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Overburden Drilling System

 Overburden Drilling System

Advantages of SPM Overburden Drilling System:
1. The drilling system comes with an eccentric bit design which ensures less material cost as compared with concentric design, and reduces oil consumption of air compressor.
2. Eccentric designed bit rotates outward to drill a larger diameter hole than the casing. This enables easy drilling and helps to avoid cave-ins and wash-outs.
3. Constructed from imported, premium quality steel, the eccentric overburden drilling system has a three-wing reamer bit that is easily retracted into the casing for easier prevention of drill sticking.

1. Casing
SPM casings boast high impact strength and exceptional portability. To meet the requirements for deeper depths, our casings have gone through unique treatments that ensure considerable increase of durability and rigidity (Yield strength: ≥515Mpa, and Tensile strength: ≥810Mpa). Smooth inner surface of casing makes it convenient for eccentric drilling tool to smoothly pass through.

2. Drill String
Our overburden drilling system employs geological drill pipe which features simple structure, high strength and outstanding performance in removal of rock dust and flakes.

3. Hammer
SPM DTH hammer with eccentric bit can produce sufficient impact energy to enable the drill string and casing to be lowered in the hole simultaneously, and at the same time ensure an extremely low breakage rate of casing.

4. Special Process
Larger diameter casing and smaller diameter drill string and hammer ensure easy drilling and retracting. For instance, it uses φ146 casing with φ108 drill string, φ168 casing with φ127 drill string and φ178 casing with φ146 drill string (Unit: mm).

Air pressure for the high pressure DTH hammer is recommended to be 0.7~2.1Mpa.
Parameters of the DTH Hammer
Ream drilling diameter (mm) 108 114 127 146 168 178 194 219 245
Rotation speed (rpm) 30-40 <40 <40 <35 <30 <30 <25 <20 <15
Bit pressure (KN) 3.2 3.4 3.8 4.4 5.1 5.4 5.8 6.6 7.35
Air consumption (M3/Min) 4.3-14.2 3.5-18 5.7-20 5.7-20 5.7-20 8.5-25 8.5-25 8.5-25 12-31

1) When start drilling, you should use the minimum propulsive force and impact force to enable the drilling tool to stably drill into the rock. The propulsive force should be reduced in a timely fashion as the weight of hammer and drill string increases.
2) Normally, the eccentric bit of the hammer rotates at a speed of 15-45rpm. Reasonable rotation speed ensures faster penetration, less energy consumption and longer service life of drill tools. When drilling in very hard rock formations, the rotation speed should be reduced to avoid fast wear of drill tools.

Working Steps
1. The overburden drilling system is composed of DTH hammer, eccentric designed reamer and pilot bit, guide device and casing. The eccentric bit rotates outward to drill a larger diameter hole than casing so as to enable the drill string and casing to be lowered in the hole simultaneously. Rock dust is blown clear out of the hole through the casing.
2. After drilling to the designated depth, the reamer bit is retracted by slightly reversing the rotation or by applying tension on the bit. The reamer bit will retract into the casing for easy removal of the drill string and hammer.
3. Pulling the casing up and meanwhile filling concrete or other things under the hole.
4. Using DTH drill bit to continuously drill the hold to required depth

Technical Specifications of the Overburden Drilling System
Models Casing O.D./mm Min. I.D. of Casing/mm Reaming Diameter/mm Min. I.D. of Casing Shoe/mm Max. Diameter of Pilot Bit/mm Matching DTH Hammer
SPM70A-70-89 89 77 98 71 70 SPM70A
SPM90-85-108 108 94 114 86 85 SPM90/SPM90-I
SPM335-85-108 108 94 114 88 86 SPM335
SPM335-90-114 114 98 127 91 90 SPM335
SPM335-100-127 127 114 136 101 100 SPM335
SPM110-110-127 127 114 136 111 110 SPM110/SPM110-I
SPM110-120-146 146 130 156 121 120 SPM110/SPM110-I
SPM4.5-120-146 146 130 156 121 120 SPM4.5
SPM340-120-146 146 130 156 121 120 SPM340
SPM350-140-168 168 152 180 142 140 SPM350/355/355K
SPM350-145-178 178 152 190 146 145 SPM350/355/355K
SPM350-150-183 183 152 198 146 145 SPM350/355/355K
SPM360-164-194 194 178 210 165 164 SPM360/S60
SPM360-186-219 219 201 240 187 186 SPM360/S60
SPM380-203-245 245 221 262 206 203 SPM380/S80
SPM380-241-273 273 260 305 244 241 SPM380/S80
SPM380-285-325 325 305 360 286 285 SPM380/S80
S100-285-325 325 305 360 286 285 S100
Product Code: SPM Hammer Model –Max. Diameter of Pilot Bit –O.D. of Casing
Example: SPM350-140-168
SPM350= Hammer model, 140= Max. diameter of pilot bit, 168=Casing O.D.
※Above technical parameters are used for reference only.