Emulsion Cleaners

Emulsion cleaners are broadly classified into four groups on the basis of stability:

• A stable single phase, or permanent, emulsion is one in which the discontinuous phase is dispersed throughout the continuous phase. This requires no more agitation to maintain a uniform dispersion than that provided by thermal gradients and the motion of the work being cleaned.

• An unstable single phase emulsion has a uniformly dispersed phase that tends to separate and form a solvent layer. Solvents with specific gravity of less than 1.0 form a top layer, and those with a specific gravity greater than 1.0 form a bottom layer. These cleaners require moderate to considerable agitation to maintain complete dispersion.

• A diphase, multiphase, or floating layer emulsion forms two layers in the cleaning tank and is used in this separated condition. Work is immersed through the solvent-rich surface layer into the water-rich lower layer, permitting both cleaning phases to come in contact with the surfaces to be cleaned. When used in a spray system, a diphase cleaner resembles an unstable single phase cleaner, because the solvent and water phases are mixed in the pumping action.

• An emulsifiable-solvent system is one in which the as-received, undiluted solvent is applied to the surface to be cleaned by hand or by use of a dip tank. It is followed by a water rinse that emulsifies and removes the solvent and soil.

Because stability is a relative term, the definitions of these four types of cleaners can overlap. The advantages and disadvantages of the first three types are as follows.

Stable emulsion cleaners are the most economical. They are practical for removing light shop soils, especially in applications where in-plant rust protection is required. These cleaners contain hydrocarbon solvents such as kerosine, which can dissolve and clean light soils. Two to three weeks of rust protection can be expected for ferrous metal parts cleaned by a properly constituted stable cleaner. Such a cleaner maintains an emulsion with water for many hours, requiring a minimum amount of agitation.

A 2% stable emulsion spray rinse often follows alkaline cleaning. This procedure has provided rust protection for as long as three to four weeks in storage areas where humidity is not excessive and unusual changes in temperature are not encountered.

Although 75 °C (170 °F) is the recommended maximum operating temperature, stable emulsions can be operated safely at temperatures up to 80 °C (180 °F). The higher temperatures, sometimes advantageous when rapid drying of the work is desired, increase evaporation rates and may cause polymerization of emulsion and the formation of a varnish-like film that is difficult to remove from work. When large quantities of parts are cleaned in a continuous production flow in automatic spray washers, stable emulsion cleaners are preferred because of their lower initial cost and ease of maintenance.

Stable emulsion cleaners do have disadvantages. Their efficiency is low in removing hydrocarbon soils if more than 10% of the soil has a solidification temperature within 10 °F of the temperature of the emulsion. In hard water, stable emulsions form insoluble precipitates that may plug drains and increase maintenance.

Unstable emulsion cleaners, although higher in cost than stable emulsion cleaners, perform more efficiently in removing heavy shop soils, such as oil-based rust preventatives and lubricants used in stamping and extruding. The hydrocarbon fraction of unstable emulsion cleaners makes more intimate contact with the work surface, permitting greater action of the solvent on soil. Unstable emulsions are also successful in hard waters that cause stable emulsions to break down.

Unstable emulsions, as well as the equipment required for using them, are less costly than diphase emulsions. However, their cleaning power approaches that of diphase systems, and they are widely used for the removal of heavy hydrocarbon soils. Phosphates may be added to hard waters to increase the efficiency of unstable emulsions.

The concentration of an unstable emulsion can generally be determined by gravimetric separation. Operation above or below the preferred concentration range lowers cleaning efficiency or causes excessive cleaner consumption. The operating temperature of an unstable emulsion is critical and must not exceed 70 °C (160 °F). The usual range is 63 to 68 °C (145 to 155 °F).

Diphase emulsion cleaners are used for removing the most difficult hydrocarbon soils, such as lapping compounds, buffing compounds, and oxidized oils. They provide a higher degree of cleanliness than can be obtained with stable or unstable emulsions. The flash points of diphase emulsion cleaners cover a wide range, permitting operating temperatures up to 80 °C (180 °F). The monomolecular layer of oil that remains after diphase cleaning provides good rust protection.

In diphase cleaning, the solvent in the bottom phase is very powerful and a 100% concentrated product. It is not an emulsion with water. Hence, these cleaners provide better cleaning than regular emulsion cleaners.

Diphase cleaners are most frequently used in dip tanks. However, with specially designed equipment or the addition of emulsifiers to retard separation into solvent and water layers, these cleaners can be used in recirculating spray washers. Diphase cleaners also have disadvantages:

• They are adversely affected by hard water, and preconditioning the water with phosphates is unsuccessful.

• They cost more than stable or unstable cleaners.

• Vaporization of hydrocarbon layers requires more ventilation than is needed for stable and unstable cleaners to avoid fire and health hazards.

• No easy test is available for determining diphase cleaner concentration.

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