What Helps Skeleton Oil Seals for Robot Shaft Systems Prevent Lip Shrinkage at Low Temperatures?

Number of hits：342026-01-09 15:14:54　

In low-temperature operating conditions, robot shaft sealing systems are often required to run continuously for extended periods. Many engineering cases show that skeleton oil seals performing reliably at ambient temperatures may exhibit oil leakage, increased start-stop wear, or unstable sealing once exposed to low-temperature environments. In most cases, the root cause is not improper assembly, but the loss of effective lip interference compensation under low-temperature conditions.

This article systematically analyzes how low temperature affects lip interference from multiple perspectives and proposes practical design optimization strategies.

Impact of Low Temperature on Lip Interference

The sealing performance of a skeleton oil seal relies on the ability of the lip to apply stable contact pressure to the shaft surface. Under low-temperature conditions, this balance is disrupted by several interacting factors.

First, elastomer materials experience a significant increase in modulus at low temperatures, becoming stiffer and less compliant. As a result, the seal lip loses its ability to conform closely to the shaft surface. Second, rubber materials, metal cases, and shafts have different coefficients of thermal expansion. As temperature decreases, inconsistent thermal contraction alters the effective interference, reducing the actual contact pressure at the sealing interface. Third, lubricant viscosity increases significantly at low temperatures, making it difficult to establish a stable lubricating film during start-up. This causes the contact state between the lip and shaft to deteriorate into boundary or even dry friction, accelerating wear.

It is important to note that low-temperature seal failure is not simply a matter of insufficient initial interference. Rather, it is the inability of the interference to continuously deliver effective contact pressure that leads to a systematic degradation of sealing performance.

Interference Selection and Optimization Guidelines

Interference is a parameter that requires precise optimization. Some studies recommend controlling lip interference within a range of 0.35 mm to 0.55 mm to balance sealing capability and service life. For certain high-load or high-pressure applications, values around 0.8 mm have also been proposed.

These findings indicate that interference values must be determined based on specific operating conditions, including pressure, speed, material properties, and shaft diameter. Simulation and experimental validation are essential. Blindly increasing interference does not guarantee better sealing and may introduce new risks.

Material Selection Focused on Low-Temperature Resilience

In low-temperature applications, the ability of the seal lip to maintain effective interference depends primarily on the elastomer’s low-temperature elasticity and rebound capability.

Fluorosilicone rubber (FVMQ), for example, maintains good flexibility and elastic recovery even in extremely cold environments, while offering moderate oil resistance. It is suitable for collaborative robot joints or cold-region transmission shafts where high compliance is required. Low-temperature formulations of fluoroelastomer (FKM) improve rebound performance while retaining oil resistance and aging resistance, making them suitable for medium-to-low temperature applications with higher durability requirements. Hydrogenated nitrile rubber (HNBR) offers a balanced combination of low-temperature elasticity and mechanical strength, making it suitable for moderately cold environments with impact loads or high durability demands, such as outdoor equipment and construction machinery.

Therefore, the key criterion in material selection is not simply whether the material is “cold-resistant,” but whether it can still recover elastically at low temperatures.

Spring Systems as the Primary Compensation Mechanism

In low-temperature environments, the elasticity of the rubber lip alone is often insufficient to maintain sealing contact pressure. Under these conditions, the spring-loaded structure becomes the core compensation mechanism.

An effective spring system should provide sufficient working travel to maintain contact pressure after elastomer stiffening. Its force-displacement characteristics should remain stable within the low-temperature range, avoiding loss of preload due to temperature effects. Additionally, the spring and lip geometry should work together to share the contact load, improving overall adaptability.

In extremely cold environments, lip seals with radial garter springs are commonly used, further demonstrating the critical role of springs as the primary compensation element under low-temperature conditions.

Structural Design Is More Effective Than Simply Increasing Interference

Increasing initial interference indiscriminately often leads to higher friction and accelerated wear during cold start-up. A more effective approach is to improve structural elasticity so the seal lip can better adapt to temperature changes.

Reducing lip cross-section thickness lowers bending stiffness and improves compliance. Extending the elastic arm length enhances tracking capability and reduces localized stress concentration. Optimizing the contact angle helps distribute contact pressure more evenly, minimizing edge wear.

The core design philosophy is to allow the lip to respond dynamically to temperature changes, rather than passively enduring material property degradation.

Shaft Surface Condition as a Critical System Factor

At low temperatures, lubricant films are more difficult to establish, making shaft surface condition a decisive factor in sealing performance.

Optimizing shaft surface roughness, typically within Ra 0.2 to 0.4 micrometers, helps balance oil retention and sealing conformity. Introducing micro-textured surfaces, such as cross-hatched patterns or micro-grooves, can improve lubrication during start-stop cycles and enhance sealing stability. At the same time, surface defects such as flaking of hardened layers or micro-cracks must be avoided, as they can cause premature lip wear or damage.

System-Level Thermal Matching and Coordinated Design

Low-temperature sealing stability cannot be achieved through lip design alone. A system-level approach to thermal matching and tolerance control is required.

This includes coordinating thermal contraction behavior among the shaft, metal case, and spring; accounting for tolerance amplification at low temperatures; and selecting lubricants with appropriate low-temperature flow and adhesion characteristics. Only through coordinated thermomechanical design at the system level can effective lip interference be maintained under low-temperature conditions.

In low-temperature robot shaft applications, there is no single universal solution for compensating lip interference in skeleton oil seals.

Rather than pursuing larger interference values, greater attention should be paid to designing sealing structures that can continuously adapt to temperature variations. This approach represents a more robust and sustainable direction for low-temperature sealing design.