Enamel Casting Stress
Enamel stress is one of the causes of defects in enamel products.
(1) Generation of stress:
Internal force and stress: The attraction and repulsion generated by the change in the distance between atoms in the metal are collectively referred to as internal force. The internal force per unit area is called stress.
Casting stress: When the shrinkage of the casting is hindered during solidification and cooling, the stress generated inside the casting is called casting stress.
Casting stress can be divided into two types according to different internal forces: when the internal force is suction, it is called tensile stress; when the internal force is repulsive force, it is called compressive stress. When each part of the casting is condensed, the cooling rate is inconsistent, the slower cooling part forms tensile stress, and the faster cooling part forms compressive stress.
Casting stress is divided into thermal stress, deformation stress and mechanical resistance stress according to the cause. After the cause of the stress is eliminated, the stress that still exists in the casting is called residual stress. Bending deformation caused by thermal stress, the concave surface is always on the slower cooling side of the casting. This can be used as the basis for judging whether the deformation is caused by improper placement of the casting during heating or a problem with the shape of the casting itself when the product is deformed during production.
When the casting stress is too large and exceeds the strength of the casting, the casting will be damaged.
(2) Measures to reduce the stress generated by castings
a. Try to choose a material with a small shrinkage coefficient; b. Adopt the principle of simultaneous solidification; c. Cool slowly to reduce the temperature difference between each part of the casting; d. Use sand with good concessions; e. When designing, the deformation amount is made in the opposite direction that the casting may be deformed, and the deformation amount made in advance is called the reverse deformation amount).
(3) Methods to eliminate internal stress of castings a. Natural aging: place the castings stably and store them for a long time; b. Artificial aging: anneal the castings; c. Vibration aging: The stress can be eliminated by vibration.