Hot cracks are cracks caused by the blocking of solid-state shrinkage of the castings when the castings are still in a state of very low strength and plasticity at the end of solidification or shortly after solidification. Hot cracking is one of the common casting defects in the production of steel castings, malleable iron castings and some light alloy castings. Hot cracks initiate at grain boundaries and extend along the grain boundaries, and their shapes are uneven, tortuous and irregular. The surface of the crack is oxidized and has no metallic luster. The cracked surface of steel castings is approximately black, while the aluminum alloy is dark gray. External cracks are visible to the naked eye and can be distinguished from cold cracks according to their shape and fracture characteristics.
Hot cracks can be divided into external cracks and internal cracks. Hot cracks that can be seen on the surface of the casting are called external cracks. External cracks often occur at the corners of castings, where the thickness of the section changes sharply, or where the local solidification is slow, and where stress concentration is likely to occur. Its characteristics are that the surface is wide and the inside is narrow, and it is tear-like. Sometimes the fracture will run through the entire casting section. Another characteristic of hot cracks is that the cracks are distributed along grain boundaries. Internal cracks generally occur in the final solidified part of the casting. The shape of the crack is very irregular, and the cross section is often accompanied by dendrites. Usually, the internal crack does not extend to the surface of the casting.
The causes of hot cracks are reflected in the process and casting structure, including: uneven wall thickness of the casting, too small inner angle; too many forks in the lap joint, and the outer frame and rib of the casting hinder the normal shrinkage of the casting; the gating and riser system hinders the normal shrinkage of the casting. Normal shrinkage of castings, such as the casting riser close to the box belt or the high sand strength between the casting risers, which limits the free shrinkage of the casting; the riser is too small or too large; the shrinkage rate of the alloy wire is too large; the low melting point phase is formed in the alloy The elements exceed the standard, and the content of sulfur and phosphorus in cast steel and cast iron is high; the castings are thrown out of the box too early, and the cooling is too fast.
ABOUT KEVA
Keva Casting is a professional casting company that focuses on Construction, Machinery, Automobile, Hardware, Pipeline and many other industries.
We provide top quality products with the best service based on our complete production chain including our own mold design, advanced production techniques, and full management of the supply chain. Keva Casting has two factories located in Zhucheng, China's Shandong province.
We use "shell molding", which is a new technique that has been developed in recent years.This new technique has simplified production procedures and reduced air pollution compared with traditional sand casting and investment casting. Shell making and core making are faster to ensure production in enormous quantities. The dimensions and surface finishing are satisfactory for all kinds of industrial requirements. Besides supplying our own formwork & scaffolding systems, our casting products also supply OEM services in various industries.