ROBUST Series. High-Speed Precision Angular Contact Ball Bearings for Machine Tool Spindles

Transcription

1 ROBUST Series High-Speed Precision Angular Contact Ball Bearings for Machine Tool Spindles Temperature tolerance and low heat generation Smooth running even during sudden rapid acceleration Higher speed and longer life

2 High-Speed Precision Angular Contact Ball Bearings Bearing features indispensable to motorized main spindles temperature tolerance, seizure resistance and low heat generation have been improved to enable higher speeds with minimal thermal deformation. A major trend in the machine tool industry is for higher maximum spindle speeds. In addition, machines are being required to perform a wider variety of tasks and undergo frequent tool changes. Under such conditions, excellent high-speed performance is imperative and spindles must accelerate and decelerate faster. During periods of rapid acceleration or deceleration, spindle bearings are subjected to severe thermal load conditions. These conditions are caused by drastic changes in the ambient environment that result from heat generated by the motor, housing cooling and other factors. Performing well under such conditions and being capable of higher speeds than conventional precision bearings, the ROBUST Series bearings provide solutions for highspeed spindles of the 21st century. 1. Features S type (balls and rings: bearing steel) H type (balls: silicon nitride, Si 3 N 4 /rings: bearing steel) These bearings are designed for motorized and non-motorized spindles and feature the optimal internal structure for minimizing heat generation and improving seizure resistance. The H type can be lubricated with grease at speeds where conventional bearings require oil/air lubrication (Fig. 1). Additionally, both the S type and H type are capable of speeds 2% higher than conventional precision angular contact ball bearings. H type angular contact ball bearings X type (balls: silicon nitride, Si 3 N 4 /rings: SHX steel) While this hybrid ceramic bearing has the same design as the S and H types, its rings are made of SHX steel, a new steel developed by NSK. SHX has excellent seizure and wear resistance during critical lubrication shortages. Also, its heat resistance is nearly equal to M5 steel, which is widely used in bearings for jet aircraft engines. With the X type, grease lubrication is feasible at even higher speeds than the H type (Fig. 1). In terms of both surface and subsurface fatigue, SHX steel provides longer life (Figs. 3 ~ 6). 1

3 ROBUST Series EX type (balls: silicon nitride, Si 3 N 4 /rings: SHX steel/spinshot Technology) EX bearings have the same specifications as the X type, but employ NSK s exclusive Spinshot lubrication system (Fig. 7). While previously only oil jet lubrication has been feasible at speeds exceeding 2,, dmn, the Spinshot lubrication system utilizes a mixture of oil and air to enable the EX type to sustain such speeds (Fig. 1). The use of oil/air instead of oil jets reduces overall costs by allowing the structure of the spindle to be simplified and cutting down on the consumption of oil, an added environmental benefit. Please note that the EX type is not dimensionally interchangeable with conventional precision angular contact ball bearings. Notes: 1. Special heat-resistant, high-strength polyimide resin cages are used in the X and EX types for extremely high speeds. In the S and H types and the X and EX types at low to moderate speeds, phenolic or polyamide cages are used. 2. For X and EX type bearings with outside diameters exceeding φ15, please consult NSK. Conventional Bearings Steel balls Ceramic balls Grease Oil/air Grease Oil/air S type Grease Oil/air H type Grease Oil/air ROBUST Series X type Grease Oil/air EX type Position preload Oil/air Constant-pressure preload d m n x1 6 Note: Limiting speeds vary depending not only on the bearing and lubrication method used, but also on the main spindle driving system, cooling method, structure and other factors. Consider the above as a general reference guide and consult NSK for limiting speeds of specific applications. Fig. 1 Comparison of application ranges of conventional and ROBUST Series bearings under position preload 2

