Freshness on the Line: Examining effective conveying solutions for fresh-cut produce
Many fresh-cut produce processors and packers have traditionally relied on belt conveyors to transport bulk and packaged product on their production lines, in part because low capital costs make these conveyors seem so affordable. But when on-going maintenance and sanitation costs are factored in, the affordability equation shifts in favor of other conveyor types. Add performance issues like gentle handling and throughput into the analysis and each fresh-cut product and application points to its own ideal conveying solution.
This look at the strengths and weaknesses of several options — belt conveyors, vibratory conveyors and horizontal motion conveyors — should help processors and packers identify the most effective conveying solutions for their applications.
Belt conveyors typically offer the lowest initial capital cost of all the conveying solutions, which contributes to their popularity. But such a simple cost analysis is shortsighted because high maintenance and sanitation costs cause the total cost of ownership of a belt conveyor to quickly rise.
Although a total cost of ownership analysis indicates that vibratory and horizontal motion conveyors are less expensive than belt conveyors in the long run, there are fresh-cut applications that are best served with belt conveyors, warranting their use despite the higher cost. As for specific applications, belt conveyors are ideal for:
• achieving significant changes in elevation (vibratory shakers are effective if the required incline angle is 10 degrees or less, but beyond 10 degrees, a belt conveyor is needed);
• layering belts where incoming product is loaded either manually or automatically because of the slow rate of movement (typically three to four feet per minute) needed to achieve a well-mixed product;
• serving trim tables since they offer the most flexibility in speed;
• two-level storage conveyors that convey fresh-cut produce from a washer to a dryer; and
• conveying packaged product, which can be achieved with either a belt conveyor or a vibratory shaker, but the sanitation advantage of a vibratory shaker is less of a factor with packaged product.
There are two main types of vibratory conveying systems: true natural frequency conveyors that feature mechanical drives and electromagnetic conveyors that feature electromagnetic drives. Both use frame-mounted drives and spring-arm assemblies to distribute energy to the conveyor bed, producing a diagonal, harmonic motion that moves product forward.
Compared to belt conveyors, vibratory conveyors are inherently cleaner with stainless-steel product zones and no belt-to-pulley/gear laminations. They also reduce maintenance, which results in a lower total cost of ownership over the life of the conveyor. Some newer vibratory shakers take low maintenance to the extreme with “lube-for-life” mechanical drives that eliminate the need to lubricate or change oil.
As for specific applications, vibratory conveyors are ideal for:
• dewatering, as the vibration releases the bond between surface moisture and product;
• product distribution on processing lines and packaging lines because gates can be easily opened and closed to divert product to multiple points;
• scale feed applications where accurate metering to scales greatly enhances scale and bag performance;
• feeding a cutter or slicer, where product orientation and singulation improves the effectiveness of the operation; and
• cooling and drying as they can be equipped with a device that circulates chilled air through the product during conveying.
Horizontal Motion Shakers
Like vibratory conveyors, horizontal motion conveyors offer more gentle production handling than belt conveyors and lower maintenance and sanitation requirements lead to a lower total cost of ownership than belt conveyors.
Horizontal motion conveyors provide gentle handling for delicate products, such as whole mushrooms, that can slide on the conveyor bed without being damaged. Leafy greens, however, get scuffed and damaged by riding on the bed of a horizontal-motion shaker, so vibratory conveyors provide gentler handling for these types of products. This gentle handling advantage must be considered on a product-by-product basis. Also, the slower conveying speed of horizontal motion sometimes encourages processors to run product deeper to get the throughput they need, and loading delicate products deep can cause damage.
Another significant difference between horizontal motion and natural frequency vibratory conveyors results from dynamic loading. Horizontal motion shakers create high dynamic loads during operation and require isolation via a separate deck, while vibratory shakers require no additional isolation and can be suspended from overhead, mounted to other machinery or supported from the floor. Thus, horizontal motion conveyors have less installation flexibility and higher installation costs compared to vibratory conveyor systems.
Specific applications in which horizontal shakers are ideal include:
• reversing product flow;
• reducing product drumming because some products, such as baby whole carrots, would make a drumming noise on vibratory shakers (but horizontal shakers’ electromagnetic drives are the most quiet of all, so if product drumming is not an issue, an electromagnetic vibratory shaker will be the quietest solution); and
• providing some bulk storage capacity on the production line when conveying product in which gentle handling is not important.
To help navigate this complicated analysis, processors and packers should consider working with an equipment supplier that offers expertise in the fresh-cut industry and provides a full range of conveying solutions to choose from because, if designed properly, conveyors can do much more than simply move product throughout the plant. Gentle handling, effective dewatering, and chilling, to cite just a few examples, can improve product quality and extend shelf life.
Teri Johnson is the fresh-cut industry manager at Key Technology. For more information, visit www.key.net. This was originally published in the April 2010 Food & Beverage Engineering & Maintenance supplement.