About the riser | Vhandy Ceramics

Aluminum titanate ceramics not only have a high melting point (1860°C) and a low thermal expansion coefficient (α≤2.0×10-6/K), but also have the property of not being wetted by many non-ferrous metal melts such as aluminum. Therefore, they are an excellent material for manufacturing riser tubes for aluminum casting.

1. Metal riser

Metal riser is mainly made of seamless steel pipe welding or gray cast iron casting, and the inner and outer layers are brushed with refractory coating.
The advantages of metal riser are good mechanical properties, good air tightness, easy processing and low price.
The disadvantages of metal riser are that the thermal expansion coefficient of metal and coating is very different, the coating is easy to peel off, the metal riser is very easy to corrode, pollute the alloy liquid, and the metal riser is seriously deformed during use, which will affect the flow rate and direction of the alloy liquid.
In addition, the service life of cast iron riser is short, and the replacement of accessories is time-consuming and affects production efficiency.

2. Aluminum titanate ceramic riser

Aluminum titanate ceramic not only has a high melting point (1860℃) and a low thermal expansion coefficient (α≤2.0×10-6/K), but also has the characteristics of non-wetting with many non-ferrous metal melts such as aluminum. Therefore, it is an excellent material for manufacturing riser for cast aluminum. However, aluminum titanate is easily decomposed into α-Al2O3 and rutile TiO2 at 750-1300℃, resulting in reduced mechanical properties and thermal shock resistance of the material. Domestic research on aluminum titanate riser tubes mainly focuses on improving their thermal shock resistance. Compared with traditional cast iron risers, ceramic riser tubes have much lower thermal conductivity, so they can maintain heat during low-pressure die-casting.

3. Silicon nitride ceramic riser tube

As an advanced refractory material, silicon nitride has the advantages of low thermal expansion coefficient, good thermal shock resistance, high high-temperature mechanical properties and strong resistance to metal corrosion. Silicon nitride has a melting point of 1900℃ and a thermal expansion coefficient of 2.5×10-6/K, and is non-wetting to many metals. Pure silicon nitride riser tubes have better thermal shock resistance and temperature resistance than aluminum titanate riser tubes, and have a long service life but are expensive. The riser tube using silicon nitride combined with silicon carbide has a service life of more than 30 days under normal continuous operation, and the cost-effectiveness is also good.

4. Sailong ceramic riser tube

Sailong ceramic is a high-temperature sintered material of Si3N4-Al2O3 system. It is composed of Al and O atoms of Al2O3 partially converted into Si and N atoms in Si3N4 to form Si-Al-O-N system. Sailong ceramic has the advantages of good high-temperature strength, stable and excellent chemical properties at room temperature and high temperature, good wear resistance, very low thermal expansion coefficient (2.4~3.2×10-6/K) and good thermal shock resistance.
Sailong ceramic combines the comprehensive properties of silicon nitride (high strength, hardness, fracture toughness and low thermal expansion) and alumina (corrosion resistance, chemical inertness, high temperature capability and oxidation resistance), and has very excellent thermal and mechanical properties. According to data, the Sailong ceramic riser tube produced by a British company has excellent thermal shock resistance and a service life of up to 12 months.

5. Composite material riser pipe

Composite material riser pipes are mostly made of metal pipes such as cast steel and heat-resistant steel as the skeleton, and the inner and outer surfaces are coated or embedded with a certain thickness of non-metallic materials such as high-temperature resistant ceramics. They have the advantages of good air tightness and high mechanical properties of metal riser pipes and good high temperature resistance and high-temperature chemical stability of non-metallic materials. The manufacturing process of this type of riser pipe is complex and the cost is high.

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