A brighter future for metalfinishing

Bill Lambert, vice chairman of Kerry Ultrasonics, looks at some of the current options for environmentally sound cleaning techniques in surface finishing.

No single degreasing process, be it solvent or aqueous, in-line batch cleaner or closed-loop cell washer, has yet been developed to suit all types of cleaning application. In this article I will examine four different cleaning processes, all of which are environmentally safe. One or more of these is applicable to industry sectors ranging from automotive, aerospace and medical device manufacture through to machine tooling and general engineering.

Aqueous degreasers of considerable versatility are now available to metalfinishers seeking an alternative to degreasing with chlorinated solvents such as trichloroethylene.

Closed-loop processes

Batch-type single-chamber aqueous degreasers feature closed-loop cleaning processes. They run within a vacuum-tight treatment chamber fed from cleaning and rinsing reservoirs.

At the time of purchase, the machine's features can be limited to those that are relevant to users' particular degreasing requirements. Oil separation, ultrasonics, basket rotation, micro filtration and automatic loading/unloading can all be included in the process options.

Each stage of the cleaning process is independently programmable, for maximum flexibility. Users can choose immersion or spray wash with hot detergent, and baskets may be stationary, rotated or oscillated to suit component geometry. Very greasy parts carrying swarf can be cleaned with optional injection flooding while selecting ultrasonics will remove swarf from complex components. Immersion or spray rinsing is followed by an optional hot air pre-dry and a final vacuum dry removes any moisture remaining in blind holes.

The small footprint of these machines suits most metal degreasing applications and is ideally suited to cell manufacturing environments. Taking a maximum load of 50kg / 80kg in a 530 x 340 x 200mm / 620 x 400 x 410mm carrier, they will process five or six batches per hour, combining high efficiency degreasing with fast process times. Euro tote bins are also accepted.

Zero emission

A safe and economic, zero-emission process using Perchloroethylene should be considered for high throughput degreasing of ferrous parts, or where there is a high degree of organic contamination.

A single, vacuum-tight chamber delivers a pre-clean followed by immersion cleaning, spray or immersion rinse and vacuum dry. Ultrasonics, injection flooding and vapour rinsing can be added, and each step of the process is independently programmable.

Continuous internal solvent regeneration and recycling maintains solvent purity while distillation of the used solvent at the end of each cycle removes any oils. During operation, hermetic seals prevent solvent vapours escaping from the cleaning chamber. Once a cycle is finished, the air in the chamber is fed through an activated carbon filter to remove residual solvent; even accumulated solvent in the carbon air filter is recovered using an integral desorption process. The chamber door remains automatically locked until the residual solvent in air concentration has fallen to a safe level, i.e. less than 1g/m3.

As well as ensuring both personnel and environmental safety, these features also guarantee low solvent consumption levels - typically only two litres of solvent needing to be replaced for every 10 litres of contamination removed. These types of system are available in five sizes, the largest taking basket carriers up to 770 x 960 x 420mm and cleaning up to six batches per hour.

Unique to Kerry Ultrasonics, the co-solvent process comfortably handles both metal degreasing and precision parts cleaning. Microsolve co-solvent systems use an environmentally-friendly special blend of 3M's Novec HFE 71 IPA and a hydrocarbon solvating agent in the cleaning stage, followed by pure HFE in the ultrasonic and vapour rinse stages.

The hydrocarbon is able to absorb high levels of oil and grease, while for sensitive or fine bore components the Neptune generator control allows selection of ultrasonic cleaning at a safe frequency of 70kHz.

A Superheat facility ensures thorough drying of complex components, and solvent monitoring/auto top-up, together with other design features, guarantees low solvent comsumption.

Aqueous wash

A typical aqueous wash system entails a four-stage process comprising ultrasonic cleaning, mains water and closed-loop high-purity water rinsing, and a hot air dry. Again, switchable frequency generators allow safe but effective high frequency ultrasonic cleaning of delicate parts.

For special applications, aqueous systems may be combined with extra stages such as a pre-clean with oil separation, or a final stage dip in a protective coating. A programmable work transporter can be fitted to all multi-stage cleaning systems to make them fully automated.

Kerry's Autotrans, for example, can be programmed for fully automated loading and unloading of work baskets including controlled transfer through all process stages. Multiple basket processing using pick and place principles is a standard Autotrans feature.



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