Stainless Steel Deep Groove Ball Bearings

SKF stainless steel deep groove ball bearings are resistant to corrosion from moisture and several other media. These single row deep groove ball bearings have the same deep raceway grooves and close conformity between raceways and balls as standard deep groove ball bearings made of carbon chromium (rolling bearing) steel. They are without filling slots and can carry axial loads acting in both directions in addition to radial loads, even at high speeds.

SKF stainless steel deep groove ball bearings have the same running properties as conventional steel deep groove ball bearings, but have a lower load carrying capacity.

The bearings are available in open and sealed designs for shaft diameters from 1 to 50 mm.

SKF stainless steel bearings are identified by the designation prefix W, e.g. W 626-2Z.

Basic design bearings

Basic design bearings are open, i.e. unsealed (fig). Open bearings that are also available with shields or seals may have seal recesses in the outer ring (fig) for manufacturing reasons

Sealed bearings

Most SKF stainless steel deep groove ball bearings are available with shields. Some are also available with contact seals. Bearings with shields or contact seals on both sides are lubricated for life and are maintenance-free. They should not be washed or heated to temperatures above 80 �C.

Because stainless steel deep groove ball bearings are often used in food processing machines, the bearings can be delivered with a special non-toxic grease, designation suffix VT378. This grease

fulfills the requirements of the “Guidelines of section 21 CFR 178.3570” of the FDA (US Food and Drug Administration) regulations and
is approved by the USDA (United States Department of Agriculture) for category H1 use (occasional contact with food stuffs).

Please check availability of bearings with non-toxic grease before ordering.

Characteristics of the greases are listed in table 2. The standard grease is not identified in the bearing designation. The grease quantity fills some 25 to 35% of the free space in the bearing.

The grease life in sealed stainless steel deep groove ball bearings can be estimated according to the method explained for single row deep groove ball bearings (section “Sealed bearings – Grease life”):

For bearings with standard grease use diagram 2.
For bearings with non-toxic grease use diagram 1 for grease MT33, but only up to a maximum operating temperature of 100 �C.

Calculations can be made with the program “Grease life for sealed bearings”.

Bearings with shields

Bearings with shields, designation suffix 2Z (fig), have shields made of stainless steel. The shields form a sealing gap with the land of the bearing inner ring shoulder and enable high temperatures and speeds. Bearings fitted with shields are primarily intended for applications where the inner ring rotates. If the outer ring rotates, there is a risk of grease leaking from the bearing at elevated speeds.

Details regarding the suitability of the shields for various operating conditions can be found in table 1.

Bearings with contact seals

Bearings with contact seals, designation suffix 2RS1 (fig), have seals made of an oil and wear resistant acrylonitrile-butadiene rubber (NBR) with a sheet metal reinforcement. The permissible operating temperature range for the seals is �40 to +100 �C and up to +120 �C for brief periods. Contact seals run with their seal lip on the land of the bearing inner ring shoulder. The seals are fitted with their external edge in the recesses at the outer ring and seal tightly.

Under extreme operating conditions, e.g. at high speeds or high temperatures, grease may leak from bearings fitted with seals. For bearing arrangements where this would be undesirable, special steps must be taken at the design stage. Please consult the SKF engineering application service.

Details regarding the suitability of the seals for various operating conditions can be found in table 1.

Flanged bearings

For certain applications SKF also produces stainless steel deep groove ball bearings with an external flange on the outer ring. The flange enables the bearings to be axially located in the housing. Such an arrangement is very simple in design and saves space; the housing bore need not be so expensive to machine as housing shoulders are not required.

SKF flanged stainless steel bearings are available in an open design, designation suffix R (fig) and a shielded version, with a Z shield at both sides, designation suffix 2ZR (fig).

The bearings have the same internal design, including the cage, as the corresponding bearings without flange. They are able to accommodate the same loads, operate at the same speeds, and the shielded bearings are filled with the same grease.

Dimensions The boundary dimensions of the metric stainless steel bearings are in accordance with ISO 15:1998.

The dimensions of the flange correspond to ISO 8443-1983.

The boundary dimensions of the inch-size bearings follow BS 292:Part 2-1982 in part. This standard has been withdrawn.

Tolerances SKF stainless steel bearings in metric sizes are produced to Normal tolerances as standard. Some sizes are also available to tolerance class P6 or P5 specifications. The tolerances conform to ISO 492:2002, classes Normal, 6 and 5.

