Chapter 23: Cartridge Loaders

Pneumatic cartridge loaders originated in Europe and have been in use since the mid-1960s in both surface and underground operations. Early applications used metal tubes to blow cartridges into boreholes. The rigid metal pipes were made of non-sparking copper or aluminum, were easily damaged in the field and limited to relatively short boreholes. The cartridged explosives used were primarily NG dynamites or permitted type explosives, which had high loading densities with manual loading.

Cartridge loaders (See Figure 23.1) became more popular and spread to North America with the introduction of flexible thermo-plastic loading hose and water gel explosives in the 1980s. Europeans had taken the older equipment and developed flexible loading systems that increased loaded density per unit by as much as 40% to 55% in comparison with hand tamping.

There were a variety of these loaders manufactured and distributed by Nitro Nobel, Atlas Copco and others. Additional accessories such as "robot tampers" were also available which automatically withdraw the loading hose from the hole as it was filled enabling one person operation.

The introduction of water gel, slurry and emulsion explosives greatly improved the flexibility and usefulness of these machines and they are still in use today for specialized applications where extremely long boreholes up to 100 meters (328 feet) in broken ground must be loaded with cap sensitive, waterproof explosives in horizontal or uphole orientations i.e. ring and fan drilled stopes.

Figure 23.1 – Cartridge air loader. (Courtesy: Tepex Inc.)

Today's loader consists of a metal cylinder with flaps at each end mounted on a tripod with a pneumatic control circuit and valve that regulates the incoming air pressure and switches the air between the cylinder body and the loading hose as shown in figure 23.2.

Figure 23.2 – Cylinder body with air line. (Courtesy: Tepex, Inc.)

There are two cartridge loader models designated 32 and 42 to reflect the maximum cartridge diameter in millimeters. The 32 loader uses 25 millimeter and 31 millimeter (1 inch and 1¼ inch) diameter cartridges and the 42 handles 31 millimeter and 38 millimeter (1¼ inch and 1½ inch) diameter cartridges. Maximum cartridge length is 400 millimeters (16 inches). Cartridge loading hose is "special" and should not be replaced with similar looking domestic products. The colored stripe designates that it is semi-conductive to bleed off or eliminate static buildup creating a pneumatic hazard. The anti-static loading hose is grooved (rifled) as shown in figure 23.3 on the inside to reduce friction and available in sizes to accommodate a range from 25 millimeters to 38 millimeters (1 inch) to (1½ inch) diameter.

The interior cross section of the hose is also ovoid to permit the unsupported movement of the cartridges, whereas other hose is elliptical causing higher resistance and reduced transfer rates. Water is used as a lubricant to ease cartridge travel and an optional valve can be fitted to the loader to ensure the hose remains wet. The traditional alternative has been to spray water into the cartridge case just before loading. The use of soap, detergent or petroleum based lubricants is not recommended as they might have an adverse effect on the service life of the loading hose and reduce the adherence of the porcelain column lining.

CAPABILITIES

Pneumatic cartridge loaders permit high compaction ratios in the boreholes not possible with manual pole tamping of cartridges. A good loading team (near the loader, one operating the hose) can match or even surpass old manual cartridge loading rates at much higher densities.

Better explosives coupling with the rock can permit expanded patterns, reduction in drilling costs, and improved fragmentation as mentioned in the beginning of this section.

SELECTION CRITERIA AND OPTIONS

The only cartridged explosive products approved for this loading method in North America are water gel and emulsion products specifically designed for this use. The formulation is designed for rugged handling, water resistance without the packaging, polyethylene or mylar film wrapping that splits (ruptures) on contact with the rifling and tack present at the end of the loading hose, as shown in figure 23.3, permitting high compaction in the borehole.

Figure 23.3 – Loading hose with rifling tack. (Courtesy: Tepex, Inc.)

Explosives stored in unheated magazines in winter must be allowed to warm up to 0°C (32°F) before they are pneumatically loaded. Below these temperatures the cartridges may be too rigid and not deform satisfactorily to fill the borehole.

It is illegal to load NG based products in North America and most of these machines exhibit the warning against their use. The fear is that sensitive grades of dynamite like ditching powder might end up being used endangering the operator and public.

Pneumatic cartridge loaders excel at loading rough boreholes in broken ground. Once the hose is introduced you will not "lose the hole" common with manual string loading of cartridges. You can even load through overburden material which can be useful to bottom out and bypass in a trenching application.

Overfilling is less likely to occur if you encounter voids, as the column rise and cartridge count will immediately reflect this, unlike some bulk loading methods.

Priming methods are as varied as the application but usually use shock tube or detonating cord dynamite to initiate the hole. Multiple initiation is usually recommended where there is chance of cut-offs.

Never use damaged cartridges in a loader.

ADDITIONAL RESOURCES

Dick, P.R. and Jessop, D.K., 1998. Loading explosives in large diameter upholes. International Society of Explosives Engineers (ISEE) Proceedings of the 14th Annual Conference on Explosives and Blasting Research, pp. 1-27, January 31 - February 5, Anaheim, CA. ISEE, Cleveland, OH.

Palangio, T.C., 1989. Pneumatic cartridge loaders in surface and underground applications. 4th Pennsylvania Drilling and Blasting Conference, November 16. Pennstate University. State College, PA.

Palangio, T.C. 1990. Underground Bulk Loading Methods. Blasting Analysis International, Inc. (BAI) Proceedings of the 2nd High-Tech Seminar: State-Of-the-Art Blasting Technology, Instrumentation and Explosives, June 10 - 15 Orlando, FL. BAI, Allentown, PA.