American Beryllia Inc. offers a wide range of manufacturing capabilities and services designed to meet virtually any application need. These capabilities encompass a variety of BeO Ceramic material preparation (forming), firing and finishing methods to suit exact customer requirements.
Material Preparation (Forming) Methods
Dry pressing involves compacting of ceramic powder to a particular shape or form in a tungsten-lined steel die. Pressure is applied by a simple, shaped punch or a compound, multi-stage die.
Dry processing allows high production rates with routine tolerances within +1% after firing. It is generally suitable for volume production of small parts and simple shapes such as bushings, spacers, washers and other substrates where the ratio of the part’s dimension in the processing direction (length) to its dimension normal to the pressing direction (width) is less than 3 to 1. Proper design and tight process control routinely produce parts that are free of distortions, cracks and other imperfections.
Isostatic pressing involves placing ceramic powder in a liquid-tight rubber mold which is subsequently immersed in a non-compressible fluid such as oil or water contained in a pressure vessel. When the fluid is pressurized, all surfaces of the mold receive equal pressure resulting in a uniform density. It is ideal for larger parts and shapes with a high ratio of length to cross section
While use of an internal mandrel facilitates formation of cylindrical or other simple internal shapes or cavities, external dimensions cannot be accurately controlled during isopressing and must be machined before or after firing. Tooling cost is usually lower but the process itself is slower and more expensive than dry pressing.
Extrusion involves continuously forcing a plasticized ceramic material through a shaped die. Typical products produced using this method include thermocouple tubes, rods and other parts with small cross-sections.
Tooling is relatively inexpensive and tubes can be produced with outside diameters as large as 0.250 inches (6.35 mm) to diameters as small as 0.030 inches (0.76 mm) with one or more holes as small as 0.005 mm for thermocouple wires running the length of the tubing.
After forming, the ceramic is fired to high temperature (about 1600ºC for beryllia) to achieve its final density. During firing, pores are virtually eliminated and crystalline grains are bound together with virtually no glassy phase.
Grain size composition is controlled through a combination of special additives and careful attention to time and temperature variables. Each dimension of a ceramic part typically shrinks 17% as a result of sintering with a total volume reduction of 43%. Despite this reduction, the "as-fired" dimensions conform to all other physical specifications. Most production firing at American Beryllia Corporation is performed in periodic kilns with programmable instrumentation for precise time and temperature control.
Occasionally, it is more practical to machine a formed part before firing when the ceramic is soft and easier to machine. This "green machining" process entails a variety of conventional machining operations to meet dimensional specifications, provide particular features, or preparation for subsequent assembly.
Equipment required for finishing includes complex, highly accurate lapping machines; cylindrical, centerless and surface grinders; dicers and drills. Most of this equipment is automatically controlled to provide consistent dimensions and finishes, and reduce overall processing cost.