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Currently in the drilling industry, there are two main categories of drilling bits: rolling cutter bits and fixed cutter bits. Plus, bit sizes vary from 3-7/8 inch to 36 inches.
Rolling Cutter Bits
Rolling cutter bits, which some may also call roller cone bits or tri-cone bits, have three cones. Each cone can be rotated individually when the drill string rotates the body of the bit. The cones have roller bearings fitted at the time of assembly. The rolling cutting bits can be used to drill any formations if the proper cutter, bearing, and nozzle are selected.
There are two types of rolling cutter bits which are milled-tooth bits and tungsten carbide inserts (insert bits). These bits are classified by how the teeth are manufactured:
ROLLER CONE BITS
Roller cone bits have three hollow metal cones with rows of cutters on the surface. Each cone is able to rotate on a bearing as the bit turns. The cutters on each cone dig into and crush, the formation to remove it.
The Tungsten Carbide Insert Bit is one of the three types of roller cone bits.
• Tungsten Carbide Insert Bits
The tungsten carbide insert bits are also called insert or button bits. The tungsten carbide cutters are inserted or fixed into the cone. shows the different shapes of inserts available. The longer chisel-shaped inserts are good for softer rock. Cone-shaped inserts are for medium formation, and short hemispherical inserts are used for the hardest rock.
FIXED CUTTER BITS
Unlike roller cone bits, fixed cutter bits do not have moving parts. A fixed cutter bit rotates as one piece with the drill string. The cutters are made from diamonds. The properties of diamonds give these bits advantages over roller cone bits.
Diamonds are the hardest mineral on earth. Diamond bits use natural industrial diamonds or manufactured diamonds. Manufactured diamonds are made from polycrystalline diamond compact (PDC) or thermally stable polycrystalline (TSP).
• PDC Bit
PDC bits have synthetic diamond cutters set in ribs or blades on the bit. This type of bit scrapes the formation, so less weight is needed on the bit to drill efficiently. Bits using PDC cutters are as common as roller cone bits.
SPECIAL PURPOSE BITS
Besides ordinary roller cones and fixed-head bits, there are many bits that suit a particular purpose.
• Coring Bit
Polycrystalline diamond compact (PDC) core bits were originally introduced for oil drilling bits. The surface of the cylindrical-shaped PDC cutters consists of premium synthetic diamond particles sintered together by high pressure and high temperature. The cutters of the PDC coring bits have high hardness, wear resistance, and great tenacity, these drill bits are widely used in oil, gas, mining, engineering, etc drilling fields that remove a small amount of rock sample from within the formations to do the needed analysis.
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