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Bullet Teeth VS Roller Bit

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When it comes to hard rock piling, bullet teeth and roller bites are the most common tools used. What is the fundamental difference between these tools? Are they only differed by the hardness of the rock and formation. Let’s find out today.

The operational principle

1. Bullet Teeth

Bullet teeth working principle is relatively simple. It is basically a fixing part cutting tool with a hard insert tip to offer a single point load. The insert is made of tungsten carbide, which is much harder than rock. It pierces into the rock with vertical load pressure. Then shear the rock with the strong rotary rig torque.
bullet teeth cutting indication

2. Roller Bit

The roller bit is commonly used when drilling granite and other extreme hard rock. It can do this job because the working principle is totally different compared to bullet teeth, round shank chisel. It has a cone covered with lots of small inserts. The cone turns as the core barrel turns inside the hole. The inserts on the cone will alternant touch the ground and break the rock surfaces by chipping and crushing them high frequently.
roller bit rock cutting indication

When to use bullet teeth, and should you try out a roller bit?

When the hardness of rock is above 60 Mpa, you can consider using the roller bit. It can penetrate the rock from 0.2 meters to 1.2 meters each hour depending on the rock hardness, UCS( uniaxial compressive strength). It would be much faster in extreme hard rock, more than 100 Mpa, and much more durable.

1. Fast and cheap.

When the hardness of rock is above 60 Mpa, you can consider using the roller bit. It can penetrate the rock from 0.2 meters to 1.2 meters each hour depending on the rock hardness, UCS( uniaxial compressive strength). It would be much faster in extreme hard rock, more than 100 Mpa, and much more durable.

2. Smooth, nearly no vibration.

The bullet has strong vibrations in the hard rock. When using roller bit, the vibration is little. It barely has any damage to the rigs. You can save lots of money on maintenance and repairs.

3. No need to change very frequently.

Sometimes the bullet teeth can penetrate the extreme hard rock, its penetration speed is even faster than roller bits in the first few minutes. But the wearout is so quick. After this few minutes, the bullet teeth have to be replaced. The frequent replacement makes the whole project slow down again and it is also a hard thing for the workers.

But there is also a challenge to use the rollers bit. That is, roller bits require more skills both in welding and rig operation. Working life, penetration speed etc, is affected a lot by this. Many bore pile teams without any experience will find frequent problems like slow penetration, premature roller bits failure. So finding a reliable roller bit supplier who can offer professional advice and services is important.