| 摘要 |
A roller cone dill bit which has a row, preferably a gage row, of cutting elements formed into a first group of adjacent cutting elements having one pitch pattern and a second group of adjacent cutting elements having a different pitch pattern where at least one cutting element in the first group either has a different geometry, a different material property or a different material type to the cutting elements in the second group. The cutting element is preferably modified because of the expected dull condition of the cutting element. The different geometry is typically any of the crest width, the crest length or the diameter of the cutting element or the cutting element has an asymmetric crest because of a bulk on either the leading or trailing edge. The cutting elements are preferably made of tungsten carbide in a cobalt matrix and the cutting element with a different material type will typically either have less carbide or more cobalt. The different in material property is preferably due to the cutting element having increased hardness or toughness. |
