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7. Bearings - general data

7.1 Bearing design data
7.2 Main dimensions
7.3 Roller bearings materials
7.4 Cages
7.5 Shield and seals
7.6 Designation of roller bearings
7.7 NEW FORCE bearings
7.8 Technical support

7.1 Bearing design data

Besides the suitable type of bearing and the size of it, additional design characteristics that define the bearing in location design have to be defined. The location designed is the one usually responsible for the bearing design. This person has to consider the requirements for accuracy of run, service temperature and lubrication, as well as the assembly and disassembly method. In order to meet all different requirements for proper run of bearing, bearings are produced in many versions that are characterized with an additional identification of bearings. Thus, bearings with required tolerances, clearances, materials, cage design or sealing can be selected. Also, accordingly with the identification system, bearings can be specified for certain service conditions that may be characteristic with high revolutions or high temperature, or alternatives of bearings for certain locations can be selected by the knowledge of identification of other bearing manufacturers.

7.2 Main dimensions

Rolling bearings are supplied as a final machine part, and the designer has at disposal fixed dimensions that ensure easy exchangeability. Standardisation applies to outer dimensions important in the assembly point of view. It is convenient for manufacturers and users of bearings for technological and thus also economic reasons. It however does not state inner dimensions, such as the quantity and dimensions of rolling bodies, or designs of cages. Despite that, due to the long-term development and various design and production technology optimisations even the inner design of bearings becomes united to a significant extent.

The ISO international organization came up with dimension plans for roller bearings of metric dimensions that are defined in the below listed documents:

  • ISO 15:1998 applies to radial roller bearings of metric dimensions, with the exception of tapered bearings;
  • ISO 355:1997 applies to radial tapered bearings of metric dimensions;
  • ISO 104:2002 applies to thrust roller bearings of metric dimensions;
  • ISO 582:1995 applies to maximum values of bevelling the assembly edges of bearings.

7.2.1 ISO dimension plans

ISO dimension plan allocates to each bearing hole diameter d multiple outer diameters D, and to those different widths B – or – more precisely - T for radial and H for thrust bearings. Bearings with the same hole diameter and same outer diameter belong in one diameter row identified by ascending outer diameter with figures 7, 8, 9, 0, 1, 2, 3, 4. Every diameter row contains bearings of different width rows by ascending width: 8, 0, 1, 2, 3, 4, 5, 6 and 7 for radial bearings. Width rows of radial bearings correspond with height rows of thrust bearings (height rows by ascending height 7, 9, 1 and 2).

Combining the diameter and width row creates dimension rows that are identified by double figure where the first figure identified the width row, and the second figure identifies the diameter row. This system is clearly indicated in fig. 7.1.

Fig. 7.1

The ISO dimension plan also contains dimensions of bearing ring edge fillet, the so-called installation fillet (fig. 7.2). The chart section of the catalogue indicates minimum installation fillet values for individual bearing types that you need to know when designing radiuses of transmission of components forming the bearing location.

Fig. 7.2

See Chart 7.1 for an overview of the installation fillet complying with the international standard ISO 582.

Table 7.1

7.2.2 Accuracy of bearings

Accuracy of bearings means accuracy of bearing dimensions and run. Bearings are made in the accuracy classes P0, P6, P5, P5A, P4, P4A, P2, SP and UP. The P0 accuracy is general, and is not stated in the bearing identification. Descending number in the identification indicates higher bearing accuracy.

Majority locations can utilise roller bearings of normal accuracy level. Bearings with higher accuracy level are used in locations that require higher running accuracy, such as location of machine tool spindles, and where bearings exceed their limit revolutions.

The limit dimension and run accuracy values are stated in charts 7.2 to 7.12. These values comply with international standards ISO 492 a ISO 199. The P5A and P4A designation is used for bearings made in relevant accuracy level P5 and P4 but selected parameters feature higher accuracy level than is P5 and P4.

Symbols of quantities and their meaning

d . . . . . . . nominal bore diameter
d1 . . . . . . nominal diameter of bigger theoretical tapered bore diameter
d2 . . . . . . nominal diameter of shaft ring of double direction thrust bearings
Δds . . . . . deviation of individual bore diameter from nominal dimension
Δdmp . . . .  deviation of mean diameter of cylindrical bore in individual radial plane (for tapered bore applies Δdmp for theoretical bore diameter)
Δd1mp . . . deviation of mean theoretical tapered bore diameter
Δd2mp . . .  deviation of mean shaft ring bore diameter of double direction thrust bearings in individual radial plane
Vdp . . . . . dispersion of individual bore diameter in individual radial plane
Vdmp . . . . . dispersion of mean cylindrical bore diameter
Vd2p . . . . . dispersion of shaft ring bore diameter of double direction thrust bearings in individual radial plane
D . . . . . . . nominal external diameter
ΔDs . . . . . deviation of individual outer diameter from nominal dimension
ΔDmp . . . . deviation of mean diameter of cylindrical surface in individual radial plane
VDp . . . . . dispersion of individual outer cylindrical surface diameter in individual radial plane
VDmp . . . . dispersion of mean outer cylindrical bore diameter
B . . . . . . . nominal inner ring width
T . . . . . . . nominal total width of tapered bearings
T1 . . . . . . nominal effective width of inner semi-unit
T2 . . . . . . nominal effective width of outer semi-unit
ΔBs . . . . . deviation of individual inner ring width
ΔCs . . . . . deviation of individual outer ring width
ΔTs . . . . . deviation of (total) individual bearing width
ΔT1s . . . . deviation of effective width of inner semi-unit
ΔT2s . . . . deviation of effective width of outer semi-unit
C . . . . . . . nominal outer ring width
VBs . . . . . dispersion of individual inner ring width
VCs . . . . . dispersion of individual outer ring width
Kia . . . . . . radial runout of assembled bearing inner ring
Kea . . . . . radial runout of assembled bearing outer ring
Si . . . . . . axial runout of shaft ring raceway
Se . . . . . . axial runout of body ring raceway
Sia . . . . . . axial runout of basic front of assembled bearing inner ring
Sea . . . . . axial runout of basic front of assembled bearing outer ring
Sd . . . . . . axial runout of basic front
SD . . . . . . runout of outer surface against ring front
Ss . . . . . . runout of inner ring support front against basic front for single row tapered bearings

