Improvement of cold shut defect in crankshaft casting of large engine

The generation of cold shut is directly affected by the temperature of molten iron. At a certain temperature, the design of gating system is the key to the filling capacity of molten iron. Through simulation and analysis, it is found that the original runner design of gating system is unreasonable, resulting in slow filling, fast cooling and large energy loss, which is not conducive to the filling and feeding of molten iron (as shown in Fig. 1). The corresponding specific rectification measures are as follows.

Optimizing gating system

Increase the cross-sectional area of the original runner within a reasonable range (as shown in Fig. 2), so that the new gating system can ensure the filling temperature and speed of molten iron.

Optimize gate location

On the basis of finding out the appropriate proportion of each runner section of gating system, the position of water inlet will directly affect the filling effect of casting. When the hot metal enters the cavity from the original position of the second and fifth connecting rod neck (as shown in Fig. 3), the cold air gap phenomenon does not decrease. Through the simulation auxiliary analysis, the location of the inner gate is changed to the fifth and eighth balance weight positions (as shown in Fig. 4) to enter the cavity, which reduces the loss of molten iron speed and energy caused by the bending of molten iron passing through the lower part of the hanging core of 2 and 5 connecting rod neck, so as to reduce the cold shut-off.

Optimization of melting process

The melting process is changed from subcontracting process to non subcontracting process. Through the test of trial production test block, the test block performance under this process has a higher qualified rate, the overall performance is better than the subcontracting process, and the performance control is relatively stable. At the same time, the non subcontracting process can make the tapping temperature and pouring temperature more controllable than the normal process, and it is easier to ensure the pouring temperature. In addition, the best pouring temperature of 1350 ~ 1420 โ„ƒ was determined by adjusting pouring temperature for many times. The carbon content was adjusted from 3.65% – 3.85% to 3.75% – 3.85%, ensuring carbon equivalent, increasing fluidity and ensuring filling effect.