Thermal paint removal

Fluidized-Bed Method. The fluidized bed consists of inert, finely granular, inorganic material (usually alumina) that is fluidized by injecting compressed air through 

Salt Bath Method. The object from which the paint is to be removed is immersed in a salt melt heated to 300-500 C. The short time required for paint removal (30-120 s) is the result of the spontaneous heat transfer and high oxidation potential of the salt melt (e.g., alkali nitrates). 

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Cold Paint Removal. Up to a few years ago, cold paint removal based on the use of dichloromethane [75-09-2] (methylene chloride) was the most widely used paint removal method. Use of this method is declining in favor of chemical or thermal methods due to concern about the environmental and occupational safety of halo-genated hydrocarbons. 

The mechanical methods and low-temperature paint removal are restricted to a few special areas of application. Chemical and thermal methods have their specific advantages and disadvantages, not only as regards paint removal but also with respect to environmental pollution by paint slurry, rinse water, effluent, and waste air. 

A time to reach blister temperature for paint removal was used to determine the relative speed of paint removal. In each case, the paint consisted of an alkyd resin binder on painted metal and wood surfaces. A calibrated thermocouple attached to a unit with a digital temperature scale was placed directly on the surface, and the temperature was recorded when the paint blistered Table 11.12 lists the results. This test showed that a metal substrate requires more cleaning time (+5-72 sec) and a higher temperature (+77-82 °F (+22-28 °C)) than less thermally conductive substrate, such as wood. 

Internal and external surfaces to be thermally cut or welded shall be cleaned to remove paint, oil, rust, scale, grease, slag, oxides, and other deleterious material that would be detrimental to the base metal. 

Chemical contaminants for which full-scale treatment data exist include primarily volatile organic compounds (VOCs) and semivolatile organic compounds (SVOCs). These SVOCs include polychlorinated biphenyls (PCBs), pentachlorophenol (PCP), pesticides, and herbicides. Extremely volatile metals, such as mercury and lead, can be removed by higher temperature thermal desorption systems. The technology has been applied to refinery wastes, coal tar wastes, wood-treating wastes, creosote-contaminated soils, hydrocarbon-contaminated soils, mixed (radioactive and hazardous) wastes, synthetic mbber processing wastes, and paint wastes. 

I. Spectroscopic Determinations. Gas-phase infrared spectra provide a useful adjunct to vapor pressure measurements in the identification of volatile materials. The cell illustrated in Fig. 9.15 allows the sample to be quantitatively returned to the vacuum line after the spectrum has been obtained, so the process is completely nondestructive. The primary problem with a gas cell is to obtain a vacuum-tight seal between the window material and the cell body this may be accomplished with Glyptal paint or with wax- If the latter is used, it is necessary to warm and cool the alkali halide windows slowly to avoid cracking them due to thermal stress. For this purpose an infrared lamp is handy. The most satisfactory method of attaching windows is O-rings because this allows the easy removal of the windows for cleaning and polishing. 

Another example of the application of fermentation is the removal of organic compounds from exhaust air. Such biofilters are often trickle-bed reactors, in which the microorganisms grow on a solid support, such as wood chips or porous stones. Water is trickled through the reactor, whereas the exhaust air flows in the opposite direction. The bacteria digest the organic components and destroy odor-causing chemicals. Biofilters are applied in municipal wastewater treatment, food production, paint, paper, and timber industries or soil remediation. They provide an attractive alternative to thermal, chemical, and adsorptive processes for cost-effective treatment of air pollutants. 

A schematic of a rotary concentrator is shown in Fig. 9. The wheel rotates slowly (1-3 rotations per hour) with about 90% of its face exposed to the incoming air stream. The remainder of the face is in a regeneration sector where a counterflow of hot air desorbs the VOCs for subsequent incineration. The rotary adsorber increases the VOC concentration by a factor of 100, so there is little need for supplemental fuel in the small oxidizer that can be used to destroy the VOCs. This technology has been used for the removal of styrene emissions in the plastics molding industry. The process is also used with automotive paint booths where modular rotary concentrators and a regenerative thermal oxidizer are used to capture and destroy VOCs. 

Afterburning processes enable the removal of pollutants such as hydrocarbons and volatile organic compounds (VOCs) by treatment under thermal or catalytical conditions. Combinations of both techniques are also known. VOCs are emissions from various sources (e.g. solvents, reaction products etc. from the paint industry, enaml-ing operations, plywood manufacture, printing industry). They are mostly oxidized catalytically in the presence of Pt, Pd, Fe, Mn, Cu or Cr catalysts. The temperatures in catalytic afterburning processes are much lower than for thermal processes, so avoiding higher NOx levels. The catalysts involved are ceramic or metal honeycombs with washcoats based on cordierite, mullite or perovskites such as LaCoOs or Sr-doped LaCoOs. Conventional catalysts contain Ba-stabilized alumina plus Pt or Pd. 

Once the pod tree [Caesalpinia spinosa) is harvested, it is washed and dried, and then the seed is removed from the pod. Following the separation, the separately ground pit shell, which is an extraordinary product, is exported as a raw material for the production of tannic acid, which is widely used in the chemical, paint, and high-quality fur industries and pharmaceuticals. The seeds, or the pips, after undergoing a thermal-mechanical process, result in a gum from the endosperm, which is an alternative to the traditional rubber in the global food industry, pharmaceuticals, paints, and varnishes, among others. This gum has been approved by resolution of September 26, 1996 (ECC N° E-417) by the European Community for use as a thickener and stabilizer in food for human consumption. Thus came into picture the global market for food hydrocolloids as an alternative product to the locust bean gum, produced in Spain and the Middle East. 

In common culture, there is a tendency to protect the part that corrodes, for example, by painting the surface. However, painting the part that corrodes means that the anodic surface area is decreased and, when equal to the cathodic surface area, thus increases the rate of corrosion penetration in correspondence with the defects of the painted coating. A more appropriate solution would be instead to remove thermal oxides and to protect or, even better, to electrically isolate the old part, which is the cathodic one. 

The total paint system may be too thick, causing cracking from thermal expansion and contraction. In this case, the old paint must be removed. 

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