Free coating

When pulling a thin sheet out of a Newtonian liquid at velocity V, a good approximation for the final thickness of the Uquid coating formed on the sheet hoc is given by 

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Hot Dip Tin Coating of Steel and Cast Iron. Hot dipping of tin [7440-31 -5] has been largely superseded by electrolytic coating techniques, especially for sheet. However, hot dipping can be the method of choice for complex and shaped parts. Very thin layers of tin are extensively used to passivate steel used for canned goods. Tin is essentially nontoxic, is nearly insoluble in almost all foods, and easily wets and completely covers steel with a pinhole-free coating. 

In reverse-roU coating, as in forward-roU coating, instabilities can form. However, it is possible to obtain defect-free coatings at high speed and sometimes increasing the speed can lead to a smooth coating when a ribbing condition is present. 

High Solids Costings. High soHds coatings resemble the technology of solvent-free coatings but the compositions contain ca 70% by volume of soHd resin and are modified by reactive diluents, low viscosity multifunctional resins, or backbone stmctures other than the bisphenol A moiety. 

Table 5-2 Corrosion rate and specific coating resistance r ° after a long exposure of steel pipe sections with damage-free coating.

Fig. 5-8 Total adhesion loss of a 500-/xm-thick coating of EP (liquid lacquer), 0.2 M NaCI, galvanostatic = -1.5 /tA nrr, 5 years at 25"C. Left coating with a pin pore loss of adhesion due to cathodic disbonding. Right pore-free coating loss of adhesion due to electro-osmotic transport of H O. In both cases the loose coating was removed at the end of the experiment.

Tank/soil potential measurements cannot be made on objects to be protected with very high coating resistances which are found in rare cases of defect-free coating, and particularly with resin coatings. Off potentials change relatively quickly with time, similar to the discharge of a capacitor, and show erroneous values that are too positive [8]. This is the case with coating resistances of 10 Q m. If there are defects, the resistance is clearly much lower. The advice in Section 3.3.2.2 is then applicable for potential measurement. 

PTFCE (or CTFC) can be applied as a porous-free coating where the highest corrosion resistance is required. 

Applications Electrodeposition of cationic paint resin on automobiles (connected to the cathode) provides a uniform, defect-free coating with high corrosion resistance, but carries with it about 50 percent excess paint that must be washed off. UF is used to maintain the paint concentration in the paint bath while generating a permeate that is used for washing. The spent wash is fed back into the paint path (Zeman et al., Microjiltration and UltrajUtration, Marcel Dekker, New York, 1996). 

Successful solvent-free chemical syntheses have been reported for a variety of small molecules, both with and without the use of microwave irradiation, and for some polymer preparations (Varma, 2000). Solvent-free coatings formulations have also been developed. 

As with cleaning, many researchers are looking toward solvent-free coatings as the answer to solvent replacement. 

An epoxy resin formulation completely free of organic solvent was applied to carbon steel coupons using supercritical carbon dioxide (CO2) as the volatile solvent. Sleet coupons coated in this manner were compared to coupons coated with a standard military specification marine primer (MlL-P-24441) during exposure to aerated 0.5 nrl sodium chloride (NaCl). The solvent-free coating protected the steel from corrosion in this environment as well, if not better than, the solvent-based primer (Kendig et al., 1999). 

Tallmadge, J. A. Lee, C. Y. Dynamic Meniscus Profiles in Free Coating III. Predictions Based on Two Dimensional Flow Fields. AIChE J. 1974, 20, 1079-1086. 

Kendig MW Buchheit RG, Corrosion inhibition of aluminum and aluminum alloys by soluble chromates, chromate coatings, and chromate-free coatings, Corrosion, 2003, 59, 379-400. 

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