Manufactured Diamond Cutters Used in Drilling Bits
Authors: Eaton B.A. , Bower A.B. , Martis J.A. 
Published: December 2007

A method for bonding a polycrystalline diamond layer to a cemented carbide substrate has been developed. Mounted on a carbide supporting member, these manufactured diamond blanks have shown promise as drilling-tool cutting edges.

Introduction

In 1955, General Electric Co. introduced a process for commercial production of MAN-MADE TM diamonds. These were small, friable stones used for grinding and glass finishing where the friability of the material was desirable since it continually exposed new cutting edges. These diamonds did not offer the wear resistance required by applications such as stone cutting. However, second-generation manufactured diamonds were stronger, with a blockier structure, and have been used extensively in stone and masonry cutting applications. Recently, General Electric introduced a new development, known as the COMPAX diamond. This diamond drill blank, the result of many years of work with small diamond crystals, is a polycrystalline aggregate o manufactured diamond on a polycrystalline aggregate o manufactured diamond on a tungsten carbide substrate.

Diamond elements manufactured thus far consist of a layer of MAN-MADE diamond 0.020 in. thick bonded to a disk-shaped CARBOLOY substrate 0.110 in. thick. Diameter of these pills, as illustrated in Fig. 1, is 0.330 in. Though it is possible to modify these dimensions, diamond elements of this size were used throughout this study.

Although these diamond elements were not developed specifically for rotary drilling applications, the possibility of such a use was immediately identified. It was recognized that the well-drilling industry needed a cutting element with a sharp cutting edge resistant to abrasion and impact loading. It was thought that the diamond material would fulfill this need, provided it could be mounted properly in a bit.

For well-drilling applications, the diamond elements were brazed to tungsten carbide slugs, as shown in Fig. 2. Such a design would allow optimum support for the cutting edge and freedom of design for a bit, and would maintain comparability with existing bit-manufacturing methods.

These were several questions about the application of these diamond elements to rotary drilling that could be answered only by laboratory and field testing. Among these questions were (1) Do the elements offer high resistance to abrasion? (2) Do the elements offer high resistance to impact loading encountered in actual drilling practice? and (3) Could a prototype bit using these elements drill economically under full-scale field conditions?

Laboratory Testing of the COMPAX/Slug System

Experimental investigation of the element as a rock cutting tool was conducted at the U. of Tulsa Drilling Research Center. These tests were run in three categories.

Abrasion Tests

Tests were run to determine the wear resistance of the diamond elements. Cylindrical-shaped pieces of rock were mounted in a lathe that would turn the rock against the element, which was mounted as the cutting tool. A coolant of water-soluble oil was used.

Carthage marble was used in the first tests.

JPT

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