Influence of graphite content on oil-free bearing

Plug graphite oil-free bearings are primarily used in applications that need continual lubrication in hard-to-reach areas. Graphite is mechanically forced into the holes/grooves under extreme pressure. A film of lubricant is transferred to the shaft as it begins to turn. These bearings offer continuous lubrication over long periods without maintenance.

oil-free bearing
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Based Sliding Bearing Materials

Copper base graphite composite for the sliding bearing is a metal matrix composite made of pure copper or copper alloy as matrix and graphite particles as lubricating components. It has excellent mechanical properties, oxidation resistance, corrosion resistance, and wear resistance. Self-lubricating properties of copper-based ink composites are always the focus of attention. The tribological properties of copper-based ink composites are affected by factors such as graphite content, particle size, type, and graphite surface coating.

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grahite
flange oil-free bearing

Professional And Reliable Graphite Bronze Bushing Manufacturer – Bronzeoilless.com

The composite material used in graphite bronze bushing is a new type of anti-polar pressure solid lubricating material, consisting of a metal substrate and a solid lubricant paste embedded in a hole or slot in the substrate. In the friction process, the metal substrate bears most of the load. After friction, the solid lubricant in the hole or slot is transferred or counter-transferred to the friction surface, forming a well-lubricated, firmly attached, and uniformly covered solid transfer film on the friction surface, which greatly reduces frictional wear. As the friction proceeds, the embedded solid lubricant is continuously provided to the friction surface, ensuring good lubrication to the friction substrate during long-term operation.

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Effect of graphite content on compressive strength of Oil-free bearing

In the process of friction, graphite can form a lubricating film on the friction interface, so as to play a role in lubrication and friction reduction. The sintered copper matrix composites with 2%, 6%, 10%, 14%, and 18% graphite content (volume fraction, the same below) were selected as the research objects respectively. The results show that the compressive strength of the composites decreases gradually with the increase of graphite content. This is because the properties of copper and graphite are different, leading to poor binding, compared with copper, graphite is relatively soft, prone to deformation and sliding; In the composite, the soft graphite can split the matrix and prevent the copper matrix from forming a complete network framework, resulting in the reduction of the strength of the composite. With the increase of graphite content, the distribution of graphite particles in the copper matrix becomes denser, and the function of the matrix fragmentation becomes stronger, leading to the continuous decline of the compressive strength of the material.

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oil-free bearing
cast bronze bushing

Influence of graphite content on tribological properties of materials

The number of transferred graphite particles increases with the increase of graphite content, and the increase of transferred graphite particles decreases obviously in Gr/Cu composites with 14% graphite content. The number of wear particles decreased first and then increased, and the increase was small. The wear of Gr/Cu composites with 18% graphite content was still lower than 6%. When the graphite content was lower than a certain value, the wear rate decreased with increasing graphite content and increased with too high graphite content. This is because the increase of the content of graphite particles promotes the transfer of graphite particles to the friction surface, increases the number of transferred graphite particles, enhances the lubrication effect of graphite, reduces the amount of material wear. In Gr/Cu composites with 14% graphite content, the small increase in the number of transferred graphite particles is related to the relative increase of wear. The increase of wear is more severe, which increases the roughness of the wear interface and is not conducive to the formation of the graphite lubrication layer.

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Add appropriate graphite particle content

The increase of graphite content will weaken the strength of the material and make the material more prone to wear under a large load. When the graphite content is more than 10%, the Gr/Cu composites with low strength will increase the wear quantity. The addition of graphite can reduce the friction effect, but it will also cause the strength of the material to weaken, can not withstand a large load, therefore, according to the specific working conditions should be considered comprehensively the balance of material strength and lubrication performance, determine the content of graphite particles in the composite material.

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solid graphite bronze bushing

Lubrication way

What is Graphite?

Graphite is one of the very common allotropes of carbon. It is also the most stable allotrope of carbon and thus used in electrochemistry as the standard state for defining the heat of formation of carbon compounds.   Graphite is a good conductor of heat and electricity with a density of 2.09–2.23 g/cm3. Graphite was accidentally synthesized by Edward G. Acheson for the first time when he was working on a high-temperature experiment on carborundum. He found that at around 41500C, the silicon in the carborundum gets vaporized, leaving behind the carbon in the graphitic form. He was granted the patent for the graphite manufacture in 1896, and then the commercial production of the graphite started in 1897. Graphite is not an element or a compound, it’s an allotrope of carbon. It doesn’t have any chemical formula of its own. 

Structure of Graphite

Graphite is a big covalent structure with each carbon atom joined with three other carbon atoms with covalent bonds. Each carbon atom is sp2 hybridized. These carbon atoms form a layer-like structure with a hexagonal arrangement of carbon atoms. These layers have weak forces between them. Due to these weak forces, the layers can slip over each very easily. Each carbon atom has one non-bonded electron, which becomes delocalized.

Physical Properties of Graphite

  • Graphite is a good conductor of electricity due to its free delocalized electron which is free to move throughout the sheets. 
  • Graphite is insoluble in organic solvents and water, this is because the attraction between solvent molecules and carbon atoms is not strong enough to overcome the covalent bonds between the carbon atoms in the graphite.  
  • Graphite has a high melting point of 36500C near the melting point of Diamond. 
  • Due to its layer-like structure, it is soft and slippery in nature.
  • Graphite has the ability to absorb high-speed neutrons.