Paper Valve Sack The Influence of Different Sackpaper Porosity on Filling Performance

Author / Editor: Jonas Almkvist*, Thomas Hilling** / Marcel Dröttboom

In the building material producing and processing industry, various powdery products for a variety of purposes are packed into flexible packaging, in small to large quantities. Depending on the needs and requirements of the end-consumer, filling and storing the filled packages is done using various types of packaging materials. The most frequent and versatile packaging for powder products is the valve sack made of paper.

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(Picture: Haver & Boecker)

Over the recent years, filling systems have been continuously developed to keep up with the ever growing demands for filling performance, weight accuracy and cleanliness. Haver & Boecker has always been setting new standards and developing new technologies. The filling of powder materials is a rapidly developing field within process and product automation. Growing demands for performance have changed the view of filling. Modern filling systems today optimally match the requirements from the sack paper, as well as, the products that are to be filled with possibilities to adapt the filling machine. The interaction between the product, machine and sack is today generally well-known and scientifically investigated in studies and trials (Fig. 1).

Foremost, the Swedish paper manufacturer Billerudkorsnäs has set new standards by developing the high-porosity sack paper family named Quickfill. The Quickfill family contains both white and brown kraft papers for valve sacks which have been developed for today's high-speed converting and filling machines. The wide product range offers a perfect combination of high strength and excellent deaeration properties, meaning that Quickfill sacks can be optimized in size and sack weight while performing better in filling and handling. The overall filling performance is measured regarding the speed and cleanliness of the packing line.

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Haver & Boecker and Billerudkorsnäs both operate research and development centers, where the above described interactions between product and sack are studied with respect to packaging development and customer needs. Together the specialists of both companies have carried out a scientific study focusing in detail the impact of paper porosity on filling speed. The procedure, trials and results are described as follows.

Study Description

This chapter describes how the study was conducted in terms of products tested, sack types used and how packaging performance has been measured.

Tested Products

The trials were conducted with a total of three different products with different filling behaviours (Fig. 2):

  • Standard cement
  • Fine cement
  • E-PVC Powder

Beside of the characteristics mentioned above there are other important product characteristics influencing the filling behaviour such as; moisture content, flowability, deaeration, powder composition and compaction behaviour.

For the purpose of conducting analysis and trials at its own Research & Development Center, Haver & Boecker developed a series of laboratory equipment that measures process-relevant product properties. Using the measured results, the most economical packaging solution for the customer is determined. Billerudkorsnäs have also the possibility to measure key properties for packaging performance in Billerudkorsnäs Sack Lab which was a good combination for the study.

Sack Types

To reduce the amount of parameters the sack size and design was the same for both cement types and larger size for E-PVC powder. For the entire trial 1800 sacks was prepared in three different porosity levels, for each porosity level 200 sacks were used (Fig. 3).

The sack permeability is one of the most important factors influencing the performance of a packing machine. The faster a sack deaerates the air during the filling process, the more efficient the packing machine’s filling performance becomes.

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