1. Features and disadvantages of electro-galvanized products
Let’s talk about the advantages of electro-galvanized products first:
Compared with hot-dip galvanizing, electro-galvanizing has good uniformity, high control precision of coating thickness, and fine surface, which is very suitable for high coating quality requirements. And because the surface activity of the electro-galvanized zinc layer is high, there are many post-treatment methods, whether passivation, phosphating, fingerprint resistance, self-lubricating treatment, etc., there are various forms.
The control range of the thickness of the electro-galvanized coating covers a wide range from thin to thick, and the low can be plated from 3g/m2 to 90g/m2. Require. On the other hand, electro galvanizing has advantages in saving zinc resources, because the coating is uniform and there is no zinc dross, so the utilization rate of zinc is high.
The processing performance and welding performance of electro galvanizing are better, especially the welding performance.
Electrogalvanizing can be very convenient to produce single-sided plated products to meet some special requirements. For example, if the inner panel of an automobile has special welding requirements, single-sided electroplating is generally used.
Of course, electrogalvanized products also have some disadvantages. Its shortcomings are mainly related to its technological characteristics.
On the one hand, its raw materials should be annealed, continuous annealed or hood annealed, annealed, and re-plated after oiling. In this case, the quality of the substrate is required to be high, and insufficient performance may cause a series of surface quality problems;
On the other hand, due to the re-plating after annealing, the production process is longer than that of hot-dip plating, which has an impact on cost control. On the other hand, the electro-galvanized automobile sheet with thick zinc layer has a greater impact on the production capacity, the number of electroplating tanks must be increased, the equipment investment is large, and the power consumption is large, and the overall energy consumption and cost control are at a disadvantage.
2. The production process of electro-galvanizing
<1> Uncoiling, shearing, welding
After the electro-galvanized substrate arrives at the electro-galvanizing unit, it is rolled up by the uncoiler. After the coil is rolled up, the bad shape and defective parts of the head and tail plate are cut off, and then it enters the welding machine for welding.
<2> Tensile straightening and cleaning before electroplating
After welding, the preliminary cleaning of the oil on the board surface is the pre-degreasing process.
If there is a problem with the shape of the plate or special requirements for the shape of the plate need to be tensioned, the function of the tension leveler is to improve the shape of the incoming strip. If the shape of the strip is not good, it is likely to scratch the anode plate during the electroplating process. , and the strip with good shape has better coating uniformity.
Then further chemical degreasing is carried out to further clean the oil that has not been removed on the surface of the strip steel. Because electroplating must ensure the bonding force of the coating, the requirements for the surface of the steel plate are very high, so after the conventional chemical degreasing, electrolytic degreasing and electrolytic degreasing are also required. Compared with chemical degreasing, it uses the mechanical scouring effect of the gas (hydrogen and oxygen) generated by the electrolytic water on the surface of the steel strip after the strip is energized to perform the final cleaning of the oil film remaining on the surface of the steel plate, because it is difficult to use spray cleaning or brushing. The tiny particles on the surface are cleaned off, so electrolytic degreasing is a very important part.
The most direct consequence of poor degreasing is that the adhesion of the coating after electroplating is not good, and the coating falls off during stamping, or even torn off like a piece of paper.
After pickling, because the strip is exposed to air after annealing, there will be some slight oxide film on the surface. If pickling is not carried out, the future coating adhesion will be affected. Rinse should be carried out after pickling, because the surface of the strip cannot carry acid, otherwise rust will occur in the air for a long time, resulting in stain defects.
After degreasing and pickling the strip, electroplating is carried out. The difference between electroplating and hot-dip galvanizing is that in hot-dip galvanizing, the strip steel in a heated state enters the zinc pot solution, and a diffusion reaction is carried out to hang the zinc liquid on the strip steel.
Electrogalvanizing is that the strip is negatively charged after contacting the conductive roller, the strip is immersed in the electroplating solution, and the Zn ions in the electroplating solution get electrons and deposit on the surface of the strip to form a galvanized layer, so it is an electrified strip in the The electrochemical reaction in the solution is fundamentally different from hot-dip plating.
<4> Cleaning and post-treatment after plating
After electroplating, the electroplating solution on the surface is cleaned. The strip steel that has been electroplated out of the plating tank should be cleaned of the zinc layer, and the strip steel should be rinsed with pure water to clean the residual electroplating solution on the surface of the strip steel. Surface spot defects caused by net.
