Flexible Cell Cover

Apart from the above three types there are custom built rubber products such as expansion joints, flexible cell covers and large size rubber foils for the caustic soda industry, and many inflatables, fabric reinforced products and thick moulded sheets for specialty applications in certain process plants. These are all hand formed in aluminium or cast iron moulds or forms by laying up process and then cured in autoclave. Here the flow of the un-vulcanized rubber during cure is not very important as the shape is already formed rather the green strength and the stiffness of rubber stock with a low scorch time are the important requisites. A rubber expansion joint made by a hand layup method and cured in autoclave is shown in the following figure 14.1. 

The ozone concentration in the atmosphere is only a few pphm. In certain chemical plants as in electrolytic mercury cell houses in the chloralkali industry, the ozone concentration is higher. Although the atmospheric ozone level is low, it reacts with rubber double bonds rapidly and causes cracking of rubber products. Especially when rubber is under stress (stretching and bending as in the case of flexible cell covers), the crack development is faster. Neoprene products resist thousands of parts per hundred million of ozone for hours without surface cracking. This nature of neoprene is quite suitable for cell house application in chlor-alkali industries. Natural rubber will crack within minutes when subjected to ozone concentration of only 50 pphm. 

The electrolyser consists of a rectangular trough with a cover on top connected at both ends to the end boxes. The box at the mercury inlet is called the inlet box, and the other is the outlet box. The trough is of mild steel construction with ebonite lined bottom and sides. The covers are of mild steel construction with ebonite lining on the inside surface or only of rubber sheets called flexible cell covers. The covers have holes for fixing anodes. 

Flexible Cell Covers in the Caustic Soda Industry... 

When anticipated, flexing is of constant amplitude, extension modulus should be kept as low as possible in products like flexible cell covers and hoses in caustic soda industries. Another important factor is the degree of cure. Prolonged vulcanisation cycles will degrade thermally susceptible rubbers. 

FIGURE 5-3 Variation in biomembranes in different cell types, (a) A smooth, flexible membrane covers the surface of the discoid erythrocyte cell, (b) Tufts of cilia (Cl) project from the ependymal cells that line the brain ventricles, (c) Many nerve axons are enveloped in a myelin sheath composed of multiple layers of modified plasma membrane. The individual myelin layers can be seen in this electron micrograph of a cross section of an axon (AX). The myelin sheath is formed by an adjacent supportive (glial) cell (SC). [Parts (a) and (b) from R. G. Kessel and R. H. Kardon, 1979, Tissues and Organs A Text-Atlas oT Scanning Electron Microscopy, W. H. Freeman and Company. Part (c) from P C. Cross and K. L. Mercer, 1993, Cell and Tissue Ultrastructure A Functional Perspective, W. FI. Freeman and Company, p. 137]... 

FIGURE 5.8. Cross section of the DeNora mercury cell [71]. (a) Cell base (steel) (b) Side wall (rubber-lined steel) (c) Lifting gear (d) Transverse support (e) Lengthwise support (f) Anode carrier (g) Anode rod (h) Anode surface (i) Adjustment motor (k) Bus bar G) Flexible anode current strap (m) Multilayer cell cover (n) Service walkway (o) Intercell bus bar (p) Switch (q) Insulator (r) Switch drive (s) Support. (With permission from John Wiley Sons, Inc.)... 

Copper or aluminum bus bars carry the electric current to the cell covers, and then by flexible copper straps to the anode rods. The short-circuiting switches are located beneath the cells and when the cell is short-circuited, the cell bottom also acts as a current conductor. A vertical amalgam decomposer is located at the end of each cell. 

Extracellular matrix The surfaces of animal cells are covered with a flexible and sticky layer of complex carbohydrates, proteins, and lipids. This complex coating is cell-specific, serves in cell-cell recognition and communication, creates cell adhesion, and provides a protective outer layer. 

Risk analysis has been proven to retain the flexibility necessary to make it a useful model system for addressing the countless issues that are found to be associated with plant-derived pharmaceuticals (Wolt and Peterson, 2000). Over the past few years, a great deal of information and experience has steadily accumulated with respect to risk analysis of pharmaceuticals that are currently produced in bacterial and aifimal cell bioreactor systems. Risk analysis has also been performed on transgenic crops used for food production as well as for other applications. As a result, elements from each of these disciplines can be incorporated into the design of optimal production and testing policies and practices. Risk analysis has been employed to cover a series of important issues regarding the large-scale manufacture of plant-made biopharmaceuticals, and will continue to present serious issues for researchers in the academic, corporate, and public health arenas to address (Miele, 1997 Ciliberti and Molinelli, 2005). 

In cell houses, cracks can be visually seen on the upper neoprene surface of the flexible covers which are subjected to stress at a temperature of 80°C, during eighteen to twenty four months of operation, necessitating mandatory replacement of the covers. Ozone reacts with double bonds so rapidly that it has no chance to diffuse into the rubber and therefore all action is at the surface. Thus it implies surface protective agents are most useful against ozone attack. For example, waxes that bloom to the surface of rubber to form an inert film are used effectively for static protection. 

Catalyst is added to the solution of gelling agents and buffer and the mixture is poured into the cell, using a small funnel inserted into a length of flexible tubing projecting between the plates. The cell is filled to about 3 cm from the top. The slot former is then inserted to a depth of 4 cm from the top. After 0.5 hr, the top of the gel is covered with buffer and the slot former is carefully with-... 

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