I - BEARING CAPACITY

It is necessary to choose the slewing ring by comparing the loads and/or stresses associated with the intended application with the characteristics of a known slewing ring.

As the case may be:

• When there is no dimensional requirement, the optimal ring for this use will be selected according to the load requirements.

• When there are dimensional constraints (diameter, module, weight, etc.) the suitability of the slewing ring considered will be verified and its life calculated.

The load curves are calculated according to the ability of the ring considered to handle the loads shown on the coordinate axes, and this as a function of:

• Its geometric envelope,

• The type of steel used,

• The heat treatment,

• The type of rolling elements, etc.

• The contact parameters of the rolling elements.

GRAPHIC REPRESENTATION

The capacities of the slewing rings are represented graphically by two basic curves:

• LIMIT CURVE (L)
  - This curve shows the maximum capacity of the ring.
  - The "LIMIT" curve represents the maximum values that must never be exceeded even in the case of test loads or of occasional overloading.
  
  

• UTILIZATION CURVE (U)
  - This curve is derived from the max. curve and represents the maximum allowable working values for applications where this maximum load is only occasionally achieved.
  - Expected lifetime: 50,000 cycles max.
  - In the case where the maximum working load is regularly achieved, the ring selection must be based on the application factors that follow.

The capacity graph for standard slewing rings shown on page 38 onwards are the limit curves (L) having gear type 770 where applicable.

Some graphs are shown doffed to improve the presentation.

BEARING APPLICATION FACTORS

In order to recommend a slewing ring destined for a specific use, it is necessary to ensure proper strength of the race-way by comparing the operating loads in relation to the capacity of the ring chosen or to be determined. This comparison furthermore makes it possible to have an idea of the lifetime of the slewing ring; but the latter can only be calculated for working stresses and not for occasional stresses due to brief and irregular overloading nor for equipment acceptance testing.

• TEST LOADS
  - These loads may not be considered as a "fatigue".
  - These loads must be taken into consideration as determined by the customer, without applying any utilisation - coefficients or factors given developed by ROLLIX.

• WORKING LOADS
  - These loads constitute the "fatigue" element of the slewing ring.
  
  

• The graphic representation of the points characterising the operating loads must, in conformity with the parameters defined in the computer calculation files, take into consideration the particular utilisation - coefficients of each user and the lifetime and speed adjustments factors given by the graphs. This is the case of a special rather than a standard use.

  - Point located above "LIMIT" curve: life-time < 6000 H
  - Point located on "LIMIT" curve: life-time = 6000 H
  - Point located under "LIMIT" curve: life-time > 6000 H

1 - GENERAL FORMULA

• Given P representative point of the working loads
  With Px: origin on the axial loads axis
  Py: origin on the moments axis.
  
  

• General Formula

With
  Ka: utilisation - coefficient
  Ky: lifetime adjustment factor
  Kt: speed adjustment factor

2 - STANDARD APPLICATION

• Corresponds to the uses listed in the so-called "standard" applications table for which the values given assume the following:
  - Lifetime: 6000 hours
  - Average speed: indicated in the table.
  
  

• In this case the general formula becomes:

• However note that the average speed indicated is statistically derived from the maximum speed according to the formula:

3 - SPECIFIC APPLICATIONS

In this case it is not possible to use the simplified formula since the speed and/or the real lifetime associated with the utilization are different from the parameters taken into consideration in the table of standard applications.

The formula used to determine the origins of the points P is used instead of the simplified formula since the speed and lifetime factors must be adjusted.

In this case:
Kt: directly provided by the lifetime graph
Kv: correction factor to be calculated from speeds graph.

therefore:

Standard case

P = ƒ (Fa, Mt) Fa = Axial load x Ka Mt = Moment x Ka

In the case where the application has a radial load as well, it is necessary to convert this radial load into an equivalent axial load:

• Horizontal slewinq ring - vertical axis

• Vertical slewing ring - horizontal axis
  Fa equ = Fa + 1,2(Ki x Fr)

Where
 Fa = axial loads (N)
 Fr = radial load (N)
 Mt = bending moment (Nm)
  = average diameter of the ring (m)

Examples:

Therefore Fa equ = 10 + (0,65 x 20) = 23T

APPLICATION FACTORS
(Established for a lifetime of 6000 hours.)

