SKF Energy Efficient (E2) Deep Groove Ball Bearings

The new SKF Energy Efficient deep groove ball bearings are designed to improve machine efficiency and to save energy, see presentation Energy Efficient solutions.

SKF Energy Efficient deep groove ball bearing

These bearings belong to SKF E2 performance class family, providing:

• optimized internal geometry for reduced friction
• a shield on both sides to protect the friction-reducing features
• new cage design
• unique lubricant

The designation follows the basic SKF designation system. To clearly show the new performance the prefix “E2.” has been added.

SKF Energy Efficient bearings are supplied in a new standard box (fig).

Frictional moment The frictional moment of an SKF Energy Efficient bearing (E2.6306-2Z/C3) is, on average, approximately 50% reduced compared with the frictional moment of a standard SKF shielded deep groove ball bearing. This was measured under various operating conditions (diagram).

Example for the reduced frictional moment

The diagram illustrates the effectiveness of SKF Energy Efficient deep groove ball bearings as example in a 3 kW electric motor. In this example, the motor was equipped with standard SKF deep groove ball bearings and later with SKF E2 bearings. The free running time after the power was switched off was measured. With SKF E2 bearings, the free running time was about 50% longer.

Operating temperature The operating temperatures of SKF Energy Efficient bearings and standard SKF bearings were measured at certain speeds and compared (diagram). Test conditions were:

• Bearing: 6205-2Z/C3
• Running time: 24 h at each speed interval
• Ambient temperature: room temperature
• Load: 0,5 kN radial

The test showed that when compared to a standard SKF bearing, the E2 bearing ran 5 to 15 �C cooler, depending on speed.

Bearing service life

In light to normal load applications, metal fatigue is rarely an issue, but grease life is a limiting factor when determining the life of a sealed bearing.

Compared to standard SKF shielded deep groove ball bearings, SKF Energy Efficient deep groove ball bearings can more than double the mean time between failure (diagram) due to reduced heat generated by the bearings and the specially formulated SKF low-friction grease.

Recommended operating conditions for SKF Energy Efficient deep groove ball bearings:

• P = 0,125 C
• speeds greater than 1 000 r/min

Determining the service life of the grease Under the recommended operating conditions, the service life of the grease in shielded SKF Energy Efficient deep groove ball bearings defines the service life of the bearing and can be estimated using the grease life diagram. The estimate is based on an L10 grease life. This is defined as the period of time, at the end of which, 90% of a sufficiently large group of seemingly identical bearings are still reliably lubricated.

Grease life depends mainly on the following factors:

• operating temperature
• speed
• load

The grease life diagram provides grease life estimates based on operating temperature and speed. It is valid for light loads (P = 0,05 C) and bearings on a horizontal shaft. For more heavily loaded bearings, the grease life must be reduced. Appropriate reduction factors are listed in the table.

For bearings on a vertical shaft, the grease life should be halved.

The speed is considered using the speed factor A:

A = n dm

where

A = speed factor [mm/min]

n = rotational speed [r/min]

dm = bearing mean diameter [mm]

= 0,5 (d + D)

To make adjustments for other operating conditions, refer to the section “Grease lubrication” or contact the SKF application engineering service.

Designs

Bearings with shields

SKF Energy Efficient deep groove ball bearings are fitted on both sides with a shield made of sheet steel, as standard. The bearings are filled with a special low-noise, low-friction SKF grease (table). The grease fill is not identified in the bearing designation. The quantity of grease fills some 25 to 35% of the free space in the bearing. The bearings are lubricated for life and are maintenance-free. They should not be washed or heated to temperatures above 80 �C. Shielded bearings are primarily intended for applications where the inner ring rotates. If the outer ring rotates, there is a risk that the grease will leak from the bearing at high speeds.

Open bearings

For open SKF Energy Efficient deep groove ball bearings, contact the SKF application engineering service or your local SKF representative.

To achieve the maximum performance of SKF Energy Efficient deep groove ball bearings such as double the lubrication interval, open bearings must be greased with the proper quantity of SKF LEGE 2 grease.

Tolerances SKF Energy Efficient deep groove ball bearings are manufactured to P6 tolerances for dimensional accuracy. The width tolerance is reduced to:

• 0/�60 �m for bearings with an outside diameter = 110 mm
• 0/�100 �m for bearings with an outside diameter > 110 mm

The running accuracy depends on the bearing size and corresponds to:

• P5 tolerances for bearings with an outside diameter = 52 mm
• P6 tolerances for bearings with an outside diameter > 52 mm and = 110 mm
• Normal tolerances for bearings with an outside diameter > 110 mm

Cages SKF Energy Efficient deep groove ball bearings are fitted with a ball centred snap-type cage made of a temperature-resistant glass fibre reinforced composite polymer. This cage design is one of the key features of SKF Energy Efficient deep groove ball bearings The cage design is not identified in the bearing designation.

Cage behaviour The fundamental redesign produced a lighter cage that is less susceptible to deformation during operation. By comparing a polyamide cage from a standard SKF bearing and an E2 bearing both running at 8 000 r/min a reduced deformation can be experienced (fig).

Minimum load Rolling bearings should always be subjected to a given minimum load. The requisite minimum radial load to be applied to SKF Energy Efficient deep groove ball bearings can be estimated using

Frm = kr/T (5,2 n)2/3 (dm/100)2

where

Frm = minimum radial load [kN]

kr = minimum load factor

= 0,025 for bearings in the 60 and 62 series

= 0,03 for bearings in the 63 series

T = operating temperature [�C]

n = rotational speed [r/min]

dm = bearing mean diameter [mm]

= 0,5 (d + D)

When starting at low temperatures, even greater minimum loads may be required. For applications like electric motors, where the requisite radial load is not sufficient, springs can be used to apply an axial preload that is great enough.

Axial load carrying capacity If SKF Energy Efficient deep groove ball bearings are subjected to purely axial loads, this load should generally not exceed the value of 0,5 C0. Small bearings (bore diameter up to approximately 12 mm) and bearings in the 60 series should not be subjected to an axial load greater than 0,25 C0. Excessive axial load can lead to a reduction in bearing service life.

Applications The operating conditions for deep groove ball bearings typically are characterized by light to normal loads at relatively high speeds. Typical examples include electric motors, pumps, conveyors and fans. SKF Energy Efficient deep groove ball bearings are designed specifically for these applications.

Deep groove ball bearings | Single row deep groove ball bearings | Basic design bearings | Sealed bearings | Bearings with shields | Bearings with low-friction seals | Bearings with contact seals | ICOS� oil sealed bearing units | Grease life | SKF Energy Efficient (E2) deep groove ball bearings | Deep groove ball bearings with filling slots | Stainless steel deep groove ball bearings | Double row deep groove ball bearings