Posted 28th October 2016 by Admin@Solumetrix
Much has been written on the topic of water usage in the electroplating industry, and it is very commendable that there is awareness of the huge problem that faces this industry.
It is widely accepted that conductivity measurement is the parameter of choice for controlling the flow of water into rinse tanks, but, in my experience the majority of electroplating works do not have adequate controls of rinse water. This means that huge amounts of water and hence money, are wasted, yearly.
So why can this situation exist, when there are so many papers, and articles written on the subject, and yet there is poor uptake of the technology.
It is this question that was in my mind, when some years ago, I set about designing a revolutionary solution to the problem of reliable rinse water control.
It occurred to me that there were four areas which held people back, when it came to installing such a system.
Difficulty of implementation
Electroplaters are not readily equipped to design and build control systems of this sort, there being many vendors of sensors and controls, who offer partial solutions to this problem, leaving the details of implementation to the end user. Their offerings are often ad-hoc collections of controllers and sensors, which in theory should be capable of doing the job, but which have not been thought through in detail.
The controller is often a controller that is ‘borrowed’ from another industrial use, and the display and setpoint ergonomics are confusing, and ill thought out.
Attempts of this sort often lead to disappointing results, and hence the abandonment of this important objective, to save water, and cost.
In contrast, the RM-33N has been specifically designed for the purpose of rinse water control, and is so easy to use, it can be set up intuitively.
Whilst many manufacturers profess to provide rinse water control systems, very few actually offer a complete system, suitable for fitting to existing tank configurations.
So, for any solution to be implemented, it must be available as a complete solution to the user, and it should enable the user to install it easily, and start making savings immediately, and keep making those savings, without requiring maintenance.
Safety is another important factor, it is imperative that the control valve used has low voltage operation, so that if it fall into the rinse, or contact the water electrically, then operator safety is maintained.
Another area where difficulty is experienced is in the sensor itself, it must be easily mounted in a position where it can be out of the way of the workload, and it must remain accurate, even in the presence of aeration. It is also desirable that some method of providing a small flow of water past the sensor, to maintain measurement integrity in the absence of any agitation in the tank.
The system must be housed in a suitable housing to withstand the harsh environment of the electroplating industry, and all wires and cables should be protected, and be readily pluggable. The RM-33N has all these features, being the product of dedication and commitment to this product, and many features have evolved through appraisal, and re-appraisal, of units in service, in the UK plating industry.
Poor reputation of systems already in use – the technology factor
Mains tap water is the mainstay of most rinse processes, particularly intermediate rinses in general plating processes, and it can vary from very pure (80uS), to quite impure (700uS), in some areas. The impurities are mostly calcium.
In order to save water, the chemical loading must be allowed to increase by a controllable, and repeatable amount, such that a set level of loading is never exceeded. Typically, the conductivity of an intermediate rinse can be set to between700-1200 uS, depending on process. The higher the level acceptable, the greater the savings achieved.
There are two ways to measure the conductivity, firstly, by direct contact, ie, two stainless electrodes in a cell, or, secondly, ‘electrodeless’ technology.
The first method is very easy to implement, and is a very low cost technology. Usually there are two electrodes , in a plastic cell, and an alternating voltage is applied between the electrodes, the resulting current is amplified to give a reading of conductivity.
The electronics required to commonly available, and at first sight, it would appear to be an ideal way to do it, and there are some controllers on the market that operate this way.
However, in real world situations, the chemical loadings quickly cause contamination and surface resistance effects on the electrodes. These resistance effects lead to a lessening of the reported conductivity, or over-optimism of the cleanliness of the rinse water. The manufacturers of controllers that operate in this way, realizing this shortcoming, advise frequent cleaning of the electrodes to retain accuracy.
Invariably, this is not done, or done poorly, and infrequently.
It is not practical in a modern workflow situation, to break down the measurement sensor, and to clean and recalibrate it. Consequently, the control method breaks down, the result being that the system is often removed, as being unsuitable for the purpose.
The second method is electrodeless measurement of conductivity.
This is achieved buy creating a small magnetically coupled toroidal cell, having two coils, situated side by side in a plastic housing. Thus, there is no direct electrical contact with the solution, only magnetic fields are used, contact effects are totally absent.
This may seem like a small advantage, but the effects are very significant indeed.
A sensor operating on this principle, if designed correctly, will continue to give accurate readings of conductivity for weeks, month, even years, without cleaning, or recalibrating.
It is this technology that provides the ideal measurement solution for general rosewater control.
The electronics and technology required to do this accurately are quite complex, and hence, are often not used due to reasons of cost of implementation.
The RM-33N uses an electrodeless sensor, having a very advanced signal processing circuit, which is produced in volume for a multitude of applications, and hence it gives the competitive edge in this market offering ‘electrodeless performance, for electrode prices’, offering accuracy, reliability, consistency combining the signal processing and measurement cell all in one, compact, sensor body.
Commitment and investment in developing this technology has allowed us to incorporate a specially designed signal processing chip into the sensor. Smart electronics carries out our digitisation, and temperature compensation functions. A digital data stream output allows virtually unlimited sensor lead length, with no special cables, and no signal degradation.
Credibility
The process of rinsing components is apparently a simple process, and it is this apparent simplicity that leads to many misunderstandings and misconceptions in the plating industry.
How ‘dirty’ can the rinse water be, and still be effective?
This question is difficult to answer, and, unless some sort of control is used, it is very unwise to operate near the maximum acceptable level , because of the risk of staining, and chemical contamination between process tanks.
In the absence of control, each operator has their own preferred level of water usage, usually erring on the very wasteful, which is good for rinsing, but bad for the bank balance.
In fact, many rinses, when using a control system such as the RM-33N, can have quite heavily loaded rinses, which look highly loaded, but may be only 700 or 800uS, and give a very efficient water usage level.