Components for Molten Metal Contact

Non-ferrous alloys such as aluminum, copper, or magnesium, as well as super alloys of nickel, cobalt, precious metals or magnetic materials, all require variety of refractory components during melting, processing, and forming. In many of these applications, inert nature of BN and high oxidation resistance offers desired solutions at melt temperatures. As consumables, parts made with BN and composite materials offer precise production and long part life leading to reduced replacement frequency.

Saint-Gobain’s Combat® grade ZSBN is the leading boron nitride grade in molten metal contact applications. Addition of zirconia to boron nitride enhances the wear resistance and non-wetting of molten metal, even at elevated temperatures – an important feature for components coming in direct contact with metal melt at high temperatures. 

Break Rings for Horizontal Continuous Casting

Boron nitride’s high chemical resistance against a vast majority of molten metals, combined with excellent thermal shock resistance makes it ideal for a variety of molten metal contact applications. In addition, boron nitride is easily machinable into complex shapes for quick prototyping, offering advantage over traditional ceramics.

Over the past 15 years, horizontal continuous casting of steel and specialty alloys has gained widespread acceptance compared to traditional vertical continuous casting, due to favorable investment cost, small plant footprint, possible high level of automation, and low manpower requirements. Furthermore, possibility of smaller batch sizes offers manufacturers flexibility in offering a wider product range.

One key aspect of horizontal continuous casting is movement of melt without help from gravity from the holding crucible to graphite die and cooler assembly. The melt passes through a graphite die, series of holding components, and finally through a refractory ring (break ring) into the solidification zone. As the melt moves from hot zone to cool zone (solidification zone) and undergoes a sudden change in temperature, it is important that the break ring maintains integrity (low coefficient of thermal expansion) and allows the melt to continue to move without sticking or building-up at the intersection, until desirable to solidify. Though very simple part of the total assembly, breakrings are critical components of a horizontal continuous casting assembly. Any failure / breakage will result into the loss of entire heat, causing safety hazard and significant downtime from part replacement and clean-up.

Saint-Gobain's Combat® grade ZSBN offers the properties critical to this application - high thermal shock resistance for uninterrupted flow of melt, low coefficient of friction even at high temperatures for build-up free movement, and corrosion and slag resistance for a variety of metals, alloys and super alloys.

Nozzles for Powder Metal Atomization

Specialty powder metals are made to controlled particle size distribution, such as common alloys and super alloys of nickel, copper and aluminum. Key quality parameters in the manufacturing of sophisticated powder metals are high atomization yield and tight particle size distribution.

Traditional nozzles made by pressing and sintering large or coarse zirconia particles lack both tight tolerances and clean edges. Because of this, the process yields very uneven and erratic atomization, particularly at startup, causing wide particle size distribution. Additionally, since zirconia shows high friction with metals, nozzles frequently clog, further adding to unpredictable particle sizes. These limitations result in a low yield, high scrap rate, undesirable clean up and maintenance, and additional runs.

Nozzles made by Saint-Gobain Boron Nitride minimize clogging and metal-creep, reducing the frequency of nozzle replacement. Smooth surface finish and tighter tolerances thanks to low coefficient of friction of boron nitride provides predictable particle size distribution from batch to batch. Additionally, extreme thermal shock resistance allows boron nitride nozzles to be used without extensive pre-heating.

Side Dams for Thin Strip Casting

Thin strip casting of steel and its alloys at or near its final dimensions has gained popularity due to energy savings offered by reduced number of manufacturing steps, as well as reduced carbon footprint compared to traditional slab-casting.

Success of a thin-strip casting run depends on successful containment of steel melt between rotating twin-rolls, using refractory parts called side dams. Uniform thickness of steel strip, and therefore high process yields depend on a fine balance between erosion of refractory against moving rolls, corrosion of refractory against molten steel. 

Saint-Gobain's Combat® grade ZSBN offers the right balance in this application. Addition of zirconia to boron nitride adds the desired wear resistance and high corrosion resistance at operating temperatures upwards of 1400°C.