Fem Classes and DIN Norms in 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.		< 2	2 - 4	4 - 8	8 - 16	> 16
2	MEDIUM Cranes that usually lift light loads, but often maximum loads.		< 1	1 - 2	2 - 4	4 - 8	8 - 16
3	HEAVY Cranes that usually lift medium weights, but often maximum loads.		< 0.50	0.50 - 1	1 - 2	2 - 4	4 - 8
4	VERY HEAVY Cranes that generally lift maximum and near maximum loads.		< 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.

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.