Aluminum porcelain enameling

Pntnatment of Alloys for Pone lain Enameling Aluminum, Porcelain Enamel Institute Bulletin P-403(70), 1970. 

Finishes for aluminum products can be both decorative and useful. Processes in use include anodic oxidation, chemical conversion coating, electrochemical graining, electroplating (qv), thin film deposition, porcelain enameling, and painting. Some alloys respond better than others to such treatments. 

Pretreatment ofFUlojs for Pone lain Enameling A.luminum, PEI Bulletin P-403 (70) and Enamel Preparation, Application, and Firingfor Porcelain Enameling Aluminum, PEI Bulletin P-404(70), Porcelain Enamel Institute, Washington, D.C., 1970. 

The porcelain enameling industry consists of at least 116 plants enameling approximately 150 million square meters (150 km2) of steel, iron, aluminum, and copper each year (each coat of multiple coats is considered in this total). Porcelain enameling is the application of glass-like coatings to the metals mentioned above. The purpose of the coating is to improve resistance to chemicals, abrasion, and water, and to improve thermal stability, electrical resistance, and appearance. The coating... 

In general, only 10% of the porcelain enameling facilities enamel more than one type of base metal. Over 70% of the plants enamel solely on steel, 10% on aluminum, and 8% on iron. Less than 1% of the plants enamel copper, strip steel, or strip aluminum separately.3-6... 

Porcelain enameling on aluminum finds use in the cookware and housewares industry. It is also used for panels and signs. The average yearly production for a plant in this subcategory is 0.25 x 106 m2 (2.7 x 106 ft2). This figure represents the area of enamel applied. For multiple coats, the area for each coat is considered.3-6... 

The surface preparation operations for strip are dependent upon whether the basis material is steel or aluminum. The surface preparation steps for steel strip are minimal in comparison to porcelain enameling on steel sheets because precleaned strip steel is used. Steel strip is nickel immersion plated prior to the enameling step. Surface preparation for aluminum involves only cleaning. The enamel for either basis material is applied by means of spray guns that are aimed at the surface of the moving strip. Two coats are normally applied, the strip being fired after each coat. 

The introduction of enamel into the wastestream results in an increase in the concentration of metals, but these metals (antimony, titanium, zirconium, tin, cobalt, and manganese) are in solid form whereas the metals generated by surface preparation are normally in dissolved form. These solid metals increase the suspended solids concentration of the stream. Other metals that may be found in the enamel preparation and application wastestream in significant amounts include aluminum, copper, iron, lead, nickel, and zinc. Table 8.2 presents pollutant sampling data for the processes used in the porcelain enameling on steel industry. 

Wastewater from the Porcelain Enameling on Aluminum Subcategory... 

Table 8.4 presents classical and toxic pollutant concentrations for the porcelain enameling on aluminum subcategory. 

This facility produces 360 m2/h of porcelain enameled aluminum for 4000 h/yr, and uses 0.038 m3 of process water/m2 of product coated. The mixed wastewater stream is treated by equalization (settling), pH adjustment (lime or acid), polyelectrolyte coagulation, clarification, and contractor removal of the resulting sludge prior to discharge to a surface stream. Process water flow for this production consists of 8.12 m3/h and 4.37 m3/h for surface preparation and coating operations, respectively.3 5... 

Table 8.8 gives the water use for each process in the production of porcelain enameled aluminum for the above plants. Pollutant concentrations for treated effluents are presented in Tables 8.9 and 8.10.10... 

Full Scale Treatment of Porcelain Enameling on Aluminum Subcategory Wastewater by Equalization and Chemical Precipitation Using Lime and Polymer... 

Chemical precipitation is used in porcelain enameling to precipitate dissolved metals and phosphates. Chemical precipitation can be utilized to permit removal of metal ions such as iron, lead, tin, copper, zinc, cadmium, aluminum, mercury, manganese, cobalt, antimony, arsenic, beryllium, molybdenum, and trivalent chromium. Removal efficiency can approach 100% for the reduction of heavy metal ions. Porcelain enameling plants commonly use lime, caustic, and carbonate for chemical precipitation and pH adjustment. Coagulants used in the industry include alum, ferric chloride, ferric sulfate, and polymers.10-12... 

PORCELAIN ENAMEL. A substantially vitreous inorganic coating bonded to metal by fusion above 426 C (ASTM), Composed of various blends of low-sodium frit, clay, feldspar, and other silicates ground in a ball mill and sprayed onto a metal surface (steel, iron, or aluminum), to which it bonds firmly after firing, giving a glasslike fire-polished surface. 

The matching of expansion behavior is of the utmost importance to manufacturers of, for example, multi-layer capacitors, porcelain enameled cast iron sinks, fiber reinforced composites, light bulbs, etc. In all cases, various materials in rigid contact must have their expansion characteristics carefully matched. Inattention to this runs the risk of cracking and shattering of a light bulb at its seal to aluminum, delamination of metallic conductive leads from the ceramic substrate in a hybrid circuit, etc. By changing the composition of a constituent material, its... 

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