4 High-Speed Precision Angular Contact Ball Bearings Optimal Internal Design Improved temperature tolerance Today, machining involves various cutting conditions within a wide range of speeds. Consequently, spindle temperatures vary widely and cause changes in internal bearing load. The unique design of the ROBUST Series bearings minimizes the adverse effect temperature variation has on internal bearing load. Minimal heat generation To ensure the accuracy of spindles by minimizing thermal displacement, suppression of bearing dynamic frictional loss is vital. The ROBUST Series design controls dynamic frictional loss, reducing heat generation by approximately 2% when compared to conventional bearings operating at the same speed. Heat generation, W Heat generation- Calculated values (bore diameter: 65 mm; grease lubrication) Conventional bearings ROBUST Series Speed, rpm ( 1 3 ) Temperature rise of outer ring, C Temperature rise of outer ring- Measured values (bore diameter: 65 mm; grease lubrication) Conventional bearings ROBUST Series Speed, rpm ( 1 3 ) Conventional bearings Heat generation ROBUST Series PV value* Temperature difference between inner and outer rings With a lower PV value* and less heat generation, ROBUST Series bearings operate with greater stability than conventional precision bearings. * PV value measures the relationship between ball and raceway surface pressure and ball sliding speed. Fig. 2 Analysis results on bearing dynamics 3

5 SHX Steel Used for Inner and Outer Rings of X and EX Types ROBUST Series SHX steel has heat resistance nearly equivalent to that of M5 steel and is superior to M5 in wear resistance, seizure resistance and durability. As such, SHX is highly suited for use in machine tool spindles, which must run at high speeds with a minimum supply of lubricant. Heat resistance Hardness, HV SHX SUJ2 M5 2 3 Tempering temperature, C 4 Fig. 3.1 Tempering temperature and hardness 9 8 Hardness, Hv SHX SUJ2 M Temperature, C 4 5 Fig. 3.2 High-temperature hardness Wear resistance Amount of wear, g SHX SUJ2 M5 5 1 Sliding distance, m 15 2 Load Lubricant 7 rpm 1 rpm Test conditions Surface pressure: 88 MPa Sliding ratio: 3% Lubrication: Spindle oil (2 cm 3 /min) Temperature: Room temperature Fig. 4 Wear resistance (2-cylinder wear test) 4

6 High-Speed Precision Angular Contact Ball Bearings Seizure resistance Time until seizure, sec (1) Test conditions Lubrication: None Sliding condition: PV = 3,72N mm 2 m/s (38 kgf mm 2 m/s) SHX Material Notes: (1) Oil shut-off point (2) M5 seized before the oil shut-off point was reached. PV value, (kgf/mm 2 m/s) Test conditions Lubrication: Oil bath Speed: 6, rpm (constant) Load 4 (2) 4-ball test M5 SUJ2 M5 SHX Material Rotating Fixed Fig. 5.1 Dry seizure test (4-ball test) Fig. 5.2 Seizure limit test (4-ball test) These tests confirm that SHX is superior to M5 in seizure resistance. Silicon nitride balls offer even higher seizure resistance. Long life Cumulative failure probability, % SHX SUJ2 Clean lubrication Test conditions 1 Bearing: P/C:.71 Temperature: 16 C Speed: 4,9 rpm Oil film parameter, Λ: Life, h Fig. 6.1 Life test for subsurface-originated flaking Cumulative failure probability, % SHX SUJ2 M5 Contaminated lubrication Test conditions Bearing: P/C:.28 Temperature: 14 C 5 Speed: 4,9 rpm Foreign debris: Hardness: Hv54 Size: 74 ~ 147 µm Life, h Fig. 6.2 Life test for surface-originated flaking 5

7 ROBUST Series Spinshot Lubrication System The EX type features the widely accepted Spinshot lubrication system for machine tool main spindles. This system ensures a steady supply of lubricating oil to the bearing and excellent high-speed performance. The Spinshot lubrication system is illustrated in Fig. 7. Oil/air (a mixture of the minimum necessary amount of oil and compressed air) is fed from the lubrication device to the bearing via nozzles and oil scoops in the spacer. The nozzles in the spacer are inclined outward so that centrifugal force makes the oil flow into the bearing with greater velocity as speed increases. With the Spinshot lubrication system, the steady supply of lubrication and the cooling effect of the oil/air mixture greatly increase the limiting speed of the bearing. Please note that the EX type is not dimensionally interchangeable with conventional precision angular contact ball bearings. Oil/air Oil/air Oil/air Oil scoop Spinshot spacer Spinshot spacer Fig. 7 Spinshot lubrication system A View of outer ring spacer from A Fig. 8 Example of bearing arrangement (position preload) 6

