Stabilization

Why use a stabilizer in drilling a blast hole?

For reasons of economy. To reduce the cost per ton or rock removed, the most efficient use of expendable items such as rock bits and drill steel must be achieved.  Rock Bits are designed to rotate about their own centre. Stabilization assures that the bit will do this and thus cause the energies and forces exerted on it to be most efficiently utilized in an axial direction. Lateral movement or stumbling is restricted and hole is produced in the direction intended. More footage per bit and an increased penetration rate is achieved by proper utilization of the forces applied to the bit. Dull conditions of bits give evidence of this effective stabilization. Gauge wear is uniform and less severe. Shirt-tail wear problems are reduced. The inner row cutting structure is more uniformly worn – inner and outer flank wear is reduced.

 

How does a stabilizer affect drill availability?

In addition to faster penetration rate due to more efficient rock bit performance, the smooth bore produced with adequate stabilization permits faster rock bit and drill steel retractions from the bore hole. Further, the smooth bore sloughs less than a rough bore. This means that less rock particles fall to the bottom of the hole. Redrill time required is normally eliminated or drastically reduced.

 

How does a stabilizer affect powder loading efficiency?

Bulk powder loading in stabilized bore holes is easier. The smooth bore without ledges and unconformities allows more uniform loading and better distribution of explosives in the hole. This means more blasting efficiency and a reduction in secondary blasting.

 

What is meant by adequate stabilization?

Unless the guiding elements of a stabilizer are very near the bore wall, adequate stabilization of the bit is not achieved. Theoretically, the guiding elements should have the same diameter as the bit. Unfortunately, this is not practical because of the normal attrition of rock bit gauge wear surfaces. The stabilizer should therefore be held at the largest diameter practicable. Concentricity of guiding elements with the axis of the bit and steel is also quite important to proper stabilization. Eccentricities of these elements tend to avoid any hope of reducing drilling costs with a stabilizer.

 

What type of stabilizer is most efficient?

A stabilizer which maintains guiding elements close to hole wall is most efficient. The conventional welded rib or cast rib stabilizer does an adequate job when new and unworn, provided the ribs are concentric. The problems with this type of stabilizer are wear rate and maintenance cost. Rib-type stabilizers, due to their construction, necessarily drag and scrape against the bore wall and abrade rapidly. Due to the cost in maintaining close-to-hole wall contact, these stabilizers are left in the drill string long after adequate stabilization has been lost.  The most efficient stabilizer is one with true-rolling centralizers that are in rolling contact with the bore wall. Scraping and gouging of the guiding elements are eliminated and concentricities are maintained. Roller-stabilizers provide adequate stabilization without imposing excessive torque.  A six-point stabilizer design is available for angle hole drilling or severe conditions where increased stabilization or minimal hole deviation is required. This design features six tungsten carbide studded rollers in two levels, with each level of rollers staggered to produced maximum hole-wall contact.

 

Model 63-B Roller-Stabilizers

MTI’s Model 63 Series of Roller-Stabilizers opened a new ear in blast hole stabilization. It was the original Roller-Stabilizer designed especially for blast hole drilling. The elimination of maintenance time and labour costs normally required for replacement of work components or more conventional stabilizers resulted in wide acceptance of the expendable unit. Continued development brought about the Model 63-B which provides increased torsional strength and larger air circulation area. Increased life and reduced operating costs are achieved with the 63-B design through the use of rollers and bearings of the largest diameter practical within a given hole size.  Rollers with pressed-in tungsten carbide compacts, working against deeply carburized precision honed, air-cooled bearings, assure long life. Increased air circulation area is accomplished by the use of a patented aero construction which conducts air through the bearing pins to the drilling bit.