Tech Update: Size Reduction
While obtaining optimal yield is a priority in size reduction applications, other factors such as food safety, operator safety and equipment reliability are key concerns.
There are several types of size reduction machinery for cutting, grinding, granulizing, chopping, mincing, peeling, pulping and pressing products. While it’s impossible to delve into each of these devices in detail, several common denominators affect their selection. These include yield, food safety, operator safety and reliability.
When suppliers are asked what processors value in size reduction equipment, there are no surprises: Yields, uptime and food safety are the top three.
But there are several inter-related, additional concerns. For example, one aspect of yield is related to the ability to perform product size reduction while not degrading the main product itself, such as frozen vegetables or frozen products like orange pulp. The trick is to be able to pull the frozen material apart without grinding the individual pieces themselves.
The number one concern for processors is yield-getting the product at the right size without generating waste. Automation in recipe-driven equipment can help take the guesswork out of, for example, where to set the rollers in milling machines, making it easy to switch products and reset equipment automatically, reducing set-up time and getting the optimum particle-size distribution, says Brian Thomas, Modern Process Equipment’s director of business and application development.
For some processors, the leftovers or scrap from one process might be the ingredient for another product with a little help from the right size reduction equipment. For example, rather than throwing away carrot ends, why not run them through a peeler and come up with a small ball that can be added to a vegetable medley or a soup, suggests Steve Knauth, Munson Machinery general sales manager. Chicken nuggets and sausage are good examples of “recycled” product.
Reprocessing of off-spec food stuffs has always been an application for size reduction-for example, breads, cookies, snack foods and confectionery products. “It is my belief that all successful food manufacturers have for all practical purposes zero waste,” says Thomas Kendrick, director of process technology of The Fitzpatrick Company.
Keep it clean
“With sanitation an important issue in all food industries today…sloped surfaces to facilitate draining and all-stainless steel (SS) motors are key features,” says Tim O’Brien, Urschel Laboratories’ vice president of sales. In addition, increasing machine accessibility with hinged panels eases maintenance and reduces downtime.
Processors want equipment that is easily cleaned and maintained with minimal downtime. This means the equipment must be easily disassembled with a minimum number of tools, and the tools that are used must not be specialized, says Maynard Lanting, product manager with Quadro Engineering Corp.
For processors with union shops, simplifying the tools to disassemble and re-assemble the equipment can be big time savers. If the cleaning process requires the maintenance department and sheet metal or other mechanics to take apart and re-assemble the machine, inordinate times can be accumulated for what should be relatively short cleaning times. In one instance, a union shop-because of breaks and scheduling-took as long as 7.5 hours to clean a grinding machine. Simplifying the design so an operator can take the machine apart, clean it and re-assemble it reduced the total cleaning time to 1.5 hours, according to Thomas.
In moist products processing, equipment needs to be cleaned frequently, and it should be easy to take apart. SS construction makes sense in these applications, says Scott Prater, president and CEO of Prater-Sterling. “Surprisingly, a lot of the equipment we sell to the food industry is mild steel, and since most of the material going through the equipment is dry, free-flowing powder such as flour, bakery mixes and/or granules (such as sugar), [processors] don’t have to worry about contamination issues since the equipment is usually running 24/7.” With the tremendous throughput of product, the equipment virtually cleans itself, says Prater.
“Equipment suppliers must design their equipment to the specific needs of their food customer,” says Kevin Swanson, Bepex International director of marketing. Attention to design details ensures the proper finish requirements, weld preparation, material selection and CIP (clean-in-place) protocol are adequate for the application.
In addition, equipment design should meet current good manufacturing practices and end-user expectations. This includes eliminating or minimizing in the design phase all possible components that could contaminate the final product.
“In exploring solutions to eliminate spaces for bacteria to hide and grow, we have developed several solutions that include, first, casting the product enclosure area out of one single seamless stainless-steel product drum, and second, keeping mechanical zones completely separate from food contact areas,” says Terry Baggott, senior product manager at Deville Technologies. Combining designs with current recommendations from organizations such as USDA and 3A guidelines allow innovation while going beyond today’s regulatory requirements, he adds.