8 High-Speed Precision Angular Contact Ball Bearings 2. Bearing Materials and Construction Type Material Inner ring Outer ring Balls Bearing construction S SUJ2 SUJ2 SUJ2 H SUJ2 SUJ2 Si 3 N 4 X SHX SHX Si 3 N 4 EX SHX SHX Si 3 N 4 Note: SUJ2 is equivalent to ASTM Test Results H type Outer ring temperature rise, C Bearing: 65BNR1TDBB Preload when assembled: 196N (2 kgf) Lubrication: Grease H type Conventional hybrid bearing Fig. 9 Comparison of temperature rise with grease lubrication 15 Speed, rpm ( 1 3 ) d m n ( 1 6 ) Thermocouple Testing machine structure Outer ring temperature rise, C Bearing: 9BNR1TDB Preload when assembled: 382N (4 kgf) Lubrication: VG22,.3 cm 3 /16 min H type Conventional hybrid bearing Speed, rpm ( 1 3 ) 2 Without cooled housing With cooled housing Thermocouple d m n ( 1 6 ) Fig. 1 Comparison of temperature rise with oil/air lubrication Testing machine structure 7

9 ROBUST Series X type Outer ring temperature rise, C Bearing: 65BNRX1TDBB Preload when assembled: 196N (2 kgf) Lubrication: Grease X type Conventional hybrid bearing Speed, rpm ( 1 3 ) d m n ( 1 6 ) Fig. 11 Comparison of temperature rise with grease lubrication Thermocouple Testing machine structure Outer ring temperature rise, C Bearing: 65BNRX1TDBB Preload when assembled: 49N (5 kgf) Lubrication: VG32,.3 cm 3 /8 min X type Conventional hybrid bearing Speed, rpm ( 1 3 ) d m n ( 1 6 ) Fig. 12 Comparison of temperature rise with oil/air lubrication Testing machine structure EX type Outer ring temperature rise, C Bearing: 65BNRE11T62DB Preload when assembled: 98N (1 kgf) Lubrication: Under race oil/air lubrication (Spinshot) VG22,.3 cm 3 /4 min (2 nozzles) EX type Speed, rpm ( 1 3 ) 3 Thermocouple d mn ( 1 6 ) Fig. 13 Temperature rise with oil/air lubrication and position preload Testing machine structure Temperature rise of cylinder, C Bearing: 65BNRE11T62DT 55BNRE95T62DT Preload (constant-pressure): 755N (77 kgf) Lubrication: Under race oil/air lubrication (Spinshot) Lubrication is provided one shot at a time by one of 3 nozzles Rear bearings Front bearings Speed, rpm ( 1 3 ) d mn ( 1 6 ) Fig. 14 Temperature rise with oil/air lubrication and constant-pressure preload Testing machine structure 8

10 High-Speed Precision Angular Contact Ball Bearings 4. Bearing Nomenclature S type (balls and rings: bearing steel) Nominal bearing bore Indicates type of bearing BNRS: 18 BARS: 3 BTRS: 4 Cage symbol T: Phenolic cage TY: Polyamide cage Example: Size series no. 1: Bore, outside diameter and width are same as 7 series 19: Bore, outside diameter and width are same as 79 series 1X: Bore and outside diameter are same as 7 series (width is a special dimension) 65 BNRS 1 TY DB L P4 Accuracy symbol P4: ISO Class 4 P4A: NSK tolerance for BARS and BTRS P3: Dimensions- ISO Class 4 Running accuracy- ISO Class 2 P2: ISO Class 2 Preload symbol EL: Extra light L: Light CP: Preload (negative clearance) (CP1: -1 µm) CA: Axial clearance (CA1: +1 µm) Arrangement symbol DB: Back-to-back arrangement DT: Tandem DBB: 4-row arrangement H type (balls: silicon nitride, Si 3 N 4 /rings: bearing steel) Example: 65 BNR 1 TY DB L P4 Nominal bearing bore See above Size series no. 1: Bore, outside diameter and width are same as 7 series 19: Bore, outside diameter and width are same as 79 series Indicates type of bearing-bnr: 18 X type (balls: silicon nitride, Si 3 N 4 /rings: SHX steel) Example: 65 BNRX 1 T DB L P4 Nominal bearing bore See above Size series no. 1: Bore, outside diameter and width are same as 7 series 19: Bore, outside diameter and width are same as 79 series Indicates type of bearing-bnrx: 18 EX type (balls: silicon nitride, Si 3 N 4 /rings: SHX steel/spinshot Technology) Example: 65 BNRE 11 T62 DB L P4 Nominal bearing bore Indicates type of bearing Nominal bearing outside diameter See above Cage symbol T: Phenolic cage T62: Polyimide cage 9

