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Reducing energy costs with vapor degreasing

Save electricity and other valuable and costly resources by using environmentally acceptable cleaning solvents
Reducing energy costs with vapor degreasing

In the electronics product finishing world, there are four common precision cleaning processes: hydrocarbon, aqueous, semi-aqueous, and vapor degreasing. Each method has its strengths and of course its disadvantages, but one of the biggest problems with aqueous and semi-aqueous cleaning is the quantity of the electricity it takes to operate those systems.

Mike Jones, VP MicroCare Corp.; John Hoffman, New Britain, CT

All energy costs are rising and electricity is no exception. On a historical basis, electricity is expensive and getting more so. Capacity is another issue: cold winters or geopolitical turmoils can generated energy crisis and rolling black outs were inflicted on companies due to lack of sufficient providing capacity at the time. Additionally, the generation of electricity by burning hydrocarbon fuels is a key contributor to global warming. Vapor degreasing can dramatically reduce a company’s energy budget devoted to cleaning processes.
Solvent chemistries
It has only been in the past decade that companies have commercialized new, environmentally-acceptable cleaning solvents suitable for vapor degreasing. This means that the speed, convenience and energy savings of this proven technology now is available to engineers everywhere.
Unlike aqueous or hydrocarbon cleaning, vapor degreasing requires special fluids with a unique combination of characteristics. Ideally, these cleaners should be nonflammable, immiscible with water, have a low boiling point, an appropriate Kari-butanol (Kb) value, a high density, low surface tension, low viscosity, a low specific heat and a low latent heat of vaporization. Developing fluids with all of these characteristics has not been easy for DuPont, 3M, and other suppliers.
Four of these characteristics affect cleaning performance. The high density, the low surface tension and low viscosity all ensure the solvent will wet every surface, getting into (and out of) tiny nooks and apertures. As the old adage goes: if you can’t wet, you can’t clean.
The Kb value scales the strength of the fluid, and ensures the solvent will have the power to dissolve any contamination. But it is the low specific heat and a low latent heat of vaporization that are the primary reasons a vapor degreaser is significantly more energy-efficient than other technologies.
The energy inefficiency of water cleaning stems right from the chemical properties of water itself. The inherent characteristics of water render it very difficult to use and to remove water efficiently from complex surfaces. By comparison, solvent cleaning is highly energy-efficient.
The term “specific heat” defines the amount of heat required to raise the temperature of a unit mass by one degree Celsius (1°C, metric). The specific heat of water is very high, which is why oceans have such a very important function in stabilizing global climate: it takes immense energy to heat or cool water. For example, the specific heat for water is 4.186 joule/gram °C, which is four times higher than such as nPB or the popular DuPont HFC chemistries.
After cleaning, most systems evaporate the cleaning fluid from the surface of the parts. Once a liquid begins to change phase – that is, change from a liquid into vapor –specific heat is no longer used. The proper statistic to measure the energy required to evaporate a fluid is “the latent heat of vaporization.” And therein lies the rub: it takes a great deal of energy to evaporate water.
Water requires 970.4 BTU of energy to vaporize one pound of liquid. In contrast, nPB requires only 58.8 BTU for an equal weight, and the popular DuPont HFC solvents require 67.1 BTU/pound. This means it will take roughly 14 times more electricity to evaporate a pound of water than to vaporize a pound of solvent.
Remark: A BTU is the amount of heat required to raise the temperature of 1 pound (0.454kg) of liquid water by 1°F (0.56°C). The British thermal unit (BTU) is a traditional unit of energy equal to about 1055 joules. In science and beyond the English speaking world, the joule, the SI unit of energy, has replaced the BTU.
Aqueous cleaning energy consumption
Most aqueous cleaner machines are horizontal designs which use hoists or conveyors to move the parts through a series of dip tanks. A typical aqueous batch system has one wash tank and between two to five reverse-flow, cascading rinse tanks that require 2–5 gallons/minute of deionized water. These systems typically will be 50–150% larger than vapor degreasers of the same capacity, simply because of the need for more tanks, larger pumps, blowers, filters and so on. Typically, these machines consume about 8–10kWh of electricity. Most aqueous cleaning systems have three or more tanks with ultrasonic excitation, adding another 1–2kWh of consumption. Also, aqueous system cleaning cycles tend to last 20–40 minutes. Most vapor degreasers clean in 5–12 minute cycles, reducing energy costs and work in process inventory.
Removing excess water from parts is challenging because of the chemical nature of water. Evaporating excess water with heat is relatively slow and expensive, so the most common drying option is the use of an “air knife.” A typical aqueous system easily can consume 5kWh at the drying stations, and that number could double on a bigger machine simply because of the increasing size of the motors, fans and compressors. Ultimately, for final drying, heated air knives often are necessary – which simply compounds the energy consumption problem.
Water pre-treatment and post-treatment systems also use large quantities of electricity. Once the water is deionized, the water is usually heated up to 60–70°C for the cleaning process which requires at least 2–3kWh of power or more for the pumps and support equipment. On the back-end, assuming the system needs to process five gallons of waste water a minute, even the most frugal waste water system is going to need 3–5kWh.
One last consideration is the stand-by power draw. At many companies the aqueous cleaners never are shut down because of the cost coming up to temperature and the delay in re-heating. These idle systems will use 2–5kWh of electricity at a minimum, hour after hour, even when no cleaning operations are being conducted.
Here’s a detailed example: A Branson 1620 aqueous system with modest cleaning capacity costs around euro 80,000. It has four sumps and is almost 5m long, twice as large as an equivalent vapor degreaser. It uses 17kW during start-up and 12kW during use, plus ultrasonic stimulation, operating at 60°C. The total system will use approximately 25kWh.
Aqueous cleaning machines also add heat to the surrounding environment which increases the load on the air conditioning system. The Branson 1620 will add nearly 300,000 BTU/hour of heat to the room in which it is operating plus approximately 15 pounds of water (roughly 7 liters) into the air of the plant every hour, which will need to be removed by the HVAC system. Vapor degreasers using low-temperature solvents make only a minimal contribution in this manner.
Doing the numbers
It’s clear that the fundamental chemical characteristics of water make it inevitable that aqueous cleaning will consume far more kilowatt-hours to clean as the systems need to purify the water, clean the parts, dry the parts and then re-treat the water after cleaning. A general rule-of-thumb is that any aqueous cleaning system will use ten times the energy of a vapor degreaser of comparable capacity. Another calculation using the specs from two cleaning machines suggests that even a small facility will save a minimum of $300/month in direct energy costs by switching to vapor degreasing.
As substantial as those numbers are, many companies find the cost savings to be even greater. For example, a long-term US-based aqueous user, were able to document such massive savings by switching to vapor cleaning the local electrical utility provided a grant that funded 100% of the purchase of the new cleaning hardware.
But that’s just the beginning. Other savings, from faster throughput to higher yields and fewer defects all contribute to ever greater profitability. In a nutshell: with energy costs rising and the availability of adequate water supplies becoming a global concern, it makes sense to give energy-efficient solvent cleaning a chance.

