New legislation regarding the use of solvents in industry processes means that alternative cleaning methods are required. Aqueous cleaning using ultrasonic baths is effective, environmentally friendly and the perfect replacement for an existing solvent based system.
As we move into the new millennium the extent of the damage we are doing to our planet has finally been realised and measures are being implemented in order to at least slow the process of global warming before it is too late. One of these measures was the introduction of the Solvent Emission Directive (SED) which was created in 1999.
The aim of this directive was to ensure that companies are no longer pumping un-monitored and un-quantifiable amounts of solvent emissions into the atmosphere, thus speeding up the depletion of the ozone layer. These guidelines have now become law in the UK through a number of different Environmental Protection Acts (EPA) in 2002. Although full enforcement has not yet occurred by October 2007 there will be no avoiding it. So what options do companies have available to them to comply with this new stricter legislation?
The first interesting point to make is that the surface cleaning process is being separated from the en-suing coating process and will be governed by different guidelines. Looking at the former of these two processes they will predominantly be governed by the Secretary of States Guidance for Surface Treatment of Metal Processes. Now without going into too much depth about what these guidelines set out they give the manufacturer a number of different options in order to comply with emission levels.
There are basically three main options. Option 1 states that if the amount of solvent consumed is less than 2000kgs per annum the process is complying with emission levels and is exempt from enforcement. Option 2 allows for far great consumption of solvents but they must be <30 % VOC in weight. VOC being a Volatile Organic Compound, or generally a solvent. Both of these options allow for use of solvents but the type and quantity which can be used is limited. Although this may be applicable in some industries it is not ideal and a small slip up in quantity usage could result in a costly error. The third option is to emit so little exhuast vapour, or non at all thus being exempt from the restrictions.
This is clearly the most favourable option and it is this option which I would like to look at in more depth. How do you achieve surface preparation to the desired standard without using solvents though. Surely if there was an alternative method to solvents we�d all be using it right now. This is even more the case when I tell you that one of the options not only doesn�t use solvents period, but the cleaning agents it does use are both cheaper and more resistant, and therefore last longer, than their solvent counterparts.
How can this be possible I hear you ask? Ultrasonic cleaning is how.
I�m sure you�ve all heard of ultrasonic cleaning, or aqueous cleaning as it is often called. For those who haven�t here is a brief, laymens terms, description of the process. It uses high frequency sound waves, which are in-audible to the human ear, to compress and rarefact liquid. As these waves, which are emitted from piezo ceramic transducer assemblies, pass through the liquid they create microscopic bubbles. The continuous movement of the sound waves through the liquid forces these bubbles to expand until they become unstable. At this point they implode: the process of cavitation. It is this that gives ultrasonic cleaning its rapid high performance cleaning action. Each bubble implosion creates a shockwave and extremes in pressure which effectively disintegrate the contamination off the item, and with millions of these implosions happening within an ultrasonic tank every second it all adds up to a powerful cleaning process. They have the ability to reach deep into surface impurities and remove any traces lodged there. Coupled with this is its ability to clean even the most intricately shaped items. The sound waves will travel through almost any object. What is the benefit of this? Well, if an item has internal channels which are difficult to reach when being cleaned it means that once submersed into the liquid and these channels have filled with the cleaning fluid from within the tank they will be subjected to the same cleaning action as the external surface areas. In other words, the inside gets the same level of cleaning as the outside.
By adding further options to the process the cleaning action can be further intensified and it is here where ultrasonic truly takes the reins in terms of complying with the SED guidelines. Although solvents can be used within the ultrasonic tank it is unlikely they will be required. An ultrasonic detergent should have sufficient cleaning power to do the same job as a solvent, but because they are biodegradable and contain no solvents they emit little or no emissions. Adding an ultrasonic detergent will intensify the cleaning action within the tank by reducing the surface tension of the liquid and also suspending the removed debris in solution, so it cannot recontaminate the item during removal from the liquid.
Installation of an ultrasonic system can take one of three guises. Which is most applicable will depend on the items to be cleaned and what is already available within the cleaning process. A series of submersible transducers can be designed to fit into the tank and are then powered by an external ultrasonic generator. The benefit of this method is that existing tanks can be used, thus eradicating the cost of a new tank. It also allows a good level of process control as the generator can be linked up to a pc to allow for PLC control. By doing this the cleaning cycle can be tailored to the requirements of the end user and without the need for complex operation or training. The second option available is more suited to smaller items or items where a batch cleaning process is used. Here a complete ultrasonic system can be purchased. This would normally take the form of a large industrial ultrasonic benchtop. These units have built in controls for time and temperature which are stored by the digital panel meaning cycles can be carried out by a single button press. In some instances digital may be not be suitable and in this situation ultrasonic cleaners are available with analogue controls. The third and final option is to have a complete bespoke system designed and manufactured to carry out the process. Although possibly the most costly approach this option gives the end user a huge amount of flexibility. Fully automated systems can be designed which incorporate wash tanks, rinse tanks and dry tanks. The method of transferring items between these tanks can also be automated allowing ease of operation.
All of these systems use the same biodegradable detergents meaning they are green and easy to dispose of so running costs are reduced as the cost of waste management can be all but removed from the equation.
Ultrasonic cleaning is the perfect replacement process for existing solvent system and when you look at the big picture of cost, reliability, cleaning efficacy and compliance with these strict guidelines is it certainly an option to consider when the time arrives to comply.
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