The main process of mechanical galvanizing, mainly has the following 8 major processes
1. Main process flow of mechanical galvanized iron
Pre-treatment, degreasing, descaling (under-line treatment)→washing→flash plating replacement copper→water washing→mechanical galvanizing deposition transition bottom layer→mechanical galvanizing deposition→water polishing→part-out separation→hot water washing (or press Requires surface passivation of the part, immersion related protective layer) → dry and dry → inspection acceptance.
2, parts pre-treatment, degreasing, derusting
For ordinary parts, the conventional method can be applied according to the surface treatment, but the rust removal and descaling of high-strength steel base parts are particularly concerned, because the surface of the parts can be derusted and removed by using strong acid chemical materials containing hydrogen ions for a long time. Oxygen skin, this treatment will have a certain effect of hydrogen permeation on the steel base of the part, so it should be solved by mechanical method: such as sandblasting, vibrating finishing, shot blasting and so on.
3, flash plating replacement copper
The replacement copper layer has no thickness requirement, but completely covers the surface of the part substrate, and its function is to improve the adhesion of the plating layer, to facilitate the uniformity of the surface condition of the plating layer, and to block the penetration of hydrogen ions generated by the process into the substrate. Another effect was found. Because the copper layer has good conductance, the mechanical zinc-plated parts of the same zinc coating thickness and the zinc-impregnated parts were tested and tested in the salt spray box. When the salt spray test reached 11 cycles, it was found to be due to salt spray. The scouring of the water flow, the red rust appeared in the batch parts at the corners of the galvanized parts, and although the exposed base was seen at the mechanical galvanized corners, the edges and corners did not produce red rust: this is because the resistance of the replacement copper layer is small and the electronic conduction is smooth. The normal electrochemical cathode state of the iron matrix is ​​ensured. Therefore, the replacement copper layer is particularly important for the electrochemical corrosion resistance of the mechanical galvanized coating structure. Regarding the internal plating replacement process, the general technical standard for mechanical galvanizing in the United States, the designated ASTM-B695-91, has the technical requirements for the process of replacing the copper by the internal flash plating: and the National Machinery Industry Bureau of China promulgated and implemented on January 1, 2000. "Steel parts mechanical galvanizing", machinery industry standard JB/T8928-1999 does not regulate the replacement copper layer in the mechanical galvanizing process, which can be determined according to the requirements of both supply and demand.
4, mechanical galvanized deposition transition bottom layer
This process is for the replacement of the copper layer, the implementation step is a quantitative mechanical zinc plating special initiator and a small amount of plated zinc powder into the rolling plating cylinder, rolling 3-5 minutes can form the basic copper layer of the original part Converted to a silver-gray composite galvanized layer. The quality of the galvanized layer will affect the toughness and coating adhesion of the subsequent thickened coating.
5. Mechanical galvanizing deposition
Quantitative batch addition of zinc initiator, thickness of coating required zinc powder can be completed in 15-30 minutes to achieve the thickness of the galvanized layer required by industrial parts.
6, water polishing
The surface of the mechanical galvanized powder is a non-mirror semi-bright coating, and the water polishing process is after the mechanical galvanizing initiator and the zinc powder are washed away. The plated cylinder continues to rotate, so that the surface of the part coating reaches a uniform bright silver-white surface. Generally, it needs to be rotated for 5-10 minutes. Although the coating does not reach the mirror gloss of electroplating, the surface is smooth and the brightness is better than hot dip galvanizing. Floor. The water-polished plating cylinder has a maximum rotation time, and the zinc coating will have a certain degree of cutting damage when it exceeds a certain maximum value.
7, the surface of the part of the chromium passivation
The mechanical galvanized layer is easy to produce white corrosion on the surface of the coating in the humid air under the initial conditions. It must pass through the transparent chrome passivation and yellow chrome passivation to prevent the formation of the chromium passivation film to prevent white corrosion. .
