Thickness gauges for film and sheet extrusion
Thickness monitoring with SBI thickness measurement systems
Austrian company SBI manufactures thickness gauges for film and sheet extrusion since 1999. Goal and challenge were (still is) to develop high accurate, non contact measurement systems which are very easy to operate. All SBI thickness scanners don't need special permissions for installation and don't need special trained safety officers. These inline measurement systems for film and sheet extrusion are most reliable and simple to operate. Especially because of the ease of operation SBI's systems are highly accepted by the operators on extrusion lines.
NEW: Inline thickness gauge for barrier sheet - with display of EVOH layer thickness profile.
Thickness control (in combination with "automatic extrusion-dies")
All SBI thickness gauges can be equipped with hardware and software for thickness control. These features for thickness control in film and sheet extrusion can be also retrofitted on "thickness monitoring only" systems at any time. Thickness control option of SBI thickness gauges controls thermal bolts from every supplier of automatic extrusion-dies. SBI offers also retrofit able automatic systems (thermal bolts and FRAD) for extrusion-dies.
Inline thickness gauging (inline thickness monitoring):
On main screen of thickness measurement system the thickness of a film or sheet is displayed over width and over bolt-number of extrusion-die. Set tolerance-values are shown in red, production out of these tolerances will cause an alarm. This gives operator chance to adjust extrusion-die early enough and operator sees quickly on which bolt the extrusion-die needs readjustment. Corresponding bolt mapping calculates also neck-in in the edge region of the plastics film. History of last 24 hours is shown also on the main screen: Trend diagramm shows thickness average, minima and maxima as well as set tolerances.
In thickness profile diagram "thickness over width" are shown 4 graphs: set value (blue), actual measured thickness profile (green), average over last 5 measuring scans (black), "frozen" reference profile (grey). Actual thickness profile can be frozen as a reference profile, this shows the operator the success of thickness adjustment on the extrusion-die. This reference profile can be deleted, stored and reloaded at any time.
For closer inspection you can enlarge areas in the diagrams. Of course there are a number of additional screens available for displaying various parameter for extrusion (histories, quality parameters, production parameters like manufactured running meters, weight, running meters on actual roll, weight on actual roll e.g.)
With all SBI inline thickness gauges you can control the thickness average during extrusion (length profile control), if a connection to downstream is possible.
main screen of inline thickness gauge
Inline thickness gauging of barrier layer (EVOH):
SBI offers new inline thickness gauge with combination of capacitive and infrared sensors. This sensor combination enables the detection of total thickness as well as thickness profile of EVOH layer during the extrusion process.
This system was developed originally for PP//EVOH//PP, but is also available for multilayer sheet like PS//EVOH//PS, PET//EVOH//PET e.g..
Screen shot below shows total thickness over width and bolt number, third diagram shows thickness profile of barrier layer.
Screen shot: Barrier sheet - total thickness and thickness profile of EVOH
Thickness gauges for extrusion coating / extrusion lamination
On extrusion-lamination (coating) lines there are at least two scanners installed. At first the thickness of extrudet substrate (PET e.g.) will be measured and controlled (if an automatic extrusion-die is installed).
multiple scanners for extrusion coating - lamination
Total thickness will be measured (and controlled) after the lamination extruder with a 2. scanner. The difference profile of both scanner shows the thickness of the coating (lamination) layer. The thickness of the coated layer can be controlled also.
Screenshot extrusion coating (PET/PE)
on top: total thickness
center: thickness profile of laminated layer
down: profile (laminated layer) over bolt number of extrusion-die
Inline Thickness Control for film and sheet extrusion:
On the "control screen" of thickness gauge you see also thickness profile over bolt number (thermal bolts number), as well as set value. Set value must not be even. For every bolt can be adjusted a separate set value if required. With this feature dedicated areas can be produced thinner, for example where are knives for middle cut and edge trimming are located.
2. diagram shows actuating variables of every actuator (thermal bolts). If 100 % is reached, you have to readjust manually.
3. diagram shows various parameter of every single thermal bolt (scroll-able)
Automatic thickness control has one very big advantage: it is always present at the extrusion line and starts adjustment earlier than operators.
Reasons for thickness gauging and control:
There are several reasons for inline thickness measurement on extrusion lines for film and sheet,
some are listed here:
- Less material consumption, due to possibility to produce with tighter tolerances
- Reduction of wastage, due to quicker production start with an inline thickness measurement
- Proof of quality - prevention of claims
- Tool for rejection of unwarranted claims
- Enhanced productivity: quick production start, alarm if tolerance-limits are reached
- Much better machinability of extruded film and sheet for printing or thermoforming e.g.