Graphite Machining

About Graphite Machining and Graphite Machining Suppliers Including: Carbon Graphite, EDM Graphite, Graphite Anodes, Graphite Bearings, Graphite Crucibles, Graphite Electrodes, Graphite Plates, Graphite Products,  Graphite Rods, Graphite Tubes, Graphite & Machined Graphite.

Machined graphite is used in such diverse applications as pencil lead and graphite crucibles because graphite can vary greatly in terms of toughness. A polymorph of carbon, there are two main types of graphite: synthetic graphite and natural graphite. Found in different types of ore deposits, there are three main types of natural graphite; flake graphite, in which the particles are isolated, flat and plate-like, amorphous graphite, which occurs as fine particles and can be referred to as meta-anthracite, and lump graphite, also known as vein graphite, which occurs in fractures or fissure veins and is a compact crystalline aggregate. Contrarily, synthetic graphite is a petroleum-based composite material that is classified by either method of manufacturing or by production stage or both. While it is a polymorph of carbon, graphite can also be combined with amorphous carbon in order to create carbon graphite, which offers increased strength and hardness as well as a lower level of heat resistance and conductivity than typical graphite. Graphite machining processes are heavy-duty processes since it is an especially abrasive material and is difficult to fabricate graphite products such as graphite electrodes or graphite bearings in the majority of machining processes. Overall, machined graphite offers beneficial properties such as strength, hardness, corrosion resistance, dry lubrication and self lubrication. Graphite's self-lubricating and dry lubricating properties are the result of its molecular structure which consists of loose interlamellar coupling between sheets. Graphite is also a fairly good electrical conductor, and EDM graphite is often used for electric discharge machining applications. however, it can only conduct electricity within the plane of the carbon layers in its molecular structure.

Graphite machining design isn't critical in that a poorly designed process with create poor graphite designs; however, certain parts are improved by a better process design. Some of the many applications for machined graphite include degassing graphite tubes, cathodic protection anodes, boards, packing graphite rings, thrust washers, brazing fixtures and pillow blocks. A graphite tube is particularly useful for fluxing tubes in the metallurgical industry as well as in furnaces for the chemical processing industry because of graphite's low heat sensitivity. Graphite rods are used primarily in industrial applications as heaters or carbon heat sources, but are also highly popular as fishing poles. Graphite rings may sometimes be stacked in order to form graphite rods. Used to refine steel in ladle furnaces and other smelting processes, graphite electrodes are mainly used in electric arc furnaces, which are basically very large recycling machines, for steel production. Graphite bearings are used in industries such as food handling and pharmaceutical due to their self-lubrication, high temperature stability and chemical-resistance. Graphite felt is most often used as high temperature isolation in vacuum or inert atmospheres and allow for high stability with low shrinkage. Graphite crucibles are heat-resistant containers that are used to store materials and samples during fusion and other mixing processes. Able to outperform steel and titanium plates, graphite plates are machined from multiple plies of uni-directional graphite in order to form a smooth, flat body of uniform thickness. As a result of the wide-ranging applications, numerous industries benefit from the use of graphite parts including food processing, electronics, semiconductor and ceramics.

There are five common graphite machining processes: compression molding, isostatic molding, vibration molding, die molding and extrusion. All of these methods utilize a fine graphite powder that was machined from raw graphite, either synthetic or natural. Compression molding is a high-volume, high-pressure method of molding in which the graphite is generally preheated and thermally expanded, and then placed in an open, heated mold cavity. Next, the mold is closed with either a top force or a plug member, and then pressure is applied to force the graphite into contact with all areas of the mold, while maintaining pressure and heat until the graphite has cured. Isostatic molding is an alternative molding method that creates isostatic graphite, which contains isotropic properties. This process entails putting the graphite into a rubber bag and then placing the bag into a high-pressure and liquid-filled chamber. The pressure comes from all directions within the chamber causes the graphite mix to compact within the rubber bag and create isostatic graphite. Vibration molding is a graphite machining process that forms graphite powder into large cross-sectional shapes. Vibrating, or shaking, graphite within large containers induces compaction of the powder within the containers. Hydraulic compression is sometimes used in conjunction with the vibration molding process. Die molding serves to create a high volume of graphite parts or blanks that have been pressed-to-size for further machining. Die molding involves compacting the powder using uni-axial pressure that is applied to the graphite when placed in a die between two rigid punches. The extrusion process shapes the graphite powder by forcing it through a die with an opening.

