FLEXIBLE AND TORSIONALLY RIGID.

BELLOWS COUPLINGS
SERIES BK | 15 – 10,000 Nm

THE ULTIMATE COUPLING FROM 15 – 10,000 Nm

www.rwcouplings.com
TORSIONALLY STIFF METAL BELLOWS COUPLINGS

Areas of application: Properties of the product range:

■ Servo drives ■ Printing machines ■ zero backlash ■ easy mounting and dismounting
■ CNC axes ■ Packaging machines ■ high torsional stiffness ■ compensation of axial, lateral
■ Robotic axes ■ Woodworking machines ■ exact transmission of angular and angular shaft misalignment
■ Manipulators ■ Textile machinery motion and torque accompanied by quiet, uniform
■ Linear actuators ■ Metal cutting machines ■ infinite life operation
■ wear and maintenance free

MODEL PROPERTIES APPLICATION EXAMPLES

BK1
with flange mounting
from 15-10,000 Nm

■ special design application

see page 5

BK 2
with clamping hub
from 15-1,500 Nm

■ easy to mount
■ suited for space restricted
installations
■ low moment of inertia
■ finely balanced up to
40,000 rpm

see page 6

BKH
with split hub
from 15-1,500 Nm

■ for radial mounting

■ suited for space restricted
installations
■ low moment of inertia
■ finely balanced up to
40,000 rpm

see page 7

2 R+W www.rwcouplings.com
MODEL PROPERTIES APPLICATION EXAMPLES

BKL
Economy Class with clamping hub
from 2-500 Nm
■ low cost version
■ self opening clamping
system optional

see separate catalog

BK 3
with tapered conical sleeves
from 15-10,000 Nm

■ high clamping forces

■ high degree of operating
dependability
■ new draw off device suited
for space restricted installations Approach to date The new approach

see page 8

BK 4
for Fanuc-drives
from 15-150 Nm

■ for conical shaft mounting

■ easy to assemble
■ high clamping forces, due to
conical sleeves

see page 9

BK 5
with tapered press-fit connection
from 15-1,500 Nm

■ absolutely backlash-free
■ easy mounting and dismounting
■ wear-free press fit connection
■ electrically and thermally insulated

see page 10

www.rwcouplings.com R+W 3
TORSIONALLY STIFF METAL BELLOWS COUPLINGS
MODEL PROPERTIES APPLICATION EXAMPLES

BK 6
with conical sleeve and tapered
press-fit connection from 15-1,500 Nm

■ for axial mounting

■ absolutely backlash-free
■ easy mounting and dismounting
■ wear-free press-fit connection
■ electrically and thermally insulated
■ high degree of operating dependability

see page 11

BK 7
with expanding shaft
from 15-300 Nm

■ for hollow shaft mounting

■ suited for space restricted
installations
■ easy mounting

see page 12

ZA
Line shafts with clamping hub
from 10-4,000 Nm
■ removable intermediate
tube section
■ no additional bearing
neccessary
■ standart length up to 6 m

see separate cataloge

ATEX
for the use in
explosive environments

■ available for the full product range

■ for hazardous areas 1/21 and 2/22
bellows couplings are registered
according to the directive
ATEX 95/137

see page 13

4 R+W www.rwcouplings.com
 MODEL BK1
TECHNICAL SPECIFICATIONS

‡Ó (ÊÊÊä]Ó Properties: ■ special design application

ÊÈÊÝ Material: Bellows made of highly flexible high grade

Ê Èä
c stainless steel, hub material: steel
Design: The Hubs have six threaded metric mounting
holes, and the ID and OD are concentrically
(Ê ÊÇ

(Ê ÊÇ
(ÊÊvÇ

(ÊÊvÇ

machined to ISO H7 tolerances.

(Ê

Hubs with custom bore size, mounting threads and

bolt circles are available upon request.
Temperature
range: -30 to +120° C (3.6 F - 270 F)
Speeds: Up to 10,000 rpm, in excess of 10,000 with
finely balanced version.
Service life: These couplings are maintenance-free if the
technical limits are not exceeded
Backlash: Absolutely backlash-free due to bolted connection.
Ordering example
Brief overloads: Acceptable up to 1.5 times the value specified.
BK1/ 150 / 62 / XX
Tolerance: On the hub/shaft connection 0.01 to 0.05 mm
Model
Non-standard
Series / Nm
application: Custom designs with varied tolerances, keyways,
Overall length
Non standard e.g. stainless steel
non-standard material and bellows are available
upon request.

