The failure of graphite molds at high temperatures can be attributed to various factors, including chemical reactions, thermal expansion, oxidation, structural changes, and more. Here are some common reasons for the failure of graphite molds at elevated temperatures:
1.Oxidation: Graphite is susceptible to oxidation at high temperatures, leading to the formation of carbon oxides on the mold’s surface. This oxidation process compromises the performance and durability of the graphite mold, particularly in environments with the presence of oxygen.
2.Thermal Expansion: Graphite undergoes thermal expansion at high temperatures, causing dimensional changes. If the coefficient of thermal expansion is uneven or mismatched with other materials, it can result in stress concentration within the graphite mold, leading to cracking or deformation.
3.Chemical Reactions: At elevated temperatures, graphite may undergo chemical reactions with components in the processed material. These reactions can cause corrosion, erosion, or the formation of harmful compounds, thereby reducing the performance of the graphite mold.
4.Structural Changes: The structure of graphite may undergo changes at high temperatures, affecting its mechanical properties. This includes alterations in crystal structure, the formation of lattice defects, and the instability of graphite’s layered structure at elevated temperatures.
5.Thermal Stress: Thermal stress arises due to temperature gradients, especially during rapid temperature changes. This stress can lead to the cracking or damage of graphite molds, particularly in thermal processing where rapid heating and cooling are required.
6.Material Purity: The purity of the graphite mold material is crucial for its stability at high temperatures. Impurities or less pure graphite may be more prone to failure under elevated temperature conditions.
7.Heat Cycling: Repeated exposure to high and low temperatures, known as heat cycling, can induce fatigue failure in graphite molds. This gradual degradation in performance may eventually result in cracking or fracture.
To mitigate or prevent the failure of graphite molds at high temperatures, manufacturers often employ various measures. These include using high-purity graphite, optimizing heat treatment processes, selecting appropriate coating materials to enhance oxidation resistance, and avoiding abrupt temperature changes. Regular inspection and maintenance are also essential steps to ensure the long-term stable operation of graphite molds.