Household manhole covers are characterized by heavy load and light weight. Generally speaking, the greater the weight, the greater the load can be. How to ensure load-bearing when it is light? This puts forward strict requirements for ingredients, and weight loss must be supplemented by good materials. At the beginning, the selected chemical components were C3.6-3.9, SI2.6-3.0 and Mn.

Finally, I identified the production of manhole covers as follows:

1. Select high-quality pig iron with manganese content less than 0.3 and phosphorus content less than 0.07.

2. Cupola charging should be accurate, and all raw materials should be accurately weighed.

3. The tapping temperature of raw molten iron should be above 1400℃ but not more than 1500℃. If the temperature is too high, the nodulizer will explode prematurely.

4. The spheroidizing package should be fully dried, and the spheroidizing agent, silicon particles, covering agent and baking soda should be added in turn when feeding.

5. Due to the temperature fluctuation of cupola, the compactness of added materials should be adjusted in time according to tapping temperature. The general principle is that when tapping is near completion, the nodulizer is detonated. Tapping should be completed as soon as possible, and slag should be scraped as soon as possible to ensure more time for subsequent pouring and avoid spheroidization.

6. Iron tapping should be accurate and controlled at around 5% as far as possible.

After three months of continuous production by the above method, no bad spheroidization occurred. In a word, raw materials are very important to make ductile iron, and the management of each point is the most important when batching.