Limit values of individual parameters for different accuracy levels are stated in the below charts.

Table 7.2

Table 7.3

Table 7.4a

Table 7.4b

Table 7.5

Table 7.6

Table 7.7

Table 7.8

Table 7.9

Table 7.10

Table 7.11a

Table 7.11b

Table 7.12a

Table 7.12b

Table 7.13a

Table 7.13b

Table 7.14a

Table 7.14b

Table 7.15a

Table 7.15b

Table 7.16a

Table 7.16b

7.2.3 Inner clearances of bearings

Clearance in bearing is the value of length of displacement of one assembled bearing ring towards the second ring from one marginal position to another (see fig. 7.3). The displacement can be in radial direction (radial clearance), or in axial direction (axial clearance).

Fig. 7.3

In an in-built bearing we usually detect lower radial clearance than has the same bearing in unassembled state. Reduction of radial clearance is caused by the overlap sizes of bearing rings on the journal and in the body bore, and is therefore dependant on the selected tolerances of location surface diameters for the bearing. Further change of radial clearance, particularly its reduction, takes place during the operation due to temperature induced by the bearing operation itself, and by external sources, and also due to flexible deformations caused by load. Decisive is for bearing in stabilised service effects. Small prestress between the balls and raceways usually does not have negative effect.

Cylindrical roller, tapered roller, sphecical roller bearings feature higher rigidity, and therefore they are supposed to have smaller service clearance that is necessary to ensure safe and reliable run, mainly in heavy service conditions. If extremely high rigidity of location is required, e.g. for machine tools, prestressed bearings are mounted.

For normal design bearings the clearance is adjusted so that one of the bearing rings could be located firmly which is sufficient for majority of service ratios in location. Special cases of location with other requirements for radial clearance require bearings with radial clearance designated C1 to C5.

Values of different inner clearance levels according to ISO 5753 standard are for individual design bearing groups stated in charts 7.17 to 7.23 whilst these values apply to non-mounted bearings in zero load during measuring.

Table 7.17a

Table 7.17b

Table 7.18

Table 7.19

Table 7.20

Table 7.21

Table 7.22

Table 7.23

For double row ball bearings with angular contact, axial clearance measured at axial load of 100 N is stated instead of radial clearance.

If different clearance is selected than normal, one needs to process carefully and consider the effect if operating conditions at stabilised state. Radial clearance smaller than normal is selected quite rarely, e.g. in roller bearings for machine tool spindles. More often bearings with radial clearance bigger than normal are needed. This happens mostly in case the limit revolutions are exceeded, or in case of higher temperature gradient between the inner an outer ring and, finally, to increase axial load capacity of single row ball bearings. Axial load capacity of these bearings is increased at the clearance of C3 by approx. 10 %, and at clearance C4 by approx. 20 % in normal conditions.

It is understandable that not only too small but also too big radial clearance has negative effect on the operation and life service of roller bearing. As we know from experience, roller bearing is more negatively affected by small radial clearance than by big. If the thermal service conditions in the bearing are unclear, it is safer to select quite bigger radial clearance that might in an extreme case reduce the service life of the bearing which is insignificant.

Single row ball bearings with angular contact and single row tapered roller bearings are usually mounted in pairs in which radial or axial clearance or prestress are adjusted during the assembly. With advantage the property of the so-called combined bearings can be utilised in which the final axial clearance is set by the bearing manufacturer.

Dependence of radial and axial clearance in some bearing types is clear from chart 7.24.

Table 7.24

Figure 7.4 shows an informative graph of dependence of radial an axial clearance in bearing, applicable to single row ball bearings.

Fig. 7.4

7.3 Roller bearings materials

7.3.1 Materials of bearing rings and rolling bodies

In terms of materials used for production of roller bearings, durability and reliability of roller bearings is specifically increased by using more accurate metallurgical technologies based on recent surveys. Previous studies already demonstrated a direct connection between micropurity of the bearing steel used, and the occurrence of subsurface fatigue damage in the rolling contact. With regard to high pressures in the area of the rolling contact, strict requirements for micropurity and uniformity of distribution of carbidic phases are reasonable. The requirement of continuous durability increase can be satisfied by highly accurate and quality production combined with using materials with low content of oxygen and non-metal intrusions, and technologically correct thermal processing of rings and bearing rolling bodies when specified hardness, microstructure and dimensional stability is achieved. This provides resistance to wear and necessary load capacity of rolling contact. Chemical composition and maximum contents of undesired elements are defined in the international standard for bearing steels ISO 683-17.

