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This article will take an in-depth look at graphite rods.
The article will bring more detail on topics such as:
Principle of Graphite Rods
Types of Graphite Rods
Applications and Benefits of Graphite Rods
And Much More…
Chapter 1: Principle of Graphite Rods
This chapter will discuss what graphite rods are, their construction, and how they function.
What are Graphite Rods?
Rods are thin, straight rods made of plastic, metal, ceramic, or organic substance. They are relatively simple to construct and can serve a variety of functions depending on their composition and size.
As a type of rod, graphite rods are produced from machined graphite or graphite compounds. They are well-known for their excellent thermal shock resistance, heat resistance, high corrosion resistance, non-reactivity, and ability to age well (because graphite is a non-fatiguing material).
Graphite is one of the world's toughest materials, having several industrial applications ranging from #2 pencils to EDM gear. Graphite has become one of the most prevalent industrial materials in factories and other heavy machinery due to its strength and longevity, outperforming basic steel and other carbon blends. However, graphite cannot be employed in any industrial applications in its raw state. Graphite must be machined before it can be used.
Graphite machining is the technique of cutting or shaping graphite material to fit a number of applications and purposes. Because graphite is nearly tough to cut and will blunt most metals, it is critical to utilize only diamond and carbide tools. However, due to its strength, graphite provides a lot of advantages. The material is incredibly robust, will not rust or break down, and can be used as natural lubrication for bearings and other machine components. This reduces the expense of other oils and lubes.
Machining of Graphite
The process of machining graphite is identical to that of machining cast iron. Fine chips, often known as swarf, are extracted as fine powder. The devices used in the procedure do not grip the workpiece but cut it in a manner similar to plowing snow.
The compressive strength of graphite is strong, and it may be kept in place by clamping force. Before operating on the piece, it is critical to calculate the amount of clamping force required. The amount of clamping force required is determined by testing a workpiece to the threshold of compressive failure.
Some methods used for machining graphite are specialized tools. The first thing to think about when planning to machine graphite is the tools that can be employed. Graphite is an abrasive material that will severely wear bare metallic tools. Diamond-edged tools are preferred, but tungsten carbide tools can also be utilized. High-speed steel can be used, though it wears out fast, limiting its application. Chipping and breakouts occur when the wrong tool, speed, or feed is used.
How Graphite is Made
Graphite is a type of carbon with carbon atoms organized in layers, giving it its distinct features. Natural graphite is mined worldwide, although the majority of it is found in China, Brazil, Canada, and Madagascar. It is prevalent in metamorphic and igneous rocks and is generated when carbon in the earth's crust is subjected to high pressure and temperature.
Synthetic graphite contains high purity carbon and is resistant to high temperatures and corrosion. Calcined petroleum coke and coal tar pitch, both of which contain graphitizable carbon, are the primary elements used to produce synthetic graphite. The manufacturing process includes the mixture materials being mixed, heat treated, molded, and baked.
Manufacturing Graphite Rods
Compression molding, isostatic pressing, or rod extrusion are the three most common ways of producing graphite rods. Many of these techniques are comparable to those used to create graphite tubes.
Compression molding is a forming process in which a substance is softened and then forced to take the shape of the mold in which it is resting. To begin, the material to be molded is preheated before being placed in an open, heated mold or hole. The mold is then closed from the top and pressured by a plug member as it softens. The graphite substance expands out and takes the shape of the mold due to the effects of pressure and heat. It's being kept here until it cures.
The mold first needs to be prepared with typical preparation steps including: cleaning the mold, applying a release agent, and heating done to induce the viscosity of the charge when it is finally loaded.
Compression molding is done on a variety of materials. Therefore, they come in many compositions, sizes, shapes, conditions, and packages. Preparation changes the material from its delivery state into one more suitable for compressing. Charge preparation includes: unpacking, cleaning, cutting, sizing, weighing, and heating.
This entails placing the charge on the mold’s lower portion. This way, the optimal compression result is ensured. The charge is then applied to the mold in the required pattern, depending on the form of the mold, required thickness, and other considerations.
