INVESTIGATION OF THE IMPROVED ‘‘INSERT CUTTER – CONE’’ CONNECTION BY INTRODUCING AN ADDITIONAL ELEMENT FOR ROLLER CONE BITS

Abstract

A new design of the rock-destroying insert has been developed, which has made it possible to increase the reliability of the connection between the tungsten carbide inset cutter and the body of the cone. This allows providing favorable conditions for the rational distribution of contact stresses in the conjugate surfaces "tungsten carbide inset cutter – bush – a body of the cone". The task was solved by improving the well-founded selected prototype, which is the design of the rock-destroying insert of the drill bit. The construction includes a carbide inset cutter, which is made with a two-stage shank with equal steps in height. The developed design of the rock-destructive insert creates opportunities to increase the strength of the connection "inset cutter – the body of the cone". This is realized because a reliable fit of the conjugate contact surfaces is obtained and prevents the tungsten carbide inset cutter from falling out of the bush. Resistance increases to the brittle fracture of the carbide inset cutter in a dangerous section. The proposed joint allows to improve the tightness of the conjugate surfaces of the "shank of the inset cutter – bush" in the technological operations of assembling the rock-destructive insert. The obtained results of stress state modeling indicate that, as expected, with the same forces acting on the inset cutter from 50 kN to 68 kN, the most intense place on the cone will be the "flange" near the inset cutter. The stress will be up to 1070MPa in this place for cones with serial rock-destroying equipment. Therefore, the developed construction of the destructive insert provides new opportunities not only to increase the strength of the connection with the body of the cone. Conditions secure the cracking of tungsten carbide insert cutter with surge stresses in the press connection when we have an overload during the destruction of high-strength rocks. At that time, this stress will be up to 912MPa, which is 17% less for cones with developed rock-destroying equipment. It is established that the structural parameters of the rock-destroying insert allow to qualitatively changing the rigidity of the carbide insert cutter. This effect is due because the balance created in the conjugations and the intermediate sleeve is applied. Therefore, the developed construction of the destructive insert provides new opportunities not only to increase the strength of the connection with the body of the cone. There are also opportunities for the use of hard alloys with higher strength and prevent the formation of cracks in the body of the cone during the pressing of the inserts and in the process of rock’s destruction. The developed design of the rock-destroying insert not only makes it possible to organize selective assembly but also successfully eliminates the allowed defect during the formation of holes.