Series
Model BK 1 15 30 60 150 200 300 500 800 1500 4000 6000 10000
Rated torque (Nm) TKN 15 30 60 150 200 300 500 800 1500 4000 6000 10000
Overall length (mm) A 30 37 36 44 43 53 50 62 53 65 56 70 64 77 81 100 145 138 150
Outer diameter of bellows (mm) B 49 55 66 81 90 110 124 133 157 200 253 303
Fit length thread depth (mm) C 7.5 10 10 13 14 14 16 18 22 30 30 36
Inner diameter H7 (mm) D 25 28 38 50 58 65 70 75 85 100 145 190
6 x fastening threads E M5 M5 M6 M6 M6 M8 M8 M10 M16 M20 8xM20 8xM24
Hub bolt circle ± 0.2 (mm) F 35 37 46 62 70 80 94 90 110 140 190 234
Outer diameter f7 (mm) G 49 55 66 81 90 110 122 116 140 182 235 295
Moment of inertia (10-³ kgm²) Jtotal 0.07 0.08 0.14 0.15 0.30 0.32 0.90 0.95 1.30 1.40 1.95 2.10 3.0 3.4 4.3 10.6 46 132 350
Approx. weight (kg) 0.15 0.2 0.3 0.6 0.8 1.5 1.4 1.6 3.3 8.9 13.9 23.7
Torsional stiffness (10 ³ Nm/rad) CT 20 15 39 28 76 55 175 110 191 140 450 350 510 500 780 1304 3400 5700 10950
axial (mm) 1 2 1 2 1.5 2 2 3 2 3 2.5 3.5 2.5 3.5 3.5 3.5 3.5 3 3
Max.
lateral (mm 0.15 0.2 0.2 0.25 0.2 0.25 0.2 0.25 0.25 0.3 0.25 0.3 0.3 0.35 0.35 0.35 0.4 0.4 0.4
values
angular (degree) 1 1.5 1 1.5 1 1.5 1 1.5 1 1.5 1 1.5 1 1.5 1.5 1.5 1.5 1.5 1.5
axial spring stiffness (N/mm) Ca 25 15 50 30 72 48 82 52 90 60 105 71 70 48 100 320 565 1030 985
lateral spring stiffness (N/mm) Cr 475 137 900 270 1200 420 1550 435 2040 610 3750 1050 2500 840 2000 3600 6070 19200 21800
(1Nm 8.85 in lbs)

www.rwcouplings.com R+W 5
MODEL BK2
TECHNICAL SPECIFICATIONS

Properties: ■ easy to mount

■ suited for space restricted installations
■ low moment of inertia

Material: Bellows made of highly flexible high-grade stain-

less steel, hub material: see table below
Design: With a single radial clamping screw per hub
ISO 4762. Any imbalance of the clamping hubs
is compensated with balancing bores located on
the inside of the hub.
Temperature
range: -30 to +120° C (3.6 F - 270 F)
Speeds: Up to 10,000 rpm, in excess of 10,000 with
a finely balanced version.
Service life: These couplings are maintenance-free if the
Ordering example technical limits are not exceeded.
Backlash: Absolutely backlash-free due to frictional
BK2 / 80 / 94 / 20 / 22 / XX clamped connection.

Model Brief overloads: Acceptable up to 1.5 times the value specified.

Series / Nm
Tolerance: On the hub/shaft connection 0.01 to 0.05 mm
Overall length
Ø D1 H7 Non-standard
Ø D2 H7 application: Custom designs with varied tolerances, keyways,
Non standard e.g. stainless steel non-standard material and bellows are available
upon request.

Series
Model BK 2 15 30 60 80 150 200 300 500 800 1500
Rated torque (Nm) TKN 15 30 60 80 150 200 300 500 800 1500
Overall length (mm) A 59 66 69 77 83 93 94 106 95 107 105 117 111 125 133 146 140 166
Outer diameter (mm) B 49 55 66 81 81 90 110 124 134 157
Fit length (mm) C 22 27 31 36 36 41 43 51 45 55
Inner diameter
possible from Ø to Ø H7 (mm) D½ 8-28 10-30 12-32 14-42 19-42 22-45 24-60 35-60 40-75 50-80

ISO 4762 fastening screw M5 M6 M8 M10 M10 M12 M12 M16 2xM16* 2xM20*
Thightening torque of the E
8 15 40 50 70 120 130 200 250 470
fastening screw (Nm)
Distance between centers (mm) F 17 19 23 27 27 31 39 41 2x48 2x55
(mm) G 6.5 7.5 9.5 11 11 12.5 13 16.5 18 22.5
Moment of inertia (10-³ kgm²) Jtotal 0.07 0.08 0.14 0.15 0.23 0.26 0.65 0.67 2.5 3.2 4.5 5.4 8.5 10.5 17.3 19.6 24.3 49.2
Hub material (standard)
Al Al Al Al steel steel steel steel steel steel
(steel on request)
Approx. weight (kg) 0.15 0.3 0.4 0.8 1.7 2.5 4 7.5 7 12
Torsional stiffness (10 ³ Nm/rad) CT 20 15 39 28 76 55 129 85 175 110 191 140 450 350 510 500 780 1304
axial (mm) Max. 1 2 1 2 1.5 2 2 3 2 3 2 3 2.5 3.5 2.5 3.5 3.5 3.5
lateral (mm) values 0.15 0.2 0.2 0.25 0.2 0.25 0.2 0.25 0.2 0.25 0.25 0.3 0.25 0.3 0.3 0.35 0.35 0.35
axial spring stiffness (N/mm) Ca 25 15 50 30 72 48 48 32 82 52 90 60 105 71 70 48 100 320
lateral spring stiffness (N/mm) Cr 475 137 900 270 1200 420 920 290 1550 435 2040 610 3750 1050 2500 840 2000 3600
(1Nm 8.85 in lbs) max. angular misalignment see BK 1 * two screws each hub, 180° apart

