Dewatering by compression

When making a large article such as a mattress, a metal mold may be filled with the foamed latex and heated by steam at atmospheric pressure. After removing the foamed rubber article from the mold, it may be dewatered by compressing it between rolls or by centrifuging and by drying with hot air in a tunnel dryer. In foamed rubber formulation a part of the NR latex can be replaced by a synthetic rubber latex. One such combination is shown in Table 2.3. 

In dewatering by mechanical compression, the prerequisite compressibiHty of the cake is usually expressed by an empirical exponential equation which relates cake voidage to appHed pressure. 

Another feature of salt-marsh peat restricting its buoyant response is the interconnectedness of the bulk material Peat near the surface is not isolated, but is enmeshed by its roots into a semiinfinite layer of peat some tens of centimeters thick. The buoyant-peat model predicts that if periodic recharge of this perched-water table was prevented, then substantial dewatering and compression would occur. As it turns out, this experiment has already taken place Diking of salt marshes was one of the means used in the past to reclaim them for agricultural purposes, and following that treatment the marshes were reported to have shrunk considerably, in some cases as much as 3 feet (Smith, 1907). 

In dewatering by mechanical compression, the necesary prerequisite is the compressibility of the cake and this is usually expressed by one of two widely used empirical equations which relate average cake porosity av to the final applied pressure across the cake Apc ... 

The purpose of the press section is to increase the dry content of the paper web as much as possible by compression. This kind of mechanical dewatering reduces steam consumption in the dryer section and increases the strength of the web in order to avoid web breaks during production. 

A 10-mile section of hne was being dewatered following a hydrostatic test. A foam pig driven by compressed air was used to displace the water. The water was being removed from a 12" bypass hne. 

The main development of the filter press from the simpler versions just described has been to include an impervious elastomeric sheet in each plate compartment (one for each plate on the feed side of the filter medium, butting up against the corresponding sheet of the next plate). These flexible sheets can be inflated pneumatically so as to press down on the drained cake, once filtration is complete, and so dewater it by compression. This type of filter press is then known as the diaphragm filter press (as shown in Figure 3.72). (Initially this sheet was referred to as a membrane, and the term membrane filter press became quite confusingly well-known. 

Cake Dewatering. Dewatering (qv), identified as a separate entity in filtration, is used to reduce the moisture content of filter cakes either by mechanical compression or by air displacement under vacuum pressure or drainage in a gravitational or centrifugal system. Dewatering of cakes is enhanced by addition of dewatering aids to the suspensions in the form of surfactants that reduce surface tension. 

Some horizontal belt vacuum filter designs incorporate a final compression stage for maximum mechanical dewatering. This is achieved by another compression belt which presses down on the cake formed in the preceding conventional filtration stage. 

EUtration can be foUowed by dewatering, washing, and drying. In some appHcations, compression roUs or belts are used to close possible cracks in... 

Theoretical studies (30) comparing the abihty to dewater compressible sohds by sedimenting and filtering centrifuges to pressure filters, have shown that at high G levels, scroU decanters produce drier cakes than pressure filtration. 

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