How to save material by gravimetric control
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| Extruders or blend units without gravimetric feed control have variations
in throughput because of bulk density, material temperature and other material
properties which have an impact on the feeding characteristic. |
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| To get reasonable quality in production the set-point has to be increased
up to a level which makes sure that the minimum in throughput never goes lower
than the specified low limit. A higher variation means to increase the
set-point appropriately. |
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| Gravimetric throughput control reduces the variation and the deviation to a
given set-point. The improvement in quality of the throughput signal can be
used to scale down the setpoint. The principle is shown in the figure. |
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| From experience the margin in set-point of a line without gravimetric
control is 3 ... 8%, if production is in good manual supervision and control
before. If not, a margin of more than 10% may be used to meet the specification
of a product. |
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| With gravimetric control the margin can be reduced to 1...2%.
Accordingly material saving of 1 ... 6% or more is achievable. |
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| Please check your own process conditions and make calculations, whether an
investment is profitable to you. The calculation of the return on investement -
ROI - will help you to come to a decision to invest in gravimetric control.
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