11 ROBUST Series 5. Tolerances for Boundary Dimensions and Running Accuracy For most tolerances, i.e., P2, P3 and P4, refer to NSK catalog number E124, Precision Rolling Bearings for Machine- Tool Spindles. However, for the tolerances of BARS1X and BTRS1X series, which have Class 4A tolerance, refer to Tables 1.1 and 1.2. Class 4A tolerance is an NSK specification. In Class 4A, all of the tolerances are the same as ISO Class 4 except for those related to the outside diameter. Table 1.1 Inner ring tolerances of BARS1X and BTRS1X series Units: µm Bore dia. variation Single plane Deviation in a single Brg bore mean bore of a single radial plane d dia. deviation bore dia. Vdp (mm) dmp ds Diameter series 9 Mean bore dia. variation Vdmp Assembled brg Radial runout Inner ring inner ring Inner ring of assembled reference face face runout widthvariation brg inner ring runout with bore with raceway VBs Kia Sd Sia Deviation of a single inner ring width Bs ( Cs) over incl high low high low max max max max max max max high low Table 1.2 Outer ring tolerances of BARS1X and BTRS1X series Outside dia. variation Brg outside Single plane Deviation in a single diameter mean outside of a single radial plane D dia. deviation outside dia. VDp (mm) Dmp Ds Diameter series 9 Units: µm Variation of brg Assembled brg Radial runout Mean outside outside surface outer ring Outer ring of assembled dia. variation generatrix inclination face runout width variation brg outer ring with outer ring face with raceway VCs VD mp Kea SD Sea over incl high low high low max max max max max max max

12 High-Speed Precision Angular Contact Ball Bearings 6. Preloads for Duplex Bearings When determining the appropriate preload for your application, please consult NSK. Table 2.1 BNRS19, BNR19 and BNRX19 Series Axial Preload (N) Bearing bore diameter BNRS19 (α = 18 ) BNR19, BNRX19 (α = 18 ) EL L EL L Table 2.2 BNRS1, BNR1 and BNRX1 Series Axial Preload (N) Bearing bore diameter BNRS1 (α = 18 ) BNR1, BNRX1 (α = 18 ) EL L EL L

13 ROBUST Series Table 2.3 BARS1X and BTRS1X Series Axial Preload (N) Bearing bore diameter BARS1X (α = 3 ) BTRS1X (α = 4 ) EL L EL L Note: α is the contact angle 12

14 High-Speed Precision Angular Contact Ball Bearings BNRS19 BNR19 BNRX19 Contact angle 18 r r B r 1 r r a r a Material Inner rings Outer rings Balls D φ d φ Da φ da φ BNRS19 SUJ2 SUJ2 SUJ2 BNR19 SUJ2 SUJ2 Si 3 N 4 BNRX19 SHX SHX Si 3 N 4 a Boundary Dimensions Basic Load Ratings (mm) (N) {kgf} d D B r r 1 C r C or C r C or min min

15 ROBUST Series r b Dynamic Equivalent Load P = XF r + YF a r a Nominal Contact Angle C or * if a e F a /F r e Single, DT DB or DT F a /F r >e F a /F r e F a /F r >e X Y X Y X Y X Y Db φ da φ *For i, use 2 for DB and DF and 1 for DT. Static Equivalent Load Nominal Contact Single, DT DB or DF Angle X Y X Y P = X F r + Y F a Single or DT mounting when F r >.5F + Y F a use P = F r Bearing Numbers Abutment and Fillet Dimensions Eff. Load Center Mass Internal Free (mm) (mm) (kg) Space d a D a D b r a r b a min max max max max approx (cm 3 /row) 35BNRS19 35BNR BNRX19 4BNRS19 4BNR BNRX19 45BNRS19 45BNR BNRX19 5BNRS19 5BNR BNRX19 55BNRS19 55BNR BNRX19 6BNRS19 6BNR BNRX19 65BNRS19 65BNR BNRX19 7BNRS19 7BNR BNRX19 75BNRS19 75BNR BNRX19 8BNRS19 8BNR BNRX19 85BNRS19 85BNR BNRX19 9BNRS19 9BNR BNRX19 95BNRS19 95BNR BNRX19 1BNRS19 1BNR BNRX19 14

