Never before has the electroplating and surface finishing industry been faced with such a challenging business environment. In recent years, legislation such as the End of Vehicle Life Directive (ELV) and the Restriction of Hazardous Substances (RoHS) has had a large impact on the Industry. Coupled with tightened environmental legislation and spiraling metal, chemical, energy and water costs—together with the impact of global competition—understanding and reducing operating costs has never been more important. The industry has also suffered in recent years from ignorance and misunderstanding about its role in modern life with a few unscrupulous operators spoiling its image. Surface engineering and finishing is inherently “green” as it plays an important environmental role. It allows lower cost, easily produced substrates to be used for mass production while enhancing the properties of the original materials and providing these materials with special surface properties. These properties extend the life of components and retrospectively conserve our resources and the environment.
For example, electroplating produces thin layers of just a few microns onto base materials using valuable resources sparingly. These very thin deposits give the base material properties such as vastly improved corrosion and wear resistance while producing a surface appearance to meet end-user demands.
Keeping the point in mind that understanding and reducing operating costs are vital in operating a profitable business, why haven’t the techniques and technologies to enable this aim to be accomplished been widely adopted? The Principle of Investment in New Electroplating Systems While appreciating that this paper in being presented in a non-commercial forum, an appreciation and definition of the difference between cost and investment is vital to enable technology to be acquired. The shortest and most succinct definition the author has been able to find is as follows:
“Expenditure to acquire equipment that produces revenue.”
With this definition kept in mind, the concept of energy and waste minimization can be seen to make commercial sense as well as being correct in protecting the environment to the benefit of future generations. The prospective investor can then move on to the next important strategy, which is the selection of the “best available techniques.” Best Available TechniquesAfter understanding that an investment needs to be made in a new electroplating system, the best available technology or techniques can then be chosen for integration within the system.
“Available techniques” means those techniques that have been developed on a scale that allows implementation, under economically and technically viable conditions, taking into consideration the cost and advantages.
“Best” means, in relation to techniques available, the most effective, in achieving a high general level of protection of the environment as a whole.
“Techniques” includes both the technology used and the way the installation is designed, built, maintained, operated and commissioned. Higher Investment Cost Technology Available Many papers have been given in recent times with new methods and concepts, and it’s not this paper’s intent to go into them in any detail.
Well proven and available technology and techniques to minimize water, energy, chemical and metal usage are as follows:
- Ion exchange systems for metal recovery and reuse of rinse water
- Electrolytic plate out systems for recovery of metals
- Electrodialysis.
- Backwash media filtration systems
- Pre-cleaning with oil recovery systems
- Improved operating and control software
- Improved rinsing systems
- Low energy drying systems
- Computer-aided modeling systems to improve plated metal distribution on parts
Practical, Simple and Effective Lower Investment Cost Technology AvailableAgain, the subject matter is too large for a detailed investigation of all the techniques and technology to be discussed. One of the key areas that impact costs and the environment is water consumption, both into and out of the system. The author does not claim that any of the following points are new. However, many of them have yet to be universally adopted.
Many plating system process sequences provided concentrate entirely on the immersion times in the process baths but fail completely to address dwell times over the solution and the subsequent immersion times in the rinses. By allowing a slower lift speed and an adequate dwell time after the product has been raised out of the process stage, drainage back into the process solution can be maximized and valuable metals and salts retained in solution. In barrel systems, this effect can be further enhanced by rotating the barrel in the up position.
Some helpful recommendations:
- The use of simple rotameter type flowmeters coupled with manual diaphragm valves on the incoming rinse tank water supply can be a very cost-effective method of restricting the flow of water.
- Another simple technique is the use of automatic electrical solenoid valves coupled to either pH or conductivity sensors that shut or open the valves depending on the concentration of chemicals and metals in the rinse water.
