Super-precision angular contact thrust ball bearings for screw drives Contents A C The SKF brand now stands for more Product information Product data than ever before, and means more to you as a valued customer. SKF super-precision angular Single direction angular contact contact thrust ball bearings for thrust ball bearings ............ 26 While SKF maintains its leadership as a screw drives ................... 3 Matched bearing sets ............. 26 high-quality bearing manufacturer Sealed bearings ................. 26 throughout the world, new dimensions The most comprehensive assortment 4 Greased bearings ................ 26 in technical advances, product support Single direction angular contact thrust and services have evol ved SKF into a ball bearings .................... 4 Double direction angular contact truly solutions-oriented supplier, Double direction angular contact thrust thrust ball bearings ............ 27 creating greater value for customers. ball bearings .................... 4 Cartridge units with a flanged housing 5 Double direction angular contact These solutions enable customers to Tailored design .................. 5 thrust ball bearings for bolt mounting 28 improve productivity, not only with breakthrough application-specific prod- The new design: visible and invisible Cartridge units with a flanged housing 29 ucts, but also through leading-edge features make the difference ...... 6 design simulation tools and consultancy Optimized internal design .......... 8 Bearing data – general .......... 30 services, plant asset efficiency mainte- Raceway/shoulder transition. . . . . . . . 8 Dimensions .................... 30 nance program mes, and the industry’s Tightened tolerances ............. 8 Tolerances ..................... 30 most advanced supply management Low-friction seals ................ 9 Preload in unmounted bearings ..... 30 techniques. Unique heat treatment ............ 9 Frictional moment ............... 31 Lifting force .................... 31 The SKF brand still stands for the very For many industries: various benefits 10 Axial load carrying ability .......... 32 best in rolling bearings, but it now Cages ......................... 32 stands for much more. Load ratings for bearing sets ....... 33 B Recommendations Equivalent dynamic bearing load .... 33 SKF – the knowledge engineering Equivalent static bearing load ....... 33 company Bearing selection ............... 12 Markings on bearings ............. 34 Axial stiffness ................... 12 Packaging ...................... 35 Selecting single direction bearings Designations ................... 35 according to stiffness requirements .. 14 Designation system – table ......... 36 Selecting bearings according to speed capability ...................... 18 Product tables ................ 38 Attainable speeds ................ 18 C.1 . . . Single direction angular contact thrust ball bearings .............. 38 Bearing arrangement design ...... 19 C.2 . . . Double direction angular contact Bearing sets .................... 19 thrust ball bearings .............. 40 Accommodating misalignment ...... 20 C.3 . . . Double direction angular contact Bearings for the non-locating position 20 thrust ball bearings for bolt mounting 42 Associated components ........... 20 C.4 . . . Cartridge units with a flanged Application examples ............. 22 housing ....................... 44 Lubrication .................... 23 D Greasing open bearings ........... 23 Additional information Relubrication ................... 24 Running-in of grease lubricated SKF – the knowledge engineering bearings ....................... 24 company ...................... 46 2 SKF super-precision angular A contact thrust ball bearings for screw drives Machine tools require screw drives that can The characteristic properties of these an- SKF angular contact thrust ball bearings for position a work piece or machine compo- gular contact thrust ball bearings include: screw drives are especially suitable for nent quickly, efficiently and precisely. To screw drive applications, but are also ben- meet these requirements, screw drives are • high axial stiffness eficial in other applications, where safe ra- usually supported at both ends by super- • high axial load carrying capacity dial and axial support is required, together precision bearings that can provide a high • very high running accuracy with extremely precise axial guidance of the degree of stiffness. The bearings may also • low frictional moment shaft. What makes these bearings so special have to accommodate high acceleration and • ability to accommodate high speeds and is explained on the following pages. high speed. SKF has developed super-preci- accelerations sion angular contact ball bearings that can Comprehensive assortment meet these ever-increasing performance requirements. The SKF assortment can accommodate vir- tually any requirement placed on support bearings for screw drives. Single direction bearings enable a variety of bearing ar- rangements. Double direction bearings re- duce the number of components. Cart ridge units and bearings for bolt mounting are quick and easy to install. Sealed bearings provide more reliability in harsh envir- onments. For additional details about the SKF offer, see the following pages. 