Processing Variables

Temperature. Although significant, bath temperature is less important in emulsion cleaning than in alkaline detergent washing. The dispersed oil (solvent) phase can accomplish much of its cleaning at ambient temperature. Higher temperatures are required for high-melting greases, buffing compounds, and waxes. The maximum safe operating temperature must be kept 8 to 15 °C (15 to 30 °F) below the flash point.

Agitation. Some of the oil-based soils can be cleaned in stagnant immersion. However, to ensure full coverage and increase effectiveness, the bath should be mechanically agitated. This can be accomplished with a recirculating "tabulating" pump, mechanical stirring, or air injection. Agitation helps to flush contaminants away from the part surface, allowing the cleaner to attack the next layer.

Ultrasonic energy is another form of agitation that can significantly improve immersion cleaning efficiency and effectiveness. Energy waves go through the solution at frequencies up to 50 kHz, creating millions of tiny bubbles on the part surface that then implode, creating a scrubbing action. Ultrasonics are particularly helpful in cleaning small-diameter or blind holes.

Concentration. In immersion, emulsions are usually used in concentrations of 20 to 30%. However, concentration is not a critical factor, as shown in Table 3. The capacity for dissolving soil increases proportionally with the concentration (volume) of the emulsion, but the solubilizing rates are not similarly affected by an increase in concentration. Some soils do react to varied concentrations, as shown in Fig. 1.

Table 3 Operating conditions for emulsion cleaners

Classification of cleaner

Concentration,

%

Operating temperature

Time, min

°C

°F

Immersion systems

General-purpose

5-15

10-71

50-160

2-8

Unstable single-phase1^"1

10

21

70

1-10

Kerosine-based(b)

15-25(b)

21

70

2-10

Diphase, heavy-duty

15-25

21-54

70-130

2-10

Emulsifiable solvent

100

21-60

70-140

-2

Spray systems

General-purpose

1-5

10-71

50-160

-3

General-purpose

2-5

10-77

50-170

-3

Light cleaning

1-2

10-71

50-160

1-3

Requires vigorous agitation.

Water-in-solvent emulsion, 15 to 25% water in kerosine

3 tO

Time, mil

Fig. 1 Approximate relationship of time and concentration for emulsion cleaners used to remove two different soils

3 tO

Time, mil

Fig. 1 Approximate relationship of time and concentration for emulsion cleaners used to remove two different soils

Emulsion cleanliness may affect cleaning effectiveness, which would relate to the concentration of the cleaning agent. If smut is seen on parts, then the emulsion is saturated with dirt and can absorb no more soils. To some extent, more emulsion can be added. Then the bath must be regenerated or replaced.

Time/Exposure. Generally an emulsion can accomplish its cleaning in 30 sec to 5 min. If cleaning requires much more time, then it is likely that the wrong emulsion was used or that immersion emulsion is not the proper cleaning method for the application. The length of time can be significantly altered by increasing the heat or changing or increasing the agitation. (Some typical process cycles are shown in Table 4.) Difficult applications may be accomplished with a combination of soak and spray rather than extended soaking time.

Table 4 Cycles for immersion and spray emulsion cleaning

Process sequence

Cycle time, min

Easy cleaning

(a)

Difficult cleaning(b)

Immersion(c)

Spray(d)

Immersion(e)

Spray(f)

Clean®

2-4

-1

4-10

1-2

Rinse®

4 -

4 -

-

-

Rinse®

-1

-1

-1

-1

(a) Removing cutting oils and chips from machined surfaces, shop dirt and oil from sheet metals, and drawing compounds from automotive trim.

(b) Removing embedded buffing compounds, impregnated carbonized oils from cast iron motor blocks, and quenching oil from heat treated forgings.

(c) Concentration of cleaner, 1.5 to 6 vol%.

(h) Unheated rinse.

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