Crossed roller bearings

Crossed roller bearings  SX :

• are suitable, due to their high running accuracy, as bearings for high precision applications (such as those in robots, machine tools, handling systems, precision mechanical and medical devices, vehicle components)
• correspond in their main dimensions to the ISO dimension series 18 with very small section height
• can support axial forces in both directions, radial loads, tilting moments and any combination of loads ➤ section
• usually allow designs with two bearing positions to be replaced by one bearing position ➤ Figure
• are very rigid (they can be supplied with normal clearance, clearance‑free or preloaded)
• are suitable for supported and suspended loads
• are always a good choice for a technically and economically leading bearing solution if compact and easy-to-fit rolling bearings with high tilting moment carrying capacity and rigidity, with uniform running free from stick-slip, low rotational resistance as well as high axial and radial runout accuracy are required in only one bearing position.

For an overview of other product-specific features, see the Matrix for bearing preselection.

Bearing design

Crossed roller bearings SX are compact locating bearings with high axial rigidity

Crossed roller bearings SX are bearings for high precision applications, whose main dimensions correspond to the ISO dimension series 18 with very small section height in accordance with DIN 616. They comprise outer rings, inner rings, rolling elements and plastic spacers. The outer ring is split in the circumferential direction and is held together by three sheet metal retaining rings ➤ Figure. The cylindrical rollers correspond to DIN 5402 and are in an X arrangement with each other on the raceways. The bearings are very rigid, have high running accuracy and are supplied with normal clearance, low clearance or preload. Bearings with preload have the suffix VSP, while bearings with low clearance have the suffix RL0 ➤ Table. The bearing outer rings are easily fixed to the adjacent construction using clamping rings ➤ link.

Also available in a corrosion-resistant design

For applications requiring high corrosion protection, the bearings are also available in a corrosion-resistant design with the special coating Corrotect.

Permissible circumferential velocities

Influencing factors

The possible circumferential velocity is dependent on the bearing (normal clearance or preloaded) and on the lubrication (grease or oil) ➤ Table.

Permissible circumferential velocities

Normal clearance	Preload	Circumferential velocity
Oil lubrication	‒	up to 8 m/s (n  ·  DM = 152 800)
Grease lubrication	‒	up to 4 m/s (n  ·  DM =  76 400)
‒	Oil lubrication	up to 4 m/s (n  ·  DM =  76 400)
‒	Grease lubrication	up to 2 m/s (n  ·  DM =  38 200)

D_M = rolling element pitch circle diameter

Load carrying capacity

Suitable for axial loads in both directions, radial loads and tilting moment loads

Due to the X arrangement of the cylindrical rollers, the bearings can support axial forces in both directions, radial loads, tilting moment loads and any combination of loads by means of a single bearing position ➤ Figure. As a result, it is generally possible to reduce conventional bearing arrangements comprising two bearing positions (bearing arrangement with one radial and one axial bearing) to one bearing position ➤ Figure and ➤ Figure. This reduces the work required and the costs for the design of the adjacent construction (only one bearing position is processed) and considerably reduces the mounting of the bearings (there is no requirement for the matching of two bearings to each other).

Angular adjustment facility

Crossed roller bearings SX cannot be used for the compensation of misalignments. These bearings are precision bearings for high precision applications. In order to ensure their correct function, it is essential that the specifications for design of the adjacent construction are observed ➤ section. Skewing of the bearing rings increases the running noise, places increased strain on the plastic spacers, has a negative effect on the running accuracy and a highly detrimental influence on the operating life of the bearings.

Lubrication

Grease or oil lubrication is possible

The bearings are greased as standard but can alternatively be lubricated with oil. The decisive factors in determining the type of lubrication and the requisite lubricant quantity are:

• the size of the bearing
• the design of the bearing environment
• the lubricant feeds
• the operating conditions.

If there is any uncertainty as to whether the lubricant or type of lubrication is suitable for a particular application, please consult Schaeffler or the lubricant manufacturer respectively.

Grease lubrication

Suitable greases

If the bearing is to be lubricated with grease, a high quality lithium soap grease to DIN 51825–KP2N–20 is suitable, for example Arcanol Load150 or Load220.

Lubrication intervals

Influences on the lubrication interval

The lubrication intervals are essentially dependent on:

• the operating conditions
• the environmental influences such as contamination, water, etc.
• the type of bearings.

Precise lubrication intervals can only be determined by means of tests under the specific application conditions. The observation period selected must be sufficiently long and the condition of the grease must be checked at regular intervals.

