1, all kinds of electroplating processes, chromium plating is one of the most affected by the power waveform. Chrome plating must use low ripple DC power supply, otherwise the bright range is narrow, the coating is easy to bloom, gray, which has been recognized by many people, but in practice there is still a lack of understanding of it, often due to the ripple coefficient is too large to affect the quality of chrome and do nothing. Therefore, the choice of electroplating power supply is more important.
For electroplated hard chromium production where reverse electrolysis is often used, a power polarity reversing device is required. The easy way is to use a manual reversing switch. Due to the large current, the switch on and off will form a large spark, the switch is easy to damage. Dipping the contact in transformer oil can extend the service life. However, when the current change is relatively large, mechanical automatic reversal is the first choice, mechanical automatic reverse reversal does not require manual operation, electric commutation operation is relatively simple and easy, because it is horizontal docking commutation, will not produce spark corrosion, too much current is no pressure, durable and durable.
The power supply waveform has great influence on chrome plating. And often easily overlooked by the operator. For example, the coating ability of small parts in a factory is very poor, and the ratio of sulfuric acid and chromium anhydride in the plating solution is still ineffective. After field inspection, the 1000A old thyristor rectifier is used, and the average current is only about 200A, the load rate is very low, and the output ripple coefficient is obviously too large. When the ripple coefficient is lower than 3%, the chrome-plating fault is eliminated and becomes normal.
When the output ripple is too large, the cracks are not fine and the distribution is not uniform.
2, the bath temperature rise problem
Dc power supply and pulse power supply with large ripple coefficient will often accelerate the temperature rise. Theoretically, this is because any non-pure DC and sine wave can be decomposed into pure DC and first, second, third, and multiple harmonics. The larger the ripple coefficient, the larger the harmonic component. Under normal circumstances, AC harmonics do not contribute to DC deposition, but they can generate a large amount of ohmic heat, which accelerates the temperature rise of the bath. It can be seen that the use of low ripple coefficient DC power supply is conducive to reducing the temperature rise of the bath. The use of smooth DC is conducive to reducing the plating bath temperature.
3, chromium plating layer flower, slot voltage rise
The current waveform of chrome plating is generally good for using pure DC, three-phase full wave or square waveform power supplies, and can not use power supplies with large fluctuation factors (ripple coefficient is less than 3%). If the three-phase full-wave rectifier breaks a phase, it will cause the coating to bloom. In addition, the cathode current density of chromium plating is higher, and due to the existence of a large number of hydrogen and oxygen between the cathode and the anode, although the electrical conductivity of chromic acid is better, it is still necessary to use a power supply greater than l2V, while other plating types use a power supply below 8V
Treatment method: Select the pulse type rectifier power supply with voltage greater than 12V and ripple coefficient less than 3%
4. Low hardness and poor brightness of chromium layer
Hard chrome plating: (1) Capacity. First of all, the maximum plated area of the tank plating at full load is calculated, and then the working current density is multiplied by the total area of the plating, that is, the required current. At the same time, the necessary impulse current for the plating and the actual rated current used by the rectifier should be considered (generally 85%), and the technical requirements do not allow full load work, otherwise it is easy to trip and destroy the rectifier element. If 1600A current is required, a rectifier with a capacity of 2000A and 12V should be used.
(2) Power. Because many heating devices in the electroplating power supply will consume part of the input AC power, so that the DC output power is less than the AC input power, that is, the rectification efficiency is the ratio of the output DC power to the input AC power (%), the greater the value, the less power consumption of the rectifier itself, the better the performance. Therefore, the operating power of the electroplating power supply should be no less than 75% of the rated power to reduce the probability of AC pulsation. Because AC pulsation is very harmful to chrome plating. If the limit is exceeded, cracks will occur in the chromium coating, which will affect the hardness and brightness of the chromium layer.
(3) Specifications. The DC voltage of the electroplating power supply should be 0 ~ 12V, and the low voltage of 15V for large hard chrome plating is best. The voltage and current can be adjusted continuously, and the current ripple coefficient is not more than 5% of the pulse square wave rectifier. For special plating parts such as small aperture deep hole chrome plating must use high-power, ripple coefficient <2% rectifier. In addition, there should also be automatic protection, circulating water cooling, corrosion resistance, and can be added to the commutator control of the pulse rectifier:
(4) Select the power supply. It is best to purchase multi-group unit digital current sharing electroplating power supply. Such as the use of multiple groups of units digital galvanizing power supply. In this way, when one of the unit groups of the power supply fails, the other unit groups of the electroplating power supply can automatically balance the required current of the total power output, and truly do not stop production and do not reduce production, which is the most ideal hard-plated power supply product at present.