16 High-Speed Precision Angular Contact Ball Bearings BNRS1 BNR1 BNRX1 Contact angle 18 r r B r 1 r r a r a D d Da da Material Inner rings Outer rings Balls BNRS1 SUJ2 SUJ2 SUJ2 BNR1 SUJ2 SUJ2 Si 3N 4 BNRX1 SHX SHX Si 3N 4 a Boundary Dimensions Basic Load Ratings (mm) (N) {kgf} d D B r r 1 C r C or C r C or min min

17 ROBUST Series r b Dynamic Equivalent Load P = XF r + YF a r a Nominal Contact Angle C or * if a e F a /F r e Single, DT DB or DT F a /F r >e F a /F r e F a /F r >e X Y X Y X Y X Y Db da *For i, use 2 for DB and DF and 1 for DT. Static Equivalent Load Nominal Contact Single, DT DB or DF Angle X Y X Y P = X F r + Y F a Single or DT mounting when F r >.5F + Y F a use P = F r Bearing Numbers Abutment and Fillet Dimensions Eff. Load Center (mm) Mass Internal Free (mm) (kg) d Space a D a D b r a r b a min max max max max approx (cm 3 /row) 35BNRS1 35BNR BNRX1 4BNRS1 4BNR BNRX1 45BNRS1 45BNR BNRX1 5BNRS1 5BNR BNRX1 55BNRS1 55BNR BNRX1 6BNRS1 6BNR BNRX1 65BNRS1 65BNR BNRX1 7BNRS1 7BNR BNRX1 75BNRS1 75BNR BNRX1 8BNRS1 8BNR BNRX1 85BNRS1 85BNR BNRX1 9BNRS1 9BNR BNRX1 95BNRS1 95BNR BNRX1 1BNRS1 1BNR BNRX1 16

18 High-Speed Precision Angular Contact Ball Bearings BARS1X Contact angle 3 BTRS1X Contact angle 4 Material Inner rings Outer rings Balls BARS1X SUJ2 SUJ2 SUJ2 BTRS1X SUJ2 SUJ2 SUJ2 Note: These bearings are only available in Class 4A tolerance (Tables 1.1 and 1.2, page 1). Boundary Dimensions Basic Load Ratings (mm) (N) {kgf} d D 2B r r 1 C a C oa C a C oa min min

19 ROBUST Series 2B r 1 r r 1 r rb D φ d φ Db φ da φ Bearing Numbers 4BARS1X 4BTRS1X 45BARS1X 45BTRS1X 5BARS1X 5BTRS1X 55BARS1X 55BTRS1X 6BARS1X 6BTRS1X 65BARS1X 65BTRS1X 7BARS1X 7BTRS1X 75BARS1X 75BTRS1X 8BARS1X 8BTRS1X 85BARS1X 85BTRS1X 9BARS1X 9BTRS1X 95BARS1X 95BTRS1X 1BARS1X 1BTRS1X 15BARS1X 15BTRS1X 11BARS1X 11BTRS1X 12BARS1X 12BTRS1X 13BARS1X 13BTRS1X Abutment and Fillet Dimensions (mm) Mass Internal Free d (kg) a D b r Space b min max max approx (cm 3 /row)