Grease operating life

If relubrication is not possible, the grease operating life becomes the decisive factor. Based on experience, the guide value for the grease operating life in the majority of applications is higher by a factor of 2 than the guide value for the lubrication interval. At operating temperatures above +70 °C, the lubrication interval and therefore the grease operating life are reduced. In order to ensure operational reliability, the grease operating life should not exceed 3 years.

Oil lubrication

Selection of the oil

A lubricant film which is capable of supporting loads must form in the contact zones between the rolling elements and the raceway. Depending on the operating speed, the oil at operating temperature must have at least the nominal viscosity ν₁. The guide value for ν₁ is dependent on the mean bearing diameter d_M and the speed.

Influence of temperature on viscosity

As the temperature increases, the viscosity of the oil decreases. When selecting the viscosity, the lower operating temperature must also be taken into consideration. With increasing viscosity, the flowability of the lubricant is reduced. As a result, the level of power losses will increase.

Suitable oils

For oil lubrication, suitable oils are type CLP to DIN 1517 or HLP to DIN 51524 of the viscosity classes ISO VG 10 to 100.

With oil lubrication, oil change intervals must be observed

At higher temperatures, aged oil and additives in the oil can impair the operating life of the plastic used for the spacers. Stipulated oil change intervals must therefore be observed.

Sealing

Provide seals in the adjacent construction

Crossed roller bearings SX are not sealed. As a result, sealing of the bearing position must be carried out in the adjacent construction. This must reliably prevent:

• moisture and contaminants from entering the bearing
• the egress of lubricant from the bearing.

Schaeffler seal profiles

Material by the metre for radial and/or axial sealing of the bearing position

For sealing of the bearing position in the adjacent construction, Schaeffler supplies various seal profiles by the metre ➤ Figure. These profiles are intended for axial and/or radial sealing and – depending on the seal profile – fulfil a wide range of requirements (for example: under normal requirements for sealing, under heavy contamination, for low frictional torque, if only limited space is available, for sealing of fluids, at low speeds or under swivel operation). In addition to the seal profiles with a radial or axial sealing effect respectively, double direction profiles (with both axial and radial sealing effect) are also available. Mounting drawings can be requested for the individual seal profiles.

The seal profiles are not suitable for applications that require leakage-free operation; this applies not only to oil but also to grease lubrication. If leakage losses are unacceptable, measures such as rotary shaft seals can be used. The area around the bearing seal must be designed such that the seal profiles are not damaged during operation.

Seal profile material

The standard material for the profiles is the synthetic elastomer NBR 70. This material has good resistance to oil and grease as well as good wear resistance. Operating temperature of seal profiles ➤ Table.

For further information on the seal profiles, please contact Schaeffler.

Speeds

Limiting speeds in the product tables

Rolling bearings cannot rotate at unspecified high speeds, but are generally restricted by the operating temperature that is permissible in relation to the lubricant and the material of the bearing parts ➤ section. The product tables give the kinematic limiting speeds n_G oil and n_G grease for the bearings.

The limiting speeds n_G oil and n_G grease are the kinematically permissible speeds for a bearing and apply to oil and grease lubrication respectively. Even under favourable mounting and operating conditions, these speeds must not be exceeded without prior consultation with Schaeffler.

Noise

Schaeffler Noise Index

The Schaeffler Noise Index (SGI) is not yet available for this bearing type. The data for these bearing series will be introduced and updated in stages.

Temperature range

Limiting values

The operating temperature of the bearings is limited by:

• the dimensional stability of the bearing rings and cylindrical rollers
• the material of the plastic spacers
• the lubricant
• the seal material in the adjacent construction.

Possible operating temperatures of the bearings ➤ Table.

Permissible temperature ranges

Operating temperature	Crossed roller bearings	Schaeffler seal profiles
	–30 °C to +100 °C	–40 °C to +80 °C

In the event of anticipated temperatures which lie outside the stated values, please contact Schaeffler.

Cages

The rollers are guided by plastic spacers

In the crossed roller bearings SX, the rolling elements are separated from each other and guided not by typical rolling bearing cages but by plastic spacers ➤ Figure. The plastic selected and the design of the running surfaces for the cylindrical rollers give low-friction running of the bearings.

Internal clearance

The crossed roller bearings are available:

• with normal clearance (radial and axial clearance)
• with low clearance (radial clearance/preload)
• with preload VSP (preload min. and max.).

Dimensions, tolerances

Dimension standards

The main dimensions of crossed roller bearings correspond to dimension series 18 in accordance with DIN 616.

