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DRILL STRING

• Harder rocks reduce penetration rate.
• Harder rocks need greater percussion energy as well as rotational torque.
• Harder rocks reduce the life of the carbide inserts.
• abrasive rocks result in greater wear and a reduction in the life of the bit, driver sub and piston case.
• Fractures in ground formation and cracks tend to lead the drill string and cause more problems with bit jamming and bit shanking.
• Softer rocks require greater feed rates and require more capabilities for flushing.