Concerns and Limitations

Oil-like Residue. If the oil-like residue is not desired for protection or is not compatible with the next process, it usually can be washed off with an alkaline detergent. Parts that cannot be thoroughly rinsed, such as sintered powdered metal and parts with blind holes, should not be cleaned with emulsion cleaning. On parts that will be plated or painted, it must be ensured that all of the emulsion has been removed, because emulsion can contaminate a plating line or prevent paint adhesion.

Safety. Heat aids the cleaning and drying process, but because emulsions are distilled from petroleum, they have a flash point and are potentially volatile. Depending on the emulsion, these flash points range from 40 to 99 °C (100 to 210 °F). Operating temperatures should be kept 15 °C (30 °F) below the flash point. (Some manufacturers indicate that it is safe to operate within 8 to 10 °C, or 15 to 20 °F, of the flash point.) The margin of safety may be determined by the process control capability of the equipment.

Volatile organic compounds (VOC) are emitted from the emulsion, particularly when it is heated, so adequate ventilation is vital. Depending on the type and volume of solvent discharge, the vent may need carbon absorption or scrubbers. In either case, the process may require a permit from the local air quality management authority.

Spray. Most emulsions should not be sprayed because spraying tends to atomize the solvent phase, which is highly susceptible to "flash." However, emulsions with flash points around 95 °C (200 °F) and used with higher water content can be sprayed in equipment with proper safety controls. These include close temperature control and possibly a backup temperature sensor, extra ventilation, and explosion-proof wiring.

Heat Source. Open fire gas burners should not be used. Steam heat is safest. Electric immersion heaters can be used safely with the proper solution level and electric spark controls.

Drying. Emulsions are generally slow-drying solutions because of the petroleum base. Heating the solution will aid drying, but temperature often needs to be held down due to safety concerns. Ambient air blowoffs are effective only if the air nozzle is very close to the part and is directed into any cavity. This can work with a manual air gun or proper setup on a conveyor belt. It generally does not work for batch processing. Heated air blowoff dryers will work, but caution must be taken to keep the system temperature 15 °C (30 °F) below the flash point.

Superfund Amendments and Reauthorization Act (SARA). Depending on the solvent base and concentration, the emulsion process may need to be reported to the Environmental Protection Agency under the terms of SARA, Title III.

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