8, testing acceptance
The thickness of galvanizing and the quality of coating in the machinery industry depend on the process operation, process formulation and process qualification and quantitative specification control. Therefore, the inspection of coating quality is particularly important. The qualified inspection results will guide the mechanical galvanizing process to different batches of parts. Correct production.
Advantages of mechanical galvanizing
1. Compared with electro-galvanizing, in industrial applications, the electro-galvanizing process will deposit hydrogen gas on the cathode, which produces hydrogen permeation on high-strength steel and other materials, resulting in high-strength steel components causing hydrogen embrittlement fracture during use. This has led to serious accidents, which have occurred both at home and abroad. Mechanical galvanizing does not cause hydrogen embrittlement damage to high-strength steel parts. The advantage of this function is that electro-galvanizing is incomparable. In addition, the mechanical galvanizing operation is simple, the barrel plating of small parts is easier to control, the energy consumption is small, the plating speed is fast, and the plating layer of 50 um thickness can be completed in 0.5 h, and the production efficiency is high.
2. Compared with hot dip galvanizing, hot dip galvanizing is mostly used in large steel parts as a long-term outdoor protective coating, but the standard fasteners used outdoors are basically manually operated, plus the characteristics of the hot dip galvanizing process. It is more convenient to use mechanical galvanizing. In addition, when the hot-dip galvanized gaskets are small parts, the parts are easy to stick together; when the threaded parts are plated, the molten zinc will block the threads; the plated nuts must be re-threaded after plating; and the hot dip galvanizing is energy-consuming The process requires high temperature operation, the environment is bad, and the environment is seriously polluted.
Functionally, high-temperature melting hot-dip galvanizing will cause annealing to soften the surface of the quenched high-strength steel fasteners, affecting the quality of the plated parts and changing the original performance, thus becoming a substandard product. The mechanical galvanized layer also has the function of resisting atmospheric acid rain. Its experimental acid resistance is the three places of hot dip zinc coating. This characteristic is also outstanding.
1. Main process flow of mechanical galvanized iron
Pre-treatment, degreasing, descaling (under-line treatment)→washing→flash plating replacement copper→water washing→mechanical galvanizing deposition transition bottom layer→mechanical galvanizing deposition→water polishing→part-out separation→hot water washing (or press Requires surface passivation of the part, immersion related protective layer) → dry and dry → inspection acceptance.
2, parts pre-treatment, degreasing, derusting
For ordinary parts, the conventional method can be applied according to the surface treatment, but the rust removal and descaling of high-strength steel base parts are particularly concerned, because the surface of the parts can be derusted and removed by using strong acid chemical materials containing hydrogen ions for a long time. Oxygen skin, this treatment will have a certain effect of hydrogen permeation on the steel base of the part, so it should be solved by mechanical method: such as sandblasting, vibrating finishing, shot blasting and so on.
3, flash plating replacement copper
The replacement copper layer has no thickness requirement, but completely covers the surface of the part substrate, and its function is to improve the adhesion of the plating layer, to facilitate the uniformity of the surface condition of the plating layer, and to block the penetration of hydrogen ions generated by the process into the substrate. Another effect was found. Because the copper layer has good conductance, the mechanical zinc-plated parts of the same zinc coating thickness and the zinc-impregnated parts were tested and tested in the salt spray box. When the salt spray test reached 11 cycles, it was found to be due to salt spray. The scouring of the water flow, the red rust appeared in the batch parts at the corners of the galvanized parts, and although the exposed base was seen at the mechanical galvanized corners, the edges and corners did not produce red rust: this is because the resistance of the replacement copper layer is small and the electronic conduction is smooth. The normal electrochemical cathode state of the iron matrix is ​​ensured. Therefore, the replacement copper layer is particularly important for the electrochemical corrosion resistance of the mechanical galvanized coating structure. Regarding the internal plating replacement process, the general technical standard for mechanical galvanizing in the United States, the designated ASTM-B695-91, has the technical requirements for the process of replacing the copper by the internal flash plating: and the National Machinery Industry Bureau of China promulgated and implemented on January 1, 2000. "Steel parts mechanical galvanizing", machinery industry standard JB/T8928-1999 does not regulate the replacement copper layer in the mechanical galvanizing process, which can be determined according to the requirements of both supply and demand.