After that, it enters the post-processing stage, including phosphating treatment, passivation treatment, and fingerprint-resistant treatment. After post-processing, dry it, dry the strip with molten steel or film, and then apply oil (fingerprint-resistant but not oiled), then cut into rolls, roll up according to the roll weight ordered by the user, and weigh after rolling. After weighing, it will be packaged, and then packaged in the subsequent packaging unit. If the product quality meets the requirements and various performance standards, it will be sent out as an authentic product.
3. Introduction of post-treatment method of electro-galvanizing
In terms of phosphating treatment, the existence of phosphating film can greatly improve the adhesion of coating, and it has certain corrosion resistance, that is, after phosphating treatment, no oil is applied after drying, and corrosion and white rust will not occur for a long time. At the same time, for deep-drawing materials, the existence of phosphating film will greatly improve its forming ability, and the phosphating film can be grown in the place where the pre-phosphating film is not covered by the car factory to improve the coating process.
Because many users can process untreated electro-galvanized or hot-dip galvanized strip steel for post-treatment, such as phosphating after degreasing, but the pollution to the user’s own factory is serious, so after the steel mill performs phosphating, After rinsing and degreasing with hot water, the user can directly carry out the coating treatment, which can reduce the pressure on the user’s environmental protection.
This kind of commonly used in home appliances, such as some washing machine shells and office supply cabinets, and some electrical cabinets, etc., can be sprayed after processing.
Another kind of phosphating treatment is used more in automobiles. This phosphating is called pre-phosphating. Pre-phosphating uses the self-lubricating effect of the phosphating film to improve the flow of metal during processing, which is conducive to forming. It goes on smoothly, so the use of pre-phosphating in the later forming process has relatively few problems of stamping, and the probability of punching and roughening is low.
Phosphating products also have some problems during use.
The first one is that the degreasing time of the home appliance board is too long, and the alkalinity is too strong, which leads to partial dissolution of the phosphating film and local corrosion of the zinc layer, which may lead to problems such as bubbles or pits in the paint layer after painting. The countermeasure is generally to reduce the degreasing. Concentration, increasing the surfactant concentration, can solve the problem.
The second aspect is that in the automobile factory, the storage time of the steel coil is too long, and the surface anti-rust oil is difficult to remove. Therefore, the automobile factory must control the storage time. Once a problem occurs, the concentration of the degreasing solution must be adjusted. Peel off the surface phosphate layer.
For passivation products, we will remind ordering users that passivation products are not suitable for subsequent phosphating treatment.
In the past, it often happened that users ordered passivated products to be dephosphorized, and the phosphating did not go up or the board was very flowery, so this aspect must be paid attention to when ordering.
Anti-fingerprint treatment is that the anti-fingerprint coating is applied on the surface of the zinc layer by a roller coating machine, so that the surface of the strip has the effect of anti-fingerprint.
Fingerprint resistance is actually one of the various properties of organic coatings. Fingerprint resistance is the most basic. No obvious fingerprint traces remain on the inside after being touched by hand during processing. Fingerprint-resistant products are only one aspect of fingerprint resistance.
They are resistant to electrical conductivity, corrosion resistance, scratch resistance, alkali wash resistance, baking yellowing resistance (such as discoloration after baking at 200 °C), and black resistance (such as boiling water). There are high requirements for discoloration after 1hr), humidity and heat resistance (such as 70°C * 80% humidity * 120 hours discoloration), etc.
In addition, the self-lubricating steel plate in the fingerprint resistance has high lubricity to the steel plate, including some mechanical properties. requirements.
brand name method
The grades of steel plates and strips are composed of three parts: substrate grade, electroplating code (E) and pure zinc coating type code (Z). Among them, electroplating code (E)
Use a plus sign “+” to connect it with the coating type code.
Grade Naming Example
It is expressed as the electroplating product with the substrate grade of DC05 and pure zinc coating
b) SECC, SECD, SECE, SECF, SECG
The electroplating products with pure zinc coating based on the grades SPCC, SPCD and SPCE, SPCF and SPCG specified in Baosteel’s enterprise standard Q/BQB 408 are named SECC, SECD, SECE, SECF and SECG respectively.