| Ceramit from Ceramic Substrates is a commercial grade of the mineral pyrophyllite. Pyrophyllite is an aluminosilicate material from the montmorillonite family that has remarkable similarities to talc. Ceramit 10/14 is a machinable mineral which, after heat treatment, assumes many of the properties of fired Ceramics. It is ideal for prototypes, experimental and pilot scale productions where high accuracy is required on small parts. While it sis suited to small runs and prototypes, it can also be used for manufacture of commercial quantities. | _files/image006.jpg)
| _files/image008.jpg)
| | Figure 1. Ceramit ceramics being machined (images courtesy of Ceramic Substrates and Components Ltd). | Chemical Composition of Ceramit Ceramit has the following chemical composition. | | | Silica | SiO2 | 56.8% | | Alumina | Al2O3 | 33.7% | | Ferric Oxide | Fe2O3 | 0.79% | | Titania | TiO2 | 2.42% | | Calcia | CaO | 0.29% | | Magnesia | MgO | 0.24% | Machinability In the natural state, Ceramit can be turned, milled, drilled, tapped, filed and sawn. Heat Treatment Ceramit 10/14 can be heat treated in two ways, each yielding totally different characteristics. Thus heat treatment can be used to produce materials suited to different applications. The properties of these materials are outlined below. During heat treatment (firing) of Ceramit up to 2.0% volume expansion may occur. Due to this fact the heating rate should not be greater than 250°C/hr. A typical heating cycle would involve heating at 50°C/hr to 400°C then 100°C/hr (maximum) to 1300°C. Final temperatures are normally held for one hour. Pottery-type furnaces are suitable for this operation. Ceramit 10 – Heat Treated to 800-1000°C Typical properties of Ceramit 10 after heat treating between 800-1000°C are: • Poor heat conductivity (Thermal insulator) • Good resistance to thermal shock • Low coefficientof thermal expansion • Good mechanical stability • Can still be machined for final sizes with Tungsten carbide tools When fired to 800°C -1000°C Ceramit 10 expands around 1.75 - 2.0 % which must be allowed for when machining. However when fired to these temperatures, sizes can be adjusted with carbide tools. Components fired to 1000°C can be operated continuously at that temperature. Ceramit 14 – Heat Treated to 1250-1300°C Typical properties of Ceramit 14 after heat treating between 1250-1300°C are: • Good electrical properties in humid Conditions • High abrasion resistance • Will give <3µm surface finish • High dielectric strength • Fair dieletric constant • High Mechanical stability • Only diamond grinding can be used to adjust sizes Over 1000°C Ceramit 14 experiences a gradual shrinkage takes place and the machined component loses some of the volume expansion that has occurred. As the material densifies the sizes will return to within ± 1% of the machined sizes. Any size alteration will have to be carried out by wet grinding. Diamond tools with coolant is best suited to the job, although green grit wheels suffice on prototypes. Furnace cooling to 200°C is highly recommended before removing parts. Never wet the unfired material for machining purposes. Safe maximum operating temperature for Ceramit 14 parts is 1100°C. |