Rockwell hardness tester is also commonly used for hardness test of cast iron. For the workpiece with fine grain, if there is not enough area for Brinell hardness test, Rockwell hardness test can also be carried out. For pearlitic malleable iron, chilled iron and steel castings, HRB or HRC scale can be used. If the material is uneven, several readings shall be measured and the average value shall be taken.
Dalian castings usually have uneven structure, large grains and more carbon, silicon and other impurities than steel. The hardness varies in different small areas or at different points. However, the indenter size of the Brinell hardness tester is large and the indentation area is large, which can measure the average hardness of the material within a certain range. Therefore, the Brinell hardness tester has higher testing accuracy and less dispersion of the hardness value, and the measured hardness value can better represent the actual condition of the workpiece hardness. Therefore, Brinell hardness tester is widely used in foundry industry.
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 ferrous metals or non-ferrous metals, people still use the above methods to produce castings.
Later, due to the hard exploration of casting work, many casting theories, viewpoints and methods were published. Now the most popular casting theories are "sequential solidification", "simultaneous solidification", as well as "directional" and "diffusion solidification". Therefore, almost all foundry workers use these theories to guide teaching, design and produce their own castings.
In order to realize natural feeding, we must have the process measures that can realize "sequential solidification" in our casting process system. Many people intuitively think that the shrinkage cavity and porosity defects of castings can be solved by low-pressure casting, but this is not the case. The use of low-pressure casting process does not solve the shrinkage cavity and porosity defects of castings. If the low-pressure casting process system is not equipped with feeding process measures, then the blanks produced by this low-pressure casting method may also have shrinkage cavity and porosity defects.