Vapor degreasing concepts
Many younger engineers have never seen a vapor degreaser machine, so it is worthwhile to review this closed-loop technology. The schematic illustrates the manner in which a vapor degreaser is composed of and operates. The solvent is loaded in the boil sump (lower left chamber) where the solvent is heated to its boiling point, usually 40 to 75ºC, depending upon the solvent. As will any boiling liquid, the boiling solvent produces steam in the form of a clear, dense vapor that rises into the machine. Eventually the vapors reaches the primary condensing coils. These coils chill the solvent vapor and condense them back into the liquid state.
This liquid falls into a trough around the interior circumference of the machine. There it is routed through a water separator and directed back into the rinse sump. Since the rinse sump already is filled with clean solvent, the addition of clean, newly distilled solvent causes the sump to overflow into the boil sump, completing the distillation cycle.

Zusammenfassung
Ein enormer Verbrauch von elektrischer Energie in wasserbasierenden Elektronik-Reinigungssystemen ist nötig, um Baugruppen zu reinigen und trocknen. Als Alternative mit vielen Vorteilen bieten sich neuartige Reinigungsmittel an, die in speziell dafür entwickelten Maschinen effizient eingesetzt werden. Neben Einsparungen beim Energieverbrauch wird auch der Platzbedarf in der Fertigugn reduziert, denn die Maschinen sind deutlich kompakter. Selbst die Kosten für das Reinigungsmitttel, ein CFK, das im geschlossen Kreislauf immer wieder über viele hundert Reinigungszyklen verwendbar ist, sind deutlich niedriger, als für das zur Reinigung verwendete Wasser.
Une consommation énorme d’énergie électrique est nécessaire dans les systèmes de nettoyage électroniques basés sur l’eau afin de nettoyer et de sécher des éléments de construction. En guise d’alternative avec de nombreux avantages, on trouve des produits de nettoyage d’un nouveau type qui sont mis en œuvre de manière efficace dans des machines spécialement développées à cet effet. Parallèlement à des économies en termes de consommation d’énergie, on réduit également le besoin deplace dans la fabrication, car les machines sont beaucoup plus compactes. Même les coûts pour le produit de nettoyage, un agent CFK, qui est réutilisable en circuit fermé pour largement plus de cent cycles d’utilisation, sont bien plus réduits que ceux de l’eau nécessaire au nettoyage.
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Titelbild EPP EUROPE Electronics Production and Test 11
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11.2023
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