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Rod end bearings / Spherical bearings -Self Lubricating Liners

Spherical and Rod End bearings with PTFE Liner were first introduced in the 1950s. As it is referred "self lubricating liners", bearings equipped with PTFE Liner don't require any grease charging at all, since the PTFE Liner itself is self lubricating. In addition, PTFE Liner has excellent abrasion resistance.


PTFE

PTFE stands for Poly Tetra Fluoro Ethylene. PTFE Resin is chemically stable and has good heat resistance and high insulation properties. It performs with excellent friction coefficient of 0.03~0.05 under 288 °C , however tensile strength is relatively low (34N / mm2 { 3.5kgf / mm2 }). Therefore, to reinforce its performance, PTFE Liners are utilized which have a tensile strength of 343N / mm2 { 35kgf / mm2 }.
PTFE Liners have a woven textile backing (Glassfibers or other synthetic fibers) with phenolic resin impregnated. With thermosetting bonding agent applied on reverse side, PTFE Liners are bonded with base metal. This process is called CURING. Cured PTFE Liners can accept up to 482N / mm2 { 49.2kgf / mm2 } under static load and 220~275N / mm2 {22.5~28.1kgf / mm2} under slow fluctuation velocity. The bonding force can bear minimum of 3.5N / cm { 2lbs / inch }.
Therefore the PTFE lined bearings advance Metal/Metal type especially where static load is applied.

* Requirement of AS specification.


Summary of Properties
  1. Friction coefficient is 0.03~0.15. As shown in Figure 1 & 2, the coefficient decreases with load but increases under low temperature.
  2. Under the influence of greases, oil and moisture, PTFE Liners may swell moderately. This can cause slightly high torque before the use of bearing, however load capacity is not affected. Acid or alkaline atmosphere may influence Phenolic resin and reduce its performance quality. In such cases, seals can be considered as an effective prevention.
  3. During the first 500~1000 cycles, abrasion may occur. After the first abrasion, however, wear rate becomes quite nominal. AS specification requires that the wear rate shall be under 0.152mm. Depending on customer requirements, this figure may slightly differ, but in general, it is set that 0.150mm is the acceptable maximum wear.

For applications where life is particularly critical, wear can be reduced by hard chrome plating of balls. The efficiency of such plating has been proven by several examinations conducted inside the company. Please consult our engineers if there are any particular applications. Besides Table 4 below, NMB can provide other liners as well.


Figure 1:
Load & Friction coefficient

Figure 2:
Temperature & Friction coefficient

Table 4 : Characteristics of Principle Liner Systems
 
X-1118
X-1276 X-1276F X-1820 L-1390
MIL、SAE
Spec
MIL-B-8942     AS81820  
Backing
Material
Glass
Fiber
Polyester Polyester Nylon Glass
Fiber
Thickness 0.25 ~ 0.29mm 0.30 ~ 0.34mm 0.34 ~ 0.38mm 0.34 ~ 0.38mm 0.30 ~ 0.36mm
Temperature
range
-54 ~ +121°C -54 ~ +121°C -54 ~ +121°C -54 ~ +163°C -54 ~ +329°C
Static Load
Capacity
482N/mm2
{49.2kgf/mm2}
482N/mm2
{49.2kgf/mm2}
482N/mm2
{49.2kgf/mm2}
541N/mm2
{55.2kgf/mm2}
482N/mm2
{49.2kgf/mm2}
Dynamic
Load
Capacity
220N/mm2
{22.5kgf/mm2}
220N/mm2
{22.5kgf/mm2}
220N/mm2
{22.5kgf/mm2}
275N/mm2
{28.1kgf/mm2}
* 1
Fiction
coefficient
0.03 ~ 0.10 0.03 ~ 0.10 0.05 ~ 0.15 0.05 ~ 0.15 0.03 ~ 0.10
Characteristics
Application
Most widely utilized liner Strong under oscillating load
Suitable for racing cars
High dynamic load capacity Strong under high temperature High dynamic load capacity Strong under high temperature, Suitable for jet engine.

* 1 Depending on use conditions.
* 2 Depending on the LINER types.

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