3 The most comprehensive assortment Single direction The comprehensive SKF assortment The bearings are available open or with provides the right support bearing for angular contact thrust l ow-friction seals. virtually every screw drive application. ball bearings It is available from one single source. Double direction The assortment comprises: Single direction bearings provide all the fea- angular contact thrust • Single direction bearings for bearing tures necessary for high-performance screw ball bearings arrangements adjusted to individual re- drive supports, but are not limited to these quirements and with enhanced perform- applications. They are characterized by: ance resulting from the SKF design. SKF double direction angular contact thrust • Double direction bearings for easy and • superior axial stiffness ball bearings have been developed for ma- quick mounting in the proven SKF design. • low frictional moment chine tool applications where space is tight • Cartridge units contain SKF single direc- • designed to accommodate high speeds and easy mounting is required. They accom- tion bearings and are ready-to-mount and rapid accelerations modate axial loads in both directions. units. • excellent running accuracy according to Preload is applied by clamping the inner ring ISO tolerance class 2 (ABEC 9) halves with a precision lock nut. These bear- • dimensional accuracy according to ings are sealed and greased as standard. ISO tolerance class 4 (ABEC 7) Bearings in the BEAM series can be bolt • high axial load carrying capacity mounted to an associated component. Other • universally matchable in sets of up to four features include: bearings • unique heat treatment for constant • holes for relubrication via the outer ring preload over the entire service life of the • either contact seals or non-contact bearing shields Single direction angular contact thrust ball Double direction angular contact thrust ball Double direction angular contact thrust ball bearings bearings bearings for bolt mounting SKF series designation BSA, BSD Series designation BEAS Series designation BEAM SNFA series designation BS Bore diameter range 8 to 30 mm Bore diameter range 12 to 60 mm Bore diameter range 12 to 75 mm Open Sealed 4 • manufactured according to ISO tolerance mation, contact the application engin eering class 4 (ABEC7) service. A Cartridge units with Greased bearings a flanged housing Sealed SKF bearings and units are supplied greased, as standard. Open, single direction Cartridge units are another solution for easy bearings can also be supplied greased on and quick mounting. The units incorporate demand. Customers can choose a suitable SKF single direction bearings and all their SKF grease or specify the grease type and benefits. The main characteristics of car- quantity to meet the needs of their applica- tridge units are: tion. With this service, accuracy in terms of quantity, grease distribution and cleanliness • designed for high stiffness and heavy are maintained by the factory. axial loads • all bearing arrangements are possible Customized solutions (back-to-back, face-to-face, tandem and other combinations) Advanced modelling and virtual testing • sealed with laminar rings services enable the application engineering • grease service life is intended to outlast service to assist in all stages of product the bearing development. With core competencies in bearings, seals, lubrication, mechatronics and services, the SKF team can help to de- Tailored design sign customized solutions that meet the re- quirements of the next generation of ma- The standard SKF assortment covers a wide chine tools. variety of application conditions. But it can also be considered as the basis to develop specialized solutions. For additional infor- Cartridge units with a flanged housing SKF series designation FBSA SNFA series designation BSDU, BSQU Bore diameter range 20 to 60 mm 5 Premium performance: visible and invisible features make the difference When designing bearings, competing re- screw drives. Following are some of the fea- The outcome is measurable, especially for quirements have to be considered. The most tures of these optimized bearings: the most important factors of stiffness and important requirements for support bear- friction († diagrams 1 to 4). ings for screw drives are a high degree of • a fine-tuned osculation stiffness and a low frictional moment. How- • a 62° contact angle ever, other important requirements include • a ground transition between each adequate axial load carrying capacity, a high raceway and its shoulder degree of running accuracy as well as high • a robust cage speed capability and the ability to accommo- • a unique heat treatment date rapid accelerations and deceleration. • very clean bearing steel During the integration of SNFA into SKF • tightened manufacturing tolerances in 2008, SKF engineers used their vast ex- • universally matchable – sets of up to four pertise in this area to design an upgraded bearings can be combined assortment of super-precision single direc- • sealed versions available tion angular contact thrust ball bearings for The benefits of SKF bearings are partly visible, partly hidden in the components 6 Diagram 1 Stiffness comparison A Spring curve for two bearings BSA 202 GCA (BS 215 7P62 DUM1)) arranged face-to-face External axial load [kN] 14 12 10 8 6 Previous SKF design 4 SNFA design SKF design 2 0 0 5 10 15 20 25 30 Axial displacement [µm] 1) Where applicable, designations in parentheses and italics refer to the corresponding SNFA equivalent. Diagram 2 Diagram 3 Stiffness comparison Stiffness comparison Spring curve for two bearings BSA 207 GCA (BS 235 7P62 DUM) Spring curve for two bearings BSA 210 CGA (BS 250 7P62 DUM) arranged face-to-face arranged face-to-face External axial load [kN] External axial load [kN] 50 44 45 40 36 40 32 35 28 30 24 25 20 20 16 Previous SKF design 15 12 SNFA design SNFA design 10 8 SKF design SKF design 4 5 0 0 0 5 10 15 20 25 30 35 40 45 50 0 5 10 15 20 25 30 35 40 45 50 Axial displacement [µm] Axial displacement [µm] Diagram 4 Friction comparison Bearing series BSA 2 (BS 2), preload class B Frictional moment [%] Frictional moment [Nm] 140 3,0 120 2,5 100 2,0 80 1,4 60 1,0 40 20 0,5 0 0 12 15 17 20 25 30 35 40 45 50 60 75 Bore diameter [mm] SNFA design (%) SKF design (%) Previous SKF design (%) SKF design (Nm) 7 Optimized internal Tightened tolerances design SKF single direction bearings are