6 R+W www.rwcouplings.com
 MODEL BKH
TECHNICAL SPECIFICATIONS

A-2
Properties: ■ easy to mount
F F
■ suited for space restricted installations
G C Keyway ■ low moment of inertia
optional
Material: Bellows made of highly flexible high-grade
stainless steel, hub material: see table below
Ø D1 H7

Ø D2 H7

Design: Both clamping hubs are completely removable,

ØB

due to split hubs and two radial screws

ISO 4762 on each hub. Any imbalance of the
clamping hubs is compensated with balancing
E ISO 4762 bores located on the inside of the hub.
H-2
Temperature
range: -30 to +120° C (3.6 F - 270 F)
Speeds: Up to 10,000 rpm, in excess of 10,000 with
a finely balanced version.
Service life: These couplings are maintenance-free if the
Ordering example technical limits are not exceeded.

BKH / 80 / 94 / 20 / 22 / XX Backlash: Absolutely backlash-free due to frictional

clamped connection.
Model Brief overloads: Acceptable up to 1.5 times the value specified.
Series / Nm Tolerance: On the hub/shaft connection 0.01 to 0.05 mm
Overall length
Non-standard
Ø D1 H7
application: Custom designs with varied tolerances, keyways,
Ø D2 H7
non-standard material and bellows are available
Non standard e.g. stainless steel
upon request.

Series
Model BK H 15 30 60 80 150 200 300 500 800 1500
Rated torque (Nm) TKN 15 30 60 80 150 200 300 500 800 1500
Overall length (mm) A 59 66 69 77 83 93 94 106 95 107 105 117 111 125 133 146 140 166
Outer diameter (mm) B 49 55 66 81 81 90 110 124 134 157
Fit length (mm) C 22 27 31 36 36 41 43 51 45 55
Inner diameter
possible from Ø to Ø H7 (mm) D½ 8-28 10-30 12-32 14-42 19-42 22-45 24-60 35-60 40-75 50-80

ISO 4762 fastening screw M5 M6 M8 M10 M10 M12 M12 M16 M16 M20
Thightening torque of the E
8 15 40 50 70 120 130 200 250 470
fastening screw (Nm)
Distance between centers (mm) F 17 19 23 27 27 31 39 41 48 55
(mm) G 6.5 7.5 9.5 11 11 12.5 13 16.5 18 22.5
Distance (mm) H 29 36 35 43 41 51 47 59 48 60 51 63 55 69 62 75 65.5 71
Moment of inertia (10-³ kgm²) Jtotal 0.07 0.08 0.14 0.15 0.23 0.26 0.65 0.67 2.5 3.2 4.5 5.4 8.5 10.5 17.3 19.6 24.3 49.2
Hub material (standard)
Al Al Al Al steel steel steel steel steel steel
(steel on request)
Approx. weight (kg) 0.15 0.3 0.4 0.8 1.7 2.5 4 7.5 7 12
Torsional stiffness (10³ Nm/rad) CT 20 15 39 28 76 55 129 85 175 110 191 140 450 350 510 500 780 1304
axial (mm) Max. 1 2 1 2 1.5 2 2 3 2 3 2 3 2.5 3.5 2.5 3.5 3.5 3.5
lateral (mm) values 0.15 0.2 0.2 0.25 0.2 0.25 0.2 0.25 0.2 0.25 0.25 0.3 0.25 0.3 0.3 0.35 0.35 0.35
axial spring stiffness (N/mm) Ca 25 15 50 30 72 48 48 32 82 52 90 60 105 71 70 48 100 320
lateral spring stiffness (N/mm) Cr 475 137 900 270 1200 420 920 290 1550 435 2040 610 3750 1050 2500 840 2000 3600
(1Nm 8.85 in lbs) max. angular misalignment see BK 1

www.rwcouplings.com R+W 7
 MODEL BK3
TECHNICAL SPECIFICATIONS

A-2 ØB Properties: high clamping forces

C C E ISO 4017 high degree of operating depentability
new draw off device suited for space
restriced installations

Material: Bellows made of highly flexible high-grade

Ø D2 H7
Ø D1 H7

stainless steel, the hub material is steel.

ØG

Design: With tapered conical sleeves and strong,

captive ISO 4017 draw-off screws.
E ISO 4017 Temperature
range: -30 to +120° C (3.6 F - 270 F)
Speeds: Up to 10,000 rpm, in excess of 10,000 with
a finely balanced version.
Service life: These couplings are maintenance-free if the
Ordering example technical limits are not exceeded.
Backlash: Absolutely backlash-free due to frictional
BK3 / 60 / 76 / 20 / 22 / XX clamped connection.

Model Brief overloads: Acceptable up to 1.5 times the value specified.

Series / Nm
Tolerance: On the hub/shaft connection 0.01 to 0.05 mm
Overall length
Ø D1 H7 Non-standard
Ø D2 H7 application: Custom designs with varied tolerances, keyways,
Non standard e.g. stainless steel non-standard material and bellows are available
upon request.

