Vapor Degreasing: A Fresh Look at an Old Process

In today’s challenging manufacturing environment, parts must leave the production line perfectly clean, dry and ready for further processing. Any contamination like oils, dust and metal particulate must be removed to ensure the next stage of production, whether it is plating, coating, painting or welding, can be completed successfully.

In the finishing world, aqueous cleaning has long been used as a method for precision cleaning. Aqueous, or water-based, cleaning works well and is particularly useful when combining the cleaning process with other procedures like depositing rust-preventers and brightener coatings.

However, energy demands and new environmental concerns are generating increased interest in the vapor degreasing process. Many companies are finding vapor degreasing to be a fast, effective and affordable method for cleaning metal parts. In a world where reliability, compliance and sustainability are paramount, vapor degreasing deserves consideration as a successful, cost-effective and planet-friendly cleaning process. The two processes are examined below.

Aqueous cleaning

Aqueous cleaning uses water that is treated with a variety of compounds, including detergents or surfactants, builders, emulsifiers, saponifiers, sequestering agents and chelating agents. These additives help to enhance the cleaning profile of water.

In a metal workshop environment, aqueous cleaning is usually performed through ultrasonic cleaning, total immersion, standard spray and high-pressure spray. Water cleaning involves three steps, including washing, rinsing and drying. Parts are first washed to remove contaminants. By using detergents, high heat and agitation, aqueous systems break down soils and remove them from part surfaces. This is followed by a secondary rinse step to remove any remaining contaminant or detergent residue. The final step is drying the parts; this is achieved through the use of hot air knives or isopropyl alcohol. 

The aqueous cleaning method can be quite effective at cleaning metal parts; however, there are environmental concerns.

Aqueous systems produce a waste stream that requires treatment before discharge. Wastewater must be filtered, distilled, deionized and osmosis prepped prior to disposal. The cleaning agent added to the water can be difficult to dispose of.

In addition, aqueous systems require high temperatures to be effective. Energy required to operate an aqueous system, as well as the water used for the process, also contributes to environmental concerns. 

Vapor degreasing as an alternative

In the 1990s, many metalworking shops used chlorofluorocarbon (CFC) and hydrofluorocarbon (HCFC) based solvents inside vapor degreasing machines to clean parts. They effectively removed grease, oils and other industrial soils, however, they also had very high ozone depleting potential (ODP) ratings. By the mid-1990s, their use was highly regulated and eventually banned for metal cleaning altogether.

Solvent-based cleaning using a vapor degreaser is now seeing a resurgence following the development of innovative, environmentally safe cleaning fluids that combine effective cleaning power with efficiency and sustainability.

Vapor degreasers use a closed-loop system that requires two elements: a specially designed cleaning machine and specific low-boiling non-flammable fluid as the cleaning agent. Solvent-based cleaning fluids contain a mixture of compounds that can be combined or custom formulated to successfully remove contaminants. They are also engineered to ensure they are compatible with the substrate and materials of the part being cleaned to maximize effectiveness.

A vapor degreaser is not only a parts cleaner but also a continuous recovery and recycling system. The system contains two chambers: the boil sump and the rinse sump. In the boil sump, the solvent is heated and the parts are immersed and cleaned in the fluid. Once cleaned, the parts are mechanically transferred to the rinse sump for final cleaning in a pure, uncontaminated fluid. The cleaning fluid condenses and drips back into the vapor degreaser, from which it can be reused for many hundreds of times before needing to be refreshed or replaced.

When it is time for disposal, the vapor degreaser concentrates the soil and contaminants, minimizing the amount and frequency of waste disposal whichhelps to reduce the cost of hazardous waste removal.

The energy consumption of a vapor degreaser can be considerably less than that of an aqueous cleaner. Cleaning, rinsing and drying take place in a singular machine, which can clean a high volume of parts quickly. In addition, since vapor degreasing cleans and dries parts in just one step, there is no need for blowers, air knives or any other drying method that uses a lot of power. 

In addition, the vapor degreasing process uses no water. The energy and subsequent cost saving benefits of vapor degreasers make this method of cleaning a viable and sustainable solution. 

Modern vapor degreasers use updated, environmentally progressive fluids to deliver consistent and safe cleaning results. These can be used as drop-in replacements inside existing vapor degreasing equipment.

These fluids are engineered with the correct characteristics, for example high densities, low surface tensions and low viscosities, to wet every surface. This means they can penetrate complex shapes to completely dissolve contaminants and remove stubborn particulate. They are also compatible with a wide range of metals and plastics and clean a variety of soils. Additionally, the fluids are chemically and thermally stable, meaning they do not turn acidic with use, and are nonflammable for workplace safety.

A further benefit is that parts come out of the vapor degreaser clean, dry, spot-free and cool enough for immediate further processing or packaging. 

Contaminants – match and remove

Before investing in an aqueous or solvent-based cleaning system, it is important to also consider the contaminant to be cleaned. To remove contamination successfully, the cleaning fluid should match the contaminant itself. It is therefore essential to understand whether the contaminant is a particulate, or a polar (inorganic) or non-polar (organic) soil.

Particulate is an insoluble contaminant that will not dissolve in water or solvent-based cleaning fluids. Insoluble contaminants include metal shavings, dust, surfactants, stearates and polishing pastes. The particulate cannot be dissolved or solubilized and instead is displaced from the part and washed away. The cleaning fluid gets under the particulate, dissipates the static holding it to the part and removes it from the surface. This cleaning method is used in both aqueous and solvent-based processes.

Inorganic contamination includes salts, soaps, emulsion residue and graphite. It also encompasses oxidation like rust and tarnish, heat scale, smuts and carbonaceous and metallic compounds. These soils are soluble in water, therefore, aqueous cleaners are effective at removing the particulate because like dissolves like. Water-based detergents and surfactants emulsify and encapsulate contaminants so they can be washed away.

Organic soils are non-polar halogenated, oxygenated and hydrocarbon soils. Examples include machining and stamping oils, grease, corrosion protection agents, esters and baked-on resins. Organic contamination can be dissolved and removed with specialty solvent-based cleaning fluids.

Remember, choose your cleaning fluid according to your containment and ensure that it is chemically similar to the contaminant itself.

When choosing the cleaning process that is right for you, there are many other factors to consider, from capital investment to cycle times. For this reason, it is recommended that you work with a precision cleaning expert that specializes in both aqueous and vapor degreaser solvent cleaning. They can help assess your particular cleaning project and recommend the fluid and process that not only has long-term sustainability but also the best cleaning performance.