Mechanism of Surface Cracking of Alumina Ring in a Mechanical Seal

Abstract

Experimental and numerical studies were conducted to clarify why and how surface cracking occurs in an alumina ceramic ring of a mechanical seal. By using a Au layer vacuum-deposited onto the alumina surface except the rubbing part with a carbon ring as a part of a D. C. circuit, the moment of crack initiation was identified. Temperatures and thermal stresses produced in the seal by participation of the frictional heating were calculated using finite-element techniques. It has been found that surface-cracking is caused by high thermal tensile stresses applied in the circumferential direction. It has also been pointed out that in order to prevent cracking, it is desirable to reduce the coefficient of friction between the sealing faces and to choose a seal material with low modulus of elasticity, low coefficient of thermal expansion, high thermal conductivity and high tensile strength.