Structural Hardness
The extremely dense and wear-resistant composite material composed of tungsten and carbon atoms bound by a metallic matrix represents the premier choice for manufacturing precision piston-cylinder assemblies. This material, tungsten carbide, has a hardness that prevents scratching and wear during assembly and operation. The resistance to wear ensures that the clearance between the piston and the cylinder remains unchanged over millions of cycles.
This stability is critical for maintaining the calibrated effective area.
Thermal Stability
Dimensional changes due to temperature variations must be minimized for accurate pressure measurements. Pistons made of tungsten carbide have a very low coefficient of thermal expansion. This limits the measurement uncertainty associated with temperature fluctuations.
Pressure Resistance
Under high pressures, the piston and cylinder deform, which alters the effective area of the gauge. Tungsten carbide has a very high modulus of elasticity, meaning it resists this pressure-induced deformation far better than other metals. This high stiffness extends the operating range of the piston gauge to hundreds of megapascals.
It is essential for high-pressure primary standards.
Precision Manufacturing
The hardness of the material makes the machining of pistons and cylinders to sub-micron tolerances extremely challenging. Specialized grinding and lapping processes using diamond abrasives are required to achieve the necessary surface finish and geometry for tungsten carbide components. The roundness and straightness of the piston must be verified using high-precision roundness measuring instruments.
This manufacturing effort is justified by the extremely low rate of drift and the exceptional long-term stability of the resulting instrument.
