The replacement life of the galvanized pot
The most important equipment for hot-dip galvanizing is the zinc pot, which is generally made of steel plate. For the galvanizing industry, it is like a human heart. However, if used for a long time, the zinc pot will be damaged. Therefore, after several years of use Must be replaced.
However, there is no clear standard for replacing zinc pots.
In the past, when companies replaced zinc pots, they generally took into account the production volume, the number of years of use, and the amount of loss, and then based on the unique experience of each factory. Generally, the blow plating was replaced every 2 to 5 years. The current domestic record of hanging plating is 11 years.
Zinc pot volume calculation formula
The volume is calculated by subtracting 200mm from the depth of the zinc pot.
The depth of the pot is subtracted by 200mm, in order to prevent the zinc liquid from overflowing when the plating parts are immersed in the zinc.
The amount of lead put into the bottom of the zinc pot to prevent damage to the bottom of the zinc pot is not considered.
Calculated as follows:
V=Zinc pot length L×(pot depth H－0.2m)×zinc pot width
There is another point of view to express the scale of the zinc pot. It is expressed in terms of W/V (ton/m3) per unit volume of zinc production of the zinc pot, which is the total weight of the galvanized steel workpiece during the use of the zinc pot. The use period of the zinc pot is from the beginning of galvanizing after the zinc has melted to the end of the galvanizing operation, expressed in N (years).
The loss of zinc pot and its measurement
The loss is calculated based on the difference between the original plate thickness and the plate thickness during the survey.
Due to the difference in operating temperature, it will affect the loss of the galvanized pot. Assuming that the operating temperature is not considered, although the zinc pot has different steel grades, the difference in temperature of 10°C will cause a difference of about 10% in the loss.
The temperature of the zinc liquid in the zinc pot is 450±10℃, and the working time is 8-10 hours/day. The temperature of the zinc liquid at night is based on the principle that zinc does not solidify, and it is kept at about 435℃.
The thickness of the plate is measured by an ultrasonic thickness gauge with an accuracy of ±0.1mm.
The measurement location of the loss is divided into two areas: the general area and the heating area (the most severe loss).
Analyze the loss in the general area.
When measuring the plate thickness from the outside of the zinc pot, remove the oxide on the surface of the measuring point before measuring.
When measuring the plate thickness on the inside of the zinc pot, the zinc-iron alloy layer should be ground off first, and the steel should be exposed before the measurement.
In general, the general area of loss discussed refers to the place 500mm above the dross deposition line at the bottom of the zinc pot and 500mm below the zinc liquid level (the place where the liquid level fluctuates). And 500mm away from the center of the heating burner is also a place where the loss is relatively small.
The heating part is in direct contact with the burner flame, and the temperature is relatively high, so the loss is larger than other places. Here, because the heating air is scattered near, it generally refers to the range of 500mm from the center of the burner.
Replacement conditions for zinc pot
No matter how many years the zinc pot has been used, as long as the plate thickness is reduced by about 4 to 8mm, a new zinc pot needs to be replaced. In other words, as long as the plate thickness is reduced by about 8% to 23%, a new zinc pot needs to be replaced.
(1) The blow galvanized pot needs to be replaced after about 2 to 4 years of use, but it is not a general rule. The service life of each company is different, but the hanging plating will be longer. There are many cases in which it is used for ten or eight years.
(2) After the thickness of the zinc pot is reduced by about 8% to 23%, it should be monitored at any time and ready to be replaced (source hot dip galvanized magazine).
(3) During the period of use, the production volume per unit volume is about 1000-3000 tons/m3 (source hot-dip galvanizing magazine).
(4) During the operation time, the production volume per unit volume is about 100-400 tons/m3 (source hot-dip galvanizing magazine).