molds. 

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