As the co-owner of American Plating Power, Peter has over 30 years experience in the power electronics and metal plating industry.
Q: What is nowadays the best Control method for Type II anodizing Rectifiers?
A: Rectifier control in today’s anodizing industry is still predominantly done manually. Consequently, most anodizing companies are relying heavily on the individual experience, availability and personal condition of their operators. The disadvantages of this are obvious. However, the use of an automated process controller to control the rectifier will reduce or eliminate the drawbacks of a manual system. Ideally, the interface needs to be simple enough to operate to ensure operator confidence in using the system, and must provide the benefit of reduced operator workload and improved performance with regards to quality and through-put. Additionally, process controllers can meet the ever-increasing demand for productivity, consistency and even data-logging and/or reporting.
Here is a review of two commonly used control methods, and the challenges of their use.
Current / Time control – This method of control provides the fastest way of oxide growth rate, but has a number of issues;
- The exact surface area of the load needs to be pre-calculated to determine the total process time and current setting of the rectifier
- The racking system needs to be reliable to avoid burning and loose profiles
- It requires a skillful operator to adjust the rectifier from load to load
- Usually not applicable to service companies working for extrusion companies because of the unknown surface areas
Voltage / Time control – This is the safest control method, but also has some issues:
- The process time is longer in comparison to the current/time control method
- Here also, pre-calculation of the surface area is required to ensure that the rectifier is not overloaded
- It requires a skillful operator to adjust the rectifier from load to load
- Process voltage needs to be adjusted from load to load, or load size must be equalized
- Process time needs to be increased throughout the process in order to compensate for the losses generated by the growing oxide layer thickness
All these factors affecting type II anodizing processes can be optimized or totally eliminated by the use of a dedicated process controller which is specially designed for the purpose of controlling anodizing rectifiers. These systems, unlike standard controls which can also be used for electroplating, are featured with an advanced current density control. The advantages are as follows:
- – Pre-calculation of surface area is no longer necessary
- – Tripping of the anodizing rectifier due to an overload is avoided by use of the automatic optimizing function
- – Automatic ramping is included to ensure a constant film growth
- – Easy to reload programs to get a constant, reliable quality
- – Simplified two-button operation initiates the automatic process sequence
- – Improved productivity because of shorter process time
- – Less pre-work required
- – Most optimal use of rectifier; over-loading is not possible
Latest technology – Anodizing Controllers
The latest generation of process controllers are solely dedicated to the unique characteristics associated with the type II process. In addition to the standard current/time and voltage/time control modes, a current density control mode is added which offers the above described features. Once the operator selects the requested A/ft² and the oxide thickness, the controller will determine the process time and run the process automatically! Additional features such as bath temperature monitoring and Ah counting are helpful tools to generate an even tighter process data profile. Unlike older controllers, these units are available in a stand alone panel that can be placed right next to the anodizing bath, easily replacing the existing remote control panel.
The rectifier gets a new ‘brain’.
Process controllers are often blamed for their complexity and unfriendly user interfaces. Most of the time, a general design idea is used to comply with different tasks. To utilize the advantages of modern technologies, today’s controllers are specialized to provide the best solution and not merely more options. These new specialized controllers are adapted to the needs of type II anodizing lines to increase productivity without enlarging the rectifier capacity, a smart solution to enhance the performance of the rectifier.
In conclusion, implementing the latest generation controllers gives an optimal control of the rectifier in type II anodizing processes, while ensuring quick return of investment due to shorter process times and higher through-put.
