Initially, electroplaters used generators to provide the direct current needed for the electroplating process till they were replaced by plating rectifiers which convert alternating current AC to direct current DC.

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The plating rectifier has a transformer that reduces the voltage, diodes responsible for the conversion, a control system for both the voltage and the current, a device for cooling the rectifier and overload protection.

These rectifiers have different waveforms which you must consider before you place an order. It may be a full-wave current or half-wave but the best to use for electroplating process is the full-wave to get the best results for processes like chromium plating and other.

Rectifiers offer superior characteristics over generators, such as energy efficiency, compact and lightweight design, easy modulation, and output stability. They also have versatile applications and come with various voltage power supply types.

Plating Explained

Plating involves coating a conductive surface with metal for numerous reasons including enhancing aesthetic appeal, inhibiting corrosion, reducing friction, hardening the metals, improving paint adhesion, and enhancing solder capacity, among others.

The essential direct current (DC) for a successful plating process can come from a low-voltage generator or a rectifier. Initially, generators were the primary source of direct plating current, but due to their high acquisition and maintenance costs, rectifiers proved to be a more economical alternative.

Rectifiers are so versatile that many devices make use of them. Some of the devices that work with rectifiers are:

1. Radio detectors or signals
2. DC power supplies
3. High-voltage DC power transmission systems
4. Household appliances like laptops, video games. Notebooks and televisions
5. Electroplating units.

Plating rectifier is a crucial component of the electroplating process. Electrical current is essential for depositing the coating material onto metal parts. Conductive parts are immersed in the plating tank or bath, and direct current DC is supplied by the rectifier between the electrode and the parts.

The application of direct current DC creates an attraction between the electric-field-driven coating and the conductive part of the metal, resulting in the deposition of coatings on the parts. Controlling and filtering both ripple voltage and DC voltage is crucial to achieve a high-quality finish.

A rectifier's role is to convert alternating current (AC) to direct current (DC). This electrical device includes one or multiple diodes responsible for this conversion.

The diode in the rectifier acts as a one-way valve enabling current to flow in one direction. This process is called rectification. Key components of the rectifier include:

• Transformer: responsible for reducing the voltage. It has both primary and secondary magnetic cores wound with conductive wires.
• The voltage step-down rate is determined by the number of wire turns on the primary magnetic cores to the turns on the rectifier's secondary magnetic cores. Example: Primary=400 turns, Secondary=10 turns results in a 40:1 ratio. If the input is 480V, output would be 12V (480/40). Most electroplating processes use 6-18V.

Rectification and the control system

When the alternating current produces a wave on an oscilloscope that oscillates below and above the horizontal axis, the rectifier filters out the lower part of the wave, resulting in half-wave rectification.

Modern conductors use semiconductors for this process. Once AC is removed, DC flows through. Diodes are one of the devices used in this conversion.

Silicon-controlled rectifiers (SCR), also known as thyristors, are used as controllers in electroplating rectifiers. Although they are diodes, they require a control signal at a "gate" or terminal. SCRs can function as regulators and rectifiers depending on whether they are placed on the rectifier transformer's primary or secondary side.

The design and placement of the SCR will depend on the intended application, unit efficiency, cost implications, and reliability.

Suppliers should consider your requirements and provide detailed explanations to help you choose the right rectifier.

Ripple

SCRs might be efficient, but they can produce direct current distorted by "Ripple." Larger plating rectifiers may produce 5% or lower ripple at their rated capacity. Using a rectifier with higher ripple is not advisable, as ripple increases as the unit powers down.

If your process involves electroplating precious metals, chromium, alloys, etc., a lower ripple rate is essential.

However, if the ripple rate is higher, a filter can smoothen the wave. Although ripple is not a crucial factor in electroplating, it's important to specify a plating rectifier with 5% or lower ripple to ensure smooth operations.

Waveform

Rectifiers have several waveform types:

1. Full Wave: reverses the AC wave's negative part and joins it with the positive part.
2. Half Wave: allows either the negative or positive to flow through while blocking the other.
3. Single-Phase AC: a center-tap transformer creates a full-wave rectifier using two diodes.
4. Three-Phase AC: uses three pairs of diodes.