 

For locations with a risk of damage in the area of rolling contact due to passage of electric current, bearings with ceramic insulation coating of the outer ring can be supplied.

 

If there are special requirements for material, design or use of bearings, information is available at the ZKL‘s technical an consultancy centre.

Semiproducts

Besides economic criteria, a semiproduct for production of roller bearings and rolling elements has to comply with technological requirements in terms of proper course of fibres and proper distribution of carbidic phases. For the economic reason and also due to convenient passage of fibres, the most convenient is using a tube semiproduct that is cold rolled to final shape prior to thermal processing. In this way, the majority of the bearing assortment with increased basic durability is produced with the identification “NEW FORCE“.

Through-hardening steels

Majority of standard produced ZKL roller bearings are made of through-hardening steels designed for production of roller bearings. Those are carbon – chromium steels with an approximate content of 1 % carbon and 1.5 % chromium, complying with the international standard ISO 683-17 “Heat-treated steels, alloy steels and free-cutting steels, Part17: Steels for rolling bearings”. After heat treatment, material has the same structure and hardness throughout the component section. After performed martensitic or bainite hardening and subsequent tempering, the hardness of final surfaces is 58 to 65 HRC.

Depending on the type, the highest service temperature of 120 °C to 200 °C is recommended for standard ZKL roller bearings. The maximum temperature for using the bearings depends on heat treatment of bearing components. For operation at temperatures to 250 °C, bearing components can stabilize in a special heat treatment process. In case of thermal stabilization for operation at higher temperatures, the hardness of components reduces significantly, and thus also the dynamic load capacity of the bearings. If long-term operation above 250 °C is required, we recommend bearings from high alloy steels designed for high temperatures.

Case hardening steels

After saturation with carbon and hardening, bearing components feature hard surface and simultaneously also tough core. They are used for production of bearings that are loadable with big strokes, locations with big overlap or alternatively for locations with a possibility of contaminated lubrication.

Corrosion-proof steels

Tyto oceli se používají pro ložiska určená pro provoz v oxidačním prostředí, například pro leteckou techniku nebo potravinářský průmysl.

Steels for high temperatures

These materials are used for bearings operating permanently at temperatures over 250 °C whilst maintaining hardness and standard service properties, e.g. in aircraft engines.

Steels for surface hardening

These steels offer convenient combination of hardened tough raceway with tough section core. They are used mainly in large bearings, or bearings with clamp flanges which are contained in bearing rings.

7.3.2 Materials for production of cages

Materials used for production of cages are selected with regard to the service temperature of the bearing, whether the bearing will operate in standard or vibrating environment, alternatively upon the requirements for chemical or corrosion resistance.

The basic quality of materials used for production of cages is good abrasion resistance and slip properties along with sufficient ductility.

Pressed steel cages

They are pressed from low carbon steels that ensure accuracy of final cage shape, as well as sufficient ductility. To improve slip properties and abrasion resistance, the surface of pressed cages is chemically and thermally treated. They suit typical temperature regimen of bearing operation up to 300 °C.

In smaller bearings sizes, pressed cages are even made of brass sheet.

Massive brass cages

They are made in routing from roughened or spun semiproducts. Service temperature should not exceed 250 °C.

Massive steel cages

In justified cases they are an alternative to brass massive cages. Service temperature may range up to 300 °C. The surface of the cage can be chemically and thermally treated.

7.3.3 Other materials

Polymers

Polymers, usually of polyamide 66 reinforced with glass fibres, are used mainly for production of cages and cage guide rings of double row spherical roller bearings of CJ design. Service operation of these components should not exceed 120 °C in the long term with the use of common lubricants, 150 °C in the short term (within 10 hours), and 170 °C in peaks (within 20 minutes). Usefulness of bearings with polyamide components at lower temperatures is, with regard to polyamide elasticity loss, up to the temperatures of -40 °C.

Ceramic materials

Are used mostly to prevent bearings from damage by passage of electric current, either in form of thermally layered coats on the surface of the outer or inner ring, alternatively by using rolling ceramic elements. Use of rolling elements from ceramic material is justified even in special high-revolution bearings.

Other

Materials of contact seals are selected so as their thermal and degradation resistance suited the selected use.

7.4 Cages

Cage has the below functions in a roller bearing: Distributes rolling bodies uniformly around the circumference and prevents their mutual contact which reduced friction in the bearing. It prevents slippage of rolling bodies in the bearing and falling rolling bodies out of separable bearings during their assembly.

In terms of design and materials, cages are divided in pressed (fig. 7.5) and massive (fig. 7.6).

Pressed cages are made mostly by pressing from steel or brass sheet, and usually are used in dimensionally smaller up to medium bearings. Comparing to massive cages, their advantage is lower weight.

Fig. 7.5 Fig. 7.6

Massive cages are made of steel, brass, bronze, light metals or plastics in various designs. Metal cage materials are used whenever increased requirements are imposed on the rigidity of the cage, and the bearing is designed for higher service temperatures. Cages in bearing run radially on rolling elements which is the most common way, or on flange of one of the bearing rings (fig. 7.7).

