EMO: Automatic die centring - die, thickness gauge and control software

Automatically adjusted flat dies, thickness measurements and the control software – an overall solution from one supplier !

1. Automatic flat dies:

The automatic lip centring of the flat die uses innovative EMO expansion elements.

These EMO expansion-elements are differential elements witch are controlled contrary: one part of the element expands, the other part contracts. Controlled by means of energy optimised solid-state heat pump elements (thermoelectric coolers). Thermoelectric coolers (TECs) are solid-state heat pumps utilising the Peltier effect. During operation, DC current flows through the TEC causing heat to be transferred from one side of the TEC to the other, creating a cold and hot side.

In EMO’s expansion-elements there are no heating cartridges, so the average power consumption for cross profile controlling is only about 20 W. From its original length the elements are able to work in both directions (contraction or expansion). The length of the expansion-elements is according to the temperature difference between the to parts of it. Automatic die-lip adjustment is controlled via this temperature difference (equal the voltage on the TEC’s). So it is possible to create an exact temperature difference and consequently it is simple to adjust an exact length of the expansion-element.

With these elements the electronic lip adjustment range is 700 microns. Besides controlling an accurate thickness cross profile also an electronically change of the lip-gap is possible without manual adjustment, during production!

Therefore only few minutes are necessary to change from production with a die-lip gap of 0,5 mm to production with 0,8 mm gap – just by feeding a new gap distance into the operator station – the lip will move automatically to the given gap. This happens parallel across the die, and consequently the system remains stable.

This additional feature of electronically lip gap positioning is a special tool for manufacturing low shrinkage thermoforming films also when production changes are often requested.

2. Thickness measurement for film and sheet

Non-contact thickness measurement units with capacitive and eddy current sensors.

The thickness-measuring unit is equipped with a dual sensor. A capacitive sensor measures the film thickness (via dielectric constant of the film). The result of the capacitive measurement depends on the gap between sensor and roller. Therefore an eddy current sensor measures permanently the distance sensor – roller on the same axis.

So thermal expansions, tolerances of the reference roller or a possible roll bending are compensated due to permanent distance measurement.

The scanning speed is adjustable up to 300 mm/sec (speed back up to 1000 mm/sec) enables a quick new cross profile picture on the screen every 20 sec (for a 1500 mm width unit)!

3. Length- and cross profile controlling

Length- and cross profile controlling completes this overall solution. This software is installed on the PC in the thickness measurement unit. Cross-profile controlling software is necessary for the automatic die adjustment. The signal of the controller is set-value for the EMO expansion-elements. Controlling the length profile means controlling the thickness average. In this case the signal of this controller is set-value for the speed of the downstream or the extruder output.
This system enables quick changes of production, especially when EMO expansion elements are employed for automatic lip adjustment (short changing times means less wastage). This system enables to produce an alternating thickness profile during the film extrusion, so the edge trim wastage is reduced dramatically (no film traversing for winding is necessary). EMO offers a whole package from one supplier, so there are no chances for eventual interface problems - simply connect and run.

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