Considerations when planning a bagging system
Sept. 18, 2014
by Thomas Ziolko
Bagging the end product is a work-intensive processing step in a milling operation. That’s why this part of the plant is automated as much as possible. At the same time, the bagging line capacity is directly linked to all of the up and downstream processes. This demands close coordination of the bagging with the production logistics and the following storage and distribution logistics.
In Europe, North America and Australia, the majority of milling products are filled into trucks as a bulk product. In Latin America, Africa and Asia, bagging into open-mouth or valve bags is predominant. Globally, open-mouth bags are the most widespread, because this is advantageous for packaging milling products. In addition to the simple function of packaging, more and more mills are using flour packaging also as a marketing tool. The surface of the bag, the type of closure and/or the material used permit a company to add value themselves to a unique and distinctive brand through what is basically an interchangeable mill product.
The woven plastic bag and the paper bag have mostly superseded the traditional jute or cotton bag. The paper bag, as a disposal bag, corresponds to today’s requirements for sanitation. The extensive cleaning work as well as the removal of bugs and contamination is dispensed with. While Europe, North America and Australia primarily use paper as a packaging material, Latin America, Asia and Africa use woven polypropylene for 10- to 50-kg bags. In addition to just the habits of the end customers, the climate conditions or bags being handed with too little care speak for the use of the inexpensive, woven polypropylene bags.
The ecological balance, however, is influencing the discussion about packaging material in Europe as well. Since the manufacturing of paper is very energy intensive, the ecological balance of woven plastic bags when correctly recycled is preferred.
Open-mouth or valve bags?
For small bagging volume and low sanitation requirements, bagging with valve bags is the simpler solution for automated bag placement as well as for no bag closure. In addition to improved sanitation, bagging in open-mouth bags offers more accurate weights, more flexibility in regards to bag size and bulk weight of the product, and easy opening for the end customer. These advantages explain the trend toward bagging in less expensive, open-mouth bags when packaging milling products.
Manual or automated?
Selecting a manually operated plant or an automated one depends directly on the product, the local conditions and the size of the operation. For designing a bagging plant, criteria such as bag weight, bag size, bag quality, required bagging volume, closure type and logistics can be considered.
Single spout bagging stations are suitable for paper, plastics and fabric bags holding 10 to 50 kg. Depending on the type of single spout bagging station, the bagging volume for flour in 25-kg bags is approximately seven bags per minute.
For higher bagging volume, bagging machines with multiple spouts can be used. These can also be operated with different kinds of bagging material. If they are operated with woven polypropylene bags, the bag quality must be suitable for automated filling as a prerequisite for high operational safety.
The new Bühler bagging station Maia, for bags of 10 to 32 kg, provides a low-energy consumption alternative for bagging milling products. It offers high operational reliability and sanitation for fully automated bagging of powdered, free flowing or friable products.
Consideration of the upstream elements – such as bins, product feed and weighing – when configuring a bagging plant is important. In many plants, they are the limiting factors for bagging capacity and therefore need to be adjusted to the desired volumes. Properly dimensioning them is also a requirement for a high weight accuracy and for the reproducibility of the bagged product.
Higher productivity by reduced personnel costs, traceability and availability of product as well as permanent inventory options are increasingly important.
Expanding bagging plants with direct loading for bags onto trucks using pallets increases productivity since the bagged goods can be provisionally kept in pallet storage. This increases bagging line productivity because downtime for the bagging plant is decreased. Pallet storage additionally supplements storage capacity for finished products in the storage silos.
Pallet storage is an advantage for very low logistic costs and generous space allotment, or as a preparation zone for loading pallets. Shelf storage allows every pallet to be accessed. Costs for storage installations are low, but needs for personnel and space are high. Flow storage is suitable for the milling industry and is distinguished by its ideal price-performance ratio at higher turnover rates. Pallet storage in the milling industry is done on a first in, first out principle (FIFO principle). High-bay storage provides many functional possibilities with high space utilization and requires preventive maintenance for smooth operation.
Control of bagging systems
A reliable control system guarantees efficient control of the bagging plant. The skills of the operating personnel must also be taken into consideration. Hardware which is resistant to influences such as vibration, dust and temperature is decisive for high reliability.
With an integrated control system, all processing units can be centrally controlled from the bagging bins to the finished pallets. The module permits flexible and user-friendly plant operation: It includes the bin discharge and product feed, all scales, including the filling of them, the bagging stations and bag sealing as well as bag transport and palletizers.
Bag closing systems for open-mouth bags
For closing open-mouth bags, sealing, gluing, sewing or combined systems can be used. Depending on the bag material, bagging volume and degree of automation, different systems for manually or automatically sewing the filled bags closed may be used. For sealing bags with pre-applied adhesive (pinch bags), no consumables are needed and the bag feed must be very secure. Bag closures using hot seal are very user friendly (tear strips, sealing ribbons) and suitable for conventional open-mouth bags.
The proper design of an automated bagging plant for milling products in the 10- to 50-kg range requires competent advising. Questions such as bagging volume, discharging elements, weighing systems, bag types, bag sealing options, palletizing, storage logistics, etc., are decisive in the planning, but so are considerations of the up and downstream process steps as well.
Customers should also increasingly be able to include the desired bag volume per shift or day in their decision instead of a short-term volume per minute. Very close coordination of the bagging with the production logistics and the following storage and distribution logistics can only be made possible through a long-lasting, complete solution.
Thomas Ziolko is product manager for Bühler’s grain milling unit. He can be reached at Thomas.firstname.lastname@example.org