Tolerances

The dimensional and running tolerances are based on DIN 620-2 and DIN 620-3 and are in the range P6 and P5.

Suffixes

Suffixes describe the design and features of a bearing in more detail.

Suffixes and corresponding descriptions

Suffix	Description of suffix
RR	Corrosion-resistant design, with Corrotect coating	Special design, available by agreement
RL0	Low clearance	Standard
VSP	Preloaded	Special design, available by agreement
VSP+PRL50	Preloaded, axial and radial runout tolerance restricted by 50%	Special design, available by agreement

Structure of bearing designation

With medias interchange, equivalent Schaeffler bearing designations can be determined for bearing designations from other rolling bearing manufacturers http://www.schaeffler.de/std/1B69.

Example

The designation of bearings follows a set model ➤ Figure.

Dimensioning

Static load carrying capacity

For bearings under static loading, the static load carrying capacity applies

Crossed roller bearings that undergo rotary motion only infrequently, undergo slow swivel motion, rotate only slowly or are subjected to load while stationary are dimensioned on the basis of their static load carrying capacity. The size of a statically loaded bearing can therefore be checked in approximate terms using the basic static load ratings C₀ and the static limiting load diagrams.

Checking the static load carrying capacity

It can be checked in approximate terms if the correct load arrangement is present and all the requirements relating to clamping rings, location, mounting and lubrication are fulfilled ➤ Figure.

Where load arrangements are more complex or there are variations from the conditions, please contact us.

In order to check the static load carrying capacity, the following equivalent static operating values must be determined:

• the equivalent static bearing load F_0q
• the equivalent static tilting moment load M_0q.

Checking is possible for applications with or without radial load.

Determining the equivalent static bearing load without radial load

In the presence of axial and tilting moment loads only ➤ Equation and ➤ Equation:

Equivalent axial bearing load (static)

Equivalent tilting moment load (static)

Legend

F0q	kN	Equivalent axial bearing load (static)
F0a	kN	Axial static bearing load
fA		Application factor ➤ Table
fS		Factor for additional safety ➤ link
M0q	kNm	Equivalent tilting moment load (static)
M0k	kNm	Static tilting moment load.

The values for F_0q and M_0q are used to determine the load point in the static limiting load diagram for the raceway.

In addition to the raceway, the dimensioning of the fixing screws must also be checked.

The static limiting load diagrams for the raceway and the fixing screws are indicated in the product tables.

The load point must lie under the raceway curve, otherwise the bearing is not adequately dimensioned.

Determining the equivalent static bearing load with radial load

Radial loads can only be taken into consideration if the radial load F_0r is smaller than the basic static radial load rating C_0r.

The equivalent static bearing load with radial load is determined as follows:

• Calculate the parameter for the load eccentricity ε according to ➤ Equation
• Determine the static radial load factor f_0r. In this case:
• determine the ratio F_0r/F_0a in ➤ Figure or ➤ Figure respectively
• based on the ratio F_0r/F_0a and ε, determine the static radial load factor f_0r from ➤ Figure or ➤ Figure respectively
• Determine the application factor f_A ➤ Table and, where necessary, the safety factor f_S
• Calculate the equivalent axial bearing load F_0q and the equivalent tilting moment load M_0q using the equations ➤ Equation and ➤ Equation
• Using the values for F_0q and M_0q, determine the load point in the static limiting load diagram for the raceway.

The load point must lie under the raceway curve, otherwise the bearing is not adequately dimensioned.

Load eccentricity parameter

Equivalent bearing load (static)

Equivalent tilting moment load (static)

Legend

ε		Load eccentricity parameter
M0k	kNm	Static tilting moment load
F0a	kN	Axial static bearing load
DM	mm	Rolling element pitch circle diameter
F0q	kN	Equivalent bearing load (static)
fA		Application factor ➤ Table
fS		Factor for additional safety ➤ link
f0r		Static radial load factor ➤ Figure or ➤ Figure
M0q	kNm	Equivalent tilting moment load (static).

Application factors

The application factors f_A are empirical values obtained in practice ➤ Table. They take account of the most important requirements, such as the type and severity of operation, rigidity and running accuracy. If the precise requirements of an application are known, the values may be altered accordingly.

Application factors ＜ 1 must not be used.

A large proportion of applications can be statically calculated using the factor 1, for example in the case of bearings for gearboxes and rotary tables.

In addition to static calculation, the rating life should also always be checked ➤ link.

