What should be paid attention to when producing and processing cast iron manhole covers?

Cast iron manhole covers  are one of the ways to exercise. According to the demand for goods, hot melt and cold processing may be temporarily suspended. Cast Iron Manhole cover is a special exercise method in conservative exercise techniques. It will lose its precise shape and high motion accuracy.

1.  Be careful when handling molded shells to avoid damaging them.

2. When dewaxing, the door of the dewaxing kettle must be locked tightly to prevent heat dissipation, and there should be no damaged or scratched sealing aggregates on the furnace door. If there are scars, they should be converted immediately.

3. The faster the repeated loading measures, the better. If the time is advanced, the mold shell will be heated earlier because the wax material has shorter heat than the mold shell, making it easier to maintain the mold shell.

4. Coincidentally, it will clean the dewaxing filter and trajectory to prevent clogging. When releasing the wax pot door, never place your feet on the guard to prevent hot water from flowing out and burning people.

5. Wear gloves during operation.

The application of ductile iron manhole covers is becoming increasingly widespread. While improving product quality, the processing technology is becoming increasingly complex, and tempering technology is one of the important ones.

(1) Low temperature tempering: usually carried out between 150-250 degrees. After tempering, it can be air-cooled, oil cooled, or water-cooled. The purpose is to eliminate quenching stress while maintaining the high strength and hardness of cast iron manhole covers. Mainly used for carburizing, surface quenching, and wear-resistant cast steel parts requiring high hardness.

(2) High temperature tempering: The high temperature tempering temperature is between 500 and 650, and it should be maintained for an appropriate period of time before cooling. Mainly used to adjust the microstructure of cast steel after quenching or normalizing, making it a high-strength and wear-resistant carbon steel and medium low alloy steel cast iron manhole cover. Tempering brittleness is a difficult problem that should be noted when developing the tempering process for alloy steel cast iron manhole covers. It may occur within the following two temperature ranges.

250~400 brittleness: Cast steel with martensitic structure undergoes tempering brittleness after quenching. If the tempering temperature is slightly higher than the brittle temperature zone, the tempering brittleness can be eliminated. Moreover, during tempering within the aforementioned temperature range, there is no occurrence of tempering brittleness, hence it is often referred to as a type of tempering brittleness.
Brittleness occurs between 400 and 500 (even 650): Most low-alloy cast steels will experience this situation, that is, the cast steel will undergo high-temperature tempering brittleness. If the steel castings that become brittle within this temperature range are heated to above 600 (or 650) and then rapidly cooled in water or oil, brittleness can be eliminated. However, if the cast iron manhole cover that eliminates brittleness is heated to the temperature where tempering brittleness occurs, brittleness will reappear. This is commonly referred to as the second tempering brittleness.