These factors are determined statistically and are based on a large number of observations for each type of application. The standard parameters retained are as follows:

• Lifetime: 6000 hours

• Average speed indicated: 0.6 x max. speed

• Work under normal weather conditions

• Conventional application (and not specific)

Attention: The speed factor is not the same for all applications. It might be necessary to determine the speed corrective factor:

Ky real	from the corresponding curve
Ky standard

THE "LIFETIME" CORRECTION FACTOR

For an application whose lifetime is different than that indicated in page 15.

ROLLIX slewing rings are normally designed for a minimum lifetime of 6000 hours of operation :This capacity and this lifetime are represented on the particular curves of each ring by the "Limit" curve.

A precise estimate of the real lifetime can be made using the graph shown below, if, however, all of the other parameters used in determining the application point have been respected.

METHODOLOGY

• Given a ring having a "Limit" capacity of L

• Given P which represents the real utilisation characteristics of the user:

  • bearing load (Fa - Fr - Mt)

  • average rotation speed.

Lifetime correction factor

B is projection parallel to L of P.

• Since Kt is known, the graph 2 back gives with sufficient accuracy the lifetime in terms of hours and operation.

NOTE:
In the case where operation cycle(c) of the machine is given, it is necessary to calculate the lifetime of each cycle; the total lifetime is therefore:

THE SPEED CORRECTION FACTOR

For applications where the speed required is different from that indicated (See Application Factors)

The speed of rotation of a slewing ring is an important factor where the lifetime of the ring is concerned. It is therefore necessary to take this parameter into consideration in order to determine or to check a ROLLIX ring, by applying a speed correction factor to the load data (see graph below)

- However the speed to be considered is the average speed of rotation:

In the case of a special type of ring with a bearing cage the average speed is:

APPLICATION EXAMPLES

DETERMINATION OF A SLEWING RING FOR A TOWER CRANE - SLEWING JIB TYPE.

ASSUMPTION 1: Case of standard use

Lv = 6,000 hours
Vav = 1 Rpm

Determining the application point P1

Application coefficient for a high-tower crane: 1.65 (Ka)

{	P1 (x) = Fa x 1.65 = 24.75 T	(247,500N)
	P2 (y) = Mr x 1.65 = 46.2 Tm	(462,000Nm)

The ring having the load curve opposite is suitable since the application point P1 is located under the limit curve.

ASSUMPTION 2:

Lv = 16.000 hours Vav: 2,3 Rpm

Determining the application point P2

- corrective factor for Vav of 2,3 Rpm = 1.36
- corrective factor for Vav of 1 Rpm = 1
- corrective factor for Lv of 16.000 hours = 1.4

P2 (x) =	15 x 1,36	x 1.65 x 1.4 = 47.25 T (472,500N)
	1
P2 (y) =	28 x 1,36	x 1.65 x 1.4 = 88.2 Tm (882,000Nm)
	1

The ring having the load curve opposite is suitable since the application point P2 is located under the curve.

ASSUMPTION 3: Vav of 1,6 Rpm

The ring having been selected, we would now like to determine its life

Determining the application point P3

corrective factor for Vav of 1,6 Rpm = 1.18

P3 (x) =	Fa x 1,18	x 1.65 = 29.25 T (292,500 N)
	1
P3 (y) =	Mr x 1,18	x 1.65 = 54.6 Tm (546,000 Nm)
	1

Point P3 is located above the limit curve

  The lifetime corrective factor is:
  Kv = OL/OB = 52/60 = 0.86

After consulting the curve below, we find that the lifetime is 3,800 hours.

Point P3 is below the limit curve

  The lifetime corrective factor is:
  Kv = OL/OB = 82/62 = 1.32

By consulting the curve below, we find that the lifetime is 14,000 hours.

II - DETERMINE THE GEAR TYPE

ROLLIX DEFONTAINE make several types of gears and can offer either the alone, or the "ring + pinion" or worm drive in the following forms:

The great majority of slewing rings fall into the spur gear ring (or parallel) category.

Most of the Rollix slewing ring have a great correction. It is also recommended to correct the pinion by positive offsetting which will modify the distance between the axes.

Gear correction makes it possible to considerably improve the operating and meshing characteristics:

- suppression of interference,
- increasing the tensile strength,
- improving the surface pressures,
- improving sliding, etc.

It should be noted that the contact ratio will be slightly decreased in the case of corrected gears.

