The document introduces roller cone bits, covering their design elements, including cone geometry, tooth and insert structures, and materials used in manufacturing. It discusses critical aspects like heat treatment, hardfacing, and the importance of bearings and seals in terms of performance and durability. Additionally, it emphasizes the need for quality engineering to ensure the effective operation of seals and bearings under harsh conditions.

1. Cone bit Course

2. Introduction to Roller Cone Bits
• First Roller Cone bits:

3. ROLLER CONE BIT TERMINOLOGY

4. ROLLER CONE BIT TERMINOLOGY

5. ROLLER CONE BIT TERMINOLOGY

6. FUNDAMENTALS OF BIT DESIGN
• Available Space
• Basics of Cone Geometry Design
Journal Angle:
It influences the design of many key bit features,
including:
• Depth of intermesh,
• Insert extension and milled tooth depth,
• Heel surface length and angle,
• Gage contact and length,
• Cone diameter, (oversize angle),
• Cone shell thickness,
• Space available for bearings,
• Leg strength and,

7. Basics of Cone Geometry Design
• Oversize Angle:
• Oversize angle, is provided when it is desired to increase the diameter of a cone.
• Increasing oversize angle enlarges a cone and increases scraping action on the borehole wall.
• This, in turn, requires that the gage tip be moved toward the center of the bit to prevent over-
gage geometry.
• This results in a degree of scraping by the gage inserts on a cone having an oversize angle; if the
amount of oversize is reduced, scraping will be decreased.

8. Basics of Cone Geometry Design
• Offset:
• "Offset" is the horizontal distance between the axis of the bit and a vertical plane through
the axis of the journal.
• To increase scraping, bit designers generate additional working force by offsetting the
centerlines of the cones so that they do not intersect at a common point on the bit.
• In abrasive formations, offset can reduce cutting structure service life to an impractical
level. As a result, bits designed for these applications typically utilize a relatively small
offset in order to minimize scraping.

9. Basics of Cone Geometry Design
• Teeth and Inserts:
• Structural requirements for the tooth or insert, and,
• Formation requirements

10. Basics of Cone Geometry Design
• Teeth and Inserts:
• Structural requirements for the tooth or insert, and,
• Formation requirements

11. Basics of Cone Geometry Design
• Teeth and Inserts:
• Structural requirements for the tooth or insert, and,
• Formation requirements

12. Additional Design Criteria
• Tooth-to-tooth and tooth-to-groove clearances,
• Bottom-hole coverage,
• Cone-shell thickness, and,
• Bearing configuration.

13. Additional Design Criteria
• Cone-Shell Thickness
• Cone-shell thickness is of crucial importance from a strength
standpoint.
• Insufficient cone-shell area can result in cone failure and down-hole
loss of components.
• Varying shell thicknesses are used for different bit types.
• The design engineer must adhere to established, minimum values,
however.

14. Additional Design Criteria
• Bearings Factors
• The primary function of the balls is to secure cones to leg journals; under
certain loading, balls can resist thrust loading, however.
• Roller cone bit bearings must normally withstand extremely high values of
unit and impact loading.
• Within the limited space available, overly large roller and ball bearings
necessitate reduced journal diameters. This condition decreases the
wear life of the journal and increases its potential for fatigue failure.

15. Materials
• Important physical property requirements for legs and cones include:
• Legs are forged from aircraft grades of wrought material
• Nickel-chrome or nickel-chrome-molybdenum steel is used to produce case-harden able journals
that provide both optimum resistance to wear and to structural failures in bearing races caused by
spalling.
• Hardenability
• Forge ability
• Chemical and grain structure uniformity and cleanliness
• Machinability and weld ability
• Impact resistance
• Especially tough steels, characterized by high resistance to chipping
• or breaking at high hardnesses, are used for ball and roller bearings.

16. ROCK BIT METALLURGY
• Physical properties of a bit component:
• Type of heat treatment
• Material from which the component is made
• structural requirements need for abrasion / erosion resistance.
• WHY FORGED COMPONENTS?
• When forgings (both legs and cones) are purchased, it is specified that
they be made from wrought material. This means that cast ingots from
• the steel mill have been rolled. Rolling results in grain refinement that,
when correctly oriented, improves forging and end product structural
strengths.

