Deep Groove Radial Ball Bearings

Technical information

Deep groove radial ball bearings are used to transmit loads from rotating parts to housings with minimum friction loss.

This will be obtained by a high hardness, minimizing the deformation of the bearing elements. Additional design measures ensure an undisturbed free rolling action.

These measures are

1. Radial clearance 2. Materials 3. Precision

Only by adapting the bearing execution to the specific application the design requirements can be exhausted, which needs compromising between supplier and customer.

Basically, bearing rings are non supporting elements, rather they are the intersection of associated components and the set of balls. The influence of the associated components to the bearing geometry must always be taken into consideration.

Particular important are

4. Preload 5. Accuracy of the associated components 6. Bearing fits 7. Lubrication

Some explanations and definitions to facilitate your selection.

1. Radial clearance

The internal clearance defines the amount by which one bearing ring can be displaced relative to the other without gauging load. The internal clearance is not a quality- but a design feature. It is standardized in DIN 620/T4.

1) Radial clearance: shifting in radial direction

The amount of radial clearance is, first of all, depending on the fits. For a reliable performance, the lubricant film must provide a complete separation of the bearing elements.

In case the radial clearance is too small the lubricant film will brake down, leading to metal to metal contact of balls and races. As a result, temperature and wear increase or the bearing even fails by seizing up.

Installation with press fits leads to a reduction of radial clearance as rings are expended (inner) and contracted (outer). Differences in temperature between inner and outer ring affect the radial clearance as well.

2) Axial clearance: shifting in axial direction:

The axial clearance is related to the radial clearance. Depending on the bearing geometry it is 8,5-10 times the radial clearance.

The axial clearance is a design feature, if a defined axial lift is required, please contact our application engineers.

2. Materials

Rings:
Basically GMN rings are made from vacuum degassed chrome steel 100Cr6, which is heat stabilized for temperatures up to 150° C (302° F). On request, an additional heat stabilization can be carried out for working temperatures between 150° C and 300° C (572° F). Bearings for working temperatures up to 500° C (932° F) are made of high temperature tool steel.

Balls:
Standard material for balls is vacuum degassed chrome steel 100Cr6. For the increase of speed value and lifetime, all bearings can be delivered with ceramic balls.

Further special materials are available on request.

3. Precision

The precision of a spindle bearing does affect the guiding properties as well as lifetime, especially with applications at max. speed.

The tolerances for dimensional, form and running accuracy of GMN high precision ball bearings are specified in international (ISO 492) and national standards (DIN 620). GMN high precision bearings are manufactured to precision class 4 and class 2 (P4 and P2) as well as ABEC 7 and ABEC 9. For special applications, e.g. vacuum pumps, gyroscopes as well as measuring engineering and optical systems, GMN manufacture bearings to the internal tolerance classes HG (high precision) and UP (ultra precision). Apart from the requirements mentioned, the tolerance classes contain additional selection criteria. All GMN high precision ball bearings are also available in compliance with the American AFBMA standards. The relationship between the various standards are explained below.

4. Preload

Single bearings
Deep groove bearings at higher speed have to be preloaded in axial direction. For single bearings adjusting springs are used. The minimum spring load for your application can be calculated by GMN.

Matched deep groove bearings
In many cases, bearing applications demand higher axial or radial capacity and smaller bearing dimensions or higher rigidity or a certain range of axial play. Such requirements can be met by matched bearings. Only bearings from the same series and same dimension can be matched.

Universal matching By universal matching single bearings can be assembled to DF, DB or DT configuration. Bearings with the same kind of matching (e.g. universal matching with same axial play, without axial play or with same preload) can be interchanged within their respective group. When mounting universal matched bearings in the DT arrangement, with or without axial play or with preload the axial load is equally distributed. Universal matched bearings from the same type of matching can be combined to form larger groups in the DF/DT arrangement or DB/DT arrangement with more than two bearings if required. Universal matching takes place with a measured load or a preload as shown in the chart below. When mounting universal matched bearings the etching on the rings (type designation) must be noted according to the illustrations.

DF arrangement Tandem arrangement DB arrangement

Universal matching with axial play. Symbol DUA.
The bearings are prepared in such a way that with inner and outer rings locked together in DF or DB arrangement, a certain axial play is included. As the magnitude of the axial play depends on the operating conditions, the axial play must be specified for each individual application. For example with axial play 40 to 60 microns, the symbol reads DUA 40.60

Universal matching without axial play. Symbol DUO.
The bearings are prepared in such a way, that when inner and outer rings are locked together in DF or DB arrangement, there is no axial play in the bearing set.

