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SKF hybrid bearingsfor professional hand toolsFor servicing and upgrading products

Servic

esaving

bearings


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Materials properties Bearing steel Bearing grade silicon nitride

Density [g/cm3] 7,9 3,2

Hardness, HV10 [kg/mm2] 700 1 600

Thermal expansion [10-6/ C] 12 3

Electrical resistivity [cm] 0,410-6 (conductor) ~1014 (insulator)

Elastic modulus [GPa] 210 310

SKF has selected a range of grease-

lubricated hybrid bearings1) that areespecially suitable for the repair andupgrading of high-speed hand toolspowered by:

air-turbine motors electrical motors pneumatic motors

This range of hybrid bearings offers areplacement of conventional all-steelgrease-lubricated bearings in profes-

sional hand tools.

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1) Hybrid bearings have rings of bearing steel and rolling elements of bearing grade silicon nitride. The ceramicmaterial silicon nitride is produced by a powder compacting process acting at high temperature (~1 800 C) andhigh pressure (~200 MPa). The SKF specified process creates a solid ceramic material without any porosity, andwith good toughness.

SKF hybrid bearings fo

Improved service life will beachieved for hybrid bearingsdue to:

extended grease life, good performance in air-streams

and condensing water, high wear resistance against

particulate contaminantion(sand, pigments, abrasives,steel, iron oxides etc),

resistance to electric current.


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rofessional hand toolse ISO standard dimensionsdeep groove ball bearings

o apply to hybrid bearings.F hybrid bearings arenufactured with bearingel outer and inner rings andaring grade silicon nitrideing elements.

ower grease fill than normal (F1) ensures a combinationgood high-speed properties and long grease life.

F WT grease has been selected for its very long grease life inbrid bearings (see diagram on grease life), wide temperaturege and high-speed capability.

eater bearing clearance than normal (C3) has been chosenake account of temperature variations between the bear-rings, which can occur at high speeds.

e silicon nitride balls (HC5) are produced to a surfaceghness less than Ra 0,020 m. The ceramic balls givebearings:

igh-speed performance thanks to low density and lowiction;

ow wear rate due to their high hardness;mproved grease-life, and resistance to seizure;esistance to electrical currents due to their insulatingroperties.

Fs low-density, high-strength, cage of glasse reinforced polyamide 6,6 (TN9) is stand-. Polyamide cages with their flexibility show

od performance in deep groove ball bearingshigh speeds.

e bearings are sealed at both sidesSKF low-friction seals (2RZ) of ni-e rubber reinforced with sheet steel.ese have been specially developedgood protection against dust at

rmal and high speeds.

608 2RZ TN9 HC5 C3 F1WT- /


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SKF selection of hybrid bearingsfor hand tools

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SKF stocks1) the following selectionof hybrid bearings for servicing2) pro-fessional hand tools. For other bear-ing dimensions and designs, pleaseask your SKF supplier for availability.

Principal dimensions Maximum Mass Designation4)

speed3)

d D B r1,2min

mm r/min g

5 16 5 0,3 98 000 5 625-2RZTN9/HC5C3WTF1

6 19 6 0,3 77 000 8 626-2RZTN9/HC5C3WTF1

7 19 6 0,3 77 000 7 607-2RZTN9/HC5C3WTF1

22 7 0,3 68 000 12 627-2RZTN9/HC5C3WTF1

8 22 7 0,3 68 000 12 608-2RZTN9/HC5C3WTF1

10 26 8 0,3 56 000 18 6000-2RZTN9/HC5C3WTF1

30 9 0,6 50 000 32 6200-2RZTN9/HC5C3WTF1

12 28 8 0,3 50 000 22 6001-2RZTN9/HC5C3WTF1

32 10 0,6 45 000 37 6201-2RZTN9/HC5C3WTF1

15 32 9 0,3 42 000 30 6002-2RZTN9/HC5C3WTF1

35 8 0,6 39 000 44 6202-2RZTN9/HC5C3WTF1

17 35 10 0,3 38 000 38 6003-2RZTN9/HC5C3WTF120 42 12 0,6 32 000 62 6004-2RZTN9/HC5C3WTF1

25 47 12 0,6 28 000 73 6005-2RZTN9/HC5C3WTF1

1) 609, 61902, 6203, 6204 and 6205 bearings can also be delivered in the2RZTN9/HC5C3WTF1 design, but are not generally held in stock.