Series
Model BK 3 15 30 60 150 200 300 500 800 1500 4000 6000 10000
Rated torque (Nm) TKN 15 30 60 150 200 300 500 800 1500 4000 6000 10000

Overall length (mm) A 48 55 57 65 66 76 75 87 78 90 89 103 97 110 114 141 195 210 217

Outer diameter of bellows (mm) B 49 55 66 81 90 110 124 133 157 200 253 303
Fit length (mm) C 19 22 27 32 32 41 41 50 61 80 85 92
Inner diameter
from Ø to Ø H7 (mm) D 10-22 12-23 12-29 15-38 15-44 24-56 24-60 30-60 35-70 50-100 60-140 70-180

Fastening screws 6x M4 M5 M5 M6 M6 M8 M8 M10 M12 M16 M16 8xM16

Tightening torque of the E
4 6 8 12 14 18 25 40 70 120 150 160
fastening screws (Nm)
ISO 4017 draw-off screw 3x F M4 M4 M5 M5 M6 M6 M6 M6 M8 M10 M10 4xM10
Outer diameter of hub (mm) G 49 55 66 81 90 110 122 116 145 175 246 295
-
Moment of inertia (10 ³ kgm²) Jtotal 0.12 0.59 0.3 0.34 0.54 0.73 1.2 1.6 1.7 2.5 5.1 5.9 9.1 9.9 13.2 34.9 85.5 254 629
Approx. weight (kg) 0.25 0.4 0.8 1.2 1.8 3 4.2 5.6 8.2 23 32.6 45.5
Torsional stiffness (10 ³ Nm/rad) CT 20 15 39 28 76 55 175 110 191 140 450 350 510 500 780 1304 3400 5700 10950
axial (mm) Max. 1 2 1 2 1.5 2 2 3 2 3 2.5 3.5 2.5 3.5 3.5 3.5 3.5 3 3
lateral (mm) values 0.15 0.2 0.2 0.25 0.2 0.25 0.2 0.25 0.25 0.3 0.25 0.3 0.3 0.35 0.35 0.35 0.4 0.4 0.4
axial spring stiffness (N/mm) Ca 25 15 50 30 72 48 82 52 90 60 105 71 70 48 100 320 565 1030 985
lateral spring stiffness (N/mm) Cr 475 137 900 270 1200 420 1500 435 2040 610 3750 1050 2500 840 2000 3600 6070 19200 21800

(1Nm 8.85 in lbs) max. angular misalignment see BK 1

8 R+W www.rwcouplings.com
MODEL BK4
TECHNICAL SPECIFICATIONS for Fanuc-Motors

‡Ó Properties: ■ for conical shafts

■ easy mounting and dismounting
Ê-"Ê{ä£Ç  ■ high degree of operating dependability

 Material: Bellows made of highly flexible high-grade

stainless steel, the hub material is steel.
Design: Spindle-side:
(Ê ÊÇ

£\£ä >˜ÕV
(Ê

With conical sleeves and strong captive

œÌœÀ ISO 4017 draw-off screws
Motor-side:
(Ê
(Ê

Conical hub 1 : 10 and a keyway.

Ê-"Ê{ä£Ç
Temperature
range: -30 to +120° C (3.6 F - 270 F)
Speeds: Up to 10,000 rpm, over 10,000 rpm with a
finely balanced version.
Ordering example Service life: These couplings are maintenance-free if the
technical limits are not exceeded.
BK4/ 150 / 82 / 20 / XX
Backlash: Absolutely backlash-free due to frictional
Model
clamped connection.
Series / Nm Brief overloads: Acceptable up to 1.5 times the value specified.
Overall length
Ø D H7 Tolerance: On the hub/shaft connection 0.01 to 0.05 mm
Non standard e.g. stainless steel Custom Designs: With varied tolerances, keyways, non-standard
material, and bellows are available upon request.

Series Technical instructions:

Model BK 4 15 30 60 150
Rated torque (Nm) TKN 15 30 60 150 Before mounting the coupling, the concial sleeve (1) has to be removed.
Overall length (mm) A 47 54 68 76 72 82 82 94 After sliding the coupling on to the motor shaft (3) the nut (4) can be put
on through the bellowsbody (4).
Outer diameter of bellows (mm) B 49 55 66 81
Fit length (mm) C 19 22 27 32 To tighten the nut a special key DIN 896 B is used. The boring (5) is used
Inner diameter
from Ø to Ø H7 (mm) D 10-22 12-23 12-29 15-37 for holding while tightening the nut.
Fastening screws 6x M4 M5 M5 M6
Tightening torque of the E
4 6 8 12
fastening screws (Nm)
DIN 933 draw-off screw 3x F M4 M4 M5 M5
Shaft diameter (mm) G 20 27 30 30
Shaft length (mm) H 8.5 22 18 20
Moment of inertia (10-³ kgm²) Jtotal 0.10 0.12 0.22 0.27 0.58 0.61 1.1 1.4
Approx. weight (kg) 0.25 0.4 0.8 1.35
Torsional stiffness (10 ³ Nm/rad) CT 20 15 39 28 76 55 175 110
axial (mm) Max. 1 2 1 2 1.5 2 2 3
lateral (mm) values 0.15 0.2 0.2 0.25 0.2 0.25 0.2 0.25
axial spring stiffness (N/mm) Ca 25 15 50 30 72 48 82 52
lateral spring stiffness (N/mm) Cr 475 137 900 270 1200 420 1500 435
cone Ø (Fanuc Motor) (mm) I 11 16 16 16
Keyway wide (mm) K 4 5 5 5
(1Nm 8.85 in lbs) Higher torques on request max. angular misalignment see BK 1

www.rwcouplings.com R+W 9
MODEL BK5
TECHNICAL SPECIFICATIONS Press-fit precision metal bellows couplings