Application factors f_A

Application	Operating and requirement criteria	Application factor fA
Robots	Rigidity	1,25
Antennae	Accuracy	1,5
Machine tools	Accuracy	1,5
Metrology	Smooth running	2
Medical equipment	Smooth running	1,5

Safety factors

The factor for additional safety f_S is 1.

It is not normally necessary to factor in any additional safety in calculation.

In special cases, such as approval specifications, internal specifications, requirements stipulated by inspection bodies etc., the appropriate safety factors must be applied.

Calculation example

The static load carrying capacity of the crossed roller bearing SX011860 is to be checked.

Given

Static bearing load (axial)	F0a	=	70 kN
Static bearing load (radial)	F0r	=	17,5 kN
Static tilting moment load	M0k	=	22,5 kNm
Rolling element pitch circle diameter	DM	=	340 mm
Application factor	fA	=	1,25
Safety factor	fS	=	1

Required

Static load carrying capacity of the bearing

Solution

Load eccentricity parameter

Legend

ε		Load eccentricity parameter
M0k	kNm	Static tilting moment load
F0a	kN	Static bearing load (axial)
DM	mm	Rolling element pitch circle diameter
F0r	kN	Static bearing load (radial)
f0r		Static radial load factor ➤ Figure or ➤ Figure.

Equivalent bearing load (static)

Legend

F0q	kN	Equivalent bearing load (static)
F0a	kN	Static bearing load (axial)
fA		Application factor
fS		Factor for additional safety.

Equivalent tilting moment load (static)

Legend

M0q	kNm	Equivalent tilting moment load (static)
M0k	kNm	Static tilting moment load
fA		Application factor
fS		Factor for additional safety.

Determining the load point in the static limiting load diagram – checking the static load carrying capacity

Using the values for F_0q and M_0q, the load point in the static limiting load diagrams for the raceway and fixing screws is determined ➤ Figure and ➤ Figure.

The load point is below the raceway and screw curves. The bearing is adequately dimensioned and thus suitable for the application.

Dynamic load carrying capacity

For bearings under dynamic loading, the dynamic load carrying capacity applies

Dynamically loaded crossed roller bearings, i. e. bearings that undergo predominantly rotary motion, are dimensioned in accordance with their dynamic load carrying capacity. The size of a dynamically loaded bearing can therefore be checked in approximate terms using the basic dynamic load ratings C and the basic rating life L or L_h.

Determining the basic rating life

The life formulae for L and L_h are only valid:

• with a load arrangement according to ➤ Figure
• if all the requirements are fulfilled in relation to location (the bearing rings must be rigid or firmly connected to the adjacent construction), mounting, lubrication and sealing
• if the load and speed can be regarded as constant during operation. If the load and speed are not constant, equivalent operating values can be determined that will result in the same fatigue conditions as the actual loads
• if the load ratio is F_r/F_a ≦ 8.

For more complex load arrangements, if a ratio F_r/F_a ＞ 8 is present or there are variations from the specified conditions, please contact us.

Determining the basic rating life for bearings subjected to combined loads

For bearings subjected to combined loads, in other words bearings with axial, radial and tilting moment loads, the rating life L or L_h is determined as follows:

• Determine the ratio of the radial dynamic bearing load F_r to the axial dynamic bearing load F_a (F_r/F_a)
• Calculate the load eccentricity parameter ε ➤ Equation
• Using the values for ε and the ratio F_r/F_a, determine the dynamic load factor k_F ➤ Figure
• Calculate the equivalent dynamic axial bearing load P_a = k_F  ·  F_a ➤ Equation
• Enter the equivalent dynamic axial bearing load P_a and the basic dynamic axial load rating C_a in the rating life equations L or L_h respectively and calculate the rating life ➤ Equation and ➤ Equation
• If swivel operation is present, enter the operating speed n determined in the rating life equation L_h ➤ Equation.

Load eccentricity parameter

Equivalent dynamic axial bearing load

Basic rating life in millions of revolutions

Basic rating life in operating hours

Operating speed

Determining the basic rating life for bearings subjected to radial loads only

For slewing rings subjected to radial loads only, the following values are entered in the rating life formulae L and L_h:

• P_r = F_r
• the basic dynamic radial load rating C_r.