Machined graphite manufacturers are often able to assist in recycling used and excess graphite scrap, parts or particles. In recent years, environmental regulations concerning waste disposal have tightened making regulation machine graphite recycling difficult to accomplish without the aid of a knowledgeable machined graphite recycler. The two most common instances in which machine graphite parts are recycled are when synthetic graphite electrodes, anodes or cathodes are manufactured and pieces are then discarded and when the synthetic graphite part is used all the way down to the last usable piece. For instance, in a graphite electrode a new electrode will replace the old one; however, a sizeable piece of the old electrode will remain. This left-over machine graphite part is then crushed and sized, resulting in graphite powder. The most common use of this powder is to raise the carbon content of molten steel. Graphite-containing refractories can also be recycled, but are often not due to the type of graphite used. In fact, the largest-volume items, such as carbon-magnesite bricks, often contain too little graphite to be recycled. However, if these carbon-magnesite bricks are recycled, they are either used for furnace repair materials or crushed for slag conditioners. Another machined graphite part that is not often recycled or has very little to recycle is graphite crucibles, which have a high graphite content, but use the majority of the volume. Machined graphite recycling is an important step in improving environmental conditions.

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Images Provided by Becker Brothers Graphite Corporation

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Graphite Machining Types

• Carbon graphite is used in mechanical applications due to its strength and hardness. Carbon graphite has a lower level of heat resistance and conductivity than graphite.
  
• Extruded graphite has relatively fine grain size, and has good mechanical, electrical and thermal properties, with a preferential grain orientation and low ash content. Density, mechanical strength and oxidation resistance can be improved by means of further impregnation.
  
• EDM graphite is an important component of electrical discharge machines. The use of graphite causes less wear and tear on the EDM electrodes and removes metal quickly and efficiently.
  
• Graphite bearings are often used in load capacity systems along with graphite bushings.
  
• Graphite composites are beneficial because they are lightweight, yet strong and durable. Graphite composites are used in the automotive, airplane, and aerospace industries to provide structural support and reinforcement.
  
• Graphite crucibles are used to store materials and samples during fusion and other mixing processes.
  
• Graphite design produces many products from machined graphite.
• Graphite electrodes are used in ladle furnaces and electric arc furnaces. Graphite electrodes are advantageous for their high conductivity and performance under high temperatures.
  
• Graphite fixtures consist of packaging fixtures and sealing fixtures. Graphite fixtures are used in the automation and semiconductor industries.
  
• Graphite machining is the process that produces parts out of synthetic graphite materials.
• Graphite rods are used in the fiber optics and semiconductor industries to produce a wide variety of machine components, including dies, spindles, and chucks.
  
• Graphite tubes are used in furnaces because of graphite's low heat sensitivity. Graphite is also used in the production of fluxing tubes used in the metal manufacturing industry; other industries using graphite tubes include chemical and scientific industries.
  
• Isostatically pressed graphite is an especially fine grain, dense, isotropic graphite, which can be produced in large dimensions.

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Graphite Machining Terms

Angstrofine - The most advanced type of EDM graphite. Angrostofine is used when fine detail and a smooth finish is required.

Billet - An uncut block of graphite produced by the manufacturer that ranges from two to seven square inches. A billet is commonly used for longer projects.

Breakthrough - The exit end of a through-hole cavity which occurs at the moment of completion.

Carbon - An abundant element of natural occurrence, often used instead of the word graphite. Graphite is a type of the element carbon.

Coke - A processed form of coal. Processed coke burns more steadily and is stronger than metallurgical coke.

Composite - Two or more materials combined. An example is copper graphite, which is a metallic/carbon composite.

EDM - Electrical Discharge Machining; a process in which metal is removed through burning or erosion instead of through cutting.

Electrode - A tool used in EDM which mirrors the desired shape. The electrode must be made out of materials that can carry an electric current.

Filler - The carbonaceous particles in manufactured graphite comprising the base aggregate in an unbaked green-mix formula.

Flash - Thin fin or web of metal extending beyond the confines of the casting, usually along the joint line as a result of poor contact between cope and drag molds.

Grain - Referring to a region in a carbon or graphite body that is identifiable as being derived from a particle of filler.

Horn Gate - Curved gate in the shape of a horn arranged to allow entry of molten metal at the bottom of the casting cavity.

Isotropic - Having uniform properties in all directions. The measured properties of an isotropic material are independent of the axis of testing.

Machined - To shape, cut or finish a product by the use of a machine.

Premium Graphite - A material with a particle size of five microns or less.

Transducer - Changes one form of energy into another; in EDM it is used to change electromagnetic force into mechanical force for the machining of graphite. Although there is sound produced when machining graphite, it is too high pitched for most human hearing.

Trim Die - Die used for shearing or trimming a workpiece.

Workpiece - Material that is being machined. The material will continue to be operated on until it is a replica of the original.