Fig. 7.7

Massive polymer cages are made by injection moulding. The injection moulding technology allows to production such cage shapes that enable designing bearings with high load capacity. Elasticity and low polyamide weight applies positively in shock stress of bearings, high acceleration and deceleration. Polyamide cages feature good slip properties. During lubrication of bearings with oil, the additives contained in the oil may affect negatively the service life of the cage.

Cages made of phenological resin are light but not suitable to high temperatures. They however feature good resistance to centrifugal forces. They are typically use in accurate ball bearings with angular contact.

Journal cages are made of steel; the condition is use of holy rolling bodies (fig. 7.8). Journal cages are used mainly in large bearings.

Fig. 7.8

Cageless bearings, i.e. fully complement, are used rarely – only in some types of bearings, e.g. single row cylindrical roller bearings.

In texts to individual design bearing groups the section dedicated to cages always states an overview of cages made in the general design, and delivery option of bearings with cages in different designs.

7.5 Shield and seals

Bearings with covers on one or both sides are made with shields (Z, 2Z, ZR, 2ZR – fig. 7.9), or with contact seal ((RS, 2RS, RSR, 2RSR – fig. 7.10). Shields create create contact-free sealing. In Z or 2Z version, the fitting for shield is on the inner ring; ZR or 2ZR variants have shield adhered to the smooth flange of the inner ring.

Fig. 7.9 Fig. 7.10

The seal consists of sealing rings of nitrile rubber vulcanized on metal reinforcements that form an efficient contact seal in a design with rounded fitting on the inner ring (RS, 2RS), or in a design with contact on the smooth flange of the inner ring (RSR, 2RSR).

Shields and sealing rings are fastened in the outer ring recess, and are not detachable.

Bearings in basic design are filled with a quality plastic lubricant with temperature range between -30 °C and +100 °C, in the short term even up to +120 °C. Filler of grease usually ensures greasing throughout the service life in normal service conditions. Bearings in this design cannot be additionally greased.

7.6 Designation of roller bearings

Bearing is designated by basic designation and extension expressing the difference between this bearing and the standard version bearing. Designation of bearings contains numerical and literal characters that determine the type, size and design of the bearing. Overview of symbols and their order is based on the scheme shown in figure 7.11.

Fig. 7.11

7.6.1 Standard bearing version

In standard version, bearings are identified with basic designation consisting of the identification of the type and size of the bearing. The designation usually consists of a symbol expressing the design of the bearing (position 3 of the scheme), and a symbol for the dimensional group or diameter row (positions 4 and 5), e.g. type 223, 302, NJ22, 511, 62, 12 and so on. Designation of the bearing size contains characters for nominal bearing bore diameter d (position 6).

Bearings with bore diameter d < 10 mm:

Figures separate with fraction line or the last digit states directly the nominal bore dimension in mm, e.g. 619/2, 624.

Bearings with bore diameter d = 10 up to 17 mm:

double issue 00 identifies the bore d = 10 mm, e.g.: 6200
  01   d = 12 mm, e.g.: 51101
  02   d = 15 mm, e.g.: 3202
  03   d = 17 mm, e.g.: 6303

Exception in designation are single row ball bearings of separable type E and BO where the double issue states directly the bore diameter in mm, e.g.: E17.

Bearings with bore diameter d = 20 mm up to 480 mm

Bore diameter is quintuple of the last double issue, e.g. bearing 1320 features bore diameter d = 20 x 5 = 100 mm.

Exceptions are bearings with bore diameter d = 22, 28 and 32 mm where the double issue separated with fraction line stated directly the diameter of bore in mm, e.g. 320/32AX, and some bearing types, such as e.g. separable single row ball bearings of E type, and single row ball bearings of NG type where the double or triple issue states directly the bore diameter in mm, e.g.: E20, NG160.

Bearings with bore diameter d > 500 mm:

The last double issue or triple digit separated with fraction line states directly the bore dimension in mm, e.g. 30/530M, NU29/1060.

7.6.2 Full designation of bearings

Bearing produced in designs different from the standard are identified by the so-called designation, as is shown in the scheme in fig. 7.11. It consists of the basic designation and supplementary characters that express the difference from the basic version.

Meaning of supplementary characters

The following part states, in accordance with full designation, an overview and meaning of supplementary characters used. The digit in the bracket stated with individual groups corresponds with the position number in the scheme. The scheme also states positions in full designation of the bearing that us separated with a gap.

Other characters are written together without a gap. Characters for extension of designation that mean a digit are separated with a dash from the basic designation, e.g. 6305-2Z.

The meaning of supplementary characters for design variances of different bearing types is described in relevant chapters of the chart section of the catalogue.