Basic rating life in millions of revolutions

Basic rating life in operating hours

Legend

ε		Load eccentricity parameter
Mk	kNm	Dynamic tilting moment load
Fa	kN	Axial dynamic bearing load
DM	mm	Rolling element pitch circle diameter
Pa	kN	Equivalent dynamic axial bearing load. For bearings subjected to radial load only, enter Pr
kF		Dynamic load factor ➤ Figure
L10	106	Basic rating life in millions of revolutions
Ca, Cr	kN	Basic axial or radial dynamic load rating. For bearings subjected to radial load only, enter Cr
p		Life exponent for crossed roller bearings: p = 10/3
L10h	h	Basic rating life in operating hours
n	min–1	Operating speed
nosc	min–1	Frequency of oscillating motion
γ	°	Half of swivel angle
Pr	kN	Equivalent dynamic radial bearing load
Fr	kN	Radial dynamic bearing load.

Calculation example

For the crossed roller bearing SX011820, the basic rating life L in millions of revolutions is to be checked.

Given

Crossed roller bearing	SX011820
Rolling element pitch circle diameter	DM	=	112 mm
Basic dynamic load rating (axial)	Ca	=	28 kN
Life exponent for crossed roller bearings	p	=	10/3
Dynamic bearing load (axial)	Fa	=	20 kN
Dynamic bearing load (radial)	Fr	=	4 kN
Dynamic tilting moment load	Mk	=	1 kNm

Required

Basic rating life L₁₀ in millions of revolutions

Solution

Load eccentricity parameter

Legend

ε		Load eccentricity parameter
Mk	kNm	Dynamic tilting moment load
Fa	kN	Axial dynamic bearing load
DM	mm	Rolling element pitch circle diameter
Fr	kN	Radial dynamic bearing load
kF		Dynamic load factor ➤ Figure.

Equivalent bearing load (static)

Legend

Pa	kN	Equivalent dynamic axial bearing load. For bearings subjected to radial load only, enter Pr
kF		Dynamic load factor ➤ Figure
Fa	kN	Axial dynamic bearing load.

Basic rating life in million revolutions

Legend

L10	106	Basic rating life in millions of revolutions For bearings subjected to radial load only, enter Pr
Ca, Cr	kN	Basic axial or radial dynamic load rating
Pa	kN	Equivalent dynamic axial bearing load. For bearings subjected to radial load only, enter Pr
p		Life exponent for crossed roller bearings: p = 10/3.

Determining the load carrying capacity of the fixing screws

In addition to the raceway, the load carrying capacity of the fixing screws must also be checked. This is based on the information in ➤ link.

The load carrying capacity of the fixing screws can be checked if the following conditions are fulfilled:

• the criteria according to ➤ link
• the screws are tightened as specified using a torque wrench
• screw tightening factor α_A = 1,6
• tightening torques ➤ Table to ➤ Table
• the permissible contact pressure is not exceeded
• screws of the recommended size, quantity and grade are used.

Indicator of load carrying capacity

The load carrying capacity of the screws is described by:

• the curves in the static limiting load diagrams for fixing screws in the product tables
• the maximum permissible radial load F_r per (friction locking).

The screw curves are shown in the static limiting load diagrams for fixing screws. The curves are based on screws of grade 10.9, tightened to 90% of their proof stress, including the torsion content.

If screws of grade 8.8 or 12.9 are used, the equivalent static loads F_0q and M_0q, ➤ link, must be converted using the following factors:

• grade   8.8 (F_0q  ·  1,65, M_0q ·  1,65)
• grade  12.9 (F_0q ·  0,8, M_0q ·  0,8).

Static limiting load diagram for fixing screws – example

Checking the static load carrying capacity of the screws

The static load carrying capacity of the screw is limited by its proof stress.

For applications with and without radial load

The equivalent static bearing loads F_0q and M_0q must be determined.

Using the values F_0q and M_0q, the load point is then determined in the static limiting load diagram for fixing screws.

The load point must be below the appropriate screw curve.

Radial load and static load carrying capacity of the screws

If radial loads occur in uncentred bearing rings, the screw connections must prevent displacement of the bearing rings on the adjacent construction.

In order to check this:

• multiply the radial bearing load by an application factor f_A ➤ Table
• compare the values determined with the maximum permissible radial load F_r per.

The maximum radial load F_r per on the fixing screws is dependent on their friction locking and not on the radial load carrying capacity of the bearing.

If the radial load on the bearing is higher than the friction locking of the fixing screws or very high radial loads are present (F_r/F_a ＞ 4), please contact us.

Checking the dynamic load carrying capacity of the screws

The dynamic load carrying capacity of the screws corresponds to the fatigue strength of the screw.

Dynamic load carrying capacity

Based on the dynamic loads present, the equivalent loads F_0q and M_0q are determined.

