The inside (including the taper) is usually made of cement or thermoplastic, since this material must be drilled out if the well is to be deepened beyond the casing point.

浮鞋的内部（包括锥型段部分）通常由水泥或热塑性材料组成，如果在套管鞋处井眼还需要继续加深的话这种材料必须被钻掉。

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The asbestos dust that can be so deadly is released when cement sheets are sawn into convenient lengths or drilled with holes so they can be fixed into place.

BBC: News Online