SOLVENT VAPOR DEGREASERS

How Vapor Degreasers Work

Solvent degreasing involves the exposure of a workpiece to pure solvent vapors released by a boiling solvent. The workpiece is usually suspended in the vapors just above the boiling solvent. When the warm vapors touch the comparatively cool workpiece, a condensing action occurs which dissolves the contamination and flushes it away as it runs off the part. This cleaning action will continue until the workpiece and the solvent vapor are the same temperature. Beyond this basic procedure a number of additional cleaning operations are often used, including immersion rinsing and ultrasonic cleaning. The degreaser styles depicted in this brochure are primarily designed for use with n-propyl bromide and chlorinated solvents, including trichloroethylene, methylene chloride, and perchloroethylene. Although these systems can also be used with Fluorinated fluids like HFE, HFC and their azeotropes, Greco Brothers suggests that you request literature depicting our more sophisticated line of High Performance Degreasers degreasing equipment for those solvents.

Degreasing Applications

Aqueous-based cleaning systems are effective in many applications, but some aspects of aqueous-based cleaning can make it impractical or unusable for certain types of workpieces. Solvent degreasers are used for removal of oil, grease, wax and other stubborn solvent-soluble soils from electrical and electronic subassemblies, intricate metal and plastic parts, and a wide variety of other materials prior to assembly, inspection or further processing. Nearly any part can be cleaned in a solvent degreaser without concern for quality control issues like part oxidation, effective drying, and water spots, because no water is used in the process.

Safety Controls & Solvent Retention Systems

All solvent degreasers depicted here are designed to meet or exceed the latest EPA guidelines for safety and solvent retention.

Safety Controls: Each design includes safety interlocks which interrupt power to the machine if the system runs low on liquid, high on vapor, or if the temperature in the wash sump rises significantly above the boiling point of the solvent . Additionally, power to the spray pump will be interrupted if the vapor level drops by more than four inches.

Solvent Retention Systems: One of the prime objectives in degreaser-design is solvent efficiency. Retaining the vapors within the machine is important for worker safety and economic operation. Several factors effect the overall efficiency of the system:

The Primary Cooling System:

A multiple pass perimeter cooling coil is used as a heat exchanger to condense the vapors, creating a sustainable vapor zone. The primary coil must be maintained at a temperature that will cause the vapors to readily condense. This function can be performed by directly refrigerating the coil, or by passing chilled water through it.

Refrigerated Machines: An integral direct-expansion refrigeration system is attached directly to the primary cooling coil. The refrigeration system operates continuously; removing the precise amount of heat required to ensure proper vapor condensation.

Water-Cooled Machines: In a water-cooled machine, a coolant flows through the primary cooling coil. If a constant supply of cool water is available, the machine can operate on water alone. More commonly however, to save water and to assure constant temperature, a combination of coolant and water is circulated through a refrigerated water chiller. The water chiller may be dedicated entirely to the degreaser, or it may be serving the cooling requirements of other equipment simultaneously. Water-cooled machines which are connected toa water chiller perform as efficiently as refrigerated machines.

Secondary Cooling System: The secondary cooling system consists of an additional cooling coil that is mounted directly above the primary coooing coil and maintained at sub-zero temperatures, creating a cold blanket of air which further reduces solvent consumption. EPA guidelines call for a freeboard chiller on vapor degreasers containing trichloroethylene, perchloroethylene, or methylene chloride. Given that a properly-designed freeboard chiller will reduce evaporative losses by 30% to 45%, the cost of a freeboard chiller can easily be justified as a solvent-saving measure with a short payback period; regardless of whether the degreasing fluid is a chlorinated solvent or a newly developed fluorinated solvent.

Freeboard Ratio: Freeboard is the area within the machine above the vapor zone. The freeboard ratio is the comparison of the measurement of the width of the system, compared to the freeboard height. Higher freeboard ratios have been demonstrated to aid in solvent retention. All of the systems depicted in this brochure include freeboard ratios of between 1.0:1 and 1.25:1. Freeboard ratios of 1.5:1 are standard on our High Performance Degreasers and are optionally available on these systems if overall height considerations permit.

Drop-Seal Cover: Unlike common sliding covers that leave gaps around their perimeter, this unique cover is designed to roll into place, and seal the work chamber from the atmosphere; virtually eliminating evaporative losses during downtime.

The Three Basic Designs

Vapor Spray Degreasers

The Greco Brothers vapor/spray degreaser is a one compartment system cleaning system with the vapor zone located directly above the boiling solvent. This unit is designed for cleaning applications that require suspension in pure solvent vapors only. Typically, the work piece is lowered in the vapor zone and sprayed with freshly distilled solvent to remove oil, chips, solder flux or other soils. The work piece is then suspended in the pure solvent vapor until condensation stops as the work piece reaches the temperature of the boiling solvent. It is then raised through the freeboard area clean, dry and ready for the next operation. Standard work chamber sizes range from 25" x 14" x 22" to 60" x 30" x 36". Custom sizes are also available to meet nearly any application requirements.

Immmersion/Vapor Spray Degreasers

Certain applications require that the work piece be immersed in a bath of warm solvent for either rinsing or cleaning. When this is required, a Greco Bros. immersion/vapor spray unit should be used. The cleaning cycle is similar to the vapor spray, except before initial spray cleaning, the part is immersed in the warm solvent sump. This gives additional cleaning, and also lowers the temperature of the part to allow for final vapor condensation prior to removal from degreaser. Standard work chamber sizes range from 12" x 14" x 12" to 28" x 20" x 20". Custom sizes are also available to meet nearly any application requirements.

Ultrasonic Immersion/Vapor Spray Degreasers

Ultrasonic degreasing incorporates both ultrasonic immersion cleaning and conventional vapor degreasing as discussed in the prior sections. This combination offers advantages for many of the following typical cleaning applications: Stubborn organic soils such as mold release agents, wax and impregnated grease. Excessive particulate contamination on the work piece. Inaccessible surfaces, blind holes, and intricate passageways on the work piece. Critical cleaning of high-reliability components such as printed circuit boards, & hybrid/microcircuits. The ultrasonic vapor degreaser incorporates the same features as the Greco Brothers immersion/vapor spray degreasers, with the addition of ultrasonics in the rinse sump. The cleaning cycle remains the same, with the work piece being suspended in the ultrasonic sump for the required time. Standard work chamber sizes range from 12" x 14" x 12" to 28" x 20" x 20". Custom sizes are available with surprisingly short lead times.