1. Roller-bearing systems VS Journal-bearing systems
Roller-bearing systems
Roller bearings are widely used in bit-bearing systems. They handle heavy loads effectively and perform well in drilling conditions (Figure. 1). These bearings are commonly found in larger-diameter bits (> 14 in.), as they require more space for the rollers. To improve durability, manufacturers focus on advancing materials, sizing, and design. Their ongoing research aims to extend bearing life and enhance performance.
Attention: The IADC codes of roller-bearing bits end with the digit of “3” (roller -gauge protection), “4” (roller – sealed) or “5” (roller – gauge protection – sealed), for example, IADC 533, 534, 535… And they are typically for larger-diameter bits (> 14 in.)
Click here to know more about IADC codes.
Journal-bearing systems
Journal bearings have at least one rotating surface. A lubricant film separates this surface from the journal. The surfaces are designed to stay apart using the lubricant. If they touch, the bearing parts could gall or fuse. Journal bearings work efficiently with proper lubrication and within load limits. Figure. 2 shows a comparison between roller-bearing and journal-bearing assemblies.
Journal bearings require balanced geometry, strong journals, and a thick high-pressure lubricating film. The film thickness (Figure. 3) depends on:
- Surface areas
- Journal and cone diameters
- Clearances between journal and cone
Precise manufacturing tolerances are critical. Surfaces must run true, and roundness of journal and cone surfaces is essential. If any part is out of round, lubrication effectiveness will decrease.
Bearing metallurgy must balance heat reduction during boundary lubrication. Cone-bearing surfaces are made of steel. Journals use soft, silver-plated sleeves. Silver polishes easily, smoothing out minor machining irregularities. This creates a low-friction surface and ensures even lubricant flow across the bearing (Figure. 4).
Attention: The IADC codes of journal-bearing bits end with the digit of “6” (journal -sealed), or “7” (journal – gauge protection – sealed), for example, IADC 537, 637… And they can be smaller-diameter bits (< 14 in.)
Click here to know more about IADC codes.
2. Seal systems
In general, seal systems are classified as either static or dynamic. Roller-cone bits use both types of seals. Dynamic seals involve sealing across surfaces that are moving in relationship to one another, as would be the case for a bearing seal. Seal parts or surfaces that do not move in relationship to one another during bit operation, such as the seal between a hydraulic nozzle and a bit to prevent leakage around the joint, are static seals.
Bearing seals
Roller-cone bearing seals operate in an exceptionally harsh environment. Drilling mud and most cuttings are extremely abrasive. Drilling fluids often contain chemicals, and operating temperatures can be sufficiently high to break down the elastomers from which seals are made. Pressure pulses often occur in downhole drilling fluids that apply lateral loading on seals that must be resisted.Visualize the difference in the nature of these two duties. On the interior side, the seal is excluding clean, functional lubricant from escaping the bit, while on the exterior side, the seal is excluding dirt and chemicals from penetrating the bit. The separation of these two extremely different functions takes place at a small point between the two sides of a seal. If either of these functions breaks down, the bearings and the bit could be destined for failure.
Seal definitions
In a rotating bearing, the two working sides of a seal are called the static energizer and the dynamic wear face. These two parts are directly opposite each other, with the energizing portion bearing on the gland and the dynamic wear face bearing against the rotating unit. For the energizing portion of the seal to function properly, it must have a surface against which to react. This is provided by a channel-shaped groove called a seal gland.
The wearing portion of the seal must have the capability to withstand the heat and abrasion generated as the rotating surface passes over it. The energizer, when functioning correctly, is not a high-wear area. Ideally, it simply bears against the gland and provides the pushing energy that maintains firm contact between the wear surface and rotating cone.
O-rings
Donut-shaped O-rings are used in many roller-cone bit applications. O-rings are manufactured from elastomers (synthetic rubbers) that withstand the temperatures, pressures, and chemicals encountered in drilling environments. They are a traditional, but still consistently reliable, seal system.
An O-ring is installed in a seal gland to form a seal system. The gland holds the O-ring in place and is sized so that the O-ring is compressed between the gland and the bearing hub at which sealing is required. It presses the interior wall of the O-ring against the hub and the exterior diameter of the O-ring against the gland. These latter forces prevent the seal from turning in the gland and experiencing wear on the outer surfaces by rotational contact with the gland (Figure. 5).
3. Identification of several nomenclatures and Kingdream’s patent
Rubber Seal
Mostly adopted seal type in early roller cone bits. Still the most popular and reliable type in this industry.
Composite Seal
It is actually an improved type of rubber seal, as the radical and key functions of sealing is still implemented by rubber part.
Most of the world-class players in this industry like SMITHS and KINGDREAM have been developing composite seal products.
Although in some regions out of China, COMPOSITE SEAL is not a fromal nomenclature. People still recognize it as a RUBBER SEAL product.
Metal Seal
A real product in another level, design for the harshest drilling conditions. Has longer service life in hardest rock or formations with extreme pressure.
But such products are usually EXPENSIVE.
Kingdream holds an exclusive patent in metal seal bearing in tricone bits.