Instead of the application factor f_A, the operating load must always be increased by the following factor:

• grade  8.8 (factor 1,8),
  grade 10.9 (factor 1,6),
  grade 12.9 (factor 1,5).

The load carrying capacity must then be checked in the static limiting load diagram for the fixing screws.

The load point must be below the appropriate screw curve.

Minimum load

In order to prevent damage due to slippage, a minimum load is required

In order that no slippage occurs between the contact partners, the crossed roller bearings must be constantly subjected to a sufficiently high load. In most cases, however, the load is already sufficiently high due to the weight of the supported parts and the external forces.

Design of bearing arrangements

The design of the adjacent construction has a considerable influence on the function of the bearings

Crossed roller bearings SX can support high loads. Due to the X arrangement of the cylindrical rollers, these bearings can support axial forces in both directions, radial loads, tilting moment loads and any combinations of loads. In order that these advantages can be utilised comprehensively, the adjacent construction must be designed so that it is appropriately rigid. The bearing rings must always be rigidly and uniformly supported over the circumference and width of the rings ➤ Figure.

The adjacent construction must be designed only in accordance with the information in this section. Any deviations from the specifications, material strength and adjacent components will considerably reduce the load carrying capacity and operating life of the bearings.

Shaft and housing tolerances

For normal applications, the tolerance class K7 Ⓔ for the housing and h7 Ⓔ for the shaft are sufficient ➤ Table and ➤ Table.

In precision applications, the bearing seat in the housing should be designed to tolerance class K6 Ⓔ and on the shaft to h6 Ⓔ ➤ Table and ➤ Table.

Mounting tolerances for the shaft

Nominal dimension di		Tolerance classes
mm
＞	≦	h6		h7
		Upper deviation	Lower deviation	Upper deviation	Lower deviation
		μm	μm	μm	μm
65	80	0	–19	0	–30
80	100	0	–22	0	–35
100	120	0	–22	0	–35
120	140	0	–25	0	–40
140	160	0	–25	0	–40
160	180	0	–25	0	–40
continued ▼

Mounting tolerances for the shaft

Nominal dimension di		Tolerance classes
mm
＞	≦	h6		h7
		Upper deviation	Lower deviation	Upper deviation	Lower deviation
		μm	μm	μm	μm
180	200	0	–29	0	–46
200	225	0	–29	0	–46
225	250	0	–29	0	–46
250	280	0	–32	0	–52
280	315	0	–32	0	–52
315	355	0	–36	0	–57
355	400	0	–36	0	–57
400	450	0	–40	0	–63
450	500	0	–40	0	–63
continued ▲

Mounting tolerances for the housing bore

Nominal dimension Da		Tolerance classes
mm
＞	≦	K6		K7
		Upper deviation	Lower deviation	Upper deviation	Lower deviation
		μm	μm	μm	μm
80	100	+4	–18	+10	–25
100	120	+4	–18	+10	–25
120	140	+4	–21	+12	–28
140	160	+4	–21	+12	–28
160	180	+4	–21	+12	–28
180	200	+5	–24	+13	–33
200	225	+5	–24	+13	–33
225	250	+5	–24	+13	–33
250	280	+5	–27	+16	–36
280	315	+5	–27	+16	–36
315	355	+7	–29	+17	–40
355	400	+7	–29	+17	–40
400	450	+8	–32	+18	–45
450	500	+8	–32	+18	–45
500	560	0	–44	0	–70
560	630	0	–44	0	–70

Location using clamping rings

For the location of crossed roller bearings SX, clamping rings have proved effective ➤ Figure.

The bearing rings must always be rigidly and uniformly supported over the circumference and width of the rings.

The thickness of the clamping rings and mounting flanges must not be less than the minimum thickness s.

Counterbores to DIN 74, type J, for screws to DIN 6912 are permissible. For deeper counterbores, the thickness of the clamping ring s must be increased by the additional counterbore depth.

Mounting dimensions ➤ Table and ➤ Figure . Minimum strength of clamping rings ➤ link .

Bearing seat depth

In order that the clamping rings retain the bearing securely, the bearing seat depth t must be in accordance with the specification ➤ Table and ➤ Figure.

The depth of the bearing seat influences the bearing clearance and the rotational resistance.

Bearings with preload (suffix VSP) have a considerably higher rotational resistance.

If particular requirements for rotational resistance apply, the depth t must be produced to match the relevant height of the bearing ring. It has proved effective to tolerance the depth t to deviations that are the same as or further restricted compared to the dimension h in the product tables. For safety, internal tests should in any case be carried out.

