In order to transmit the loads previously defined, it is necessary
to realise an adequate mechanical fastening of the bearing on
the associated frames, thus forming rigid connection of the ring and its supports.
While several fastening methods are feasible, the most efficient one remains
the use of screws and nuts.

Welding operations are absolutely prohibited.
The correct functioning of the slewing ring and the application safety
dependent on the correct bolting definition and fastening method during installation,
complying with our workmanship.

BOLTS QUALITY
The ISO 898-1 standards define the bolting grade adapted to structure
assemblies such as slewing rings. ROLLIX recommends the use
of HIGH TENSILE bolts grade 10.9 and exceptionally grade 8.8 or 12.9. 
The nuts must be of a same or higher grade as the associated screw. For a screw diameter d, a nut height of 1.d is recommended.
For a ring in normalized steel Z or N, the use of hardened flat washers is required. Maximal properties should be :
 
. a yield strength greater than or equal to 600 MPa, 
. a diameter : DR = 2 d, 
.
a thickness : h>= 0,3 d

Minimal mechanical charateristics ( according to ISO)

Grade
Tensile (MPa)
Yield (MPa)
FATIGUE(MPa)
8.8
800
640
40
Exceptional
10.9
1040
940
40
Recommanded
12.9
1220
1100
40
Exceptionnal


External hexagon head screws are preferred to cap screws (internal hexagon) whenever possible. 
ROLLIX recommendation : screws and nuts, with guaranteed mechanical properties, matched, prelubricated, so as to obtain a known and permanent screw/nut friction factor. 
The surface coating on the bolts must not generate any embrittlement.


BOLTING CALCULATION
The ROLLIX calculation formulae take into account the current standards and regulations as well as the many research and experimental findings. These calculations are mainly inspired by the AFNOR FD E 25.030, the recommendation VDI 2230 (1988) and the standard API 2C (1995).

Supported loads must be distinguished from hanging (suspended) loads acting in tension. Consult ROLLIX, in the case of hanging (suspended) loads.    

Supported Load

 

 

 

Hanging Load
 
 
     

Standard calculation hypotheses
.
Supported loads acting in compression. 
.
Equispaced bolts ; i.e equally positioned on the pitch circles. 
. Steel rings and supports. 
. Support complying with our instructions : thickness, stiffness, surface eveness 
. Ring bolted directly onto its supports. 
.
In cases of heavy radial loads, we recommend to use pilots or to glue so that bolts will not be subjected to shear stresses.
. The clamping length must be at least equal to five times the diameter :    LK > ou = 5.d

Calculation of the number of bolts
When the ring has been previously selected according to its utilization and its load capacity, the bolting is then determined to correspond to the bearing capacity. The calculation of the minimum number of fasteners is carried out according to the following formula for the most unfavourable load case. In any case, a sufficient number of bolts ensuring an effective connection between ring and support frames must be kept, in order to avoid any ring deformation.

Where :
N = Number of bolts theoretically necessary.
1,6 = Tightening factor (assembly error factor) for torque wrench Grade B according to FD E 25-030.
Fk = Bolt stretch factor, see sketch.
MT = Total tilting moment applied to the ring in kNm.
FA = Axial load in kN.
Df = Fastener pitch circle diameter in m.
D = Bolt diameter in mm.
Øm = Raceway mean diameter in m.
Ts = Tighteningt tension.
Fpc = Loss of tension due to embedding in kN, see graph.
Lk = Clamping length in mm.
N = 1,6 . FK (4 . MT - FA . Df) / Df (Ts - Fpc)

Bolt stretch factor F k   
This factor takes the assembly geometryn into account. It is based on the bolt diameter and the ratio of clamping length to diameter.
The best fastening is obtained with throug-holes in the ring and the supports : by using screws and nuts, the clamping length is long, bolt stiffness is satisfactory and tension losses are minimised.
In case of screw fastening into tapped holes, the setting depth must not be less than 1,25.d

Tightening tension : T s
Thightening tension of fastening bolts must be sufficient to warrant the absence of looseness which is essential to ensure the resistance of the assembly fatigue.

Calculation of the minimum fastener preload :
It is useful to check that the standardized preload of the chosen bolt diameter is sufficient compared to the dynamic stresses imposed when operating.
T s   > (2,25/N) [ (4.M T /Øm) - F A   + 80 N.D 10 -3   ]

The standardized tightening tension at 80% of Re must be selected from the following table according to the chosen bolt diameter : bolting grade 10.9.

Diamètre (mm)
12
14
16
20
22
24
27
30
33
Tension (kN)
56
77
106
166
208
239
315
385
480

Loss of tension  
During tightening and under external loads, penning of the surface roughness of the contact part occurs, reducing the initial bolts elongation and thus oriducing a loss of tension which decreases the preload in the assembly. This loss of tension has been tabulated on the following graph which shows values in function of diameter d and the ratio L k /d.

Calculation of under head contact pressure :
Usually, this calculation is not required when treated flat washers are used. It is however recommended when cap screws are used(Chc).

We must have :
FB max / Ac < P adm
with
FB max = Ts + 0,13 . FE
with
FE = ( 1/N )[ (4. MT/ Øm) - FA ]
And
Ac = ( π /4 ) ( dw ² - D i ² )

   


Allowable pressure :
For steels N and Z 400 Mpa
For steels D and X 620 Mpa
For steels type E36 270 MPa

IMPORTANT REMARK  
The use of elastic washers  whatever
the type or model is
absolutely prohibited
and will cancel the warranty.


Slew Bearing Design Functions Fastening function
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