By Luke Byrne
The history of pneumatic hammers is thought to date back to 1844 when they were originally designed for hard rock drilling in quarry environments. The hammer remained at the surface of the hole whereby more drill pipe was added once the head reached the table. At this time the systems used were inefficient and resulted in inaccuracies of the borehole which in turn resulted in inaccurate control of the blasting process. Once the DTH system was engineered by Andre Stenuik from Belgium in 1954 it was quickly implemented and then soared to the top as the premier method for hard rock drilling diameters of 5” and above.
While significant product developments have been made over the years to the DTH hammer category the hazards involved within assembly and disassembly of the product largely remain the same. Mincon Rockdrill’s take its responsibility seriously in all HSE matters and strictly adheres to the following controls measures when assembling our DTH hammers in our manufacturing environment. All employees prescribe to the safe work practices, manual handling techniques, correct use of tooling, lifting aids, housekeeping and personal protective equipment appropriate for the task as highlighted from the relevant risk assessment.
Safe Assembly of a Reverse Circulation Hammer
Ensure all components, except for the sample tube, are liberally coated with good quality rock drill oil and threads with thread grease. Check the condition of all O rings and the check valve seal before assembly. Assembly of all hammers should be completed with the following PPE steel cap boots, gloves and safety glasses. Tooling such as dolly’s and hammers should be inspected and dressed as appropriate before use.
Identify the chuck end of the hammer and stand the wear sleeve with the chuck end facing up (ensure the wear sleeve is on even ground and the area is free of spill hazards). Insert the piston retaining ring in to the groove provided. Ensure the extraction groove on the retaining ring is facing the chuck end of the hammer.
Insert the Aligner (with the smaller outside diameter facing the piston retaining ring) in to the wear sleeve. Using a soft steel drift, tap the aligner in to place against the piston retaining ring.
Place the bit retaining rings on top of the aligner.
Grease the chuck then screw (with the chuck sleeve assembled on it) in to the wear sleeve.
Seal up the chuck end of the hammer as to reduce the likelihood of rock oil running from the bottom end producing slip hazards.
Lay the hammer horizontally then lubricate the piston and feed into the wear sleeve (as the piston is heavy and lubricated be careful for the pinch point between the two parts)
Stand the hammer with the back head end facing up (Be sure the environment is clean so the hammer will not slip thereby generating a crush point)
Insert the Sample tube mount in to the inner cylinder and fit the seating rings around the round holes on the inner cylinder.
Insert the Inner cylinder assembly in to the wear sleeve. Tap the assembly in to place using a soft steel drift (inspect the drift before use as metal fragments can lodge in the skin at velocity).
Place the lock ring on top of the sample tube mount.
Fit the spacer on to the sample tube with the flat face facing down to the drill bit end of the sample tube. Place the check valve spring on to the locating recess on the spacer and fit the check valve in to place.
Spray the area under the rings of the sample tube with penetrating oil (e.g. CRC / WD40). If hammer oil is used then the sample tube will not go in to place properly because a hydraulic lock will occur between the sample tube shoulder and the sample tube mount.
Insert the sample tube assembly in to the hammer.
Pour hammer oil in to the hammer.
Fit the screen to the adaptor tube and insert the assembly in to the back head. Insert the circlip in to the back head to lock the assembly in to place.
Screw the back head assembly in to the wear sleeve. There should be a standoff gap of between 0.5mm - 1mm (0.020” – 0.040”) between the back head and wear sleeve shoulders. If the shoulders meet up then the lock ring needs to be replaced so that all internal parts are properly locked in place.
Seal up the top of the hammer.
Store the hammer on its side and rotate it periodically if it is being stored for an extended period of time. If a hammer is to be stored for a long period of time, we would recommend that the hammer be disassembled, oiled up, and stored in a clean, dry environment.