manufac- SKF single direction angular contact thrust tured to tight tolerances, especially for the ball bearings have been optimized in terms bore, outside diameter and stand-out. With of stiffness and friction. High stiffness values these improvements, sets made of univer- and low friction levels were achieved by sally matchable bearings have reached the fine-tuning the osculation, increasing the performance level of matched sets. contact angle to 62° and modifying the tol- Inventory reduction is an additional ben- erance range of the contact angle. Other im- efit resulting from these tighter tolerances. provements include the transition between Virtually any set of up to four bearings can the raceway and shoulder to increase the be arranged using universally matchable axial load carrying capability and cage im- bearings, eliminating the need to order and provements to extend speed capability. inventory different matched sets. All SKF single direction angular contact ball bear- Tightened tolerances for the bore, outside ings are universally matchable. Raceway/shoulder diameter and stand-out transition Changing demands in machine tool applica- tions require bearings that can accommo- date heavy axial loads. These loads can change the contact conditions in a bearing. When an axial load is present, the pressure- ellipses in the ball-raceway contact areas become larger and the point of contact be- tween a ball and raceway moves closer to the shoulder. Under these conditions, edge stresses may occur in conventional bear- ings, which can have a detrimental effect on bearing service life. SKF single direction bearings have a ground transition radius between the race- way and shoulder. This radius reduces edge stresses by approximately 30 %, which ena- bles these bearings to accommodate incidental overloading better than conven- tional designs. Transition between the raceway and shoulder Typical stresses in the contact area in a bearing subjected to heavy axial load Conventional bearing Bearing with a ground transition 8 Low-friction seals A When comparing a sealed bearing to an open bearing and external seals, a sealed bearing provides the following benefits: • fewer components • reduced assembly time • no risk of over or under greasing the bearing • reduced risk of grease contamination • less need for maintenance • extended service life Because of their versatility, sealed bearings are becoming more and more common in screw drive applications. SKF sealed bear- ings, which use low-friction seals, have vir- tually eliminated the need to order bearings or bearing sets with a special seal configu- ration on one side or the other. The seal forms an extremely narrow gap with the shoulder or recess profile of the in- ner ring and is practically non-contacting. Because of this, these bearings do not gen- SKF sealed single direction bearings can replace open bearings and bearings with a special seal erate any more friction than a seal on only configuration one side of the bearing, enabling them to operate at the same high speeds as bearings without seals. SKF single direction angular contact thrust ball bearings are available with low-friction seals. Unique heat treatment SKF single direction angular contact thrust ball bearings undergo a unique heat treat- ment. This heat treatment process is similar to that applied to SKF Explorer bearings. It optimizes the balance between hardness and dimensional stability. Hardness is es- SKF super-precision bearings in the BSA/BSD (BS) series sential for low friction and long service life. Dimensional stability is a key factor in main- Features Benefits taining proper preload, which has a direct • fine-tuned osculation • optimized in terms of stiffness and friction impact on the service life of the bearing and • 62° contact angle • high axial load carrying capacity the stiffness of a bearing arrangement. SKF • ground transition between raceways • less sensitive to incidental overloading single direction bearings are stabilized for and shoulder • constant preload over the entire service life temperatures up to 150 °C. Screw drives • unique heat treatment • suitable for high speeds operate typically at much lower tempera- • stabilized for temperatures up to 150 °C • no need for matched sets tures. This means that dimensional changes • robust cage design during operation are negligible. • universally matchable in sets with up to four bearings • low-friction seals available 9 For many industries: various benefits SKF super-precision angular contact thrust In machine tools, these bearings, which The wide assortment provides solutions ball bearings can provide a variety of ben- can accommodate very fast starts and stops, for virtually all application requirements. It efits to applications in and outside the ma- and high speeds, enable quick movements covers universally matchable bearings to be chine tool industry. and precise positioning; prerequisites for arranged in different sets as well as ready- high quality products and high output levels. to-mount units for quick assembly or fast In printing applications, these bearings con- replacement. Via the SKF logistics system, tribute to high-quality output and increased the bearings are available worldwide with machine uptime. They can fulfil the unique short delivery times. requirements of the aerospace industry for reliability and traceability. Industries Requirements Solution • Machine tool • High positioning accuracy • Aerospace • Reliable positioning repeatability • Printing • Safe operation under rapid acceler- • Material handling ations and high speeds • Injection moulding • Suitable for heavy axial loads • Low energy consumption • Long service life without maintenance • Easy and quick mounting • Increased machine uptime • High power density for compact designs 10
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