FRICTION MATERIALS

A materials ability to absorb total energy or heat is a key factor in determining its durability and suitability in specific applications. When energy capacity is exceeded, material breakdown and thermal failure begin. The term “energy capacity” refers to both the rate of energy absorption (i.e., power absorption) and the total energy or heat to which the material is exposed (including thermal stability).

The sustained temperature which a friction material can withstand is determined by binders and other materials which form the continuous matrix of the material. Sintered metal, for example, can withstand temperatures well above those at which cooling fluid will become thermally unstable. These materials are often selected because of their high thermal stability. On the other hand, thermal breakdown in many organic paper materials typically starts at 175 degrees Celsius.


Paper Materials:
Versatile Performers


Paper materials offer the widest range of performance features available in any wet friction material. For example, high dynamic friction and close static-to-dynamic ratio make paper materials ideal for applications where smooth, chatter-free performance is essential. Paper friction materials—sometimes called “organic” materials— are blends of fibers and fillers which are formulated using paper making processes. These compounds are mixed with water, then rolled and dried to form a continuous sheet of material. Paper materials may be formulated to offer one or more of the following advantages:

      • lowest cost for high volume production
      • high dynamic friction
      • high static friction
      • low static-to-dynamic ratio
      • high power absorption capacity
      • ability to withstand high compressive loads
      • good thermal stability
      • good durability
      • adaptable to rough mating surfaces

 

Elastomeric Materials:
Maximum Energy & Power Absorption Capacity

Elastomeric wet friction materials were developed in the mid-1970’s to provide high power absorption capability for high speed/high energy powershift applications. Consisting of rubber, inorganic fibers, friction particles and lubricants, this offers superior resiliency and excellent strength. Good conformity with mating surfaces means pressure, energy and power loads are uniformly distributed to eliminate “hot spotting” and maximize total energy and power absorption.

 

Sintered Metal Materials:
Durability for High-temperature Applications

Sintered metal materials are compacted mixtures of metallic powders—primarily copper—and friction modifiers which are sintered at temperatures In excess of 600°F. High metallic content enables these materials to withstand elevated operating temperatures without thermal decomposition. The thermal conductivity of sintered metal allows it to become part of the total clutch heat sink. This feature is particularly important for applications with low oil flow or where oil flow may be periodically interrupted. Although applications are limited and highly specialized, sintered metal friction materials are sometimes used without oil or “dry.” Often preferred for the “added” safety they bring to an application, sintered metal materials can survive thermal abuse and offer long product life. These features have led to wide acceptance in heavy duty industrial and military applications such as powershift transmissions, steer clutches and steer brakes. Sintered bronze brake linings have helped P-51 Mustang fighter planes land safely and sintered iron racing clutches have propelled top fuel dragsters a quarter mile in 5 seconds.