Another crucial factor to consider is the current waveform of the plating rectifier. While rectifiers can have any of the above waveforms, full-wave rectifiers are appropriate for many plating processes.

This is important because, for processes like chromium electroplating, a half-wave rectifier will not work.

Other essential parts of a plating rectifier include voltage and current control, overload protection, and a cooling device.

Silicon is the commonly used material in rectifier diodes. Several diodes are used to handle the load, and rectifiers generate significant heat during operation, managed by water cooling systems or fans.

All electroplating rectifiers use variable output control, either infinitely variable control or tap switches. Fixed-output rectifiers are also available but are not suitable for busy plating shops due to potential breakdowns from varying load factors. Additional controls include current density control, and automatic voltage and current control, making a plater's work easier by providing consistent output.

Rectifiers come in various physical forms, such as solid-state diodes, mercury forms, vacuum tube diodes, silicon-controlled rectifiers, and silicon-based semiconductor switches.

Characteristics of a Rectifier

Several characteristics make rectifiers more suitable than low-voltage generators for electroplating processes:

• Plating rectifiers save energy by using a high-frequency switching power supply transformer, improving conversion efficiency.
• They are lightweight and compact; thyristor rectifiers are 1/5 to 1/10 the size and weight of traditional rectifiers, making them easier to expand, install, maintain, and move.
• Easy modulation; rectifier output waveforms can be modulated. High-frequency use lowers the cost of output waveform adjustment, allowing changes based on user requirements. This improves on-site efficiency and product quality.
• Stable output; the system's high response speed enables rectifiers to adapt to load changes and electricity networks, ensuring accuracy of more than 1%. High-efficiency switching power supplies enable precise control, enhancing product quality.

Application features of a rectifier

There are many rectifier application features like:

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1. Reduction of porosity; as the rate at which nuclei forms is greater than the rate of growth, it leads to nuclei refinement.
2. Improve the binding force; rectifier enable the film to break down, and as a result, there will be a strong bond between the coating film and substrate.
3. It enhances the capacity for coverage and dispersion
4. It helps to reduce the stress on the coating; a rectifier help to reduce internal coating stress and as a result, there will be a reduction of additive and an achievement of a crack-free coating film.
5. Rectifier helps a lot if you want to achieve an alloy coating composition that is stable
6. With a rectifier, there will not be a need for anode activator since it improves the dissolution of an anode

Plating rectifiers improve coating mechanical properties by increasing density, reducing volume and surface resistivity, improved wear resistance, toughness, corrosion resistance and also enable the controlling of the electroplating coating hardness.

Rectifier Placement

The ideal placement for the rectifier is as close to the electroplating tank as possible. Placing the rectifier too far from the tank can lead to longer bus runs, resulting in current loss and increased maintenance. Keeping the rectifier close to the tank helps in cooling its components, which in turn helps to avoid drawing corrosive elements faster and extending the rectifier's lifespan.

A practical solution is to position the rectifier over a wall near the plating tank. Keeping the rectifier controls next to the electroplating station can facilitate easier operations. If this isn’t possible, using air-tight or water-cooled units, either directly or via heat exchange, can be an alternative. Ambient air above the required temperature might necessitate water cooling for the rectifier.

Maintaining and repairing a rectifier

A rectifier includes pumps or fans as its moving parts for cooling purposes. Proper installation and operation at specified temperature levels can ensure longevity. Maintenance routines can be carried out regularly, including cleaning or replacing air filters, and ensuring no objects inhibit airflow. Regularly inspect fan blades for security, maintain filters and pumps, and individually clean the heat sinks and semiconductors for enhanced cooling.

Inspect all control instruments like buttons and lights regularly, and replace malfunctioning components immediately. High-quality rectifiers often come with onboard diagnostics which indicate trouble areas on digital displays. Voltmeters, Ammeters, and oscilloscopes aid in locating issues. No advanced engineering skills are required for rectifier repairs, only a solid understanding of electrical equipment and the dangers of high currents and voltages.

