Gravimetric Dosing Systems and Line Control
There are two dosing methods in the gravimetric dosing world :
The first method is continuous or loss-in-weight, whereby all of the mixture components are fed simultaneously to the machine’s throat. Sysmetric uses this method when:
- The dosing capacity is greater than 1500 kg/hour (3,300 lbs/hour).
- Dosing with one additive only i.e. main material and one additive such as M/B.
- The materials used have vastly different properties e.g. powder and granules.
- When materials have to be separated before entering the extruder e.g. additives in CPET due to temperature differences.
- Upon customer request.
The second method is batch type dosing whereby the recipe components are fed one after another into a common weighing cell and mixing chamber.
This is the most common dosing method due to the following reasons:
- High dosing accuracy for a wide range of capacities
- Simplicity and reliability
- High cost/efficiency ratio (Value for money)
- Fast material changing
- Suited to a wide range of raw materials including regrind materials
- Modular system that can be expanded
- Possibility of combining batch systems with loss-in-weight systems for unique solutions
- Possibility of expansion and integration for “line – control”
Line Control:
The main role of line control is to significantly improve the extrusion process. Stable and consistent production allows decreasing the average product weight whilst improving the properties and thus save a great deal of money.
Our customers report that in their experience they achieve a reduction of 6% in raw material use just by controlling the gram/meter. The Sysmetric system controls several components in order to carry out the line control:
- Screw speed (RPM) in order to control the extruder throughput (kg/hour – lbs/hour)
- Supervises and controls the layer ratio in multi layer lines (%)
- Supervises and controls line speed (m/min – feet/min)
- Supervises and controls gram/meter of the product (lbs/feet)
- Width control in blown film extrusion
- Advanced control including digital IBC and cage control (ABCD)
- Sheet profile control