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和绳索取心钻具相似的可收缩的金刚石取心钻头最近正进入现场试验阶段,该试验将继续进行至一九八○年八月。然后将由美国矿物局特温城(Twin city)研究中心来完成对该钻具的实验室鉴定和在花岗岩中
Shrinkable diamond coring bits similar to rope coring tools are currently entering the field trial phase and will continue until August 1980. The laboratory of the boring machine will then be completed by the Twin Cities Research Center of the US Mineral Bureau and will be completed in granite