Metal Preparation

The bond and appearance of porcelain enamel is heavily dependent on closely controlled cleaning of the metal surface. Complete removal of oil, drawing compounds, and other surface contaminants is essential. Steel may be prepared for porcelain enameling by the "clean only" method, and acid etch/nickel deposition process, or mechanical procedures.

Preparation of Steel for Porcelain Enameling

The "clean only " process has emerged in recent years as the dominant method for preparing steel components for porcelain enameling, especially for large-volume production using electrostatic dry powder application systems. Metal preparation using the "clean only" system requires at least the same amount of cleaning as is achieved using the acid etch/nickel deposition method, but no acid etching or nickel deposition is used. Benefits realized from using the "clean only" method include reduced operating costs, lower equipment costs, increased yield, reduced environmental problems, lower chemical usage, and reduced water consumption. Figures 7 and 8 illustrate the "clean only" cycle for both the spray process and the immersion process.

1,

2.

3.

4.

Clean

Clean

Rinse

Rinse

Deiûrtizèd water rir se

Dry

1

To porcelain enamel coating operations

Stage

Solution composition

Temperature

Cycle time, min

°C

°F

1-Clean

Alkaline cleaner 30-60 g/L (4-8 oz/gal)

82-100

180-212

5-15

2-Clean

Alkaline cleaner 30-60 g/L (4-8 oz/gal)

82-100

180-212

5-15

3-Rinse

Tap water

49-71

120-60

1-2

4-Rinse

Tap water

Ambient

Ambient

1-2

5-Rinse(a)

Deionized water

Ambient

Ambient

1-1 2

(a) Deionized water rinse is required for two-coat/one-fire finish with excellent appearance

Fig. 7 "Clean only" metal preparation, immersion process

1.

-

2.

3,

4,

5-

6,

Frewash

Wash

Rinse

Wash

Rinse

Rinse

Deionized water rinse

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