Supplementary characters before basic designation Other material than common steel for roller bearings (1)

C . . . . . . . rolling elements from ceramics – e.g. C B7006CTA
HSS . . . . high speed steel, e.g.: HSS 6215
X . . . . . . . corrosion resistant steel, e.g.: X 623
T . . . . . . . case hardening steel, e.g.: T 32240

Bearing incompleteness (2)

L . . . . . .  separate detachable ring of separable bearing, e.g. L NU206, in thrust ball bearings without a shaft ring, e.g. L 51215
R . . . . . . separable bearing without detachable ring, e.g. R NU206 nebo R N310
E . . . . . . separate shaft ring or thrust ball bearing, e.g. E 51314
W . . . . . separate body ring of thrust ball bearing, e.g. W 51414
K . . . . . . cage with rolling elements e.g.: K NU320

Supplementary characters behind the basic designation
Difference in inner design (7)
A . . . . . . .  single row angular-contact ball bearings with contact angle α = 25°, e.g. B7205ATB P5
. . . . .  single row tapered bearings with higher load capacity and higher limit revolution frequency, e.g. 30206A
. . . . .  thrust ball bearings with higher limit revolution frequency, e.g. 51,105A
AA . . . . . .  single row angular-contact ball bearings with contact angle α = 26°, e.g. B7210AATB P5
B . . . . . . . single row angular-contact ball bearings with contact angle α = 40°, e.g. 7304B
. . . . . single row tapered bearings with contact angle α > 17°, e.g. 32315B
BE . . . . . single row angular-contact ball bearings with contact angle α = 40°, in new design, e.g. 7310BETNG
C . . . . . . .  single row angular-contact ball bearings with contact angle α = 15°, e.g. 7220CTB P4
. . . . . double row spherical roller bearings in new design, e.g. 22216C
CA . . . . . . single row angular-contact ball bearings with contact angle α = 12°, e.g. B7202CATB P5
CB . . . . .  single row angular-contact ball bearings with contact angle α = 10°, e.g. B7206CBTB P4
D . . . . . . . single row ball bearing of type 160 with higher load capacity, e.g. 16004D
E . . . . . . . single row cylindrical roller bearings with higher load capacity, e.g. NU209E
. . . . double row spherical roller bearings with higher load capacity, e.g. 22215E
. . . . Spherical roller thrust bearings with higher load capacity, e.g. 29416E

 

Difference in main dimensions (8)

X . . . . . . . Change in main dimensions, established by new international standards, e.g. 32028AX

Covers (9)

RS . . . . . seal on one side, e.g. 6304RS
2RS . . . . seal on both sides, e.g. 6204-2RS
RSN . . . .  seal on one side and snap ring groove on the outer ring on the opposite side than the seal, e.g. 6306RSN
RSNB . . .  seal on one side and snap ring groove on the outer ring on the same side as the seal, e.g. 6210RSNB
2RSN . . .  seal on both sides and snap ring groove on the outer ring, e.g. 6310-2RSN
RSR . . . .  seal on one side, adhering to the smooth inner ring collar, e.g. 624RSR
2RSR . . .  2RSR – seals on both sides adhering to the smooth inner ring collar, e.g. 608-2RSR
Z . . . . . . . shield on one side, e.g. 6206Z
2Z . . . . . . shields on both sides, e.g. 6304-2Z
ZN . . . . .  shield on one side and snap ring groove on the outer ring on the opposite side than the shield, e.g. 6208ZN
ZNB . . . .  shield on one side and snap ring groove on the outer ring on the same side as the shield, e.g. 6306ZNB
2ZN . . . .  shields on both sides and snap ring groove on the outer ring, e.g. 6208-2ZN
ZR . . . . .  shield on one side, adhering to the smooth inner ring flange, e.g. 608ZR
2ZR . . . .  shields on both sides, adhering to the smooth inner ring flanges, e.g. 608-2ZR

Design change of bearing rings (10)

K . . . . . . . Tapered bore, taper ratio 1:12, e.g. 1207K
K30 . . . . Tapered bore, taper ratio 01:30:00, e.g. 24064K30M
N . . . . . . . snap ring groove on the outer ring, e.g. 6308N
NR . . . . .  snap ring groove on the outer ring, and inserted snap ring, e.g. 6310NR
NX . . . . .  snap ring groove on the outer ring, dimensions of which do not comply with ČSN 02 4605, e.g. 6210NX
D . . . . . . . split inner ring, e.g. 3309D
W33 . . . . groove and lubrication bores on the outer ring circumference, e.g. 23148W33M
O . . . . . . . lubrication slots on outer ring fillet of the bearing , e.g. NU1014O

Cage (11)

Material of cages for standard design bearings is usually not specified.
J . . . . . . . cage pressed from steel plate, guided on rolling elements e.g.: 6034J
J2 . . . . . .  cage pressed from steel plate, guided on rolling elements. New design of single row tapered bearings, e.g. 30206AJ2
Y . . . . . . . cage pressed from brass sheet, guided on rolling elements e.g.: 6001Y
F . . . . . . . massive steel cage, guided on rolling elements e.g.: 6418F
L . . . . . . . massive light metal cage, guided on rolling elements e.g.: NG180L C3S0
M . . . . . . massive brass or bronze cage, guided on rolling elements e.g.: NU330M
T . . . . . . . massive textite cage, guided on rolling elements e.g.: 6005T
TN . . . . .  massive cage of polyamide or similar plastic, guided on rolling elements e.g.: 6207TN
TNG . . . .  massive cage of polyamide or similar plastic, reinforced by glass fibres, guided on rolling elements e.g.: 2305TNG

Cage design (stated characters are always used in combination with cage material characters).

