Sintering molds

Isostatic graphite is used throughout the pressure sintering industry to produce molds for diamond saw segments, diamond core drills, ceramic cutting tool inserts, and ceramic armor plates. It combines high thermal conductivity with a low coefficient of thermal expansion, which gives the dimensional stability a sintering mold requires.

How the grade is chosen

The choice depends largely on the environmental conditions and process parameters in which the graphite will be used.

• Electrical resistivity — in diamond-segment die bodies and punches, relatively high resistivity shortens the time required to reach operating temperature. It is also preferred for very large cross-section dies.
• Thermal conductivity — where similar mechanical properties are needed but the cycle calls for faster heat extraction or distribution.
• Strength and density — where the mechanical requirements of the application are at their highest.
• Spark plasma sintering (SPS) — the die is part of the electrical circuit; grade resistivity and high-temperature strength become selection criteria.
• Resistance heating — mold components that carry the current are chosen for high electrical resistivity, so high operating temperatures can be reached in shorter times.

Ceramic dressing rolls need a contour machined on the inner diameter of a cylinder, with diamonds hand set on that diameter and the inside filled with a metal matrix. A grade that machines to tight tolerances with a good surface finish is required.

In many cases the best way to select an optimal grade is through actual trials. Share the drawing, temperature, pressure, and atmosphere to validate the grade.