Friction couple

Brakes and clutches operate both dry and wet. In dry friction couples, the heat is removed by conduction to the surrounding air and stmctural members. Wet friction couples operate within a fluid, usually an oil, which absorbs the heat and maintains the couple at relatively low (below 200°C) temperatures. The fluid also traps the wear debris. 

There is much interest and concern for noise/vibration-free brake systems and there is much activity toward friction couples having reduced noise/vibration properties. In addition to better noise insulators, brake modifications in the form of different materials, different designs, and improved friction materials formulations and/or processes are being developed and implemented. 

The SCRF models should be useful for any of the adiabatic cases, but a more quantitative treatment would recognize at least three time scales for frictional coupling based on the three times scales for dielectric polarization,... 

During the running-up period some heat is always generated in the friction coupling as is often noticeable by formation of smoke. This is quite normal and has no importance at all. 

Ball bearings of friction coupling At least once a year Ball bearing grease... 

PMS liquids have mediocre lubricating capacities for steel-on-steel friction, although some combinations of friction couples, e.g. bronze-on-steel, brass-on-plastic, perform satisfactorily if lubricated hydrodynamically with PMS liquids. The use of PMS as liquid media in oils and lubricants compounded with various antiwear additives and dispersions, creates favourable conditions for selective adsorption of additives on friction surfaces and helps to form an antiwear film which greatly increases the pressures and slip velocities. 

These expensive carbon-carbon fiber composites are used for thermally demanding applications like aircraft and racecar brakes. Typically, both pads and rotors are made of carbon composite. These friction couples have a relatively low friction level, which is insensitive to the high temperatures experienced in operation. Friction couple components are expensive to manufacture as they are fabricated by time-consuming chemical vapor deposition techniques. Carbon-carbon systems suffer from low cold friction and are best suited for hot operation. 

Ceramic friction couples have been developed for use in race and high-performance Porsche and Mercedes... 

Fig. 4 schematically represents transfer layers that usually form on the friction and mating surfaces of friction couples. These complex layers are formed from... 

In simple terms, the objective of designing friction materials is to maintain a desirable friction level while keeping friction couple wear and noise/vibration to a minimum. 

Friction materials are often characterized in terms of friction, wear, and noise performance. However, as explained earlier, these are characteristics of the complete brake system and not of the friction couple alone. Friction material characterization techniques... 

Additionally, the higher viscosity of the organic phase makes it more likely that the diffusion resistance is predominant in the organic phase in respect to the aqueous one. A correct description is then to model diffusion inside the droplet with the Maxwell-Stefan diffusion law [39], where the chemical potential and not concentration differences represent the driving force. However, a problem up to now is to get information in respect to an exact value of the cross-diffusion coefficients. They represent the frictional coupling of the fluxes of the species involved and can only be neglected in very dilute systems. 

A friction coupling adjusted to slip at a predetermined torque to protect the rest of the system from overload. 

Material Friction Couple Total Wear (mg) Friction Coefficient... 

FIGURE 2.7 Tribological characteristics ofArmco iron-polymer material friction couple. 

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