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Most consumers have probably never considered the relationship between carbon graphite and the glass industry. Actually graphite is the ideal material for glass manufacturing due to its physical and chemical composition properties.
Home Products Glass Industry / Graphite Mold for Manufacturing Quartz Glass
In the production of technical glass, laboratory glass, pharmaceutical glass, tube glass, container glass or hollow glass, the materials have to comply with many parameters such as purity, precision, physiological safety, dimensional accuracy, energy and cost efficiency. In order to ensure a constant quality of the glass product, all materials that come into contact with hot glass must withstand high challenges and work reliably.
High Temperature Resistance: Quartz glass production often involves temperatures exceeding 1600°C. Graphite can withstand these temperatures without melting or significantly deforming.
Chemical Inertness: Graphite is chemically inert to molten quartz, meaning it won't react with or contaminate the glass. This is crucial for maintaining the purity of the final product.
Thermal Shock Resistance: Graphite has good thermal shock resistance, meaning it can handle rapid heating and cooling cycles without cracking. This is important in many quartz glass manufacturing processes.
Machinability: Graphite is relatively easy to machine into complex shapes and intricate designs, allowing for the creation of custom molds for specific quartz glass products.
Low Thermal Expansion: Graphite has a relatively low coefficient of thermal expansion compared to many metals. This minimizes the risk of cracking or distortion of the quartz glass as it cools.
Self-Lubricating: Graphite's self-lubricating properties can aid in the release of the solidified quartz glass from the mold, preventing damage.
Crucibles and Liners: Graphite is used to make crucibles and liners for furnaces used to melt and process quartz sand into molten glass.
Mold Cavities: Graphite molds are used to directly shape molten quartz glass into various forms, such as tubes, rods, plates, and custom shapes.
Drawing Dies: Graphite dies are used in the drawing process of quartz glass tubes and rods.
Sintering Molds: Graphite molds are used to sinter quartz powder into solid forms.
Purity of Graphite: The purity of the graphite is critical. Impurities in the graphite can contaminate the quartz glass, affecting its optical and mechanical properties. High-purity graphite grades are required.
Density and Porosity: The density and porosity of the graphite can affect the mold's thermal conductivity and its ability to prevent gas permeation. Lower porosity is generally preferred to minimize gas absorption which could affect the quartz glass.
Oxidation: Graphite oxidizes in air at high temperatures. To mitigate oxidation, processes are often carried out in an inert atmosphere (e.g., argon or vacuum). Coatings can be used to reduce or prevent oxidation.
Mold Design: The design of the graphite mold is crucial for achieving the desired shape, dimensions, and surface finish of the quartz glass product. Factors to consider include shrinkage, cooling rates, and ease of removal.
Release Agents: Sometimes, release agents (e.g., boron nitride coatings) are applied to the graphite mold to prevent sticking and facilitate the removal of the solidified quartz glass.
Tube Drawing: Molten quartz is drawn through a graphite die to create tubes of specific diameters and wall thicknesses.
Rod Drawing: Similar to tube drawing, rods are formed by pulling molten quartz through a graphite die.
Mold Casting: Molten quartz is poured into a graphite mold to create a specific shape.
Sintering: Quartz powder is placed in a graphite mold and heated to a high temperature, causing the powder to fuse together.
Coatings are often applied to graphite molds to improve their performance and longevity. Common coatings include:
Boron Nitride (BN): Provides excellent release properties and helps prevent the quartz glass from sticking to the mold.
Silicon Carbide (SiC): Improves oxidation resistance and hardness.
Aluminum Oxide (Al2O3): Provides a hard, wear-resistant surface.
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