With many flour millers diversifying production with specialist flours and bakery mixes, the range of flours being packed into bags continues to grow. The wide range of product material types demands a variety of bagging and handling techniques. Filling speed, maintaining the purity of the product and reduced dust levels are some key features millers demand.
Many factors have to be considered when determining the best bag type and size for a particular flour bagging application. Apart from cleanliness, stability, compact form and protection of the flour, bags have to be suitable for easy sealing, palletizing and stacking.
Consequently, these diverse requirements encourage millers to look for greater guidance in finding a particular application solution. By forming a partnership with the supplier, the miller can select the optimum bag material, bag type and filling/closing system for their particular needs prior to making any capital outlay.
Selecting the bag type
Open-mouth bags are predominantly used in most parts of the world, and many bag filling systems have been designed to handle them. Complementing the filling systems is a range of bag mouth forming and sealing systems to close the various bag types that the miller can select from, including:
• cross bottom multi-ply paper bags and block bottom multi-ply bags, which require folding and stitching;
• pinch bottom multi-ply paper bags, which are closed by reactivating pre-applied glue;
• cross bottom paper bags with a carrying handle, which require stitching and over-taping;
• jute bags are still used in some regions, which just require stitching.
Valve bags are used in some mills, particularly in Continental Europe and increasingly in the U.S. and Asia, and while the bags are often more expensive and slower to fill, the shape of the filled bag tends to improve palletization and storage. However, the introduction of ultrasonic valve bag closing systems to reduce infestation and contamination has taken away one of the traditional cost savings from valve bags, which did not typically require a closing system.
Traditional mills might only be producing a few types of flour and bran. For these situations, the equipment choice is relatively straightforward, and the main considerations become the output requirement and degree of automation needed.
However, many mills are now creating a range of value added products, such as specialist bread flours, cake and bakery mixes. Because many of these are sold via retail outlets and to in-store bakeries, there is a need to comply with manual handling directives. Also, bag sizes are being reduced. Where previously 50 kilogram and 32 kg have been typical bag sizes, 25 kg, 16 kg and even smaller bag sizes are now common requests from millers around the world.
To maintain output tonnage while still meeting the need for smaller-sized bags, millers are looking for faster bagging systems. In turn, manufacturers have started to introduce innovative designs for both static bagging lines, and perhaps the most common type of flour packing system, the Carousel.
A direct effect of the need for higher output rates is the need for enhanced weighing accuracies at these higher speeds. As a prime requirement, the weighing controller needs to store multiple sets of weighing parameters to facilitate simple product changeover.
To help ensure the maximum bagging system availability or uptime, the equipment must be kept open and accessible, while still maintaining a dust controlled environment. This ensures that any changeovers to different products or to different filling weights is achieved quickly and efficiently. Coupled with a good control system, these changeovers can be stored as pre-programmed routines for quick and simple implementation.
Meeting The Output Requirements
An essential element of any flour bagging system is the need to allow sufficient time to settle the product in the bag. This is necessary to ensure that the optimum size of bag is used and that a well-formed and de-aerated bag is produced. Time, therefore, becomes a critical factor in selecting bagging equipment, as the need to allow sufficient de-aeration time has to be balanced against not reducing the bagging output to an unacceptable level.
Some typical output expectations for different types of flour bagging systems are presented in Table 1, but these are likely to vary depending on the individual handling characteristics of a particular product and individual site conditions. All data is based on the assumption of using a screw-fed automatic load cell net weigher with self-optimizing control.
The Carousel systems (equipment options 2, 3 and 4) enable bag placing, filling, possing and release of filled bags to occur simultaneously, thereby ensuring optimum output without the loss of product possing time. Equipment options 1, 2, 3 and 5 can also be supplied with automatic bag placers. While not significantly increasing the overall bagging rate, the use of these automatic systems can make a major contribution to the mills production consistency. Option 4 represents an optimum open-mouth bagging system for the modern flour mill, as it provides the best opportunity for reducing dust and improving hygiene in the mill (see Figure 3).
Bagging equipment manufacturers can provide: dust tight bag clamps; bag transfer devices to move the filled bag from the filling spout to the closing system without opening the bag again; interlocked access points; and automatic, motorized height adjustment on conveyors and bag possers, which help settle product in the bag.
More and more, flour mills are now incorporating automatic palletizers into their bagging lines. In many cases, these palletizing systems also include automatic slip-sheet applicators and hooding and wrapping systems. These complete systems enable mills to achieve maximum warehouse utilization when storing loaded pallets, and filled bags are better protected during transportation.
Millers should carefully consider the benefits of upgrading all types of bagging equipment, not just when the equipment wears out, as an effective means of reducing costs. Readily available is bagging technology that enables millers to benefit from increased filling outputs, improved accuracies, enhanced machine reliability and better hygiene conditions. Millers should work with their supplier to jointly develop a customized bagging solution for maximum return on investment.