Design details BK 5 / BK 6
Properties: ■ absolutely backlash-free and torsionally stiff
■ easy mounting and dismounting
■ electrically and thermally insulated
■ wear-free and maintenance-free
■ low moment of inertia
■ compensation for misalignment
Temperature
range: -30 to +120° C (3.6 F - 270 F)
Speeds: Up to 10,000 rpm, over 10,000 rpm with a finely
balanced version.
Service life: These couplings have an infinite life and are main-
tenance-free if the technical specifications are not
exceeded.
Backlash: Absolutely backlash-free due to frictional clamped
connection and axial pretensioning of the tapered
press-fit segments.
Brief overloads: Acceptable up to 1.5 times the value specified.
Ordering example BK 5 / BK 6 Tolerance: On the hub/shaft connection 0.01 to 0.05 mm
BK5 / 30 / 71 /18 / 19 / XX Material BK 5: Bellows made of highly flexible, high-grade stain-
less steel; clamping hubs up to series 80 aluminium
150 and up steel. Tapered segment on hub face:
Model glass-fiber reinforced plastic sprayed onto an
Series / Nm aluminium hub.
Overall length
Design BK 5: One side with a single radial clamping screw
Ø D1 H7
ISO 4762. One side includes backlash-free clamping
Ø D2 H7 hub and tapered press-fit device. Any imbalance
Non standard e.g. stainless steel of the clamping hub, is compensated with
balancing bores located on the inside of the hub.

Series
Model BK 5 15 30 60 80 150 300 500 800 1500
Rated toque (Nm) TKN 15 30 60 80 150 300 500 800 1500
Overall length (inserted) (mm) A 60 67 71 79 85 95 94 106 95 107 114 128 136 149 150 172
Outer diameter (mm) B 49 55 66 81 81 110 124 133 157
Fit length (mm) C1 22 27 32 36 36 43 51 45 55
Fit length (mm) C2 28 33 39 43 43 52 61 74 94
Inner diameter from
from Ø to Ø H7 (mm) D1 8-28 10-30 12-32 14-42 14-42 24-60 35-60 40-75 50-80
Inner diameter from
from Ø to Ø H7 (mm) D2 8-22 10-25 12-32 14-38 14-38 24-58 35-60 40-62 50-75

ISO 4762 screw M5 M6 M8 M10 M10 M12 M16 2xM16* 2xM20*

E
Tightening torque (Nm) 8 15 40 50 70 130 200 250 470
Distance between centers (mm) F 17 19 23 27 27 39 41 2x48* 2x55*
(mm) G 6.5 7.5 9.5 11 11 13 16.5 18 22.5
Pretensioning approx. (mm) H 0.2 up to 1.0 0.5 up to 1.0 0.5 up to 1.5 0.5 up to 1.5 0.5 up to 1.5 0.5 up to 1.5 1.0 up to 2.0 1.0 up to 2.5 1.0 up to 2.5
Axial recovery force of
20 12 50 30 70 45 48 32 82 52 157 106 140 96 200 650
coupling max. (N)
Mass moment of inertia (10-³ kgm²) Jtotal 0.07 0.08 0.14 0.15 0.23 0.26 0.65 0.67 2.2 2.4 7.4 7.9 13.7 14.4 26.2 51.4
Approx. weight (kg) 0.1 0.1 0.3 0.3 0.4 0.4 0.9 0.9 1.8 1.8 4 4 6.5 6.7 8.2 15.3
Torsional stiffness (10 ³ Nm/rad) CT 10 8 20 14 38 28 65 43 88 55 225 175 255 245 400 650
axial* (mm) Max. 0.5 1 0.5 1 0.5 1 1 2 1 2 1.5 2 2.5 3.5 3 2
lateral (mm) values 0.15 0.2 0.2 0.25 0.2 0.25 0.2 0.25 0.2 0.25 0.25 0.3 0.3 0.35 0.35 0.35
Lateral spring stiffness (N/mm) Cr 475 137 900 270 1200 420 920 290 1550 435 3750 1050 2500 840 2000 3600
(1Nm 8.85 in lbs) * allowed following maximum pretensioning * two screws each hub, 180° apart
Higher torques on request
Missing bellows values see BK1
10 R+W www.rwcouplings.com
MODEL BK6
TECHNICAL SPECIFICATIONS Press-fit precision metal bellows couplings

Material BK 6: Bellows made of highly flexible, high-grade stain

less steel; conical sleeves and tapered segment
on bellows face are made of steel.

Tapered segment on hub face: glass-fiber

rein forced plastic sprayed onto a steel hub.

