The Development Of Grinding Equipment For The Pin With A Spherical Head And The Research On Tribological And Contacting Mechanism Of Sphere

The spherical sample can be easily controlled in contacting state during tribological testing in laboratory, but it is difficult to make. So, there is not enough variety of spheres to chose and only few kinds of spheres are used in tribological testing for a long time. This problem exists for many years and is not solved so far. In addition, the research before on contacting surfaces neglects the contribution of changes in size, deformation, friction and wear of single micro-spherical model, which restricts the research on tribological contacting model.In this paper the key technology of "sway and revolving method" -a new method used to grind high-quality sphere- is studied. Besides, the grinding equipment for the pin with a spherical head is developed and the technique of making the pin with a spherical head is discussed. Many kinds of pin-samples of different materials with different radiuses are made by the equipment, and the relations between the radiuses of the sphere, the load, the contacting stress, and the friction coefficient are investigated and the contacting mechanism of tribological micro-spherical model is researched with the pin-samples of spherical head.Main innovations and results are described as below.Ⅰ. A new working method for pin with a spherical head- "sway and revolving method" to grind high-quality sphere- is development, and two important conditions which are necessary to form sphere are found.Ⅱ. A new kind of equipment to make the pin with a spherical head is built and patented in China (patent No: 200320116160.X). Many kinds of materials can be made into pins of which Ra=90~250nm by the equipment.Ⅲ. A new measuring tool is made that can be used in measuring radius of a spherical head.Ⅳ. The relationship between radius of the sphere, contacting stress, and friction coefficient is investigated and the contacting mechanism of tribological micro-spherical model is studied. Some conclusions are obtained:(1) If a sphere contacts with a plane, there is a fitted formula of contacting area Sd with radius of the sphere R and load W shown as below when elastic deformation and plastic deformation exist at the same time:Sd=0.181R0.535W0.463(2) When the pin with a spherical head made of UHMWPE contacts and slides on the disk made of steel, the friction coefficient increases as the radius of the sphere or the contacting stress goes up, and the friction coefficient decreases as the load goes down. When the contacting stress is more than the σs of the material, the friction coefficient tends to become a constant.(3) The relation of the friction coefficient/and the average contacting stress pd is shown belowf = 17.445pd-2.1607+0.14 which looks like another formula which derives from classic "tribological two items...