One mechanism of bit failure in geothermal drilling is thought to be directly related to the overheating of the bearings. High temperatures alter the microstructure of the bearing material and reduce its wear resistance. This paper presents a laboratory study on bit bearing temperatures in rotary drilling using a two-roller cone micro-bit drill rig and a statistical approach referred as response surface methodology. The effects of the drilling variables on bearing temperatures were investigated. The range of bearing temperatures for the test conditions under study was determined. A second-order bearing temperature predicting equation is presented.

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