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3. Criteria for selection and use of bearings

3.1 Types of rolling-contact bearings
3.2 Criteria for selecting bearings

Rolling-contact bearings are an indispensable component of machinery, which are constantly subjected to the process of innovation. They enable mutual rotational motion of machine parts, while simultaneously transferring acting forces. They usually consist of two rings, roller-bearing cases, and a cage. Grease and packing elements are also an integral component of rolling-contact bearings. Proper rolling-contact bearing operation thus requires not only the selection of the proper type and size of bearing, but also the appropriate method of lubrication, heat dissipation, corrosion protection, and design to prevent entry of contaminants into the housing. The housing design a well as bearing connection dimension tolerances and supplemental lubrication method must be adequate. The correct installation, disassembly or de-installation procedure must also be designated to ensure proper bearing operation. A service manual and maintenance instructions should be provided in cases of complicated housing designs and where high operating reliability are needed.

These principles must particularly be observed in housings in which bearing price, high reliability, or costs associated with bearing installation and economic losses due to shutdown of equipment play a significant role. Such housings require a highly qualified approach in the design phase with the use of computations and testing.

3.1 Types of rolling-contact bearings

ZKl Company manufactures a full range of bearings, from which the designer can choose the bearings that best meet the specific requirements.

3.1.1 Based on load direction

Rolling-contact bearings are generally divided according to the direction of force, for whose transfer they are predominantly designed, into two basic groups:

Radial bearings
Axial bearings

Přesný rozdíl mezi oběma skupinami ale není, protože většina radiálních ložisek může zachytávat i axiální síly a některé typy axiálních ložisek i radiální síly. Toto rozdělení má ale význam pro stanovení únosností ložisek. U radiálních ložisek se udává únosnost pro radiální síly, zatímco u axiálních ložisek se vztahuje na síly působící v axiálním směru.

There is no exact difference between the two groups, however, because the majority of radial bearings can also capture axial forces and certain types of axial bearings also radial forces. This division, however, is important for determining the load-bearing capacity of bearings. The load-bearing capacity in radial bearings specifies the magnitude of radial forces, whereas in axial bearings the value refers to axial forces.

We divide bearings, according to shape, into ball (single-point contact) bearings and roller (line contact) bearings. Contact in ball bearings theoretically occurs at a single point, hence the designation “single-point contact bearings.” In roller, spherical, tapered roller, and needle roller bearings, contact occurs in a line or straight line, resp., thus they are commonly designated as straight-line (vector) or line-contact bearings.

The following overview provides a classification of individual bearing types based on this characteristic.

Single-point contact bearings

Single-row ball bearings . . . . . . . . . . . . . . . . . . . . . . . (Fig. 3.1)
Single-row angular-contact ball bearing . . . . . . . . . . . . . (Fig. 3.2)
Double-row angular-contact ball bearing . . . . . . . . . . . . . (Fig. 3.3)
Four-point contact bearing . . . . . . . . . . . . . . . . . . . . . . . . (Fig. 3.4)
Double-row, self-aligning ball bearing . . . . . . . . . . . . . . . (Fig. 3.5)
Single direction thrust ball bearings . . . . . . . . . . . . . . . . . (Fig. 3.6)
Double direction thrust ball bearings . . . . . . . . . . . . . . . . .(Fig. 3.7)

Single-row ball bearings (Fig. 3.1) Single-row angular-contact ball bearing (Fig. 3.2)
Double-row angular-contact ball bearing (Fig. 3.3) Four-point contact bearing (Fig. 3.4)
Double-row, self-aligning ball bearing (Fig. 3.5) Single direction thrust ball bearings (Fig. 3.6)
 
Double direction thrust ball bearings (Fig. 3.7)  

Line-contact bearings

Single row cylindrical roller bearing . . . . . . . . . . . . . . . . . . . . . . .(Fig. 3.8)
Double row cylindrical roller bearing . . . . . . . . . . . . . . . . . . . . . .(Fig. 3.9)
Single row full complement cylindrical roller bearing . . . . . . . . .(Fig. 3.10)
Double row full complement cylindrical roller bearing . . . . . . . .(Fig. 3.11)
Tapered roller bearing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(Fig. 3.12)
Double row tapered roller bearing . . . . . . . . . . . . . . . . . . . . . . . .(Fig. 3.13)
Double row spherical roller bearing . . . . . . . . . . . . . . . . . . . . . . .(Fig. 3.14)
Thrust cylindrical roller bearing . . . . . . . . . . . . . . . . . . . . . . . . . . .(Fig. 3.15)
Thrust spherical roller bearing . . . . . . . . . . . . . . . . . . . . . . . . . . .(Fig. 3.16)

We separate each type of roller bearing then into several types according to dimensions and design variations. Specific information on characteristics of individual types of bearings is available in the sections of text provided before the tables of individual bearings.

Single row cylindrical roller bearing (Fig. 3.8) Double row cylindrical roller bearing (Fig. 3.9)
Single row full complement cylindrical roller bearing (Fig. 3.10) Double row full complement cylindrical roller bearing (Fig. 3.11)
Tapered roller bearing (Fig. 3.12) Double row tapered roller bearing (Fig. 3.13)
Double row spherical roller bearing (Fig. 3.14) Thrust cylindrical roller bearing (Fig. 3.15)
 
Thrust spherical roller bearing (Fig. 3.16)  

3.1.2 Separable and non-separable bearings

Separable bearings allow separate installation of both rings, which is of particular advantage when installing both rings with an overlap. Sequential installation of individual parts can also be used in certain complex housings and assembly units. Separable bearings are, e.g. four-point contact bearings, double-row ball bearings with split inner ring, roller bearings, tapered roller bearings, thrust ball bearings, thrust roller bearings, and spherical roller thrust bearings.

In contrast, non-separable bearings include, e.g. single row ball bearings, single row angular-contact ball bearings, self-aligning ball bearings, and double-row spherical roller bearings.

3.2 Criteria for selecting bearings

The ZKL production program offers a full range of bearings, from which the designer can choose the bearings that best meet the specific requirements. The bearing type and size are generally chosen according to its loading capacity with consideration to its operating conditions and expected bearing service life. To determine the proper type of bearing thus requires a thorough knowledge of the loading capacity of the bearing during operation. Proper principles for selecting, fitting, and installing them must be followed, but it also requires knowledge of the prerequisites for which the proposed results apply. In the following chapters, we thus present general principles for selecting and using contact-roller bearings, which may be used by drafting engineers in the bearing design process. The chapters are organized in logical consecutive order. The technical part of the publication contains important regarding calculations, design data, housing, lubrication designs, as well as installation and removal information on rolling-contact bearings. The table provides a list of currently manufactured ZKL rolling-contact bearings with main dimensions and functional parameters.

Even though they list detailed information, this publication is unable to provide full information on all housings for their wide varieties of application. We therefore recommend that complex housing designs be consulted with ZKL technical and consultation service specialists.

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