To put the two parts of the mold as close together as possible, relative motion is created. The charge is compressed as the parts move closer together. Compression can be used to accomplish forcing the charge to fill the entire planned volume in the mold’s cavity. It also ensures the proper density of the product and facilitates curing.
Curing in the Molding Process
This stage of the molding process aids in the hardening of the compressed charge into the finished product. To enable setting and hardening, it may simply be necessary to lower the temperature or to use hardening agents and catalysts. Condensation type and addition type are some of the cure types.
Cooling ensures the mold has the perfect temperature for subsequent molding cycles. Ensuring the mold develops the preferred thermal and mechanical properties is important for the removal and usage or storage.
Ejection is the release of the graphite after curing. Automated ejection often uses a plunger that moves from the mold’s underside when ejection is needed, or a separate system of suckers. Ejection is frequently accompanied with a releasing agent and a coating put to the mold to prevent the product from clinging to the mold and to facilitate ejection.
Rod extrusion simply engages in the standard extrusion molding process. This process begins with the collection of graphite stock and any needed additions in a hopper, where they are heated until molten. When the stock is molten (or liquid), it is pressed through a tube-shaped die. After cooling, the stock takes on the size and shape of the die. It can be released from the die as a solid shape once it has cooled.
Hot Extrusion Process
This is a hot working technique, which means it is carried out above the graphite’s recrystallization temperature. This prevents the graphite from solidifying and makes it easier to push through the die. The hot extrusion process is generally carried out on horizontal heavy hydraulic presses. Their pressures range between 30 and 700 MPa (4,400 - 101,500 psi). Thus, lubrication is required. For lower temperature extrusions, oil or graphite can be utilized, while glass powder can be used for higher temperature extrusions.
Isostatic pressing is a forming method that employs pressure from all sides. The graphite substance is placed within a high pressure containment vessel to work. An inert gas, such as argon, is used to pressurize the containment vessel. Once the graphite is within, the vessel is heated, raising the pressure and causing the graphite to form in this manner.
Hot Isostatic Pressing (HIP)
It is not only used for powder consolidation and two-step work of traditional powder metallurgy forming and sintering are completed simultaneously, but also for the elimination of casting defects, diffusion bonding of the workpiece, and the production of complex shape parts. In hot isostatic pressure, argon, ammonia, and other inert gasses are commonly employed as the pressure transfer medium, and the package of components is typically made of metal or glass. The operating temperature is often 1000 to 2200°C, and the working pressure is frequently 100 to 200MPa.
Cold Isostatic Pressing (CIP)
Cold isostatic pressing is advantageous for creating parts where the initial high cost of pressing dies cannot be justified, or extremely big or complex compacts are required. On a commercial scale, a wide range of powders, including metals, ceramics, polymers, and composites, can be pressed isostatically. Compacting pressures range from less than 5,000 psi to greater than 100,000 psi (34.5 - 690 MPa). In either a wet or dry bag process, powders are compacted in elastomeric molds.
ESM and CGI series are pressed graphites, isostatically, produced by the technique of (CIP). Cold Isostatic Pressing This super fine grain graphite substance allows high densities to be achievable.
Cokes - is a component in oil refineries that is created by heating hard coal (600 to 1200°C). This procedure is carried out in a specifically built coke oven, which employs combustion gasses and has limited oxygen availability. Its calorific value is higher than that of traditional fossil coal.
Pulverizing - After the raw ingredients have been thoroughly inspected, they are pulverized to a specific grain size. Specific machines that grind the material transfer the resulting very fine coal dust into special bags, which are then sorted according to grain size.
Kneading - After the coke grinding process is finished, it is blended with pitch. At high temperatures, the raw materials are combined such that the coal melts and combines with the coke grains.
Second Pulverizing - Following the mixing process, little carbon balls form, which must then be ground into very fine grains.
Isostatic Pressing - The pressing stage begins once the fine grains of the necessary size are ready. The powder is then deposited in huge molds with sizes that correspond to the final block sizes. The powdered carbon in the molds is subjected to high pressure (above 150 MPa), which imparts equal pressure and force to the grains, resulting in symmetrical arrangement and even distribution. This process allows for identical graphite properties to be obtained across the whole mold.
