Oil seals, often referred to as rotary shaft seals or lip seals, play a critical role in preventing oil or fluid leaks in machinery. They are typically crafted from elastomers such as rubber or silicone, featuring an outer metallic casing and a sealing lip on the inner side. These seals are essential components in various industrial applications where leakage prevention is crucial for machinery integrity.
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Oil Seals (Part 2): How to select the right oil seal
In Part 1, we discussed the structure, functions, and types of oil seals. The design of machines requires careful selection of the correct oil seal based on the types and configurations that fit specific machinery and the substances to be contained.
1. Criteria for selecting oil seals
Given the diverse range of oil seal types and sizes, it is crucial to consider the following criteria when selecting a seal for your application:
- Criterion 1: The oil seal must be suitable for the operational environment and specific demands placed upon it by the machinery.
- Criterion 2: It should be easily available for replacement, ensuring efficient maintenance and inspection.
Meeting these criteria leads to reduced machine damage, minimizes the time needed for repairs, and extends overall operational longevity. Consequently, selecting the appropriate oil seal contributes to optimizing machine design economically!
2. How to select the right oil seal
When choosing an oil seal, the following priority order should generally be followed:
However, actual selection should consider historical success and areas for improvement; strict adherence to the order may not be essential.
Table 1: The order of priority for selecting oil seals
No. Examination item
1 Seal type
2 Rubber material
3 Metal case and spring material
1) Seal type
Refer to Table 2 to determine the appropriate oil seal type.
Table 2: How to select the seal type
No. Examination item
1 O.D. (outside diameter) wall material
2 Necessity of spring
3 Lip type
Seal selection example
Based on the flowcharts, the suitable oil seal type for specified requirements as per Table 3 would be either the MHSA or HMSA type shown in Table 4.
Table 3: Requirements
No. Requirements
1 Housing: Made of steel, solid design with a housing bore surface roughness of 1.8 μmRa
2 Substance to be sealed: Grease
3 Pressure: Atmospheric
Table 4: Type of selected seal
Type 1: Rubber O.D. wall, Spring required, Minor lip required.
For detailed discussions on seal types and type codes, please refer to the specified sections.
2) Rubber material
Select rubber materials based on operational temperature and compatibility with substances. Refer to Table 5 for major rubber materials and their operational ranges.
Table 5: Major rubber materials and their operational temperature ranges
Rubber Material (ASTM code) Grade Features Operational temperature range (°C) Compatibility with fluids
Nitrile rubber (NBR) Standard type with good abrasion resistance-Oil, Petroleum, and Chemicals
Silicone rubber (VMQ) Wide operational temperature range with good abrasion resistance
3) Metal case and spring material
Select the metal case and spring materials according to the chemical substance being sealed. Table 6 provides this information.
Table 6: Selection of metal case and spring materials
Substance to be sealed: Oil, Grease, Water, Seawater-Recommended materials include cold-rolled carbon steel or stainless steel.
3. Shaft and housing design
Effective sealing performance relies on a well-designed shaft and housing. The following considerations are essential:
1) Shaft design
Table 7: Shaft design checklist
1 Material: Use carbon steel, stainless steel for robust performance.
2 Hardness: Minimum shaft hardness of 30 HRC for general and up to 60 HRC for severe conditions needs to be ensured.
3 Shaft diameter tolerance: Should comply with h8 tolerance specifications.
2) Housing design
Table 8: Housing design checklist
1 Material: Steel or cast iron is preferred; aluminum requires special consideration due to thermal expansion differences.
2 Bore diameter tolerance: Should align with standard specifications H7 or H8.
4. Seal characteristics
Factors affecting oil seal performance extend beyond the type and material used. Operating conditions, total eccentricity, rotational speeds, and nature of the substances should also be considered for optimal operation.
5. Conclusion
It is vital to ensure that your selected oil seal aligns with the operational requirements and is readily available for replacement. This way, you can enhance sealing performance and ultimately the lifespan of your machinery.
If you have any technical questions or thoughts regarding oil seals, feel free to reach out using the provided contact form.
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