August 2021 Volume 3

MATERIALS

Why Graphite for Forging Lubricants? By Bob Hartsough and Frank Sobnosky

Have you ever asked yourself, “Why do we need to use these graphite-based forging lubricants?” Most people in the forging industry have wondered this at some point. Well, here is the simple answer: Because it works! However, while this simple response is true, it is important to understand why this black substance works so well in forging lubricants. Graphite has many unique properties which make it ideal for various metal forming, and it is available at a relatively low cost. These properties include lubricity, resistance to heat, and resistance to oxidation. In some less demanding applications, synthetic (non-graphite) lubricants may be an option, having the necessary properties to allow themetal forming operation to take place while helping to maintain a cleaner environment. There are two specific classes of graphite, based on their origins: natural and synthetic. Natural graphite is mined from the earth, and its properties vary based on the region where it is mined. Graphite is also manufactured, and this synthetic graphite varies significantly based on the rawmaterials and processes used to create it.

The lubricity of all graphite comes from its particular arrangement of carbon atoms within its structure which create a “chicken wire” matrix with the layers stacked on one another. These layers are held together by somewhat weak Van der Waals forces. These forces allow the individual ‘graphene’ layers to sluff off easily in the C (horizontal) plane. These layers are able to slide over one another with a very low coefficient of friction giving graphite its lubricity. Strong covalent forces exist between the atoms in the A and B (perpendicular) plane, which allow these layers to be very resistant to breaking. The covalent forces also make the layers highly resistant to thermal decomposition allowing graphite to stand up to the high temperatures and pressures used in forging. The microscopic particles of graphite coat the die and workpiece then slide over one another. This allows these particles to orient themselves in the direction of sliding, preventing metal-to-metal contact between the tooling and the workpiece greatly lowering friction and wear.

Graphite X50,000

Graphite Structure

FIA MAGAZINE | AUGUST 2021 42