当钻头上下钻时，要把钻孔保持在中心。
Keep the drill centred in the borehole while it ascends and descends.
钻头通常属于刮刀型，装备有PDC或者天然金刚石切削齿，但取芯钻头的特别之处在于钻头中心有一孔。
The bit is usually a drag bit fitted with either PDC or natural diamond cutting structures, but the core bit is unusual in that it has a hole in its center.
这样允许钻头围绕岩石的中心圆柱体钻进，并通过钻头进入取芯桶。
This allows the bit to drill around a central cylinder of rock, which is taken in through the bit and into the core barrel.
后者在其中心有一圆柱形沟槽，这样能生成整体芯在钻孔作业过程中引导钻头。
The latter has a cylindrical groove at its center, thus generating a solid core, which guides the tool as it proceeds during the drilling operation.
为了更合理地分析中心偏析，还对不同直径的取样钻头造成同一铸坯中心偏析的分析偏差进行了必要的研究。
In order to analyze central segregation more accurately, the error in chemical analysis caused by sampling with two drills of different diameters is studied.
为了更合理地分析中心偏析，还对不同直径的取样钻头造成同一铸坯中心偏析的分析偏差进行了必要的研究。
In order to analyze central segregation more accurately, the error in chemical analysis caused by sampling with two drills of different diameters is studied.
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