Design BK 6: One side concial sleeve with 6 fastening screws

ISO 4762 and 3 draw-off threads. One side with
backlash-free tapered concial sleeve with press-
fit connection and 3 draw-off screws
axial mounting for space constrained applications

Design details BK 5 / BK 6

Due to the press-fit design the complete drive unit can be simply
removed to the rear when servicing is required.
Six self-centering, tapered drive projections (2) have been formed into the
plastic conical element, which has been molded onto an aluminium hub (1).
The six axially arranged projections are configured conically in a longitudinal
direction (3). The mating piece consits of a metal bellows with a tapered
mounting (4). Absolutly backlash-free torque transmission is ensured due
to the axial pretensioning (5) of the metal bellows during its mounting. This
slight pretensioning has no negative influence on the operation of the metal
bellows coupling or of the shaft bearing.

Material description of the plastic segment:

This is a glass-fiber reinforced plastic of the duromer group.
With a glass-fiber content of 65% it achives a strength roughly that of steel.

Series
Model BK 6 15 30 60 150 300 500 800 1500
Rated toque (Nm) TKN 15 30 60 150 300 500 800 1500
Overall length (inserted) (mm) A 58 65 68 76 79 89 97 109 113 127 132 145 140 158
Outer diameter (mm) B 49 55 66 81 110 124 133 157
Fit length (mm) C1 13.5 16.5 18 23.5 27 32 42 53
Fit length (mm) C2 29 34 39 49.5 59 68 74 90.5
Inner diameter
from Ø to Ø H7 (mm) D1 10-22 12-24 12-32 15-40 24-56 30-60 40-62 50-75
Inner diameter
from Ø to Ø H7 (mm) D2 10-22 12-24 12-32 15-40 24-56 30-60 40-62 50-75

ISO 4762 screw M4 M5 M5 M6 M8 M8 M10 M12

E
Tightening torque (Nm) 3.5 6.5 8 12 30 32 55 110
Diameter of clamping cone (mm) F 46.5 51 60 74 102 114 126 146
(mm) G 9.5 10.5 11.5 17.5 20 23 27 32
Pretensioning approx. (mm) H 0.2 up to 1.0 0.5 up to 1.0 0.5 up to 1.5 0.5 up to 1.5 0.5 up to 1.5 1.0 up to 2.0 1.0 up to 2.0 0.5 up to 1.5
Axial recovery force of
20 12 50 30 70 45 82 52 157 106 140 96 400 650
coupling max. (N)
Moment of inertia (10-³ kgm²) Jtotal 0.1 0.12 0.2 0.25 0.4 0.45 2.0 2.5 5.4 6.1 8.4 9.1 19.5 44
Approx. weight (kg) 0.3 0.32 0.5 0.52 0.82 0.84 1.6 1.7 4.1 4.2 6.0 6.3 9.4 16.2
Torsional stiffness (10 ³ Nm/rad) CT 10 8 20 14 38 28 88 55 225 175 255 245 400 660
axial* (mm) Max. 0.5 1 0.5 1 0.5 1 1 2 1.5 2 2.5 3.5 3 2
lateral (mm) values 0.15 0.2 0.2 0.25 0.2 0.25 0.2 0.25 0.25 0.3 0.3 0.35 0.35 0.35
Lateral spring stiffness (N/mm) Cr 475 137 900 270 1200 420 1550 435 3750 1050 2500 840 2000 3600
(1Nm 8.85 in lbs) * allowed following maximum pretensioning Higher torques on request.
Missing bellow values see BK1
www.rwcouplings.com R+W 11
MODEL BK7
TECHNICAL SPECIFICATIONS

Properties: ■ compact design, conserves space while

saving cost
■ easy mounting
■ backlash-free and torsionally stiff
■ low moment of inertia
■ compensation of misalignment
Material: Bellows made of highly flexible high-grade
stainless steel, hub material: see in the table,
Expanding hub and cone (steel).
Design: On one side with a single radial clamping screw
ISO 4762. On one side an expanding shaft with tapered
clamping element.
Temperature range: -30 to +120° C (3.6 F - 270 F)
Speeds: Up to 10,000 rpm, over 10,000 rpm with a finely
balanced version.
Ordering example Service life: These couplings have an infinite life and are
maintenance-free if the technical specifications are
BK7 /150 / 71 / 32 / 35 / XX not exceeded.
Model Backlash: Absolutely backlash-free due to frictional clamped
Series / Nm connection.
Overall length Brief overloads: Acceptable up to 1.5 times the value specified.
Ø D1 H7
Ø D2 h7 Tolerance: On the hub/shaft connection 0.01 to 0.05 mm
non standard Custom Designs: With varied tolerances, keyways, non-standard
material, and bellows are available upon request.

Series Installation instructions:

