process characteristics of hot-plated aluminum
Zinc and siliconIn general,
The production process of hot-dip aluminized zinc silicon is much the same as that of ordinary hot-dip galvanizing, and the equipment is much the same. However, for people familiar with ordinary hot galvanizing, this "small difference" aspect is the focus of attention. It has two functions to pay attention to, understand and master the process characteristics of hot-plated aluminum, zinc and silicon. First, only by mastering these technological characteristics can we do a good job in the production of aluminum, zinc, silicon and zinc plating plates. Next, combined with # 5 and # 6 hot-plated aluminum zinc silicon units, a series of technological characteristics of hot-plated aluminum zinc silicon are described.
1. The cleanliness of the plate is the key to the success or failure of hot-plated aluminum, zinc and siliconAnyone with a rudimentary knowledge of hot-dip aluminized zinc silicon knows that aluminum-zinc silicon is "harder to plating" and "harder to serve" than zinc.How hard to plating? The main reason is that hot - plated aluminum zinc silicon is not easy to be well plated, and there are often even more leakage spots. A domestic company, hot - plated aluminum zinc silicon unit after one year of production, the rate of waste defective products is up to 40%, the largest number of defects is leakage plating spots.
Why hard plating?
Why not plating as well as hot galvanizing? This is determined by the physical properties of liquid aluminum and liquid zinc. Compared with them, the surface tension of liquid aluminum is large and the infiltration of steel plate surface is poor. The surface tension of liquid zinc is small and its wetting ability is good. Although the zinc solution of hot galvanizing contains aluminum, its content is very low, only 0.2%, and zinc content accounts for more than 99%. This zinc solution is very close to pure zinc solution, so its surface tension and infiltration are no different from pure zinc solution. Aluminum zinc silicon alloy liquid is different, its aluminum content is as high as 55%, so its surface tension is smaller than pure aluminum liquid, but much larger than zinc liquid.Its wettability is better than that of pure aluminum, but much worse than that of zinc. The difference of surface tension and wettability determines the difference of difficulty between hot-plated aluminum zinc silicon and hot-dipped zinc.
As mentioned in the previous section, hot galvanizing also has strict requirements on the cleanliness of the surface of the steel belt before entering the plating pot. When there is sundries on the board, and its scale is large (close to millimeter, millimeter or larger), there will be leakage plating point or plating spot in the sundries.However, when the size of sundries is small and the size is micron (usually from 1 to 100 microns), due to the small surface tension of the zinc liquid, the surface of the steel belt is relatively permeable, and the zinc liquid can often cover small sundries, and the coating does not appear to leak plating spots.
When hot plating aluminum zinc silicon, because the surface tension of aluminum zinc silicon alloy liquid is large, the surface infiltration of the steel belt is poor, not only the steel belt surface has a large amount of sundries will form the leakage plating point, the leakage plating spot, and when there are small sundries, it will often form the leakage plating point. This is the aluminumZinc and silicon are "difficult to be served" and are prone to leakage. The reason for the high cleanliness requirement of the steel sheet before entering the plating pot is that the zinc and silicon are difficult to be served.The cleanliness of the plate is the key to the success or failure of hot aluminum zinc silicon plating.The particularity of hot-plated aluminum, zinc and silicon has put forward very strict requirements for degreasing before entering the furnace and hydrogen reduction in the furnace. In the aspect of detoxification and lipid removal, it is required to remove the oil, iron powder and ash as thoroughly as possible through chemical alkaline washing, alkali liquid scrubbing, electrolytic alkaline washing and hot water scrubbing and rinsing, so that the remaining oil on the plate before entering the furnace is very small. The degreasing section of line 5 is designed according to this requirement. The defatted with plating factory 1 #, 2 #, 3 #, 2 #, 3 # 4 # and abundant south factory, compared to thermal degreasing of plating line have some differences in the basic structure and process parameters on: one is, degreasing tank for immersion, rather than the spray type, degreasing effect is better: the second is within the chemical degreasing tank and electrolytic degreasing tank, strip running route for "v" shape, rather than the level of operation, is advantageous to the emulsion on the surface of the strip under the bubbles escape from, degreasing and being;Third, the electrolytic degreasing current is large, up to 12,000 amperes, which is several times the actual current of line 1 and line 2, and the cleaning ability is much stronger.