What are the basic principles of the inner gate of castings?
① The orientation and number of internal gates on the casting should follow the selected solidification sequence or feeding method Do not aim towards small sand cores, mold walls, cold iron, and core supports. If necessary, use tangent lines to introduce.
③ The inner gate should be as thin as possible, and the suction area of the inner gate can be lowered by the thin inner gate, which is beneficial for the negative slag of the dry transverse gate, reducing the possibility of entering the initial slag, and reducing the workload of sorting
In order to facilitate the rapid and stable filling of the metal liquid into the mold, facilitate dry exhaust and slag removal, the metal flow direction in each inner runner should be consistent as much as possible to avoid collisions of the metal liquid within the mold, resulting in chaotic flow direction and a tendency to avoid excessive flow
Large machine tool castings are poured at high temperatures, and during the condensation cooling process, they experience shortening and phase bending due to temperature drop. If shortening and phase transformation are prevented, casting stress will occur in the castings. Casting stress can be divided into three types based on its composition: thermal stress, phase change stress, and mechanical stress. Casting stress is the sum of thermal stress, phase change stress, and mechanical stress.
The commonly used methods for removing stress are as follows:
1、 The natural aging method has a good effect on removing stress, but to achieve the goal of removing residual stress, it is necessary to expose the casting to the air for several years. Long term storage is not suitable for modern enterprise production and is generally not used.
The thermal aging method can remove stress, but it has high equipment cost and energy consumption. Depending on the power of the aging air, it generally requires more than 30 hours. It is a commonly used process method for removing residual stress. But in the increasingly tense situation of power, it is not suitable for use, and its economic cost is high, which does not meet the comprehensive economic benefits of enterprise production. So we need to find a process method that can replace thermal aging.
3、 The essence of oscillatory aging method is to apply additional stress to the workpiece in the form of oscillation. When the additional stress and residual stress are combined and reach or exceed the yield limit of the data, the workpiece undergoes micro or macro plastic deformation, which reduces and homogenizes the residual stress of the workpiece, thereby stabilizing the geometric scale of the workpiece. This process method has low energy consumption, simple equipment and convenient use, and is now widely used.
Most of the materials for machine tool castings are made of gray iron cast iron, and there are also a few cast steel machine tool castings. The proportion of modern machine tool castings using structural steel to lift the bed is gradually increasing, and machine tool castings have good dimensional stability, which is beneficial for maintaining machine tool accuracy in the long term.