2) The use of SKF tools is recommended for replacement of bearings. This reduces the riskof damage to bearings.

3) The maximum speed should only serve as an approximate guideline. Lower speed limitsmay apply under high loads, high temperatures and other conditions. The hybrid bear-ings are intended for replacement of existing all-steel bearings, working under normalspeeds and temperature conditions (see SKF General Catalogue).

4)

SKF is devoted to continuously improving the quality of hybrid bearings. Therefore,changes to the material, design and grease of hybrid bearings for hand tools may bemade without prior notice. There will be no detrimental effects on bearing performanceas a result of such changes and interchangeability will be guaranteed.

Br

r1

r1

2

r2

D d


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0 0,2 0,4 0,6 0,8 1,0

0 1000 2000 3000 4000 5000 6000

Properties of hybrid bearings

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Grease life in hybridbearingsThe use of silicon nitride bearingballs with SKF WT grease givessuperior grease life at high speedsand high temperatures. This has, forexample, been demonstrated in SKF

R0F grease tests on bearings withTN9 cages, and shaft sizes of 20mm. SKF hybrid bearings with SKFWT grease showed significantlyextended grease-life, compared toall-steel bearings and hybrid bearingswith ordinary grease. The tests wereperformed at 20 000 r/min (0,67 mil-lion mm/min) and +120 C.

*Speed rating for all-steel bearing with grease lubrication (L10 life of 150 000 hours).

All-steel & ordi-nary grease*

All-steel &SKF WTgrease

Hybrid & ordi-nary grease*

Hybrid &SKF WTgrease

All-steel bearing

Hybrid bearing

Centrifugalforce

Median grease life, L50 [hours]

(no failures)

ndm [million mm/min]

*

Centrifugal forces in

bearingsSKF hybrid bearings for professionalhand tools can often be used athigher speeds than indicated by thespeed ratings for grease-lubricatedall-steel bearings given in the SKFGeneral Catalogue. This is due tothe lower density of silicon nitridecompared to steel. The centrifugalforce from a ceramic ball in a bearingis 40 % of that of a steel ball at the

same speed. In the diagram the cen-trifugal forces from steel and siliconnitride balls are compared for bear-ings. Higher centrifugal loads causehigher bearing temperatures.

ndm = n dm [mm/min]

n = rotation speed [r/min]dm = (d + D) / 2

= mean diameter [mm]L10h = basic rating life, operating

hours

*At +120 C (maximum temperature for ordinary grease).


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Hybrid bearings underdry running conditions

SKF tests have shown that hybridbearings resist dry running much bet-ter than all-steel bearings under poor

lubrication. All-steel bearings seizeearlier and at higher vibration levelscompared with hybrid bearings. Thegood dry running properties of hybridbearings are due to the thermalstability of the silicon nitride balls.The ceramic balls will not weld to thesteel rings. Bearings, shaft size 25mm, were tested without lubricationat a speed of 4 500 r/min. Thesetests showed that SKF hybrid bear-ings had smoother running with lower

vibration and did not seize.

SKF bearing fittingtools and maintenanceproducts

SKF bearing fitting tools (for exampleTMFT 7D, TMFT 33) are designedfor quick, precise and safe mountingof bearings with bore diameters from

5 to 50 mm. They can also be usedto mount bushings, seal rings, beltpulleys etc. SKF delivers kits consist-ing of impact rings and one to threehighstrength aluminium sleeves.The rings as well as the impact sur-face of the sleeves are made of ahigh strength engineering plastic,

Copyright SKF 1999The contents of this publication are the copyright of the publisher and may not be reproduced(even extracts) unless permission is granted. Every care has been taken to ensure the accuracyof the information containd in this publication but no liability can be accepted for any loss ordamage whether direct, indirect or consequential arising out of the use of the informationcontained herein.

Publication 4699/I E

R

Vibration(relatively

)

Time [s]

SKF Ceramic Bearings the SKF Groupsteam of specialists in ceramics for bearing applications

All-steel (seizure)

Hybrid (no seizure)

giving high mechanical strength andimpact fatigue resistance at a verylow weight. All parts of the kits areclearly arranged in practical carrying

cases. Selection charts are included.A variety of pullers, heaters, meas-uring equipment, lubricants etc. arealso available from SKF to improvethe quality of bearing performance.

www.skf.com

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