Most consumers have probably never considered the relationship between carbon graphite and the glass industry. If people associate any other material with glass, it may be lead (which glass was once impregnated with to increase glass’s aesthetic properties). That being said, there is a heavy reliance on carbon graphite in the glass industry. Graphite is the ideal material for glass manufacturing due to its physical and chemical composition properties. If you’ve ever witnessed glass blowing, you may have an idea why graphite material is so useful in this industry. Hint: it has to do with a property of graphite material that we often discuss in this blog — it’s amazing lubricating capabilities.
Molten Glass is Hot and Sticky--but Not to Carbon Graphite
Molten glass will stick to almost anything, but it will not stick to carbon graphite. Graphite material’s non-wetting properties mean that it is ideal for coming into contact with molten glass without any adherence. Additionally, carbon graphite is a lubricating material often used as a deliberately wearing part in machinery. This means there is no need for oil or other lubricants when graphite tools are used to mold or shape glass. Once the glass is cooled, it can be removed easily from a graphite mold. Graphite is to the glass industry what a well-seasoned cast iron pan is to many cooks.
And further, graphite can withstand extended exposure to high temperatures. Glass becomes molten around 1500°C or higher. That’s pretty hot, considering your typical wood stove only gets up to about 540°C. Many materials that may be used as molds just don’t stand up well to those high temperatures. Graphite can take the heat, and the stickiness.
Graphite Material is Strong, but Also Gentle
If you have never dropped a glass yourself (and really, who hasn’t?), you’ve probably eaten in a restaurant when a waiter dropped a glass and all heads turned to look. Glass is a beautiful and indispensable material in modern life, despite its fragile and delicate qualities. It also scratches easily. The delicate nature of glass requires gentle handling to avoid scratching. Because graphite is inherently soft, it is the ideal material for use in glass manufacturing. When glass is tooled with carbon graphite equipment, glass doesn’t risk being scratched.
Here’s another scenario you may have witnessed. On a cold morning, the car windshield is covered in a thick layer of ice. The kids have to get to school soon, and no one can find the ice scraper. So someone gets some hot water and throws it on the windshield, and…crack! That’s called temperature shock, and glass is prone to it. Graphite has high levels of thermal conductivity, meaning that heat travels quickly through it. Like a chameleon changing color to match its surroundings, the graphite changes temperature and avoids the risk of the glass being subject to temperature shock.
Graphite and Non-Industrial Glass Production
The glass industry uses carbon graphite in many ways, mainly as tooling. Bearings, rods, rollers, and molds are some of the graphite tools commonly used in glass manufacturing. It isn’t just industrial sheet glass production where you are likely to find graphite tools, though. Many artists who specialize in glass blowing use graphite to shape their product, and for all the same reasons that the industrial producers of sheet glass use it. Carbon graphite is a versatile material, and one that you’ll find in the studios of artists working in many mediums.