BEARINGS FEATURE


• Ball • Roller • Plain • Slewing • WHICH BEARING SHOULD YOU


SPECIFY FOR YOUR APPLICATION?


Not only are there many different bearing styles available to the design engineer, but also a wide choice of bearing geometries and materials of construction. SKF’s


Phil Burge, marketing and communications manager, goes ‘back to basics’ by looking into the various types and styles available, and their suitable applications


B


earings are ubiquitous mechanical components that can be found in


all manner of machinery – from heavy industrial plant, transportation systems and construction equipment, to instrument bearings measuring a few millimetres in diameter. While there are some more exotic types (such as air and magnetic bearings) available, in this article I shall concentrate on those that are in common use, particularly rolling element bearings and plain bearings. I’ll also touch upon special styles such as slewing bearings, which have very specific applications.


The most commonly used rolling element bearing is the ball bearing


BALL BEARINGS The most commonly used rolling element bearing is the ball bearing which, in its basic form, is an assembly of four parts: a large outer ring (forming the outer raceway), a smaller diameter inner ring (forming the inner raceway), the balls – sized so that they are free to rotate between, and make contact with, the raceways – and a cage to retain the balls, preventing them from touching one another. Basic ball bearings will handle both


radial and axial loads, but as the point of contact with the balls and the raceways is very small, there is considerable pressure created, so the load capacity of ball bearings is limited. Let’s look at four key types. Single row, deep groove, ball


bearings are the simplest and most versatile of all ball bearing designs so tend to be the most widely used. They are suitable for high and very high speed applications, are robust in


operation and – assuming they


are properly lubricated and used within their specified operating


parameters – require little maintenance. Variations include hybrid types


comprising ceramic balls and steel raceways (often used in electric motors subject to stray electrical currents) and polymer bearings for applications subject to contact with corrosive substances. Double row deep groove ball bearings


are essentially a tandem arrangement of the single row deep groove type, where a single ring combines two raceways. They are suitable for applications where the load carrying capacity of a single row bearing may not be sufficient. For the same bore and outside diameter, double row bearings are slightly wider than single row bearings, but have a considerably higher load capacity. The self-aligning ball


bearing is a type that placed SKF at the forefront of bearing design and development over one hundred years ago! The modern version has two rows of balls running in two inner raceway grooves and a common single spherically contoured raceway in the outer ring. This novel design renders the bearings insensitive to angular misalignment (shaft relative to the housing) up to a maximum of 3˚. Typically, self-aligning ball bearings are an ideal choice for light- to medium-load conveyor applications as they manage varying loads well with minimal friction, enabling higher conveyor speeds and longer bearing service life. Angular contact ball bearings have


raceways in the inner and outer rings that are displaced relative to each other in the direction of the bearing axis. This means that they are designed to accommodate combined loads (simultaneously acting radial and axial loads). Special configurations include single row angular contact ball bearings (accommodating


/ DESIGNSOLUTIONS


radial loads as well as axial loads in one direction only), double row angular contact ball bearings (accommodating radial loads as well as axial loads in both directions) and four-point contact ball bearings (supporting only axial loads in both directions).


ROLLER BEARINGS In roller bearings, the ball is replaced by a rolling element that generally takes one of four distinct forms: cylinder (cylindrical roller bearings), barrel (spherical roller bearings), tapered cylinder (tapered roller


Tapered roller bearings


bearings) or very thin cylinder (needle roller bearings). An important aspect of the roller bearing design is that the contact between the inner and outer raceways is not a point, as is the case with a ball bearing, but a line. This enables the load to be distributed over much larger areas of the raceways, allowing the bearing to handle far greater loads than are possible with a ball bearing of similar size. Most roller bearings are capable of high speed operation but because of their higher load capacities, larger sized bearings tend to be used in low-speed, high load applications – wind turbines, steel rolling mills and the like.


DESIGN SOLUTIONS | SEPTEMBER 2018


> 12 11


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44