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Fem Classes in Cranes

59     Admin     ARTICLE    17/08/2021       308

Fem Classes in Cranes

Selection of Travelling Cranes according to FEM Class is determined according to the working hours of the cranes.

In the design of crane hoists, lifting machines and their components, it shows great difficulty to determine risks and working life of mechanical parts due to dynamic and static stresses. Therefore, in terms of design characteristic, being able to fulfill the requirements of the system is the most important feature. According to the FEM (Federation Europenne de la Manutention) standard of the system to be designed in line with this destination, the loading class (according to the working conditions), the number of working hours per hour and the daily working hours should be determined. FEM is the European Federation for materials, loading, lifting and storage equipment. FEM provides services for technical progress and developments in safe work by establishing business codes and guidelines. Lifting machines according to FEM standard;
  1. The appliance as a whole,
  2. The individual mechanism as a whole,
  3. The structural and mechanical components divided into three groups.

The classification is based on two criteria, namely;

  1. The total duration of use of the item considered,
  2. The hook load, loading or stress spectra to wich the item is subjected.

Higher FEM group does not mean more loading capacity; however, it means more operating mode in operation and the ability to be subjected to greater maximum loads and dynamic forces in operation cycles. (Table 1 )


Table-1: FEM Group Selection Table
FEM GROUP SELECTION TABLE
LOADING CLASS "t" AVERAGE DAILY WORKING DURATION
1 LIGHT
Cranes that usually lift light weights, only in special cases (rarely) maximum loads. 
  <?=$value->baslik; ?> < 2 2 - 4 4 - 8 8 - 16 > 16
2 MEDIUM
Cranes that usually lift light loads, but often maximum loads.
  <?=$value->baslik; ?> < 1 1 - 2 2 - 4 4 - 8 8 - 16
3 HEAVY
Cranes that usually lift medium weights, but often maximum loads.
  <?=$value->baslik; ?> < 0.50 0.50 - 1 1 - 2 2 - 4 4 - 8
4 VERY HEAVY
Cranes that generally lift maximum and near maximum loads.
  <?=$value->baslik; ?> < 0.25 0.25 - 0.50 0.50 - 1 1 - 2 2 - 4
     Mechanism Group  FEM 9.511/86 1Bm 1Am 2m 3m 4m
ISO 4301/88 M23 M4 M5 M6 M7
Intermittent Working (%) FEM 9.683/95 25 30 40 50 60
Intermittent Working (h-1) FEM 9.683/95 150 180 240 300 360

Parameters required to calculate the FEM Group; Lifting Qapacity(Q), Loading Class, Hook Height (H), Number of Operations per Hour (n), Daily Working Hours (T), Lifting Speed (Vh). “t” Average daily working time is not an estimate and it is calculated as below. This value allows the determination of lifting machines for the FEM class.

t=2 x H x n x T /(60 x Vh)
Example-1:
  • Lifting Qapacity (Q): 5000 kg
  • Loading Class: Heavy
  • Hook Height (H): 9 m
  • Number of Operations per Hour (n): 8
  • Daily Working Hours (T): 8 Hours
  • Lifting Speed (Vh): 6 m/min
  • t1=2 x H x n x T/(60xVh) = 3,2 Saat 
  • Example-1 from Table-1, the design is made according to the FEM 3m/M6 mechanism group for the HEAVY Loading Class and for the lifting group with an average daily working time of t=3.2 hours.
Example-2:
  • Lifting Qapacity (Q): 5000 kg
  • Loading Class: Light
  • Hook Height (H): 9 m
  • Number of Operations per Hour (n): 8
  • Daily Working Hours (T): 8 Hours
  • Lifting Speed (Vh): 6 m/min
  • t1=2 x H x n x T/(60xVh) = 3,2 Saat 
  • Example-1 from Table-1, the design is made according to the FEM 1Am/M4 mechanism group for the LIGHT Loading Class and for the lifting group with an average daily working time of t=3.2 hours.

Comparison and Conclusion:

Characteristics such as capacity, lifting height, lifting speed are the same in both examples. However, the "Loading Classes" determined according to the operating conditions of the system are different.

In Example-1, the operating conditions are generally required to lift medium weights, but frequently maximum loads. For this reason, the load class is selected as "Heavy".

In Example-2, working conditions are generally required to lift light weights, only in special cases (rarely) maximum loads. For this reason, the loading class is selected as "Light".

It is very important to determine the loading class before the calculations are made.


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