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Maintenance-free Plain Bearings
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GRAPHITE AND SOLID LUBRICATED BEARINGS
Solid lubricated bearings, especially those based on graphite and molybdenum disulfide (MoS₂), are extensively utilized in extreme environments such as high temperatures, vacuums, or nuclear radiation settings where conventional liquid lubricants fail to function effectively. Here is a detailed introduction to graphite and solid lubricated bearings.
Solid lubricated bearings, particularly those based on graphite and molybdenum disulfide, are indispensable in extreme environments due to their excellent high-temperature resistance, wear resistance, and self-lubricating properties. Selecting the appropriate adhesive and type of lubricant can significantly enhance the operational efficiency and lifespan of equipment.
CNC Machining Services CNC Milling, Turning, and Drilling Materials such as aluminum, steel, and polymers Send your drawing files for a real-time quote.
Example: Bearing Bronze Grades, CuSn10, CuSn12Ni2, CuSn7Zn4Pb7, C93200/ SAE660, CuPb10Sn10, C93700 / SAE64, C86300, C95400, CuSn5Zn5Pb5, C83600, CuAl10Fe5Ni5
Characteristics of Solid Lubricants
Graphite:
High-Temperature Resistance: Graphite can withstand temperatures up to 450°C, and in some instances, as high as 1000°F (approximately 537°C).
Self-Lubrication: Graphite has excellent self-lubricating properties, providing lubrication through its inherent structure without the need for additional lubricants.
Environmental Adaptability: In typical atmospheric conditions, graphite can adsorb moisture and gases, enhancing its lubrication performance. Its lamellar crystal structure reduces friction between sliding surfaces, thereby minimizing wear.
Wide Applications: Graphite lubricants are used across various industrial applications, including in the food and chemical sectors, particularly where contamination from liquid lubricants must be avoided.
Molybdenum Disulfide (MoS₂)
High Load Performance: MoS₂ excels under high load and high-temperature conditions, typically operating within the temperature range of -30°C to 350°C.
Wear Resistance: The lubricating properties of MoS₂ are superior to graphite, especially under extreme pressure conditions, offering enhanced wear protection.
Cost Factors: Although MoS₂ performs better, it is relatively more expensive, necessitating a balance between application requirements and cost-effectiveness.
CNC machining supports surface treatment options： milling, turning and drilling
Adhesive Choices for Lubricants Solid lubricants often require combination with adhesives to ensure adherence to bearing surfaces. Commonly used adhesives include:
Thermoplastic Resins: Such as cellulose and acrylic resins, suitable for low-temperature applications (up to 150°C), easy to spray, and quick drying.
Thermosetting Resins: Such as phenolic and epoxy resins, which maintain good adhesion at higher temperatures (up to 600°C).
Inorganic Adhesives: Such as sodium silicate, suitable for high-temperature applications (over 750°C), but mainly used for graphite and not suitable for MoS₂.
the clearance and tolerance ranges for graphite plugged bearings. Graphite plugged bearings, or graphite self-lubricating bearings, are designed to operate without additional lubrication. The clearance in these bearings is crucial as it impacts the self-lubrication capabilities and overall performance of the bearing under various loads and temperatures.
Clearance Range
Clearance in graphite plugged bearings is generally determined based on the operating conditions and the diametrical size of the bearings:
- For smaller bearings (under 50 mm in shaft diameter), typical radial clearance might be around 0.001 to 0.002 inches (0.025 to 0.05 mm).
- For larger bearings (over 50 mm in shaft diameter), clearance might increase to 0.002 to 0.004 inches (0.05 to 0.1 mm).
Tolerance Allowance
The tolerance for graphite plugged bearings relates to the precision with which these bearings are manufactured, affecting how they fit into their housings or onto shafts:
- ISO Tolerance Classes: These bearings are commonly produced within the ISO tolerance classes of IT7 or IT8, which define the allowable limits of variation.
- Fit Type: Depending on the application, bearings may be designed for a loose fit (for easier installation or higher thermal expansion) or a tight fit (for better load support and reduced vibration).
The exact specifications can vary based on the manufacturer and the specific application requirements. If you need precise values or have a specific application in mind, consulting the manufacturer’s datasheet or technical support team would provide the most accurate guidance.
