A lapse in safety during the handling of powders and bulk solids can be catastrophic. The proof rests in incidents of spontaneous combustion of grain-dust, the consequences of which have captured national headlines and motivated the industry to examine its safety standards. On-going problems of contamination—the kind that expose workers to dusty products, expose bulk foods to the plant atmosphere, and allow cross-contamination of multiple materials running through the same equipment—may attract less attention but are nonetheless equally significant.
“The design changes evident in much of today’s bulk handling equipment are the result of efforts to eliminate contamination of all types, mostly to contain dust,” notes David Boger, sales manager for Flexicon Corp., Bethlehem, Penna. The company manufactures flexible screw conveyors, pneumatic conveying systems, bulk bag dischargers, bulk bag fillers, weigh batchers, bag dump stations, drum dumpers and automated systems.
“An overriding objective of our engineers is to isolate the process environment from the plant environment in the most efficient manner possible,” explains Boger. “At the same time, we want to maintain or improve the ability of the equipment to handle bulk food products and blends, many of which are prone to dusting, packing, caking, seizing, degrading or separating.” In general, Boger says, if you can see, touch, feel or smell your bulk food product, or if it comes in contact with the dirty (exterior) side of its package, you may be compromising the purity of your product and the safety of personnel.”
“The food industry is asking for 3-A dairy requirements even if their product is not dairy related,” observes Kathy Hunter of Pitman, N.J.-based K-Tron America. “They want that degree of cleanliness.” Hunter claims that most of K-Tron’s 12 models of volumetric and gravimetric feeders can be customized to meet 3-A sanitary design requirements.
“The three issues I see right now are ergonomics, safety, and compact, modular equipment,” states Brian Wilson, national product manager for PIAB, a manufacturer of industrial vacuum conveyors and components. According to Wilson, equipment manufacturers are attempting to minimize injuries resulting from lifting and repetitive activities involved in moving product.
But the variety of problems presented when powdered product gets into the processing environment poses serious short-term and long-term dangers. That is why pneumatic equipment is becoming standard in many plants where the prospect of volatile dust mixing with oxygen raises the possibility of fire or explosion.
PIAB’s latest generation of equipment is designed to minimize waste and limit the amount of dry product released into the plant environment. Its C-series conveyors, designed for food and dairy applications, use pneumatically driven vacuum pumps capable of transporting 10 to 15 tons of powders and granules per hour in almost any manufacturing environment.
The pneumatic pump offers a sizable safety advantage. A nitrogen purge displaces the oxygen content and reduces the chance of explosions without altering system performance. A system conductive from top to bottom can dissipate the static charge from the conveyor.
“We are also trying to make our vacuum pump more efficient,” says Wilson. “Our L-series allows higher flow with less air consumption.” The system cycles the pump on and off so that it consumes less energy.
Made of stainless steel AISI 316L, the conveyors demonstrate a 25 percent improvement in vacuum-assisted flow without additional energy consumption. Its filter, which can trap 0.3-micron particles, can also be equipped with a HEPA (high efficiency particle arrestment) filter. The C-21 and C-33 conveyors comply with 3-A dairy standards.
The geometry of PIAB conveyors has changed with the last two design modifications, the most recent in November. “The new pump, the geometry of the new modules and increased discharge opening have allowed us to increase our throughput about 25 percent. It is also easier to use and clean and has fewer moving parts. Because of its size, it is easy to transport,” says Wilson.
An ice cream processor searching for conveyor mobility and cleanability took advantage of several features of PIAB’s C33 Vacuum Conveyor. The conveyor moved dry ingredients for ice cream production from drums into mixers. The processor welded the connection unit to an extra volume module and to the cone module. A portable stand enabled the processor to lift the vacuum conveyor via a hand winch. Specially designed brackets welded to the conveyor and the hand winch also helped to facilitate cleaning. The result was a portable unit that was easy to clean yet met extremely high sanitary standards.