Carbonizing - The next and most time-consuming stage (2 to 3 months) is baking in the furnace. Material that has been uniformly crushed is placed in enormous furnaces that reach temperatures of 1000°C. The temperature in the furnace is constantly maintained to avoid any faults or cracks. After baking, the block has reached the necessary hardness.
Pitch Impregnation - To reduce porosity, the block might be impregnated with pitch and burnt again at this step of the process. A pitch with a lower viscosity than the pitch used as a binder is typically used for impregnation. To fill any gaps more precisely, a low viscosity is required.
Graphitizing - At this point, the matrix of carbon atoms is now ordered, and the process of transitioning from carbon to graphite is known as graphitizing. Graphitizing is the process of heating the created blocks to around 3000°C. After graphitizing, the electrical conductivity, density, thermal conductivity, and corrosion resistance all improve dramatically, as does machining efficiency.
Graphite Material - It is critical to inspect all graphite parameters after graphitization including grain size, bending, density, and compression strength.
Machining - Once the material has been thoroughly prepared and examined, it can be manufactured into graphite rods.
Materials in Graphite Rods
A fabrication method is determined based on the specific application’s needs for which a graphite rod is to be used. Similarly, the type of graphite used in a graphite rod forming process is determined by the application’s needs. Most graphite rods, for instance, are produced from finer grain graphite, which provides a nicer surface finish to the rods. When a smooth finish or surface is not required, coarse grain and or high density graphite stock might be utilized instead.
Specifications of Graphite Rods
The specifications of graphite rods include the standard density of each grade as it determines where the grade of the rod can be applied. Compressive strength is also a similarly important feature and it ranges from 11 000 to 38 000 pounds per square inch.
Modulus of elasticity is 14 K10-5 psi at room temperature and 27 K10-5 psi at 2315 degrees Celsius (G purified grades). Thermal expansion is 6 in./in./°C x 10-7 at room temperature and 18in./in./°C x 10-7 at 2315 degrees Celsius (G purified grades). Electrical resistivity is from 29 to 36 ohm-in. x10-5.
Thermal conductivity is 179W/(mK) at room temperature and 154 W/(mK) at 2315 degrees Celsius (G purified grades). Maximum grain size, flexural strength, and coefficient of thermal expansion are also important specifications.
How a Graphite Rod Functions
A graphite rod can function as a flaring tool due to its strength and durability. It can also function as support posts due to the same properties. In laboratories, they function as electrodes and as stir sticks. Other common uses are as anode and DCFCs fuel. Other functions are recreational.
What to Consider When Choosing Graphite Rods
Customers and manufacturers alike must examine a few key variables when purchasing graphite rods to ensure that graphite is the correct material for the task. Considerations include the expected time of exposure to weather elements, the expected sorts of weather elements, the anticipated length of exposure to excessive heat, the intended usage, predicted tension or stress levels, and the required rod dimensions.
Chapter 2: Types of Graphite Rods
Graphite rods are machinable from graphite blocks for use in various industries and applications. Standard sizes are manufactured and machined from Extruded Graphite.
JC3 Fine-Grained Graphite Rods
JC3 is a dense fine-grained rod that can be machined and has a high temperature rating of 5432°F to 3000°C. Its grade is extruded graphite JC3 and apparent density is 1.72 to 1.74g/cc. Its characteristics enable strong electrical conductivity. JC3 graphite rods are machinable to extremely tight tolerances.
Graphite rods have good thermal conductivity because graphite is an excellent heat conductor and has a high thermal shock resistance. The rod compressive strength ranges from 11K to 38K lbs/in2. Corrosion resistant for all practical purposes and it is resistant to many acids, alkalis, solvents, and related compounds.
It has seal face flatness due to the high modulus of elasticity and stability to stay flat during operation at the rubbing faces. It also has non-galling features and built-in lubrication. The molecular structure of graphite generates an extremely thin covering on moving parts. Products will not seize or gall in the most severe applications. Graphite is porous but impregnates are utilized to fill these pores, which can range from high to completely impervious depending on the application.