- A smart control system can turn on the water supply for a set period depending on the throughput of the equipment, i.e water is allowed to flow into the rinse water tanks for a certain period of time after a predetermined number of flight bars or barrels have been processed. Another useful tool is that the control system will turn off the water supply if the machine is allowed to idle.
- The principles of counterflow rinsing have been well documented for many years and the use of three cascade rinses with the large savings in water consumption has been common practice for a long time in Germany.
- If the space available does not allow this, spray rinsing installed on the second tank in the counterflow rinse system can assist in reducing water consumption, especially if the newer type “fog” spray nozzles are used. Similarily, these systems can be employed above tanks with a high operating temperature—such as nickel to compensate for evaporation losses and dragout and with a minimal amount of effort can achieve equilibrium between loss and replenishment.
- Another technique common in Germany is the use of “Eco” rinses. Drag-out from process solutions working at ambient temperature (but not limited to) can be recovered through a single rinse station in which the workload is dipped before and after being Processed. The “Eco” rinse station can be made up with diluted process solution from the very beginning or filled with deionized water only. In this case it will take some time until the final concentration will be reached. The solution has to be changed only when the tank itself and/or the tank walls have to be cleaned. During normal operation no water has to be added assuming that drag-in is equivalent to drag-out.
- Turning to energy consumption, an area frequently ignored yet responsible for large quantities of energy consumption is the exhaust or ventilation system. Valuable process chemicals can be sucked into the system and heat losses from the process tanks mean higher levels of heating need to be employed.
- The open areas of all tanks requiring fume extraction should be carefully considered and minimized where appropriate or possible. Anode bar and flight bar covers can act as a cost-effective method of minimizing tank open areas.
- The rate of extraction should be carefully considered and calculated so that compliance with legislation is met and not exceeded.
- A “push-pull” system, properly designed, can provide effective exhaust while reducing the extraction rate for the process tank, especially on large tanks.
- Again, a “smart” control system together with a variable speed exhaust fan can be used to reduce the capacity and, therefore, energy being consumed in the system. The extraction rate can be reduced when the equipment is idle.
- Another very useful technique is the replacement of air agitation in process tanks by the use of venturi nozzles. Air agitation is still specified in the majority of cases yet the case for venturi systems is not well established. Uniform and efficient agitation can be achieved by using a separate circulation pump driving solution through nozzles, which if correctly designed, can provide four times the outlet flow of the incoming flow. As the venture nozzles do not create fumes, extraction of the tank can be reduced along with the corresponding losses of chemicals and metals into the fume exhaust hoods and ductwork and scrubber sizes can be minimized. Another valuable advantage is that the process efficiency is improved.
Practical, Simple and Effective Methods of Selecting Best Available Techniques A simple cost/benefit analysis can easily determine whether this is the right investment choice. The following needs to be taken into account:
- Expected payback period.
- Throughput of racks, barrels or flight bars per hour
- Equivalent plated area per hour
- Equivalent plated parts per hour
- Dragout from parts per hour
- Acceptable rinse ratio
- Quantity of incoming rinse water flow per year and cost and/or cost of energy per unit.
- Quantity of outgoing rinse water flow per year and cost and/or cost of energy per unit
- Investment required to add the technology
ConclusionIt can be seen that many tried and tested techniques and technology can help greatly in minimizing the environmental impact and the operating costs of electroplating equipment without the need to invest large sums. The selection of the best available techniques can be undertaken only when a thorough understanding of the true current operating costs versus the savings that can be realized by new investment takes place.
References
- D.Hemsley, The Surface Engineering 2000 Model Plating Plant Project, Transactions of the Institute of Metal Finishing, 2000.
- Integrated Pollution Prevention and Control (IPPC) - Surface Treatment of metals and plastic materials using electrolytic or chemical process, 2002.
- L.Hartinger, Handbook of Effluent Treatment and Recycling for the Metal Finishing Industry , 2nd Edition, Finishing Publications Ltd.,1994
