Each plating type is given a current density range, which is also called the allowable current density range or the current density range for obtaining a qualified coating. During electroplating production, the current density applied to the surface of the plated part must be strictly controlled within this range.
Author: Marisa
Each plating type will be given a current density range, which is also called the allowable current density range or the current density range for obtaining a qualified coating. During electroplating production, the current density applied to the surface of the plated part must be strictly controlled within this range. For various reasons (refer to previous articles on the current density of roller plating), it is difficult to determine the allowable current density range for roller plating, and it is difficult to determine the effective plating area of the plated part. Therefore, it is difficult to use mathematical calculation methods like rack plating to obtain the allowable current range. However, roller plating can achieve its purpose of controlling current density by controlling the upper limit of current (allowed for each roller), that is, during roller plating production, try to use a larger current without exceeding the upper limit of current. Since roller plating generally does not deliberately use a small current, the lower limit of current is generally not considered. So, what are the purposes of controlling current density in roller plating?
1. Obtain a finely crystallized, qualified coating
During electroplating production, the current density applied to the surface of the plated part must be strictly controlled within the permitted range. Otherwise, if the current density exceeds the upper limit, the coating will be rough or burnt, and if it is lower than the lower limit, the deposited coating may not meet the requirements or no coating will be deposited. Only when the current density is within the permitted range can a finely crystallized, qualified coating be obtained. This current density range is also called the current density range for obtaining a qualified coating. Therefore, the purpose of controlling the current density during electroplating is first to obtain a finely crystallized, qualified coating.
2. Speed up the deposition rate of the coating
As mentioned above, the principle of the current for roller plating is to use a larger current as much as possible without exceeding the upper limit. Many people have misunderstandings on this point and dare not open a large current, thinking that a large current will cause the coating to be rough. This is wrong, because they have not really figured out the relationship between current and coating crystallization. Electroplating is an electrochemical method that relies on electron flow to reduce and deposit metal ions at the cathode. Without a large electron flow, there will be no large electrochemical polarization at the cathode, and a fine crystallized coating will not be obtained. Therefore, a large current will not only not make the coating rough, but will make the coating crystallization more fine.
However, when the current used exceeds the upper limit, the cathode current efficiency of any plating solution will drop sharply. At this time, the coating will be rough at the lightest and burnt at the worst. Roll plating will produce "roller eye marks". Therefore, people who think that a large current will make the coating rough often use too much current and exceed the upper limit. If it does not exceed the upper limit, the larger the current, the finer the coating crystallization will be.
3. Improve the plating performance of low current areas of complex parts
In addition, the purpose of using high current as much as possible in roll plating is to improve the plating performance of low current areas of complex parts. Because the given current is small (the current density at this time is the average current density), the current density of the low current area of the part is even smaller. When rolling complex parts, the current density of the low current area often cannot reach the lower limit and cannot obtain a good or qualified coating. Therefore, under the premise of not exceeding the upper limit, high current should be used as much as possible to maximize the current density of the low current area of complex parts and improve their plating performance. This example is not uncommon in production. Some people are afraid of rough coating and dare not use high current. Therefore, the coating of the low area of complex parts is not satisfactory. After increasing the current, the problem is improved or solved.
In short, the purpose of controlling the current density of roll plating is, on the one hand, for "quality" and on the other hand, for "quantity", that is, to obtain high-quality coating and efficient production. Simply put, it is for our roll plating production to be "good and fast".