Radial deep groove ball bearings are used to transfer loads from rotating parts to housings with the least amount of friction.
In order for the bearing components not to be deformed when in use, they must be extremely hard and durable. There are a few additional factors that are also important to ensure radial ball bearings are operating at pique performance, they are:
- Radial & Axial Clearance
- Radial Ball Bearing Materials
- Precision
Internal Clearance
Internal clearance is the total distance one raceway can be moved in relation to the other. This clearance is measured radially and axially.
Radial Clearance
Radial Clearance: The space between the ball and the raceway perpendicular to the bearing axis. Clearance defines the amount by which one bearing ring can be displaced relative to the other without gauging load. The internal clearance is standardized in DIN 620/T4.
The amount of radial clearance depends on the fit. For reliable performance, a lubricant film will provide a complete separation of the bearing elements.
If the radial clearance is too small the lubricant film will brake down fast and lead to metal-on-metal contact of the balls and raceways. Temperature and wear will increase and a bearing failure is likely to occur. Installation with press fits leads to a reduction of radial clearance as inner rings are expanded and outer rings are contracted.
Axial Clearance
Axial Clearance: The space between the ball and the raceway parallel to the bearing axis. The axial clearance is related to the radial clearance.
Depending on the bearing geometry axial clearance is 8.5-10 times the radial clearance.
Radial Ball Bearing Component Material
Rings & Raceway Material
Our radial ball bearing rings are manufactured containing Vacuum Degassed Chrome Steel 100Cr6 and comes heat stabilized for temperatures up to 302°F (150°C).
On request, we can add additional heat stabilization for any working temperatures between 302°F to 572°F (150°C to 300°C).
Any radial ball bearings needed for working temperatures up to 932°F (500°C) are also available and are manufactured with high temperature tool steel.
Ball Material
Our steel balls are manufactured with Vacuum Degassed Chrome Steel 100Cr6.
We also offer every radial ball bearing size with the option of ceramic (Silicon Nitride) ball material, commonly referred to as hybrid bearings.
Precision Class
All our GMN high precision bearings are specified in International (ISO 492) and National standards (DIN 620). Our high precision bearings are also manufactured to Precision Class 4+ and Precision Class 2 (P4+ & P2) and adhere to ABEC 7 and ABEC 9 classifications.
Preload for Radial Ball Bearings
Single Bearings: Radial deep groove ball bearings need to be preloaded in the axial direction when used at higher speeds.
For single bearings we use adjusting springs. Our onsite engineers can calculate the minimum spring load needed for your application. Contact us to get that started for you.
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: Universally matching single bearings can be assembled to DF, DB or DT configurations.
Bearings with the same kind of matching 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.
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.
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
| Type of Matching | Measuring Load | Measuring Load |
| DF DB DT DUA DUO |
d 3 – 7 mm 8 – 15 mm 15 – 30 mm over 30 mm |
12 N 22 N 32 N 50 N |
| DUV Preload meeting the individual application | 2% of the dynamic carrying number, however max. 300 N |
| Type of Matching | Width tolerance B1 [µm] |
| DF DB DT | 0 – 250 |
| DUA DUO DUV | 0 – 500 |
Accuracy of the 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.
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.
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.
Grease lubrication:
Use when:
- 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 manufacturers 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.
Oil lubrication:
Use When:
- 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.