ASTM G194-08(2013)

5.1 Rolling friction like sliding friction depends upon many factors. It is a system effect that involves the nature of the rolling surface and the counterface. The sliding friction force (F) is usually considered to be the sum of forces arising from deformations of surface features (F_s), from attractive forces (atomic, molecular, etc.) at contact points (F_a) and force from interaction of films and particulates on the rubbing surfaces (F_f):


The rolling friction force includes these force contributions plus effects from the relative stiffness of the contacting surfaces, the diameter (curvature) of the spherical shape (ball, orange, etc.) and other factors. Because there are so many factors involved in a rolling tribosystem, rolling resistance can best be quantified by an actual test of the sphere of interest on the intended counterface, as in this test method.

5.2 There are countless applications where it is important to quantify the rolling characteristics of a particular spherical shape on a particular surface. The interlaboratory tests conducted for this test method were performed on hardened steel balls like those used in ball bearings. This test method could be used to assess the effect of different counterface surfaces on the rolling characteristics of balls for ball bearings. Conversely, it could be used as a quality control test on balls. Surface imperfections/defects/films, etc. on the balls can affect how they roll: the distance traveled on a common counterface.

5.3 Industrial applications of this test method can include assessing conveying surfaces for spherical or nearly special parts: check valve balls, cabinet knobs, Christmas ornaments, toilet floats, etc. Many medical devices use special shapes where rolling characteristics are a consideration. Similarly, many pharmaceutical products (pills) are spherical or nearly spherical in shape, and this test method can be used to assess rolling characteristics for conveying or other reasons such as size (mass) check.

5.4 Rolling friction of spherical shapes can be a consideration in countless sports (soccer, golf, lacrosse, etc.) and game applications (billiards, bocce, toys, etc.). This test method can be used to rank the rolling resistance of different ball compositions, masses, shapes, surface textures, design, stiffness, etc. Similarly, the test method can be used to assess the ease of rolling of balls on different playing or game surfaces.

5.5 This test method is very applicable to spherical or mostly spherical food products. For example, it is common to use rolling distance of apples, citrus, nuts, etc. to classify them by size for marketing. They are rolled down an angled surface and the rolling distance becomes a function of size (mass/diameter). This test method can be used to assess the suitability of various rolling surfaces (carpet, metal, wood, etc.) for suitability in classification equipment. It could also be used for food conveyance on spherical-shaped processed foods (gumballs, hard candy, meatballs, etc.)

5.6 Finally, this test method can be a valuable teaching tool for physics and tribology students. The equipment is simple, low cost and student proof. It can be used to demonstrate the concept of rolling friction and the factors that affect it.

1.1 This test method covers the use of an angled launch ramp to initiate rolling of a sphere or nearly spherical shape on a flat horizontal surface to determine the rolling friction characteristics of a given spherical shape on a given surface.