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Diamond Bearing Tribology Fundamentals
Tribology comes from the Greek word ‘tribos’ which means ‘rubbing’. It is a relatively new science that considers the friction, wear and lubrication at moving contacts. Diamond bearing tribology looks at the physics between two diamond surfaces moving relative to one another, most of the time in the presence of a lubricant.Diamond Bearing Tribology Fundamentals
What is PCD?
Polycrystalline Diamond (PCD) is diamond grit that has been fused together under high-pressure, high-temperature conditions in the presence of a catalytic metal.
The extreme hardness, wear resistance, and thermal conductivity of diamond make it an ideal material for bearings. Individual diamond crystals cleave quite easily when struck parallel to certain planes (the process used to facet diamond gemstones takes advantage of these relatively weak planes). Diamond sintering overcomes the problem of weak planes in diamond gemstones by bonding a mass of small diamond particles onto a larger, coherent structure. Sintered diamond provides greater toughness and durability than single crystals because the individual crystals in a sintered body are randomly oriented. This prevents cracks from propagating along the weak planes where traditional diamond crystals cleave most easily. Sintered diamonds also provide more uniform wear than a single crystal, while maintaining similar thermal conductivity and hardness properties. All of these factors combine to make sintered diamond the ideal material for many bearing applications.
High Pressure High Temperature Cubic Press (0:22)
At US Synthetic, the sintering process begins with premium saw-grade diamond crystals. These crystals are sintered together at temperatures of approximately 1400°C and pressures around 60 kbar in the presence of a liquid metal catalyst (see video below). Typically, the polycrystalline diamond (PCD) is bonded to a tungsten carbide substrate during the same high-temperature, high-pressure process. This sintered diamond and tungsten carbide composite is known in the oil and gas drilling industry as a Polycrystalline Diamond Compact (PDC) cutter.
PCD is currently used in many applications both in and outside of the oil and gas industry. Some of these applications are:
- PCD compact cutters for oil and gas drill bits (US Synthetic)
- Cutting tools for machining metals
- PCD bearings for downhole drilling tools and other bearing applications
- Wire drawing dies (US Synthetic Wire Die)
- Roof bits for mining applications (Brady Mining)