For several decades, this initial step in most finishing operations had been relegated to a general “all-purpose” status.
Stephen RudyThe accepted procedure was to use a powdered blend, containing one or more surfactants, alkaline builders, conditioners, maybe caustic (depending on basis metal processed). Cleaning was predominantly by emulsifying (i.e., “holding” or encapsulating the soils in a surfactant “cell”). When the reserve cleaner blend became saturated with emulsified oils, its ability to provide adequate surface cleanliness rapidly decreased. Maintenance or booster additions of the cleaner concentrate would restore some degree of cleaning efficiency.
This would be a finite control process, however, whereby the cleaner bath would rapidly age, necessitating eventual dumping. It was not a sophisticated control procedure, because years ago, discharge regulations were virtually nonexistent, making frequent cleaner bath replacements a tolerable operating expense.
Changes in Regulations
Let’s consider what has happened since the early 1970s that affects the way today’s cleaners work, or should work:
- The Clean Water Act.
- F-006 sludge reduction.
- Municipal, state discharge compliance regulations
- OSHA safety regulations.
- Analysis control.
- Easing or simplifying waste treatment.
- Reduction of solvent cleaning as a result of environmental factors and health concerns
- The use of more chemically different oils in stamping, forming, extruding and rust-proofing.
- More applications for plating systems that are sensitive to parts cleanliness, such as chloride & alkaline zinc.
- Reduced operating costs.
The driving forces described here clarified the need for and development of newer, more effective soak cleaning systems. Formulations are blended to meet any of today’s specific requirements.
Benefits of Newer Soak Cleaning Systems
Some of these benefits include:
- Use of biodegradable, complex surfactant mixtures, encompassing specific ratios of different types, such as anionic and nonionic.
- Higher levels of oil emulsification.
- Rapid oil displacement at operating temperature, with or without solution agitation, or preferred oil displacement on cooling.
- Oil splitting agents added directly to the working cleaner bath.
- Cleaner formulations compatible and highly effective in use with mechanical oil removal equipment.
- Stable, concentrated liquid cleaners.
- Availability of concentrated additive blends containing only surfactants and other cleaning agents. Installation provides alkalinity, such as 50% Liquid Sodium Hydroxide.
- Elimination of phosphates, silicates and hard chelates (EDTA types).
- Improved rinsing characteristics.
Surfactant technology now provides a variety of effective detergents and wetting agents that blend with selected alkaline materials to provide the emulsification or displacement action, as described. Certain surfactants, when added to the working cleaner, will directly split the oils. Additional benefits of these newer generation surfactants include improved biodegradability and replacing health concerning adjuncts such as nonyl phenols. Unique surfactant combinations can readily remove many different types of process oils, such as chlorinated, mineral, paraffins, hydrocarbon rustproofs, sulfurized and synthetics. Having these surfactant mixtures in the formulation concentrate is referred to as having complex surfactant systems. In barrel cleaning, these agents also prevent oils from adhering to polypropylene barrels exiting the cleaner bath. Specialized surfactant blends also soften and lift buffing and polishing compounds.
For the purists, the first commercial surfactant introduced in cleaner blends in the 1930’s is the sodium salt of linear alkylbenzene sulfonic acid. This surfactant is still widely used.
Recycling and purification of cleaners have become wise investments to extend bath service life. Acknowledged cost savings are infrequent cleaner dumps, less downtime, reduced demands in waste treatment, less sludge and, most importantly, satisfactory cleaning on a per-shift basis. Mechanical filtering aids range from simple belt and disk skimmers to coalescers and ultrafiltration. Based on the specific user’s operating cost data and cleaning application, the capital expense and maintenance of these devices can be readily justified. During recent years, oil displacement has become a more popular method of alkaline cleaning, thereby increasing the useful application of mechanical filtering devices. Many of the oils can be recycled by certified firms (costing as low as just a freight charge to haul off the oils) used as an additive with fuel oil in plant boilers or used to formulate assorted oil based industry wide products.
Liquid Products Improve Technology of Aqueous Cleaning
Liquid products have really contributed to improving the overall technology of aqueous (water based) cleaning. Concentrated blends, as the name implies, are not bulk water-based, but rather water present is just sufficient in volume for blending and concentrate stability. Additives, such as alkalis, conditioners and surfactants, are the heart of these concentrates just as they are in powdered blends. Many liquid concentrates are equal in dry weight of certain additives to their powdered counterparts. This even includes caustics. Liquid cleaners are just as effective as powders. Field benefits that are attributed to liquid cleaners include:
- Safer, easier to handle; can be pumped through pipes to the process tank from another plant location.
- No dust, caking, splash-back or localized boiling when making additions.
- Analysis can be accurately and quickly determined by measuring the cleaner’s conductivity, a direct function of the concentration. Conductivity or torroidal probes activate a pump, which dispenses a sufficient quantity of the concentrate. Desired cleaner concentration is maintained at the set point.
- 75% to 85% reduction in sludge.
- Empty totes of liquid cleaner concentrates are recyclable to the supplier.
- Tank dumps and new makeups are quicker.
- In many waste treatment applications, metals flocculate and settle faster as a result of reduced dissolved salts in the cleaner solution.
- OSHA-compliant because of reduced worker direct contact.
Unlike standard cleaner blends available in the past, today’s powder and liquid concentrates offer different additive packages to meet specific requirements. These include surfactants only, or surfactancy/additive systems. The finisher can maintain a cleaning system with additional detergency, as needed, without exceeding alkalis or other constituents. To optimize the cost of cleaning, proprietary concentrates can be added in ratio with the finisher’s source of caustic.
Some cleaners are formulated to be used in both soak and electrocleaning. This simplifies application, line space allocation (additional rinsing is a bonus), inventory and analysis control. Liquid soak concentrates improve rinsing characteristics based on not containing fillers such as soda ash.
Many of the changes in soak cleaning technology, therefore, are the result of meeting a new range of requirements: operations, environmental and health-related. These items continue to foster change and improvement in the science of soak cleaning. The first step in many metal finishing processes does have “the right stuff.”
Stephen F. Rudy, CEF, is president of Chem Analytic and has written extensively about the finishing industry. Visit www.chemanalytic.com or call him at 917-604-5001.
