By Mike Wilson, Carlos Schleske and Markus Lackman
While manual cement-packaging operations remain very common, more and more producers of cement, crushed stone and gravel as well as other cementitious materials are converting to fully automated packaging lines. The reasons include higher speeds, greater filling accuracy, cleaner bags, reduced labor requirements and more economical work environments.
Automated packaging operations depend primarily on advanced multispout filling machines in tandem with high-performance valve bags. When planning a changeover to automated packaging, consult early with filling machine and industrial bag suppliers. They can help you avoid potential problems and make a smooth transition to a fully automated operation.
Manual vs. Automated Packaging
Manual cement-packaging lines are labor-intensive, relatively slow and often entail manual calibration of weighing scales when switching to a different bag size or product type. Typically, the packaging operator sits close to the filling spouts and is exposed to airborne dust and debris, requiring the use of goggles and a dust mask. Nearby workers also must wear protective gear.
The speed of manual operations is limited. During packaging, the operator reaches for an empty bag and places the bag onto a filling spout. The task is tiring and repetitive, and operators are usually rotated out after a two-hour shift.
Automated filling machines, in contrast, operate at a much faster rate and exert precise control over the bag-filling process. The automated fillers come as inline or rotary systems with multiple filling spouts and are equipped with electronic weighing systems. Depending on the material, a rotary packer can fill up to 6,000 bags per hour.
The fillers are controlled from a PLC. Centralized servers manage each step of the filling process and monitor and record the amount of product going into each bag, along with the dispensing rate.
Rotary fillers have as many as 16 spouts, and operate as follows: The desired bag weight is entered into the PLC before startup. During operation the rotary machine’s bag placer feeds the bags sequentially onto the filling spouts as they rotate into position.
Each filling spout is equipped with a slide gate controlled by the centralized server. Once a bag is in place, the gate opens and releases material into the bag. When the bag is nearly filled to the preset weight, the server partially closes the gate, restricting the flow to a fine feed. The flow is stopped when the bag is completely filled. The controlled feed rate reduces the amount of dust that escapes, improving workplace air quality and overall cleanliness.
In a recent case, a portland cement and masonry supplier upgraded to automated operation by installing an eight-spout Haver RotoClassic Packer. The company’s manual bagging operation had proved inefficient and failed to keep pace with increasing product demand.
After the upgrade to an automated operation, the company was able to reduce labor costs on the line. Filling accuracy also improved, with the eight-spout packer demonstrating an accuracy of +5.3 oz. for a 50-lb. bag. In addition, the packaging operation became much cleaner.
Stronger Valve Bags
The performance of automatic filling machines is optimized with the use of high-performance valve bags, such as Mondi Americas’ Airstream valve bags, which in tandem with automated equipment, improve the filling process. High-performance bags are made of high-grade Kraft paper, which is exceptionally porous and allows air to easily pass through. The high-quality paper also exhibits greater tensile energy absorption (TEA) than lesser paper grades. It can stretch as much as 8 to 10 percent, compared with only 1 percent for standard paper.
It’s easy to demonstrate a high-performance valve bag’s strength advantage. Fill a high-performance bag and a standard bag with a cement material, and then drop the two bags flat from a height of 8 to 10 ft. onto a hard surface. The standard bag will rupture, spilling its contents. The high-performance bag is likely to remain intact. Stronger bags mean less breakage during handling and shipping, lower costs for bag returns and a more satisfied customer.
Another benefit of high-performance bags is their two-ply construction. Compared with three- or four-ply standard bags, they take up less space per bag, allowing converters to fit more high-performance bags on a pallet, thus saving weight and making empty bag storage space more efficient.
In automated cement-packaging applications, various system components must be successfully integrated for optimal performance. Filling machine and high-performance bag suppliers can be called in at the design and implementation stages to recommend system design, product features and the positioning and integration of components. Properly designed systems will help avert costly downtime.
A bag’s valve size, for example, is a key consideration. Ideally, the bag’s valve opening and the filling spouts need to be closely matched. If the valve is slightly larger than the filling spout, the bag might still be usable, but some dispensed material will escape into the air. If the valve is smaller than the spout, the bag cannot be used.
Small adjustments before production begins can make a big difference. In one case, a bag manufacturer’s technical expert viewed a newly installed packaging system and spotted that bags were folded the wrong way when loaded into the bag magazine. Changing how the bags were folded solved the problem.
A final note: In the U.S., environmental regulations governing the packaging of bulk powders, particularly state standards, are becoming increasingly strict. In Mexico, SEMARNAT regulations are prompting producers of cementitious materials to invest in equipment that collects dust during production process. Look to your filling machine and high-performance bag suppliers for help in minimizing airborne particles and complying with today’s tighter air-quality standards. F
Mike Wilson and Carlos Schleske are from Mondi Americas; and Markus Lackman is from Haver Filling Systems Inc. Information courtesy of Mondi Americas, www.mondigroup.com.