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一种专门用于卵砾石和硬基岩地层中进行大口径钻进的钻进设备于1997年4月在济南市通过由山东省科委和地矿部科技司联合组织的专家鉴定。这种由山东地质探矿机械厂研制和生产的CJF－20型钻机可钻孔径2m、孔深80m的钻孔，为目前国内最大型的冲击反循环钻机。该机的主要特点是冲击
A special drilling equipment for large-diameter drilling in gravel and hard bedrock formations was appraised by experts from Jinan Science and Technology Commission and Ministry of Geology and Minerals in Jinan City in April 1997. This kind of CJF-20 drilling rig developed and produced by Shandong Geological Prospecting Machinery Factory can drill holes of 2m in diameter and 80m in depth. It is the largest impact reverse circulation drilling rig in China at present. The main feature of the aircraft is the impact