The sealing design for industrial robot joint shafts is crucial for ensuring
long-term stable operation, especially in ±180° reciprocating motion
applications. With the increase in robot precision and load, sealing components
face greater challenges in terms of high frequency and wear resistance,
particularly as the friction between the shaft and the seal lip affects the oil
film and sealing performance. So, how can a skeleton oil seal be designed to
meet these special working conditions?
Challenges of the Working Condition and Sealing Design Requirements
In the ±180° reciprocating motion of the joint shaft, the sealing system faces frequent directional changes, which can break the lubrication film, causing the seal lip to contact the shaft surface, resulting in significant wear. This not only increases frictional torque but can also lead to heat buildup and material aging. Therefore, the sealing system must prioritize low friction and wear resistance, and actively maintain the lubrication film to extend service life and ensure sealing effectiveness.
Material Selection for Seals
Choosing the right materials for the seal is critical in this application. The primary sealing lip is typically made from PTFE composite materials, which are known for their low friction coefficient, excellent self-lubricating properties, and wear resistance—ideal for frequent directional changes. For auxiliary materials, FKM and HNBR are often used for dust lips or secondary seals, providing better sealing and temperature resistance.
For extreme temperatures or chemical exposure, FFKM is an excellent choice due to its unmatched resistance to chemicals and high temperatures, making it suitable for specific applications in industries like semiconductors and chemicals.
Seal Lip Design
For the ±180° reciprocating motion, the seal lip design needs to actively manage the lubrication interface during shaft rotation. Traditional seal lips often only provide passive sealing, but in this case, asymmetric fluid-dynamic profiles (such as Z-type or K-type) are employed to create a slight pumping effect during rotation, actively returning the leaked lubrication back into the seal chamber, achieving dynamic sealing and preventing excessive wear.
Additionally, a double-lip structure can enhance the sealing effect, where the primary lip seals the lubrication and the secondary lip prevents external contaminants from entering, providing complementary functionality.
Role of the Spring Preload System
Maintaining constant and moderate radial force is crucial in reciprocating applications. A spring preload system is essential for this. The built-in spring compensates for lip wear, ensuring consistent sealing performance throughout the service life. The spring's design must have strong fatigue resistance and chemical compatibility to avoid loosening or breaking under long-term dynamic loading.
Efficient Wear Resistance Design
Wear resistance is key to extending the service life of the sealing system.
PTFE is self-lubricating properties significantly reduce friction and wear.
Furthermore, solid lubrication coatings, such as molybdenum disulfide, can be
added to the lip surface to further enhance wear resistance.
For higher-end solutions, a rolling seal design can be adopted, utilizing rolling elements like balls to reduce sliding friction, effectively converting friction into rolling motion, significantly decreasing wear and friction.
To meet the sealing requirements for industrial robot joint shafts in ±180° reciprocating motion, the design should focus on low friction, wear-resistant materials, innovative lip designs, and efficient spring preload systems. Through comprehensive optimization, skeleton oil seals can ensure stability and reliability under high-frequency reciprocating motions, improving robot efficiency and extending service life.
