Engineers selecting plain bearings for industrial machinery often face the choice between PTFE-lined composite bearings and solid bronze bushings. The coefficient of friction (CoF) is typically the first parameter compared, yet the real selection decision involves a more complex interplay of load capacity, speed limits, temperature range, and maintenance requirements. This article presents side-by-side friction data for both bearing types and explains when each offers a clear advantage.

PTFE (polytetrafluoroethylene) lined bearings consist of a steel or bronze backing, a sintered porous bronze interlayer, and a PTFE-based sliding surface. The PTFE layer may be filled with lead, graphite, MoS2, or other additives to improve wear resistance. Solid bronze bushings, in contrast, are machined from continuous cast or centrifugal cast bronze alloys such as SAE 660 (CDA 932), phosphor bronze (CDA 544), or aluminum bronze (CDA 954). The friction behavior of each type differs significantly depending on lubrication condition.

Under dry running conditions, PTFE-lined composite bearings consistently outperform solid bronze bushings. Typical CoF values for PTFE composite bearings against steel range from 0.02 to 0.10, with a running-in period during which the initial CoF may reach 0.15 before settling to a steady-state value of 0.04 to 0.08. Spyraflo, a manufacturer of PTFE-composite bronze bearings, reports a CoF range of 0.03 to 0.25 depending on load and speed, with PV ratings up to 50,000 psi x fpm. Bronze bushings running dry exhibit CoF values of 0.10 to 0.20, roughly double or triple the PTFE value. This difference is significant: a 66 percent reduction in friction coefficient translates directly into lower heat generation and reduced energy consumption.

When lubrication is introduced, the gap narrows considerably. Grease-lubricated bronze bushings operate at CoF values of 0.03 to 0.06, while oil-bath lubrication pushes the CoF down to 0.01 to 0.04. PTFE-lined bearings with marginal grease lubrication show CoF values of 0.05 to 0.15. The bronze bushing with oil bath becomes competitive or even superior in friction, but at the cost of a more complex lubrication system with seals, lines, and filters.

Load capacity tells a different story. Solid bronze bushings support static loads up to 4,000 psi for SAE 660 and up to 8,000 psi or more for aluminum bronze, with graphite-plugged versions reaching 30,000 psi for slow oscillating motion. PTFE-lined composite bearings typically handle dynamic loads of 8,000 to 14,000 psi depending on the backing material and PTFE formulation. The steel-backed PTFE bearing carries more load than the bronze-backed variant because the steel shell is stiffer, but the bronze-backed version offers better thermal conductivity and corrosion resistance.

Temperature range is another critical factor. PTFE-lined bearings perform well from minus 200°C to plus 260°C in continuous service. Above 260°C, the PTFE layer begins to soften and wear rates accelerate dramatically. Bronze bushings, particularly graphite-plugged grades, operate from minus 248°C to plus 400°C in oxidizing conditions and up to 600°C in non-oxidizing environments. For applications above 260°C, solid bronze with graphite plugs is the only viable self-lubricating option.

Speed capability favors PTFE-lined bearings. The low CoF of PTFE reduces frictional heat at higher surface speeds, allowing PV values that suit shaft velocities up to 2.0 m/s in dry operation and 5.0 m/s with marginal lubrication. Bronze bushings generally perform best at low speeds, below 0.5 m/s dry and 2.0 m/s lubricated, because their higher CoF generates more heat per unit of sliding distance.

Wear rate data from bearingface.com shows that PTFE-lined composite bearings with PTFE and MoS2 additives achieve CoF of 0.02 to 0.10 dry, while metal-polymer bearings with lubrication achieve 0.10 to 0.25. Graphite-embedded bronze bushings maintain CoF below 0.05 under heavy loads, according to bronzeoilless.com data. For phosphor bronze (Cu-Sn-P), the typical range is 0.05 to 0.10, and for sintered bronze with oil impregnation, 0.04 to 0.07.

The selection summary is clear: for dry or marginally lubricated applications at moderate temperatures, PTFE-lined bearings provide lower friction and higher speed capability. For high-load, high-temperature, or shock-load applications where lubrication can be supplied, solid bronze bushings deliver superior performance and longer service life. Engineers should evaluate the full PV diagram, not just the friction coefficient, before making the final choice.