Designing modern bagging lines that meet the requirements

By Peter Naef, Bühler AG, Switzerland

A bagging line in a production plant is closely tied to the associated production and distribution processes, including the upstream and downstream logistics. This may have an impact on the availability of the entire production plant and must therefore be taken into account in evaluating and designing the line. To achieve the best possible performance, it is essential that the production management and distribution department cooperate closely in defining the basic concept of such a line.

Operating reliability and automation
In the design and specification of a bagging line, it is essential to satisfy the specific plant requirements. But a number of fundamental requirements must always be met by bagging lines in food applications. One key requirement is high operating reliability and maximum flexibility. Due to the complexity of a bagging line, the individual components must be of high quality and carefully matched in order to ensure high operating reliability and maximum availability. Today, automatic bag attachers and bag transfer and spreading units are normally part of the standard equipment of bagging lines. If the proper bag materials are used, an automatic bag attacher will be capable of processing woven plastic bags as well as the paper bags commonly applied. A bag transfer and spreading unit transfers the bag from the bagging spout and feeds it automatically to the bag closing system. Both automatic units increase the throughput capacity and reduce the manpower requirement. Both units can be integrated either with a single-bag packer or in a bagging carrousel equipped with three, four, or six spouts.

Accuracy and hygiene
Modern bagging lines are characterized by their very high bagging weight accuracy and their top hygienic standard. To achieve accurate and consistent bagging weights, a product feed system operating at a constant capacity is needed in addition to specialist know-how in the design of product storage systems and of bagging bins and their dischargers. The feed and weighing system selected must be matched to the product in question. Despite optimal electronic weight monitoring and automatic weight correction, it is of advantage to install a check scale with an automatic scrap bag ejector between the bagging line and the palletizer or loadout point to ensure complete monitoring of the packed bags.

In the food sector, hygiene-related legal requirements are becoming increasingly stringent. They must be satisfied by applying the proper system design and preventing product contamination. In this area, a substractive bagging scale with direct bag filling will significantly reduce the risk of contamination compared to conventional batch bagging scales. Another advantage of substractive weighing is that every actual filling weight is registered and corrections can be made as required even with fast bagging cycles.

Bag compacting and centralized control
New, mechanical compacting systems allow more efficient reduction of the volume of bagged product and give bags a more stable form. At the same time, this reduces the handling volume. As in other areas, automation and centralized control are becoming increasingly important for minimizing the manpower requirement of bagging lines. A state-of-the-art control system will enable an entire bagging line including the automatic palletizer to be controlled and monitored from a single touch-screen terminal. Such control systems are capable, say, of selecting a different bag weight together with the appropriate bag size, or of changing the bag layer pattern created by a palletizer. This is done fully automatically and without manual intervention. Moreover, these systems allow fast error diagnostics of the entire bagging line, which slashes line downtimes and makes it easier to familiarize new employees with bagging operations.

Balanced warehouse logistics
The performance and cost-effectiveness of a bagging line also depends on the warehousing system applied, which must be matched to the specific needs. More and more, the method of direct loadout straight from the bagging line is being abandoned. On the one hand, this is due to the high bagging capacity required. On the other hand, the direct linking of bagging and loadout and the increasing number of loadout variants with the related downtimes make this former approach uneconomical. An analysis of the plant-specific requirements is a prerequisite for selecting the adequate warehousing concept, which must also take account of the plant’s uptime and therefore its profitability. A number of warehouse variants are possible, which all have their specific advantages and disadvantages. Today, very many plants apply the block storage method due to its low capital cost. But it also has drawbacks: The first-in-first-out (FIFO) approach is not possible; a large surface area is needed, with poor space utilization; automatic inventory control is not possible; the storage and retrieval capacity is low; and the number of possible variants or items is low. In addition, the manpower costs of a block storage system are very high, since several forklift drivers are needed simultaneously. The drawbacks of rack storage systems are similar to those of block storage installations, though they do allow FIFO operation to some extent. They also permit order-picking thanks to the access they allow to individual items in combination with flow-rack or high-bay storage systems. For many packing installations, a flow-rack store will be found to be an adequate solution. Flow-rack storage systems offer the following advantages: FIFO is possible; the space utilization rate is high; the capacity and uptime are high; the manpower requirement is low; the capital cost is relatively low, with an excellent price-to-performance ratio; and supply readiness is optimal. Fully automated high-bay warehouses are the Rolls Royces in the field of warehousing. But despite their outstanding advantages, they are too expensive and complex for many plants. A high-bay storage system is especially suitable if a very large number of items must be stored and if access to each individual item must be possible at any time.

Parameters

The main company-specific parameters determining the selection of a bagging line are:

• Output per week (exclusive of products shipped in bulk, Big Bags and small packages).
• Number of products and their respective quantities, plus precise product specifications including bulk densities.
• Actual working hours per shift and day.
• Number of workdays per week.
• Number of bag weight and product changes per shift.
• Shares of the different bag weights of the entire product volume to be packed.
• Minimum storage time in storage and bagging bins (for “deaerating” or reducing the volume before packing).

Profitability

The profitability of a bagging line depends essentially on the following factors:

• Investment matched to the actual requirements.
• Employment of operating personnel carefully planned.
• Level of automation matched to specific needs.
• Highly accurate bag weights.
• Low energy consumption.
• Low cost of expendable materials.
• High uptime and flexibility.
• Short times for product and bag weight changes, or none at all.
• Best possible design of the entire logistics chain from bag warehouse to loadout point.
• Minimized maintenance and servicing.

Author:
Peter Naef
Bühler AG, Uzwil (Switzerland)
E: mu.buz@buhlergroup.com
www.buhlergroup.com