Blog - Advint Incorporated

Achieve a profound change in electroplating process control by asking inquisitive questions. Use emotional intelligence with curiosity, be intuitive, lay emphasis on quality over cost, and maximize human and automation potentials.  


 

Who does not want to advance their process performance? If we can improve the process without adding cost it is a windfall, correct? Maximizing automation of power supplies on electroplating, anodizing and electropolishing metal finishing applications is one such method. Automation helps process control. Above automation comes intuitive mind. Intuition is a derived from knowledge and experience. You ought to combine intuition with equipment capability. In this short paper we will review functions, capabilities and advantages of insulated gate bipolar transistor (IGBT) switch mode rectifier and silicon-controlled rectifier (SCR).

 

Intuition

Einstein nurtured his intuition from his experience working as a patent clerk while developing his theory of Special Relativity. His presence of mind and theoretical knowledge was instrumental in his brilliant work. Intuition and experience also played a significant role. Likewise, you can use your keen and meticulous observation skills, creativity, innovative mind, knowledge and experience to automate your plating and other metal finishing processes. Managing desires and possessing a non conforming mindset are nuts and bolts to achieve this trait.

Combine this attribute with knowledge in automation and on capabilities such as ampere hour reading and application of current during electrolysis for the finest results. Required capabilities for processes such as anodizing of aluminum, hexavalent or trivalent hard chrome plating, nickel and cadmium plating vary because of electrolytic conditions and electrode potentials.

 

Automation


Start with questions!

What are the automation opportunities?

Which option makes available the most benefit with less cost and complication?


 

Automating DC power supply is one of the best choices on an electrolytic process. An excellent choice on a rectifier allows the cathode to receive optimal current. Note, there is a difference between applied and received current. One can read previous articles in this page on current distribution, throwing and covering powers.

 

A rectifier with RS 485 and 4-20mA analog signal capability and ampere hour (AHR) meter can enable metering of process chemicals during electrolysis. Who doesn’t want consistent output quality? We must reduce variations within input variables to get the desired output quality. Among input variables there are parameters which vary by electrolysis and others vary primarily because of drag in and drag out of chemicals. It is pertinent to account for both types of variables. Rectifier, PLC and metering system can be programmed ingeniously to realize this aim.

 

With power supplies, begin by choosing between IGBT switch mode or SCR thyristor DC rectifiers. Ripple factor, unit weight, voltage and amperage accuracy are better with the IGBT rectifier. Ripple is a measure of purity of DC output of a rectifier. Many electrolytic processes, especially precious metals plating like gold and silver plating are sensitive to a higher ripple percentage. When a SCR rectifier is used at a lower amperage than the rated capacity of a rectifier, ripple is high. Whereas with IGBT rectifiers ripple factor is consistent and independent of DC output voltage. Green Power’s DSP digital control allows increased longevity with less maintenance of rectifier and comes with a very high accuracy. The DSP technology is proprietary to Green Power Co. Ltd. When compared with SCR thyristor rectifiers, IGBT power supplies possess higher efficiency and power saving capability.

 

In a nutshell, by choosing IGBT rectifier you choose better technology, save space and power, improve accuracy resolution and accuracy, and negate the effect of ripple factor. Use of RS485 MODBUS protocol can integrate with programmable logic controller (PLC) and control current, dosing systems and enable trickle current mode at the start of the process.

 

An Idea in Brief

 

 


Achieve a profound change in electroplating process control by asking inquisitive questions. Use emotional intelligence with curiosity, be intuitive, lay emphasis on quality over cost, and maximize human and automation potentials. 


We can automate hoist, process sequences, filtration and dosing systems, and rectifiers technologies with this outlook. A splendid choice of DC power supply is important. Both IGBT and SCR rectifiers offer unique advantages depending on the electrolytic process. Aluminum and hydrogen electrolysis, electrowinning and electroforming requirements differ from that of electroplating, anodizing and electropolishing. We recommend considering your process requirements with the capabilities of IGBT and SCR rectifiers.

On precious metals plating applications distinguish between applied and actual current. Due cognizance can affect the consistency of deposit thickness and the deposit characteristics. When sourcing a rectifier consider buying from reputed a manufacturer who conducts active research and continuously improve on their design and functionality.

 

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On a metal finishing processing line, among many design factors, choosing a rectifier with correct technical specifications and capacity based on production capability is very important. Predicting a production capability on most lines on a long term, particularly for a job shop is tough.


However, a correct choice on the capacity of a rectifier and on technical specifications will turn errors to account on a process performance.


 

Besides specifications, cost of a rectifier, power consumption and automation capability are significant considerations for a meticulous procurer.

 

IGBT and SCR Rectifiers

There are two types of rectifiers - Insulated gate bipolar transistor (IGBT) switch mode and silicon-controlled rectifier (SCR) thyristor. SCR rectifiers are suitable for high voltage and high ampere applications, but IGBT rectifiers possess higher efficiency, greater power factor, higher resolution, faster response time and constant ripple. Ripple matters in a plating application with an SCR rectifier and on precious metals plating.

 

DC rectifier Power supply

 

Using a rectifier at the lower end of its rated capacity affects the ripple factor. On some applications there will be a negative influence on current distribution and throwing power of the deposit. A few deposits are tolerant than others. Precious and other transition elements differ in this attribute. Much of them are because of price. At a sub optimal capacity combined with a poor specification, a rectifier can yield a deposit with defective morphology compromising adhesion and the physical characteristics.

 

Note: Ripple is not the only cause a compromise can occur on the morphology of a deposit. Among many other variables, Helmholtz electrical double layer effect has a substantial effect on the morphology with the continuity of the deposit.

 

Other than ripple, there are cost impacts. A client of Advint, about 3 years back, purchased a 25,000 amperes rectifier. On most loads they had applied ~ 10,000 amps and seldom they applied 15,000 amperes. And the applicator does not foresee applying 20, 000 amperes within the next few years. The tank volume and the rack capability do not support the calculation. In hindsight, the applicator could have saved by considering a lower ampere rectifier (written with the Applicator’s consent).

 

On high ampere applications, power consumption is an important factor. When the distance between shunt and electrode terminals are higher, power consumption (resistivity) and cost is high.

 

Automation and Digital Control

On automatic applications, metal finishing industry uses human-machine interface (HMI) and programmable logic controller (PLC) capabilities for a long time. These interfaces are useful for current density calculations, plating time, ampere hour (AHR) control and chemical metering or dosing system, though the options are limitless. All chemical variables in a process are not consumed by electrolysis, rather a few follows adsorption mechanism. On these cases the use of PLC’s ladder logic, count down or count up timer will help. The MODBUS RS 485 serial communication protocol is the standard now to monitor and control the system. When a rectifier possesses higher end capability, and we maximize utilization even on a manual application, an applicator can see an advantage in labour cost and process control.

 

Ensuring we do not overload a rectifier, can extend the life of the rectifier. A periodic preventative maintenance program will support the same cause.

 

A Brief Idea


This short paper has brought to light the advantages of IGBT rectifier and the use of HMI/PLC interfaces with MODBUS RS 485 serial communication protocol.


Due diligence on specifications and productivity planning reduces fixed and marginal costs, improves the quality and consistency of the coating (electroplating deposit and anodized layer) processes.

 

 

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