Z₁ = number of teeth on pinion
Z₂ = number of teeth on wheel
Σ δ = δ₁ + δ₂
where
δ₁ = pinion correction factor
δ₂ = wheel correction factor.

TOOTH FORM PRECISION

In the case where no quality class is required by the customer or indecated on the drawings, ROLLIX DEFONTAINE manufactures the slewing rings according to the standard DIN or AFNOR quality as follows:

GEAR NOT SURFACE HARDENED

SURFACE HARDENED GEARS

- in general, by surface tempering for approx. 55HRc
- The classes of gear mentioned above are therefore shifted and specifications cannot be then maintained, but Rollix is able to respect AFNOR and DIN classes 10-11-12.

In the case where it is imperative to obtain a higher quality of gear (class 5 or 6), such quality can only be obtained by grinding the gear (consult our design office).

III - FASTENER SELECTION

The standard bolting arrangement proposed is designed to suit the capacity of the ring.

Specific bolting patterns are available and can be designed for the application on demand.

Calculating the number of bolts required is carried out using the formula shown on page 22 based on the loads to be applied. In all cases it is assumed that the ring is supported and is not unslung.

The ISO standard has defined a bolt and assembly elements classification. According to this standard and also calculations based on the specificion VDI 2230. ROLLIX DEFONTAINE recommends for its slewing rings, the use of high tensile bolts and studs, the classes, descriptions and tightening requirements of which are given below.

SCREW AND STUD CLASSIFICATION

The quality classes of screws and studs are designated by a symbol consisting of two numbers separated by a point. Multiplying these two numbers together will give the approximate yield strength of the screws or studs used. For the attachment of slewing rings, ROLLIX-DEFONTAINE recommends the use of the following classes of bolts.

NUT CLASSIFICATION

The quality classes of nuts are designated by a grade number.
The grades indicated by ISO are:
Classes: 4 - 5 - 6 - 8 - 10 - 12.

For the attachment of slewing rings, ROLLIX DEFONTAINE recommends the use of high-strength nuts, the grade of which depends upon the grade of the screws.

DESIGNATION

Bolt designation is to specify all the main characteristics of the thread and nut:

• Shape of the head

• Diameter

• Length

• Finishing code symbol

• Quality class.

To ensure satisfactory bolting down of their slewing rings, ROLLIX DEFONTAINE recommend the use of:
- Hexagonal head bolts code H
- Square head bolts code Q

Moreover, the surface finish of the bolt heads must meet the requirements of a semi fine class, code T.

Example reference: Bolt HM 18 - 90 1 - Class 10.9.

SELECTION OF THE MOUNTING BOLTS

To ensure that the slewing ring is correctly and efficiently clamped down, the following parameters must be taken into consideration:

• number of bolts

• class and quality of the bolts

• necessary clamping force

• bolt head, bearing and seating surfaces must be machined and must comply with our specifications regarding supports and surface finish.

• number of bolts and screws must be sufficient not only to ensure good fitting but also to avoid any deformation of external and internal rings. It must correspond to the number of fixing holes which are in the ring.

CALCULATION CONDITIONS

• equidistant bolts; ie. equally positioned on the pitch circle.

• slewing rings and supports in steel.

• rigid structure.

• slewing ring bolted directly to its support without using plastic cement.

• use of centring spigots; in this case, there is practically no shear loads on the bolts.

• high tensile bolts.

• calculations based on the ring having the most heavily stressed bolts.

• calculations carried out on the fixed ring are the most usual.

TIGHTENING STRESS - TIGHTENING TORQUE

It this table, the tightening tension is equal to 80% of the elastic limit. (coefficient of friction: 0.12 to 0.16)

CALCULATING THE BOLTS AND NUTS:

- Determine the number of bolts

• Known loads

• Ring selected

• Bolt class selected

N =	1,6 x Fk [4 x Mt - Fa x D]
	D x [Ts - Fpc]

- Determining the stretch length coefficient Fk:

This coefficient not only takes into consideration the dimensions of the bolt but also the type of the slewing ring.

The diagram below directly indicates the value Fk as a function of the Ls/d

- Determining the loss of tension Fpc:

This parameter takes into consideration the dimensions of the bolt.

• Ratio of stretch length to diameter

• Diameter of the attachment bolt

The values of Fpc are directly given in the table and may be considered to be a good approximation.

Use graph corresponding to bolt diameter.