Bulk Bag Filling - Maximum Densification and Accurate Weighing

Ingredients Handled
This customer ships talc in bulk bags. Talc is a mined mineral; the producer removes it from a nearby open-pit mine. At the plant, the talc moves through a jaw crusher for primary size reduction. Secondary reduction through cone crushers reduces the talc to a 14-mesh size, similar to sand grains. A screw conveyor then moves the talc into dry ore silos. From there, the talc is screw conveyed to fine-grinding pebble mills.

Pebble mills further reduce the talc to various size grades, such as a 200-mesh grade for ceramic applications. A 325-mesh grade for use in paints is produced by additional reduction in jet mills. The 325-mesh talc has a bulk density of about 40 lb/ft3, while the 200-mesh talc's density is about 50 LB/ft3.

Dust collection equipment draws away fines throughout the milling process. After milling, pneumatic conveyors transport the talc to storage silos. From there it goes to packaging or bulk loadout. The talc is distributed via 50-pound bags, bulk bags, trucks, and railcars.

Control and Metering's Customer
Gouverneur Talc, Gouverneur, N.Y., is a subsidiary of R.T. Vanderbilt Co., which supplies minerals and chemicals worldwide. Gouverneur Talc produces approximately 200,000 t/y of industrial talc and distributes it for use in the paint and ceramics industries.

Gouverneur Talc mill superintendent Bill Goodheart said the company works to provide uniform grades in their talc varieties. "We put a great deal of effort in quality control and product consistency."

Customer's Reason For Using Bulk Bags
For many years, Gouverneur Talc had filled bulk bags with 325-mesh talc using one bulk bag filler. But as demand for packaging other talc grades in bulk bags increased, the company wanted a bulk bag filler for each grade.

"Number one, there was only one bulk bag filler," Goodheart said. "We wanted to expand the bulk bagging so we could bag the different grades or grinds, and we didn't want to do it on one machine because of contamination chances."

The three bulk bag fillers allow Gouverneur Talc to fill different grades of talc in bulk bags without cross-contamination concerns. Beyond packaging 325-mesh talc, Gouverneur now ships bulk bags filled with 200-mesh talc as well as a talc grade between 200 and 325 mesh.

"We hadn't been shipping either of these products in bulk bags before we installed these three machines," Goodheart said. "Only one of the finer mesh products had ever been shipped in bulk bags."

Because of the filler's densification table, Gouverneur Talc can fill a smaller bag with the same amount of talc as before. A 56-inch bag is used for 325-mesh product, while 48-inch bags are used for the other talc grades. Goodheart said the bulk bag fillers also produce less dust than the old machine.

Most importantly, the new fillers have improved weight accuracy. Gouverneur Talc fills 2,000-pound bulk bags to an accuracy within 3 pounds, exceeding the required ½ percent of the target weight. Each filler can fill eight bags an hour.

"[The new bulk bag fillers have] eliminated customer complaints about weight," Goodheart said, "We haven't had any since we started using these machines."

Control and Metering Application Solution
Gouverneur Talc replaced their 15-year-old bulk bag filler with three new Model B fillers from Control and Metering. The filler uses a microprocessor-based controller with an operator keypad that controls such filling functions as empty bag tare, target weight, fast or dribble feed, densification timing, liner inflation, table up or down functions, automatic or manual operation, filling start, and filling stop.

A large platform allows one operator to attend all three bulk bag fillers. As one bag is removed, the operator loops an empty bag on specially fitted trombone arms that slide under the fill head. A fork lift takes the full bags from the filler for warehousing or directly loads them in trucks or railcars for transport.

Application Challenges and Their Solution
The most critical requirement on this project was to properly densify the bulk bag. Talc is notoriously difficult to densify properly. A system that could quickly achieve a high level of compacting was required. The Model B filler was chosen due to its combination of features including hang filling and the patented coned densification table.

In operation, bulk bags are filled and weighed by the Model B as they hang from their loops, which ensures straight bag sides. Only the bag, the fill head, and the hanger arms are weighed, aiding fill accuracy.

The bulk bag filler has a coned lift table that is raised into the bag at the start of the filling sequence, forcing the initial flow into the bag' corners. The lift table then descends, allowing the bag to hang from it loops. The sides straighten under the material weight. The lift table rises again into the bag and vibrates for continuing densification while producing a flat-topped bag. At Gouverneur enhanced vibrators were supplied to ensure talc at the top of the taller bags is properly densified and to allow for varying climate conditions. "You can also adjust the machine to accommodate different bag heights," Goodheart said. "The old machine really didn't have those adjustments"

Why The Customer Chose Control and Metering
Besides the need for additional equipment, Goodheart said it was time to replace their existing bulk bag filler. Among it drawbacks, the 15-year-old filler didn't fill bags to accurate weights.

"There seemed to be a lot of problems with maintaining accuracy," Goodheart said. "Part of it I think was the way the machine filled the bags. It didn't have any means of dribble-fill control, so you couldn't slow it down as you neared the target weight."

As a result, Gouverneur Talc was filling the bulk bags with extra talc. The overfill not only cost the company money, Goodheart said, but it also increased customer complaints.

"A customer isn't going to want extra material or be shorted either," he said. "Sure, the extra is free when we charge them for 2,000 pounds and put 2,050 in the bag. But they need accuracy for their process too. They need to know what the weight of that bulk bag is."

In addition to being inaccurate, the bulk bag filler leaked talc during the filling process, creating a messy work environment. The filler also lacked densification equipment to compact the talc and create a stable bulk bag.

Gouverneur Talc's concerns about their existing bulk bag filler and their need to expand the bagging operation prompted them to seek new equipment. To begin the search, Gouverneur Talc contacted the manufacturer of their existing bulk bag filler. They also contacted a manufacturer who had installed a bulk bag filler in a nearby Gouverneur Talc plant 2 years earlier. The producer had specific criteria: The bulk bag filler had to include dribble-feed control for fill accuracy, a densification method to produce a tightly packed bag, and containment during filling. They wanted to fill bags with 1,000, 1,500, and 2,000 pounds of talc.

Gouverneur Talc discovered the original manufacturer's bulk bag filler still didn't include a means to densify bagged material. Goodheart said the second manufacturer's filler had dribble-feed control and a densification method, but that method still didn't meet their needs.

"[With their filler] the bag is weighed as it sits on a table," Goodheart said. "Then a device lifts the table a few inches and drops it. That's how the material is densified, but it doesn't seem like it packs very tightly."

As the producer continued their search for a bulk bag filler, Goodheart said he responded to a filler ad in a trade publication. The filler's densification method caught his attention, and he requested a brochure.

"It really looked to us like the advertised filler's coned vibrating table, which goes up into the bag, helps to settle the product or densify it," Goodheart said. "It looked like it worked quite well, and it was better than anything we'd seen."

The filler had all the features Gouverneur Talc wanted: dribble-feed control, a densification method, and cleaner operation during filling. The producer sent the filler manufacturer a talc sample for testing.

"We wanted to see a stable filled package, as compact as possible," he said. "They ran a test and videotaped it. They sent the video and a finished package for us to look at. That made the difference – the fact that we could see how the filler worked and see results in a finished package."

The video showed that the bulk bag filler could produce accurately filled, tightly packed bulk bags of the often difficult-to-handle talc. And the operating environment was cleaner with the filler. Gouverneur Talc decided to purchase the Model B bulk bag filler made by Control & Metering.

"As far as price goes I think we paid little more for their equipment," Goodheart said, "but it just looked like the best way for us."

For further information on Maximum densification and accurate weighing contact contact us at info@spiroflow.com or call 1-704-246-0900.