JC3 graphite rods are mainly used in heat treating and electrochemical applications. They are also used to support beams or hearth rails to allow for thermal expansion. More uses include fixtures or support posts, stir sticks, electrodes, and other reaction purposes.
JC4 Fine-Grained Graphite Rods
JC4 is a sturdy fine-grained rod that is machinable and graded to a medium temperature (Heat Treating 1355°F to 735°C). Its grade is extruded graphite JC4 and its density is 1.76g/cc.
When higher temperatures are not necessary, its properties allow for good density and strength. The rest of its characteristics are similar to those of JC3 which have already been mentioned above. These rods are typically utilized in mechanical applications.
Superfine Molded Graphite Rod
Its characteristics are super fine grain size, high density, unreactive, superior strength, and molded graphite rod. It’s suggested for high temperature metal, glass, and electrochemical applications including crucibles, stirring rods, molds, electrodes, anodes, bushings.
Diameter tolerances: +.010" / -.005". Superfine graphite is rated at a temperature of up to 2760 degrees Celsius. Particle size is 0.001in, Density is 1.8gr/cm, Compressive Strength is 13K psi, and Resistivity is 0.00050 ohm/inch.
Medium Grained Graphite Rods
The construction of these rods are ideal for roughing and finishing operations in various industrial applications. These rods are produced by use of an alternate manufacturing procedure which reduces cost over the isostatic molding procedure.
The label of medium grain graphite typically refers to materials with individual particles that range in size from 0.0508mm up to 1.575mm, which have been compression molded or extruded into their raw material form. 12 to 20% of a rod’s volume is made up of pores between individual particles which are visible to the naked eye. When talking of uses, medium grain graphite rods represent a perfectly appropriate substitute to fine grain graphite rods
Coarse Grained Graphite Rods
There are several circumstances where coarse grain graphite rods are desired and satisfactory for an application. Usually when discussing a coarse grain graphite rod, it’s an extruded graphite. The distinct particle size of this graphite material will vary from 1.016mm up to 6.096mm and have a large quantity of pores in the material.
This coarse grain material is a great material for the manufacture of graphite rods. Because of its big particle size and open pores the rods handle thermal shock extremely well and can handle changes in temperature as molten metals touch its surface. While these rods also have about 12 to 20% of its volume made up of pores between individual particles, these pores are quite visible to the naked eye because of the particles that make up the rods. These rods are mostly used as graphite electrodes for ladle furnaces and electric arcs in the steel industry.
Higher Density Graphite Rods
High density graphite is an exceptionally special material with high strength, high density, and a fine microstructure. It can be used for making rods because of its ability to handle exceedingly high temperatures while maintaining its shape and strength. Furthermore, these rods are low-cost and simple to machine in any form.
In the present day tech, graphite samples were produced from coal tar pitch based semi coke powders without the use of any supplementary binder. Isostatic graphite rods display greater features when compared to man-made graphite made from the old-style filler and binder procedure. This is then carbonized, pore filled, and graphitized.
Pyrolytic Carbon Coated Graphite Rods
A pyrolytic carbon layer on graphite reduces gas permeability, improves oxidation stability, and protects against particle release. It is created by means of a Chemical Vapor Deposition (CVD) procedure. Pyrolytic carbon coatings, like graphite, have exceptional thermal stability and chemical inertness. Furthermore, pyrolytic carbon can be utilized to penetrate and densify graphite, considerably reducing internal porosity.
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Chapter 3: Applications and Benefits of Graphite Rods
This chapter will discuss the applications and benefits of graphite rods.
Applications of Graphite Rods
Graphite rods are often utilized for fiber optics and semiconductor applications, both of which need precision and sensitivity. More popular uses of graphite rods are fishing rods and small fishing rods (since graphite is sensitive, durable, and lightweight).