The inch-size bearings are produced with Normal tolerances for inch-size bearings as specified in BS 292:Part 2-1982 (now withdrawn).

Internal clearance SKF stainless steel deep groove ball bearings are produced as standard with Normal radial internal clearance in accordance with ISO 5753:1991 and BS 292:Part 2-1982 (now withdrawn). The clearance limits are valid before mounting under zero measuring load.

Misalignment Single row stainless steel deep groove ball bearings have only limited ability to accommodate misalignment. The permissible angular misalignment between inner and outer rings, which will not produce inadmissibly high additional stresses in the bearing, depends on the radial internal clearance of the bearing in operation, bearing size, the internal design and the forces and moments acting on the bearing. Because of the complex relationship between these factors, no generally applicable specific values can be given. Depending on the various influences of the factors, the permissible angular misalignment lies between 2 and 10 minutes of arc. Any greater misalignment will result in increased noise in operation and decrease bearing service life.

Materials The bearing rings are produced from stainless steels X65Cr13 according to ISO 683-17:2000 or X105CrMo17 according to EN 10088-1:1995, depending on size. The balls are made of stainless steel X105CrMo17 and the shields and cages of stainless steel X5CrNi18-10, both according to EN 10088-1:1995.

Cages Depending on the bearing series and size, SKF stainless steel single row deep groove ball bearings are supplied with one of the following stainless steel cages (fig) as standard

a pressed snap-type steel cage, ball centred, no designation suffix (a)
a pressed ribbon-type steel cage, ball centred, no designation suffix (b)
a riveted pressed steel cage, ball centred, no designation suffix (c).

For bearings an injection moulded snaptype cage of glass fibre reinforced polyamide 66 (d), please check availability prior to ordering.

Minimum load To achieve satisfactory operation, stainless steel deep groove ball bearings, like all ball and roller bearings, must always be subjected to a given minimum load, particularly if they are to operate at high speeds or are subjected to high accelerations or rapid changes in the direction of load. Under such conditions, the inertia forces of the balls and cage, and the friction in the lubricant, can have a detrimental influence on the rolling conditions in the bearing arrangement and may cause damaging sliding movements to occur between the balls and raceways.

The requisite minimum radial load to be applied to stainless steel deep groove ball bearings can be estimated using

where

Frm = minimum radial load [kN]

kr = minimum load factor (see product data)

? = oil viscosity at operating temperature [mm2/s]

n = rotational speed, r/min

dm = mean diameter of bearing

= 0,5 (d + D) [mm]

When starting up at low temperatures or when the lubricant is highly viscous, even greater minimum loads may be required. The weight of the components supported by the bearing, together with external forces, generally exceeds the requisite minimum load. If this is not the case, the stainless steel deep groove ball bearing must be subjected to an additional radial load. For applications where stainless steel deep groove ball bearings are used, an axial preload can be applied by adjusting the inner and outer rings against each other, or by using springs.

Axial load carrying capacity If the bearings are subjected to a purely axial load, this axial load should generally not exceed the value of 0,25 C0. Excessive axial loads can lead to a considerable reduction in bearing service life.

Equivalent dynamic bearing load

P = Fr when Fa/Fr = e

P = 0,56 Fr + YFa when Fa/Fr > e

The factors e and Y depend on the relationship f0 Fa/C0, where f0 is a calculation factor, see product data, Fa the axial component of the load and C0 the basic static load rating.

In addition, the factors are influenced by the magnitude of the radial internal clearance; increased clearance enables heavier axial loads to be supported. For bearings mounted with the usual fits as listed in tables T1, T5 and T6, the values for e, X and Y are listed in table 3.

Equivalent static bearing load P0 = 0,6 Fr + 0,5 Fa

If P0 < Fr, P0 = Frshould be used.

Supplementary designations The designation suffixes used to identify certain features of SKF stainless steel deep groove ball bearings are explained in the following.

Design of bearing arrangements

In most cases the cross section of the bearing rings of a stainless steel deep groove ball bearing is very thin and the side faces correspondingly slim. The transitions from the side faces to the ring bore or outside diameter are also very small. It is therefore necessary to make sure that the adjacent components are appropriate for the bearings and are produced to the required accuracy.

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