A full range of options enhancing cleanliness should include WIP (wash-in-place) and CIP designs where spray nozzles are integrated into the equipment, mechanical seals and FDA-approved lubricants. Additional options include autoclave designs, motors and variable speed drives rated for high-pressure water spray, and in all cases, sealed gearboxes and a simple, yet innovative design with a small number of parts to make disassembly for cleaning easy to do, according to Lanting.
For wet products, equipment should be designed with solid, one-piece construction blades and rotors, and the body of the machine should be welded together. All internal parts must be polished with smooth welds, and motors and gearboxes should be SS and wash-down rated, says Jack Paddock, vice president of Atlantic Coast Crushers.
Direct drive may help
Swanson says his customers place machine safety at the top of their size reduction equipment lists. Safety encompasses all aspects of the machine, starting with a sound mechanical design that safeguards access to internal elements and ensures easy cleaning.
Several other machine safety recommendations include the following:
Keep the wheels turning
To maximize uptime and yield, it’s necessary to match the equipment to the task, once the task has been defined. Trying to take short-cuts may save a little money in the short term, but in the long term, it can be expensive. For example, says Baggott, “You do not want to use a vegetable dicer to cut a product which is much more difficult, such as cheese. This will more likely result in unpredictable and increased downtime-not to mention unusable or inferior product. This will also lead to unexpected costs and possibly hinder scheduled production runs.”
At the same time, processors want some degree of flexibility, and this challenges suppliers. “With today’s ever-changing market requirements, it is important for equipment manufacturers to be flexible and accommodating,” says Baggott. In some cases, this means equipment will process a variety of products despite their shape, size or consistency-such as high-moisture cheese trims in a shredding or dicing unit, because cheese is not always a perfect shape or texture. This observation also applies to many other foods, such as dicing frozen vs. cooked or fresh meats, fruits and vegetables.
Most size reduction operations put wear and tear on the equipment. But the proper choice of materials and monitoring of the machine can help extend its life. “Unfortunately, the grinding of what would normally be considered a soft material becomes abrasive if the vegetable matter includes entrained sand,” says Roy R. Scott, ARDE Barinco sales engineering manager. Even a small percentage by weight can add up to tons of sand in high-capacity applications. Scott recommends the use of 17-4PH (precipitate hardened) SS because it is both hard and shock resistant. Its rated strength (1100-1300 MPa) is maintained up to about 600°F. There are harder materials, but they are susceptible to shattering upon impact with hard objects.
The use of 17-4PH for SS equipment is a good choice since it is much harder than 304 SS, says Prater. Some processors specify 316 SS for salt applications, and others specify 400 SS because it’s magnetic, allowing easy pick-up of metal shards out of product. Since each application is different, knowing which SS to apply and how it works with high-speed equipment takes experience and time.
Uptime, efficiency and energy optimization are all based on sizing the equipment properly for the application, right-sizing the motors and picking equipment that works well for a particular product. Samples should be run so current (amperage) readings can be taken to pick the proper size motors. Specifying too small a motor can prevent a machine from operating efficiently and cause jams, adding to downtime. For dry applications, operating at higher rotor speeds means more energy and more dust, according to Paddock.
Higher-than-necessary speeds also place needless wear on equipment. With grinding and milling operations, usually the speed should be minimized to the point at which it gets the job done. While breaking up the product causes wear and tear, there is more friction on the roll as the speed is increased, shortening the parts’ lifetime, says Thomas.
Properly matching equipment to an application can mean long lifetime for moving parts. ForesTrade, Inc. set up an organic cinnamon plant in Padang, West Sumatra. To cut cinnamon as it is received in rolled sticks or quills that range in lengths from 3 in. to 40 in., it chose to use a Munson SCC-15-MS high-speed classifying cutter. The unit’s horizontal rotor contains dozens of cutter blades, attached to a helical array of staggered holders called interconnected parallelograms. The blades are chisel-shaped, with replaceable carbon tips. Driven by a 20-hp motor, the blades rotate at 2,200 rpm and continuously shear the quills against twin stationary bed knives, cutting them into 2-in. lengths.