Model BK 7 15 30 60 150 300
Rated toque (Nm) TKN 15 30 60 150 300 By tightening the screw through the bellow body, the shaft is expanded.
Overall length (inserted) (mm) A 45 52 53 61 62 72 71 83 84 98 The coupling is designed for high dynamic hollowshaft connections eg.
Outer diameter (mm) B 49 55 66 81 110 gear boxes. Recommended bore tolerance: ISO H7
Fit length (mm) C1 22 27 32 36 43
Inner diameter
from Ø to Ø H7 (mm) D1 8-28 10-30 12-37 19-42 30-60
Fit length (mm) C2 20 25 27 32 45
Shaft diameter
from Ø to Ø h7 (mm) D2 13-25 14-30 23-38 26-42 38-60
ISO 4762 fastening screw E½ M5 M6 M8 M10 M12
Tightening torque of
the fastening screw (Nm) E½ 8 14 38 65 120
Distance between centers (mm) F 17 19 23 27 39
Distance (mm) G 6.5 7.5 9.5 11 13
Moment of inertia (10-³ kgm²) Jtotal 0.07 0.08 0.14 0.15 0.23 0.26 2.2 2.4 6.5 8.9
Hub material (standard)
Al Al Al Steel Steel
(steel on request)
Approx. weight (kg) 0.15 0.3 0.4 1.7 4
Torsional stiffness (10 ³ Nm/rad) CT 20 15 39 28 76 55 175 110 450 350
axial (mm) Max. 1 2 1 2 1.5 2 2 3 2.5 3.5
lateral (mm) values 0.15 0.2 0.2 0.25 0.2 0.25 0.2 0.25 0.25 0.3
axial spring stiffness (N/mm) Ca 20 12 50 30 72 48 82 52 105 71
lateral spring stiffness (N/mm) Cr 315 108 730 230 1200 380 1550 435 37501050
(1Nm 8.85 in lbs) Max. angular misalignment 1 degree

12 R+W www.rwcouplings.com
MODEL ATEX
FOR USE IN HAZARDOUS AREAS AND EXPLOSIVE ATMOSPHERE AT mosphere EX plosible

The ATEX 95 / ATEX 137 is regulated by the new Mounting,

European directive. Generally the explosive atmosphere Design: For security reasons all misalignment values and
is classified in 3 different zones. torque ratings are decreased by 20%

Zone 0: Installation and

Operation
A place in which an explosive atmosphere is consisting out of
instructions: Installation and operating instructions are an
a mixture of air and flammable substances in the form of gas,
essential part of the BK-EEx metal bellows
vapor or mist is present frequently, continuously or for longer periods.
couplings.
Zone 20:
Is relevant for an explosive atmosphere in the form of clouds of com- Including the following facts:
bustible dust in air under the same conditions as above. ■ Design of the BK EEx metal bellows couplings
■ Exact tightening torques and misalignment
values
Zone 1: ■ How to put in operation
Described as a place in which an explosive atmosphere is existing of a ■ Maintenace intervals
mixture of air and flammable substances in the form of gas, vapor or mist is ■ Trouble shooting
likely to occur in normal operation occasionally. ■ Marking of the coupling
■ Declaration of conformity
Zone 21:
Is relevant for an explosive atmosphere in the form of clouds of com- Identification: All BK-EEx couplings are permanent labeled to
bustible dust in air under the same conditions as above. display manufacturer and accreditation data.

Example
Zone 2:
Accreditation data:
A Place in which an explosive atmosphere is consisting out of mixture Type: BKL 150 EEx-2003
with air of flammable substances in the form of gas, vapor or mist is not ll 2 G D
likely to occur in normal operation but, if it does occur, it will persist for a EEx ll c 40°C
short period only. Ser.No.: A 44305
Tech.Ref.No.:2003/003RW
Zone 22:
Relevant for an explosive atmosphere in the form of a cloud of combus-
tible dust in air under the same conditions as above.

For the classified zones 1/21 and 2/22 the metal bellows
couplings BK-EEX do have an accreditation according to ATEX 95/137

Design of the BK-EEX metal bellows couplings

All BK-EEX metall bellows couplings are designed that neither sparking nor an 4° 4°
increasing in excess of the allowable temperature at the surface can occur,
even while malfunctions.

All dimensions of the standard models are retained. The coupling hubs are generally
equipped with internal jaws for additional support of the bellows. If the bellows were to
tear or break, the internal jaws would eliminate the risk of sparking or heating and
continue to drive the load. In case of damage the angle of turn between the
driving and the driven side is ± 4° degrees . All hubs are made of steel or
engaging jaws
stainless steel materials only.

ATTENTION!
A monitoring of the driving- and driven face is required.
The shut off function has to take place immediately.

www.rwcouplings.com R+W 13
THE SELECTION
THE SELECTION PROCESS FOR TORSIONALLY STIFF METAL BELLOWS COUPLINGS

According to torque

In most cases couplings are rated according to the maximum peak torque to be
regularly transmitted.
The peak torque may not exceed the rated torque of the coupling.
TKN = rated torque of coupling (Nm)
By rated torque we mean: the torque that is continuously transmittable within the
specified acceptable speed and misalignment ranges. TAS = peak torque uf motor (Nm)
The following calculation has proven itself to be a good rule of thumb:

According to acceleration torques

For precise rating, the acceleration torque and moments of inertia of the entire
machine have to be taken into consideration.
In the case of servo motors ensure that their acceleration or deceleration torque is
greater than their torque by a multiple. TKN = rated torque of coupling (Nm)
TAS = max. acceleration torque on the (Nm)
SA = Shock or load factor on the drive face
SA = 1 (uniform load) - or max. deceleration torque of the (Nm)
SA = 2 (non-uniform load) load face

SA = 3-4 (Shocking load) JL = maschine´s moment of inertia (kgm2)

(Spindle + slide + workpiece+
Values for SA = 2-3 are usual for servo drives on maschine tools. half of coupling)
JA = motor´s moment of inertia (kgm2)

