January 3, 2016
When a fire gutted a 9000 sq ft (837 sq m) building on the property of the Canadian head office and manufacturing and distribution center of the Henry Company, the company re-engineered its processes, achieving a two-fold increase in production along with improvements in safety, morale and environmental practices.
One major improvement was the replacement of manual bag dumping with an automated bulk bag weigh batch discharging system from Flexicon Corp., a move that dramatically boosted productivity, quality and safety while cutting labor and material costs.
Bulk bag discharge system replaces manual bag dumping
Previously, workers manually carried 50 lb (23 kg) bags containing a polymer additive to a 6000 gal (22,710 l) mixing tank containing asphalt, cut open the bags and dumped them. A typical batch required 2,000 to 6,000 lb (907 to 2,721 kg) of polymer, or 40 to 120 bags. “That’s a lot of manual slogging,” says Plant Manager Todd Thertell.
Henry engineers evaluated equipment that would allow purchasing of the polymer powder in bulk bags, ultimately selecting a Flexicon Bulk-Out® bulk bag weigh batching system comprised of a model BFF bulk bag discharger with integral flexible screw conveyor and weigh batching controls.
Thertell says, “We now buy the polymer in 2,000 lb (907 kg) bulk bags, so depending on batch size, we’re handling just one bulk bag or two, with no risk of losing count of paper sacks,” adding, “The process of carrying, opening and dumping bags, which previously required one hour, can now be accomplished in just 15 to 20 minutes.”
Devices promote complete discharge of bag contents
With the new system, an operator attaches the bulk bag to a lifting frame and forklift-loads the frame and bag into receiving cradles atop the bulk bag discharger. With the bag secured over the 8 cu ft (226 l) capacity hopper, the operator pulls the bag spout through a Power-Cincher® flow control valve that cinches the bag spout to regulate flow, prevent product leakage, and permit dust-free retying of partially emptied bags.
Below the flow control valve is a manual Spout-Lock® clamp ring that is raised by a Tele-Tube® telescoping tube for a dust-tight connection to the bag spout. With the connection secure, the operator unties the bag spout and opens the flow control valve to initiate flow. The telescoping tube lowers, applying continual downward tension to keep the spout taut as the bag empties, promoting complete discharge into the hopper. At the same time, Flow-Flexer® bag activators raise and lower the bottom edges of the bag, directing material into the outlet spout and raising the bag into a steep “V” shape to promote total discharge. Additionally, Pop-Top™ extension arms at the top of the four discharger posts stretch the bag into a cone shape as it empties and elongates, aiding in complete discharge.
Automated loss-of-weight batching accomplished directly from bulk bags
Hot Melt products are made to order, so batch sizes vary. The operator enters the required batch weight into the PLC controller. “It works on a net loss system,” Thertell explains. The discharger frame sits on four load cells, so when you load the bulk bag, the weight of the bag is displayed on the screen.
When the operator initiates a cycle, the 4.5 in. (114 mm) diameter 35 ft (10.7 m) long Flexicon conveyor transports the powder to a height of 19 ft (5.8 m). The material exits the conveyor below the point at which the rotating screw connects to the gear reducer, preventing material contact with seals, and flows through a transition adapter, slide gate valve and downspouting before entering the mixing tank.
The PLC receives loss-of-weight information from the load cells, running the conveyor at full discharge rate until the target weight is approached, and then reduces the feed rate to dribble, stopping the conveyor and closing the Power-Cincher valve when the accurate batch weight has been lost.
The 8 cu ft (226 l) capacity floor hopper is equipped with a large door, bag tray support and safety screen for oversize/foreign material, allowing operators to manually add pre-weighed minor ingredients to the batch.
As the bulk bag contents flow into the hopper, displaced air and dust are drawn into a Bag-Vac® dust collector attached to the discharger frame. Reverse pulse air jets dislodge material collected on the filter for the particles to return to the material stream. Because the connection of the bag to the hopper is sealed, activating the dust collector causes the empty bag to collapse under vacuum, extracting air and residual dust.
Short batching cycles enhance a time-sensitive process
Speed of processing was another consideration. Once the polymer has been transferred to the mixing tank, the polymer and asphalt undergo “pre-mix” blending at 148.9°F (69.4°C) for two hours. Then the mixture is pumped to one of three 3000 gal (11,355 l) “let-down” tanks, used to finish the product. Additional polymer fillers are manually added, and the let-down batch undergoes another two hours of processing.
Thertell explains that once the material has been added to the mixing tank, the process is time sensitive. “We have 18 hours to convert it to a finished product and package it for shipment before its properties change. Instead of a nice rubbery balanced mixture, it becomes thick and stringy and difficult to melt. Typical batch processing time for pre-mix formulations has been halved, from four hours to just two.”
“We also don’t have the waste that we had previously,” he continues. “Just one sack that’s returnable. Now we have a poly sack that we flatten down and return to our supplier to be refilled with polymer. It’s more environmentally friendly, because we’re not generating any waste for landfills.”