When selecting the length of solid lubricant sleeve bearings, it is critical to consider factors such as load, speed, and application type. These factors not only affect the performance of the bearings but also directly impact the stability and efficiency of the entire mechanical system. Here are some detailed design guidelines and considerations:
Length Selection
- Load and Speed: Higher loads and speeds typically require longer bearings to distribute pressure and reduce the load per unit area.
- Recommended Ratio: The ratio of bearing length to diameter is recommended to be between 1:1 and 1:2. This ratio helps balance load-bearing capacity and axial stability, preventing bearing damage due to edge loading.
- Maximum Stability: Choosing an appropriate length can reduce shaft deflection, providing greater stability, thus enhancing the reliability of the overall mechanical equipment.
Lubricant Coverage
- Design Coverage: The coverage of solid lubricant should be designed to be between 30% to 35%. This range is sufficient to ensure good lubrication performance while avoiding issues related to excessive lubricant that can cause friction and wear.
- Uniform Distribution: Lubricants should be evenly distributed on the inner surface of the bearing, ensuring sufficient lubrication throughout the bearing’s operating cycle.
Considerations
- Wall Thickness Selection: Choose the appropriate wall thickness based on the specific requirements of the application, to support the bearing’s performance under various working conditions.
- Material Selection: Material choices should be based on the working environment (such as temperature, corrosive environments, etc.), ensuring that the bearing materials can withstand specific working conditions.
- Adaptation to Actual Application: When designing, also consider potential abnormal conditions that may occur in actual applications, such as high impact loads or extreme temperatures, and choose the most suitable bearing type and material.
Through careful design and selection of appropriate parameters, solid lubricant sleeve bearings can perform excellently in various industrial applications, extending service life and reducing maintenance needs.
When designing graphite bearings, the wall thickness plays a crucial role in ensuring that the solid lubricant—whether in the form of grooved configurations, plugs, or sticks—remains securely retained within the bearing structure. The wall thickness must be adequate to support the lubrication system without compromising the mechanical integrity of the bearing. Here's a breakdown on how to calculate and consider the wall thickness for graphite bearings:
Factors Influencing Wall Thickness
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Lubricant Retention: The primary purpose of the wall thickness is to ensure that the lubricant (graphite) remains securely held. The configuration of the graphite—whether as plugs, grooves, or sticks—requires enough depth in the material to prevent the lubricant from falling out or becoming ineffective during operation.
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Bearing Load and Size: Higher loads and larger bearing sizes typically demand thicker walls to provide sufficient mechanical strength and stability.
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Manufacturing Tolerances: The process of drilling holes or creating grooves for the graphite inserts affects how much material is needed around these modifications to maintain structural integrity.
Basic Calculation Guidelines
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Minimum Wall Thickness: As a rule of thumb, the minimum wall thickness should at least be equal to the diameter of the largest hole drilled for graphite insertion. This ensures that there is enough material around each hole to prevent structural weaknesses.
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Enhanced Thickness for Load Capacity: For applications involving higher radial loads, it may be necessary to increase the wall thickness beyond the minimum. A common approach is to add 50% to 100% of the diameter of the lubricant hole to the wall thickness.
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Safety Factor: Including a safety factor (commonly ranging from 1.2 to 1.5) in the calculation can help accommodate unexpected stresses and manufacturing imperfections.
Example Calculation
Suppose you have a bearing where graphite sticks are to be inserted into holes with a diameter of 5 mm. If you are applying a safety factor of 1.2, the calculation for minimum wall thickness might look something like this:
Minimum Wall Thickness=Diameter of Hole×(1+Safety Factor)text = text times (1 + text) =5 mm×(1+0.2)= 5 , text times (1 + 0.2) =6 mm= 6 , text
This is a simplified guideline. Actual calculations may need to account for additional factors like thermal expansion, specific application requirements, and environmental conditions. Consulting with material engineers or using detailed design standards (like ASTM or ISO for bearings) is recommended to ensure reliability and safety in your specific application.
Application Areas Solid lubricated bearings have a wide range of applications, particularly in:
Nuclear and Aerospace: In nuclear radiation and vacuum environments, solid lubricants effectively reduce friction and wear.
High-Temperature Industries: In high-temperature furnaces, heavy machinery, and chemical equipment, solid lubricants provide lasting lubrication.
Self-Lubricating Bearings: These bearings, embedded with solid lubricants, operate without external lubrication, suitable for extreme and harsh environments.