4, mechanical galvanized deposition transition bottom layer
This process is for the replacement of the copper layer, the implementation step is a quantitative mechanical zinc plating special initiator and a small amount of plated zinc powder into the rolling plating cylinder, rolling 3-5 minutes can form the basic copper layer of the original part Converted to a silver-gray composite galvanized layer. The quality of the galvanized layer will affect the toughness and coating adhesion of the subsequent thickened coating.
5. Mechanical galvanizing deposition
Quantitative batch addition of zinc initiator, thickness of coating required zinc powder can be completed in 15-30 minutes to achieve the thickness of the galvanized layer required by industrial parts.
6, water polishing
The surface of the mechanical galvanized powder is a non-mirror semi-bright coating, and the water polishing process is after the mechanical galvanizing initiator and the zinc powder are washed away. The plated cylinder continues to rotate, so that the surface of the part coating reaches a uniform bright silver-white surface. Generally, it needs to be rotated for 5-10 minutes. Although the coating does not reach the mirror gloss of electroplating, the surface is smooth and the brightness is better than hot dip galvanizing. Floor. The water-polished plating cylinder has a maximum rotation time, and the zinc coating will have a certain degree of cutting damage when it exceeds a certain maximum value.
7, the surface of the part of the chromium passivation
The mechanical galvanized layer is easy to produce white corrosion on the surface of the coating in the humid air under the initial conditions. It must pass through the transparent chrome passivation and yellow chrome passivation to prevent the formation of the chromium passivation film to prevent white corrosion. .
8, testing acceptance
The thickness of galvanizing and the quality of coating in the machinery industry depend on the process operation, process formulation and process qualification and quantitative specification control. Therefore, the inspection of coating quality is particularly important. The qualified inspection results will guide the mechanical galvanizing process to different batches of parts. Correct production.
Advantages of mechanical galvanizing
1. Compared with electro-galvanizing, in industrial applications, the electro-galvanizing process will deposit hydrogen gas on the cathode, which produces hydrogen permeation on high-strength steel and other materials, resulting in high-strength steel components causing hydrogen embrittlement fracture during use. This has led to serious accidents, which have occurred both at home and abroad. Mechanical galvanizing does not cause hydrogen embrittlement damage to high-strength steel parts. The advantage of this function is that electro-galvanizing is incomparable. In addition, the mechanical galvanizing operation is simple, the barrel plating of small parts is easier to control, the energy consumption is small, the plating speed is fast, and the plating layer of 50 um thickness can be completed in 0.5 h, and the production efficiency is high.
2. Compared with hot dip galvanizing, hot dip galvanizing is mostly used in large steel parts as a long-term outdoor protective coating, but the standard fasteners used outdoors are basically manually operated, plus the characteristics of the hot dip galvanizing process. It is more convenient to use mechanical galvanizing. In addition, when the hot-dip galvanized gaskets are small parts, the parts are easy to stick together; when the threaded parts are plated, the molten zinc will block the threads; the plated nuts must be re-threaded after plating; and the hot dip galvanizing is energy-consuming The process requires high temperature operation, the environment is bad, and the environment is seriously polluted.
Functionally, high-temperature melting hot-dip galvanizing will cause annealing to soften the surface of the quenched high-strength steel fasteners, affecting the quality of the plated parts and changing the original performance, thus becoming a substandard product. The mechanical galvanized layer also has the function of resisting atmospheric acid rain. Its experimental acid resistance is the three places of hot dip zinc coating. This characteristic is also outstanding.
WENZHOU TENGCAI ELECTRIC CO.,LTD , https://www.tengcaielectric.com