Graphite has many beneficial characteristics, such as its strength, hardness, its capabilities of dry lubrication and self-lubrication, and is highly resistant to corrosion. However, graphite is a highly abrasive material, and products such as graphite electrodes and graphite bearings are difficult to manufacture using most machining processes. Therefore, the process of graphite machining is a heavy duty procedure designed to fabricate graphite products.
Graphite is a polymorph of carbon, and fall under two types: synthetic and natural graphite. Natural graphite can be found in different types of ore deposits and can be categorized into three main types: Flake graphite, which is made of isolated, flat, plate-like particles; Amorphous graphite, also known as meta-anthracite, which is made of fine particles; and finally, Lump graphite, which is a compact crystalline aggregate that occurs in fissure veins and thus is also referred to as vein graphite.
Synthetic graphite, on the other hand, is petroleum-based. This material can be categorized by production stage, method of manufacturing, or both. Machined graphite, can drastically vary in levels of toughness. Machined graphite can be found in applications such as graphite crucibles or pencil lead. Carbon graphite is a combination of graphite and amorphous carbon. It has a higher level of hardness and strength than regular graphite, and is less conductive and heat resistant.
Graphite’s molecular structure consists of sheets that are loosely laced together. This type of composition gives graphite its ability to self-lubricate and dry lubricate. Because graphite can adequately conduct electricity, EDM graphite is utilized in applications involving electrical discharge. However, EDM graphite is limited to conducting electricity among the carbon layers within its molecular structure. Read More…
Graphite can be used in a variety of applications, such as pillow blocks, brazing fixtures, thrust washers, packing graphite rings, boards, cathodic protection anodes, and degrassing graphite tubes. The metallurgical industry uses graphite tubes for fluxing tubes. The chemical industry makes use of these tubes as well, taking advantage of the material’s low resistance to heat by using them in furnaces.
Applications such as heaters, carbon heat sources, and fishing poles consist of graphite rods, which can also be formed from stacking a group of graphite rings on top of one another. Graphite electrodes are utilized in the steel production industry as a component of large recycling machines known as electric arc furnaces. Graphite bearings are used in the pharmaceutical and food industries because of their resistance to chemicals, their high temperature stability, and their self-lubricating properties.
Graphite felt allows for high stability with minimal shrinkage, and is frequently utilized as high temperature isolators in inert or vacuum atmospheres. Graphite crucibles store various materials during blending processes, and are highly resistant to heat. Graphite plates are smooth bodies of even thickness, formed from multiple uni-directional layers of graphite. Many industries benefit from using graphite products, such as ceramics, semiconductor, electronics, and food processing.
Five of the most common graphite machining processes are compression molding, isostatic molding, vibration molding, die molding, and extrusion. All five of these methods make use of fine graphite powder made from either natural or synthetic graphite. The first process, compression molding, involves preheating and thermally expanding the graphite before placing it into heated open mold cavity.
The next step involves closing up the mold and using pressure to force the material to conform to every area of the mold. The heat and pressure are maintained until the graphite is fully cured. In the isostatic molding process, graphite that contains isostatic properties is created, known simply as isostatic graphite. The first step of the process entails putting the graphite into a rubber bag. The next step involves inserting the bag into a high-pressure chamber filled with liquid.
The graphite mixture is forced to compact within the rubber bag by the pressure, which comes from all directions inside the chamber, and ultimately creates isostatic graphite. Another graphite machining process is vibration molding. In this process, large cross-sectional shapes are formed from graphite powder. The powder material is compacted when the graphite is shaken or vibrated within its confines. Often times, hydraulic compression is used alongside the vibration molding procedure.
Die molding involves the application of uni-axial pressure to the graphite material—which is placed in a die between two punches—to force it into a compact state. The graphite powder takes its shape when it is extruded through a die with an opening. The die molding process is used to create high amounts of graphite blanks or parts that have been compacted to undergo further machining processes.
It is possible for graphite scrap, particles, or parts can be recycled, but the process is not simple. Environmental regulations that address disposal of waste have become stricter over the years. Thus, it takes a machined graphite recycler who is well-versed in the process in order to safely address this issue. As complicated as the processes is, machined graphite recycling can greatly benefit the environment. Machined graphite parts are recycled in instances such as when synthetic graphite anodes, cathodes, or electrodes have to be discarded due to excessive wear.
For example, within a graphite electrode, a piece of the old electrode will remain despite a new electrode taking its place. The part of the old electrode is crushed back into graphite powder and resized. This powder is often integrated with molten steel in order to increase its carbon content. It is also possible to recycle graphite-containing refractories, but due to the type of graphite used, it is not an often occurrence.
Large volume items including carbon-magnesite bricks, often times cannot be recycled due to its low levels of graphite. Carbon-magnesite bricks can be used for materials to repair furnaces, or they can be crushed down and used for slag conditioners. Graphite crucibles are another component made from machined graphite, and are also rarely recycled. Although they have a higher graphite content than carbon-magnesite bricks, they are absorbent of other materials, which make recycling difficult.