Silicon Nitride Protect Tube

Silicon nitride ceramics possess extremely high flexural strength (typically above 800-1000 MPa at room temperature, and high-performance ceramics can reach over 1000 MPa) and compressive strength.
It has extremely high hardness (with a Mohs hardness of approximately 9 and a Vickers hardness of HV10 of about 1600-1800), second only to a few materials such as diamond and cubic boron nitride, and excellent wear resistance.

Silicon nitride materials have relatively high fracture toughness among ceramic materials, which makes them more resistant to crack propagation and impact damage than many other ceramics, enhancing the reliability of their use.

Silicon nitride ceramics have a very low coefficient of thermal expansion (about 2.5-3.2 × 10⁻⁶ /K, from room temperature to 1000°C). They have good dimensional stability when the temperature changes and are not prone to excessive stress or deformation due to thermal expansion and contraction.

It also has excellent thermal conductivity, which is better than that of most oxide ceramics (about 15-30 W/(m·K)), which is conducive to heat transfer and dissipation. Silicon nitride has excellent thermal shock resistance and can withstand drastic temperature changes without cracking. This is one of its most crucial advantages.

Silicon nitride ceramics have good electrical insulation properties.

1: Preheat strictly (to avoid thermal shock cracking).
New silicon nitride protect tube or cold-state protective tubes must be strictly preheated before being inserted into high-temperature aluminum liquid! This is the correct way to take advantage of the excellent thermal shock resistance of silicon nitride.
Inserting the cold tube directly into the molten aluminum without preheating is the main cause of the thermal shock rupture of the protective tube!

2: Standardized installation and operation (smooth insertion/removal to ensure immersion depth).

3: Proper maintenance (natural cooling and slag removal, gentle and non-contact cleaning, avoid HF).
The correct way to clean the aluminum shell: Let the protective tube with the aluminum shell cool naturally in the air to room temperature. Due to the difference in shrinkage between aluminium (with a large expansion coefficient) and silicon nitride (with a small expansion coefficient), aluminium shells usually loosen and fall off by themselves.
Auxiliary cleaning: If the aluminum shell has not completely fallen off, you can gently remove the remaining aluminum slag with a wooden mallet, plastic mallet or copper brush. It is strictly prohibited to use steel brushes or hard objects to scrape
Avoid contact with hydrofluoric acid (HF) and fluorine-containing compounds, as they can severely corrode silicon nitride.

By following these norms, silicon nitride protect tube can provide long-term, stable and precise temperature monitoring for the aluminum smelting and casting processes, becoming an important guarantee for improving the level of process control and product quality.