Coating, automatic

Vacuum metallizing of polymer films, such as cellulose acetate, butyrate, and Mylar, is performed in essentially the same way. Film rolls are unreeled and rewound during the deposition process to metallize the desired surface. A protective abrasion-resistant coating is then applied to the metallized surface in an automatic coating machine. 

Coating consistency is crucial when producing screens for photorealistic printing. If the emulsion thickness is not controlled, it could lead to uneven ink deposits and visual distortions such as moire. For this reason, automatic coating devices are recommended. But if the cost of such devices is prohibitive, then maintain consistency by introducing as few variables as possible to the manual screen-coating process, including the number of personnel involved. 

Fig. 3-32. Schematic of noncontinuous profiles being automatically coated with plastics.

Pig. 16. Automatic coating device. On the left, the magazine with glass plates and beneath it the conveyor belt and motor drive. To the right, the aligning tray and layer-thickness adjuster. The slurry is fed into the funnel in which it is stirred. [661]... 

Erba, C., S. p. A., 24 Via Imbonati, Milano, Italy (Apparatus for automatic coating, TLC-accessories, adsorbents). 

Enclosed agitated filters are useful when volatile solvents are in use or when the solvent gives off toxic vapor or fume. Another significant advantage is that their operation does not require any manual labor. Control can be manual or automatic, usually by timers or by specific measurements of the product. Most filters are made of mild steel, with the exposed surfaces protected by lead, tile, mbber lining, or by coating or spraying with other substances as necessary. Filtration areas up to 10 m are available and the maximum cake thickness is 1 m. Apphcations are mainly in the chemical industry for the recovery of solvents. 

Fig. 1. An automatic spray-coating system, where air-automized electrostatic spray guns are mounted on reciprocators.

Automatic filters are made with either viscous-coated or dry filter media. However, the cleaning or disposal of the loaded medium is essentially continuous and automatic. In most such devices the air passes horizontally through a movable filter curtain. As the filter loads with dust, the curtain is continuously or intermittently advanced to expose clean media to the air flow and to clean or dispose of the loaded medium. Movement of the curtain can be provided by a hand crank or a motor drive. Movement of a motor-driven curtain can be actuated automatically by a differential-pressure switch connected across the filter. 

Tanks that are enamelled or that have other high-resistance coatings with volumes below 4 m do not require automatic exhausts if they are equipped with galvanic anodes in which the surface area does not exceed 5 dm per square meter of surface to be protected, or with controlled impressed current anodes with a low current output of 150 mA. 

Six iron anodes are required for corrosion protection of each condenser, each weighing 13 kg. Every outflow chamber contains 14 titanium rod anodes, with a platinum coating 5 /tm thick and weighing 0.73 g. The mass loss rate for the anodes is 10 kg A a for Fe (see Table 7-1) and 10 mg A a for Pt (see Table 7-3). A protection current density of 0.1 A m is assumed for the coated condenser surfaces and 1 A m for the copper alloy tubes. This corresponds to a protection current of 27 A. An automatic potential-control transformer-rectifier with a capacity of 125 A/10 V is installed for each main condenser. Potential control and monitoring are provided by fixed zinc reference electrodes. Figure 21-2 shows the anode arrangement in the inlet chamber [9]. 

The more automatic the method of coating application, the more economical and efficient it is, since automation lends itself more readily to more even coatings than do manual methods, e.g. large surface areas lend themselves more readily to spraying techniques, whereas open work structures are more suitable for dipping methods. The coating should also be applied to a specified minimum thickness which is adequate for the service conditions and life envisaged. 

Surface preparation is of prime importance, and optimum performance of modern protection coatings can be achieved only if the surface of the steel has been adequately treated. The method of surface preparation depends on the shape and size of the structure or component. Thus it is preferable to blast-clean an openwork steel structure by manual methods, since with this type of structure automatic blast cleaning would lead to excessive impingement of the abrasive on the machine itself. 

The dipping processes are of three basic types (1) continuous lengths of strip, wire or tube pass through the molten coating metal (2) semimanufactured products such as cut tube lengths or sheets are dipped into the molten metal in batches in specially designed and automatically operated plants and (3) fabricated products are dipped into the molten metal. 

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