The total output of spheroidal graphite iron castings in China has exceeded 31 million tons. With the improvement of the quality of China's spheroidal graphite iron castings, the strengthening of overall strength and the improvement of core competitiveness have made great progress in China's spheroidal graphite castings industry. For the ductile iron parts, his maintenance is also very important. Only when the ductile iron parts are well-maintained, it is possible to exert his great effect. For the ductile iron parts, the spheroidal iron parts should be thoroughly inspected before use. In a place that is too flat, the surface should be cleaned. If the ductile iron parts are recessed, the recess of the spheroidal iron castings filled with vinyl chloride should be used. The coating should not be too thick each time. The thickness of the coating is generally About 0.5 mm, the ductile iron castings can not be filled once, and the next time the material is to be dried, it will be carried out. For the ductile iron cast bollard, the water-grinding technology should be used in the grinding process. In order to prevent the spheroidal iron castings from rusting during the grinding process, the rust-proof water must be used for grinding during the grinding. The spheroidal graphite iron parts are cleaned and polished. When painting spheroidal graphite iron parts, be careful that the primer must be thoroughly stirred before use, diluted to an appropriate density, and then painted or painted.
The foundation of the ductile iron castings is a box-shaped structure, and a lot of strong ribs are added. Some parts of the ductile iron parts, such as the rail surface, the shaft hole and the T-shaped groove, are thicker, and are more likely to cause shrinkage and shrinkage. Matsuo, also because the performance of ductile iron castings is sensitive to wall thickness, it is easy to make the structure loose, graphite is coarse, low hardness, not wearable. When the thickness of this portion is too large to the surrounding connecting wall, crack defects are less likely to occur. Due to the development of automatic, high-speed, and powerful cutting of ductile iron castings, the emergence of CNC machine tools has caused some changes in the structure of ductile iron castings, which has brought about some casting process problems. For the defects and positions that are easily generated by ductile iron castings, after analyzing the above problems, based on the above problems, a reasonable ductile iron casting structure can be designed.
To produce ductile iron parts, pay attention to the following principles:
1. Casting principle The parting surface is placed in the bottom box as much as possible, which is conducive to the process design. The sand box is rigid and has a small amount of sand, and it is balanced and solidified. The thick part is directly cooled with cold iron or sand. Get a qualified organization. The design principle of the gating system is fast pouring, slag blocking, feeding, economical and easy to clean. The shape of the ingate is easy to fill with a good distance (rectangular or approximately square), and the temperature difference of filling is small. The semi-circular or triangular ingate should not be provided with poor feeding effect, and the semi-circular or triangular gate center is strong in heat preservation, and the joint between the center of the gate and the casting is easy to form a shrinkage hole.
2. After solidification, the solidification quickly improves the smoothness and intrinsic density of the casting. The simplification of the process without the riser saves the cost. The riser is easy to operate with the dark pressure riser. If the large-scale piece cannot be filled once, it must be manually fired. (Tie iron water) role is great.
3. The production of spheroidal graphite iron parts should be controlled to prevent white and hard edges from occurring. Solution:
(1) Control chemical composition
(2) increase the gate
(3) The temperature of the molten iron is >1450 °C to increase the pouring temperature.
Precautions for pouring molten metal in ductile iron parts:
(1) It is necessary to dry and dry before pouring and pouring the inoculant and spheroidizing agent for pre-furnace disposal.
(2) It is necessary for the pouring personnel to wear the factory clothes as required and wear protective glasses. The work site should be unobstructed. The molten metal in the ladle should not be overfilled to avoid spillage and injury during transportation and pouring.
(3) Correctly select the pouring speed, that is, it should be slowly poured at the beginning, which is convenient for aligning the gate, reducing the impact of molten metal on the sand type and facilitating gas discharge; then pouring quickly to avoid cold separation; it should be slow before pouring Pouring, that is, following the guidelines of slow, fast, and slow.
(4) For castings with large liquid shortening and condensation shortening, such as medium and large steel castings, timely pouring from the gate or riser after pouring.
(5) When pouring, the gas emerging from the mold should be shunned in time to avoid the occurrence of pores due to the formation of helium gas, and the insufficiency of gas incineration to harm the human health and pollute the air.