Minimum strength of clamping rings

For screws of grade 10.9, the minimum strength under the screw heads or nuts must be 500 N/mm². Seating washers are not necessary for these screws.

For fixing screws of grade 12.9, the minimum strength must not be less than 850 N/mm², otherwise quenched and tempered seating washers under the screw heads or quenched and tempered nuts must be used.

Mounting dimensions

Designation	Mounting dimensions in mm
	di	Da	t		s	dRa	dRi	DRi	DRa	Li	La
	h7 (h6)	K7 (K6)			min.					max.	min.
SX011814	70	90	10	–0,005–0,015	8	78	42	82	118	60	100
SX011818	90	115	13	–0,005–0,020	10	100	61	104	144	80	125
SX011820	100	125	13	–0,005–0,020	10	110	71	114	154	90	135
SX011824	120	150	16	–0,005–0,025	12	132	84	138	186	108	162
SX011828	140	175	18	–0,005–0,030	14	154	94	160	221	124	191
SX011832	160	200	20	–0,02–0,05	15	177	111	183	249	144	216
SX011836	180	225	22	–0,02–0,05	17	199	121	205	284	160	245
SX011840	200	250	24	–0,02–0,06	18	221	139	229	311	180	270
SX011848	240	300	28	–0,02–0,06	21	269	166	274	374	216	324
SX011860	300	380	38	–0,04–0,10	29	335	201	345	479	268	412
SX011868	340	420	38	–0,04–0,10	29	375	241	385	519	308	452
SX011880	400	500	46	–0,04–0,10	35	445	275	455	625	360	540
SX0118/500	500	620	56	–0,04–0,10	42	554	350	566	700	452	668

Fixing screws

For the location of the bearing rings or clamping rings, screws of grade 10.9 are suitable ➤ Table.

Any deviations from the recommended size, grade and quantity of screws will considerably reduce the load carrying capacity and operating life of the bearings.

For screws of grade 12.9, the minimum strength of the clamping rings must be achieved or quenched and tempered seating washers must be used.

Fixing screws

Crossed roller bearings	Fixing screws Grade 10.9		Tightening torque
	Dimension	Quantity	MA Nm
SX011814	M5	18	7
SX011818	M5	24	7
SX011820	M5	24	7
SX011824	M6	24	11,7
SX011828	M8	24	27,8
SX011832	M8	24	27,8
SX011836	M10	24	55,6
SX011840	M10	24	55,6
SX011848	M12	24	98,4
SX011860	M16	24	247
SX011868	M16	24	247
SX011880	M20	24	481
SX0118/500	M24	24	831

Securing of screws

Normally, the screws are adequately secured by the correct preload ➤ Table and ➤ Table. If regular shock loads or vibrations occur, however, additional securing of the screws may be necessary.

Not every method of securing screws is suitable for crossed roller bearings. Never use spring washers or split washers.

General information on securing of screws is given in DIN 25201-4:2004. If these are to be used, please consult the relevant companies.

Tightening torques M_A for the torque-controlled tightening of socket headless screws

Fixing screw	Clamping cross‑section	Core cross‑section	Tightening torque MA** in Nm for grade
	AS	Ad3	8.8	10.9	12.9
	mm2	mm2
M4	8,78	7,75	2,25	3,31	3,87
M5	14,2	12,7	4,61	6,77	7,92
M6	20,1	17,9	7,8	11,5	13,4
M8	36,6	32,8	19,1	28	32,8
M10	58	52,3	38	55,8	65,3
M12	84,3	76,2	66,5	97,7	114
M14	115	105	107	156	183
M16	157	144	168	246	288
M18	192	175	229	336	394
M20	245	225	327	481	562
M22	303	282	450	661	773
M24	353	324	565	830	972

^**M_A in accordance with guideline VDI 2230 (February 2003) for μ_K = 0,08 and μ_G = 0,12.

Assembly preload forces F_M for the torque-controlled tightening of socket headless screws

Fixing screw	Clamping cross‑section	Core cross‑section	Mounting preload force FM** in kN for grade
	AS	Ad3	8.8	10.9	12.9
	mm2	mm2
M4	8,78	7,75	4,05	5,95	6,96
M5	14,2	12,7	6,63	9,74	11,4
M6	20,1	17,9	9,36	13,7	16,1
M8	36,6	32,8	17,2	25,2	29,5
M10	58	52,3	27,3	40,2	47
M12	84,3	76,2	39,9	58,5	68,5
M14	115	105	54,7	80,4	94,1
M16	157	144	75,3	111	129
M18	192	175	91,6	134	157
M20	245	225	118	173	202
M22	303	282	147	216	253
M24	353	324	169	249	291

^**F_M in accordance with guideline VDI 2230 (February 2003) for μ_G = 0,12.

