Skip to Content

Hammers an Back Hammers

DTH & Back-Hammer Operations


1.0 Purpose of this Briefing

This memo is a fundamental review of the two key components of our hard rock drilling system: the Down-the-Hole (DTH) Hammer, which is our primary tool for making the hole, and the Back-Hammer, our essential tool for string recovery. Understanding how they work independently and as a system is non-negotiable for safe and profitable drilling.

2.0 The Rock Breaker: Understanding the DTH Hammer

The DTH hammer is the business end of our drill string. Its job is to fracture hard rock formations with brutal efficiency.

2.1 Principle of Operation The mechanism is robust and effective. We send a massive volume of high-pressure air down the inside of the drill pipes. This air powers a free-moving, heavy piston inside the hammer's casing.

  • Actuation: The piston strikes the back of the drill bit in a rapid, continuous cycle (percussion). We're not grinding the rock; we are systematically shattering it.
  • Hole Cleaning: The air used to drive the piston is then discharged directly through the face of the bit. This forceful exhaust clears the pulverized rock (cuttings) from the bottom of the hole, carrying them up the annulus (the gap between the pipe and the hole wall) to the surface. If cuttings stop coming up, your bit is no longer advancing.

While the hammer delivers the impact, the rig's top drive provides slow, constant rotation to ensure the bit strikes a fresh rock face with each blow, resulting in a straight, uniform borehole.

2.2 Correct Application The DTH hammer is our solution for drilling through competent, hard formations like granite, dolerite, and quartzite. It is the wrong tool for unconsolidated materials like sand, gravel, or soft clays, where a mud rotary system is more effective.

3.0 The Extraction Tool: Using the Back-Hammer

A stuck drill string is a driller's worst nightmare. It halts all progress, and the value of the equipment stuck downhole can easily exceed R500,000. The back-hammer is our mechanical solution to this problem.

3.1 Purpose and Placement The back-hammer's sole purpose is to free a stuck string. It is not a drilling tool. It is typically positioned in the drill string just above the DTH hammer. During normal drilling, air passes through it and it remains dormant.

3.2 The Recovery Process When the string becomes lodged (due to a collapse, fault line, or swelling clay), you must follow a clear procedure:

  1. Cease Drilling: Immediately stop rotation and downward feed.
  2. Attempt Initial Pullback: Apply upward tension with the rig's hydraulics to see if the string will come free. Do not apply excessive force that could damage the rig or snap the pipe.
  3. Activate the Back-Hammer: If the string is firmly stuck, engage the back-hammer system. This redirects the airflow to power the back-hammer's internal piston.
  4. Apply Steady Tension & Percussion: The back-hammer will begin delivering powerful upward blows. This percussive shock travels up the drill string, vibrating it intensely. This action, combined with the steady upward pull from the rig, works to dislodge whatever is binding the string.
  5. Exercise Procedural Discipline: This can take time. It is a loud, violent process that requires patience. Let the tool do the work. Rushing the process or pulling too hard is how you make a bad situation worse.

4.0 The Integrated System & Critical Safety Points

Running a back-hammer in the string is a proactive measure. It means the recovery tool is already in place when trouble strikes, potentially saving a full day of "fishing" or the total loss of the equipment.

Always adhere to the following safety protocols:

  • Air Line Integrity: High-pressure air is dangerous. Ensure all hoses have whip checks (safety cables) and that all connections are secure before starting the compressor.
  • Tool & Thread Care: Before adding any tool to the string, ensure its threads are clean, undamaged, and properly lubricated. A stripped thread downhole is a major failure.
  • Situational Awareness: Listen to the sound of the drill. A change in pitch or labouring sound from the hammer can be the first warning that you are entering a problem formation.
  • Personal Protective Equipment (PPE): Hard hats, steel-toed boots, safety glasses, and hearing protection are mandatory for anyone on or near the drill rig.

5.0 Summary

Think of the DTH hammer and back-hammer as a single system designed for hard rock environments. One provides the force to drill the hole, and the other provides the force to ensure our investment comes back to the surface. Know your tools, respect the ground conditions, and follow procedure.

Let's keep the rigs turning safely.