From the origin of metal casting to now, both at home and abroad, people in gravity casting to a large extent use molten metal, then pour it into the pre cast mold, with the help of self weight feeding and solidification of the metal, so as to obtain the designed castings. Whether it is black metal or non-ferrous metal, people still use the above methods to produce castings. Subsequently, due to the hard exploration of casting work, many casting theories, viewpoints and methods were published. The prevailing casting theories are "sequential solidification", "simultaneous solidification", as well as "directional" and "diffusion solidification".
The structural design of Dalian castings is reasonable. For example, the arrangement of fulcrum, the arrangement of reinforcement, the location of opening and the design of connecting structure should be conducive to improving the strength and stiffness of the box. Good workmanship. Including the process of blank manufacturing, machining and heat treatment, assembly and adjustment, installation and fixation, hoisting and transportation, maintenance and repair, etc. Good design, small quality. The design of different boxes may focus on the above requirements.
For example, in the 15th ~ 17th century, Germany, France and other countries successively laid many cast iron pipes to supply drinking water to residents. After the industrial revolution in the 18th century, steam engine, textile machine, railway and other industries rose, casting entered a new period of serving the large industry, and casting technology began to have great development.
Small residual sand particles in the mold rush into the mold cavity with molten iron. During mold closing, sand particles fall off due to extrusion between molds or between molds and sand cores. Poor performance of casting sand (e.g. low moisture and low strength) is easy to cause sand washing if water is injected too quickly in the scheme design. Main cause: the sand in the mold cavity is not clean. Sand particles are intruded from open places such as sprue or riser before pouring. The sand mold is not strong enough and falls off due to external force. The casting is discontinuous or the casting speed is too slow, so the sand particles in the mold cavity can not float to the riser smoothly, but stay in the place with low temperature.
As the cooling rate of the surface and the center of the parts is different during quenching, the sequence of martensite formation is also different. When martensite is first formed on the surface of the part, it will give a tensile force to the center which is still in the austenite state. At this time, due to the good plasticity of austenite, this stress can be relaxed through the plastic deformation of austenite.