Good suppliers usually provide detailed manuals and parts lists for easy rectifier repairs, reducing equipment downtime.

Things to consider before buying a plating rectifier

When considering a rectifier purchase, several factors must be evaluated. Take into account any shortcomings in your current rectifier that you want to improve upon, or maintain these attributes in your next purchase. Suppliers can also offer valuable suggestions to improve your work efficiency.

General factors to consider before buying a rectifier include:

1. Ease of installation
2. Maintenance costs
3. Repeatability
4. Reliability
5. Warranty
6. Conversion Efficiency

While it is challenging to know the superiority of a rectifier beforehand, seeking others’ experiences and maintaining a trusted relationship with suppliers can provide truthful insights.

How Plating Rectifier Works in Plating Process?

The plating rectifier adopts high frequency switching pulse technology and has the reasonable product structure and strong reliability. Because of its small size, light weight, high efficiency and high reliability, the power supply has become a new generation of silicon controlled rectifier and has been widely used in various plating solutions in the electroplating industry. Electroplating process includes four aspects: Electroplating solution, electroplating reaction, electrode and reaction principle, and electrodeposition process of metal.

1. Electroplating solution

There are six elements of electroplating solution: Main salt, complexing agent, additional salt, buffering agent, anode activator and additive.

2. Electroplating reaction

Electrochemical reaction in plating reaction: The part to be plated is the cathode, which is connected to the negative electrode of the DC plating rectifier power source. The metal anode is connected to the positive electrode of the rectifier. Both the anode and the cathode are immersed in the plating solution. When a certain potential is applied between the anode and the cathode, a reaction occurs at the cathode: Metal ions Mn diffused from the inside of the plating solution to the electrode and the plating solution interface obtain n electrons from the cathode and reduce to metal M. On the other hand, a completely opposite reaction occurs at the anode, that is, the metal M is dissolved at the high-frequency switching power supply at the anode interface, and n electrons are released to generate metal ions Mn.

3. Electrode and reaction mechanism

A. Electrode potential

When a metal electrode is immersed in a solution containing the metal ion, the following equilibrium exists: the reaction where the metal loses electrons and dissolves in the solution and the reverse reaction where the metal ion gains electrons to precipitate the metal should coexist. In order to accurately compare the effect of the nature of the substance on the equilibrium potential, it is stipulated that when the solution temperature is 25°Ϲ and the concentration of metal ions is 1mol/L, the measured potential is called the standard electrode potential. Metals with a large negative electrode potential are liable to lose electrons and oxidized, while metals with a large positive electrode potential will obtain electrons easily and get restored.

B. Polarization

The so-called polarization refers to the phenomenon that the electrode potential deviates from the equilibrium electrode potential when a current passes through the electrode. Therefore, the current-potential curve is also called a polarization curve. The main causes of polarization are electrochemical polarization and concentration polarization.

(1). Electrochemical polarization: Because the speed of the electrochemical reaction on the cathode is less than the speed of the electrons supplied by the external power source, the electrode potential moves in a negative direction and causes polarization.

(2). Concentration difference polarization: The polarization due to the difference between the concentration of the liquid layer near the surface of the electrode and the concentration of the solution body is called concentration polarization, which is caused because the diffusion speed of the ions in the solution is smaller than the speed of the electron movement.

4. Electrodeposition process of metal

The electroplating process is a process in which metal ions in a plating solution are reduced to metal atoms by an electrode reaction under the action of an external electric field, and metal deposition is performed on a cathode.

In short, the working principle of plating rectifier in electroplating process is: In the salt solution containing the metal to be plated, the substrate metal to be plated is used as the cathode, and the cations to be plated in the plating solution are deposited on the surface of the substrate metal by electrolytic action, so as to form a plating layer.

Contact us to discuss your requirements of Precious metal plating rectifier factory. Our experienced sales team can help you identify the options that best suit your needs.