According to resonace frequency

For the mech. substitutional model of the

2-mass-system is valid:

CT = torsional stiffness of the coupling (Nm/rad)

fe = resonance frequency of the (Hz)
2 mass system
fer = frequency of the drive (Hz)

As a value of practise is valid: fe ≥ 2 x fer

According to torsional stiffness

Transmission errors due to the torsional load:

(degrees)

ϕ = angle of turn (degrees)

CT = torsional stiffness of coupling (Nm/rad)
TAS = max. torque (Nm)

14 R+W www.rwcouplings.com
INSTALLATION INSTRUCTIONS
SERIES BK
KLEMMNABEN-VERBINDUNG: MODELL MK2 / MK 5 / ECOFLEX
■ When mounting the coupling ensure that the metal bellows are not damaged or bent.
Misalignments
■ During mounting, the torque and axis misalignments may exceed 2 times the value
specified without the operation of the coupling being restricted.
lateral ■ However, for continuous operation, the axial and lateral misalignments specified in
the catalog must not be exceeded. Only then the coupling will provide infinite
performance.
■ Lateral axis misalignment requires special attention (see table values).
axial
■ In the case of models BK 2/3/4/5/6 the tolerance between shaft/hub connection must
not exceed 0.01 and 0.05 mm.
■ Prior to mounting check for smooth running of the coupling hub on the shaft.
angular ■ Prior to mounting, make sure that the shaft is slightly oiled. Shaft keyways have no
effect upon the function of the clamped connection.

Model BK 2 / BK 5 page 6 / page 10

■ The torque values of the fastening screws must be precisely applied in order to ensure
secure clamping of the hubs.
■ The dimensions for application of the mounting bore can be found under „F“ and „G“
in the table.
■ No additional securing of the screw is necessary. Loosening of the fastening screws is
sufficent to dismount the coupling.

Model BK 3 / BK 4 / BK 6 page 8 / page 9 / page 11

■ It is absolutely essential that the fastening screws (1) are evenly tightened.
■ Perform tightening of the fastening screws crosswise in order to avoid any distortion of
the coupling hubs.
■ Extraction of the tapered bushings for repair purposes is possible by means of 3x captive
hexagonal draw-off screws (2).
■ When dismounting assure during draw off that constant, synchronous unscrewing of the
3x hexagon screws is maintained.
The alignment surfaces on the outer faces of the hubs are for the purpose of checking hub
distortion during mounting and for retromeasurement of the misalignment of the axes.
Caution! An increase of tension on the tapered bushings is still achievable even after
the screws have been tightened several times crosswise (max.3 times). This must be
avoided without fail, otherwise destruction of the clamped connection may be the result.

Model BK 5 / BK 6 page 10 / page 11

■ The press-fit couplings do not need mounting holes on the intermediate flange.
Model BK 6 will be mounted axial.
■ The six axially arranged projections (1) are configured conically in a longtitudinal
approx. 0.5-1 direction. Due to this a axial pretensioning (2) is needed.
The metal bellows (3) is used as a spring
■ Please maintain the pretensioning values which are printed in the table (page 8 + 9)
Caution! When mounting the drive unit the pretensioning must be noticed.

approx. 0.5-1

www.rwcouplings.com R+W 15
 THE R+W-PRODUCT RANGE
TORQUE LIMITERS
Series SK

From 0,1 – 2.800 Nm, Bore diameters 3 – 100 mm

Available as a single position, multi-position,
load holding, or full disengagement version
Single piece or press-fit design

Experience and BELLOWS COUPLINGS

Series BK
Know-how
for your special From 15 – 10.000 Nm
Bore diameters 10 – 180 mm
requirements. Single piece or press-fit design

BELLOWS COUPLINGS
ECONOMY CLASS
Series BKL

From 2 – 500 Nm
Bore diameters 3 – 62 mm

R+W Antriebselemente GmbH

Alexander-Wiegand-Straße 8 LINE SHAFTS
Series ZA/ZAE
D-63911 Klingenberg/Germany
Tel. +49-(0)9372 – 9864-0 From 10 – 4.000 Nm
Fax +49-(0)9372 – 9864-20 Bore diameters 10 – 100 mm
Available up to 6 mtr. length
info@rw-kupplungen.de
www.rwcouplings.com
MINIATURE BELLOWS COUPLINGS
Series MK

From 0,05 – 10 Nm
Bore diameters 1 – 28 mm
Single piece or press-fit design

SERVOMAX®
ELASTOMER COUPLINGS
Series EK

From 5 – 2.000 Nm, Shaft diameters 3 – 80 mm

backlash-free, press-fit design

LINEAR COUPLINGS
Series LK

From 70 – 2.000 N
Thread M5 – M16

TGA-ZM-05-91-00
Registration No. 9605022
POLYAMID COUPLINGS
The information mentioned in this document is
MICROFLEX
based on our present knowledge and experiences Series FK 1
and does not exclude the manufacturer’s own
395/01/06/3.000

substantial testing of the equipment. So this is no

obligatry assurance even with regard to protection Rated torque 1 Ncm
rights of Third Parties. The sale of our products
is subject to our General Conditions of Sale and Bore diameters 1 – 1,5 mm
Delivery.