| 摘要 |
An earth-boring bit for drilling a borehole comprises a bit body having a bi t axis, at least two rolling cone cutters rotatably mounted on the bit body, a plurality of inner row cutter elements positioned on at least one cone cutter in a first inner row, a plurality of gage-cutting cutter elements positioned in a first fanned-gage row on a first one of the one cutters, and a plurality of gage-cutting cutter elements positioned in a second fanned-gage row on a second one of the one cutters, wherein the gage-cutting cutter elements on the bit define a gage curve and cutter elements in the first fanned-gage row and the second fanned-gage row contact the gage curve at different points. In one embodiment, each cutter element has an extension, and the extensions of the uppermost fanned-gage row cutter element and the first inner row cutter element define a step distance such that the ratio of the step distance to the extension of the first inner row cutter element is greater than 0.5. Alternatively, the first and second fanned-gage rows are positioned to have different oversize angles, positioned such that the ratio of the diameter of the largest fanned - gage row cutter element to the diameter of the first inner row cutter elements is not greater than 0.75, or positioned such that the lowermost fanned-gage row contains more cutter elements than any other fanned-gage row.
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