BREAKTHROUGH TECHNOLOGY FOR TRUE FERRIC CHLORIDE BASED ETCHANT REGENERATION
Until now, there were essentially three methods of working with ferric chloride etching.
The first method starts with fresh ferric and continuing to etch until depleted. You work your way through the various metals typically starting with the highest quality stainless and working your way down through the different metals until no more etching is possible. There are many drawbacks to this method. One is the continual slowdown of the etching process. Another is that you need to change to different metals as the etchant will no longer etch the metal that you started with.
Lastly, when the etchant is nearly depleted, you need to drain the etcher, clean out the sludge, refill the etcher with new starter ferric chloride and start the whole process over again. Two major drawbacks to this method include a lack of etchant consistency since the etch rate is slowing down as etching occurs and the requirement of changing to different metals down the periodic table since the etchant will no longer etch the stainless steel or carbon steel that you started with.
The other methods of etching with ferric chloride attempt to address the etch rate consistency problem by using a controller to maintain or regenerate the etchant. These controllers either use a combination of conductivity to control hydrochloric acid (HCl) adds and an Oxidation Reduction Potential or ORP (also called Redox) probe to control oxidizer adds or they use an electrolytic process for removing metal. A major problem with the conductivity/ORP method is that it does not achieve full regeneration consistently without resulting in releases of chlorine gas.
The conductivity portion of these controllers can be very reliable but in usual operation, the ORP part has a very serious drawback. ORP tends to work correctly when etching only one metal such as iron or copper but doesn't usually work well when alloys are etched. That's because as the metals are etched, in order to regenerate the solution, the metals must be chemically converted such as ferrous to ferric chloride, chromus to chromic chloride and so on.
These reactions occur at different ORP values which the ORP probe cannot distinguish the difference between. For this reason these controllers essentially become a “best guess” system because an ORP value is selected that comes close to regenerating the etchant without overdoing it resulting in chlorine gas. In the end, the etchant still loses its ability to etch and must be dumped or removed for batch treating.
While this is an improvement over the first method mentioned earlier, it is still a far cry from truly regenerating the etchant and you are still left with a gradually diminishing, inconsistent etchant. The electrolytic method requires large amounts of electricity, can be slow to regenerate, and uses very expensive and fragile membranes.
Enter the VUE Ferric®…
The VUE Ferric® is the world's first patented regeneration system using light sensors or “cells” to monitor and control the regeneration process to maintain the etchant at all times. A conductivity sensor is included to be able to custom tailor the etchant to allow for different etching conditions while still maintaining fully regenerated etchant because of the light cell control.
This takes care of the consistency problem completely since the etchant condition no longer changes over time. This sounds great all by itself but the real benefits come from the fact that you are now making fresh etchant that can be used to etch further metals in another etcher.
Many traditional methods for ferric etching involve buying fresh etchant, using it, then either sending it away as waste or removing it from the etcher and batch treating it for reuse. When using the VUE Ferric® to regenerate the etchant, HCl and oxidizer are added as you etch your metal actually making fresh etchant.
Since you are adding more liquid to the sump from the regeneration chemistry, a built-in overflow spent system in the VUE Ferric® allows this excess to be channeled into a holding tank as new etchant for a second etcher.
The best part is that you are no longer buying fresh ferric since you are now making your own brand new etchant from the metal being etched. Naturally, the idea of cost comes to mind since you may think that fresh ferric is cheaper than the cost of the HCl and oxidizer on a per gallon (or liter) basis.
In fact, the thing to think about is that with fresh ferric chloride etchant, you are purchasing an etchant that is already loaded with iron to begin with so there is much less metal that you can add before it is depleted and you still have the consistency problems anyway.
When you use the VUE Ferric® controller to make your own etchant, all the metal loading in the etchant comes from the metal being etched making the full regeneration VUE Ferric® by far the most efficient controller with the lowest operating cost. OK, this all sounds very good but how does it work?
When the etchant is fully regenerated, it forms a relatively clear solution. As you etch, the metals coming into solution are not clear. The light cells in conjunction with a Programmable Logic Controller (PLC) built and programmed by Oxford V.U.E., Inc. sense these changes in the etchant and perform tests necessary to add the correct chemistry and in the correct amounts to maintain a stable, consistent regenerated etchant that can continue etching indefinitely.
It would take far too much space here to explain all the variables involved in the test and add process but suffice it to say that the correct methods are called upon in the PLC memory to get the job done. The best part is that all the complexities of control are done without the need for operator intervention. In fact, once properly setup, very little simple maintenance is required for normal operation.
How does the VUE Ferric® handle different metals?
The VUE Ferric® can be programmed to regenerate the etchant used for etching a variety of different metals but it is important to pick just one type of metal to etch in your etcher controlled by the VUE Ferric® (i.e.: 300 series stainless steel or 400 series stainless steel, etc.). This is required because otherwise the etchant would be in a constant state of transition between the different metals with varying amounts of each metal becoming chlorides. On the surface, this sounds like a drawback but in reality it is no drawback at all.
Most chemical millers have more than one etcher because they need to be able to switch etchers as the existing etchant degrades. When using a VUE Ferric®, since you are now making your own etchant, you can easily dedicate an etcher to VUE Ferric® control while using its overflow as fresh etchant in the next etcher.
After all, you can etch any metal you would normally want to in the next etcher with the etchant made by the VUE Ferric® since this solution would then be used as if it were starter ferric anyway. Also, if you have multiple etchers, you can dedicate a few to VUE Ferric® control and use the remaining etchers for other metals.
All you need to do is to see how much fresh etchant you need to finish the job in the non-VUE Ferric® etchers and setup the VUE Ferric® etchers accordingly.