20 For more details, please contact any of the following NSK offices. Worldwide Manufacturing and Marketing Organization NSK LTD.-Headquarters Japan: Tokyo AMERICAS & EUROPE DEPARTMENT Phone: ASIA MARKETING & SALES DEPARTMENT Phone: NSK AMERICAS, INC. [AMERICAN HEADQUARTERS] U.S.A.: Ann Arbor Phone: NSK CORPORATION U.S.A.: Ann Arbor Phone: [Precision Products Business Unit] U.S.A.: Chicago Phone: [TECHNICAL CENTER] U.S.A.: Ann Arbor Phone: [BRANCHES and DISTRIBUTION CENTERS] U.S.A.: Los Angeles Phone: NASTECH U.S.A.: Vermont Phone: NSK SAFETY TECHNOLOGY, INC. U.S.A.: Detroit Phone: NSK-RHP AMERICAN DISTRIBUTION CENTER, INC. U.S.A.: Miami Phone: (35) NSK-RHP CANADA INC. Canada: Toronto Phone: NSK RODAMIENTOS MEXICANA, S.A. DE C.V. Mexico: Mexico City Phone: NSK DO BRASIL INDUSTRIA E COMERCIO DE ROLAMENTOS LTDA. Brazil: São Paulo Phone: NSK-RHP EUROPE LTD. [European Headquarters] England: Ruddington Phone: NSK-RHP EUROPE LTD. WARSAW LIAISON OFFICE Poland: Warsaw Phone: , 1526 NSK BEARINGS EUROPE LTD. England: Peterlee Phone: NSK-RHP EUROPEAN TECHNOLOGY CO., LTD. England: Ruddington Phone: NSK-RHP UK LTD. England: Ruddington Phone: NSK-RHP DEUTSCHLAND GMBH. Germany: Düsseldorf Phone: NSK-RHP FRANCE S.A. France: Paris Phone: NSK-RHP NEDERLAND B.V. Netherlands: Amsterdam Phone: NSK-RHP EUROPEAN DISTRIBUTION CENTRE B.V. Netherlands: Amsterdam Phone: NSK-RHP ITALIA S.P.A. Italy: Milano Phone: NSK-RHP IBERICA, S.A. Spain: Barcelona Phone: NSK ISKRA S.A. Poland: Kielce Phone: NSK-RHP BEARINGS MIDDLE EAST TRADING CO., LTD. Turkey: Istanbul Phone: NSK-RHP SOUTH AFRICA (PTY) LTD. South Africa: Johannesburg Phone: 11 (458) 36 NASTECH EUROPE LTD. England: Coventry Phone: NSK INTERNATIONAL (SINGAPORE) PTE LTD. Singapore: Singapore Phone: NSK SINGAPORE (PRIVATE) LTD. Singapore: Singapore Phone: NSK-RHP AUSTRALIA PTY. LTD. Australia: Melbourne Phone: NSK Ltd. has a basic policy not to export any products or technology that have been designated as controlled items by export related laws. When exporting such products that are shown in this pamphlet, the laws of the exporting country must be observed. NSK-RHP BEARINGS NEW ZEALAND LTD. New Zealand: Auckland Phone: NSK BEARINGS (THAILAND) CO., LTD. Thailand: Bangkok Phone: ~58 NSK SAFETY TECHNOLOGY (THAILAND) CO., LTD. Thailand: Chonburi Phone: (38) SIAM NASTECH CO., LTD. Thailand: Chachoengsao Phone: ~35 PT. NSK BEARINGS MANUFACTURING INDONESIA Indonesia: Jakarta Phone: NSK BEARINGS (MALAYSIA) SDN. BHD. Malaysia: Kuala Lumpur Phone: NSK MICRO PRECISION (M) SDN. BHD. Malaysia: Kuala Lumpur Phone: RANE NASTECH LTD. India: Madras Phone: , Phone: , 662 NSK KOREA CO., LTD. Korea: Seoul Phone: NSK-RHP HONG KONG LTD. China: Hong Kong Phone: KUNSHAN NSK HS CO., LTD. China: Kunshan Phone: GUIZHOU HS NSK BEARINGS CO., LTD. China: Anshun Phone: TAIWAN NSK PRECISION CO., LTD. Taiwan: Taipei Phone: NSK REPRESENTATIVE OFFICES India: Chennai Phone: China: Beijing Phone: ~3 RHP BEARINGS LIMITED England: Newark Phone: Specifications are subject to change without notice and without any obligation on the part of the manufacturer. Every care has been taken to ensure accuracy of the data contained in this catalog, but no liability can be accepted for any loss or damage suffered through errors or omission. We will gratefully acknowledge any additions or corrections. CAT. No. E G-11 Printed in Japan NSK Ltd. 1999