A patented, locally manufac- tured mechanical tamp- ing device, the advanced tamping device (ATD), which offers a significant improvement on panel advance, improved fragmentation, and a significant reduction of dust and fine rock, has been released by safety systems and equipment suppliers Booyco Electronics.

Booyco Electronics MD Anton Lourens says that the ATD is a lightweight and portable tamping device which offers an unlimited shelf life and significant savings on explosives as well as reduced fuse igniter costs. “This device has been accepted favourably by the workforce as there is no preparation requi- red, and it is simple and easy to use. “Unlike other conventional tamping systems, there is no wastage,” he says.

Lourens says that among the advantages of the ATD is that it is unaffected by wet holes, it is fully recoverable and reusable in the event of a misfire, it is impervious to all working temperatures, and it is ideal for slow-release propellant blasting. The ATD is manufactured from fire-retardant and antistatic polypropylene.

The ATD was tested locally at a gold mine, and the results verified that the blasted rock contained less fines, and that hanging and sidewall control was satisfactory.

Lourens explains that tamping is the blocking of a charged shot hole with suitable stemming material, such as clay tamping capsules. “The purpose of tamping is to effectively contain and distribute explosive energy in the blast hole. “If tamping is not used, a great deal of blast energy is lost, resulting in a poor blast,” he says.

Tamping is also used to retain the flame caused by the initiating explosives in the hole. By not using tamping, the fire hazard risk is increased significantly. Tamping is a legal requirement, and there are several types of tamping systems available.

Lourens further explains that tamping devices are inserted into the blast hole after charging it with the explosive charge to ensure that the effect of the explosion is directed to the rock, thereby increasing rock breakage. “When blasting is done without a tamping device of any sort, most of the expanding gases created during the explosion simply escape through the blast hole drilled into the rock, resulting in a far less efficient process,” he says.

He adds that various tamping compositions and devices have been employed in the mining industry over the years. The most commonly used tamping composition currently in use comes in the form of a clay plug, which is inserted into the hole and clamped down with a wooden stick. While these clay plugs are adequately effective as tamping, this method has a shortcoming in the event of a misfire, when it becomes very difficult to remove the tamping capsule from the blast hole.

When a misfire occurs, it is necessary, before working in the blast area, to remove the entire charge from the blast hole where the misfire occur-red. This is normally done by means of a water lance, through which water is fed under high pressure into the hole, which forces out the explosive charge.

“However, because of the sticky consistency of the clay, it can take a long time to properly wash out a misfired charge from a blast hole. “An alternative form of tamping is a polymeric foam composition which is introduced into the blast hole. “This arrangement, though, has the disadvantage of being relatively expensive,” adds Lourens.

He says that the ATD offers distinct advantages over traditional tamping systems, which include a reduction in wast- age, the achievement of better advances and a better applica- tion, as it is mechanical and, therefore, not prone to human error.