Foam Stops

Rigid poly(vinyl chloride) (PVC) foam has commonly been used to make foam stops for windows. However, this foam type may be relatively expensive, and it may not provide the desired physical characteristics. 

ABS foam compositions have been developed that contain about 10 parts of a foam modifier and 0.5-2.0 parts of a blowing agent. Sodium bicarbonate is a suitable blowing agent. The foaming modifier is preferably adapted to decrease the foam density and to increase the foam swell of the composition (82). In particular, the foam modifier consists of SAN. The ingredients are admixed and then extruded. Articles with a specific gravity of 0.3-0.47 gem-3 are obtained. 

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The final density was predicted from Eq. (9.37) assuming that all the initial blowing agent evaporates and expands up to T = 355 K (experimental temperature at which the foam stops rising). The predicted value was Ptheor = 145 kg m 3, while the experimental value was pexp = 128 kg m 3. 

Silicone foam thus formed has an open ceU stmcture and is a relatively poor insulating material. Cell size can be controlled by the selection of fillers, which serve as bubble nucleating sites. The addition of quartz as a filler gready improves the flame retardancy of the foam char yields of >65% can be achieved. Because of its excellent dammabiUty characteristics, siUcone foam is used in building and constmction fire-stop systems and as pipe insulation in power plants. Typical physical properties of siUcone foam are Hsted in Table 10. 

The foam and froth in the bearing oil, increases the volume and artificially raises the oil level, which leaks through the seals. When enough has leaked to stop foaming, the air bubbles leave the oil resulting in inadequate oil levels. Too much friction heat and failure is the result. 

When heat stable salt buildup becomes a problem a variety of options may manage it. These include partial or total solution replacement, heat stable salt removal, or adding caustic to neutralize the heat stable salts. Many operators choose caustic addition because it is perceived to be a more economical way to stop corrosion and subsequent foaming and loss problems. 

Another unorthodox application is to form a U-F foam on airport runways to act as an arrester bed to stop aircraft that overshoot during emergency landings or abortive take-offs. 

Fire Hazards - Flash Point (deg. F) 20 CC Flammable Limits in Air (%) 2.8 - 14.4 Fire Extinguishing Agents Stop flow of gas. Use water spray, carbon dioxide, or dry chemical for fires in water solutions Fire Extinguishing Agents Not to be Used Do not use foam Special Hazards of Combustion Products Vapors are eye, skin and respiratory irritants Behavior in Fire Not pertinent Ignition Temperature (deg. F) 756 Electrical Hazard Data not available Burning Rate 4.5 mm/min. 

A chemical treatment added to prevent the possibility of foaming occurring in the boiler and reduce the risk of BW carryover. Commonly also known as a defoamer, although this type of treatment is designed to stop foaming after it has already occurred and may involve different chemistries. 

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