In the casting process of nodular cast iron piston ring, it can be divided into two types: single piece casting, double piece casting and barrel casting. These casting processes mainly have the following characteristics.
(1) The shape of blank casting is simple: the blank shape of single ring, double ring and barrel ring is very simple, even if it is single! The double piece has an elliptical shape, but the ovality is very small, which is not different from the normal circle shape. It can be regarded as a simple ring normal circle casting. The cylinder blanks produced by various casting processes are basically simple normal cylinder shape, and the wall thickness is uniform.
(2) In addition to the cylinder, single piece and double piece rings belong to small thin-walled parts. For example, the cross-sectional size of motorcycle C hioo single piece nodular iron ring blank is only 2.2mm x 3.5mm, and the double piece ring size of 6110 Diesel engine is only 6.8mm x9.5mm The 6mm “thin-walled casting has fast cooling speed, which requires good molten iron fluidity and high pouring temperature to prevent casting defects such as insufficient pouring and cold shut.
(3) Single piece, double piece and sand mold cylinder casting, which is formed by clay sand machine modeling method, has high requirements for the performance of green sand, such as wet compression strength, moisture, air permeability, compactness and mud content of old sand.
(4) The principle of sand casting is basically the same, but the equipment and process methods of centrifugal casting and EPC are completely different. Centrifugal casting adopts centrifugal pouring machine, and the equipment and process methods are relatively simple, while EPC is much more complex.
(5) In order to prevent the blank of single and double piece nodular iron rings from cooling too fast to produce white structure, the quality requirements of raw molten iron are very high. The raw molten iron generally requires high carbon, low silicon, low manganese, low sulfur and low phosphorus. After spheroidization, the temperature of molten iron decreases more, the surface tension is large, and it is easy to form oxide film, which affects the fluidity of molten iron and is not conducive to filling the cavity.
(6) The solidification characteristic of nodular cast iron is’ paste solidification ‘, and its shrinkage porosity, shrinkage cavity and white mouth tendency are large. No matter what kind of casting process method, it is easy to produce these casting defects unique to nodular cast iron. Therefore, for raw materials such as pig iron, scrap steel and alloy and melting! The five techniques of spheroidization have very strict requirements.