DX/SF-2 Boundary-Lubricated Bearing

1. Introduction

DX/SF-2 is a metal-polymer composite plain bearing for boundary lubrication. 
 

Material structure (4 layers, outside to inside):

Layer	Material	Thickness	Function

Sliding layer	Modified POM (with PTFE/fiber filler)	0.30–0.50 mm	Low friction, wear resistance; spiral oil indents on surface
Intermediate layer	Sintered spherical bronze	0.20–0.35 mm	Load capacity, heat dissipation, bonding strength
Backing	Low-carbon steel	0.4–2.2 mm	Overall mechanical strength
Plating	Tin / copper plating	0.005–0.008 mm	Corrosion protection

Working principle: The oil indents are pre-filled with grease (lithium-based or silicone grease) at assembly; during operation the grease slowly migrates to the sliding surface and forms a boundary lubricating film. It is designed for conditions where a hydrodynamic film cannot form - high load and low speed, oscillating motion, and frequent start-stop under load.

Lead-free variants: SF-2Y / SF-2S share the same structure and performance as SF-2, for applications with environmental requirements.
 

2. Performance

Property	Value

Max. load P	Static 250 N/mm²; dynamic 140 N/mm²; rotating/oscillating 70 N/mm²
Max. sliding speed V	2.5 m/s (grease); >2 m/s (continuous oil supply)
Max. PV value	2.8 N/mm²·m/s (grease); up to 22 N/mm²·m/s (oil)
Coefficient of friction μ	0.05–0.25 (as low as 0.06–0.12 with good lubrication)
Operating temperature	-40°C ~ +130°C
Thermal conductivity	4 W/(m·K)
Coefficient of thermal expansion	11×10⁻⁶/K (close to steel)

Key features:

High load capacity, good impact resistance and excellent wear resistance;

Long maintenance-free service under boundary lubrication; re-greasing during service significantly extends life;

Even if grease is temporarily depleted, the POM layer retains self-lubricating properties and will not seize instantly;

The POM sliding layer has machining allowance and can be reamed/bored after press-fitting for a precise fit;

Shaft-friendly: does not score or damage the shaft surface.

Mating shaft requirements: surface hardness >200 HB (>350 HB recommended for longer life); surface roughness Ra ≤ 0.4 μm.

3. Applications

Suitable for normal-temperature, low-speed, medium-to-heavy load positions where an oil film is hard to form or re-lubrication is difficult:

Automotive: chassis bushings, door hinges, pedal mechanisms, seat adjusters, steering joints, motorcycle shock absorbers

Construction machinery: bulldozers, winches, loader articulation points, cranes and aerial work platforms

Metallurgy & mining: steel rolling equipment, forging and press machines, mining machinery, continuous casting machines

Hydraulics & pneumatics: hydraulic cylinder guide sleeves, hydraulic motors, plunger pump oscillating parts, pneumatic components

Agriculture & water conservancy: farm machinery joints, water conservancy equipment

Textile & printing/dyeing: dyeing machines and imported textile equipment (lead-free SF-2Y preferred)

4. Q&A

Q1: What is the relationship between DX and SF-2? A: They are the same product under two names. DX is the registered trade name of INA/Schaeffler; SF-2 is the common Chinese industry designation. Structure, dimension series and performance are identical and interchangeable.

Q2: Can SF-2 run completely dry? A: Not recommended. SF-2 is designed for boundary (grease) lubrication. Under fully dry running its PV limit and wear resistance drop significantly. For long-term dry operation, choose SF-1 instead.

Q3: Is greasing mandatory at assembly? A: Yes. The oil indents must be fully filled with grease (lithium-based or silicone grease) - this is the precondition for its long maintenance-free service life.

Q4: What is the difference between SF-1 and SF-2? A: SF-1 has a PTFE sliding layer for dry/self-lubricated operation; SF-2 has a modified POM layer with oil indents for grease-lubricated boundary conditions, with higher load capacity.

 

Hot Tags: DX/SF-2 Boundary-Lubricated Bearing,Self Lubricating Bearing