A . . . . . . cage guided on outer ring, e.g. NU226MA
B . . . . . . cage guided on inner ring, e.g. B7204CATB P5
P . . . . . . massive window cage, e.g.: NU1060MAP
H . . . . . . open single-piece cage, e.g.: 629TNH
S . . . . . . cage with lubrication slots, e.g.: NJ418MAS
R . . . . . . silver-plated cage, e.g.: 6210MAR
V . . . . . . bearing without cage with full number of rolling elements, e.g. NU209V

Accuracy level (12)

P0 . . . . . normal accuracy level (is not designated), e.g. 6204
P6 . . . . . higher accuracy level than normal, e.g. 6322 P6
P5 . . . . . higher accuracy level than P6, e.g. 6201 P5
P5A . . . . higher accuracy level than P5 in some parameters, e.g. 6006TB P5A
P4 . . . . . higher accuracy level than P5, e.g. B7204CBTB P4
P4A . . . . higher accuracy level than P4 in some parameters, e.g. B7205CATB P4A
P2 . . . . . higher accuracy level than P4, e.g. B7200CBTB P2
P6E . . . . higher accuracy level for rotary electrical machines, e.g. 6204 P6E
P6X . . . . higher accuracy level for single row tapered bearings, e.g. 30210A P6X
SP . . . . . higher accuracy level for roller bearings with tapered bore, e.g. NN3022K SPC2NA
UP . . . . .  higher accuracy level such as SP for roller bearings with tapered bore, e.g. N1016K UPC1NA

Clearance (13)

C2 . . . . . . smaller clearance than normal, e.g. 608 C2
. . . . . normal clearance (is not designated), e.g. 6204
C3 . . . . . . bigger clearance than normal, e.g. 6310 C3
C4 . . . . . . bigger clearance than C3, e.g. NU320M C4
C5 . . . . . . bigger clearance than C4, e.g. 22330M C5
NA . . . . . radial clearance in bearings with incommutable rings (is indicated always behind the radial clearance group), e.g. NU215 P63NA
R… . . . . radial clearance in non-standardised range (range in μm) , e.g. 6210 R10-20
A… . . . . . axial clearance in non-standardised range (range in μm) , e.g. 3210 A20-30

Noise level (14)

C6 . . . . . . reduced noise level lower than normal (is not designated), e.g. 6304 C6
C06 . . . . reduced noise level lower than C6, e.g. 6205 C06
C66 . . . . reduced noise level lower than C06, e.g. 6205 C66

Specific values for C06 and C66 are determined based on an agreement between customer and supplier.
Note: Bearings in accuracy level P5 and higher feature noise level within C6.

Increased operational safety (15)

C7, C8, C9 . . . . . bearings with increased operational safety designed mainly for use in aviation industry, e.g. 6008MB P68

Combining characters (12-15)

Characters/symbols of accuracy level, clearance in bearing, noise levels and increased operational safety are combined with simultaneous omission of C character and following special property of bearings, e.g.

P6 + C3 = P63 . . . . . . . . . . . . . . . e.g.: 6211 P63
P6 + C8 = P68 . . . . . . . . . . . . . . . e.g.: 16002 P68
C3 + C6 = C36 . . . . . . . . . . . . . . . . e.g.: 6303-2RS C36
P5 + C3 + C9 = P539 . . . . . . . . . . e.g.: 6205MA P539
P6 + C2NA + C6 = P626NA . . . . . e.g.: NU1038 P626NA

Bearing association (16)

Designation of associated pair, triplet or quaternion of bearings consists of characters expressing arrangement of bearings and of characters defining the inner clearance or prestress of associated bearings.

Apart from characters stated in the chart the U character is used to identify that relevant bearings can be associate universally, example of designation B7003CTA P4UL.

Fig. 7.12

Inner clearance or prestress

Stated characters are always used in combination with association characters.

A . . . . . . . Association of bearings with clearances, e.g. 7305OA
O . . . . . . . Association of bearings without clearances, e.g. 7305 P6XO
L . . . . . . . Association of bearings with small prestress, e.g. B7205CATB P4UL
M . . . . . . Association of bearings with medium prestress, e.g. B7204CATB P5XM
S . . . . . . . Association of bearings with big prestress, e.g. B7304AATB P4OS

Stabilisation for operation at higher temperature (17)

Both rings have stabilised dimensions for operation at higher temperature.

S0 – for service temperature . . . . . . .up to 150 °C
S1 . . . . . . . . . . . . . . . . . . . . . . . . . . .up to 200 °C
S2 . . . . . . . . . . . . . . . . . . . . . . . . . . .up to 250 °C
S3 . . . . . . . . . . . . . . . . . . . . . . . . . . .up to 300 °C
S4 . . . . . . . . . . . . . . . . . . . . . . . . . . .up to 350 °C
S5 . . . . . . . . . . . . . . . . . . . . . . . . . . .up to 400 °C

Example of designation NG160LB C4S3

Friction torque (18)

JU . . . . . . reduced friction torque, e.g. 619/2 JU
JUA . . . . . bearings with defined friction torque at start-up 632 JUA
JUB . . . . . bearings with defined friction torque at after-running, e.g. 623 JUB

Grease (19)

For bearings with shield or seal on both sides, the plastic lubrication other than common is designated by means additional characters. The first two characters define the range of service temperature, and the third character (letter) defines the name or type of lubricant according to the manufacturer‘s specification, or another character (digit) defines the amount of grease that fills the covered space of the bearing.

