The Influence of Different Sackpaper Porosity on Filling Performance

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TRM Filter d.o.o.

Donadon SDD Srl

Frewitt fabrique de machines SA

HAVER & BOECKER OHG - Drahtweberei

Measuring Packaging Performance

For a modern sack solution a number of key properties are important; strength, deaeration, filling, barrier properties, printing and appearance all needs to match in order to have a smart packaging solution. This study is concentrated on the filling performance and therefore the tests concerning deaeration and filling performance are described in detail below.

Gurley

Gurley is the most common test to describe the paper porosity. The gurley equipment measures the time in seconds for 100ml of air to pass a specific surface of the paper at a certain pressure difference and is applied on single ply paper sheets (Fig. 4).

Haver Big Gurley

With the Haver Big Gurley (Fig. 5), the air permeability of packaging material can be measured and assessed. The test equipment provides information about the porosity and air permeability of the sack wall, not only with clean/unused p aper, but also with contaminated paper. It shows the influence of the product to the paper during filling (Fig. 6). The fine product particles can decrease the permeability by blocking the holes between the fibers. It is depending on many factors such like particle size, moisture content, temperature, and so on. With this instrument it is possible to test the whole sack wall construction.

The results show the big influence of the permeability of clean and contaminated paper (with product after filling). During these trials the permeability decrease is 10 to 15 %. Depending on the product and the paper type the permeability can drop down up to 90 %. This is based on experience of many different studies and customer related tests.

Gallery

Gallery with 18 images

Haver Airflow TesterWith the Haver Airflow Tester (Fig. 7), the air permeability of the entire bag, including all paper and plastic layers and glued areas, can be determined. The data contains important information about the filling behaviour. By involving all bag components, especially the glued areas, a total assessment is possible. Worldwide it is today a common standard to describe the sack permeability with this equipment.

The amount of permeability is directly influencing the filling performance, the cleanliness and the weight accuracy. Many years of experience in filling operations have led to recommendations about the permeability levels needed for different types of filling goods (see horizontal dotted lines in Fig. 8).

Filling Trials

The filling trials with cement are made with a vertical impeller packer (Fig. 9) which is the most common and effective technology for filling powdery goods such like cement. Due to the fact that E-PVC has a tendency to agglomerate and plasticise, the filling of this product was made with an air packer (Fig. 10). In general all kind of product can be filled with the air packer. Because of the fluidisation during filling the amount of air is much higher during filling with air packers, this generates a higher need of sack permeability.

For the purpose of comparing results, the following values were recorded for all trials:

• Filling time (blue curve; show coarse and fine feed)

• Sack weight (red curve is the mass flow in kg/s)

• Pressure inside the sack (green curve)

As a standard rule it is given that a higher permeability of the empty sack will reach better filling performance. Different sack constructions like the 5+5 Gurley seconds made from Quickfill paper in comparison with the 15+15 Gurley seconds will result in a 20 % quicker filling time and 50 % lower internal pressure inside sack like in this example (Fig. 11 and 12). The filling time is a result of the E-PVC powder used and the paper sack. It could change with a better flowable E-PVC powder.

Dearation can be increased by perforating the paper to reach similar filling performance (filling time and internal pressure) as in this example for E-PVC filling (Fig. 13 and Fig. 14). This will however result in heavy dusting coming out of the perforation holes which have negative influence on strength, cleanliness, appearance, and working environment, as seen in Fig. 15 for E-PVC filling (Fig. 15).

As a standard rule it is given that a higher permeability of the empty sack will reach better filling performance.

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