Mounting and dismounting

Mounting of crossed roller bearings

The bores and edges of the adjacent components must be free from burrs. The support surfaces for the bearing rings must be clean.

The seating and locating surfaces for the bearing rings on the adjacent construction must be lightly oiled or greased.

Lightly oil the thread of the fixing screws in order to prevent varying friction factors (do not oil or grease screws that will be secured by means of adhesive).

Ensure that all adjacent components and lubrication ducts are free from cleaning agents, solvents and washing emulsions. The bearing seat surfaces can rust or the raceway system can become contaminated.

Mounting forces must only be applied to the bearing ring to be mounted; forces must never be directed through the rolling elements or seals. Avoid direct blows on the bearing rings in all cases.

Locate the bearing rings consecutively and without application of any external load.

The outer ring is split and is held together by three retaining rings 

➤ Figure. Never apply tensile loads to the retaining rings.

Locating the outer bearing ring

Mounting of the ring ➤ Figure:

• Insert or press the bearing 

  

  into the external adjacent construction 

  

  with the outer ring first
• Position the external clamping ring 

  

• Insert the fixing screws 

  

  in the clamping ring and tighten in steps up to the specified tightening torque M_A
• tighten the screws in a crosswise sequence in order to prevent unacceptable fluctuations in the screw tensioning forces
• tightening torques M_A for fixing screws➤ Table

Locating the inner bearing ring

Mounting of the ring ➤ Figure :

• Insert the bearing 

  

  into the internal adjacent construction 

  

• Position the internal clamping ring 

  

• Insert the fixing screws 

  

  in the clamping ring and tighten in steps up to the specified tightening torque M_A
• tighten the screws in a crosswise sequence in order to prevent unacceptable fluctuations in the screw tensioning forces.

Checking the function

Once mounting is complete, the operation of the mounted crossed roller bearing must be checked. If the bearing runs irregularly or roughly, or the temperature in the bearing shows an unusual increase, the bearing must be dismounted, checked and mounted again in accordance with the mounting guidelines described.

Checking the running accuracy

Possible causes of deviations in values

The running accuracy must be checked by means of a dial gauge. The corresponding values are taken from the mounting drawing or the product tables. Deviations from the values may be the result of:

• inaccuracies in the adjacent construction
• braced bearings due to incorrectly tightened clamping rings, fixing screws or locknuts.

Checking the rotational resistance

Factors influencing the rotational resistance

The rotational resistance is essentially determined by:

• the rolling resistance of the rolling elements
• the internal clearance or bearing preload
• the friction of the spacers
• the friction of the seals
• the grease
• a deformed or defective adjacent construction
• errors during mounting.

Preload, rotational resistance, bearing temperature

Due to the preload in the rolling element system, the rotational resistance is higher than in a bearing with clearance. At higher speeds, a high preload can lead to generation of significant heat in the bearing. In such applications, tests must be carried out if necessary with bearings preloaded to various values.

Checking the bearing temperature

Possible causes of high temperatures

After commissioning, the temperature in the bearing can increase; in the case of grease lubrication, this may continue until the grease is evenly distributed in the bearing. A further increase or unusually high temperatures may be caused by one of the following:

• The bearing is lubricated using an unsuitable grease
• There is too much lubricant in the bearing
• The bearing load is too high
• The bearing is mounted unevenly
• The adjacent construction deviates from the specifications.

Schaeffler Mounting Handbook

Rolling bearings must be handled with great care

Rolling bearings are well-proven precision machine elements for the design of economical and reliable bearing arrangements, which offer high operational security. In order that these products can function correctly and achieve the envisaged operating life without detri­mental effect, they must be handled with care.

The Schaeffler Mounting Handbook MH 1 gives comprehensive infor­mation about the correct storage, mounting, dismounting and mainten­ance of rotary rolling bearings http://www.schaeffler.de/std/1D53. It also provides information which should be observed by the designer, in relation to the mounting, dismounting and maintenance of bearings, in the original design of the bearing position. This book is available from Schaeffler on request.

Further information

In addition to the data in this chapter, the following chapters in Technical principles must also be observed in the design of bearing arrangements:

• Determining the bearing size
• Rigidity
• Friction and increases in temperature
• Speeds
• Bearing data
• Lubrication
• Sealing
• Design of bearing arrangements
• Mounting and dismounting.