Keyed Mandrel

I. The Functions and Importance of Keyed Mandrel

1. Torque and rotational speed transmission: Transmitting the torque and rotational speed generated by the motor to the drill bit without reservation is the "final link" of power transmission.

2. Bearing huge axial loads: During the drilling process, the weight of the entire drill string (drilling pressure) is applied to the drill bit through the mandrel. Therefore, the mandrel must have extremely high compressive strength and fatigue strength.

3. Bearing radial loads and bending moments: In directional drilling, the wellbore is not vertical, and the keyed mandrel operates in the curved well section, bearing additional radial forces and bending stresses.

4. Guiding drilling fluid: The keyed mandrel is usually hollow and serves as a channel for the drilling fluid to flow towards the drill bit, ensuring smooth passage of the drilling fluid to cool the drill bit and carry cuttings.

II. Structural Composition of the Core Shaft Assembly of Keyed Mandrel

The keyed mandrel rarely works alone. It usually serves as a core component and, together with other parts, forms the "drive shaft assembly". This assembly mainly includes:

1. Mandrel body: The main structure, usually with external splines or threads.

2. Bearing system: This is the key of keys, used to withstand axial and radial loads.

3. Thrust bearings: A set of angular contact ball bearings or tapered roller bearings connected in series, specifically designed to withstand extremely high drilling pressure.

4. Radial bearings: Usually sliding bearings (such as wear-resistant bushings), they are used to keep the mandrels centered and withstand radial forces.

5. Sealing system: It is usually a high-grade TC (mechanical seal) or similar structure, used to isolate the drilling fluid from the lubricating oil in the gearbox and prevent sand and mud from entering the precision bearings.

6. Connection thread: The upper end is connected to the universal joint housing, and the lower end is connected to the drill bit.

The keyed mandrel plays a pivotal role of "connecting the upper and lower parts" in the downhole motor. It not only has to transmit powerful force, but also withstand harsh underground working conditions (high pressure, high temperature, vibration, and abrasive media). The design, materials and manufacturing quality of the downhole motor directly determine its working life and reliability. Therefore, when choosing or replacing mandrel accessories, it is essential to strictly pay attention to their material certificates, heat treatment processes and non-destructive testing reports.