Through “What is a roller cone bit? “, we learned that there are many classifications of roller cone bits, among which, tri-cone bits are the most widely used and most common roller cone bits at home and abroad. So what are its specific structures?

Tri-cone bit consists of more than 20 parts such as cutting structure, bearing structure, locking element, oil storage sealing device, and nozzle device.

1. Shirttail

Shirttail is the main part of roller cone bit. A drill bit consists of three pieces of shirttails assembled and welded together. It has a connecting thread on the upper part, which is connected with rock drilling tools, and the lower part has a certain inclination journal, which forms a bearing pair with the inner hole of shirttail. Shirttail has a water hole runner and is also fitted with an oil storage pressure compensation device. Journal bears the load and needs high wear resistance and hardness, while the inner part of the matrix needs to have sufficient strength and impact resistance toughness.

2. Cutting structure: cone and carbide

The cone is a cone equipped with carbide, there are two types single cone and compound cone. The single cone is composed of main cone and back cone. The movement of single cone is pure rolling at the bottom of the well, which is suitable for drilling in hard strata. The compound cone consists of the main cone, the second cone, and the back cone. This kind of cone works in the bottom of the well not only by rolling but also by sliding and is used for drilling in softer formations.

There are two types of carbide on the cone: insert bit and steel tooth bit. The rows of teeth on the tri-cone bit mesh with each other, which can effectively and completely break the bottom rock without repetition and prevent alveolar mud bagging. The shape, size, quantity, and length of the carbide of drill bit depending on the hardness of the formation being drilled. The softer the formation, the larger, sharper, and the smaller the number of carbide. Conversely, the harder the formation, the smaller, shorter, and the greater the number of carbide.

3. Bearing structure

Roller cone bit bearing consists of the inner hole of cone, the journal of shirttail, the locking element, and so on.

① Bearing pair has large, medium, and small shafts and thrust surfaces, etc. The large and small bearings are subjected to radial loads, the middle shaft is mainly used for locking and positioning, and the thrust surface bears axial loads.

② According to the structure of bearing pair, the drill bit bearings are generally divided into two categories of rolling bearings and sliding bearings. According to the sealing of bearings, it can be divided into sealed and non-sealed.

③ To ensure that cone and shirttail are assembled securely, the cone must be locked. The locking methods mainly include steel ball locking and circlip locking.

④ The sealing methods of bearings are divided into metal seals, O ring seals, floating seals, etc.

4. Oil storage pressure compensation system

This device is composed of a bearing sealing ring, oil storage capsule, protection cup, gland, plug, retaining ring, and other parts. Its function is to balance the pressure difference inside and outside the bearing cavity when the cone is working so that the bearing sealing ring can work normally for a long time under the small difference between inside and outside, preventing drilling fluid from entering the bearing cavity and avoid the loss of lubricating grease, and can store enough grease to continuously replenish the bearing cavity so that the drill bit bearing is in a sealed state and works under good lubrication conditions.

5. Nozzle

Nozzle shape structure is divided into standard type and protective cover type. The standard type has a simple structure, low manufacturing cost, no tab protection, is easy to load and unload, and is often used for low abrasive soft ground steel tooth drill bits. It is often used for steel tooth drill bits in low abrasive soft formations. The protective cap type is protected by a tab on the top, which can reduce the erosion effect of abrasive materials on the locking retaining ring. All sliding bearing drill bits adopt the protective cover type, which can work for a long time under the condition of high-pressure injection in the well and is safe and reliable.