Mechanical Foam

Cleaning is frequently aided mechanically. Foam balls scour the center of tubes, and hoUow-filter systems can be back-flushed. HoUow fibers and membranes attached to rigid supports can be back-pressured, thereby eliminating the pressure drop that holds redispersed films on the membrane surface. 

Mechanically foamed plastic Cellular plastic whose structure is fabricated by physically incorporated gases. 

The two other foam sensors mentioned above are ultrasound and rotating disks. The ultrasound sensor is a transmitter and receiver mounted opposite to each other and operating at 25—40 kHz. In the bioreactor, the waves are absorbed by the foam and the signal is generated. The rotational disk foam sensor is a mechanical foam breaker which is used by increasing the rotational resistance. 

Goldberg, M. and Rubin, E. Ind. Eng. Chem. Process Design and Development 6 (1967) 195-200. Mechanical foam breaking. 

Until 1920, the only flexible foam available was the natural sponge, but chemically foamed rubber and mechanically foamed rubber latex were introduced before World War II. These foams may consist of discrete unit cells (unicellular, closed cell), or they may be composed of interconnecting cells (multicellular, open cells) depending on the viscosity of the system at the time the blowing agent is introduced. Over 1.5 million tons of foamed plastic is produced annually in the United States. 

Zlokarnik M. Design and scale-up of mechanical foam breakers. Ger Chem Eng 1986 9 314-320. 

Foam A sudslike extinguishing agent formed by mixing a foam-producing compound with water. Mechanical foam is produced by agitation, chemical foam is produced when two or more chemicals react. 

Foam Generators Devices for mixing chemical or mechanical foam in proper proportion with a stream of water to produce foam. 

Air mechanical foam is the most universal fire extinguisher in silicone production. The introduction of 20-30% (weight) of urea into the solution of foaming agent improves its performance and neutralising characteristics. 

Hydrideorganosilanes should be extinguished with air mechanical foam and in some cases with sprayed water (the intensity of water supply from the top should be limited). 

A number of factors contribute to the effectiveness of foam as a vapor-suppressant. These include the type of foam, its expansion ratio, its drainage time, the rate of application of the foam (gal per min/ft2), and its application density (gal/ft2). Chemical foams have become obsolete, with mechanical foams now being used worldwide. A mechanical foam that has recognized attributes for vapor suppression is aqueous film-forming foam (AFFF). It is a synthetic foam (as compared to protein foams) with a surfactant that is part fluorochemical and part hydrocarbon. It suppresses vapors by forming an aqueous film produced by draining its foam bubbles. 

It has already been pointed out that experiments in differently scaled models are inevitable if physical properties cannot be changed and therefore one has to use the same material system (Example 8 Mechanical foam breaker, section 6.1). The same is true if the acceleration due to gravity is influencing the process under investigation. However, as we all know, gravity cannot be varied on Earth (Example Surface aeration, section 10.3.2). 

Zlokarnik, M., Ger. Chem. Eng. 9 (1986), 314-320 Design and Scale-up of Mechanical Foam Breakers... 

On the other hand, some substances, even in minute concentrations, promote coalescence. Some of the non-ionic surfactants often used as antifoaming agents are so effective that a concentration of 3 ppm is sufficient to halve the kLaL of pure water (Zlokarnik, 1979). Clearly the use of surfactants for foam prevention should be avoided whenever possible, and an efficient mechanical foam breaker should be used (Zlokarnik, 1986). 

In the foam process, a concentrated solution of the finishing chemicals compounded with suitable foaming agents and, If necessary, foam stabilizers Is mechanically foamed so as to Incorporate by volume 50 to 95% air, This foam, having an appearance quite similar to shaving cream, Is applied to the fabric. The foam-coated fabric Is then subjected to a mechanical pressure which collapses the foam. The fabric Is then dried and cured In the conventional manner. 

In continuous foam finishing, a concentrated solution containing the finishing chemicals and a suitable foaming System Is mechanically foamed and the precise quantity of foam Is applied to the fabric. 

The mechanical foaming of PVC pastes has been carried out for some time on the basis of air or gas being whisked into specially formulated plastisols, which are cured using microwave or infrared ovens. The lightweight material is used for sound deadening or domestic applications. There has been a relationship established between the effects of residual emulsifier in the E-PVC resin grade and foaming behaviour (101). 

The presence of surfactants make possible the mechanical foaming of poly(vinyl chloride) (PVC) pastes, which... 

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