Maintenance Technology May 2015 - (Page 27)

COVER STORY ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Budget Application (radial, axial and planular) Load Speed Space Clearance and fit Length of machine warranty Bearing reliability specification Lubrication entry design and method Expected operating conditions When a machine goes into service, the reliability baton passes to the end-user maintenance department that must work with the engineer's ﬁnal design and an often-vague machine operations and maintenance (O&M) instruction manual that rarely spells out good lubrication instructions. Many maintenance planners will recognize the catch-all instruction "lubricate as necessary," placing responsibility on the end-user to develop a lubrication strategy suitable for the ambient conditions in which the machine is expected to perform. Unless the maintenance department literally starves the bearing of lubricant in the ﬁrst year, most bearings will surpass their warranty period, and the manufacturer probably won't learn if their design is truly robust and reliable. Ultimately, the design conditions are set, and machine availability and reliability depend on how well the maintenance department understands: 1) bearing design and their lubrication requirements; 2) how machine bearings fail in their working environment; and 3) their ability to design, implement and execute a strategic asset-lubrication program that adequately meets bearing needs. WHAT'S IN A BEARING? As highlighted in Part 1 of the article "The Inner Life of Bearings" by reliability expert Neville Sachs (Lubrication Technology, February 2015), when we think of a bearing, various shapes, sizes and materials come to mind. These components can take on many forms in performing their duty to support sliding or rotating parts. To recap, sliding contact bearings (commonly known as plain, sleeve or journal bearings) allow full sliding contact between mating surfaces in three speciﬁc ways: radially, in which the bearing provides a 360˚support for a rotating shaft or journal; axially, in which the bearing supports any side thrust load from the end of the rotating shaft; and planular, in which a ﬂat bearing surface A noisy bearing contaminated with paint (Courtesy ENGTECH Industries, Inc.) acts like a slipper to guide moving parts in a straight line. To help carry the impressed load with minimized friction and wear, a lubricant is introduced into the engineered clearance between the mating surfaces via a specially cut channel to generate hydrodynamic/hydrostatic full ﬂuid ﬁlm separation of the surfaces to allow them to slide freely over one another. Sliding bearings are most commonly manufactured in yellow metal or composites of brass, bronze and copper, the bearing material designed to be softer than the supported component. Rolling contact bearings (commonly known as ball bearings, roller bearings and needle bearings) provide a rolling contact that supports both radial and axial thrust-often simultaneously. These bearings are often termed "anti-friction" bearings due to their point contact area, where lightly lubricated rolling elements (balls, rollers and needles) carry the impressed load under an elastohydrodynamic lubricant ﬁlm. Rolling-element bearing manufacturers measure the reliability of their bearings using a Load-Life calculation rating, which is known as the L10 rating life. To achieve its reliability design rating, the manufacturer assumes the bearing will be operated within its Countless bearings lead a less than ideal life, often subjected to the severest conditions and many forms of abuse within industrial-plant environments. Special Section MAY 2015 LUBRICATION TECHNOLOGY LubricationTechnologyOnline.com 27 http://www.LubricationTechnologyOnline.com

Maintenance Technology May 2015

Table of Contents for the Digital Edition of Maintenance Technology May 2015