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Straight Conveyors


Determining the Number of Conveyor Rollers

The number of conveyor rollers required is calculated from the total length of the conveyor section, divided by the pitch + 1. The pitch is the spacing between two conveyor rollers.
The pitch is determined by the length and type of materials to be transported and the load capacity of the conveyor rollers.

In principle at least three rollers must always sit under the material to be transported in order to ensure that it is conveyed smoothly. The pitch should therefore be at most one third of the length of the shortest material to be transported.

Determining the Number of Conveyor Rollers
This rule of thumb only applies to the conveyance of materials to be transported with flat bases and to rollers with adequate load capacity. When pallets are to be conveyed, for example, the load is only carried by around 1/3 to 2/3 of the conveyor rollers underneath the pallet, owing to the properties of the pallet.
It is therefore necessary to check whether the load capacity of the conveyor rollers is adequate, taking into consideration the pitch and the properties of the materials to be transported. A narrower pitch or conveyor rollers with a higher load capacity may possibly have to be opted for.
All other decisions relating to the choice of the optimum pitch are the responsibility of the plant constructor and can possibly only be answered by conducting tests.

Determining the Load of the Conveyor Rollers

The load capacity of the conveyor rollers depends on the load capacity of the roller assemblies - tube, shaft and bearing.
The load capacity of the weakest assembly in each case determines the load capacity of the entire conveyor roller.
The individual assemblies are compared in terms of their load capacity and calculated together to determine the load capacity of the conveyor roller.
The load capacity of the roller is decisively affected by its length, load distribution and shaft fixing.

The permissible load figures for conveyor rollers can be found in the corresponding tables on the product pages or alternatively calculated using the Interroll roller calculation program.
The load capacity of driven conveyor rollers is often limited by other load limits, e.g. by the permissible loading on the drive chain and other drive elements or by the torque of the drive motor.

Maximum load capacity of the tube

The maximum load capacity of a tube depends on two conditions:
  • The flexural stress of the tube must be below the permitted material limit value
  • The maximum deflection of the tube should not exceed 0.1 % of the installed length.
The flexural stress and deflection can be calculated using the following formulae:
Flexural stress σ = Mb/W = F·EL/(8·W)
Deflection ft = 5·F·EL3/(384·E·I)

Mb Bending torque
W Section modulus
F Load
EL Installation length
E Modulus of elasticity
I Moment of inertia

The formulae and information on the load capacity relate to an even distribution of the load on the surface of the tube. Concentrated or even point loading must be taken into special consideration when selecting the tube.

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