The effect of back rake angle on a center vacuum bit design was investigated through factorial Analysis of Variance (ANOVA) tests for drilling in shale. Multiple performance criteria: penetration rate, specific energy and torque were used in these tests. Thrust and rotary speed were the controlled variables. Results from ANOVA tests showed that rake angle has a significant effect on penetration rate and torque but not on specific energy. Further tests of means revealed that the 20-deg bit gave the maximum penetration rate although there was no statistical difference among the 15, 20 and 25-deg angles. Tests of means also revealed that the 7-deg bit gives the minimum torque, but is statistically the same as the 15 and 25-deg bits. The results of the test will be useful for design and selection of small-diameter bits for drilling in shale and sand formations.
The Effect of Back Rake Angle on the Performance of Small-Diameter Polycrystalline Diamond Rock Bits: ANOVA Tests
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Hough, C. L., Jr. (December 1, 1986). "The Effect of Back Rake Angle on the Performance of Small-Diameter Polycrystalline Diamond Rock Bits: ANOVA Tests." ASME. J. Energy Resour. Technol. December 1986; 108(4): 305–309. https://doi.org/10.1115/1.3231281
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