Particle frictionally generated

Lubricants protect die and punch surfaces from wear and bum-out of the compact during sintering without objectionable effects or residues. They must have small particle size, and overcome the main share of friction generated between tool surfaces and powder particles during compaction and ejection. They must mix easily with the powder, and must not excessively impede powder flow (see Lubrication and lubricants). 

Boundary lubrication is defined by the properties of the surfaces and the lubricants—the properties other than viscosity. Surface friction generates the emission of electrons, photons, ions, neutral particles, gases (e.g., oxygen), and x-rays. According to the theme of this book, reaction of organic lubricating materials with triboemitted electrons will be considered in Section 8.6. 

Particles, however, generate friction as they migrate through liquid. If a particle is spherical and moving at a known velocity, the frictional force opposing motion is given by Stokes law ... 

Figure 3.14. Movement of particle 1 generates the motion of solvent molecules, which eases the motion of particle 2 in the same direction. Thus, the hydrodynamic interaction reduces friction.

The difference between the centrifugal force and the pressure force exerted by the rotating flow on the particle, which generates centrifugation, is balanced by the (drag-like) friction force associated with the relative radial movement of the particle with respect to the fluid. This result will be used in Chapter 17. 

Now imagine a "massive or Brownian particle, and suppose that in addition to the constant Langevin friction generated by the rapidly... 

To provide a specific example of soft-particle packing-generation methods, we describe discrete element simulations of bidisperse mixtures of frictional disks subjected to isotropic compression in 2D, implementing the Cundall-Strack model for static friction [8]. The position of the center of mass of each disk i (with mass m) obeys the equation of motion... 

Another example of a type of process where water is used is disk grinding. The rubber is ground by friction created by it being passed between two grinding wheels. Water can be added to the process to both remove heat and improve its efficiency. The particle sizes generated by this process can be down to around 500 pm, without water, and down to 250 pm, or less, with water. 

In order to define the extent of emissions from automotive brakes and clutches, a study was carried out in which specially designed wear debris collectors were built for the dmm brake, the disk brake, and the clutch of a popular U.S. vehicle (1). The vehicle was driven through various test cycles to determine the extent and type of brake emissions generated under all driving conditions. Typical original equipment and aftermarket friction materials were evaluated. Brake relines were made to simulate consumer practices. The wear debris was analyzed by a combination of optical and electron microscopy to ascertain the asbestos content and its particle size distribution. It was found that more than 99.7% of the asbestos was converted to a nonfibrous form and... 

---