Robot Shaft Skeleton Oil Seals for Reliable Low Temperature Operation

Robotic shaft seals often operate for long periods in low-temperature
environments. Many engineering cases show that oil seals performing reliably
at room temperature may exhibit leakage, increased start–stop wear, and
unstable sealing behavior once exposed to low temperatures. The root cause
is rarely assembly-related; instead, the lip interference loses its ability
to provide effective compensating force under low-temperature conditions.

This article analyzes how low temperatures affect lip interference from
multiple perspectives and proposes feasible design optimization strategies.

1. How Low Temperature Affects Lip Interference

The sealing performance of a metal-cased oil seal depends on the lip
maintaining stable contact pressure against the shaft surface. In low-
temperature environments, this balance is disrupted by several mechanisms:

Increased rubber modulus: Rubber becomes stiffer at low temperatures,
reducing lip flexibility and making it harder to conform to the shaft
surface.

Differential thermal contraction: Rubber, metal casing, and shaft materials
shrink at different rates, altering the effective interference.

Higher lubricant viscosity: Thickened lubricant makes it difficult to form a
stable oil film during startup, increasing the likelihood of boundary or
even dry friction, which accelerates wear.

It is important to emphasize that low-temperature seal failure is not simply
a matter of “insufficient interference.” Rather, the interference can no
longer deliver sustained, effective contact pressure, leading to systemic
degradation of sealing performance.

2. Selecting and Optimizing Interference

Interference must be carefully optimized. Some studies recommend a range of
0.35–0.55 mm to balance sealing capability and service life. For high-load
or high-pressure applications, values around 0.8 mm may be more appropriate.

This highlights that interference should be determined based on operating
conditions (pressure, speed), material properties, shaft diameter, and
validated through simulation or testing—not by blindly increasing the
interference.

3. Material Selection: Low-Temperature Elastic Recovery as the Core
Criterion

Whether the lip can maintain effective interference at low temperatures
depends primarily on the rubber’s elasticity and rebound behavior.

FVMQ (fluorosilicone): Maintains excellent flexibility and elastic recovery
in extreme cold while offering moderate oil resistance. Suitable for
collaborative robots or cold-region drive shafts requiring high compliance.

Low-temperature FKM: Retains oil and aging resistance while improving low-
temperature rebound. Ideal for medium-to-low temperature applications
requiring long service life and chemical compatibility.

HNBR: Balances low-temperature elasticity with mechanical strength, making
it suitable for outdoor equipment or machinery subjected to impact loads and
durability demands.

Thus, the key question is not “Is the material cold-resistant?” but “Can
it still rebound at low temperatures?”

4. Spring Systems: The Primary Compensation Mechanism in Low Temperatures

In low-temperature environments, rubber elasticity alone is insufficient to
maintain sealing pressure. A spring-loaded structure becomes essential.

An effective spring system should:

Provide adequate working stroke to compensate for rubber stiffening

Maintain stable force output across the low-temperature range

Work synergistically with the lip geometry to distribute contact pressure

In extreme low-temperature applications, seals with radial garter springs
are commonly used, underscoring the spring’s role as the core compensating
element.

5. Structural Design Matters More Than Increasing Interference

Simply increasing initial interference often leads to higher friction and
wear during low-temperature startup. A more effective approach is to enhance
structural compliance so the lip can adapt to temperature changes.

Examples include:

Reducing lip cross-section thickness to lower bending stiffness

Extending the elastic arm to improve followability and reduce stress
concentration

Optimizing contact angle to achieve more uniform pressure distribution and
reduce edge wear

The design goal is to ensure the lip can “move with the temperature,”
rather than passively suffer from material performance loss.

6. Shaft Surface Condition: A Critical System-Level Factor

At low temperatures, oil film formation becomes more difficult, making shaft
surface condition even more influential.

Optimized roughness (Ra 0.2–0.4 μm): Balances oil retention and lip
conformity

Micro-texturing (cross-hatch or micro-grooves): Improves start–stop
lubrication and sealing stability

Avoiding surface defects: Prevents early lip wear or scratching

7. System-Level Thermal Matching and Tolerance Coordination

Low-temperature sealing stability requires system-level coordination, not
just lip design.

Key considerations include:

Thermal contraction compatibility among shaft, casing, and spring

Amplification of assembly tolerances at low temperatures

Lubricant flow and adhesion characteristics in cold environments

Only through thermal and mechanical synergy at the system level can the lip
maintain effective interference throughout temperature fluctuations.

There is no single “correct” interference value for low-temperature
robotic shaft applications. Instead of pursuing larger interference,
designers should focus on enabling the seal structure to continuously adapt
to temperature changes. This system-oriented approach is far more meaningful
for achieving reliable low-temperature sealing performance.

Minimum Order: 1000 pieces

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