TL . . . . . . grease for low service temperatures from -60 °C to +100 °C
. . . . . . . . example of designation 6302 2RSTL
TM . . . . . grease for medium service temperatures from -35 °C to +140 °C
. . . . . . . . example of designation 6204 2ZRTM
TH . . . . . grease for high service temperatures from -30 °C to +200 °C
. . . . . . . . example of designation 6202 2ZTH
TW . . . . . grease for both low and high service temperatures from -40 °C to +150 °C
. . . . . . . . example of designation 6310 2ZC4TW
Note: The TM marking need not be stated on bearings and packing.

Bearings by special technical conditions

Single purpose bearings dimensions of which comply with the dimensional plan but the list of all characters of extension expressing their technical characteristics would cause confusion of marking, can be upon agreement between manufacturer and customer replaced with basic designation, attaching the TPF or TPFK marking and a two- or three-digit number behind the basic designation of the bearing, which defines the number of the agreed technical specification determining all technical parameters of bearings.

TPF . . . . .  bearings made by special technical conditions agreed with customer, e.g. bearing 6205MA P66 by technical terms TPF 11142-71 is designated as follows: 6205MA P66 TPF 142.

TPFK . . . . bearings by special technical terms agreed with customer which have high number of characters stating changes against the basic version. In this case, basic characters are replaced with designation TPFK containing relevant number of technical terms, e.g. bearing NU1015 made by technical terms. TPFK 11137-70 is designated as NU1015 TPFK137.

Bearings by special drawing documentation PLC

Bearings which by some of their dimension do not comply with the dimensional plan or are in line with the next development are marked with PLC by their manufacturer, as well as with other numerical characters. Usually they are single purpose bearings for one customer or a certain application method.

PLC ABC-DE.F (designation structure until 2012)
PLC . . . . identification of special roller bearing
A . . . . . . . design assembly
0 . . . . . . . single row ball bearings
1 . . . . . . . double row ball bearings
2 . . . . . . . thurst ball bearings
3 . . . . . . . Not completed
4 . . . . . . . single row cylindrical roller, spherical-roller and needle roller bearings
5 . . . . . . . double and multirow cylindrical roller, spherical-roller and needle roller bearings
6 . . . . . . . single row, double row and four row tapered roller bearings
7 . . . . . . . special double row bearings
8 . . . . . . . assembly units and separate parts
9 . . . . . . . thrust cylindrical roller, spherical roller, tapered roller and needle roller beariings
BC . . . . . dimensional assembly – two digit characters
DE . . . . . ordinal number within dimensional assembly – two digit characters
F . . . . . . . difference in design - one digit or combination of numerical character and letter

Due to extending the assortment of special bearings, it was decided in 2013 to change the structure of designating special bearings: Upon the establishing of a new system, the designation on already produced bearings will not be changed.

PLC AB-CD-EF.G (designation structure since 2013)
PLC . . . . identification of special roller bearing
A . . . . . . . design assembly
1 . . . . . . . ball bearings
2 . . . . . . . thrust ball bearings
3 . . . . . . . cylindrical roller bearings
4 . . . . . . . thrust cylindrical roller bearings
5 . . . . . . . needle roller bearings
6 . . . . . . . spherical-roller bearings
7 . . . . . . . spherical roller thrust bearings
8 . . . . . . . tapered roller bearings
9 . . . . . . . thrust tapered roller bearings
0 . . . . . . other bearings and mounting assemblies
B . . . . . . . number of rolling units or bearings in mounting assemblies
CD . . . . . dimensional assembly – two digit characters
EF . . . . . . ordinal number within dimensional assembly – two digit characters
G . . . . . . . difference in design - one digit or combination of numerical character and letter

7.7 NEW FORCE bearings

In order to satisfy the needs of technically advanced customers, ZKL pays particular attention to technical development of products and investments in new technologies. The outcome of one of the recent key innovations is initiation of successive start up of production of ZKL bearings with higher quality standard with designation NEW FORCE.

The NEW FORCE bearings represent a new generation of ZKL bearings. Launching of bearings brings customers higher durability of bearings, enhanced operational safety, prolonged maintenance intervals and thus substantial reduction of operating costs. NEW FORCE bearings are designed for extreme locations of transmissions, railway vehicles, presses, rolling mills, paper machines, pumps, machine tools, power engineering plants, polygraphic machines, etc.

As the first integrated new generation bearings, the radial spherical-roller bearings were launched on the market, double row self-aligning ball bearings, double row angular-contact ball bearings and thrust ball bearings. The next phase of launching bearings of this standard was the production assortment of bearings with outer diameter over 400 mm.

The achieved parameters of NEW FORCE bearings are the result of ZKL development in the following areas:

  • Material of roller bearing components
  • Technology of bearing ring flaring
  • Optimisation of inner construction
  • Surface treatments of bearing components

The achieved results allowed ZKL to offer NEW FORCE roller bearings with high utility properties to their customers:

  • high dynamic load capacity
  • low friction
  • reliability in the extreme operating conditions

High durability of bearings

Increase of dynamic load capacity by 8 % to 25 % brings increase of durability of bearings by 30 % up to 110 %, comparing to the up-to-now designs.

Increase of dynamic load capacity allows customer to design construction with smaller dimensions to transfer the same load. Thus ZKL brings to their customer an opportunity to reduce total price of the equipment, and achieve power savings during operation.

Fig. 7.13

Use of quality bearing material

Steels for production of bearings meet the parameters of international standards defined by ISO 683-17. Production of bearing rings and rolling elements utilised high quality material of selected smelting houses. Long-term cooperation with suppliers ensures continuous process of improving parameters of input material.

