The bearing components can be located to the installation by bolting, tack-welding, full welding or mortar embedment, and the appropriate type of bearing should be chosen according to the installation method. The PTFE should be adequately protected against weld spatter, paint spray, metal swarf etc, during installation.
In a wide range of applications, PTFE Slide bearings are superior to conventional expansion plates, rollers and rocker arm type supports. They support petrochemical plant, heavy machinery, pipelines, buildings and bridge girders; they accommodate expansion, contraction and other reciprocating motions of any structure that moves as a result of thermal, seismic or differential forces.
Bearings for such applications must operate at high loads and low speeds, and it is under just these conditions that the self-lubricating properties of PTFE are at maximum. This factor, together with its no stick-slip and anti-weathering characteristics, is the principle reason why PTFE has proved to be so successful as a slide bearing material.
Advantages
1 The simplicity of the bearing design and its ease of fabrication and installation make the unit cost efficient.2 The costs of a construction can be reduced by designing for expansion rather than strain.3 Coefficient of friction over the bearing surface remains constant, even under worst case conditions.4 The bearings are maintenance free – PTFE is inherently self-lubricating, while dirt particles are absorbed into the material. Only simple protection is required against the significant ingress of dirt.
Coefficients of Friction
The coefficient of friction of PTFE materials is dependant on many variable, including pressure, sliding velocity and temperature. Opinion is divided about the effect of some variables, although it is agreed that high pressure and low velocities favour low friction.
The coefficient is less than that of any other solid engineering material. It has been variously reported from 0.02 to 0.2, but this depends on surface preparation and the test method. The load/friction chart shows the effect of the load.
In general, the coefficient of friction between the mating surface and the PTFE slide bearing pad will be at a minimum when the stress in the PTFE is at a maximum (consistent with acceptable limits of creep), the bearing is made from unfilled PTFE, and the finish of the mating surface is highly polished.
In addition, one of the most important frictional characteristics of PTFE is the absence of ‘stick-slip’, because unlike all other conventional bearings, the static friction of PTFE is equal to or only marginally higher than the dynamic friction.
Post time: Sep-01-2020