In robotic shaft sealing applications, low temperature is rarely an occasional condition. For many systems—such as outdoor robots, cold-region logistics equipment, or industrial manipulators—skeleton oil seals (radial shaft seal) must operate continuously in sub-zero environments.
It is under these conditions that problems typically emerge. Seals that perform consistently at room temperature may begin to leak, wear rapidly during start-up, or show abnormal friction behavior once temperatures drop.
In many cases, the instinctive reaction is to question installation quality or nominal interference values. However, practical experience across multiple projects shows that the real issue lies elsewhere:
lip interference loses its effective compensating capability at low
temperature.
Why Does Interference Lose Its Effectiveness in Cold Conditions?
Lip interference is usually defined under ambient conditions. When temperature decreases, the mechanical behavior of the sealing system changes in several ways.
First, elastomers stiffen. As temperature drops, rubber modulus increases and elastic recovery diminishes, reducing the contact pressure generated by the lip.
Second, different materials contract at different rates. Elastomers, metal cases, and shafts respond differently to temperature change, altering the actual interference and contact force during operation.
Finally, lubrication conditions deteriorate. Higher lubricant viscosity at low temperature delays oil film formation during start-up, increasing the likelihood of boundary friction and accelerating wear.
As a result, nominal interference may still exist, but effective sealing pressure does not.
Why Increasing Interference Is Not the Right Solution
Simply increasing interference is a common but risky approach.
Excessive interference raises friction torque during start-up, accelerates lip wear, and may even affect actuator precision in robotic systems. In low-temperature environments, this strategy often creates more problems than it solves.
Effective compensation is not about larger interference values, but about maintaining stable contact pressure over temperature changes.
Material Selection: The First Layer of Compensation
In low-temperature applications, material selection should focus on elastic recovery rather than temperature rating alone.
Fluorosilicone rubber (FVMQ) maintains flexibility at very low temperatures and is suitable for robot joints requiring responsive sealing behavior.
Low-temperature formulated FKM provides a balance between chemical resistance and low-temperature rebound, making it suitable for complex industrial environments.
Hydrogenated nitrile rubber (HNBR) combines moderate low-temperature elasticity with higher mechanical strength, ideal for shafts subjected to load variation or impact.
The Spring: From Supporting Role to Primary Contributor
As elastomer stiffness increases, the spring becomes the primary source of contact force.
Spring preload, effective stroke, and low-temperature force stability directly determine whether the seal can maintain contact under cold conditions.
In low-temperature shaft sealing, the spring is no longer a secondary element—it becomes a core functional component.
Structural Design: Allowing the Lip to Adapt
Rather than forcing higher initial pressure, structural optimization focuses on adaptability:
Reduced lip cross-sections help limit stiffness growth at low temperature;
Longer elastic arms improve tracking capability;
Optimized contact angles distribute pressure more evenly and reduce localized wear.
The objective is not resistance, but responsiveness.
A System-Level Perspective
Low-temperature sealing reliability cannot be achieved through component optimization alone.
Shaft surface condition, tolerance changes under thermal contraction, and lubricant flow behavior all influence how interference performs in practice.
Only by addressing these factors at the system level can interference
compensation remain effective.
Low-temperature sealing failure is rarely caused by insufficient nominal
interference. The real challenge is sustaining effective contact pressure as
conditions change. Coordinated optimization of material, structure, spring
design, and system behavior is the foundation of reliable robotic shaft sealing
in cold environments.
