(1) The slow cooling rate is not only related to the design, pouring system and metal composition, but also related to other factors, such as the low compactness of molding sand, the need to use but not to use cold iron, the long time interval between pouring and sanding, and the stacking of hot castings after sanding.
(2) Improper heat treatment is also one of the main reasons for the coarseness of some metal particles.
(3) For all metals, too high pouring temperature is easy to cause coarse grain defects
(4) Improper machining and improper machining will make the dense castings look like the defects with coarse grains. The so-called improper machining refers to the unreasonable grinding of the cutting tools, the blunt cutting tools, the wrong cutting speed or feed control, and the improper rough machining methods, etc., which will cause a porous appearance with some damage, and this appearance will make people think that there is a defect of coarse grains in the castings.