Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/468007
www.machinerylubrication.com | January - February 2015 | 37 tion depth is measured. Most metals are tested using the "C" scale, which employs a diamond tip to aid in the indenting process. The higher the number in the Rockwell scale, the harder the substance. Vickers Hardness Like the Rockwell scale, the Vickers hardness test uses a diamond tip and relies on indenting a surface to measure how hard it is. The higher the value, the harder the material. However, the measurement is a little different. While the Rockwell scale measures the indention depth, the Vickers test involves locating the indention and comparing it with the force required to achieve it. Once this ratio is determined, you are left with a measurement of the material's hardness. Mohs Hardness The Mohs hardness scale is a much older method used primarily by jewelers and those who are concerned with minerals. It was based on a scale of 1 to 10, with diamond being at the top (the 10 value). Materials were tested against each other, and if one scratched the other, it would be given a higher value. For instance, gypsum can scratch talc; there- fore, gypsum would have a higher Mohs value than talc. Since diamond scratches ever ything, it was given the highest value. The Mohs scale is easy to interpret, but it lacks the certainty of the other tests. The difference between a 5 and a 6 on the Mohs scale cannot truly be determined, whereas the hardness differences on the Rockwell and Vickers scales are much more tangible. Applications Most bearings are created using a type of chrome steel. Although there are many variations of this material, the majority come in at approximately 60 on the Rock- well hardness scale (848 on the Vickers hardness scale). In contrast, quartz has a Vickers hardness of approximately 1,200 (7 ML PARTICLE TYPE SOURCE TYPICAL SPECIFIC GRAVITY MOHS HARDNESS* GENERAL APPEARANCE Burrs and machining swarf B 6 – 9 3 - 7 Curls, spirals Grindings B,I 6 – 9 3 - 7 Curls, chunks, chips Abrasives B,I 3 – 6 7 - 9 Sharp-edged chips Floor dust B,I 1 - 5 2 - 8 Chips, flakes, chunks Road Dust (mostly silica) I 2 - 6 2 - 8 Rounded chunks Mill scale I 5 NA Flakes, tree bark appearance Coal dust I 1.3 – 1.5 NA Black, shiny flakes Ore dust I Various Various Irregular-shaped chunks Wood Pulp I 0.1 – 1.3 1.5 - 3 Fibrous RR ballast dust (limestone) I 2.68 – 2.8 5 – 9 Chips and chunks Quarry dust (limestone) I 2.68 – 2.8 5 – 9 Chips and chunks Foundry dust I 2.65 7 Chips and chunks Fibers I, G, B Various Various Fibrous Slag particles (blast furnace) I, G, B 2.65 7 Silica, sharp edges, vitreous Aluminum oxides I, G, B NA 9 Crystals, colorless Red iron oxides (rust) I, G, B 2.4 – 3.6 5 – 6 Red-orange crystals Black iron oxides (magnitite) I, G, B 4 – 5.2 5 – 6 Black/bluish chunks Copper oxides G, B 6.4 3.5 – 4 Small, shapeless Tool steel G, B 7 – 8 6 – 7 Various shapes Forged steel G, B 7 – 8 4 – 5 Various shapes Cast iron G, B 6.7 – 7.9 3 – 5 Granular or flake-like Mild steel G, B 7 – 8 3 Various shapes Alloys of copper, bronze G, B 7.4 – 8.9 1 – 4 Various shapes Alloys of aluminum G, B 2.5 – 3 1 – 3 Various shapes Babbitt particles G 7.5 – 10.5 1 Various shapes, gray Soot G 1.7 – 2.0 NA Vitreous, brown or black INGRESSION SOURCES B = Built in during manufacture or repair I = Ingested from the atmosphere G = Generated from within the machine NA = Not available Aluminum Oxide Quarry Dust Road Dust Tool Steel Rust Forged Steel Mild Steel Bronze Aluminum Babbitt INCREASING HARDNESS *MOHS HARDNESS SCALE Scale 1-10 Diamond = 10 Fingernail = 1