According to Mary Porter, Indonesian operations manager, even with the high rotation speed, there is little to no heat generation and minimum fines. After close to two years of operation, the original carbide tips have not needed replacing, says Porter, even though cinnamon is abrasive. The cutter contributes to quality by producing more-uniform pieces and by making a cleaner cut, with less waste than under the old system, she adds. The drying operation is also more consistent.
While it may seem that machine suppliers want to make money selling replacement parts, the case for using OEM parts can be analogous to not buying cheap inks for a color photo printer; they can ruin the device and void the warranty. “We have seen many instances where machines are not performing because of so-called copycat or jobber parts,” says Baggott. These parts are often less expensive to buy initially but in the long run have a shorter life expectancy. Also, some of these parts do not meet the same specification and tolerances as original parts, thus creating issues that contribute to much larger and more expensive component failures, he adds.
For more information:
Steve Knauth, Munson, 800-944-6644, email@example.com
Brian Thomas, Modern Process Equipment, 773-254-3929, firstname.lastname@example.org
Pete Johnson, Carruthers Equipment Co., 503-468-0441, email@example.comJack
Paddock, Atlantic Coast Crushers, 908-259-9292, firstname.lastname@example.org
Maynard Lanting, Quadro Engineering, 519-884-9660, email@example.com
Roy R. Scott, ARDE Barinco, 800-909-6070, firstname.lastname@example.org
Kevin Swanson, Bepex, 612-331-4370, email@example.com
Bill Wade, Breddo Likwifier div. of Caravan Ingredients, 800-669-1108, firstname.lastname@example.org
Scott Prater, Prater-Sterling, 630-759-9595, email@example.com
Tomas Johansson, The Fitzpatrick Company, 630-433-3131, firstname.lastname@example.org
Terry Baggott, Deville Technologies, 514-366-4545, email@example.com
Thomas Kendrick, The Fitzpatrick Company, 630-530-3333, firstname.lastname@example.org
Tim O’Brien, Urschel Laboratories, 219-464-4811, email@example.com
Keeping employees safe from explosions
Two factors figure into operator safety. For grinding dry powders or granules, preventing explosions is a major concern. Second, keeping people safe from physical injury is a must. Prater-Sterling is a supplier to sugar producers and the baking industry. “With the recent sugar explosions, there has been a lot of discussion on how to better protect these systems and the people who work near the equipment and the systems,” says Scott Prater of Prater-Sterling. Fine-grinding equipment should be designed to handle up to a 10-bar (145 psi) explosion, and it should include the latest explosion suppression systems that meet or exceed NFPA (National Fire Protection Agency) regulations, he adds.
Jack Paddock of Atlantic Coast Crushers suggests one simple way to minimize the dust: When possible, operate a machine at a slower rate. For example, rotor rpm of 1800-3500 will create a lot of dust, where equipment operating at speeds of 30-100 rpm will create less dust.
Sometimes dust generation is unavoidable, and in this case, processors must have information about the product to find out, for example, the auto-ignition temperature and Kst value. Kst (in bar • m/s) reflects the ability of a powder to explode, with higher numbers being more unstable, e.g., wood dust = 102, milk powder = 90, barley grain dust = 240. Both NFPA and Factory Mutual recognize these numbers. Armed with this information and the assistance of safety experts, it’s then possible to design a safe hammer mill or any other system that creates dust.
According to Tomas Johansson of the The Fitzpatrick Company, its FCM classifier equipment can mill icing sugars, which generally fall into the Class St2 category, i.e., with Kst levels between 200 and 300 bar • m/s. The German code of practice (VDI 3673 ) defines three levels of increasing dust volatility with Class 1 less than 200, and Class 3 greater than 300 bar• m/s. The sealed mill uses mechanical impact size reduction, which keeps operating energy costs low.