Name: Anshan Iron and steel machinery development private enterprise machinery plant
Contact: Shen Taisheng
Mobile phone: 13942222400
Zip code: 114000
Site: Anshan Iron and steel plant
Office address: Xi min, Tiexi District, Anshan, Liaoning
No. 111 Sheng Lu
1. storage of zinc pots
The surface of a zinc pot that has been corroded or rusted will become quite rough, which will cause more serious erosion of liquid zinc. Therefore, if the new zinc pot needs to be stored for a long time before use, corrosion protection measures should be taken, including paint protection, put into the workshop or cover to avoid rain, bottom cushion to avoid water immersion, in any case do not allow water vapor or water to accumulate on the zinc pot.
2. installation of zinc pot
When installing the zinc pot, it must be placed in the zinc furnace according to the requirements of the manufacturer. Before using the new pot, be sure to remove rust, residual welding slag splash and other dirt, corrosion on the pot wall. The rust needs to be removed mechanically, but it can't damage the surface of the zinc pot or cause roughness. It can be cleaned with a hard brush of synthetic fiber.
The zinc pot expands when heated, so there is room for free expansion. In addition, the zinc pot is in high temperature for a long time, and it will produce "creep". Therefore, attention should be paid to the design of the zinc pot to adopt appropriate support structure to prevent its gradual deformation in the use process.
3. stacking of zinc ingots in zinc pot
In order to reduce the harmful effect of liquid metal on zinc pot, zinc ingot with better quality must be selected when loading zinc ingot into new zinc pot. When the zinc ingot is loaded into the pot, it should be placed in accordance with the method shown in Fig. 1-2, so as to ensure good heat conduction between the zinc ingot and the pot wall. Zinc ingots can be covered with a layer of charcoal, which can not only play a role in heat insulation, but also play a role in preventing zinc oxidation; can also be covered on the zinc pot insulation cover to reduce heat loss. Since the coefficient of thermal expansion of zinc is three times that of iron, in order to prevent the expansion of zinc on the wall of the pot during heating, zinc ingots should be placed in the middle of the length direction of the pot to leave enough gap, in this gap can be placed some wood. During the heating process of the zinc pot, the strips are extruded by the expanded zinc ingot, then burned, and the unburned strips and combustion products are finally floated to the surface of the zinc liquid.
During the heating process, the zinc ingot near the pot wall melts first, and the molten zinc reacts with the pot wall to form a protective layer of Fe-Zn alloy.
4. heating zinc melting
Before the zinc ingot melts and reaches the working temperature, the zinc pot is in danger of cracking and damage under the action of temperature difference inside and outside the wall of the zinc pot and corrosion of the liquid metal.
The tensile strength of steel decreases with the increase of temperature, and its tensile strength is less than 100MPa at 450. Temperature difference between inside and outside of zinc pot wall will produce tensile stress inside the pot wall. For example, when the temperature difference between inside and outside of zinc pot wall reaches 60 degrees Celsius, the tensile stress of 120-130MPa on the pot wall will be produced, which is higher than the tensile strength of steel. The hydrostatic pressure of the zinc solution on the wall will also cause tensile stress on the wall. The maximum tensile stress value produced by the superposition of tensile stress caused by these two reasons occurs in the turning zone between the vertical wall and the bottom of the zinc pot, especially in the middle of the long side of the pot, so this part is the most dangerous area in the heating process. In order to avoid cracking damage of zinc and aluminum, heating and cooling must be very slow in order to minimize the temperature difference between the parts of the zinc pot.
Under normal conditions, the reaction of pure zinc with zinc pot will evenly form a layer of iron-zinc alloy on the inner surface of the pot, as shown in Fig. 1-3a. If lead is added to the ingot in the new zinc pot, the liquid lead layer containing unsaturated zinc is accumulated at the bottom of the zinc pot before the protective ferro-zinc alloy layer is formed. The contact between the liquid lead layer containing unsaturated zinc and the zinc pot steel plate will cause the intergranular damage of the zinc pot steel plate, as shown in Fig. 1-3b. The intergranular failure occurs at the turning point between the side surface and the bottom of the zinc pot, which is especially dangerous.
When the zinc pot is used in the critical temperature range, the rate of liquid zinc eroding the zinc pot will be greatly increased and the zinc pot will be damaged prematurely. If there are four holes in the wall of the zinc pot, the temperature of the thinner wall is higher, and the erosion rate of zinc on the zinc pot will increase. If the heating of the zinc pot wall is uneven, the erosion rate of the zinc solution to the wall will be accelerated.
The new zinc pot for heating up zinc melting must be carried out according to the requirements of the manufacturer of zinc pot, must be very slow and uniform.
This will significantly increase the cost of heating and equipment operation, but far less than the damage to the zinc pot and the resulting shutdown. In the heating process, it is important to maintain a certain temperature balance throughout the zinc pot, that is, the temperature of the inner wall of the pot must be lower than 480 degrees C, the temperature difference between the pot wall and the bottom must be less than 11 degrees C, and the temperature difference between the inside and outside of the pot wall must be lower than 50 degrees C.
The heating time required for heating zinc melting depends mainly on the size and geometry of the zinc pan. In order to maintain a certain temperature balance, the heating time of the larger zinc pot heating zinc is relatively longer. The heating curve of heating zinc in a zinc pot is shown in Figure 1-4. The inner wall of the zinc pot should be heated slowly before 300 C. Keep it at 300 C for a period of time so that there is no danger to the pot. The final heating stage above 300 C can be faster, but it must be noted that the above critical temperature difference can not be exceeded.
Brick furnace (or part of the furnace is brick) galvanizing furnace, before the use of the zinc pot, must be slowly drying brick, and then according to the curve shown in Figure 1-4 heating up zinc melting.
In order to make the temperature measurement and control accurate, we should correctly select the temperature measurement point and configure a perfect temperature measurement and control system. Choosing the outer wall and bottom of the zinc pot as the temperature measuring point of the thermocouple and adopting appropriate control equipment, the temperature difference between the wall and bottom of the pot (the hottest and the coldest part) can be easily controlled within 100 C.