For accurate control of raw material of varying moisture content it is necessary to compensate for the moisture content of the material. Experience has shown that dry material flows more readily than damp material. This can be demonstrated by observing the slope of a pile of material.. Damp material will have a steeper slope than dry material. This variable is amplified by the fact that Feed Rate and Material Moisture is an inverse relationship. We eliminate feed rate variation due to varying moisture by controlling the Dry Feed Rate. We generate a "Dry Feed Rate Signal" (Raw Feed - Raw Feed Moisture) for use in a PID control loop. Controlling this variable achieves the following :
Helps to stabilize the
level in the Pug Mill and Vacuum Chamber.
Helps to stabilize the extrusion rate, (slugs or cuts / min.)
Helps to stabilize extrusion dimensions.
Below is a bunker of ground clay ready for the pugmill. This clay is around 14% moisture. If ground clay is dry enough it will flow like water. I have seen it spill from a clay feeder when the feeder was stopped.
This is a typical clay belt feeder. The gate height is a rough
adjustment for clay feed rate. A VFD on the clay feed belt will get you a
little closer. To get it right you need to weigh the material.
Measure the moisture content. Control the "Dry Feed Rate" using
the VFD on the clay feed belt.
That solves part of the problem. The other part of the clay feed variable
is the "Returns Material". The Pugmaster Plus solves both
problems by controlling the "Total Dry Feed Rate".
It goes without saying that if you are going to vary the incoming clay feed to compensate for material moisture and return material you had better have a way of controlling all additives as a ratio of the "Raw Material Dry Feed Rate". We do that with the Pugmaster Plus Moisture Control System.
The "Normal" method for additive addition (manganese to be specific) is to adjust the manganese feeder for a fixed rate and then adjust the clay feeder to match the manganese feeder. A $ 2,000.00 feeder is determining the clay feed rate for a $ 1,000,000.00 Brick Machine. The Tail is wagging the Dog.
The above pictures were taken at Pine Hall Brick Co's Paver Plant in Madison, NC
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