Added flexibility and throughput
The industry is also moving toward compact, modular equipment to add flexibility to production lines. Add sanitary design and ease of maintenance to equipment credentials, and you find yourself back to the age-old concerns of safety and profit.But few processors would trade production capability for modular design. Processors today want flexibility as well as throughput. Wider belt widths on K-Tron’s new weigh-belt feeders have increased handling feed rate potential to 88,000 lb./hr. using belts of 600 mm widths. Weigh-belt feeders are used in cereal processing, snack foods, snack mixes, pet foods and many products requiring gentle handling. “Our weigh-belt feeders can handle even fragile material like flakes and snack or nut mixes,” says Hunter.
Discharge a concern
The newest generation of bulk bag unloading equipment addresses the gamut of powder/bulk concerns from waste to efficiency and safety and lower cost operations.Plants that handle bulk bags, for example, may experience contamination if discharging equipment lacks provision to seal the product environment from the plant atmosphere. Many units currently employ iris valves to regulate the flow of bulk material falling through the bag spout and to cinch the spout for retying. But, according to Boger of Flexicon, iris valves allow bag spouts to hang loosely inside of intake chutes. They permit dust to escape between the chute and spout while exposing the product atmosphere to the contamination from the underside of the bag and dirty (exterior) side of the bag spout.
Flexicon’s new generation dischargers address the problem with a Spout-Lock clamp ring that creates a seal between the clean side of the bag and the clean side of the intake chute. The device operates in conjunction with a telescoping tube that creates constant downward tension as the bag empties and elongates, thus promoting complete discharge.
A Bag-Vac dust collector creates negative pressure within the sealed system to collapse empty bags prior to retying. This eliminates dust commonly emitted when bags are flattened manually.
For retying of partially empty bags, Flexicon introduced a pneumatically actuated flow control valve called Power-Cincher that cinches the bag spout concentrically on a horizontal axis for easy tie-offs, as well as vertically in a tight zigzag pattern to prevent the leakage of fine powders.
The sealed system concept extends upstream or downstream of dischargers when they are integrated with any of the company’s conveyors, or specified as part of a plant-wide bulk handling system.
“From taking delivery of bulk food ingredients from railcars, trucks, bulk bags, drums or 50 pound sacks, to packaging finished product for shipping, today’s food processors are winning the battle against contamination while increasing productivity by integrating entire processes and isolating them from possible contamination sources,” says Boger. The days of open hoppers, clouds of dust and bulk material underfoot are history, he says, “at least for processors willing to employ current day bulk handling technology.”
PIAB’s Bulk Bag Unloader also reduces dust contamination during material handling with a spout mechanism. With the bulk bag lifted above the station, the spout is secured to an inflatable seal sandwiched between the material and a stainless steel ring. The dust-free connection does not employ glove boxes, doors, or other enclosures. A pneumatic cylinder at the base compresses or expands the bag by retracting and extending. The feature permits dispensing of non-free flowing material.
“Its biggest feature may be its small size,” says Wilson. “You can have a contained system before you even open the bag for dispensing.” Like PIAB’s conveyors, the Bulk Bag Unloader is modular.
What’s next?
Mike Latimer of Eriez Magnetics, Erie, Penna., sees the industry trending toward the removal of smaller and smaller contaminants to protect both the product and process equipment. He notes that some customers require the removal of micron-size particles and contaminants today. Such requirements have driven improvements in Eriez’s separators, vibratory screeners, and metal detection devices for increasing accuracy detection at increasingly higher speeds.“Faster processing speeds in today’s computers make it easier to isolate what you want and don’t want,” says Latimer. Product conductivity and electrical noise can cause signals that may be misread. “Now machinery can more easily distinguish between electrical noise and a metal particle, even at high processing speeds…As Intel comes up with better chips, our ability to detect (contaminants) improves.”
Extracting more profit from improved inventory, waste prevention and recovery, and increased throughput and productivity may well hinge on how effectively your company handles and tracks its powder and bulk ingredients. u
For more information:
Brian Wilson, PIAB Vacuum Conveyors, 800-321-7422
David Boger, Flexicon Corp., dboger@flexicon.com, 610-814-2400
Kathy Hunter, K-Tron America, khunter@ktron.com, 856-582-0500
Mike Latimer, Eriez Magnetics Inc., mlatimer@eriez.com, 814-835-6000
