RC drilling (reverse circulation) with down the hole hammer for mining exploration
The RC drilling (reverse circulation) with down the hole hammer for mining exploration:
With this method the drilling needs to generate enough air pressure and rotational force on the tool, the pneumatic hammer and a drill string 10 , to generate sufficient percussion energy to create rock samples.
The compressed air (injected by the air flow swivel 1/ travels through the outer chamber of the drill rod (between the outer diameter of the inner. tube and the inner diameter of the external rod, blue arrow) to the down the hole hammer 2/ where it drives up and down a piston between two chambers. The air is evacuated through valves which are opened and closed depending on the displacement of the piston with a cycle of up to 2000 movements per minute. At the end of its’ course the piston comes into contact with the tool and the energy transmitted to the tool 3/ is sufficient to break the rock. The rock sample once broken is called «cuttings» and flows back up by the inner part of the dual pipe (through the inner tube, green arrow) by the effect of the pressure of the injected air.
Most of the time samples are collected with a cyclone system. The three main components of this system are:
4/ CYCLONE: The air escapes from the drill string, to avoid premature wear of the flexible 5 , we can use an elbow 6 that will effectively cushion the cuttings. The samples then go through the flexible to the cyclone where the samples fall to the bottom of it.
7/ DROP BOX: Samples are taken from the upper part. The dump door bottom allow to continue drilling whilst the samples are divided. At the end of each drilling interval (typically 1m / 3 feet) the drill pipes and the hole are carefully cleaned to avoid contamination of the next specimen collection.
8/ SPLITTER: Samples that arrive from the drop box shall be placed in the splitter and are then recovered through the bags 9 Then they are divided into separate boxes and labeled.
Rotary drilling RC :
Reverse circulation rotary drilling is a slower method, but it has the advantage of being less affected by back pressure and water inflows. It is common to see this technique used at high altitudes where it is impossible to pressurize the air enough, to create the impact energy required for standard reverse circulation drilling (with dth hammer).
This method uses the same principle to get back the cuttings to the surface, but does not require the use of a down the hole ham- mer to break the rock. Instead a special tricone is used to crush and scrape the rock face.
Drilling companies also use this technique to help drill in areas of high water inflow. It is common to use a conventional system until it becomes unproductive because of the back pressure to finally finish the hole with the tricone system.
Sampling that does exactly the same way as in the previous method.
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