Core drilling

Core drilling a modern core drill is a drill specifically designed to remove a cylinder of material, much like a hole saw. The material left inside the drill bit is referred to as the core.

Core drills used in metal are called annular cutters. Core drilling used for concrete and hard rock generally use industrial diamond grit as the abrasive material and may be electrical, pneumatic or hydraulic powered. Core drills are commonly water cooled, and the water also carries away the fine waste as a slurry. For drilling masonry, carbide core drills can be used, but diamond is more successful when cutting through rebar.

Core drilling are used frequently in mineral exploration where the coring may be several hundred to several thousand feet in length. The core samples are recovered and examined by geologists for mineral percentages and stenographic contact points. This gives exploration companies the information necessary to begin or abandon mining operations in a particular area.

An oriented core goniometer, commonly used when analyzing cores for contacts and other structural features

Before the start of World War Two, Branner Newsom, a California mining engineer, invented a core drill that could take out large diameter cores up to 16 feet in length for mining shafts. This type of core drill is no longer in use as modern drill technology allows standard drilling to accomplish the same at a much cheaper cost.

Core drills come with several power choices including electric, pneumatic, and hydraulic (all of which require power sources, such as a generator

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How Does It Work?

Core drilling The basic concept of core drilling is using a hollow bit to extract a sample from a certain surface. There are two types of core drilling, and each of these processes works in a slightly different way.

Soft Coring

Soft coring is used for unconsolidated material. The process is effective up to depths of 500 feet. However, the equipment for soft coring can reach deeper depths, provided the right conditions are met.

This process uses nested barrels. It has an inner barrel that pushes out and captures the samples, while the outer barrel protects the hole from collapse, serving as a sort of case. This also ensures that there’s no contamination from air or fluids when the sample is extracted.

Hard Coring

Hard coring is used for extracting competent rock samples. While this process also uses nested barrels, it’s the outer barrel that extends in this process. This washes the surface with drilling fluid or air before the drilling takes place. That way, the sample remains undisturbed.

This process can reach depths of up to 5,000 feet and is also called diamond coring due to the diamond-coated drill bit needed to penetrate the rock. This is widely used for samples that are harder than sandstone.