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Rick Terrien, Universal Separators
The best technologies are not necessarily the newest. Finding new ways
to use existing tools can often deliver smarter and less expensive
solutions. Suction skimming, gravity separators and oil splitting cleaners
are just such a combination for heat treating parts washers. Washers
already on the shop floor can be easily upgraded to take advantage of these
tools. This article describes how and why to implement those upgrades.
When solvent cleaners were used to clean quench oil from heat treated
parts prior to tempering, few treatment options were necessary. Changing
environmental laws have brought about a switch from solvents to aqueous
cleaners for most parts washers.
While this solved the problems associated with solvents, the deployment of
aqueous cleaners has created a new set of problems which have to date not
been adequately addressed.
Early aqueous cleaners tried to mimic the cleaning action of solvents.
Most were designed to emulsify as much quench oil as possible. The goal
was to keep oil off the surface of the washers where it can contaminate
parts being washed. These early cleaners were typically aggressive, high
pH formulations. However, even the most aggressive emulsifiers take time
to work; a significant portion of the quench oil continued to rise to the
surface where it still recontaminated parts. On washers in steady use,
such as batch washers serving several furnaces or those deployed on
continuous quench furnaces, layers of surface oil quickly builds up. This
has led to a spate of new management problems specific to aqueous cleaners.
The bath life of emulsifying cleaners lasts only as as long as the
available emulsifying capacity of the cleaner. Once the emulsifiers in the
solution are used up, the bath is spent and it must be hauled away and
replaced. By design, emulsifying cleaners continuously degrade in
effectiveness. Every wash shortens the life of the parts cleaning bath.
Many operators have tried to stretch out the process by installing
oil-water drag out devices, such as belts, disks, drums, and mops. These
units create an additional oily waste stream for the plant by dragging out
solutions which are typically 50% aqueous cleaner and 50% oil. The
effectiveness of oil-water dragout systems in applications where large
amounts of oil are present, such as heat treating, are limited. Media
coalescers have also been tried, but these blind over quickly due to the
presence of grit and other solids in the wash solution.
Tests using membrane filters, such as microfilters (MF) and
ultrafilters (UF) to remove emulsified oil from parts washing baths have
shown that these devices often damage the cleaners. MF and UF systems
filter out surfactants, defoamers, rust inhibitors and other valuable
components from the cleaning solution. Because they are also susceptible
to blinding over in the presence of oil and grit, they are a bad choice for
heat treating parts washers.
However, a new combination of existing tools is available for keeping
parts washing baths clean and effective. This combination is easy to
retrofit on to existing washers. The hardware and the cleaners are simple
to maintain, yet can deliver big net gains to the heat treating process.
At the heart of this approach are a relatively new family of cleaners
known as oil-splitters. Oil splitting cleaners do not emulsify, and
they are an excellent cleaner for heat treating applications. All the
quench oil removed by oil splitters pops to the surface immediately where
it can be readily managed. Because oil splitters preserve quench oil for
recycling, very little oil is emulsified. There is no saturation of the
bath; with no saturation, there is no need for frequent dumps. Parts
washing baths can be maintained in a clean and effective state for much
longer periods than have been typical. When surface oil is quickly
removed, even the most heavily used oil splitting baths can be kept clean
for well over a year. To effectively remove the surface oil, operators are
turning to a combination of suction skimmers and gravity separators.
Effective skimming and separation, combined with the use of oil
splitting cleaners, also delivers important benefits for reclaming quench
oils. According to Dave Morrison, Development Scientist with Castrol
Industrial North America, cleaners that emulsify quench oils make it
extremely difficult to reclaim that oil for future use. Getting the oil
out of such systems is usually chemical and energy intensive. High
alkaline/caustic cleaners that promote splitting make the job of
reclamation easier by floating the used oil on the surface. Cleaners that
are designed to split oils have the added benefit of neutralizing the
emulsifying tendencies of used quench oils.
Suction skimmers remove surface oil and contaminants by placing a self
leveling suction intake just below the surface. These devices
automatically compensate for level changes in the washers, putting a self
adjusting drain right at the surface. Suction skimmers continuously
remove the oily top layer of fluid from the washer for treatment. When
treated in a gravity separator, oil and grit are removed without any moving
parts or the need for any consumables.
The Maintenance staff at Treat-All Metals in Milwaukee, Wisconsin devised a
unique system for deploying suction skimmers, gravity separators and oil
splitting cleaners. Their centralized washers serve a number of different
furnaces, primarily integral quench and pusher furnaces. The most common
parts being run through the washers are gearing, auto parts and farm
related implements . Their old washing system used emulsifying cleaners
with an oil-mop drag-out treatment system. This required time and labor to
check and could result in big swings in cleaner concentrations between
checks. Figure 1 shows the difference between the old concentration
profile and the new profile they have developed using suction skimmers,
gravity separators and oil splitting cleaners. Similar results have been
achieved at captive heat treating operations such as Caterpillar and at
commercial plants in the U.S. and Canada. | 