Industrial applications include heat treating; they are used to support beams or hearth rails to enable thermal expansion because graphite can withstand extreme temperatures. Also as hot and melting metal stirring rods, graphite electrode cylinder rods. In electrolysis, graphite rods are used as well as the numerous delocalized electrons allow electricity to move through graphite swiftly.
Graphite rods can be used to extend a blown-in hole in a tube, as a flaring device, or to make an indentation in a glass sidewall. Graphite rods are applied as moderators in nuclear reactors to control the reaction rate. Graphite enables fission chain reaction by slowing neutrons in a graphite reactor. A few rods are inserted and absorb more neutrons that become available then the chain reaction accelerates. The level of power in the reactor starts to rise.
Machined graphite is commonly made of a composite or mixture of graphite and copper. Pure graphite with the additional copper yields its sought after properties of elevated strength and secured conductivity. As was alluded to, graphite rods are extremely resistant to heat. To define and quantify “extreme,” it is to be noted that graphite rods can keep their form even when exposed to “extreme” temperatures such as 5000 degrees.
Benefits of Graphite Rods
Graphite is commonly thought of as the material that makes pencil lead, yet it is a lot more than that, a fact that graphite rods show. They conduct electricity and are inert. Good thermal conductivity because graphite is a superior thermal conductor and has a high thermal shock resistance.
Compressive strength varies from 11K to 38K lbs/in2 for fine grain rods. In designing mechanical parts, it is prudent to take advantage of materials with high compressive strength. Machinability to extremely tight tolerances. Corrosion resistant, for all practical purposes, they are resistant to most acids, alkalis, solvents, and similar substances. Seal face flatness as a result of high size of elasticity and stability to stay flat during operation at the rubbing faces.
Non-galling and built-in lubrication because the molecular structure of graphite generates an extremely thin covering on moving parts, products will not seize or gall in the most severe applications. Also porosity. Graphite is porous, but impregnates are utilized to cover these pores, which can range from high to completely impervious depending on the application. Because some graphite has small pores, not all kinds of graphite require impregnation. It is critical to choose the right substance for the impregnation process.
Furthermore, they are very durable and strong. As a matter of fact, the structural quality of machining a graphite rod is such that, not only can it maintain its form while under very high temperature, but it then becomes stronger and more durable as temperature rises. Graphite rods may be cut to fit the volume, diameter, length, and shape requirements for all types of applications.
Drawbacks of Graphite Rods
Synthetic graphite and natural graphite have historically been the most common negative electrode materials, but the high temperature treatment necessary in the creation of artificial graphite has substantially increased its cost and harmed the environment.
In humans graphite causes graphitosis which is benign pneumoconiosis. Dyspnea, coughing, black sputum, bronchitis, ventricular enlargement, and impairment of pulmonary function are signs of graphite-induced pneumoconiosis.
The environmental consequences of graphite mining are comparable. The use of explosives can cause dust and tiny particles to be released into the atmosphere, causing health issues in local people and contaminating soils around the site. Brazil, China, and Turkey account for over 80 percent of natural graphite reserves.
Manufacturing graphite rods give a high carbon footprint and energy consumption trials. The energy use is usually lower than injection molding but higher than the rest of the molding processes.
A graphite rod is one which is produced from machined graphite or graphite compounds. It is mostly for its excellent thermal shock resistance, heat resistance, high corrosion resistance, non-reactivity, and ability to age well. Graphite rods come from graphite machining which is the technique of cutting or shaping graphite material to fit a number of applications and purposes. After the graphite is machined, it is manufactured into graphite rods. Compression molding, isostatic pressing, or rod extrusion are the three most common ways of producing graphite rods. Many of these techniques are comparable to those used to create graphite tubes. Types of graphite rods available are fine grain, medium grain and coarse grain which come from extruded graphite. Each type has its own advantages which makes it suitable for a required application. Graphite rods are applied in a lot of industries due to their high thermal conductivity and durability. They are also used for recreational activity in fishing rods since they are light and strong. However they do have their downside since fabricating graphite rods leaves a high carbon footprint and demands a lot of energy. Also the mining of graphite has its negative effect on the ecosystem however the effect is better compared to its substitutes, such as metal.
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