Universal matching with preload. Symbol DUV.
When a rigid bearing arrangement, free from play, is required, a matching of bearings with preload is used. Bearings matched with preload have the advantage that under the effect of an external load only a small elastic deformation takes place, compared to unmatched bearing pairs or single bearings. The bearings are prepared in a way that if inner and outer rings are locked together they are under the effect of a preload. The preload has to be considered as an additional axial load in the life time calculation. The preload of DUV matched bearings is 2% of the dynamic load rating, however the max is 300N. A preload can be specified to suit your requirements.

Special matching These bearings will be packed in pairs. DB arrangement. Symbol DB. The matching in the DB arrangement is free fro play. Should a definite axial play be required, the numbers will be added to the symbol e.g. bearing pair with axial play 20 to 40 microns: DB/20.40.

When mounting the bearings, care must be taken that the arrows on the outer surface correspond to the arrangement shown in the opposite drawing. The bearings may not be exchanged for bearings of the same type of matching. The matching takes place with the measuring load according to the chart below.

DF arrangement. Symbol DF. With the DF arrangement the bearing pair has an axial play of 5 to 15 microns. In case a definite axial play is required, the numbers will be added to the symbol, e.g. bearing pair with axial play 40 to 60 microns: DF/40.60.

When mounting the bearings care must be taken, that the arrows on the outer surface correspond to the arrangement shown in the opposite drawing. The bearings may not be exchanged for bearings of the same type of matching. The matching takes place with the measuring load according to the chart below.

DT arrangement. Symbol DT. This configuration is applied if axial loads from one direction are supported by two bearings. When mounting the bearings, care must be taken that the arrows on the outer surface correspond to the arrangement shown in the opposite drawing. The bearings may not be exchanged for bearings of the same type of matching. The matching takes place with the measuring load according to the chart below.

Measuring loads and tolerances

Width tolerance of matched deep groove bearings Type of matching Width toleranceB1 [µm] DF   DB DT 0 - 250 DUA   DUO DUV 0 - 500

5. Accuracy of the associated components

The machining quality of the abutment surfaces and bearing seats are of great importance for running accuracy and low operating temperature of a bearing application. Reference values for form and position tolerances are available on request.

6. Bearing Fits

The machining quality and the correct selection of fits with regard to bearing seats are of great importance for the proper operation of a precise bearing application.

To get support for the selection of the correct fits for your application, please click here.

7. Lubrication

The correct choice of lubricant and method of lubrication is as important for the proper operation of the bearing as the selection of the bearing and the design of the associated components.

	Maintenance-free operation over long periods of time is desired,
	the maximum speed of the bearing does not exceed the speed factor n x dm of the grease,
	the heat generated is almost uniformly dissipated by the environment,
	low friction losses are required with bearings working under small loads and at high speeds.

Running-in period with grease lubrication
In order to obtain an optimum lubrication effect and grease life it is advisable to provide for a running-in period for bearings for high-speed applications. A better grease distribution and, at the same time, a low bearing temperature are thus achieved.

Grease manufacturer offer a multitude of greases suitable for high speeds. The n x dm factor is a criterion for the selection of the grease taking into consideration bearing size and operating speed.

D: Outside diameters of the bearing [ mm] d: Bohrungsdurchmesser des Lagers [mm] n: Betriebsdrehzahl des Lagers [1/min]

	High speeds do not permit the use of greases,
	the lubricant must simultaneously serve to cool the bearing.

The most widely used lubricating methods are:

	Oil mist lubrication: The oil mist is produced in an atomizer and conveyed to the bearings by an air current. The air current also serves to cool the bearings and the slightly higher pressure prevents contamination from penetration.
	Oil-air lubrication (total loss lubrication): The oil is conveyed to the bearing in droplets by compressed air. The droplet size and the intervals between two droplets are controlled.
	Oil-jet lubrication (cooling lubrication): Considerable amounts of oil are carried through the bearing by injection, the frictional heat generated in the bearing is dissipated. The cooling of the oil is achieved e.g. with an oil-to-air heat exchanger.