Key quality parameters of steel and its processing affect the service properties of bearing, i.e. resistance to fatigue damage, abrasion resistance and dimensional stability. These are:

  • chemical composition and heat treatment

Selection of the type of bearing steel and optimisation of heat treatment conditions is conducted by the dimension of the component. The heat treatment processing technology of NEW FORCE bearings ensures stabile hardness values of bearing components in the entire section. Spherical-roller bearing components are heat treated to ideal material structure and hardness that enable using of the bearings at service temperatures to 200 °C. The final material structure ensures dimensional stability of bearing components throughout their service life.

  • Content of non-metal intrusions – micropurity

Reduction of content of non-metal intrusions is the key quality parameter in the bearing steel metallurgy development. In production of bearings, ZKL utilises bearing steel with minimum oxygen content.

  • Type of semiproduct

The quality of bearing and production economics are affected also by selection of the semiproduct type. The level of forming and positive angle of forming fibre contact towards the orbit are the parameters that positively increase resistance of the NEW FORCE bearings against fatigue damage.

Technology of bearing ring rolling

Basic research demonstrated effect of material fibre direction towards the contact surface to the durability of bearings. Most convenient is such layout of fibres when their direction is in parallel with the contact surface. With increasing fibre direction angle towards the contact surface the durability decreases. The technology of cold or semi-heating rolling brought an ideal material structure of the NEW FORCE bearings in order to achieve higher durability of bearings.

Fig. 7.14

Fig. 7.15

Optimised design and inner geometry

Advanced design and calculation programs, together with new bearing production technologies, enabled optimisation of inner construction of bearings and improved accuracy of functional areas. Thus the NEW FORCE version bearings achieved better quality of functional surfaces and improved course of discharge voltages in bearing component sections, comparing to the standard bearing designs. This brings reduced noise level and higher accuracy of bearing run, as well as extended durability of bearings.

Special surface treatment

Within innovation programs, a new design of sheet cages for radial and thrust spherical-roller bearings was launched in the production. Cages are made of steel plate with surface treatment in order to improve slip properties and reduce wear of cages. The design of cages allows achieving better lubrication and extended service life of bearings. Surface treatments of bearing components represent a well tested way of improving bearing properties for certain locations. The benefit of surface layers lies in better keeping the lubricant in the rolling contact, reduced friction and enhanced resistance to wear and corrosion. We recommend that suitability of surface treatment for special operating condition is discussed with the technical and consultancy services of ZKL.

Bearings NEW FORCE +

ZKL bearings with NEW FORCE+ marking represent a brand new generation of ZKL bearings which is characterised by an innovated modification of the bearing inner structure geometry towards optimum voltage course in the area of rolling contact. This ZKL bearings‘ innovation is associated with further enhancement of accuracy, comparing to the standardly produced bearing assortment, including the NEW FORCE bearings.

Optimisation of the shape of rolling surfaces brings improved dynamic load capacity of bearings and thus also significant extension of bearings‘ durability. Development of the NEW FORCE+ generation is associated with the introduction of new calculation methods in the structure of bearings based on FEM and production upgrade by introducing numerically controlled machines that enable achieving final shapes of functional surfaces with modified geometry.

With regard to the fact that the entire design optimisation and production process of modified parts is unique for every bearing application, the NEW FORCE+ bearing generation is not designed to be launched in the standard production program of ZKL. The bearings will be manufactured upon request for extreme locations for selected OEM customers.

7.8 Technical support

ZKL operates as bearing manufacturer and supplier already since 1947. Since the beginning, the company has been cooperating with their customers worldwide. This allows continuous expansion of the ZKL rolling bearing production assortment offered in maximum quality at reasonable price. Experience in operation of bearings obtained in cooperation with customers, along with continuous education of their employees allows ongoing development of technical support to ZKL customers and extension of services for ZKL bearing users.

Proposal verification

The ZKL bearings‘ structure and their basic parameters are designed by the ZKL‘s own well tested methodologies that adhere to the international ISO standards. Designing new bearings utilises most sophisticated design and calculation CAD systems. Designs of new bearings are optimised and their rigidity checked by means of FEM based numerical calculations. When creating designs, information obtained in achieved test results and experiences from production and operation of ZKL bearings are utilised.

Verification of quality parameters of ZKL bearings

Parameters of ZKL rolling bearings are verified in tests within development, as well as in periodical quality assessment during series production. Tests are conducted according to the company‘s own methods in the test stations of the bearing test room. Bearing and input material tests results are analysed and serve as the basis for new design, technological and investment solutions.

Technical support for ZKL bearing users

Customer needs are solved by fully available workers of ZKL technical and consultancy services. Expert workers are ready to solve operatively requests and questions of ZKL bearing users in the area of selection of bearings, design of rolling location and assembly procedures. ZKL technical support provides users with information in the area of roller bearings, accessories and tribology. Upon user‘s request it also provides professional supervision over assembly and disassembly of bearings directly at customer, and organizes professional training course of user employees. It cooperates with manufacturers in development of rolling location. It draws up expert opinions on broken bearings. It determines causes of accidents and proposes measures to prevent them.

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ZKL

ZKL is the biggest manufacturer of large-scale spherical-roller, special and split bearings in Central Europe.

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