Carbon-graphite

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Overview of Carbon-Graphites

Carbon-graphites showcase both fine and very fine particle sizes and can exhibit a high degree of anisotropy due to the axial process. These materials are composed of graphite impregnated with amorphous carbon.

These materials are specifically designed with properties in terms of tribology and electricity, which can be enhanced through impregnations with resins or phosphates. However, unlike traditional graphites, carbon-graphites are not very efficient thermal and electrical conductors.

We stock three grades of carbon-graphite:

• EK24 (without impregnation)
• EK2240 (phenolic resin impregnation)
• EK305 (antimony impregnation)

A product that is 100% graphite is relatively soft. The addition of amorphous carbon makes it very hard, making machining with high-speed steel tools nearly impossible; ideally, a diamond tool should be used. Additionally, carbon-graphite is less resistant to extreme temperatures compared to pure graphite.

Key Features of Carbon-Graphite

• Excellent corrosion resistance
• Very good mechanical strength
• Good sliding properties
• High thermal shock resistance
• Low wettability
• Anti-wear
• Long-term stability
• Adaptable properties (depending on the impregnation product)
• Can operate dry without lubrication or in wet environments

Applications of Carbon-Graphites

• Sealing rings
• Sealing gaskets for agitators and autoclaves
• Bearings
• Pumps for hot/cold water, fuels, and chemicals

Feel free to contact us so we can evaluate your specifications and assist you in choosing the most suitable carbon-graphite for your application. Based on your needs, we also offer a complete machining service for your parts, from prototyping to high-volume production.

If our carbon-graphite characteristics do not meet your application requirements, we also offer the option to produce parts in materials such as silicon carbide, zirconia, or boron nitride.

Technical Data of Carbon-Graphites

Properties

EK24

EK2240

EK305

Impregnation

No impregnation

Phenolic resin

Antimony

Density (g/cm3)

1.70

1.8

2.55

Flexural Resistance (MPa)

60

70

80

Compressive Strength (MPa)

180

200

290

Young’s Modulus (GPa)

18

For more information, please visit graphite cathode.

19

21

Rockwell B Hardness

105

110

115

Thermal Conductivity (W/m.K)

14

15

33

Linear Expansion (20/200°C, 10-6.K-1)

4.1

5.0

6.0

Temperature Resistance (°C)

350

200

500

Carbon-Graphite Materials

Carbon-graphites offer the design engineer a unique family of mechanical materials. Manufactured entirely from carbon and including high temperature carbonaceous bonding, these materials combine the strength, hardness, and wear resistance of carbon with the corrosion resistance and self-lubricating properties of graphite. The precisely controlled inherent porosity of carbon-graphites can be filled with a variety of impregnants to enhance chemical, mechanical, and tribological properties.

Types of Carbon

The terms ‘carbon’ and ‘graphite’ are often used interchangeably. This is unfortunate since each form of the element carbon offers specific properties that can benefit different types of applications.

Amorphous Carbon

Amorphous carbon is a very hard, strong compound. The crystals exhibit a turbostratic disorder, making the material extremely resistant to wear. The strength and wear resistance properties of this material make it of interest in some applications. However, these strengths can also be a weakness — carbon generates high friction when rubbed against another surface.

Graphite

Graphite, on the other hand, is softer and relatively weak because of the crystalline order and closer spacing between the monoplanes and stacks. A graphite structure can be compared to a deck of cards with individual layers able to easily slide off the deck. This phenomenon gives the material a self-lubricating ability which is unmatched by any other material. External lubricants are simply not necessary.

Combining amorphous carbon and graphite allows for full advantage of the strengths and weaknesses of each type of carbon. The optimal mixture is strong, hard, and has low friction. This composite has excellent corrosion resistance and operates at temperatures exceeding 315 °C for extended periods, depending on the specific grade. This ability to create materials with these properties underpins the manufactured mechanical carbon materials that perform well in difficult tribological situations, such as in pumps.

Processing Carbon-Graphites

Carbon-graphites are created by combining the two forms of carbon with coal tar pitch. The coal tar pitch acts as a temporary binder holding the structures together during the compression molding process, forming near-net shapes. Following the molding operation, the parts are sintered at temperatures high enough to carbonize the coal tar pitch, resulting in a structure entirely carbon-bound and containing both carbon and graphite. This structure is extremely strong in compression and will not creep under load.

Micro-scale holes form during the carbonization of the binder, turning the sintered body into a black sponge. These holes hold resins, metals, carbon, or inorganic salts to enhance the material's strength, thermal conductivity, and tribological characteristics. Additionally, carbon-graphite can be sintered to even higher temperatures to convert the entire structure to graphite for exceptionally good performance in high-temperature, high-speed applications.

Carbon-Graphites vs Traditional Lubricants

Carbon-graphites are used in various applications where traditional lubricating methods are not appropriate. For example, oil-lubricated bearings struggle at temperatures below -40 °C due to the high viscosity of the oil. Above 200 °C, oils carbonize, becoming abrasive and ineffective. Graphite bearings can endure extended use at temperatures above 600 °C.

Chemically Aggressive Environments

Chemically aggressive applications represent another niche for carbon-graphite. Sterilization processes can leach oil from the structure of an oil-lubricated bearing. Solvents and radiation can break down lubricating oils, and low pressures can cause the oil to vaporize. Carbon-graphite materials are inherently stable and chemically resistant, making them ideal for these types of applications.

High Load Applications

Lubricants are inappropriate in certain applications for various reasons. High loads can squeeze the lubricant from a surface. Without the hydrodynamic layer of lubricant, failure is imminent if the material cannot provide self-lubrication. Moreover, food-handling applications avoid lubricants to prevent contamination of the surrounding environment. Specific grades of carbon-graphite are approved for use in food handling.

Design Factors

Carbon-graphite bearings are used in both wet and dry operating conditions, allowing designers to specify bearings close to the boundary-lubricated condition without the risk of seizure. Permissible loads and running speeds depend on the allowable wear rate, and shaft materials and surface finishes significantly influence wear rates. Typically, harder and more polished surfaces result in lower wear, and materials like aluminum and bronze should be avoided for shaft applications.

Carbon-graphite materials are widely used as rotating shaft and face seal materials. They perform well when running against metal and ceramic counterfaces. Seals are manufactured from solid, split, and segmented rings for use in both liquid and dry-running applications across various industries.

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