Kernbohrer

Kernbohrer, literally "core drill" in German, refers to a drill bit designed to cut and recover a cylindrical core from a borehole. Unlike standard drill bits that grind away material, a kernbohrer produces a hollow hole and keeps the extracted sample inside the bit, allowing immediate retrieval and analysis of the core.

Construction and operation

Most kernbohrer are hollow tubular bits with wear-resistant outer elements. Diamond segments are used for hard rocks, while carbide tips are common for concrete and inherited masonry applications. The bit is attached to a drill string and rotated while downward pressure is applied. Inside the bit, a core barrel and a core catcher retain the cylindrical sample as drilling proceeds. Core retrieval can be performed through wireline or by lifting the drill string after the cutting sequence. Cooling and lubrication are often used to reduce heat and extend tool life.

Types and materials

Diamond core bits are the dominant choice for geological and mining applications because they can cut through hard, abrasive rock while preserving a relatively intact core. For softer materials such as certain concretes or bricks, carbide-tipped or steel-bodied kernbohrer are common. Diameters range from a few millimeters up to several inches, with longer lengths enabling deeper coring in a single run.

Applications and use

Kernbohrer are widely used in geological and mineral exploration, civil engineering investigations, geothermal and hydrogeological drilling, and laboratory testing where a representative sample of the material is required for petrographic, porosity, or strength analyses. They enable core-based interpretation of subsurface conditions and properties.