If appearance isn’t an issue, particle damage isn’t a concern. Unfortunately, people eat with their eyes, and candy-coated chocolate, freeze-dried coffee and other human consumables won’t pass quality checks if there are cracks or shattered particles.
Modulating particle speed isn’t an option — “with vacuum conveying, you only have one atmosphere to convey the product,” Hayes observes — leaving the feed pressure the best opportunity to minimize damage. Positive displacement pumps are fine for flour and other raw materials, but for goods at or near their finished state, Volkmann relies on a multijector pump outfitted with a series of venture that produce pressure that is close to a full vacuum.
In addition to pump selection, engineers of pneumatic systems incorporate filters and assorted “energy absorbing techniques” to minimize product damage. But striking a balance between velocity and gentle handling is an ongoing challenge, he says. “You never really know if any one product can be conveyed until you test it.
“I get powders I’ve never seen before every day, and I’ve worked with this technology since 1973,” Hayes continues. Size, shape, moisture content and other variables affect performance, which is why food manufacturers are advised to submit materials for testing in a lab before installing a system. “If you don’t test it, you’re just playing Russian roulette,” he emphasizes.
Spiral conveyors are used in multiple segments of food production, from bakery coolers to poultry freezers. They rely on friction between the rotating drum in the core and the belt to maintain tension and drive the conveyor through the spiral.
“You’re at the mercy of friction,” notes Achraf Elhassouni, global product manager-spiral platform at Intralox LLC USA (www.intralox.com), New Orleans, “and friction is a huge variable that you can’t control.” Variations in load, oil build-up and other factors cause belt slippage, and that leads to performance issues.
To take friction out of the equation, Intralox designed a spiral with teeth along the inside edge of the belt. Those teeth engage with sprockets on the drum, resulting in consistent belt tension, regardless of the load.
Intralox has retrofitted 300 friction drives to mechanical drives since introducing the concept five years ago, Elhassouni estimates. Potato processors are particularly receptive to the frictionless belt, in part because of the build-up of non-transfat oils that occurs when French fries and other value-added potato products move through a spiral freezer. The oil coagulates and “sticks like glue,” he says, forcing processors to take the spiral off line and apply hot water and mechanical scrubbing to dissolve the build-up. With potato processors targeting three weeks of continuous production, unscheduled downtime for cleaning is becoming intolerable.
Similar issues plague most processors who use spirals as blast freezers. In that case, oil, sugar and other ingredients that coat the product get sprayed onto virtually all moving parts.
Intralox named its system DirectDrive. The first installation was at Canada Bread’s Trillium bakery in Hamilton, Ontario. Belt vibration was enough to cause buns to slide and cluster, which became an alignment headache after the buns exited the spiral and were conveyed toward slicers and packaging. Positive belt engagement resolved the issue.
Given the variety of options to convey, no single drive option can serve all applications. The issues are as various as the types of conveyors, from reliability and throughput to cleanability and hygienic design. The only constant is the need for new solutions to the problems that inevitably arise.