8" DHD380 DTH Drill Bit for Hard Rock Blasting

Professional DHD380 203mm DTH bit for heavy-duty mining. High air pressure design with flat face for abrasive rock. Bulk buy and save. Request a quote!

The DHD340 is a globally recognized standard for 3.5-inch to 4-inch down-the-hole hammers. Originally developed by Halco, this design has been widely adopted and improved upon by manufacturers worldwide. The number "340" refers to the piston weight class and internal geometry, which optimizes energy transfer for bits ranging from 90mm to 115mm in diameter.

The "4"" in our product title indicates the nominal bit diameter in inches—approximately 102mm. However, the most common variant for hard rock blasting is the 115mm (4.5") version, which provides a perfect balance between hole size and hammer energy efficiency.

1.2 How a DTH Hammer Works

Unlike top-hammer drills, a DTH hammer operates with the striking mechanism located directly behind the drill bit, down at the bottom of the borehole. Compressed air drives a piston to strike the back of the bit, transmitting high-energy shock waves directly into the rock. This design eliminates energy loss along Drill Rods, making DTH hammers superior for:

• Deep hole drilling (over 50 feet)

• Deviated or inclined holes

• Fractured and abrasive formations

The DHD340 hammer typically operates at 150–250 psi air pressure, delivering 1,500–2,200 blows per minute depending on volume flow.

2. Technical Specifications of the DHD340 Hard Rock Drill Bit

2.1 Dimensional Parameters

2.2 Face Design Options for Hard Rock

Manufacturers offer three primary face geometries for the DHD340 bit:

• Concave Face: Best for medium-hard rocks (100–200 MPa). Provides good button protection.

• Flat Face: Ideal for very hard, non-abrasive rock like granite. Maximizes energy transfer.

• Convex (Dome) Face: Preferred for extremely abrasive rock (quartzite, iron ore). The dome shape prevents button loss and reduces friction.

For hard rock blasting (UCS > 200 MPa), a convex face with parabolic or ballistic buttons is recommended. These buttons concentrate stress over a smaller contact area, inducing tensile fractures with less energy.

2.3 Tungsten Carbide Button Grade

Premium DHD340 bits use a graded WC-Co composite with 6–10% cobalt binder. The carbide grain size is fine to medium (0.8–1.5 µm) to achieve a hardness of 88–90 HRA. Buttons undergo a brazing process with silver solder to ensure pull-out strength exceeding 15 kN.

For highly abrasive conditions (e.g., sandstone with 30% quartz), a dual-metal matrix or hardened steel skirt is added to protect the bit body from premature wear.

3. Performance Advantages for Hard Rock Blasting

3.1 Penetration Rate Optimization

Field tests in granite (UCS 220 MPa) show that a DHD340 115mm bit with parabolic buttons achieves a penetration rate of 0.8–1.2 m/min at 200 psi air pressure. This compares favorably to standard cross-type bits (0.5–0.7 m/min). The gain comes from:

• Larger gauge buttons that ream the hole cleanly

• Optimized piston energy transfer (no loss through thread slack)

• Efficient chip removal via angled flushing holes

3.2 Extended Service Life

Button wear is the #1 cause of bit replacement. The DHD340’s premium carbide retains sharpness for 600–1,200 meters of drilling in hard abrasive rock, depending on rotation speed (15–25 RPM) and thrust (4–6 tons). By comparison, economy bits may fail after 300–400 meters.

The gauge row buttons are critical: once gauge wear exceeds 2mm, the hole diameter reduces, risking stuck hammer strings. Our DHD340 bits feature extra-hardened gauge protectors and recessed button seats to delay under-gauge failure.

3.3 Reduced Fuel and Air Consumption

Because the DHD340 bit strikes directly downward with minimal lateral energy loss, less compressed air is required to lift Cuttings. This translates to lower diesel consumption for the air compressor—up to 15% savings versus older bit designs. For a typical mining operation drilling 5,000 meters per month, this equals hundreds of liters of fuel saved.

4. Applications in Mining and Blast Hole Drilling

4.1 Open-Pit Mining

In iron ore, copper, and gold mines, bench blasting requires precise 102–115 mm holes at depths of 15–30 meters. The DHD340 hammer paired with a 115mm bit offers:

• Straight holes (deviation <1% due to splined shank)

• Minimal overbreak from clean hole walls

• Compatibility with ANFO or emulsion explosives

Case example: A copper mine in Arizona replaced 10 of their older 4" button bits with DHD340 convex bits. Over six months, average bit life increased from 980 m to 1,450 m, saving $18,000 in bit costs alone.

4.2 Quarrying for Dimension Stone

For granite and marble quarries, controlling fracture propagation is key. The DHD340 flat-face bit creates a smoother hole with less micro-cracking around the perimeter, reducing waste blocks. The factory-ground concentric button pattern ensures even wear, meaning less dressing of the bit between sharpenings.

4.3 Civil Engineering and Foundation Drilling

Large infrastructure projects—such as bridge piers, dam anchors, and wind turbine foundations—often drill through limestone, dolomite, or basalt. A DTH rig with a DHD340 bit delivers the required hole straightness and diameter consistency for micro-piles (150–200 kN capacity).

4.4 Water Well and Geothermal Drilling

Although not the primary application, many water well drillers use 115mm DTH bits to penetrate hard layers below overburden. The DHD340’s efficient flushing design removes sand and clay without clogging, a common problem with roller cone bits.