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Product News - Gravimetric Feed System Reduces Material Consumption By 5%

March 1, 1999

3 Min Read
Product News - Gravimetric Feed System Reduces Material Consumption By 5%

Gravimetric Feed System Reduces Material

Consumption By 5%

pn-9.jpgAn intelligent gravimetric feed system, designed to reduce material consumption by up to 5% in most profile extrusion processes, is the first product to be intr  oduced by Dynisco Polymer Test since it signed a distribution agreement with iNOEX GmbH, a German manufacturer of extrusion process control products (see Industry News, p 40).

Dubbed Saveomat, the system is said to work by maintaining constant mass throughput from the extruder. In addition, weight/ft of extruded product is tightly controlled. The reported results are tighter product tolerances, higher and more consistent quality and more product produced for the same amount of material.

According to Richard Pavero, President of Dynisco Polymer Test, manufacturers of profile extrusions know that up to 70% of their cost is material consumption. "This can present a profitability problem because the 'safe' way to meet customer specifications is to ship product with a wall thickness greater than required," he says.

"This happens due to the normal output fluctuations of the extruder. A process tuned to run at a nominal wall thickness will run both above and below the target as normal extruder and material flow phenomenon occur."

Pavero says that, in an effort to avoid scrap, the operator will adjust the extruder output such that the low output fluctuations of the extruder meet or exceed the nominal wall thickness required. "The result is a heavier shape or cross section than is required," he says. "Our experience shows that this overage in production weight normally falls into the 2 to 6% range."

A simplified example of the type of profitability problem this can represent is shown below. Note that a very conservative 1.5% improvement in efficiency is used. A 3% improvement, which can be more typical, would double the savings.

The example above is theoretical. Pavero provides the following actual example:

An extruder of PVC window profiles monitored the output of the process for 26 hr using the Saveomat system in the manual or monitoring mode. In order for the extruded product to have the proper nominal wall thickness, the required output was 860 g/meter with an allowable tolerance of about 815 to 900 g/meter.

Screw speed was held constant at a rate determined to provide output as close to the nominal as possible. The process ran over the nominal requirement for more than 50% of the time with significant excursions both above and below the desired specification. These output variations can be attributed to material bulk density variations, temperature drift and the screw rpm changes over time. Output variations ranged from 810 to 915 g/meter (±6%) over the test period.

The processor then enabled the control function of the Saveomat system and tuned it to an output of 860 g/meter. Output fluctuations ranged from a low of 850 to a high of 868 g/meter and 98% of all output ranged from 856 to 862 g/meter. This represents a process improvement in excess of 5% and a quality improvement that is even greater as no scrap was produced.

The system consists of a funnel weigher with a high-accuracy load cell, high-resolution electronics and intelligent software.

In operation, the Saveomat system constantly measures the mass throughput of the material through the extruder and compares the data to the preprogrammed setpoint. It continually adjusts the screw speed to maintain the desired mass throughput of the material. It is also capable of continuously adjusting the haul-off speed to maintain the weight/ft of the product.

A single Saveomat intelligent gravimetric feed system runs at about $20,000. Dynisco says it will be introducing more iNOEX products later this year.

Dynisco Polymer Test 
Morgantown, PA

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