Steel coating operations

Hamilton Standard of the U.S. EPA has reported several coil coating plants wastewater treatment case histories.8,9 A full-scale wastewater treatment plant system has performed well for treatment of the wastewater generated from coil coating steel subcategory operations. The process principles and operational data of the full-scale treatment of a steel subcategory wastewater are summarized herein for the convenience of readers ... 

This plant produces 130 m2/h of enameled steel and operates 3500 h/yr. It uses 0.0036 m3 water/m2 of product to coat the steel. Average process water flow is 0.144 m3/h for coating operations and 0.734 m3/h for metal preparation. The primary treatment in-place for process wastewater is clarification and settling. Other water treatment practices employed are pH adjustment with lime or acid, sludge applied to landfill, polyelectrolyte coagulation, and inorganic coagulation. 

Plant 36030 enamels both copper and steel. It uses 0.042 m3 water/m2 product in all coating operations. Process wastewater flow is 0.466 m3/h for metal preparation and 1.69 m3/h for coating... 

Recently, systems suppliers have developed subcritical cleaning systems (i.e., systems operating below the critical point for carbon dioxide) that are fabricated using low cost alloy steel coated on the inside with an appropriate plastic to protect it from attack. This approach promises to significantly reduce system costs and enhance the competitive position of carbon dioxide cleaning in less demanding applications. 

Steel surfaces do not provide any unusual difficulties during coating operations, as long as the steel is of high quality and the environmental conditions are strictly controlled. Specifications usually call for an abrasive blast that meets Steel Structures Painting Council (SSPC) Spec. 5 ("white metal") finish although steel to be used in non-nuclear areas usually receives an SSPC 10 ("near white") finish or an SSPC 6 ("commercial") finish. Areas that require special attention are welds, seams, edges, channels, etc. 

Recent information suggests that such coatings operate by increasing the electrical resistance between the steel and the concrete both epoxy and polymer-cement-based materials seem to have this effect, reducing local corrosion current exchange [9]. 

Let us consider some mechanical properties of biplates. These are steel plates onto which glass-reinforced plastics are molded, with Sprut-5M adhesive used as a binder. The types of mechanical load selected were those that were encountered in the course of the coating operation. 

Two annular vessels were designed, fabricated, and have been in operation for two years. These are composite units made to be HF resistant, with the outer vessel formed of polypropylene, and the inner one of stainless steel coated wit Kynar (vinylidene fluoride). 

Ferritic steel (coated or uncoated) for intermediate temperature operation (650 to 800 °C). While uncoated steels are chemically unstable, especially during thermal cycling, coated steels provide corrosion resistance as well as acceptable conductivity when new. However, thermal cycling performance still requires improvement. 

The chromatographic column was 85 ft. x 0.02 inch i.d. stainless steel coated with Apiezon L and operated at 90°C and 10 p.s.i. Conventional packed columns are also satisfactory. The flash heater is kept below lOO C to prevent thermal decomposition of lead alkyls. 

Use coatings to provide a barrier between the steel and the environment. Coatings have been successfully used to prevent access of moisture on the outside of stainless steel hnes, operating at 49-260° C in the chloride-laden atmosphere of the Arabian Gulf. 

The lacquer will electrocoat all uncoated metal immersed in the electrodeposition bath. It should be borne in mind that there will always be at least one area, however, small, of the can which will be uncoated. This is the point or points where electrical contact is made which enables the can to act as an electrode. This is always on the external surface. No uncoated metal must be allowed to come into contact with the contents of the can. In most cases it would be anticipated that the internal lacquer would be applied last, thus the lacquer must not adhere, damage, stain or detract from the appearance of the external decoration. It is feasible that steel cans could have an internal and external lacquer electrodeposited in the first coating operation and use a spray applied internal lacquer as the last operation. In this case, the electiocoated internal lacquer must have the characteristics of the external lacquer, particularly mobility, if a novar system is used. 

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. 

Enamel is appHed to steel in the flat before fabrication. Cans manufactured by the draw and ironing operation must be coated internally after fabrication because of the metal deformation with surface dismption that takes place. 

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