17. HEAT TREATMENT
• Carburizing,
• Heating and Quenching
• Tempering
• Cones and legs are subjected to all three processes. Ball and roller
bearings and thrust buttons are not carburized, but do undergo heating,
quenching, and tempering treatments.

18. Carburizing
• the carbon content of the surfaces of the steel is increased by heating the
material in an atmosphere made up of gases having high carbon content.
The purpose of developing such a carbon layer is to provide a tough, wear-
resistant "skin" or case.

19. Heat Treatment
• Heat treatment increases material hardness to a maximum. All roller cone
bit components are heat treated. In heat treatment, the properties of a
material (steel in the case of roller cone bits) are altered to meet
functional requirements of the part without appreciable change in its
chemical composition.

20. Tempering
• All rock bit components are tempered.
• Tempering, (or drawing), takes place at relatively low temperatures.
• Tempering is the final operation in the overall heat-treating process; it
consists of reheating a hardened material after the heating and quenching
cycle to relieve high residual stresses formed during quenching.
• Without tempering, heat-treated parts tend to be brittle and have low
toughness or impact strength.

21. HARDFACING
• Steel is a relatively soft material that has poor resistance to abrasive and erosion
wear.
• To improve service life, some bit components that are subjected to this wear are
hard-faced with tungsten carbide particles.
• In general, hard-facing or Hard-metal is applied to the leg shirttail, and bearing
surfaces on roller cone bits.
• It is welded to the base material.

22. TUNGSTEN CARBIDE MATERIALS
• Tungsten carbide is a brittle material with very high hardness and high
compressive strengths; the compressive strength of tungsten carbide is
approximately three times its tensile strength.
• Tungsten carbide will cut most natural and man-made materials.
• It cannot, conversely be cut or abraded by most materials other than diamond
materials.
• The cobalt binding provides the strength and toughness to mask the brittleness of
pure tungsten carbide and make it useful for drilling.

23. Tungsten Carbide Grade Selection For
Inserts
• Inner insert rows commonly use softer, tougher insert grades to cut rock
formation by crushing, compressing, gouging and scraping actions.
• Gage insert rows commonly use harder, and wear resistant grades to cut rock and
maintain gage.
• Heel and TruCut gage insert rows commonly use the hardest carbide grades to
maintain gage toughness, and higher impact and tensile strengths.

24. TUNGSTEN CARBIDE HARDFACING
• The process is not complex: a hollow steel tube is filled (at manufacture) with appropriately sized grains of
tungsten carbide. The tube is then held in an oxyacetylene flame until the steel rod melts and bonds, by surface
melting, with the bit feature to be hard faced. In the process, the contained tungsten carbide grains flow onto the
bit as a solid and do not melt.
• This process is highly temperature critical. Excessive temperature will cause degradation of tungsten carbide grain
boundaries and will result in decreased abrasion resistance and binder toughness.
• Insufficient temperature will not result in a quality bond between the steel of the bit and that of the hard-facing
rod that holds the tungsten carbide grains in place.

25. Components
• BEARINGS, SEALS AND LUBRICATION
• Ductility is an important property in a roller cone bit journal bearing
because of high loading and bit vibration characteristics.

26. Bearing Shape

27. Bearing Precisions and Geometry

28. SEAL SYSTEMS
• Seals have two functions in roller cone bits:
– To prevent foreign materials (mud, cuttings, chemicals, water, etc.) from entering the bearings.
(This function is called the “exclusionary” function.),
– To prevent bearing lubricant stocks from escaping the bit and eventually leading to operation
with un-lubricated bearings and seals.
• The separation of these two, extremely different, functions is only a plane through
the point of contact between them. Yet, if either of the functions breaks down,
the bearings are destined for failure! This is a tough order that demands quality
engineering.
• Seal Environment
– Seals must operate in an unusually harsh environment.

29. Seal Details
• The two working sides of a seal are called:
– The energizer, and,
– The dynamic wear face.

30. Seal Details

31. BEARING AND SEAL LUBRICATION

32. BEARING AND SEAL LUBRICATION