The Converting industry includes diverse specializations in the processing of materials:

  1. Printing
  2. Die cutting and Roll slitting
  3. Coating
  4. Flexible packaging

The Converting processes involve the unwinding or winding of a reel of different material also called web (web handling).

The web is moved along a system of rollers that must guarantee the right tension to prevent the material from tearing or wrinkling and to ensure that the final product therefore complies with the quality standards desired and required by the increasingly demanding market.

The main problems deriving from inadequate web tension regulation are productive waste and expensive new work.

To prevent this from happening, it is necessary to equip your machine with high quality integrated control systems.
There are open loop or closed loop regulation systems depending on the technology used for detecting the web tension (load cells, dancer roller, ultrasonic sensor, potentiometer, etc.).

Converting – load cell selection guide for a correct detection of the web tension

Load cells represent one of the most precise technologies and are used within closed loop regulation:

  1. Load cells detect the web tension and send an input signal to the control panel.
  2. Control panel compares the web tension detected with the ‘set point’ and send the input to the brake (or motor).
  3. Brake (or motor) – adjust the torque (or rpm if a motor) in order to obtain the web tension required.

Load cells are applied on rollers to precisely detect the tension of a web. Here’s how to select them:

1. Model selection

Select the load cell type according to the specifications of your machine:

  • Flange load cells
  • Flange load cells with clearance hole
  • Cantilever load cells
  • Base style load cells

2. Load capacity selection

Select the capacity of the load cell according to the web tension and the roller weight.

It is necessary to calculate the total of the forces applied on the load cell. These forces are related to the roller weight and the web tension.

Legend:

• = risultant direction
a = winding angle
F = resultant on load cell (daN)
T = max tension (daN)
P = roller weight (daN)


Resultant downward direction

A configuration with downward resultant enhancesthe load on the cell due to the component of the roll weight. This component has to be canceled in the setting of the control panel.

F = 2Tcosα + Pcosβ

Resultant horizontal direction

A configuration with horizontal resultant isn’t affected by the roll weight.It offers a better precision when web tension is low.

F = 2Tcosα


Resultant upward direction

A configuration with upward resultant reduces the load on the cell due to thecomponent of the roll weight. This component has to be canceled in the setting of the control panel.

F = 2Tcosα – Pcosβ

* Force F must then be divided by the number of cells applied to the roller. Ex: with 2 cells the reference force for cell sizing will be F / 2

3. Hole diameter selection

Select the cell’s hole diameter according to the pilot of the roll.

Converting – load cell selection guide for a correct detection of the web tension

Renova provides a wide range of load cells and integrated systems for the web tension regulation which stand out for their maximum accuracy, linearity, ease of use, precision and flexibility.

Renova control systems mounted on unwinders or winders are ideal with pneumatic brakes or with magnetic powder brakes.